New perspectives for CMOS image sensors in harsh radiative environments

Transcription

1 New perspectives for CMOS image sensors in harsh radiative environments P.Magnan V. Goiffon, F. Corbière, S. Rolando, M. Estribeau, P. Magnan, B. Avon, J. Baer, R. Molina and A. Chabane; ISAE-SUPAERO, Univ. Toulouse, France M. Gaillardin, P. Paillet, and C. Marcandella; CEA DAM DIF, Arpajon, France S. Girard; Univ. Saint-Etienne, Laboratoire Hubert Curien, France Imaging conference, Tuesday, Octover 7th 2015

2 Context Post Fukushima Nuclear Power Plant accident trauma Strongly exacerbated sensitivity of the civil society to the potential weaknesses and dangers of Nuclear Facilities Nuclear Power Plants Nuclear waste Next generation particle repository 2 physics facilities (ITER, LMJ)

3 Context Emphasis on the lack of vision capabilities in very harsh radiative environments, e.g. required for rescue robots actions, remote handling (decommisioning), surveillance...associated with nominal and accidental operations Robot Offers First Glimpse Into Melted Fukushima Reactor - Courtesy Tepco - April10th 2015 Growing interest for compact imaging systems that can withstand several MGy (>100 Mrad) of Total Ionizing Dose (TID) for such applications. 3

4 The ionizing dose Ionization: electron-hole pairs generation Xrays, Gamma rays,protons, Electrons, Ions,... Photocurrent/Single Event Effects(Transients) - Single Event Upset - Latchup Oxide Silicon Ionizing dose (TID) cumulative effects This talk SiO Trapped charges Interface Si traps Positive charge build-up in oxides Interface states in the Si bandgap Dose official SI Unit : Gray(Gy) = 1 J.Kg -1 (= 6.25 x ev/kg) old unit: rad (1 rad = 1 cgy gy = 100 rads) Radiation effects do modify the behavior of all components of the Image sensor : photodiodes, MOSFETS 4

5 The ionizing dose scale Chest X-ray. Radiotherapy 1-2 Gy/day Satellite & space electronics gy/yr X Radiography dose ~ mgy High energy Physics and nuclear facilities 1 mgy 0.1 rd 1 Gy 100 rd 10 Gy 1 krd 100 Gy 10 krd 1 kgy 100 krd 10 kgy 1 Mrd 100 kgy 10 Mrd 1 MGy 100 Mrd 10 MGy 1 Grd 100 MGy 10 Grd Ordinary Compnent Rad-tolerant Rad-hard 5

6 The ionizing dose scale Chest X-ray. Radiotherapy 1-2 Gy/day Satellite & space electronics gy/yr X Radiography dose ~ mgy High energy Physics and nuclear facilities 1 mgy 0.1 rd 1 Gy 100 rd 10 Gy 1 krd 100 Gy 10 krd 1 kgy 100 krd 10 kgy 1 Mrd 100 kgy 10 Mrd 1 MGy 100 Mrd 10 MGy 1 Grd 100 MGy 10 Grd Ordinary Compnent Rad-tolerant Rad-hard 6

7 Available Rad-Hard cameras technology Most available Rad-Hard cameras for nuclear environnements are using imaging tubes technology, limiting the miniaturization/functions integration In the past, the radiation hardness of Radiation-Hardened CMOS IS has been demonstrated up to several hundreds of kgy (several tens of Mrad). There is no commercially available today CMOS based Camera that can handle the Total Ionizing Dose required for the targeted applications (TID >= 1MGy(SiO2)) 7

8 Effects of ionizing dose on Image Sensors TID leads to: A dark signal and noise increase A reduction of quantum efficiency A saturation voltage reduction MOVS reduction SNR reduction Dynamic Range 8

9 Rad Hard CMOS Imagers In Europe, several R&D programs, funded by ESA, have been setup in order to develop Rad Hard CIS especially for Star Trackers / /2015 Star x512 pixels 25 µm pitch Analog out + 10 bits ADC Max 1 MGy Star1000 1Kx1K pixels 15 µm pitch Analog out + 10 bits ADC HAS/HAS2 1KxK pixels 18 µm pitch Analog out + 12bits ADC 3 KGy HAS3 1280x1280 pixels 11 µm pitch 12bits Column ADC Target 0.5 KGy ON SEMI Hardened 3T photodiode Hardened 4T pinned photodiode 9

10 CIS Design : photodiode options PMD InterfaceTraps(IT) and OT (PinningLayer depletion) Large dark current No Radiation Hardening By Design Solution (yet) STI OT & IT Large dark current Can be mitigated by design! 10

11 CIS Design : photodiode radiation hardening Four 3T photodiode designs have been studied: Standard Photodiode P+ Surround P++ Most Promising Designs for High Dose (gate isolation): Proposed Improvement: Gate Overlap Design Classical Gated Diode (gate aligned N implant) Gate with voluntary N-overlap Gate (N-aligned) 11

12 Post Irradiation Results: Raw Images Standard Photodiode Surround P+ Proposed Gate Overlap Classical Gated Before MGy (400 MGy (1 Grad) Gate Overlap 12

13 Post Irradiation Results: Raw Images Standard Photodiode Surround P+ Proposed Gate Overlap Classical Gated Before MGy (400 MGy (1 Grad) Gate Overlap Acceptable image degradation even after 1 Grad (10 MGy)! 13

14 Post Irradiation main results: 14

15 Conclusion & Perspectives After 1 Grad/10 MGy the CIS can still provide images The main degradations are Large 3.3V PMOST Vth that will be mitigated in the next design (full NMOST readout chain) A still important dark current rise which may be further reduced in the next design Gain and QE performances are weakly impacted by the ionizing radiation dose Perspectives: Further exploration of the MGy range Development of a MGy Rad-Hard Camera for ITER Remote Handling (funded by F4E) 15 15