Picoammeter based on a SCQI with current feedback

Measurement Techniques -     

Reflex triode with virtual cathode and controlled internal TEM-waveguide feedback

A reflex triode with virtual cathode (VC) was studied in which a controlled-length TEM-waveguide feedback was introduced between the region of generation (VC localization) and a diode region. At a certain feedback length, the microwave output power of the reflex triode increases by a factor of 1.6 as compared to the same system without feedback.     

Amplifier using p-n junction field-effect transistors with 1/f-type noise

Conclusions The KPS104A field-effect transistor, which produces practically no 1/f-type noise down to frequencies f2 Hz, may be used to advantage as the active element of a high-sensitivity amplifier at subsonic frequencies.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 38–39, March, 1979.     

基于场发射三极管的设计及性能研究

采用微波等离子体化学气相沉积法在不锈钢衬底上制备出了纳米非晶碳和碳纳米管混合薄膜,二极管结构测试表明薄膜材料具有优良的场发射性能。利用制备的薄膜材料作为阴极制作了前栅极结构的场发射三极管器件并对其性能进行了测试。结果表明该器件具有优良的栅控性能,亮度很高,有良好的应用前景。     

Vacuum field-emission triode based on electron multiplier concentrator

The design and technology of manufacturing a vacuum field-emission triode (VFT) based on an electron multiplier concentrator that plays the role of a field-emission cathode capable of ensuring a significantly greater current density as compared to that provided by the other existing electron emitters. Experimental current-voltage characteristics of the VFT are presented. The possibility of creating integrated circuits based on the proposed device is discussed.     

Reflex triode with virtual cathode and emitter based on magnetically confined discharge

A new reflex triode with virtual cathode (VC) was developed and experimentally studied, in which surface discharge along a ferroelectric is used as the source of electrons and loop antennas are used for extracting the radiation. The electrode system in the proposed device is designed so that magnetic forces of the discharge would confine the plasma to the dielectric surface. This system provides for a ∼20-fold increase in the generation time as compared to that achieved in prior designs. The new reflex triode generates wideband RF pulses in a range of frequencies from 20–230 MHz at a power of about 140 W.     

并三苯场效应晶体管的研制

采用有机半导体材料并三苯作为有源层,环氧树脂作为绝缘介质,通过旋涂和真空掩蔽蒸发的方法,成功研制出了倒转结构的有机场效应晶体管.经测试器件的电子迁移率为5.76×10-2cm2/V·s,跨导为0.96μS.显示出该器件具有良好的输出特性曲线.     

电泳沉积制备平行栅碳纳米管场发射阴极的研究

利用磁控溅射、光刻、湿法刻蚀和电泳技术在玻璃基片上成功制备平行栅场发射阴极阵列,用光学显微镜、场发射扫描电镜和拉曼光谱观察了碳纳米管的形貌和结构,并测试所制备的平行栅碳纳米管阴极的场发射性能.光学显微镜和场发射电子显微镜测试表明,平行栅结构阴极和栅极交替地分布,同一个平面内,CNTs有选择性地沉积在平行栅结构中的阴极表...     

Sound shielding by a piezoelectric membrane and a negative capacitor with feedback control

The design and realization of an adaptive sound-shielding system based on a method to control the effective elastic stiffness of piezoelectric materials are presented in this paper. In this system, the sound-shielding effect is achieved by a sound reflection from the piezoelectric curved membrane fixed in rigid frame and connected to an active analog circuit that behaves as a negative capacitor. The acoustic transmission loss through the curved membrane was measured for the incident sound of frequency 1.6 kHz and of acoustic pressure level 80 dB. When the negative capacitor in the system was properly adjusted, the acoustic pressure level of the transmitted sound was reduced from the initial 60 dB to 15 dB by the action of the negative capacitor. Then the system was exposed to naturally changing operational conditions, and their effect on sound-shielding efficiency was studied. It is shown that the acoustic transmission loss of the system dropped by 35 dB within 30 min from the moment of negative capacitor adjustment. Therefore, a self-adjustment of the system has been implemented by appending an additional digital control circuit to the negative capacitor. It is shown that the aforementioned deteriorating effect has been eliminated by the adjusting action of the control circuit. The long-time sustainable value of 60 dB in the acoustic transmission loss of the adaptive sound shielding system has been achieved.     

Ferroelectric field-effect transistor based on transparent oxides

We studied a Pb_xZr_1−xTiO₃/SnO₂/Al₂O₃ heterostructure as a base for transparent ferroelectric field-effect transistor. Single-crystal SnO₂/Al₂O₃ epitaxial films with the electron mobility of 25 cm²/V were grown by pulsed laser deposition using two YAG:Nd lasers. Depletion mode transistor Au/PZT/SnO₂/Al₂O₃ was produced by laser ablation and RF sputtering. All the samples demonstrate clockwise hysteresis of the source-drain characteristic. The energy distribution of traps at the PZT/SnO₂ interface was determined using a modified version of a transient current method. The effect of PZT intergrain boundaries on the retention time was taken into account for experimental data discussion.     

Theoretical study on polarization dynamics of VCSELs with negative optoelectronic feedback

We investigate theoretically the polarization dynamics of vertical-cavity surface-emitting lasers (VCSELs) subjected to negative optoelectronic feedback. As we vary the feedback delay and strength, the VCSEL exhibits interesting nonlinear dynamics in the two-linear polarized directions. The output instability and negative current modulation induced by delayed feedback can also cause polarization switching (PS) to happen. In addition, we investigate the case when the free-running VCSEL emits in the modulated-elliptical state and find that the laser experiences in succession the elliptical polarization, the x-mode polarization, and the mixed-mode polarization states with an increasing feedback strength.     

State feedback control for active magnetic bearings based on current change rate alone

This work presents a new sensorless control technique for active magnetic bearings (AMB). We consider a single-axis AMB composed of a rotor and a pair of electromagnets. It is driven by a pair of pulsewidth-modulated (PWM) switching power amplifiers. We connect the amplifier input and output terminals and the magnet coils to a simple network composed of a transformer and a sample-and-hold circuit. Then, we show that when the sampling takes place at a certain moment of each PWM cycle, the electronics gives a full state feedback that can stabilize the rotor. Although there is not an explicit controller, the closed-loop poles can be arbitrarily placed, and good performance is achieved with reasonable parameter values of the driving electronics. We include an implementation example with experimental results.     

P型硅并五苯有机场效应晶体管的研制

以P＋＋硅为衬底，热生长SiO2为栅绝缘层，真空蒸发有机半导体材料并五苯作为有源层，射频磁控溅射金作为源、漏电极，成功制作了底接触式并五苯有机场效应晶体管（OFETs）。测试表明在源漏电压为70V时，器件的载流子迁移率μ为：0．31cm^2/V.s。     

Room-temperature terahertz detectors based on semiconductor nanowire field-effect transistors

The growth of semiconductor nanowires (NWs) has recently opened new paths to silicon integration of device families such as light-emitting diodes, high-efficiency photovoltaics, or high-responsivity photodetectors. It is also offering a wealth of new approaches for the development of a future generation of nanoelectronic devices. Here we demonstrate that semiconductor nanowires can also be used as building blocks for the realization of high-sensitivity terahertz detectors based on a 1D field-effect transistor configuration. In order to take advantage of the low effective mass and high mobilities achievable in III-V compounds, we have used InAs nanowires, grown by vapor-phase epitaxy, and properly doped with selenium to control the charge density and to optimize source-drain and contact resistance. The detection mechanism exploits the nonlinearity of the transfer characteristics: the terahertz radiation field is fed at the gate-source electrodes with wide band antennas, and the rectified signal is then read at the output in the form of a DC drain voltage. Significant responsivity values (>1 V/W) at 0.3 THz have been obtained with noise equivalent powers (NEP) < 2 × 10(-9) W/(Hz)(1/2) at room temperature. The large existing margins for technology improvements, the scalability to higher frequencies, and the possibility of realizing multipixel arrays, make these devices highly competitive as a future solution for terahertz detection.     

Quartz thermometer with a field-effect transistor oscillator

A very simple quartz thermometer is described which consists of a quartz temperature probe with practically linear temperature-frequency characteristic, an oscillator system and an electronic frequency meter. The thermometer measures temperatures from 233 to 373 K with an error < 0.02 K.