Sunwoo Yuk

Polycrystalline CdZnTe thick films for low energy x-ray: system evaluation.

The X-ray response of polycrystalline-CdZnTe was measured by signal-to-noise (S/N) analysis. The CdZnTe material has optimal properties in a solid-state X-ray detector, and much research has focused on single crystal CdZnTe with a small-sized, silicon readout device. However, it would be difficult to apply CdTe or CdZnTe single crystal to large area, flat panel detectors, such as those used for radiography and mammography. As an alternative of single crystal CdZnTe, we have grown thick, polycrystalline CdZnTe films of high resistivity (>5times109 Ohm cm) using the thermal evaporation method on carbon substrate. A high signal-to-noise value has a direct impact on the performance of CdZnTe X-ray detectors. Important image parameters, such as dynamic range and detective quantum efficiency, rely on the signal and noise characteristics of the system. In this paper, we analyzed the properties of the X-ray detector and obtained images of the X-ray detector using the data acquisition system. The X-ray detector used the Cd1-xZnxTe (x=0.04), which used carbon substrate and gold as the electrode. The detector design is planar and 32 mmtimes10 mm in size, and it has a 1.75mmtimes1mm pixel electrode size and a detector thickness of 150 mum

Development of a high SNR data acquisition system for 16 channel x-ray detector module

Summary form only given. The major advantage of slip-ring technology in spiral CT is that it facilitates continuous rotation of the x-ray tube, so that volume data can be acquired from a patient quickly. Not only for such a fast scan, but also for dose reduction purposes, a high signal-to-noise ratio and fast data acquisition system are required. In this study, we have built a multi-channel photodetector and multi-channel data acquisition system for CT application. The detector module consisted of CdWO/sub 4/ crystal and Si photodiode in 16 channels. For the performance test of the preamplifier stage, both the transimpedance and switched integrator types are optimized for the photodetector modules. The switched integrator showed better noise performance in the limited bandwidth which is suitable for the current CT application. The control sequence for data acquisition and 20 bit ADC is designed with VHDL (very high speed integrated circuit hardware description language) and implemented on FPGA (field programmable gate array) chip. Our Si photodiode detector module coupled to CdWO/sub 4/ crystal showed a comparable signal with other commercially available photodiodes for CT. The switched integrator type showed higher SNR but narrower bandwidth compared to a transimpedance preamplifier. Digital hardware is designed by FPGA, so that the control signal could be redesigned without hardware alteration.

Noise performance of the charge sensitive amplifier for photodetection

An integrated circuit for charge sensitive amplifier (CSA) was developed for X-ray detection. The circuit has been optimized for reading signals from silicon strip detectors with few pF input capacitance for low power and low noise. Theoretical calculations and optimizations are presented and compared with experimental results. Noise as low as 237 ENC [electrons] was obtained including a silicon detector of 1.3 pF and 0.386 pA of leakage. The power consumption was less than 100 W. Other circuit parameters were also obtained from experiments. The circuit was fabricated in standard 0.25 um CMOS technology and the circuit occupies an area of 4 mm times 4 mm.

Noise Performance of Readout Electronics for Photodetector

A 16 channel Integrated circuit charge sensitive preamplifier (CSA) has been developed for an X-ray detector module that uses a 16 linear arrays of photodetector. The photodiode is made of 280 um thickness, 30 MOmega shunt resistivity, the measured junction capacitance 200 pF. The main performances of the CSA for photodetector are the following: the input equivalent noise charge is 300 e- rms at peaking time 200 ns, the highest gain is 10 mV/fC, the peaking time is adjustable between 50 ns and 300 us by external passive components. The noise simulation yield ENC values of 50 e- and 250 e- for thermal and 1/f noise, respectively. The design was fabricated in standard 0.35 um CMOS technology and the circuit occupies an area of 4times4 mm2 and dissipates 2 mW per channel from a 3.3 V single power supply.

Design and Evaluation of a 2D Array PIN Photodiode Bump Bonded to Readout IC for the Low Energy X-ray Detector

A 2D array radiation sensor, consisting of an array of PIN photodiodes bump bonded to readout integrated circuit (IC), has been developed for operation with low energy X-rays. The PIN photodiode array and readout IC for this system have been fabricated. The main performance measurements are the following: a few pA-scale leakage current, 350 pF junction capacitance, 30 mum-depth depletion layer and a 250 mum intrinsic layer at zero bias. This PIN photodiode array and readout IC were fabricated using a PIN photodiode process and standard 0.35 mum CMOS technology, respectively. The readout circuit is operated from a 3.3 V single power supply. Finally, a 2D array radiation sensor has been developed using bump bonding between the PIN photodiode and the readout electronics

Noise analysis of 16 channel charge sensitive amplifier for poly CZT

A 16 channel integrated circuit charge sensitive preamplifier (CSA) has been developed for an X-ray detector module that uses a 16 linear array of poly CZT. The polycrystalline CdZnTe:Cl thick films used in this experiment have 1.2times1010 Omegacm in resistivity, 150 mum in thickness. The main performances of the CSA for this poly CZT are the following: the input equivalent noise charge is 300 e- rms at peaking time 200 ns, the highest gain is 10 mV/fC, the peaking time is adjustable between 50 ns and 300 mus by external passive components. The noise simulation yielded ENC values of 50e- and 250e- for thermal and 1/f noise, respectively. The design was fabricated in standard 0.35 mum CMOS technology and the circuit occupies an area of 4times4 mm2 and dissipates 2 mW per channel from a 3.3 V single power supply.