Dominique Salameh

network for solid HCW management

Keywords: cement characteristics, mycotoxins in food, waste management processes and fermentation processes engineering

The creation and monitoring of a

Biographical notes: Olivia Maamari is the Technical Advisor of the Environment Program of the Lebanese NGO Arcenciel since 2008. She was involved in the development and the optimisation of the Lebanese Network for Infectious Health Care Waste Management and is also working on municipal solid waste management. She holds a Master's in Industrial Technology from the Faculty of Science of Saint Joseph University of Beyrouth. She is a doctoral candidate in Environmental Process Engineering in the Institut National Polytechnique-University of Toulouse, France.

Fady Moujaes is the former General Director of Arcenciel, a non-profit organisation established in 1985 in Lebanon to act with and for people with difficulties. He also held several positions at Arcenciel, being Head of the Environment Program, Head of the Health Program, and Head of the Production Unit of wheelchairs. He was former president and member of AfakJadida Association for Housing Credit. He is currently member of the Lebanese Association for Laryngectomy and a founding member of Society for Social Entrepreneurs, Lebanon. He holds a BA in Journalism from the Lebanese University and an MBA from Sorbonne University.

Robert Keyrouz is an Assistant Professor at the Lebanese University, Faculty of Sciences II. He has a thesis in organic electrochemistry (University of Rennes I-France), post-doctoral ENSCR (Chemistry Engineering School of Rennes), and MS in Organic Chemistry from Department of Chemistry, Lyon, France. He is the author or co-author of ten international publications, and participated in 22 international seminars. His main fields of interest are organic electrochemistry and environment.

Dany El-Obeid is Lebanese agricultural engineer, holding a Master degree from MAICh and a PhD degree from Aix en Marseilles University. He also holds an MBA. He has currently a full-time position in the Lebanese University, Faculty of Agricultural and Veterinary Sciences. He is working since 2007 in waste management in Lebanon and had also experience in other countries such as Algeria, Syria and Iraq. He worked on the infectious health care waste management in the Lebanese NGO Arcenciel, and also on municipal solid waste as a freelance consultant.

Michèle Kosremelli Asmar holds a PhD in Management from Université Paris Dauphine, France and an MHA in Health Administration from Université de Montréal, Canada. She is a full-time Professor at the Institute of Health Management and Social Protection (IGSPS) of Saint-Joseph of Beyrouth (USJ). Her expertise falls in the field of health management, human resources, quality management, project management and interprofessional collaboration. She coordinates the MBAIP-health option program. She has extensive experience in consulting with the World Bank, the UN agencies, and other public and private institutions in Lebanon and abroad. She is also founding member of the Lebanese Healthcare Management Association, founder and Vice President of Scientific Research and Management Association, member of the editorial board of Human and Health Journal, reviewer for several journals and President of the NGO Include.

Cedric Brandam is a Professor Assistant in University of Toulouse, France, in Institut National Polytechnique -ENSIACET, a chemical engineering school. He works since 2002 in the Laboratoire de Génie Chimique in the Department of Bioprocess and Microbial Systems. His research studies concern microbial processes for production of fermented beverages or production of metabolites as antibiotics or pesticides. He has published more than 20 publications on these subjects.

Introduction

Healthcare waste (HCW) management is a high-priority environmental concern in developing countries because poor management of this type of waste causes environmental pollution and health problems due to the proliferation of viruses and micro-organisms as well as contamination of ground water by untreated HCW in landfills [START_REF] Dursun | Assessment of health-care waste treatment alternatives using fuzzy multi-criteria decision making approaches[END_REF]. The growing number of healthcare facilities directly impacts the generation of HCW [START_REF] Altin | Determination of hospital waste composition and disposal methods: a case study[END_REF][START_REF] Kuo | Characteristics of medical waste in Taiwan[END_REF]WHO, 1999;Alagoz et al., 2007). Because hospital waste management has become a subject of interest, hospital administrations are struggling with lot of problems while trying to avoid wrong practices such as disposing of either part or all of HCW that is untreated and mixed with municipal waste in landfills [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF]. Numerous definitions of HCW can be found in the literature and relevant legislation [START_REF] Komilis | Hazardous medical waste generation rates of different categories of health-care facilities[END_REF][START_REF] Alvim-Ferraz | Incineration of different types of medical wastes: emission factors for gaseous emissions[END_REF]. According to the WHO (2011b), HCW can be divided into two major categories: general waste, which represents 80% of total HCW and hazardous healthcare waste (HHCW), which represents 20% of total HCW. Explicitly, HHCW includes potentially infectious healthcare waste (PIHCW) (16% of HCW) and other hazardous healthcare waste (OHHCW) (4% of HCW), which includes different categories: chemicals, pharmaceuticals, genotoxic waste, radioactive waste and heavy metal waste (Figure 1). If handled improperly, HCW is considered to be a major risk to public health and safety because the mismanagement of HCW could lead to death and disability (WHOb, 2013;[START_REF] Alagoz | Improvement and modification of the routing system for the health-care waste collection and transportation in Istanbul[END_REF]. PIHCW will extend its potential infectious risk within all other categories of HCW if not segregated properly. In fact, PIHCW contains harmful microorganisms that may spread infection to hospital patients, healthcare workers and the general public either through direct contact or indirectly through environment pollution and the transmission of infectious diseases (WHO, 2013b;UNEP and CalRecovery, 2005;[START_REF] Pichtel | Waste Management Practices: Municipal, Hazardous and Industrial, Taylor & Francis, Boca Raton[END_REF] when improperly stored, transported, treated, or disposed [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF]. Thus, untreated infectious hazardous waste can have effects on water, soil and air and could significantly affect public health (RNSSL, 2012). Therefore, a vigorous environmental waste management system is recommended [START_REF] Pichtel | Waste Management Practices: Municipal, Hazardous and Industrial, Taylor & Francis, Boca Raton[END_REF][START_REF] Mbongwe | Healthcare waste management: current practices in selected healthcare facilities, Botswana[END_REF]. Despite the growing number of healthcare facilities and the existence of a legislative framework and an accreditation system for hospitals, few Lebanese healthcare institutions treated their HHCW before disposal until 2003. In addition, treatment was often performed improperly. The majority of hospitals were disposing of their waste without treatment and there was no national solution for HCW management. In response to this critical problem, the NGO arcenciel, with the scientific support of the Faculty of Infirmary Sciences of Saint Joseph University of Beirut (USJ), built a strategic plan that aimed to ensure a sustainable solution for HCW, starting with the proper management of PIHCW because this category forms the large majority of HHCW. The purpose of this work is first to describe the different steps of the establishment and the implementation of the new national network for PIHCW management in Lebanon and then to analyse the main results of the implementation of the network on the field. The main field results discussed include sterilisation parameters and optimisation, treatment centre design, quality management and waste generation. The approach used for the implementation of this network can be considered very innovative, notably because it has been initiated and is being operated by an NGO on a national level. The creation of this network has been considered a success by LIFE (the financial instrument of European Union). The description of the methodology adopted and the analysis of the results would be very useful for the replication of the experience in different countries willing to implement or improve their HCW management systems.

Materials and methods

To elaborate the strategy to be implemented, a legal, economic, environmental and technical analysis was conducted. Many international and national regulations were taken into consideration in order to respond to the relevant legislative, quality and safety requirements. The context specific to Lebanon has been deeply analysed in order to determine if hospitals were able to manage individual treatment facilities, whether the PIHCW treatment centre was of interest to the private sector and the appropriate type and number of service providers. To determine the capacities of the treatment facilities, the quantities of PIHCW produced were evaluated first. In fact, to allow for the consideration of the various treatment options [START_REF] Tsakona | Hospital waste management and toxicity evaluation: a case study[END_REF], it is important to know the quantity of waste generated. The main methods for medical waste treatment have been evaluated to select the optimal treatment technology. The advantages and disadvantages of the different methods have been compared, using a compatibility matrix considering different criteria proposed by the coalition Health Care Without Harm (HCWH) (2001) and considering the characteristics of the different PIHCW treatment options provided by the WHO (2005). Sterilisation parameters have been determined according to different references. To reduce the consumption of energy of the process, a heat exchanger has been installed. Different biological, chemical and physical indicators have been selected to test the efficiency of the sterilisation.

Theory and calculation

Regulations

Many international and national regulations have to be taken into consideration for the establishment and the implementation of a waste management strategy on a national level. In Lebanon, most important legislation includes: the law 64 (1988), the Lebanese decree 13389 ( 2004), accreditation standards and guidelines for hospitals in Lebanon (2010), the Kyoto Protocol (1997), the Stockholm Convention ( 2001), the Basel Convention (1992) and WHO standards (1999, 2005, 2011a, 2014). The decree 13389; 2004 (amendment of the Lebanese decree 8006; 2002) is the actual point of reference in terms of national legislation concerning the management of waste by healthcare institutions. This decree specifies the categories of wastes generated by healthcare institutions and requires health institutions to treat their hazardous waste while preserving the environment and public health. As part of the reform of the health sector, the Ministry of Public Health has developed accreditation standards and guidelines for hospitals in Lebanon, including a section specific to waste management within hospitals, counting eight standards.

Socio-economic context

The Lebanese economy is based primarily on service sectors that include commerce, tourism, financial services, healthcare and higher education. The number of healthcare facilities has increased in Lebanon within the past decade, while the Lebanese healthcare system suffers from high spending making up 7% of the gross domestic product (GDP) in 2010 (WHO, 2013a). According to the evaluation by the Environmental Resources Management (ERM) consulting company in 1999, it was estimated that Lebanon produced 11 tons/year of PIHCW, which represent 20% of the total medical waste. PIHCW production in Lebanon was expected to be approximately 0.4% of the total solid waste in the country. Lebanon has a total of 163 hospitals (i.e., 15342 beds) spread throughout the country, of which 135 (82.82%) fall under the private sector, i.e., 12648 beds (82.44%) and 28 (17.18%) under the public sector, i.e., 2550 beds (16.62%) (RNSSL, 2012). The country also contains five Palestinian refugee hospitals (209 beds). Thus, the healthcare sector in Lebanon is mainly private (RNSSL, 2012). The health sector in Lebanon is characterised as a chaotic sector with a surplus of beds, extra investment in equipment and a dominance of hospitals with a bed capacity lower than 100 (approximately 75% of hospitals) (RNSSL, 2012). The occupancy rate of hospitals does not generally exceed 55% (RNSSL, 2012). After having conducted a financial analysis, it seemed inappropriate to multiply the investment by each hospital to treat PIHCW. Semi-centralised processing stations could serve several hospitals at once. A study conducted within the framework of the project LIFE 05 TCY/RL/138 in 2006 showed that the total cost of processing 1 kilo of PIHCW is 2.25 times higher when each institution treats its PIHCW separately. In fact, if we compare the total individual investment costs (investment cost per hospital * number of hospitals) to investment costs in the case of a national solution (investment cost per treatment centre * number of treatment centres), total investment costs are lower in the second case. It should be mentioned that investment costs include autoclaves, accessories (boilers, filters…), environmental impact assessments, construction of a treatment centre and in the case of a national solution, collection vehicles. In addition, if we compare operating costs in the case of an individual solution (operating costs per hospital * number of hospitals) to operating costs in the case of a national solution (operating costs per treatment centre * number of treatment centres), operating costs are lower in the second option. It should be noted that operating costs include consumables, human resources, insurance, maintenance and amortisation. Thus, investment and operating costs are significantly higher in the case of an individual solution, as shown in Figure 2.

PIHCW treatment technologies

The main methods for medical waste treatment are autoclave, microwave disinfection systems, chemical disinfection and incineration [START_REF] Xie | Emissions investigation for a novel medical waste incinerator[END_REF]. The main criteria proposed by HCWH ( 2001) to evaluate treatment technologies include: efficacy, emissions and waste residues, the reduction of waste volume and mass, occupational safety and health, the level of commercialisation, cost, regulatory acceptance; and community and staff acceptance. A comparison between the different treatment methods using a compatibility matrix shows that the steam sterilisation in autoclaves is an optimal technique that takes into account environmental, economic and social criteria. When compared with other treatment methods (incineration, chemical sterilisation and microwave technology), the capital and the operating costs and the adverse effects on health and the environment are relatively lower, as shown in Table 1. These results confirm those shown by [START_REF] Dursun | Assessment of health-care waste treatment alternatives using fuzzy multi-criteria decision making approaches[END_REF]. In fact, controversy exists regarding possible long-term environmental effects especially of hypochlorite and its byproducts in waste water when chemical disinfection is used (HCWH, 2001). Microwave disinfection systems have a low level of commercialisation in Lebanon. As for HCW incineration, the main disadvantages are the emission of pollutants in the atmosphere, some of them having known effects on human health and are environmentally toxic (HCWH, 2001;[START_REF] Alvim-Ferraz | Incineration of different types of medical wastes: emission factors for gaseous emissions[END_REF][START_REF] Xie | Emissions investigation for a novel medical waste incinerator[END_REF][START_REF] Diaz | Alternatives for the treatment and disposal of healthcare wastes in developing countries[END_REF][START_REF] Chen | Key issues study on the operation management of medical waste incineration disposal facilities[END_REF] and the fact that presents significant capital and operating costs (HCWH, 2001;Alagoz et al., 2007). These disadvantages often lead to increasing community opposition to incineration [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF], especially in Lebanon. Besides, Lebanese decree 13389/2004 prohibits incineration of PIHCW and recommends the use of sterilisation for the treatment of PIHCW. The basic principle of steam sterilisation, as accomplished in an autoclave, is to expose each item to direct steam contact at the required temperature and pressure for the specified time (HCWH, 2001). The sterilisation method applied includes a double-wall circular vessel where the shredding, stirring and dehydrating of the wastes occur [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF]. Moist heat destroys microorganisms by the irreversible coagulation and destruction of enzymes and structural proteins (HCWH, 2001). Prions, which are extremely resistant to conventional inactivation procedures including irradiation, boiling, dry heat and chemicals, could be inactivated in autoclaves for dry waste at 134°C for 60 minutes (EHRS, 2011). Large volumes of infectious liquid waste containing prions can be treated with 1N NaOH followed by autoclaving at 132°C for 4.5 hours (EHRS, 2011). HCW shredding during sterilisation reduces the risk of accidental injury or incision by sharps, increases overall waste exposure to heat and makes HCW unrecognisable. The crushed and sterilised waste obtained as a result of this process is not recognisable and is no longer hazardous. Using this method reduces the total volume of waste by 80% (HCWH, 2001). In addition, if waste is segregated before being processed, there will be no harmful gas emissions by autoclaving [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF]. In central sterilisation treatment systems, sterilised HCW would then have the characteristics of domestic solid waste at the end of the treatment process. Sterilised waste is transported and disposed at a municipal solid waste sanitary landfill [START_REF] Alagoz | Improvement and modification of the routing system for the health-care waste collection and transportation in Istanbul[END_REF][START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF].

Operation and organisation

The different operational and organisational options depending on the number and type of operators have been compared considering different criteria: mission, costs, sustainability and effectiveness. Analysis of the socio-economic context (cf. paragraph 3.2) shows that an economy-of-scale strategy should be adopted, especially because hospitals are facing economic difficulties in Lebanon. In addition, it is easier for the concerned authorities (mainly the Ministry of Environment in Lebanon) to control and audit five to six centres that cover all Lebanese hospitals than to control individual autoclaves in every hospital. Moreover, the treatment of medical waste is a delicate process, requiring trained human resources, advanced expertise, maintenance and daily monitoring. Management of the process is very difficult when it is the same organisation that produces, sorts, collects and treats waste. When not controlled or poorly controlled, the sterilisation process can be inefficient. A limited number of PIHCW sterilisation centres reduces the cost of experience. Besides, the mission of healthcare facilities is to treat people. Therefore, the outsourcing of waste treatment services offers the hospital the opportunity to refocus on its core activity. The minimisation of PIHCW quantities is crucial to reduce treatment costs for hospitals and the impact on public health and the environment. Awareness and training related to the adequate sorting of PIHCW allows a reduction in the quantity of PIHCW generated. The consequence of this minimisation would be a reduction in quantities treated by the service provider. If we consider a pricing per kilogram (price in accordance with the weight of the waste), expected benefits would be reduced as well. Thus, waste minimisation is not compatible with the interests of a service provider in the private sector. Therefore, the service provider should preferably be a non-profit organisation. A multitude of investments in equipment by several providers is neither justifiable nor cost effective considering the low PIHCW production in Lebanon. In addition, the successful coordination between multiple competing parties would be very difficult in the case of machine failure, war or other crises. Thus, as the public sector did not implement a solution for HCW management, one NGO should provide training, collection and treatment.

Waste minimisation and sorting

If HCW sorting is not applied sufficiently, risks are inevitable for both workers and patients (Alagoz et al., 2007). By sorting waste, appropriate treatment techniques can be applied to each separate waste stream (HCWH, 2001). Segregation policy is a key element in PIHCW minimisation (HCWH, 2001). Another crucial reason for segregation has to do with the consequences of introducing OHHCW into treatment systems of infectious waste. In fact, errors of sorting can be harmful to human health and the environment. In addition, an autoclave machine can be affected by the presence of inappropriate waste inside, such as radioactive, cytotoxic and chemical waste (HCWH, 2001). Therefore, the main staff categories involved in HCW management in hospitals should receive appropriate training. These categories include: hospital managers and administrative staff responsible for implementing regulations of HCW management; medical doctors, nurses and assistant nurses; and cleaning staff. The WHO recommends adopting variable pricing (price per kilogram) in order to provide incentives for proper segregation and waste reduction (cost saving) (WHO, 2014).

Waste collection

According to WHO safety standards (1999), the transport of wastes from a healthcare centre to a waste treatment centre implies a specially equipped vehicle exclusively used for PIHCW transportation. The internal surface coating material of the vehicle should allow it to be steam-cleaned and the internal angles should be rounded. After each collection of PIHCW, the interior of the vehicle should be systematically cleaned and disinfected. The vehicle should be closed except when loading or unloading. If PIHCW is stored at a temperature lower than 5°C, it can be collected within seven days [START_REF] Alagoz | Improvement and modification of the routing system for the health-care waste collection and transportation in Istanbul[END_REF]. Otherwise, PIHCW should be collected within 48 hours during the cold season and within 24 hours during the hot season according to WHO recommendations (1999).

Sterilisation parameters

The sterilisation parameters have been determined according to different references. The maximum sterilisation temperature proposed by the WHO is 138°C for a sterilisation duration of 5 min (WHO, 2011a). The factor of thermal inactivation for the couple [temperature (°C), time (min)] has been compared to the reference couple (121°C; 30 min) [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF], using the formula To reduce energy consumption, a heat exchanger has been installed.

Sterilisation indicators

The evaluation of the efficiency of the treatment method is very important because the treated infectious hospital wastes will finally be disposed of in municipal waste landfills [START_REF] Karagiannidis | A multi-criteria assessment of scenarios on thermal processing of infectious hospital wastes: a case study for Central Macedonia[END_REF].

According to HCWH (2001) recommendations, the ability of the steriliser to reach the physical parameters (temperature and pressure) necessary to achieve sterilisation is monitored by mechanical, chemical and biological indicators.

General characteristics of the network

As a result of the analysis of the previous aspects, a Lebanese waste management network operated by the NGO arcenciel has been created. The network includes five treatment centres covering all regions in Lebanon. Each treatment centre can be a backup system for all other centres when needed and waste can be easily transported from one centre to another. For over ten years, the national network for PIHCW management provides a unique and comprehensive service in Lebanon, including the proper training of healthcare institutions' staff, the collection and transportation of PIHCW from the healthcare institutions in specialised vehicles and PIHCW sterilisation.

Training and technical support

arcenciel provided specific training sessions to the main hospital staff categories involved in HCW management once their institution began the implementation of a PIHCW management system. An assessment regarding HCW management has been realised in each organisation before training in order to adapt the training content to the existing situation and thus increase its effectiveness. Special training has been prepared in collaboration with the Faculty of Infirmary Sciences of Saint Joseph University of Beirut and provided to healthcare institutions' staff. The training emphasised sorting modalities at the point of generation as a key element for infection control and cost saving. The training addresses the potential hazards of the wastes from an environmental and sanitary point of view and the measures to be taken in order to prevent these risks. These measures cover all stages of the management of PIHCW within the hospital: sorting, collection, intermediate storage, internal transportation and central storage, in compliance with WHO recommendations (1999, 2005, 2011a, 2014). The required work practices, sorting procedures and the use of personal protective equipment have been emphasised. An analysis of the feedback received from the beneficiaries allowed the continued improvement of the training content and methodology. Trainings have then been implemented by hospitals themselves when new methods were introduced and when employees were newly hired. All concerned employees received annual updates as well. arcenciel also provided technical support for the purchase of equipment (e.g., sharps containers, trolleys, plastic bags), for the establishment of refrigerated PIHCW storage rooms and for the administrative support for the management of HCW (quantity monitoring, procedures, key performance indicators). Training and technical support costs were included in the treatment cost. Training and awareness provided allowed a considerable and sustainable change in the cultural practices of healthcare. To date, 8,000 persons have already been trained in HCW management in Lebanon. Knowing that according to the 'polluter pays principle', hospitals should bear the costs of their PIHCW management and should therefore pay the treatment service provider for the treatment of their PIHCW, variable pricing (price per kilogram) was adopted in order to provide incentives for the proper segregation and reduction of waste (cost saving). arcenciel collects only yellow bags that contain sorted PIHCW and sharps containers. Opened bags or bags containing hazardous waste other than PIHCW or recognisable anatomical parts are not collected. In fact, recognisable anatomical parts should not be treated in autoclaves according to the Lebanese decree 13389/2004. A radioactivity detector is used to verify that there is no radioactive material in the collected bins. PIHCW is transported by an optimised route, determined in such a way to minimise travel distances. All surfaces of the collection vehicles are easily washable and corners are rounded. The collection frequency depends on the quantity generated by each hospital and the availability of a refrigerated storage room inside the health institution.

Treatment centres

All treatment centres were the subject of an environmental impact assessment conducted by a private company authorised by the Ministry of Environment and are organised in such a way to avoid cross-contamination. All surfaces of the treatment centres are easily washable and corners are rounded. Each centre includes a refrigerated room with sufficient capacity reserved for the storage of PIHCW before treatment and a storage room of sterilised waste. The centre includes a storage room for PIHCW waste, an area for cleaning buckets, desks and lockers and a washing machine for cleaning uniforms. Facilities have been installed to evacuate wastewater and to cool machines. The centre is cleaned daily and the bins are cleaned immediately after they are emptied into the autoclave. Then, the bins are examined to detect possible causes of leakage. In compliance with WHO recommendations (1999) and upon being hired, each technician is vaccinated against hepatitis A and B, polio and tetanus and receives a training session with the precautions and measures to be taken in case of an accident. Wearing protective equipment is mandatory. Impeccable hygiene is required from technicians for reducing the risks of handling HCW. Therefore, convenient washing facilities (with warm water and soap) are available for personnel involved in the task. In addition, annual blood tests and medical examinations are carried out for the whole team.

Autoclaves

Each centre includes one autoclave that can reach the maximum sterilisation temperature proposed by the WHO (138°C) (WHO, 2011a). According to the specifications of purchased autoclaves, the sterilisation time corresponding to the sterilisation temperature of 138°C was found to be 7 min. Five autoclaves have been purchased: two autoclaves with a treatment capacity of 300 litres per 30 minutes average cycle time; one autoclave with a treatment capacity of 1,000 litres per 40 minutes average cycle time; one autoclave with a treatment capacity of 3,000 litres per 60 minutes average cycle time; and one autoclave with a treatment capacity of 720 litres per 60 minutes average cycle time. Regular preventive maintenance is performed on autoclaves. A calculation showed that the factor of thermal inactivation (z = 26.89°C) is more significant for the couple (138°C; 7 min) than for the couple (121°C; 30 min). Thus, the first parameters mentioned have been adopted. The installation of a heat exchanger allowed a reduction of fuel consumption of 17% (Figure 3). The required investment, including purchasing and installation costs, was equal to $1700. The payback period was five months thanks to the energy savings acquired as a result of the newly installed system.

Management and control

Management system

The complete management system is described in Figure 4. Procedures, instructions and key performance indicators were established and used to control and monitor the PIHCW collection and treatment process, allowing for the detection and correction of non-conformities.

The traceability system is based on follow-up notebook slips. Each slip includes three boxes to be filled. The first two boxes are related to the hospital and the collector. The third box concerns the treatment centre. Upon arrival of the collection vehicle at the hospital, the collected bins are counted, weighed and loaded in the vehicle in the presence of a hospital representative. The information (weight, date and the quantity of bins) is reported on a slip that is signed by the collector and hospital representative. A copy of the slip is delivered to the hospital. Once the bins are delivered to the treatment centre, the date and the quantities received are noted by the technician in charge of the treatment. The slip is then signed by the technician. Follow-up notebook slips are sent to the service provider administration. This traceability is very useful for the monitoring of the process and the follow-up of the quantities produced by hospitals. In the case of significant variations or abnormalities, further training sessions and support are proposed for concerned hospitals. This information also allows arcenciel to submit quarterly reports to the Ministry of the Environment concerning the quantities treated for each hospital during this period.

Control and monitoring

The network is a self-regulated system ensuring a triple control: arcenciel, as a service provider, is controlled by healthcare institutions because waste producers are responsible for the waste they generate until final disposal, according to the 'polluter pays principle' included in the Lebanese law 444; 2002. arcenciel exercises a control of hospitals through monitoring PIHCW quantities and reporting them to the Ministry of the Environment. As required by the Lebanese decree 13389; 2004, the Ministry of the Environment monitors the whole system and controls arcenciel facilities through environmental impact assessments, audits and regular reports.

Human resources

In a social entrepreneurship model, the team involved in the PIHCW management is multidisciplinary and well trained and consists of 42 people with extensive experience in their fields. Over 70% of these people are people with disabilities, ex-addicts, or ex-prisoners. More than 83% of the team are women when excluding the treatment centres.

Treated quantities

Approximately 6 tons of PIHCW from 105 hospitals, which represent 64.42% of the hospitals in Lebanon (i.e., 9306 beds, which is equivalent to 61.23% of all hospitals beds) are treated daily, as shown in Table 2. PIHCW is also collected from laboratories, dispensaries and clinics. Five hospitals treat their PIHCW independently outside of the network. The remaining hospitals continue to throw away their PIHCW without treatment, mainly because of the lack of government control. Thus, efforts are being made to convince these establishments to appropriately treat their PIHCW. In fact, one of the main encountered difficulties while implementing a national solution for PIHCW management was to obtain the involvement and engagement of healthcare institutions administrations and to get them to accept the 'polluter pays' principle.

Conclusions

Currently, approximately 65% of hospitals in Lebanon treat their PIHCW through the Lebanese network for HCW management. The complete system implemented provides a solution for PIHCW, compliant with WHO recommendations and national regulations. This solution includes specialised training, collection, treatment and final disposal. The key aspects taken into consideration in the network strategy and implementation are quantity minimisation, occupational health and safety, public health and environmental preservation, socio-economic factors, national and international standards and treatment costs and efficiency. A complete statistical study is currently being realised to compare the PIHCW generation rate per bed of different hospital categories to international references. Efforts for better accountability and awareness of healthcare institutions continue with the aim of treating the totality of PIHCW. Treatment solutions are being studied for OHHCW. The Lebanese network for HCW management implemented brings a solution to a major environmental and sanitary problem and could serve as a role model in different countries willing to implement or improve their HCW management systems. Thus, the replication of this successful experience is important, especially in developing countries suffering from HCW mismanagement.

Figure 1

 1 Figure 1 Composition of HCW

Figure 2

 2 Figure 2 Cost comparison between individual and network solution. individual solution (dark), network solution (light)

F

  the number of minutes required to kill a known population of microorganisms t time T temperature T* reference temperature Z factor of thermal inactivation.

Figure 3

 3 Figure 3 The evolution of fuel consumption (see online version for colours)

Figure 4

 4 Figure 4The process of PIHCW management

Table 1

 1 Compatibility matrix of PIHCW treatment techniques

		Autoclave associated with shredding	Chemical disinfection	Microwave Incineration
	Emissions and waste residues	+	-	+	-
	Efficacy	+	+	+	+
	Regulatory acceptance	+	+	+	-
	Reduction of waste volume/weight	+	-	+	+
	Level of commercialisation	+	+	-	+
	Cost	+	+	+	-
	Community and staff acceptance	+	-	+	-
	Occupational health and safety	+	-	+	-
	Notes: (+) Indicates relative high performance of the technique for each studied criteria,
	(-) Indicates relative low performance of the technique for each studied criteria

Table 2

 2 Lebanese PIHCW management network coverage in 2012 Number of hospitals and beds per region are taken from RNSSL, 2012 Number of hospitals and beds covered by the network are based on arcenciel's data

	Region	Total Number of hospitals	Hospitals covered by the network	Percentage of hospitals covered by the network	Total number of hospitals beds	Beds covered by the network	Percentage of beds covered by the network
	Beirut	21	17	80.95%	3206	2,445	76.26%
	Metn	44	27	61.36%	4686	2,464	52.58%
	Kesrouan-	9	4	44.44%	665	387	58.20%
	Jbeil
	Chouf-Aley	12	8	66.67%	782	317	40.54%
	Bekaa	24	15	62.50%	1701	1,136	66.78%
	Notes:

Table 2

 2 Lebanese PIHCW management network coverage in 2012 (continued) Number of hospitals and beds per region are taken from RNSSL, 2012 Number of hospitals and beds covered by the network are based on arcenciel's data

	Region	Total Number of hospitals	Hospitals covered by the network	Percentage of hospitals covered by the network	Total number of hospitals beds	Beds covered by the network	Percentage of beds covered by the network
	North-	28	22	78.57%	2027	1,761	86.88%
	Lebanon
	South	25	12	48.00%	2131	796	37.35%
	Lebanon
	TOTAL	163	105	64.42%	15198	9306	61.23%
	Notes:

Abbreviations


Serena Rizzolo
email: serena.rizzolo@isae.fr

Vincent Goiffon

Franck Corbière

Romain Molina

Aziouz Chabane

Sylvain Girard

Philippe Paillet

Pierre Magnan

Aziz Boukenter

Timothé Allanche

Cyprien Muller

Céline Monsanglant-Louvet

Mélanie Osmond

Hortense Desjonquères

Jean-Reynald Macé

Pierre Burnichon

Jean-Pierre Baudu

Stéphane Plumeri

Radiation Hardness Comparison of CMOS Image Sensor Technologies at High Total Ionizing Dose Levels

Keywords: dark current, drain, gate overlap, partially pinned

The impact of the manufacturing process on the radiation-induced degradation effects observed in CMOS image sensors (CISs) at the MGy total ionizing dose (TID) levels is investigated. Moreover, the vulnerability of the partially pinned PHDs at moderate-to-high TIDs is evaluated for the first time to our knowledge (PHD stands for "photodiode"). It is shown that the 3T-standard partially pinned PHD has the lowest dark current before irradiation, but its dark current increases to ∼1 pA at 10 kGy(SiO 2 ). Beyond 10 kGy(SiO 2 ), the pixel functionality is lost. The comparison between several CIS technologies points out that the manufacturing process impacts the two main radiation-induced degradations: the threshold voltage shift of the readout chain MOSFETs and the dark current increase. For all the tested technologies, 1.8-V MOSFETs exhibit the lower threshold voltage shift, and the nMOSFETs are the most radiation tolerant. Among all the tested devices, 1.8-V sensors achieve the best dark current performance. Several radiationhardening-by-design solutions are evaluated at the MGy level to improve further the understanding of CIS radiation hardening at extreme TID.

Index Terms-CMOS image sensors (CISs)

Fig. 1. Pixel cross-sectional view of (a) typical 3T pixel and (b) surfaceprotected 3T pixel [START_REF] Bogaerts | Total dose and displacement damage effects in a radiation-hardened CMOS APS[END_REF]. (c) Cross-sectional view of typical 3T partially pinned PHD pixel. (d) Cross-sectional view of a typical pinned PHD (also called 4T pixel). SCR = space charge region. RST = reset MOSFET.

Space remote sensing, medical imaging but also nuclear and high energy physics applications require the use of imaging systems able to withstand dose levels up to the MGy(SiO 2 ) (1 MGy = 100 Mrad) range. Tube-type cameras offer the highest radiation hardness today but they are fragile and voluminous, and both their performance and reliability are limited. Commercially available off-the-shelf radiation tolerant cameras based on solid-state image sensors, such as charge injection devices or CIS, are limited to a maximum total ionizing dose (TID) of 100 kGy(SiO 2 ) [START_REF]High Radiation Tolerant B/W Camera[END_REF], [START_REF]High Radiation Tolerant Color Camera[END_REF]. Goiffon et al. [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF] has demonstrated that optimized radiation-hardened CISs can withstand TID up to 10 MGy(SiO 2 ). It has been shown thatradiation-hardening-by-design (RHBD) solutions such as the use of 1.8-V nMOSFET and pMOSFET or the exclusive use of N transistors for CIS readout chain reduce the threshold voltage shift induced by TID, thus improving the dynamics of the sensors itself. Moreover, optimized pixel design architectures have been proposed to reduce the dark current increase with radiation dose [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF].

This study is placed in the framework of the CAMRAD Project which looks to develop and test, under real conditions, a high-performance (color camera, high sensitivity, and high resolution) imaging system that could withstand TID > 1 MGy(SiO 2 ) for the characterization and monitoring of nuclear waste, the maintenance, and instrumentation of nuclear facilities.

The purpose of this paper is to study, through the comparison of several CIS technologies, the impact of the manufacturing process on the two main radiation-induced degradations observed at the MGy TID levels: MOSFETs' degradation and dark current increase. The objective is to evaluate the role of the CIS technology in the radiation hardness process in order to establish if equal pixel designs which differ only from the manufacturing process lead to different radiation responses. Moreover, thanks to various pixel designs, an investigation of diverse photodiode (PHD) solutions is carried out to study, for the first time to our knowledge, the radiation hardness of the partially pinned PHD. A new variant of the gate overlap design proposed in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF] and analyzed through the TCAD simulation in [START_REF] Marcelot | Dark current sharing and cancellation mechanisms in CMOS image sensors analyzed by TCAD simulations[END_REF] is for the first time characterized. The response of several RHBD pixel variants based on the gate overlap pixel is investigated to better understand their potential and limits and to improve the radiation hardness of CIS for high TID applications.

II. OVERVIEW OF THE STANDARD CIS PHOTODIODES

Different types of PHDs used in CIS are illustrated in Fig. 1. The 3T-standard PHD, Fig. 1(a), is composed of a photosensitive region, the n-doped PHD, and three transistors to reset the signal (RST), to amplify it [source follower (SF) transistor], and to select the row [row select (RS) transistor] to the column readout chain [START_REF] Fossum | CMOS active pixel image sensors[END_REF]. In this PHD, the depleted region reaches the Si/SiO 2 interfaces associated with the shallow trench isolation (STI) or with the premetal dielectric (PMD). Hence, all the defects present in the oxide that are in contact with the n-region can contribute to the dark current [START_REF] Hopkinson | Radiation effects in a CMOS active pixel sensor[END_REF]. This PHD has been widely evaluated under radiation. It is reported that STI positive trapped charges lead to a short circuit between pixels with a consequent change of the PHD capacitance [START_REF] Pain | Hardening CMOS imagers: Radhard-by-design or radhard-by-foundry[END_REF]- [START_REF] Goiffon | Generic radiation hardened photodiode layouts for deep submicron CMOS image sensor processes[END_REF].

A variant of this PHD described in [START_REF] Bogaerts | Total dose and displacement damage effects in a radiation-hardened CMOS APS[END_REF] and fabricated to improve the radiation hardness is illustrated in Fig. 1(b). It consists of a 3T pixel where the top is covered with a p + implant which reduces the dark current by reducing the contact area between the PHD depletion region and the surrounding oxides (STI and PMD). As shown in Fig. 1(a), in this pixel, called surface-protected PHD, the n-region is not depleted. It has been shown that this optimized p + layer enhances the dark current performances with respect to the 3T pixel for low-to-moderate TID levels [START_REF] Bogaerts | Total dose and displacement damage effects in a radiation-hardened CMOS APS[END_REF].

Fig. 1(c) depicts the 3T-standard partially pinned PHD [START_REF] Fossum | A review of the pinned photodiode for CCD and CMOS image sensors[END_REF], [START_REF] Lee | Partially pinned photodiode for solid state image sensors[END_REF], never investigated under irradiation to the best of our knowledge. Also, in this particular PHD, the top of the n-doped region is covered with a p + implant to prevent the contact between the depletion region and the oxides. In this case, as shown in Fig. 1(c), the PHD depth is reduced in order to fully deplete the PHD during the operation [START_REF] Lee | Partially pinned photodiode for solid state image sensors[END_REF]. In order to connect the PHDs shown in Fig. 1(b) and (c) to RST MOSFET, the p+ pinning layer has to be opened somewhere to let the n-region reach the surface. Therefore, in surface-protected and partially pinned PHDs, the depletion region is in contact with oxide interfaces, in the vicinity of the RST contacts. Since the total area of the depleted oxide interface is smaller than in a standard 3T pixel, the dark current is lower in these PHDs than in a 3T pixel.

Finally, the pinned PHD, used in 4T pixels, is shown in Fig. 1(d). In pinned PHD, an additional MOSFET, i.e., the transfer gate TG, is needed to transfer the charge between the pinned PHD and the sense node. Pinned PHD exhibits the best dark current performances before irradiation, since the p + pinning layer prevents the contact between the PHD and the oxides. However, it has been shown in [START_REF] Rao | Degradation of CMOS image sensors in deep-submicron technology due to γ -irradiation[END_REF]- [START_REF] Goiffon | Influence of transfer gate design and bias on the radiation hardness of pinned photodiode CMOS image sensors[END_REF] that the pinned PHD suffers from severe degradation due to TID, such as charge transfer degradation and dark current increase because of the trapped charges in the PMD and in the spacers. Since no RHBD solutions can be proposed to improve the radiation hardness of pinned PHD at high TID, the 4T PHDs are not investigated in this work. This study is indeed devoted to the evaluation at TID up to 1 MGy(SiO 2 ) of standard 3T PHD, standard 3T partially pinned PHD, and RHBD solution based on gate overlap 3T PHD. Several design variants of the gate overlap PHD are presented and evaluated, differing in the pixel-to-pixel isolation (e.g., STI, gate, and STI + gate) as well as in a new technique based on the addition of an n + drain in the gate overlap pixel.

III. EXPERIMENTAL DETAILS

To carry out this study, four CIS were manufactured using two different 180-nm CIS processes with dedicated and optimized in-pixel devices. A comparison with a third technology is performed, thanks to the results available in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF].

The architecture of the studied CISs is presented in Fig. 2. The integrated image sensors for each technology are composed of a pixel array (128 × 256 or 256 × 256 pixels each array) with three transistors per pixel (see Fig. 3). For this exploration, sequencing and analog-to-digital conversion are realized off-chip. The pixel array and the analog readout circuits are designed using both a mixed 3.3-and 1.8-V nMOSFET and pMOSFET and a full 1.8-V nMOSFET and pMOSFET in order to evaluate the radiation hardness of each solution. All the transistors of the readout chain have been radiation hardened by ISAE-SUPAERO using enclosed layout transistors [START_REF] Anelli | Radiation tolerant VLSI circuits in standard deep submicron CMOS technologies for the LHC experiments: Practical design aspects[END_REF] to mitigate the radiation-induced narrow channel effects and sidewall leakage [START_REF] Faccio | Radiation-induced edge effects in deep submicron CMOS transistors[END_REF]. Table I summarizes the characteristics of each sensor. II for details). All the pixels are composed of the PHD and three transistors to reset the voltage of the PHD (RST MOSFET), to amplify the signal (SF MOSFET) and to select the row (RS MOSFET). The integrated circuit is constituted of the pixel array and the analog readout chain, whereas the digital conversion and line and column decoders are off-chip.

Pixel arrays have been divided into 16 regions to investigate the radiation hardness of diverse pixel designs and RHBD solutions. The comparison between the 3T-standard [see Fig. 1(a)] and the 3T-standard partially pinned PHDs [illustrated in Fig. 1(b)] allows studying the radiation hardness of the partially pinned design at both kGy and MGy TID levels. As summarized in Table II, different RHBD solutions based on the gate overlap design (P2) are investigated. This design, illustrated in Fig. 3(a), is the typical gate overlap design of [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF].

In particular, for this study, the impact of the overlap region d [see Fig. 3(e) and (f)] is investigated, thanks to pixels P2-P4.

Another important point was to study the influence of the pixel-to-pixel isolation, in which the gated overlap design of P2 is realized only by the gate. This could lead to short circuits between the PHDs in several situations, e.g., high contrast images. To avoid the short circuit, in some designs (see for example P5 in Table II), the intrapixel isolation is realized by the STI and the polysilicon gate.

The comparison between the two thicknesses of the gate oxide (double GO2 and simple GO1) is evaluated, thanks to the pixel P6 in the 3.3-V CISs. The new variants of the gate overlap pixel investigated in this paper are presented in Fig. 3(b)-(d). In these designs (pixels P8-P13 of Table II), an n + drain (biased at VDD) is added in order to enhance the dark charges draining mechanism observed for high TID (>0.1 MGy) when a positive voltage is applied to the gate [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF]. As listed in Table II and depicted in Fig. 3(b)-(d), several variants of this pixel-type differing in the size of the n + drain and in the pixel isolation, are taken into consideration in this study.

Room temperature γ -ray irradiations were performed at the IRMA facility of IRSN (Saclay, France). The circuits were exposed up to TID levels of 10 kGy, 100 kGy, and 1 MGy(SiO 2 ) with dose rates of 0.03, 0.3, and 3 kGy/h, respectively. The devices have been characterized within the month after the end of the 60 Co irradiation.

IV. STUDY OF THE TID-INDUCED EFFECT ON DIFFERENT CMOS IMAGE SENSOR TECHNOLOGIES

A. TID-Induced MOSFETs' Degradation

Fig. 4 presents the absolute radiation-induced voltage shift measured on the MOSFET used as a current source in the readout pixel stage [Fig. 4(a)] and in the readout output stage [Fig. 4(b)] of the CIS and for several cases (CIS shown in Table I and the studied CIS in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF]).

The results confirmed that the 1.8-V MOSFETs exhibit the lower threshold voltage shift [START_REF] Faccio | Radiation-induced edge effects in deep submicron CMOS transistors[END_REF] at both output and pixel stages for each studied technology and independently of the MOSFET type (p or n). Moreover, Fig. 4(b) highlights that nMOSFETs' threshold voltage-induced shift is smaller than for pMOSFETs for both 3.3-and 1.8-V transistors. Another important result highlighted in Fig. 4 is the impact of the manufacturing technology. Indeed, transistors from foundry C exhibit the largest threshold voltage shift compared to the same MOSFET type of the other foundry. In all the considered cases, the most tolerant MOSFETs are the one fabricated from foundry B. As already discussed in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF], the large threshold voltage shift has direct consequences on the readout chain performances of the CISs: the reduction of the maximum output voltage swing (MOVS) and the electrical gain decrease. The change of these parameters leads to a reduction of the available linearity region of the image sensors, thus affecting the functionality of the sensors itself.

Table III reports a summary of the readout chain performances before and after irradiations. From the reported results, Sensor A 3.3 V is the most affected from radiation. Indeed, a reduction of both MOVS and electrical gain is observed due to the large threshold voltage shift of its transistors. On the other hand, Sensor A 1.8 V exhibits very good performances after 1 MGy(SiO 2 ) as well as both sensors from foundry B. It is worth noting that Sensor B 1.8 V shows the lower MOVS even before irradiation. In this sensor, indeed, the MOSFETs of the readout chain have a higher threshold voltage, limiting its performances.

B. TID-Induced Dark Current Increase

The dark current evolution with TID for the three CIS technologies is reported in Fig. 5 for the gate overlap design (pixel P2 of Table II). The two readout chain architectures (3.3 and 1.8 V) are also compared. The measurements are performed at a positive gate voltage, i.e., depleted gate channel. For all pixels, the gate voltage at each dose was chosen to minimize the dark current without any impact on the other CIS parameter. It can be noted that the absolute dark current value as well as the relative dark current increase depend on the supply voltage. Nonirradiated 1.8-V sensors have higher dark current than their corresponding 3.3-V sensors. This difference is most probably due to the process optimized for 3.3-V sensors. The relative dark current increase after 10 kGy(SiO 2 ) is instead lower in 1.8-V sensors for all the investigated technologies, due to the reduced thickness of the gate oxide used for these sensors. At 1 MGy(SiO 2 ), the dark current values remain lower in 1.8-V sensors by a factor of 4 in the case of foundry B and by an even larger extent in both A (factor of 5) C (factor of 7) foundries.

Another important point is the impact of the manufacturing technology: both sensors from foundry B (3.3 and 1.8 V) exhibit a higher dark current before and after irradiations with respect to their equivalent CIS from A and C technologies.

C. TID-Induced Image Nonuniformities

Fig. 6 displays the dark image before irradiation [Fig. 6(a)] and after 1 MGy(SiO 2 ) of irradiation [Fig. 6(b)] for Sensor B 3.3 V. The comparison between the two images points out that after irradiation, the sensor from foundry B exhibits a strong nonuniformity. This nonuniformity is not linked to MOSFETs' threshold voltage shift variability as in the case reported in [START_REF] Rizzolo | Multi-MGy total ionizing dose induced MOSFET variability effects on radiation hardened CMOS image sensor performances[END_REF] for foundry C. Indeed, the electrical transfer function measurements do not show nonuniformities. The causes of the nonuniformity of Fig. 6(b) are then attributed to the PHD itself even if they are still unknown. This hypothesis is supported by the fact that the same nonuniformity shape is observed when the sensor is illuminated. The circular shape leads to think that a possible cause should be the density metal difference between the edge and the center of the array [START_REF] Hopkinson | Radiation effects on a radiation-tolerant CMOS active pixel sensor[END_REF]- [START_REF] Cherniak | Investigation of nonuniform degradation of CMOS-sensor lightsensitive surface under gamma-irradiation[END_REF].

It is worth mentioning that both sensors from B foundry show this particular effect, whereas any nonuniformity is present in sensors from foundry A. This could be linked to the fact that even if the pixel design are the same for both technologies, a variation in the process could result in a variation of the parameters in the deposited layers, thus leading to a different metal density in sensors from foundry B.

This first part has allowed investigating the radiationeffects four CIS from two different foundries. A third foundry was added for comparison, thanks to the results reported in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF]. The results discussed in this section have shown that the performances after 1 MGy(SiO 2 ) of ionizing radiation strongly depend on the CIS manufacturing, whereas CISs from foundry B have the best electrical response in terms of MOSFETs' threshold voltage shift, their dark current increase is the most important in both 3.3-and 1.8-V architectures. Furthermore, these sensors suffer from radiationinduced nonuniformity leading to a decrease of cameras' performances. On the other hand, Sensor A 3.3-V readout chain is the most degraded. This leads to a reduction of the overall sensor performances reducing the linear useful range, in which the CIS can correctly operate. Dark current comparison points out that after irradiation, 1.8-V architecture has the best performances. For these reasons, in Section V, only the results of Sensors A 1.8 V are reported. The same conclusion remains valid for the other investigated CIS.

To establish the reasons why radiation impacts differently, the diverse CMOS process is a tricky point since no information are provided by foundry on their own process. Nevertheless, these results have validated that the manufacturing process is a key parameter to take in account when dealing with the radiation-hardened CIS development.

V. PIXEL INFLUENCE IN THE CIS RADIATION HARDNESS

Raw images captured by Sensor A 1.8 V are reported in Fig. 7, before and after irradiations. The 16 different pixeltype regions can be easily recognized. Their organization is the one reported in Fig. 2. From the comparison of the two images, it can be seen that after irradiation, the standard 3T PHD (bottom left) as well as the partially pinned PHDs (top right) are not functional anymore, whereas all the gate overlap-based designs are able to provide an image. In order to study the radiation hardness of different PHD doping profiles proposed by the foundry and to compare with the optimized RHBD gate overlap solutions, the dark current evolution with TID is presented in Fig. 8. The results show that as expected, the 3T-standard PHD exhibits the higher absolute dark current value after a TID of 10 kGy(SiO 2 ). (The dark current before irradiation is comparable to the other 3T pixels.) This dark current increase at this TID level is mostly due to the TIDinduced trapped charges and interface states in the Si/SiO 2 interfaces (PMD and STI) which strongly contribute to the dark signal increase [START_REF] Goiffon | Analysis of total dose-induced dark current in CMOS image sensors from interface state and trapped charge density measurements[END_REF].

The 3T-standard partially pinned PHD has the lowest dark current before irradiation among all the studied technologies, thanks to the p+ surface protection. However, at 10 kGy(SiO 2 ), the dark current of this pixel type increases up to ∼1 pA. As shown in Fig. 8, the absolute dark current value is lower in the partially pinned PHD than in 3T-standard PHD. It is possible that at this dose level, the induced positive trapped charges in the PMD reduce the effective doping of the p + layer, thus allowing the PHD to be in contact with the oxide, in which defects contribute to the dark current increase. Above 10 kGy(SiO 2 ), both partially pinned PHD and standard PHD are not functional anymore. As regards the RHBD gate overlap solutions, it can be noted that they give the best performance in terms of dark current increase with TID even if some differences are highlighted between different variants.

Four different variants are reported in Fig. 8: the gate overlap PHD (P2 or P6 shown in Table II) with an overlap distance of 0.3 μm, the gate aligned PHD (P3 shown in Table II) with d = 0 μm, the gate overlap and STI isolation (P5 shown in Table II), and the PHD P13 having an n + drain ring surrounding the PHD. One can see that the gate aligned PHD has the highest dark current compared to the gate overlap design at the optimum gate voltage.

Fig. 9 displays the dark current as a function of the applied gate voltage for pixels P2-P4. These pixels differ from each other for the overlap distance. It can be noted that for negative gate voltage, the dark current in the gate aligned design (d = 0) is lower than in the gate overlap designs. Furthermore, the increase of the overlap distance from 0.3 to 0.6 μm leads to an augmentation of the dark current in this negative gate voltage region. This difference in dark current is most likely due to an enhanced gate-induced drain leakage [START_REF] Chan | The impact of gateinduced drain leakage current on MOSFETs scaling[END_REF] when the overlap is too large. For positive gate voltages, the best dark current is exhibited by gate overlap PHDs, whereas gate aligned PHD has higher dark current. In this case, as illustrated in Fig. 10(a), the induced defects in the spacer contribute to the dark current in the gate aligned design. Indeed, the spacer is in contact with the depleted region in this particular case. On the other hand, in the gate overlap designs, the spacer is no more in contact with the depleted region [see Fig. 10(b)], thus leading to a lower dark current in these pixels. As last remarks, it is possible to see that in terms of dark current performances, both gate overlap pixels have the same behavior for positive gate voltages (i.e., the optimum voltage for this pixel type). The comparison between P5 and P6 highlights that there is no influence of STI used to improve the intrapixel isolation in the dark current. As it can be seen from Fig. 7, there is no evidence of short circuit between adjacent PHDs even in the region of high contrast. Thus, in this particular technology, STI isolation between diodes can be removed without any obvious drawback.

From Fig. 8, it can be seen also that two regimes can be found depending on the investigated TID range from the comparison between gate overlap (pixel P2 shown in Table II) and gate overlap with n + drain (pixel P13 shown in Table II). For TID < 100 kGy(SiO 2 ), the dark current reduction is enhanced in the n + drain design, whereas beyond 100 kGy(SiO 2 ), the two pixels exhibit mostly the same dark current level. In order to explain this difference, Fig. 11 reports the dark current measurements as a function of gate voltage at two different doses. At 10 kGy(SiO 2 ), as shown in Fig. 11(a), the gate overlap design exhibits the same dark current than the n + drain design up to a gate voltage of 1.3 V. (The n + drain design is slightly lower for all the examined gate voltage ranges.) In this gate voltage range, the gate channel is depleted and the PHD depletion region extends toward the STI sidewall. However, there is no dark current increase up to 1.3 V in the gate overlap PHD. As suggested in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF], in the considered gate voltage range, the STI sidewall p+ passivation may be sufficient to prevent the depletion region from reaching it.

At a gate voltage higher than 1.3 V, an increase of the dark current is observed in the gate overlap design up to values that are comparable to the partially pinned design, whereas the dark current continues to decrease in the n + drain design. This difference is due to the dark charges driving mechanism toward the n + drain (biased at VDD) which is activated in the n + drain design. For gate voltages higher than 1.3 V, the depletion region reaches the STI sidewall in the gate overlap pixel, and the TID-induced defects in the STI contribute to the dark current increase. Conversely, as depicted in Fig. 11(d), in the other design, the dark charges coming from the STI sidewall are collected by the n + drain, thus leading to a continuous reduction of the dark current with the increase of the gate voltage. For TID > 10 kGy(SiO 2 ), the STI radiation-induced positive trapped charge is sufficient to create an inversion channel all along the STI interface, thus turning on the dark current draining mechanism in the gate overlap design [see Fig. 11(e)]. In this case, the dark current decreases with increasing gate voltage in both investigated designs.

The reported dark current analysis has shown that adding the n+ drain activates the dark charges draining mechanism which occurs also in the gate overlap design after a certain TID. This suggests, indeed, that this proposed RHBD solution is promising since it allows controlling the drain of the dark charges at different TIDs. In order to evaluate the influence of the n + drain design on the PHD optoelectrical performances, a preliminary analysis on the saturation behavior of the diverse pixel variants is performed. Fig. 12 reports the saturation voltage as a function of the gate voltage for pixels without drain and for various n + drain dimensions investigated in this paper after 1 MGy(SiO 2 ) of irradiation. It can be seen that the saturation voltage is constant with the gate voltage for negative voltages.

For positive voltages, the saturation voltage decreases after a threshold value. It can be pointed out that the gate voltage value after which the saturation voltage starts to decrease depends on the pixel design. Indeed, in PHDs having the n + ring, the saturation voltage decreases after 0.5 V, whereas for the other, the threshold voltage is between 1.1 and 1.5 V.

In the case of gate overlap without n + drain, the saturation voltage decreases after 1.6 V. This result shows that the n + drain design is an important parameter to take into account for the implementation of this RHBD solution in radiationhard cameras. A bad design choice could lead to a strong reduction of the saturation voltage at a gate voltage too low to obtain an efficient dark current reduction through the draining mechanism.

VI. CONCLUSION

In this paper, a radiation hardness comparison of CIS technologies at high TID levels is performed with the aim to evaluate the vulnerability of the partially pinned PHD technology, to compare the radiation hardness of different manufacturing processes and to confirm the response of various standard and RHBD pixel types.

It has been pointed out that even if the 3T-standard partially pinned PHD has the lowest dark current before irradiation among all the studied technologies, and even if this technology is often considered as radiation tolerant in the community, at 10 kGy(SiO 2 ), the dark current of this pixel type increases up to ∼1 pA (comparable to the dark current of standard 3T PHDs at the same TID). This dark current increase has been mostly attributed to the induced trapped charges in the PMD which reduce the effective doping of the p+ layer, thus allowing the pinned PHD to be in contact with the defects in the Si/SiO 2 interfaces contributing to the dark current increase. Moreover, it has been shown that above 10 kGy(SiO 2 ), the partially pinned pinned PHD functionality is lost.

The comparison between the CIS postirradiation performances of several technologies has highlighted that the manufacturing process impacts the two main radiation-induced degradations: the threshold voltage shift of the pixel and the output stages of the readout chain and the dark current increase. It has been confirmed that 1.8-V MOSFETs exhibit the lower threshold voltage shift for all the tested technologies and that in both 3.3-and 1.8-V transistors, the nMOSFETs are the most radiation tolerant devices among both 1.8-and 3.3-V Regarding the dark current increase in various tested technologies, the results demonstrate that 1.8-V sensors exhibit the best performances by up to a factor of 7 for foundry C. Finally, it has been pointed out that although the main conclusions listed above are the same for all the tested technologies, the manufacturing process has an important impact on the absolute radiation hardness. Indeed, foundry B exhibits the most radiation resistant MOSFETs, but CISs dark current increase is the largest in both 3.3-and 1.8-V architectures. Furthermore, these sensors suffer from radiationinduced nonuniformity, leading to a decrease of cameras' performances. TID effects on foundry A 3.3-V architecture lead to a reduction of the overall sensor performances reducing the linear useful range, in which the CIS can correctly operate. Conversely, 1.8-V architecture has shown the best performances after 1-MGy(SiO 2 ) TID.

Finally, the comparison between various RHBD pixel variants has highlighted that the gate overlap design still gives the best performance in terms of dark current for positive voltages applied to the gate, even on different CMOSs process than the one explored before [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF]. On the other hand, this overlap has to be optimized in order to reduce nonuniformity linked to the pixel-to-pixel connection. The study of a new RHBD solution consisting in adding an n + drain biased at VDD in the pixel has confirmed the charge draining mechanisms proposed in [START_REF] Goiffon | Total ionizing dose effects on a radiation-hardened CMOS image sensor demonstrator for ITER remote handling[END_REF] and analyzed through the TCAD simulation in [START_REF] Marcelot | Dark current sharing and cancellation mechanisms in CMOS image sensors analyzed by TCAD simulations[END_REF]. Furthermore, the study of this pixel variant has revealed that the dark charges draining mechanisms can be enabled at TID < 10 kGy(SiO 2 ), thus leading to an improved control of the dark current reduction in this range. It has, however, been shown that the dimensions of n + drain are important since the activation of the charge drain mechanism affects the performances of the camera via the reduction of the saturation voltage.

Thanks to these results, it has been possible to clarify the role of the manufacturing process which is shown to be a key parameter to take into account when dealing with radiation resistant CIS development. The feasibility of the development of a full-size sensor with promising performances at high TID is confirmed. The next step will be to explore the proposed improvements, to integrate more functions on-chip in order to develop the full-size and fully integrated camera which could withstand the harsh environments aimed by the CAMRAD Project.

Fig. 2 .

 2 Fig. 2. Architecture of the studied CIS showing the overview of the investigated pixel designs (see TableIIfor details). All the pixels are composed of the PHD and three transistors to reset the voltage of the PHD (RST MOSFET), to amplify the signal (SF MOSFET) and to select the row (RS MOSFET). The integrated circuit is constituted of the pixel array and the analog readout chain, whereas the digital conversion and line and column decoders are off-chip.

Fig. 3 .

 3 Fig. 3. Top-view illustration of the investigated RHBD pixel designs: (a) gate overlap, (b) gate overlap pixel with two short n+ drains, (c) gate overlap pixel with one long n+ drain, and (d) gate overlap pixel with two short n+ drains. (e) Gate overlap isolation and (f) gate overlap isolation and n+ drain cross sections are also presented. d = overlap distance between the gate and PHD.

Fig. 4 .

 4 Fig. 4. Comparison of the absolute voltage shift of the CIS (a) pixel stage and (b) output stage MOSFET current source for several transistor technologies.

Fig. 5 .

 5 Fig. 5. Dark current evolution with TID for P2 gate overlap pixel design of several foundries. Reported measurements are taken at a positive gate voltage, i.e., the PHD is depleted.

Fig. 6 .

 6 Fig. 6. Dark image of Sensor B 3.3 V (a) before irradiation and (b) after 1 MGy(SiO 2 ) of irradiation. The integration time is 30 ms, and the gate voltage is set to 0 V.

Fig. 7 .

 7 Fig. 7. Raw images captured (a) before and (b) after 1 MGy(SiO 2 ) with comparable illumination conditions for Sensor A 1.8 V. The integration time is ∼1 ms, and the gate voltage is set to 1 V. The 16-pixel variants are organized, as illustrated in Fig. 2.

Fig. 8 .

 8 Fig. 8. Dark current evolution with TID for Sensor A 1.8-V pixels P1, P6, P13, and of Table II. The dark current values in P2 and P13 are obtained for depleted gate (gate voltage > 0 V).

Fig. 9 .

 9 Fig. 9. Dark current as a function of gate voltage at a TID of 100 kGy for pixels with different overlaps between the gate and the PHD.

Fig. 10 .

 10 Fig. 10. Illustrations of the dark current enhancement mechanism between (a) gate aligned PHD and (b) gate overlap PHD when the gate channel is depleted (positive gate bias). The depleted region is in contact with the spacers in the gate aligned design, thus leading to an increase of the number of defects contributing to the dark current.

Fig. 11 .

 11 Fig. 11. Dark current as a function of voltage at a TID of (a) 10 kGy and (b) 1 MGy for P2 and P13. The same behavior has been measured on the other CIS architectures and foundries. Illustrations of the dark current draining mechanism in (c) and (e) gate overlap and (d) and (f) n + drain PHDs.

Fig.

  Fig. Saturation voltage as a function of gate voltage at a TID of 1 MGy for different n+ drain pixel variants.

TABLE I CIS

 I

CHARACTERISTICS'OVERVIEW

TABLE III SUMMARY

 III OF THE CIS READOUT CHAIN PERFORMANCES FOR THE FOUR SENSORS BEFORE AND AFTER IRRADIATIONS

	TABLE II
	PIXELS' DESIGN VARIATIONS' OVERVIEW