毫米波肖特基势垒混频二极管本征噪声温度测试评价

本文对一些毫米波肖特基势混频二极管本征噪声温度进行了测试和分析。介绍了在常温和致冷下混频二极管本征噪声的测试方法。     

Defect state assisted tunneling in intermediate temperature molecular beam epitaxy grown GaAs

Current transport in molecular beam epitaxy (MBE) GaAs grown at low and intermediate growth temperatures is strongly affected by defects. A model is developed here that shows that tunneling assisted by defect states can dominate, at some bias ranges, current transport in Schottky contacts to unannealed GaAs material grown at the intermediate temperature range of about 400°C. The deep defect states are modeled by quantum wells which trap electrons emitted from the cathode before re-emission to semiconductor. Comparison of theory with experimental data shows defect states of energies about 0.5 eVbelow conduction band to provide the best fit to data. This suggests that arsenic interstitials are likely to mediate this conduction. Comparison is also made between as-grown material and GaAs grown at the same temperature but annealed at 600°C. It is suggested that reduction of these defects by thermal annealing can explain lower current conduction at high biases in the annealed device as well as higher current conduction at low biases due to higher lifetime. Quenching of current by light in the as-grown material can also be explained based on occupancy of trap states. Identification of this mechanism can lead to its utilization in making ohmic contacts, or its elimination by growing tunneling barrier layers.     

能量脉冲下高能ZnO压敏电阻的老化现象

研究了用于水轮发电机灭磁与过电压保护的高能ZnO压敏电阻在贮能电感释放的能量脉冲作用下的老化现象。研究表明,能量脉冲后,压敏电阻的特征电压、非线性系数和预击穿区V-I特性都发生跌落,而且这种跌落随脉冲次数增加而增加;能量脉冲使压敏电阻发生非对称老化。能量脉冲可以分解直流电压和能量两个分量。高能ZnO压敏电阻在能量脉冲下老化的原因是发生在晶粒耗尽层中和富铋晶界层中的离子迁移使双Schottky势垒降低。     

Soot suppression by nonthermal plasma in coflow jet diffusion flames using a dielectric barrier discharge

The effect of nonthermal plasma on diffusion flames in coflow jets has been studied experimentally by adopting a dielectric barrier discharge (DBD) technique. The plasma reactor had wire-cylinder-type electrodes with AC power supply operated at 400 Hz. The effect of flame on the behavior of electrical discharge was first investigated to identify the regime of plasma generation, discharge onset voltage, and delivered power to the plasma reactor. The generation of streamers was enhanced with a flame by the increase in the reduced electric field intensity due to high-temperature burnt gas and by the abundance of ions in the flame region. The effect of streamers on flame behavior reveals that the flame length was significantly decreased as the applied voltage increased. The yellow luminosity by the radiation of soot particles was also significantly diminished. The temperature of burnt gases, the concentrations of major species, and the spatial distribution of OH radical, PAH, and soot have been measured. The formation of PAH and soot was influenced appreciably by the nonthermal plasma, while the flame temperature and the concentration of major species were not influenced much with the plasma generation. The results demonstrated that the application of nonthermal plasmas can effectively suppress PAH and soot formation in the flames with low power consumption even in the order of 1 W.     

MBE growth and microstructural evaluation of Zn(S,Se)-based LEDs and diode lasers

The use of a nitrogen radio frequency plasma source together with an appropriate quantum well configuration have recently resulted in the successful realization of p-type ZnSe by molecular beam epitaxy. This has enabled a variety of pn heterojunction based devices to be built including the first semiconductor injection lasers operating in the blue/green portion of the spectrum first reported by 3M and the Brown/Purdue group. In this paper, we discuss two lattice matched multiple quantum well structures that produce laser emission in the blue and blue/green portion of the spectrum.     

Magnetic tunnel junctions with doubly-plasma oxidized AlOx insulation layer

Magnetic tunnel junctions (MTJ), with the tunnel barrier plasma oxidized in two steps, were fabricated in order to obtain structurally uniform AlO_x insulator. The doubly oxidized junctions exhibited the magnetoresistance (MR) ratio of 27-31% without showing any noticeable drop in the MR ratio even after oxidation time was extended well beyond the optimal oxidation time for the normal junctions. Transmission electron microscopy of the junctions confirmed that the AlO_x thickness was thinner for the doubly oxidized junctions compared to the singly oxidized MTJ. X-ray photoelectron spectroscopy of the doubly oxidized junction also strongly suggested that the initial oxide layer prevents the over-oxidation of the bottom electrode. The AlO_x tunnel barrier oxidized in two steps improved the junction performance and widened the processing window.     

Developing a conductive oxygen barrier for ferroelectric integration

For high-density FeRAM memories, the 1T–1C architecture has been proposed. In this scheme, the ferrocapacitor (FeCAP), a metal\ferroelectric film\metal-like sandwich, is placed directly on top of polysilicon or tungsten plugs contacted to the underlying CMOS technology. Our ferroelectric material of choice, SrBi₂Ta₂O₉ (SBT), requires crystallization anneals ranging from 650 to 800 °C in full oxygen. The bottom electrode (BE) needs to be conductive, as well as an oxygen barrier to protect the underlying plug from oxidation. We have developed a BE stack combination consisting of Pt/IrO₂/Ir/Ti(Al)N. Each layer plays a critical role in the performance of the barrier. Issues such as thermal expansion, stress relaxation, grain growth, and oxidation can be critical in order to have a working bottom electrode. For capacitor formation, the complete stack is etched and covered by SBT. Since all layers are in contact with SBT, it is important to understand how the ferroelectric interacts with both the individual layers and the combined structure. In this paper, we will present our understanding of the chemical reactivity between SBT and the BE stack, which has been successfully engineered to prevent oxidation of the underlying plug.     

Increased sensitivity and selective capacity of gas sensors based on SnO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> films exposed to light-emitting diodes

Effects are described for the increase in sensitivity of thin film gas sensors based on SnO_2−x alloyed with Sb and In, with emission by red, yellow, green, and blue light diodes for organic liquid vapors with a volume concentration of less than 10 ppm. An attempt is made to explain this effect on the basis of analyzing aerogenic reactions. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 69–72, June, 2008.