ChromAIX2: a large area, high count-rate energy-resolving photon counting ASIC for a Spectral CT Prototype (#1987)
R. Steadman1, C. Herrmann1, A. Livne2
1 Philips Research Europe, Eindhoven, Netherlands
Spectral CT based on energy-resolving photon counting detectors is expected to deliver additional diagnostic value at a lower dose than current state-of-the-art CT. The capability of simultaneously providing a number of spectrally distinct measurements not only allows distinguishing between photo-electric and Compton interactions but also allows discriminating contrast agents that exhibit a K-edge discontinuity in the absorption spectrum, referred to as K-edge Imaging. Such detectors are based on direct converting sensors (e.g. CdTe or CdZnTe) and high-rate photon counting electronics. To support the development of Spectral CT and show the feasibility of obtaining rates exceeding 10 Mcps/pixel (Poissonian observed count-rate), the ChromAIX ASIC has been previously reported showing 13.5 Mcps/pixel. The ChromAIX has been improved to offer the possibility of a large area coverage detector, and increased overall performance. The new ASIC is called ChromAIX2, and delivers count-rates exceeding 15 Mcps/pixel with an rms-noise performance of 260 e-. It has an isotropic pixel pitch of 500 µm in an array of 22 x 32 pixels and is tile-able on three of its sides. The pixel topology consists of a two stage amplifier (CSA and Shaper) and a number of test features allowing to thoroughly characterize the ASIC without a sensor. A total of 5 independent thresholds are also available within each pixel, allowing to acquire 5 spectrally distinct measurements simultaneously. The ASIC also incorporates a baseline restorer to eliminate excess currents induced by the sensor (e.g. dark current and low frequency drifts) which would otherwise cause an energy estimation error. In this paper we report on the inherent electrical performance of the ChromAXI2 as well as measurements obtained with CZT (CdZnTe)/CdTe sensors and X-rays and radioactive sources.
Keywords: Photon Counting, ASIC, Spectral CT, Computed Tomography, CZT, k-edge
ALTAIR: A Low-Noise, Low-Power and Wide Dynamic Range ASIC for X and γ Ray Applications with CdTe/CdZnTe Pixel Detectors (#3241)
M. Gandola1, D. Macera1, M. Sammartini1, G. Bertuccio1
1 Politecnico di Milano, Department of Electronics, Information and Bioengineering, Como, Italy
We present Altair, an Application Specific Integrated Circuit (ASIC) designed for the readout of CdTe/CdZnTe pixel linear detectors for X-gamma ray spectroscopic imaging. The circuit is composed of 16 channels each with analog and mixed signal sections and it is developed for high energy resolution, high rate applications with the constraint of low power consumption. The ASIC has been designed and manufactured in CMOS 350nm technology and successfully tested. Altair has three selectable input charge signal ranges covering the photon energy from few keV up to 300 keV. A digital section is devoted to internal configuration and communication with external devices (ADC, microcontrollers) through an SPI interface. Altair power consumption is about 1 mW/ch and in stand-by operating conditions becomes negligible. Output signal peaking time ranging from 0.2 µs to 2.3 µs can be selected. Measurements at room temperature have been done both with and without connected detectors. A minimum Equivalent Noise Charge of 40 electrons r.m.s (425 eV FWHM in CdTe) has been measured at 500 ns peaking time. With a CdTe pixel detector connected to Altair, a pulser FWHM of 1.7keV (160 el. r.m.s.) has been achieved at +20°C, mainly determined by the detector leakage current noise and stray capacitance at the ASIC input.
Keywords: ASIC, Low-power electronics, Low-noise electronics, Spectroscopy, CdTe
Wide Bandgap Semiconductor Detector Optimization for Flash X-Ray Measurements (#1920)
C. D. Roecker1, R. Schirato1
1 LANL, ISR-1, Los Alamos, NM, United States of America
Charge trapping, resulting in a decreased and spatially dependent electric field, has long been a concern for wide bandgap semiconductor detectors. While significant work has been performed to characterize this degradation at varying temperatures and radiation environments, no analysis, that we know of, has been performed examining the event-to-event response in a flash X-ray environment. The following work investigates if charge trapping is a problem for CZT detectors, with particular emphasis on flash radiation fields at cold temperatures. Preliminary results in a non-flash radiation field, using an Am-241 alpha source, have been performed after a temperature transition from room temperature to -30C. A response shift and spectral differences were observed over the span of 180 hours. To expand upon these results, we are currently performing event-to-event experiments as a function of temperature using a flash X-ray system.
Keywords: Flash X-Ray, CZT, Charge Trapping
Fabrication and evaluation of vertical-type BGaN neutron detection diodes (#1105)
T. Nakano1, K. Mochizuki1, T. Arikawa1, H. Nakagawa2, S. Usami3, Y. Honda4, H. Amano4, 5, K. Kojima6, S. F. Chichibu6, 4, H. Mimura7, Y. Inoue1, T. Aoki7
1 Shizuoka University, Dept. of Electronics and Materials Science, Hamamatsu, Japan
We have proposed a novel neutron semiconductor detector using BGaN. BGaN is a semiconductor material in which B atoms having a large neutron capture cross section are mixed with GaN having low γ ray sensitivity. Because of these properties, only neutrons generating α-particles by a B(n, α)Li reaction are detected in BGaN detectors, and it is possible to achieve a high n / γ discrimination. Previously, we had indicated the possibility of neutron detection using a BGaN Schottky diode. However, the thickness of the sensitive layer was thin and needed to be increased. In this study, we fabricate vertical-type BGaN diodes by developing BGaN epitaxial growth technique and evaluate their radiation detection properties.
The BGaN diodes were fabricated by metal organic vapor phase epitaxy (MOVPE) using NH3, trimethylgallium (TMGa) and trimethylboron (TMB) as source gases of N, Ga and B, respectively. In order to suppress the gas phase reaction of B sources with nitrogen, TMB with low reactivity was used. The thickness of the radiation sensitive layer in these vertical type diodes is about 2 μm.
We evaluate the detection property of the fabricated BGaN diodes by irradiating 1.47 MeV α-particles, which is equivalent to the energy of the α-particle generated by the B(n, α)Li reaction. Comparing the detection properties of BGaN diodes with those of GaN diodes, we found that the signal rise time is comparable, but the signal intensity in BGaN diodes is as small as 35 % from that in GaN diodes. We consider that this decrease of the signal intensity is caused by high defect density and low mobility of BGaN. Furthermore, we evaluate the neutron detection property by irradiating thermal neutrons. We succeeded in the detection of neutron pulse signal by using this BGaN diode. Comparing the detection signal of neutron with that of 1.47 MeV α-particle, we found that these signal intensities were similar. These results indicate that neutrons can be detected by BGaN vertical-type diodes.
Keywords: BGaN, neutron detector, semiconductor detector
The P4DI characterization results and application in the localization of radioactive spots (#3410)
D. Chatzistratis1, I. Kazas3, C. Papadimitropoulos2, C. Potiriadis2, I. Kaissas2, D. Loukas3, C. P. Lambropoulos1
1 Technological Education Institute of Sterea Ellada, Psahna-Evia, Greece
The P4DI CMOS and hybrid pixel detector has 1250 pixels with 400um pitch. Pixels give simultaneously the collected charge and the time of occurrence of the hit. With different combinations of gain and peaking time it can measure signal up to 218000 electrons. A detecting plane consisting of 8 hybrids with 10000 pixels using two different bump bonding processes and Al/CdTe/Pt Schottky diodes 0.75mm and 1mm thick has been assembled. Energy resolution from the cumulative spectrum from all pixels is: 2.9KeV FWHM at 59.54 KeV, 3 KeV FWHM at 122 KeV and 5.74 KeV FWHM at 356 KeV at 23oC. Timing resolution is 7μs FWHM. The detecting plane is used in experiments for the localization of radioactive sources with the aid of coded apertures. A second detecting plane is under construction. Characterization results and application performance will be presented.
Keywords: Hybrid detectors; Pixelated detectors and associated VLSI electronics; Coded aperture imaging; Compton imaging; Front-end electronics for detector readout
Progress in the Design of CMOS Charge Sensitive Preamplifiers for Low Capacitance Semiconductor Detectors for Room Temperature Applications (#3681)
G. Bertuccio1, 2, M. Ahangarianabhari1, 2, M. Gandola1, 2, M. Sammartini1, 2
1 Politecnico di Milano - Como Campus, Dept. of Electronics, Information and Bioengineering, Como, Italy
We present the progress in the design of CMOS fully integrated charge sensitive preamplifiers specifically designed for ultimate low-noise performance with low-capacitance semiconductor detectors operating at room temperature. The preamplifiers show input leakage currents of the order of 1 fA at room temperature, so that the parallel noise of the system is fully determined by the detector, allowing to achieve the best possible energy resolution. The series white and 1/f noise have been minimized with a novel circuit design. The preamplifiers operate in pulsed reset mode with reset times as short as tens of nanoseconds, allowing a very high input pulse rate. The intrinsic noise has been measured at room temperature from 3.8 electrons r.m.s. at 0.4 µs down to 1.0 electrons r.m.s. at 50 µs peaking time of triangular shaping. Experimental results using different small capacitance semiconductor detectors show 60 eV FWHM of the pulser line at room temperature, lower than the Fano limit for photon energy above a few keV, allowing a spectroscopic characterization of semiconductor detectors no more limited by the noise of the front-end electronics.
Keywords: Charge sensitive preamplifiers, CMOS ASICs, front-end electronics, room temperature semiconductor detectors, X-ray spectroscopy