  The High Resolution Energetic X-Ray Imager (HREXI) CZT detector development
program at Harvard is aimed at developing tiled arrays of finely pixelated CZT
detectors for use in wide-field coded aperture 3-200 keV X-ray telescopes. A
pixel size of $\simeq$ 600 $\mu m$ has already been achieved in the ProtoEXIST2
(P2) detector plane with CZT read out by the NuSTAR ASIC. This paves the way
for even smaller 300 $\mu m$ pixels in the next generation HREXI detectors.
This article describes a new HREXI calibration facility (HCF) which enables a
high resolution sub-pixel level (100 $\mu m$) 2D scan of a 256 $cm^2$ tiled
array of 2 $\times$ 2 cm CZT detectors illuminated by a bright X-ray AmpTek
Mini-X tube source at timescales of around a day. HCF is a significant
improvement from the previous apparatus used for scanning these detectors which
took $\simeq$ 3 weeks to complete a 1D scan of a similar detector plane.
Moreover, HCF has the capability to scan a large tiled array of CZT detectors
($32cm \times 32cm$) at 100 $\mu m$ resolution in the 10 - 50 keV energy range
which was not possible previously. This paper describes the design,
construction, and implementation of HCF for the calibration of the P2 detector
plane.
