7.1 Integration of Thin-Film Sensors with aVLSI Circuits

The collective architectures presented in Chapters 4, 5, and 6 are best utilized when integrated in the sensing plane as the sensors themselves. This “smart pixel” technique has worked well in focal plane processing applications because phototransistors and photodiodes can be made compactly using standard CMOS fabrication techniques. The operation of a typical photodetector causes minimal interference with the surrounding surface; light interference in the surrounding circuits can be easily minimized by using guard rings or by covering the circuits in a sacrificial layer of opaque material such as metal. The fabrication of chemical sensors on substrates designed for integrated circuits, however, is not as straightforward. Such fabrication is complicated by the following key issues: