Programmable semiconductor switch for a display matrix or the like and method for making same

摘要

A semiconductor switch having symmetrical, nonlinear current-voltage characteristics has a threshold value which is programmed using a light beam after assembly of the switch. The switch preferably comprises an n+-i-n+ device where the intrinsic material is an amorphous semiconductor alloy such as amorphous, hydrogenated or fluorinated silicon having a density and energy distribution of localized defect states in the band gap thereof forming deep traps which affect the threshold value. The highly doped n+ layers function to inject electrons into the intrinsic material and block the migration of holes. The device exhibits space charge limited current conduction and thus, increased nonlinearity under AC excitation. The switch may be employed in addressing display elements such as liquid crystal pixels in order to increase the rise time of pixel response and isolate the pixels from cross-talk, noise or other spurious signals. The n+-i-n+ device is deposited on a glass substrate along with electrodes and address lines required for switching the pixels. Following deposition, the threshold voltage of the device is programmed by directing a light beam through a partially transparent metal contact covering the n+ -i-n+ material sandwich. The programming may be performed near the end of the fabrication process by directing the light beam through the glass plate on which the device is deposited. Following threshold programming, the device is sealed against further exposure to ambient radiation which might subsequently alter the threshold voltage.