Development of high spectral resolution CdZnTe pixel detectors for astronomical hard X-ray telescopes

Cadmium zinc telluride detectors (CdZnTe) offer the possibility of achieving excellent spectral and spatial resolution for compact hard X-ray sensors operated without cryogenics. These characteristics make these detectors ideal for several astrophysical applications, including focal plane sensors for multilayer hard X-ray telescopes, and in the image plane of coded-aperture imagers. We are developing a CdZnTe pixel detector and low-noise VLSI readout for use at the focal plane of the balloon-borne High Energy Focusing Telescope (HEFT). In particular, we have concentrated on achieving excellent spectral resolution in a device with 600 μm pixels. Here we report results from the testing of our fully functional prototype hybrid detector. The detector (an 8×7×2 mm3 single crystal of CdZnTe with an 8×8 pattern of platinum contacts on one side and a monolithic contact on the other) is indium bump-bonded to our 64-channel readout chip, which contains a charge-sensitive preamplifier, shaping amplifier, and combination peak stretcher/discriminator for each pixel. In this paper, we present results taken at room temperature, demonstrating a low-energy threshold near 5 keV and electronic noise of 1.5 keV FWHM at 60 keV. Subsequent testing of this detector at −10°C, reported in Cook et al. [Proc. SPIE 3769 (1999) 92], achieved 670 eV FWHM resolution at 60 keV, with electronic noise of 340 eV.