Design issues of two-dimensional amorphous silicon position-sensitive detectors

Abstract

The two-dimensional amorphous silicon position-sensitive detector (PSD) is usually in the form of large-area, continuous p-i- n silicon layer structure coupled with resistive layers next to the p and n Si layers. The device has many applications (e.g. light position measurements, light-pen input devices, etc.) and can be fabricated by using low-cost PECVD process. When used as a light-pen-based input device, several material-related design issues must be critically considered for achieving acceptable performance. The present work addresses three important issues, namely the spectral response of PSD, the uniformity requirement of the resistive layers, and the design of optical filter on the input side of PSD. They correspond to the signal-to-noise ratio of the device, the accuracy of light-position determination, and the integration problem with liquid crystal displays (LCD), respectively. Analytical analysis and computer simulation results draw the following important conclusions: (1) red-light-sensitive PSD can be obtained by properly tuning the thickness of p-layer and i-layer, which suppress the interference of background light when using the input device under sun light or similar illumination (2) the spot size of input light has little effect on position determination, as long as the size does not differ too much from that of required resolution. And a conservative uniformity requirement for the resistive layers can be obtained as | Δh/ h|≤4/ n with n being the required number of pixels of display and h being the film thickness (3) multi-layered filters made of oxides can be deposited on PSD to reflect non-signal light for LCD display while preserving the input-signal when the PSD is placed under a TN LCD.