Semiconductor matrix type sensor for very small surface pressure

Abstract

An analog finger print reader comprises a matrix of electronic switches selectively controlled from a matrix of individually associated electrodes. A thin film having a conductive surface is suspended over the electrodes to apply control potentials to the electrodes in response to the pressure applied by a mountain in the pattern of a finger print (a ridge is viewed as a string of mountains). The area of contact between the conductive film and the electrode varies as an analog of the amount of applied pressure. Shift registers scan the electrodes to identify the address of a finger print mountain which is turning on the associated electronic switch. A detector responds to the address by giving an output which is an analog of the area of contact and, therefore, of the amount of applied pressure. The entire unit is built on a semiconductor substrate. Thus, the amount of wiring is greatly reduced. The reader is a unified device made with the precision of an integrated circuit.