X-Ray Beam Studies of Charge Sharing in Small Pixel, Spectroscopic, CdZnTe Detectors (original) (raw)

Electric Field Dependence on Charge Collection of CdZnTe X-Ray Detectors

Journal of X-Ray Science and Technology, 1997

In this study, the electric field dependence on the charge collection process of CdZnTe detectors, at different x-ray tube settings, within the x-ray diagnostic energy range, is investigated. In addition, the detector contrast at different applied bias voltages and xray tube settings have been experimentally determined. The experimental results suggest that an efficient charge collection process is obtained by increasing the applied bias voltage. Once the applied bias voltage is sufficiently high, charge collection becomes complete and the detector operates in the saturation region. This is a prerequisite for high contrast and spatial resolution. As a result, the detector contrast is enhanced significantly. Therefore, CdZnTe detectors appear to be potential candidates for digital radiographic applications. ᭧ 1997 Academic Press 198

Measurements of charge sharing in small pixel CdTe detectors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014

CdTe detectors with a thickness of 1 mm and a pixel pitch of 250 mm have been flip-chip-bonded to the HEXITEC read-out ASIC. The detectors record both the position and energy of X-ray interactions producing an X-ray spectrum for each of the 6400 pixels in the energy range 2-200 keV. In this arrangement, detectors have been shown to produce excellent spectroscopy with FWHM better than 1.2 keV at an interaction energy of 59.5 keV. Due to the use of small pixels, a significant number of events experience charge sharing where the total energy of the event is distributed between multiple pixels. Under normal operating conditions, the proportion of events that experience charge sharing was measured to be 36.4%. Without correction these events lead to a reduction in the spectroscopic performance of the detector, the production of pronounced fluorescence and X-ray escape peaks, and the detection sensitivity. In this paper, the effect of different correction algorithms and operating conditions on the detector performance is presented. Crown

X-ray performance of pixilated CdZnTe detectors

… Record, 2008

Abstract-The X-ray performance of CdZnTe detectors with 300μm pixels was investigated. 2mm thick CdZnTe from eV Products Inc. was bump bonded to ERD2004 detector modules. Preliminary experiments with an eV Products detector at room temperature and -400V bias gave a FWHM of 1.93keV at 59.9keV and a peak to valley ratio of 14.9. The performance of individual pixels varied significantly across the devices due to the non-uniformities in the CdZnTe. Experiments at the Diamond Light Source were conducted to investigate the spatial nonuniformity of the detector. A monochromatic X-ray beam was used to measure the energy resolution and peak position to quantify the spatial charge collection efficiency of the detector. A collimated X-ray beam was used to scan the detector. The scanning experiment was used to investigate charge sharing and lateral electric fields within the detector.

Comparison of the X-ray performance of small pixel CdTe and CZT detectors

2010

The Rutherford Appleton Laboratory has built a small pixel detector for spectroscopic measurements of high energy X-rays using CdTe and CdZnTe. The detector has an array of 20x20 pixels on a 250μm pitch with each pixel bonded to a separate channel on an application specific integrated circuit (ASIC). Each channel in the ASIC contains a charge preamplifier, leakage current compensation circuit, shaping amplifier and peak hold circuit. In recent years there has been an increase in the availability of high quality CdTe and CdZnTe material and the contacting technology required for low leakage current small pixel devices. The energy resolution and stability of the X-ray performance of 1mm thick CdTe with Aluminum Schottky contact pixels and 2mm thick CdZnTe grown by travelling heater method (THM) are measured. The CdTe detectors had an energy resolution of 1 to 1.1keV at 75keV. The THM CdZnTe had an energy resolution of 1.3keV at 75keV. The stability of the performance was measured over a 12 hour exposure with the detectors biased to -500V and held at 25 ºC. The CdZnTe exhibited stable performance whereas the CdTe suffered from bias induced polarization, the onset of which was delayed by cooling the detectors to 12ºC.

Preliminary performance of CdZnTe imaging detector prototypes

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001

The promise of good energy and spatial resolution coupled with high e$ciency and near-room-temperature operation has fuelled a large international e!ort to develop cadmium}zinc}telluride (CdZnTe) for the hard-X-ray region. We present, here, preliminary results from our development of small-pixel imaging arrays fabricated on 5;5;1-mm and 5;5;2-mm spectroscopy and discriminator-grade material. Each array has 16 (4;4) 0.65-mm gold readout pads on a 0.75-mm pitch, with each pad connected to a discrete preampli"er via a pulse-welded gold wire. Each array is mounted on a three-stage Peltier cooler and housed in an ion-pump-evacuated housing which also contains a hybrid microassembly for the 16 channels of electronics. We have investigated the energy resolution and approximate photopeak e$ciency for each pixel at several energies and have used an ultra-"ne beam X-ray generator to probe the performance at the pixel boundaries. Both arrays gave similar results and at an optimum temperature of !203C we achieved between 2% and 3% full-width at half-maximum energy resolution at 60 keV and around 15% at 5.9 keV. We found that all the charge was contained within one pixel except very close to the pixels edge, where it would start to be shared with its neighbor. Even between pixels, all the charge would be appropriately shared with no apparently loss of e$ciency or resolution. Full details of these measurements will be presented, together with their implications for future imagingspectroscopy applications.

A study of charge sharing in pixellated cadmium-zinc-telluride detectors

… Record, 2001 IEEE, 2001

In this paper we present the status and preliminary results from a CZT development program of fine pixel detectors. These are to be used at the focus of high-energy grazing-incidence optics (20-75 keV) of the HERO-Experiment under construction at the Marshall Space Flight Center.

Charge-sharing observations with a CdTe pixel detector irradiated with a57Co source

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

Charge sharing is a limiting factor of detector spatial resolution and contrast in photon counting imaging devices because multiple counts can be induced in adjacent pixels as a result of the spread of the charge cloud generated from a single X-ray photon of high energy in the detector bulk. Although this topic has been debated for a long time, the full impact of charge sharing has not been completely assessed. In this work, we look at the importance of charge sharing in CdTe pixel detectors by exposing such a device to a low-activity (37 kBq) 57 Co source, whose main emission line is at 122 keV. The detectors used are 1 mm thick with a pixel pitch of 55 µm. These detectors are bumpbonded to Medipix2 photon counting chips. This study gives an insight on the impact on the design and operation of pixel detectors coupled to photon counting devices for imaging applications.

The simulation of charge sharing in semiconductor X-ray pixel detectors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2002

Two simulation packages were used to model the sharing of charge, due to the scattering and diffusion of carriers, between adjacent pixel elements in semiconductors X-ray detectors. The X-ray interaction and the consequent multiple scattering was modelled with the aid of the Monte Carlo package, MCNP. The resultant deposited charge distribution was then used to create the charge cloud profile in the finite element semiconductor simulation code MEDICI. The analysis of the current pulses induced on pixel electrodes for varying photon energies was performed for a GaAs pixel detector. For a pixel pitch of 25 mm, the charge lost to a neighbouring pixel was observed to be constant, at 0.6%, through the energies simulated. Ultimately, a fundamental limit on the pixel element size for imaging and spectroscopic devices may be set due to these key physical principles. r (K. Mathieson).

Investigating the small pixel effect in CdZnTe Hard X-ray detectors—The PIXIE ASIC

… Record (NSS/MIC), …, 2010

An Application Specific Integrated Circuit (ASIC) has been developed at the Rutherford Appleton Laboratory (RAL) to study the small pixel effect in spectroscopic CdTe and CdZnTe detectors. The PIXIE ASIC consists of four arrays of 3x3 channels flip chip bonded directly to the detector pixels. The active circuitry of each channel is a charge sensitive preamplifier and an output buffer which is multiplexed directly off chip. Each of the four arrays has different anode geometry.