Multi-MGy Radiation Hard CMOS Image Sensor: Design, Characterization and X/Gamma Rays Total Ionizing Dose Tests

Abstract

International audienceA Radiation Hard CMOS Active Pixel Image Sensor has been designed, manufactured and exposed to X and 60Co γ-ray sources up to several MGy of Total Ionizing Dose (TID). It is demonstrated that a Radiation-Hardened-By-Design (RHBD) CMOS Image Sensor (CIS) can still provide useful images after 10 MGy(SiO2) (i.e. 1 Grad). This paper also presents the first detailed characterizations of CIS opto-electrical performances (i.e. dark current, quantum efficiency, gain, noise, transfer functions, etc.) in the MGy range. These results show that it is possible to design a CIS with good performances even after having absorbed several MGy. Four different RHBD photodiode designs are compared: a standard photodiode design, two well known RHBD layouts and a proposed improvement of the gated photodiode design. The proposed layout exhibits the best performances over the entire studied TID range and further optimizations are discussed. Several original MGy radiation effects are presented and discussed at the device and circuit levels and mitigation techniques are proposed to improve further the radiation hardness of future Rad-Hard CIS developments for extreme TID applications (e.g. for nuclear power plant monitoring/dismantling, experimental reactors (e.g. ITER) or next generation particle physics experiments (e.g. CERN))

Total Ionizing Dose Effects on a Radiation-Hardened CMOS Image Sensor Demonstrator for ITER Remote Handling

“…Previous work has demonstrated that reaching a 10 MGy (1 Grad) radiation hardness with a CMOS Image Sensor (CIS) is feasible [2], [3]. In order to confirm this conclusion and to demonstrate that a full camera can also be made radiation hard up to several Mega-gray, the FUsion for energy Radiation Hard Image sensor (FURHI) and Imaging System (FURHIS) demonstrators have been developed.…”

“…The illumination system power and the sensor integration time will be tuned to achieve the sensitivity required by the application at the camera level. It is worth noting that the final Large voltage shifts in RHBD CIS analog readout chain due to 3.3V ELT P-MOSFETs 2 mitigation techniques proposed [2] Only use 1.8V ELT N&P-MOSFETs [3] Only use ELT N-MOSFETs (3.3V) (this work) Figure 1. Overview of the explored radiation hardening approaches for the CIS analog readout chain.…”

“…The whole circuit is radiation-hardened-by-design [6], especially by using enclosed geometries (Enclosed Layout Transistors (ELT) [7]) for all N and P MOSFETs (1.8 V and 3.3 V ones) to mitigate Radiation Induced Narrow Channel Effect (RINCE) [8], sidewall leakages and junction leakages. In previous explorations [2], [3], it appeared that 3.3 V P channel transistors were too sensitive to TID to be used beyond 100 kGy because of large gate oxide trapped charge induced threshold voltage shifts (∆V ot ). On the other hand 3.3 V N-channel transistors did not exhibit any ∆V ot after several MGy and their threshold voltage was only influenced by a limited interface state induced shift (∆V it ) [2].…”

“…In previous explorations [2], [3], it appeared that 3.3 V P channel transistors were too sensitive to TID to be used beyond 100 kGy because of large gate oxide trapped charge induced threshold voltage shifts (∆V ot ). On the other hand 3.3 V N-channel transistors did not exhibit any ∆V ot after several MGy and their threshold voltage was only influenced by a limited interface state induced shift (∆V it ) [2]. Such enhanced sensitivity of P-channel MOSFETs has been reported on several technology nodes and foundries [9]- [11] and its root cause, that seems to differ from one node to another, is still under investigation.…”

“…2), all based on the gate overlap design proposed in [2], with and without a color filter array (CFA) on top of them (to confirm the high radiation hardness of CFA). It should be emphasized that FURHI pixel A design is exactly the same as the pixel C design in [2] (i.e. the gate overlap layout) and it will be referred to as pixel A design from [2] in this manuscript for the sake of clarity.…”