A monolithic mosaic of photon sensors for solid-state imaging applications

Monolithic silicon mosaics of photosensor elements have been developed for solid-state imaging applications. The physical structure, design considerations, and performance characteristics of these electrooptical devices as applied to image converter applications are discussed. The sensing monolith consists of a square 50 by 50 mosaic of phototransistor elements on 0.010 inch centers which are interconnected both by internally diffused strips and by vapor deposited surface bars. Fifty and fifty external leads provide access to any individual element of the mosaic. Fabrication of this 2500 element mosaic involves the techniques of planar passivation, epitaxial growth, solid-state diffusion, and thin-film vacuum evaporation. A discussion of sensor operation includes mechanisms of phototransistor action, electrooptical conversion efficiency, and element-to-element crosstalk minimization. An evaluation of the electrooptical transfer characteristics of the mosaic sensor elements are presented. Uniformity of element response is typically better than 85% for response within a 3 : 1 range and 75% for response within a 2 : 1 range. Several shades of gray can be imaged simultaneously. The mosaic dynamic range extends over 3.5 orders of incident illumination energy or five orders of output photocurrent. The minimum and maximum detectable signals are approximately 10.0 nW and 1.0 roW, respectively. Sensitivity is of the order of 10²to 10³µA/mW in the linear portion of the transfer curve.