Rad Tolerant CMOS Image Sensor Based on Hole Collection 4T Pixel Pinned Photodiode

1.4μm pixel pitch CMOS Image sensors based on hole collection pinned photodiode (HPD) have been irradiated with 60Co source. The HPD sensors exhibit much lower dark current degradation than equivalent commercial sensors using an Electron collection Pinned Photodiode (EPD). This hardness improvement is mainly attributed to carrier accumulation near the interfaces induced by the generated positive charges in dielectrics. The pre-eminence of this image sensor based on hole collection pinned photodiode architectures in ionizing environments is demonstrated

A Review of the Pinned Photodiode for CCD and CMOS Image Sensors

The pinned photodiode is the primary photodetector structure used in most CCD and CMOS image sensors. This paper reviews the development, physics, and technology of the pinned photodiode

Radiation Effects on CMOS Active Pixel Image Sensors

Today, Complementary-Metal-Oxide-Semiconductor (CMOS) Image Sensors (CIS), also called Active Pixel Sensors (APS), are the most popular imager technology with several billions manufactured every year. They represent about 90% of the imager market and should exceed 95% in a couple of years. Compared to the main alternative imager technology, the Charge Coupled Device (CCD), CISs have several major benefits such as low-power consumption, high-integration, high speed and the capacity to integrate advanced CMOS functions on-chip (and even inside the pixel). Thanks to the latest technology innovations, CISs are now matching the performances of CCDs in terms of image quality and sensitivity placing them at the forefront even in high-end applications such as digital single-lens reflex, scientific instruments, and machine vision. Thanks to these advantages, CISs are also used in harsh radiation environment for applications such as: space applications, X-ray medical imaging, electron microscopy, nuclear facility monitoring and remote handling (nuclear power plants, nuclear waste repositories, nuclear physics facilities…), particle detection and imaging, military applications etc.. Designing, hardening and testing a sensor for such applications require the understanding of the CIS behavior when exposed to radiation sources. Understanding and improving further the intrinsically good radiation hardness of APS has been a topic of interest since its invention. This interest has been recently growing with the coming of new behaviors brought by the profound evolution of CIS technologies (as discussed throughout this manuscript) compared to the older generation mainstream CMOS processes used in early work. The aim of this chapter is to give an overview of the parasitic effects that can undergo a modern CIS when it is exposed to a high energy particle radiation field

MOSFET Modulated Dual Conversion Gain CMOS Image Sensors

In recent years, vision systems based on CMOS image sensors have acquired significant ground over those based on charge-coupled devices (CCD). The main advantages of CMOS image sensors are their high level of integration, random accessibility, and low-voltage, low-power operation. Previously proposed high dynamic range enhancement schemes focused mainly on extending the sensor dynamic range at the high illumination end. Sensor dynamic range extension at the low illumination end has not been addressed. Since most applications require low-noise, high-sensitivity, characteristics for imaging of the dark region as well as dynamic range expansion to the bright region, the availability of a low-noise, high-sensitivity pixel device is particularly important. In this dissertation, a dual-conversion-gain (DCG) pixel architecture was proposed; this architecture increases the signal to noise ratio (SNR) and the dynamic range of CMOS image sensors at both the low and high illumination ends. The dual conversion gain pixel improves the dynamic range by changing the conversion gain based on the illumination level without increasing artifacts or increasing the imaging readout noise floor. A MOSFET is used to modulate the capacitance of the charge sensing node. Under high light illumination conditions, a low conversion gain is used to achieve higher full well capacity and wider dynamic range. Under low light conditions, a high conversion gain is enabled to lower the readout noise and achieve excellent low light performance. A sensor prototype using the new pixel architecture with 5.6μm pixel pitch was designed and fabricated using Micron Technology’s 130nm 3-metal and 2-poly silicon process. The periphery circuitries were designed to readout the pixel and support the pixel characterization needs. The pixel design, readout timing, and operation voltage were optimized. A detail sensor characterization was performed; a 127μV/e was achieved for the high conversion gain mode and 30.8μV/e for the low conversion gain mode. Characterization results confirm that a 42ke linear full well was achieved for the low conversion gain mode and 10.5ke for the high conversion gain mode. An average 2.1e readout noise was measured for the high conversion gain mode and 8.6e for the low conversion gain mode. The total sensor dynamic range was extended to 86dB by combining the two modes of operation with a 46.2dB maximum SNR. Several images were taken by the prototype sensor under different illumination levels. The simple processed color images show the clear advantage of the high conversion gain mode for the low light imaging