ALBERT

Description: The effects of biased irradiation on Ge MOS capacitors with Hf x Zr 1– x O y (0.43 〈 x 〈 1) gate dielectrics have been investigated. These devices were irradiated by a 662-KeV Cs $^{137} gamma $ -ray radiation source with 0.5 or –0.5 V gate bias. Prior to irradiation exposure, leakage behavior and bias-instability of Hf x Zr 1– x O y films were also examined. Gate leakage current density increases with the increasing of Zr composition in gate oxide. In addition, Zr-containing dielectrics under positive bias (PB) exhibited more oxide negative trapped charges than that of HfO 2 , which suggested that the oxygen-vacancy concentration in Hf x Zr 1– x O y was increased by the addition of Zr. Larger flat-band voltage shifts ( $Delta V_{mathrm {FB}})$ were extracted under positive biased irradiation than the bias only results. The results indicate that radiation-induced interface traps ( $Delta N_{mathrm {it}})$ are the dominant factor for $Delta V_{mathrm {FB}}$ in HfO 2 thin films, whereas the radiation response for Zr-containing dielectrics under PB was mainly due to oxide traps. Under negative biased irradiation, $Delta V_{mathrm {FB}}$ was attributed to the combined effect of the net oxide trapped charges and the passivation of Ge dang- ing bonds at the Ge/high-k interface. Additionally, both bias-induced and radiation-induced charge trapping have a crucial effect on radiation response of Hf x Zr 1– x O y at each dose level. Hf x Zr 1– x O y is identified as a promising gate dielectric for advanced complementary metal–oxide–semiconductor technologies.

Description: This paper presents the implementation of a high-resolution time-to-digital converter (TDC), which is adapted to varying environmental conditions. The TDC is implemented in field-programmable gate arrays (FPGA), using carry chains to achieve fine time measurement. Multiple carry chains are integrated in a single TDC channel for resolution enhancement. The TDC performance would suffer greatly without temperature compensation due to its sensitivity to the operating temperature. In order to improve the TDC adaptability, we analyzed the temperature-dependent delay variation function, and designed a powerful offset canceler to ensure stable performance of our TDC over a wide temperature range. The offset canceler can effectively correct the delay offset over temperature for the carry chain as well as for the signal transmission path. The TDC channels are tested to be fully functional with the operating temperature continuously varying from −20 °C to 60 °C. The averaged TDC bin size is 1.15 ps, and the single-shot precision is 3.5 ps. The duplications of the TDCs in three FPGA chips show good performance reproducibility according to the tests in a temperature chamber.

Description: A Monte Carlo model was proposed to evaluate the reliability for single-event transient (SET) on combinational circuits. The masking effects, including logical, electrical, and timing masking effects, and the randomicity of SET are considered in the proposed model. Based on the reported model, an electrical masking model is also presented to apply for the reliability model. For ISCAS’85 benchmark circuits, the effects of SET duration, the masking effects, and the multi-SETs on the reliability are analyzed by the proposed model. The results are reported showing that the proposed model can be effectively used to analyze the reliability of a complex circuit.

Description: The electrical properties of CdZnTe(CZT) above the melting point of tellurium (Te) inclusions were determined during in situ annealing. The thermal annealing cycles of the CZT detectors were 490 °C, 530 °C, and 570 °C continuously, which were higher than the melting points of elemental Te and Te inclusions and lower than the sublimation temperature of CZT. Unexpectedly, the CZT detectors exhibited very low leakage current at room temperature after the thermal annealing cycles due to the formation of rectifying contacts. The activation energy of high-resistivity CZT was 0.81 eV indicating pinning of Fermi level nearly in the middle of bandgap. At room temperature, CZT detectors with rectifying contacts showed clearly the 59.5-keV gamma-ray peak of Am-241. Observed fluctuations of the leakage current at about 470 °C might have originated from a mixed conductivity of liquid and solid CZT due to the melting of Te inclusions.

Description: This paper reports on the development and commissioning of the GP2 detector. GP2 was developed to address the requirement for a high-resolution event-mode imaging detector, for application in energy-resolved neutron radiography. The name GP2 derives from the use of gadolinium as a neutron conversion material, combined with a second-generation mass spectrometry sensor known as PImMS2. Theoretical and measured characteristics of GP2 are compared, with emphasis on the usability and functionality of the detector. The development of the detector has been steered by a design philosophy which was established to ensure that the detector has unique and novel impact. The motivation and consequences of the design philosophy are discussed. The key parameters reported are the neutron detection efficiency (7.5% at 2.5 Å), gamma sensitivity ( $1.5 times 10^{-3})$ , and a spatial resolution (modulation transfer function at 10%) of 6.4 lp/mm for a 4- $mu text{m}$ -thick natural gadolinium neutron converter film.

Description: The ability to measure pulse times of arrival with resolutions at or below 100 ps is becoming increasingly desirable in various fields, typically for signals originating from photon detectors such as photomultiplier tubes (PMTs) or silicon photo-multipliers. Achieving the best results has typically required digitizing signals at rates between 4 and 20 giga-samples/second (GSps), followed by off-line processing, since such in-line processing technologies as digital signal processors and field-programmable gate arrays (FPGAs) cannot handle the data rates. For multichannel applications, the cost of GSps digitizers also becomes an issue. In this paper, we present two new methods for achieving similar time resolutions that are designed for FPGA in-line implementations operating with digitizers running at 250–500 mega-samples/second (MSps), approximately a factor of ten times slower. The first method uses a modified sinc function to interpolate the arriving pulse twice, once to precisely estimate its maximum M and once on its leading edge to locate the constant fraction point $f cdot M$ as the pulse’s arrival time. The second method takes the ratio of two points captured from a rapidly changing region of the pulse, either on its leading edge or near its peak, and uses this ratio with a preconstructed lookup table to generate the arrival time. We examine the algorithms’ improved timing capability by comparing their coincidence timing resolutions to those from three standard algorithms, all applied to three data sets of pulses with different characteristics. At 500 MSps, the interpolation technique achieves about 7-ps full-width at half-maximum (FWHM) for an analog trigger pulse split between two ADC channels; for a fast laser pulse illuminating two ADIT L25D19 PMTs, better than 50-ps FWHM, and at 250 MSps, for two - tex-math notation="LaTeX"〉$phi ~25$ mm $times25$ mm LaBr 3 crystals exposed to 60 Co, 137-ps FWHM for gamma rays in a 0.95- and 1.33-MeV window.