Spatial resolution of SCD's InSb 2D detector arrays

The two-dimensional spatial response of a pixel in SCD's back-side illuminated InSb Focal Plane Array (FPA) is measured directly for arrays with a small pitch, namely 30, 20 and 15&mgr;m. The characterization method uses a spot-scan measurement and de-convolution algorithm to obtain the net spatial response of a pixel. Two independent methods are used to measure the detector spatial response: a) direct spot-scan of a pixel with a focused beam; b) uniform illumination upon back-side evaporated thin gold coating, in which sub-pixel apertures are distributed in precise positions across the array. The experimental results are compared to a 3D numerical simulation with excellent agreement for all pitch dimensions. The spatial response is used to calculate the crosstalk and the Modulation Transfer Function (MTF) of the pixel. We find that for all three pixel dimensions, the net spatial response width (FWHM) is equal to the pitch, and the MTF width is inversely proportional to the pitch. Thus, the spatial resolution of the detector improves with decreasing pixel size as expected. Moreover, for a given optics and smaller array pitch, the overall system spatial resolution is limited more by the optical diffraction than by the detector. We show actual improved spatial resolution in an imaging system with a detector of smaller array pitch.