Interface of amorphous silicon thin film sensor with A/D converter

The feasibility of a new concept for rapid processing of photosensor signals is studied. The major feature of the new approach is to deposit a thin-film photosensor array on top of a silicon processor array. By using a high level of parallelism in two-dimensional processing, the speed of this system can be several orders higher than that of the existing bit stream systems. Results on the interface of a thin-film sensor with the first stage of the data processing circuit, the A/D (analog-to-digital) converter, are reported. The thin-film sensor used here is based on hydrogenated amorphous silicon. The sensor was found to have a high photosensitivity of 2 × 10⁴. The photocurrent from a sensor element was able to drive the A/D converter directly. The system response times were about 0.3 ms and 1 μs when using a CMOS successive-approximation-type A/D converter and a flash-type A/D converter, respectively. Thus, the new concept of a vertically integrated sensor/processor array is shown to be very promising