A 10 cm × 10 cm CdTe Spectroscopic Imaging Detector based on the HEXITEC ASIC

Abstract

The 250 µm pitch 80x80 pixel HEXITEC detector systems have shown that spectroscopic imaging with an energy resolution of < 1 keV FWHM per pixel can be readily achieved in the range of 5-200 keV with Al-pixel CdTe biased to −500 V. This level of spectroscopic imaging has a variety of applications but the ability to produce large area detectors remains a barrier to the adoption of this technology. The limited size of ASICs and defect free CdTe wafers dictates that building large area monolithic detectors is not presently a viable option. A 3-side buttable detector module has been developed to cover large areas with arrays of smaller detectors. The detector modules are 20.35 × 20.45 mm with CdTe bump bonded to the HEXITEC ASIC with coverage up to the edge of the module on three sides. The fourth side has a space of 3 mm to allow I/O wire bonds to be made between the ASIC and the edge of a PCB that routes the signals to a connector underneath the active area of the module. The detector modules have been assembled in rows of five modules with a dead space of 170 µm between each module. Five rows of modules have been assembled in a staggered height array where the wire bonds of one row of modules are covered by the active detector area of a neighboring row. A data acquisition system has been developed to digitise, store and output the 24 Gbit/s data that is generated by the array. The maximum bias magnitude that could be applied to the CdTe detectors from the common voltage source was limited by the worst performing detector module. In this array of detectors a bias of −400 V was used and the detector modules had 93 % of pixels with better than 1.2 keV FWHM at 59.5 keV. An example of K-edge enhanced imaging for mammography was demonstrated. Subtracting images from the events directly above and below the K-edge of the Iodine contrast agent was able to extract the Iodine information from the image of a breast phantom and improve the contrast of the images. This

Characterization of the Uniformity of High-Flux CdZnTe Material

“…Previous measurements with large-area CdZnTe and CdTe detectors have demonstrated spatial variations in the detector response due to crystalline defects, such as tellurium inclusions, or due to local variations in the electric field. If HF-CdZnTe devices are going to be suitable for imaging applications, then it is a prerequisite that large detection areas with a high degree of uniformity can be produced [ 8 , 9 ]. In this paper, the spatial uniformity of 10 2.0-mm-thick HF-CdZnTe detectors were characterized using the High Energy X-ray Imaging Technology (HEXITEC) spectroscopic imaging Application Specific Integrated Circuit (ASIC) [ 10 ] operating at a flux of <10 4 ph s −1 mm −2 .…”

In situ mapping of chemical segregation using synchrotron x-ray imaging

“…For multi-element mapping by XFM, increases in X-ray flux will enable better sensitivity and reduced scan times, which may then become simply limited by sample raster speeds and detector count rates [42]. For full FoV XRF imaging with EDI detectors, detection integration times may be reduced to 1-10ms, and by tiling the EDI detectors, it will be possible to image larger areas without losing temporal resolution [43]. Although full FoV XRF imaging is unlikely to achieve the spatial resolution of conventional XFM, the ability to investigate large areas relatively quickly -without moving the sample -ensures the further development of EDI detectors and new applications.…”

Element Specific Imaging Using Muonic X-rays

“…The ASIC is wire bonded to a PCB on the 4 th side of the module and the ASIC I/O is routed through a connector on the underside of the aluminum block so that the modules can be closely butted on 3 sides [13] but only single modules were used here. A detector module with the 2 x 2 cm active area is shown in Fig.…”

“…This would improve the spatial resolution of the technique but with some loss in efficiency. The ability to tile the HEXITEC detector, as in [13], could enable multiple views of a sample to be captured simultaneously and increase the imaging rate.…”