膜片钳放大器的低噪声设计

本文论述用于测量细胞膜离子通道电流的放大器的电路方案.因被测电流在1pA到nA级的范围内,而输出电压要求达到计算机便于处理的数值.故需采用多级放大电路.被测电流属极微弱的信号,噪声问题是设计中的关键.对于多级放大器来说,前置放大级(探头电路)的低噪声设计至关重要.文中分析放大电路中的主要元、器件的背景噪声,用噪声电流和噪声电压的功率密度谱(PDS)S_I(f)和S_v(f)来表征其特性.给出了所设计的PC-Ⅱ型膜片钳放大器的主要性能参数和记录的电流波形.     

Annealing effect on physical and electrical characteristics of thin HfO2, HfSixOy and HfOyNz films on Si

We report the effect of annealing on electrical and physical characteristics of HfO₂, HfSi_xO_y and HfO_yN_z gate oxide films on Si. Having the largest thickness change of 0.3 nm after post deposition annealing (PDA), HfO_yN_z shows the lowest leakage current. It was found for both as-grown and annealed structures that Poole-Frenkel conduction is dominant at low field while Fowler-Nordheim tunneling in high field. Spectroscopic ellipsometry measurement revealed that the PDA process decreases the bandgap of the dielectric layers. We found that a decreasing of peak intensity in the middle HfO_yN_z layer as measured by Tof-SIMS may suggest the movement of N toward the interface region between the HfO_yN_z layer and the Si substrate during the annealing process.     

Annealing before gate metal deposition related noise performance in AlGaN/GaN HEMTs

For a further improvement of the noise performance in AlGaN/GaN HEMTs, reducing the relatively high gate leakage current is a key issue. In this paper, an experiment was carried out to demonstrate that one method during the device fabrication process can lower the noise. Two samples were treated differently after gate recess etching: one sample was annealed before metal deposition and the other sample was left as it is. From a comparison of their Ig-Vg characteristics, a conclusion could be drawn that the annealing can effectively reduce the gate leakage current. The etching plasma-induced damage removal or reduction after annealing is considered to be the main factor responsible for it. Evidence is given to prove that annealing can increase the Schottky barrier height. A noise model was used to verify that the annealing of the gate recess before the metal deposition is really effective to improve the noise performance of AlGaN/GaN HEMTs.     

A direct digital frequency synthesizer with high-speed current-steering DAC

A high-speed SiGe BiCMOS direct digital frequency synthesizer (DDS) is presented. The design in tegrates a high-speed digital DDS core, a high-speed differential current-steering mode 10-bit D/A converter, a serial/parallel interface, and clock control logic. The DDS design is processed in 0.35 μm SiGe BiCMOS standard process technology and worked at 1 GHz system frequency. The measured results show that the DDS is capable of generating a frequency-agile analog output sine wave up to 400+ MHz.     

10 Gb/s OEIC optical receiver front-end and 3.125 Gb/s PHEMT limiting amplifier

A 10 Gb/s OEIC (optoelectronic integrated circuit) optical receiver front-end has been studied and fab ricated based on the φ-76 mm GaAs PHEMT process; this is the first time that a limiting amplifier (LA) has been designed and realized using depletion mode PHEMT. An OEIC optical receiver front-end mode composed of an MSM photodiode and a current mode transimpedance amplifier (TIA) has been established and optimized by simu lation software ATLAS. The photodiode has a bandwidth of 10 GHz, a capacitance of 3 fF/μm and a photosensitive area of 50×50 μm~2. The whole chip has an area of 1511×666 μm~2. The LA bandwidth is expanded by spiral inductance which has been simulated by software HFSS. The chip area is 1950×1910μm~2 and the measured results demonstrate an input dynamic range of 34 dB (10-500 mVpp) with constant output swing of 500 tnVpp.     

Surface leakage current analysis of ion implanted ZnS-passivated n-on-p HgCdTe diodes in weak inversion

Effects of fixed charge on R₀A value of ZnS-passivated x=0.3 HgCdTe n-on-p diode are explained as a shunt resistance that affects current-voltage (I-V) and dynamic resistance-voltage (Rd-V) characteristics. The fixed charge of 1×10¹¹/cm² to 2 × 10¹¹/cm² which is usually obtained with ZnS passivation makes the surface weakly inverted and reduces HgCdTe diode R₀A value owing to the short generation lifetime of HgCdTe substrate. The gate-controlled diode and specially fabricated diode are used to explain the surface leakage current in the weak inversion and charge sheet model is used to explain the characteristics. It is found that the surface leakage current by the inverted channel in the weak inversion can reduce R₀A more than other currents such as the generation current and tunneling current which are usually used to explain the surface leakage current of HgCdTe diode.     

基于脉冲感应的水下光缆探测技术及仿真

针对交流磁场探测法和绝对磁场探测法应用上的不足,提出了基于脉冲感应的水下光缆探测系统(OFCDS-PI).简要介绍了系统原理及其功能模型;详尽介绍了高速数据采集电路及与PC机接口电路的设计、数据处理软件的编制.对提出的系统方案进行了计算机仿真测试.仿真结果表明,电压衰落斜率越大,线圈与光缆间的距离越远,因此OFCDS-PI系统设计方案是有效和可信的.     

外部光反馈对980nm垂直腔面发射激光器振荡特性的影响

研究了外部光反馈对980nm垂直腔面发射激光器(VCSEL)振荡特性的影响.计算了垂直腔面发射激光器及边发射半导体激光器的光反馈灵敏因子.基于复合腔理论,分析了外部光反馈对垂直腔面发射激光器的阈值电流及微分量子效率等振荡特性参数的影响.实验结果表明,当反馈率为10%时,垂直腔面发射激光器的阈值电流由0.63A下降至0.59A,同时斜率效率和输出功率也有所下降.实验结果和理论分析符合得较好.     

3D Carbonaceous Current Collectors: The Origin of Enhanced Cycling Stability for High‐Sulfur‐Loading Lithium–Sulfur Batteries

The cycling stability of high‐sulfur‐loading lithium–sulfur (Li–S) batteries remains a great challenge owing to the exaggerated shuttle problem and interface instability. Despite enormous efforts on design of advanced electrodes and electrolytes, the stability issue raised from current collectors has been rarely concerned. This study demonstrates that rationally designing a 3D carbonaceous macroporous current collector is an efficient and effective “two‐in‐one” strategy to improve the cycling stability of high‐sulfur‐loading Li–S batteries, which is highly versatile to enable various composite cathodes with sulfur loading >3.7 mAh cm^?2. The best cycling performance can be achieved upon 950 cycles with a very low decay rate of 0.029%. Moreover, the origin of such a huge enhancement in cycling stability is ascribed to (1) the inhibition of electrochemical corrosion, which severely occurs on the typical Al foil and disables its long‐term sustainability for charge transfer, and (2) the passivation of cathode surface. The role of the chemical resistivity against corrosion and favorable macroscopic porous structure is highlighted for exploiting novel current collectors toward exceptional cycling stability of high‐sulfur‐loading Li–S batteries.