Philippe Martin-Gonthier

Radiation Effects in Pinned Photodiode CMOS Image Sensors: Pixel Performance Degradation Due to Total Ionizing Dose

Several Pinned Photodiode (PPD) CMOS Image Sensors (CIS) are designed, manufactured, characterized and exposed biased to ionizing radiation up to 10 kGy(SiO2 ). In addition to the usually reported dark current increase and quantum efficiency drop at short wavelengths, several original radiation effects are shown: an increase of the pinning voltage, a decrease of the buried photodiode full well capacity, a large change in charge transfer efficiency, the creation of a large number of Total Ionizing Dose (TID) induced Dark Current Random Telegraph Signal (DC-RTS) centers active in the photodiode (even when the Transfer Gate (TG) is accumulated) and the complete depletion of the Pre-Metal Dielectric (PMD) interface at the highest TID leading to a large dark current and the loss of control of the TG on the dark current. The proposed mechanisms at the origin of these degradations are discussed. It is also demonstrated that biasing (i.e., operating) the PPD CIS during irradiation does not enhance the degradations compared to sensors grounded during irradiation.

RTS noise impact in CMOS image sensors readout circuit

CMOS image sensors are nowadays widely used in imaging applications even for high end applications. This is really possible thanks to a reduction of noise obtained, among others, by Correlated Double Sampling (CDS) readout. Random Telegraph Signal (RTS) noise has thus become an issue for low light level applications especially in the context of downscaling transistor dimension. This paper describes the analysis of in-pixel source follower transistor RTS noise filtering by CDS circuit. The measurement of a non Gaussian distribution with a positive skew of image sensor output noise is analysed and dimension (W and L) impact of the in-pixel source follower is analysed.

Evidence of a Novel Source of Random Telegraph Signal in CMOS Image Sensors

This letter reports a new source of dark current random telegraph signal in CMOS image sensors due to meta-stable Shockley-Read-Hall generation mechanism at oxide interfaces. The role of oxide defects is discriminated thanks to the use of ionizing radiations. A dedicated RTS detection technique and several test conditions (radiation dose, temperature, integration time, photodiode bias) reveal the particularities of this novel source of RTS.

Novel Readout Circuit Architecture for CMOS Image Sensors Minimizing RTS Noise

This letter presents a novel readout architecture and its associated readout sequence for complementary metal-oxide-semiconductor (CMOS) image sensors (CISs) based on switch biasing techniques in order to reduce noisy pixel numbers induced by in-pixel source-follower transistor random telegraph signal noise. Measurement results done on a test image sensor designed with 0.35-μm CIS technology demonstrate an efficient reduction of noisy pixel numbers without a pixel performance decrease.

In-Pixel Source Follower Transistor RTS Noise Behavior Under Ionizing Radiation in CMOS Image Sensors

This paper presents temporal noise measurement results for several total ionizing dose (TID) steps up to 2.19 Mrad of an image sensor designed with a 0.18-μm CMOS image sensor process. The noise measurements are focused on the random telegraph signal (RTS) noise due to the in-pixel source follower transistor of the sensor readout chain inducing noisy pixels. Results show no significant RTS noise degradation up to 300 krad of TID. Beyond this TID step, a limited RTS noise degradation is observed, and for the 2.19-Mrad step, an additional increase of total noise, including thermal, 1/f, and RTS noises, is noted. Noisy pixels have been studied for high TIDs, and three cases have been observed: 1) no change on RTS behavior; 2) creation of RTS behavior; and 3) modifications of RTS behavior.

Vulnerability of CMOS image sensors in megajoule class laser harsh environment

CMOS image sensors (CIS) are promising candidates as part of optical imagers for the plasma diagnostics devoted to the study of fusion by inertial confinement. However, the harsh radiative environment of Megajoule Class Lasers threatens the performances of these optical sensors. In this paper, the vulnerability of CIS to the transient and mixed pulsed radiation environment associated with such facilities is investigated during an experiment at the OMEGA facility at the Laboratory for Laser Energetics (LLE), Rochester, NY, USA. The transient and permanent effects of the 14 MeV neutron pulse on CIS are presented. The behavior of the tested CIS shows that active pixel sensors (APS) exhibit a better hardness to this harsh environment than a CCD. A first order extrapolation of the reported results to the higher level of radiation expected for Megajoule Class Laser facilities (Laser Megajoule in France or National Ignition Facility in the USA) shows that temporarily saturated pixels due to transient neutron-induced single event effects will be the major issue for the development of radiation-tolerant plasma diagnostic instruments whereas the permanent degradation of the CIS related to displacement damage or total ionizing dose effects could be reduced by applying well known mitigation techniques.

Study of CCD Transport on CMOS Imaging Technology: Comparison Between SCCD and BCCD, and Ramp Effect on the CTI

This paper presents measurements performed on charge-coupled device (CCD) structures manufactured on a deep micrometer CMOS imaging technology, in surface channel CCD and in buried channel CCD mode. The charge transfer inefficiency is evaluated for both CCD modes with regard to the injected charge, and the influence of the rising and falling time effect is explored. Controlling the ramp and especially reducing its abruptness allows to get much lower charge transfer inefficiency in buried CCD mode. On the contrary, we did not observe any effect of the ramp on surface channel CCD mode because of the presence of interface traps at the silicon-oxide interface.

Overview of CMOS process and design options for image sensor dedicated to space applications

With the growth of huge volume markets (mobile phones, digital cameras...) CMOS technologies for image sensor improve significantly. New process flows appear in order to optimize some parameters such as quantum efficiency, dark current, and conversion gain. Space applications can of course benefit from these improvements. To illustrate this evolution, this paper reports results from three technologies that have been evaluated with test vehicles composed of several sub arrays designed with some space applications as target. These three technologies are CMOS standard, improved and sensor optimized process in 0.35μm generation. Measurements are focussed on quantum efficiency, dark current, conversion gain and noise. Other measurements such as Modulation Transfer Function (MTF) and crosstalk are depicted in [1]. A comparison between results has been done and three categories of CMOS process for image sensors have been listed. Radiation tolerance has been also studied for the CMOS improved process in the way of hardening the imager by design. Results at 4, 15, 25 and 50 krad prove a good ionizing dose radiation tolerance applying specific techniques.

High-performance monolithic CMOS detectors for space applications

During the last 10 years, research about CMOS image sensors (also called APS - Active Pixel Sensors) has been intensively carried out, in order to offer an alternative to CCDs as image sensors. This is particularly the case for space applications as CMOS image sensors feature characteristics which are obviously of interest for flight hardware: parallel or semi-parallel architecture, on chip control and processing electronics, low power dissipation, high level of radiation tolerance... Many image sensor companies, institutes and laboratories have demonstrated the compatibility of CMOS image sensors with consumer applications: micro-cameras, video-conferencing, digital- still cameras. And recent designs have shown that APS is getting closer to the CCD in terms of performance level. However, he large majority of the existing products do not offer the specific features which are required for many space applications. ASTRIUM and SUPAERO/CIMI have decided to work together in view of developing CMOS image sensors dedicated to space business. After a brief presentation of the team organization for space image sensor design and production, the latest results of a high performances 512 X 512 pixels CMOS device characterization are presented with emphasis on the achieved electro-optical performance. Finally, the on going and short-term coming activities of the team are discussed.

A digital high-dynamic-range CMOS image sensor with multi-integration and pixel readout request

A novel principle has been developed to build an ultra wide dynamic range digital CMOS image sensor. Multiple integrations are used to achieve the required dynamic. Its innovative readout system allows a direct capture of the final image from the different exposure time with no need of external reconstruction. The sensor readout system is entirely digital, implementing an in-pixel ADC. Realized in the STMicroelectronics 0.13&mgr;m CMOS standard technology, the 10&mgr;m x 10&mgr;m pixels contain 42 transistors with a fill factor of 25%. The sensor is able to capture more than 120dB dynamic range scenes at video rate.