Parallel readout of two-element CdZnTe detectors with real-time digital signal processing

Readout electronics, especially digital electronics, for two-element CdZnTe （CZT） detectors in parallel are developed. The preliminary results show the detection efficiency of the two-element CZT detectors in parallel with analog electronics is as many as 1.8 and 2.1 times the single ones, and the energy resolution （FWHM） is limited by that of the single one by the means of analog electronics. However, the digital method for signal processing will be sufficiently better by contrast with an analog method especially in energy resolution. The energy resolution by the means of digital electronics can be improved by about 26.67%, compared to that only with analog electronics, while their detection efficiency is almost the same. The cause for this difference is also discussed.

Design and performances of a low-noise and radiation-hardened readout ASIC for CdZnTe detectors

In this paper,we present the design and performances of a low-noise and radiation-hardened front-end readout application specific integrated circuit（ASIC） dedicated to CdZnTe detectors for a hard X-ray imager in space applications.The readout channel is comprised of a charge sensitive amplifier,a CR-RC shaping amplifier,an analog output buffer,a fast shaper,and a discriminator.An 8-channel prototype ASIC is designed and fabricated in TSMC 0.35-μm mixed-signal CMOS technology,the die size of the prototype chip is 2.2×2.2 mm^2.The input energy range is from 5 to 350 keV.For this 8-channel prototype ASIC,the measured electrical characteristics are as follows：the overall gain of the readout channel is 210 V/pC,the linearity error is less than 2%,the crosstalk is less than 0.36%,The equivalent noise charge of a typical channel is 52.9 e^- at zero farad plus 8.2 e^- per picofarad,and the power consumption is less than 2.4 mW/channel.Through the measurement together with a CdZnTe detector,the energy resolution is 5.9%at the 59.5-keV line under the irradiation of the radioactive source ^（241）Am.The radiation effect experiments show that the proposed ASIC can resist the total ionization dose（TID） irradiation of higher than200 krad（Si）.

Influence of sub-bandgap illumination on space charge distribution in CdZnTe detector

The space charge accumulation in CdZnTe crystals seriously affects the performance of high-flux pulse detectors.The influence of sub-bandgap illumination on the space charge distribution and device performance in CdZnTe crystals were studied theoretically by Silvaco TCAD software simulation.The sub-bandgap illumination with a wavelength of 890 nm and intensity of 8×10−8 W/cm2 were used in the simulation to explore the space charge distribution and internal electric field distribution in CdZnTe crystals.The simulation results show that the deep level occupation faction is manipulated by the sub-bandgap illumination,thus space charge concentration can be reduced under the bias voltage of 500 V.A flat electric field distribution is obtained,which significantly improves the charge collection efficiency of the CdZnTe detector.Meanwhile,premised on the high resistivity of CdZnTe crystal,the space charge concentration in the crystal can be further reduced with the wavelength of 850 nm and intensity of 1×10−7 W/cm2 illumination.The electric field distribution is flatter and the carrier collection efficiency of the device can be improved more effectively.