Kaifeng Qin

A CMOS charge sensitive preamplifier for CdZnTe detector

In this work, a low noise and low power charge sensitive preamplifier (CSA) based on CSMC 0.6 µm double poly mix CMOS technology was designed and simulated. In this design, two MOSFETs were used as a feedback resistor and a feedback capacitor respectively to replace an on-chip resistor in parallel and an on-chip capacitor in a conventional CSA. Simulation results show that this design can reduce the noise level of the CSA and the area of the layout. The noise of the CSA can be less than several electrons, which can be calculated from the simulation results, and the power consumption is about 2.2mW/channel. Four channels can be placed in a 0.6×0.6 mm2 chip.

Effects of substrate temperature on morphology, structure and chemical composition of Cu2S films

Cu2S thin films have been deposited on CdS/ITO (In2O3:Sn) substrates with various substrate temperatures by DC magnetron sputtering method. The effects of substrate temperature on the crystallization behavior and morphology are studied. Chemical composition of the films is confirmed by energy dispersive X-ray (EDX) spectroscopy. X-ray diffraction (XRD) analysis of the films reveals they have polycrystalline chalcocite structure with (110) texture. Field emission scanning electron microscopy (FESEM) show the crystalline nature of the films at higher substrate temperature, which is in accordance with XRD measurements. Stoichiometric analysis exhibits element composition with Cu/S concentrations ratio equal to 2 approximately.

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.

The research of package for CdZnTe detector based on the capacitive Frisch grid structure

In this paper, the design and fabrication of a capacitive Frisch grid structure for CdZnTe (CZT) detector were investigated. The aging tests were first used to investigate the degradation of the mechanical and electrical characteristics of the CdZnTe detector based on the capacitive frisch grid structure. The effects of the degradation on the performance of CdZnTe detectors were investigated by scanning acoustic microscopy (SAM) test, current-voltage test, and multichannel pulse-height spectrum analysis. In particular, a passivation layer obtained by a two-step passivation processing, combined with a Teflon tape, was used as an insulated layer of the capacitive Frisch grid detector, improving its stability effectively at high voltages. However, further improvements in material and device fabrication (including insulated layer) were required to realize the potential of CZT detectors with the capacitive Frisch grid structure.

Investigation on the two-step passivation process for CdZnTe detectors

In this paper, the composition, morphology and electrical properties of the passivation layer for CdZnTe detectors were investigated. A two-step passivation was performed under different conditions, including passivation time, temperature and NH4F/H2O2 concentration. The obtained passivation layers were characterized by XRD, SEM, XRF and I-V methods. The results showed that the best passivation condition was with the NH4F/H2O2 concentration of 10wt%, passivation time of 40min and temperature of 20ºC. Under this condition, the passivation layer was purely oxidized and compact, and the surface leakage current of CZT crystals was most effectively reduced.