Variable sensitivity floating gate photosensor

摘要

An improved floating gate photosensor is operable in either an enhanced voltage sensitivity mode or an enhanced transit speed mode. This photosensor has a floating gate assembly that includes two overlapping, independent and complementary-shaped gate electrodes connected to separate circuits as a means of controlling the depth of the channel in which the signal charge flows. As a result, the two key operating parameters of responsivity and signal transit time are variable. Structurally, each gate includes a plurality of prongs that overlap the recesses defined by the prongs of the other electrode. The photosensor may be operated in the WC (side channel) mode where the two gate electrodes are both used as floating gate sensors. In this instance the photosensor operates like that of a conventional floating gate sensor, with the width of the channel equal to that of the entire floating gate assembly and the depth of the channel being about 4 microns below the surface of the device. The photosensor can also be operated in the NC (narrow channel) mode where only one of the gate electrodes is in the floating gate sensing mode while the other is biased so that the channels beneath its prongs act as barriers to signal charge flow, thereby restricting charge flow to a plurality of narrow channels under the fingers of the first gate which are only about one micron below the surface of the device.