Area image sensor

R. A. Street, Large Area Image Sensor Arrays, in Technology and Applications of Amorphous Silicon, R.A. Street (Ed.), Springer, Heidelberg, 2000. 

An a-Si H photosensor array has been successively applied to a long linear image sensor and high-performance area image sensor. A photodiode in which a-Si H is sandwiched between ITO and metal electrodes is used because of its short photoresponse time. In this structure, blocking contacts at both electrodes are necessary to prevent carrier injection from the electrodes. 

Thin-film technology is useful in fabricating these devices. CdS-CdSe photoconductive sensors (Boronkay et al., 1978 Komiya et al., 1981) and As-Se-Te photodiodes (Tsukada et al., 1977) were applied to the long linear-image sensor. As-Se-Te photodiodes (Tsukada et al., 1979) and ZnSe - ZnCdTe photodiodes (Terui et al., 1980) were used in the area image sensor. However, there are some problems with these sensors long photoresponse time for the CdS-CdSe sensor, thermal instability, and low yield for the As-Se-Te sensor, and a high-temperature process for the ZnSe-ZnCdTe sensor. 

In the area-image sensor, it is expected that highly sensitive solid-state image sensors with high resolution, competitive with vidicons, will become available. The solid-state image sensor, which is made of an a-Si H photodiode array on a Si IC scanner, is the most suitable device for this purpose. 

Apart from the sampling principle, sensor layouts can also be subdivided into point-probe sensors, giving averaged information about the analytes within the sensitive field, and imaging sensors, delivering a spatially as well as spectrally resolved image of the investigated area. 

Electron-hole pairs are only produced in areas illuminated by the light and spatially resolved photocurrents can be achieved using a focused scanning beam. Therefore the main advantage of LAPS is that it can work as a chemical imaging sensor the light-addressability of the LAPS allows one to obtain a two-dimensional map of the distribution of the ion concentration. 

G Yu, J Wang, J McElvain, and AJ Heeger, Large-area, full-color image sensors made with semiconducting polymers, Adv. Mater., 10 1431-1434, 1998. 

Fig. 21. The output current ID from an elemental integrated-image sensor as a function of the incident photon flux N. The experimental points were obtained when the sensor was addressed individually ( ) and as part of an array (O). It is found that / N% . The photosensor area was 1.4 X 10 3 cm2. The full line was calculated from the individual characteristics of the FET and the a-Si H photoconductor. (From Snell et al. (1984).]...

With a scanning circuit and a-Si H, it is possible to provide an a-Si H monolithic large area solid-state image sensor, although it is necessary to improve high-frequency characteristics. 

FIGURE 6.3.2 An image of electronic artificial skin attached on the robot surface. A plastic film with organic transistors, a pressure-sensitive rubber sheet, and a plastic film with top electrodes are laminated together to form a large-area pressure sensor. Some parts of films are removed intentionally to show the inner structures. 

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