Using a scanning electron microscope (SEM) in the back-scattered electron (BSE) mode the composition of multi-element specimens may be determined based on the strong dependence of emission coefficient η on the averag...Using a scanning electron microscope (SEM) in the back-scattered electron (BSE) mode the composition of multi-element specimens may be determined based on the strong dependence of emission coefficient η on the average atomic number of elements Z. The output video signal of the usual BSE detectors is produced from their sensors, and the larger proportion of high-energy electrons with modified spectrum is added. Since η = is/ip (is and ip currents of specimen and probe), better accuracy must be achieved by direct measurements those currents on the specimen surface. Here, an experimental model of a current detector for a presented specimen is described. The cage is mounted on the carousel of the moving specimen stage. The input of the preamplifier is connected to the specimen holder in the form of a disk, the diameter of which is 12 mm. When the probe along its surface scanned, the input potential begins to pulsate with a negative polarity. The output of this preamplifier is connected to a small light-emitting diode, which creates intensity-modulated radiation in the chamber. Thus created the light video signal will be picked up by the photomultiplier of the E-T detector. The modes of true SE and BSE are set by applying tens bias volts of various polarities to the specimens or the cage itself.展开更多
In this paper, we study the effect of the drain current on terahertz detection for Si metal-oxide semiconductor fieldeffect transistors(MOSFETs) both theoretically and experimentally. The analytical model, which is ...In this paper, we study the effect of the drain current on terahertz detection for Si metal-oxide semiconductor fieldeffect transistors(MOSFETs) both theoretically and experimentally. The analytical model, which is based on the smallsignal equivalent circuit of MOSFETs, predicts the significant improvement of the voltage responsivity Rv with the bias current. The experiment on antennas integrated with MOSFETs agrees with the analytical model, but the Rv improvement is accompanied first by a decrease, then an increase of the low-noise equivalent power(NEP) with the applied current. We determine the tradeoff between the low-NEP and high-Rv for the current-biased detectors. As the best-case scenario, we obtained an improvement of about six times in Rv without the cost of a higher NEP. We conclude that the current supply scheme can provide high-quality signal amplification in practical CMOS terahertz detection.展开更多
A novel structure for a charge pump circuit is proposed, in which the charge-pump (CP) current can adaptively regulated according to phase-locked loops (PLL) frequency synthesis demand. The current follow technolo...A novel structure for a charge pump circuit is proposed, in which the charge-pump (CP) current can adaptively regulated according to phase-locked loops (PLL) frequency synthesis demand. The current follow technology is used to make perfect current matching characteristics, and the two differential inverters are implanted to increase the speed of charge pump and decrease output spur due to theory of low voltage difference signal. Simulation results, with 1st silicon 0. 25μm 2. 5 V complementary metal-oxide-semiconductor (CMOS) mixed-signal process, show the good current matching characteristics regardless of the charge pump output voltages.展开更多
In this work, we investigate the performance of InGaAs p-i-n photodetectors with cut-off wavelengths near 2.6 μm. The influences of different substrate materials on the optoelectronic properties of InGaAs detector ar...In this work, we investigate the performance of InGaAs p-i-n photodetectors with cut-off wavelengths near 2.6 μm. The influences of different substrate materials on the optoelectronic properties of InGaAs detector are also compared and discussed. GaAs-based device shows a significant enhancement in detector with a better performance for a InGaAs photodetector compared to InP- based device. In addition, our results show that the device performance is influenced by the conduction band offset. This work proves that InAlAs/InGaAs/GaAs structure is a promising candidate for high performance detector with optimally tuned band gap.展开更多
文摘Using a scanning electron microscope (SEM) in the back-scattered electron (BSE) mode the composition of multi-element specimens may be determined based on the strong dependence of emission coefficient η on the average atomic number of elements Z. The output video signal of the usual BSE detectors is produced from their sensors, and the larger proportion of high-energy electrons with modified spectrum is added. Since η = is/ip (is and ip currents of specimen and probe), better accuracy must be achieved by direct measurements those currents on the specimen surface. Here, an experimental model of a current detector for a presented specimen is described. The cage is mounted on the carousel of the moving specimen stage. The input of the preamplifier is connected to the specimen holder in the form of a disk, the diameter of which is 12 mm. When the probe along its surface scanned, the input potential begins to pulsate with a negative polarity. The output of this preamplifier is connected to a small light-emitting diode, which creates intensity-modulated radiation in the chamber. Thus created the light video signal will be picked up by the photomultiplier of the E-T detector. The modes of true SE and BSE are set by applying tens bias volts of various polarities to the specimens or the cage itself.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFB-0402403)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20141321)+1 种基金CAST Project,China(Grant No.08201601)the National Science Foundation for Young Scholars of China(Grant No.61404072)
文摘In this paper, we study the effect of the drain current on terahertz detection for Si metal-oxide semiconductor fieldeffect transistors(MOSFETs) both theoretically and experimentally. The analytical model, which is based on the smallsignal equivalent circuit of MOSFETs, predicts the significant improvement of the voltage responsivity Rv with the bias current. The experiment on antennas integrated with MOSFETs agrees with the analytical model, but the Rv improvement is accompanied first by a decrease, then an increase of the low-noise equivalent power(NEP) with the applied current. We determine the tradeoff between the low-NEP and high-Rv for the current-biased detectors. As the best-case scenario, we obtained an improvement of about six times in Rv without the cost of a higher NEP. We conclude that the current supply scheme can provide high-quality signal amplification in practical CMOS terahertz detection.
文摘A novel structure for a charge pump circuit is proposed, in which the charge-pump (CP) current can adaptively regulated according to phase-locked loops (PLL) frequency synthesis demand. The current follow technology is used to make perfect current matching characteristics, and the two differential inverters are implanted to increase the speed of charge pump and decrease output spur due to theory of low voltage difference signal. Simulation results, with 1st silicon 0. 25μm 2. 5 V complementary metal-oxide-semiconductor (CMOS) mixed-signal process, show the good current matching characteristics regardless of the charge pump output voltages.
文摘In this work, we investigate the performance of InGaAs p-i-n photodetectors with cut-off wavelengths near 2.6 μm. The influences of different substrate materials on the optoelectronic properties of InGaAs detector are also compared and discussed. GaAs-based device shows a significant enhancement in detector with a better performance for a InGaAs photodetector compared to InP- based device. In addition, our results show that the device performance is influenced by the conduction band offset. This work proves that InAlAs/InGaAs/GaAs structure is a promising candidate for high performance detector with optimally tuned band gap.