Speaker
Dr
Hidenori Toyokawa
(Japan Synchrotron Radiation Research Institute)
Description
Single X-ray photon counting pixel detector was expected to be a next generation 2D X-ray detector from the early stage of the third generation synchrotron radiation facilities. In fact, silicon-based hybrid pixel detectors such as PILATUS became commercially practical. To improve the detection sensibility in the high energy X-ray region, cadmium telluride (CdTe) is regarded as a promising semiconductor sensor material because of its high density and high atomic number. Therefore, we are developing CdTe-based pixel sensors and their readout ASICs for synchrotron radiation application.
We have investigated three-type electrode configurations of the ohmic contact structures on both sides with platinum electrodes (Type-1), a Schottky contact with an indium common electrode on the front side (Type-2), and a Schottky contact with aluminum electrodes on the pixel side (Type-3). Type-2 is operated in the hole-collection mode. On the other hand, Type-3 is operated in the electron-collection mode. Type-3 is expected to realize much superior performance because of the higher mobility of electrons than holes.
We designed and fabricated a prototype of a CdTe pixel detector (SP8-01). The format was 16 pixels × 16 pixels with a pitch of 200 μm × 200 μm. The sensor thickness was 500 μm. A full-custom ASIC with TSMC 0.25 μm technology was designed as a readout circuit, which is equipped with a preamplifier, a shaper, a window-type discriminator and 20-bits counter. The sensors were bump-bonded to the ASIC chips by a gold-stud bonding technique.
Operation temperature dependence study was performed by placing the type-3 prototype in a thermostatic chamber. The temperature was controlled at -20, -10, 0, 10 and 20 degree and the detector was irradiated with X-rays from 241-Am radio-isotope. Charge collection and energy resolution characters were examined by continuous threshold scans. The performance deteriorated in a short time and discontinuity behavior happened at 20 degree. On the other hand, the detector attained a long-term stable operation at lower temperatures.
We submitted the next step SP8-02 prototype with the same architecture for ASIC, but with the pixel format of 50 × 20. We could not achieve any valuable result for ohmic and indium-Schottky sensors in SP8-01 because of vendor failures in processing the In/Au stud bonding unfortunately. Three type sensors will be processed to try again in SP8-02.
Primary author
Dr
Hidenori Toyokawa
(Japan Synchrotron Radiation Research Institute)
Co-authors
Dr
Goro Sato
(Institute ofSpaceandAstronauticalScience,JAXA)
Dr
Hirokazu Ikeda
(Institute ofSpaceandAstronauticalScience,JAXA)
Mr
Morihiro Kawase
(Japan Synchrotron Radiation Research Institute)
Dr
Tadayuki Takahashi
(Institute ofSpaceandAstronauticalScience,JAXA)
Ms
Toko Hirono
(Japan Synchrotron Radiation Research Institute)
Dr
Toru Ohata
(Japan Synchrotron Radiation Research Institute)
Dr
Yukito Furukawa
(Japan Synchrotron Radiation Research Institute)
