CMOS based imagers are beginning to compete against CCDs in many areas of the consumer market because of their system-on-a-chip capability. Sensitivity, however, is a main weakness of CMOS imagers and enhancements and deviations from standard CMOS processes are necessary to keep up sensitivity with downscaled process generations. In the introductory section several definitions for the sensitivity of image sensors are reviewed with regard to their potential to allow meaningful comparison of different detector structures. In the main section, the standard CMOS sensor architecture is compared to detector structures designed to improve the sensitivity, namely the photogate (PG), the pinned photodiode (PPD) and the thin film on ASIC (TFA) approach. The latter uses a vertical integration of the photodiode on top of the pixel transistors. A careful analysis of the relevant electrical, optical and technological parameters and many previously published experimental data for different imagers reveals that only the PPD and the TFA enhancements provide satisfactory sensitivity and withstand scaling down to 0.18 /spl mu/ processes. Due to the higher fill factor and the higher quantum efficiency TFA provides significantly better values than PPD. The radiometric sensitivity of a 5 /spl mu/m/spl times/5 /spl mu/m TFA pixel is found to amount to 11.9 V/(/spl mu//cm/sup 2/) for a 0.25 /spl mu/m process and 27.5 V/(/spl mu/J/cm/sup 2/) for a 0.18 /spl mu/m process.

Sensitivity of CMOS based imagers and scaling perspectives

An integrated color pixel (ICP) with at least one integrated metal filter is presented. Rather than utilizing a separate color filter, the wavelength responsivity of the ICP is specified and integrated at pixel level into the ICP itself using metal materials already available for standard integrated circuit design and fabrication process. The ICP of the present invention is thus distinguished from a conventional color pixel constructed in a two-stage process that combines an image sensor with a color filter array or other optical material.

Integrated color pixel ( ICP )

Image sensors in thin film on ASIC (TFA) technology are composed of amorphous silicon (a-Si:H) thin-film detectors on top of crystalline ASIC's. With regard to advanced imaging systems, TFA provides enhanced performance and more flexibility than conventional technologies. Extensive on-chip signal processing is feasible, as well as small pixels for high-resolution imagers. Several prototypes of TFA sensors have been developed, optimized for considerably different applications. This paper focuses on a TFA sensor for automotive vision systems that allows each pixel to adapt its individual sensitivity to the local illumination intensity. By this means, a dynamic range of 120-dB minimum along with high local contrast is achieved. The recent second prototype array consists of 368/spl times/256 pixels with an area of 40/spl times/38 /spl mu/m/sup 2/ each. The ASIC's were fabricated in a 0.7-/spl mu/m CMOS technology, whereupon the a-Si:H thin film was deposited in a plasma-enhanced chemical vapor deposition cluster system.

Design and fabrication of a high-dynamic-range image sensor in TFA technology

A locally autoadaptive image sensor LARS II (Lokal-AutoadaptiveR Sensor) with 368/spl times/256 pixels was designed and fabricated in thin film on ASIC (TFA) technology. Every pixel contains an automatic shutter, made of 17 transistors and two capacitors on an area of 40/spl times/38.3 /spl mu/m/sup 2/, that adapts the integration time to the local intensity. This allows the capture and processing of scenes with extremely high dynamic range. For the amorphous detector system, local contrast and temperature stability are demonstrated to be excellent while the transient response is sufficient for imaging applications. Sample images shown in this paper verify the total dynamic range of 120 dB.

100000-pixel, 120-dB imager in TFA technology

Image sensors in TFA (Thin Film on ASIC) technology are composed of amorphous silicon (a-Si:H) thin film detectors on top of crystalline ASICs. A TFA prototype for automotive vision systems is presented which allows each pixel to adapt its individual sensitivity to the local illumination. By this means, a dynamic range of 120 dB minimum along with high local contrast is achieved. The ASICs were fabricated in a 0.7 /spl mu/m CMOS technology.

Design and fabrication of a high dynamic range image sensor in TFA technology

TFA (Thin Film on ASIC) image sensors consist of an amorphous silicon based optical detector on top of an ASIC which performs signal readout and signal processing. In this paper recent results on TFA prototypes are presented. The detector multilayer was deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition) in a cluster deposition system, whereas for the ASIC a standard 0.7 u.m CMOS process was employed. Focus is put on two locally adaptive sensor arrays that allow the control of sensitivity for each pixel individually. These types of sensors are ideally suited for automotive vision systems, since they do not exhibit certain disadvantages inherent to devices using logarithmic data compression or global sensitivity control and image fusion. Moreover, the reduced chip size of vertically integrated TFA devices leads to a significant reduction of manufacturing costs in comparison to CMOS imagers. In addition to the locally adaptive arrays simpler devices with global sensitivity control and a concept for color recognition in TFA devices are discussed.

High Dynamic Range Image Sensors in Thin Film on ASIC Technology for Automotive Applications

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High Dynamic Range Image Sensors in Thin Film on ASIC Technology for Automotive Applications