Multipixel characterization of imaging CZT detectors for hard x-ray imaging and spectroscopy

Abstract

We report our in-depth study of Cd-Zn-Te (CZT) crystals to determine an optimum pixel and guard band configuration for Hard X-ray imaging and spectroscopy. We tested 20x20x5mm crystals with 8x8 pixels on a 2.46mm pitch. We have studied different types of cathode / anode contacts and different pixel pad sizes. We present the measurements of leakage current as well as spectral response for each pixel. Our I-V measurement setup is custom designed to allow automated measurements of the I-V curves sequentially for all 64 pixels, whereas the radiation properties measurement setup allows for interchangeable crystals with the same XAIM3.2 ASIC readout from IDEAS. We have tested multiple crystals of each type, and each crystal in different positions to measure the variation between individual crystals and variation among the ASIC channels. We also compare the same crystals with and without a grounded guard band deposited on the crystal side walls vs. a floating guard band and compare results to simulations. This study was carried out to find the optimum CZT crystal configuration for prototype detectors for the proposed Black-Hole Finder mission, EXIST.

CZT imaging detectors for Proto EXIST

“…The overall noise increase from the case with no bias is about 0.3 keV, which means the leakage currents alone generate about 1.0 -1.5 keV FWHM noise. This corresponds about 1.0 -1.5 nA/pixel leakage currents, which matches with properties of other Orbotech crystals with blocking contacts and no guard band [6]. Table 1 summaries the electronics noise of the current batch (Rev1) of DCUs.…”

Experiments and Evaluation Based Pixellated CZT Semiconductor Detector

“…The anode surface is pixelated in 16 x 16 array of pixels with pitch of 2.46 mm. Typical gap between pixel pads is 0.6 mm [3] . The floating…”

Spectral Response of THM Grown CdZnTe Crystals

“…The I-V measurement uses a computer-controlled Keithley 237 source unit that measures the leakage current on individual pixels, which are read sequentially through a custom-made set of logic gates while the radiation setup has the pixellated anode side mounted on a pogo pin fixture, with the unsoldered electrical contact provided by a fuji-poly connector. The pogo pins rest on a chip-on-board module whose contacts are routed to a pair of ASICs, where charge signals are collected, pre-amplified and read out by an IDEAS XaIm 3.2 system [33]. Fig.…”