Micropipe and dislocation density reduction in 6H-SiC and 4H-SiC structures grown by liquid phase epitaxy

We investigated silicon carbide (SiC) epitaxial layers grown by liquid phase epitaxy (LPE). The layers were grown on 6H-SiC and 4H-SiC well-oriented (0001) 35 mm diameter commercial wafers as well as on 6H-SiC Lely crystals. A few experiments were also done on off-axis 6H-SiC and 4H-SiC substrates. Layer thickness and growth rate ranged from 0.5 to 50 microns and 0.5 to 10 μm/h, respectively. Layers were investigated by x-ray diffraction, x-ray topography, and selective chemical etching in molten KOH. It was found that dislocation and micropipe density in LPE grown epitaxial layers were significantly reduced compared with the defect densities in the substrates.     

CuO掺杂Ba_(0.6)Sr_(0.4)TiO_3陶瓷的结构与性能

采用传统陶瓷制备工艺,以容差因子为依据进行CuO掺杂,制备了可在较低温度烧结成瓷的Ba_(0.6)Sr_(0.4)TiO_3(BSTO)基陶瓷.结果表明,w(CuO)=0.5%～4.0%的BSTO基陶瓷可在1 200 ℃烧结成瓷,且不会引入杂相.介电性能测试表明,在室温低频下,随CuO掺杂量的增加,BSTO陶瓷的介电常数增加,而介电损耗降低;在微波频段下,BSTO基陶瓷的介电常数和介电损耗均随CuO掺杂量的增加而增大.可调性测试表明,在1 kV/mm的直流偏压下,各BSTO基陶瓷掺杂样的可调性均大于10%,其中,试样w(CuO)=1%的可调性达到13.2%.     

Indium phosphide microwave oscillators

A detailed examination has been carried out on the characteristics of transferred electron microwave oscillators constructed from epitaxial indium phosphide. Seven slices have been used, for which the layer thicknesses varied between 5.4 and 28 µm. It is shown that the mechanism of oscillation has a transit-time dependence and that the transit velocity which emerges (1.5-2 × 10⁷cm/s) is approximately the same as the peak electron drift velocity. It is therefore concluded that propagating space-charge layers are responsible for the oscillations. However, in view of the high transit velocities involved, it is unlikely that the space-charge layers are well-formed dipolar domains. Despite the transit-time dependence, individual devices have been made to oscillate over very wide frequency ranges (8-28 GHz). Operation of devices at frequencies up to 40 GHz has established the high-frequency capability of the oscillators. The best pulsed results obtained have included 0.5 W, 6.3 percent at 13.8 GHz; 1.05 W, 4.2 percent at 18.0 GHz and 0.65 W, 2.6 percent at 25.0 GHz. Continuous operation of these diodes has not yet been possible due to material and thermal technology limitations.     

Selection of Call Progress Tones for Digital Systems

The precise tone system based on the four basic frequencies 350, 440, 480, and 620 Hz is extensively used in switching systems to indicate readiness to dial, ringing of the called subscriber, lines or trunks busy, and other conditions. In digital switching systems it is normally advantageous to generate and process these tones in a digital form. It is shown that by judicious selection of the tone frequencies, considerable simplification of digital tone generators may be achieved. Modification of the precise tone frequencies within ± 0.5 percent reduces the number of samples which must be stored in ROM's from 1650 to 326. Another set of frequencies is given which requires only 228 samples and simplifies the tone generator readout logic.     

1.8GHz AlN薄膜体声波谐振器的研制

提出了基于AlN压电薄膜多层结构的1.8 GHz射频薄膜体声波谐振器(FBAR),并进行了研究。采用修正后的MBVD等效电路模型对器件的谐振特性进行了分析和模拟。给出了采用半导体加工工艺制备器件的工艺流程,并实际制做谐振器样品,样品的测试结果:器件的串联谐振频率fs和并联谐振频率fp分别为1.781和1.794 GHz,相应的有效机电耦合系数为1.8%;串联谐振频率处和并联谐振频率处的Q值分别为308和246。该谐振器样品实际尺寸为0.45 mm×0.21 mm×0.5 mm,可以用来制备高性能的滤波器、双工器和低相噪射频振荡器等。     

不同PT厚度的PZT/PT复合薄膜的性能研究

采用改进的sol-gel法在Pt/Ti/SiO2/Si衬底上制备PZT/PT复合薄膜(共10层),PT的层数分别为2,4,6和8层。结果表明,600℃热处理的PZT/PT复合薄膜为钙钛矿结构,无第二相。随着PT厚度的增加,εr变小,100kHz时为313～228。tgδ在频率低于100kHz时,不随PT厚度变化,为0.015左右;频率为100kHz～1MHz时,PZT6/PT4tgδ最大,1MHz时仍小于0.06。     

羰基铁材料太赫兹光谱研究

为了评估羰基铁材料在太赫兹波段的屏蔽性能,采用太赫兹时域光谱技术分别对参考样品、0.5 mm羰基铁样品和1mm羰基铁样品进行了透射光谱测量。分析表明,随着羰基铁样品厚度的增加,太赫兹时域光谱脉宽增加、峰值减小,频域光谱范围减小。羰基铁样品的最大屏蔽效能为66 dB左右。0.5 mm和1 mm羰基铁样品的屏蔽效能大于60dB的区间分别是0.76 THz～1.46THz和0.49THz～1.48THz。     

High-power GaAs FET's prepared by ion implantation

High-power GaAs FET's have been developed by using ion implantation to form channel layers and n⁺ohmic contact regions. The burn-out characteristics have been improved by introducing n⁺regions with high surface carrier concentration. The source-drain burnout voltage has been found to be more than 40 V. The distributions of saturated source-drain current (Idss) and RF output power of the devices have been found much more uniform than those of power GaAs FET's prepared by metalorganic chemical vapor deposition (MOCVD). Multichip operation of the FET's has demonstrated an excellent power combining efficiency due to the good uniformity among the chips. The two-chip device (total gate width WG= 14.4 mm) has delivered 5 W at 10 GHz with 4-dB gain and 23-percent power added efficiency (ηadd). The four-chip device (WG= 28.8 mm) has given 10 W at 8 GHz (gain = 4.5 dB, ηadd= 23 percent). The four-chip device (WG= 48 mm) has developed 15 W at 5 GHz (gain = 8 dB, ηadd= 30 percent).     

Investigation of HgCdTe p-n device structures grown by liquid-phase epitaxy

The microstructure of p-n device structures grown by liquid-phase epitaxy (LPE) on CdZnTe substrates has been evaluated using transmission electron microscopy (TEM). The devices consisted of thick (∼21-μm) n-type layers and thin (∼1.6-μm) p-type layers, with final CdTe (∼0.5 μm) passivation layers. Initial observations revealed small defects, both within the n-type layer (doped with 8×10¹⁴/cm³ of In) and also within the p-type layer but at a much reduced level. These defects were not visible, however, in cross-sectional samples prepared by ion milling with the sample held at liquid nitrogen temperature. Only isolated growth defects were observed in samples having low indium doping levels (2×10¹⁴/cm³). The CdTe passivation layers were generally columnar and polycrystalline, and interfaces with the p-type HgCdTe layers were uneven. No obvious structural changes were apparent in the region of the CdTe/HgCdTe interfaces as a result of annealing at 250°C.     

Effect of Separation from Ground on Human Whole-Body RF Absorption Rates

Whole-body absorption rates of human volunteers exposed in E-polarization are reported as a function of the separation between the subject's feet and the ground plane. Little difference is observed between the results for the EKH and EHK orientations. At frequencies below the grounded resonance (7 to 25 MHz), and air gap of 3 to 6 mm reduces the absorption rate to half the grounded rate. On the other hand, near the grounded resonance (at 40.68 MHz), an air gap of 50 to 80 mm is required for the same effect. Typical footwear provides some radiation protection by reducing the RF absorption rate by approximately 50 percent at below-resonance frequencies, or 20 percent at near-resonance frequencies. Experiments with different dielectric materials between the soles of the feet and the ground plane support the idea that those two surfaces effectively form a parallel-plate capacitor. The experimental results are compared to the predictions of the cylinder and block-model calculations.     

Gyrator video filter IC with automatic tuning

A single-chip gyrator filter for separating the components of the video signal in a TV receiver is described which is suitable for mass production in a standard bipolar process (f/SUB T//spl ap/400 MHz). The 11 mm/SUP 2/ filter chip operates at frequencies up to 10 MHz, requires no tuning or alignment and has Q-factors which are stable with temperature. The IC contains an automatic tuning system which tunes the five resonators of the filter by aligning an auxiliary gyrator resonator with the crystal oscillator present in the color decoder of a TV receiver. Problems of matching the frequencies of the individual gyrator resonators are discussed, showing how alignment accuracy of 0.5 percent can be obtained when resistivities and specific capacitances have production spreads of at least 10 percent. Various gyrator circuit configurations are given which minimize the circuit complexity and, hence, the chip area. Computer aided design techniques for the filter using geometrically scaled models and macromodeling are presented and it is shown how a complete simulation of the chip led to a significant improvement in bandstop performance. Finally, the measured responses are presented and the filter performance is discussed in the light of present-day requirements.     

Submicron-gate ion-implanted In/sub 0.15/Ga/sub 0.85/As/GaAs MESFETs with graded indium composition

0.25 mu m and 0.5 mu m gate ion-implanted MESFETs have been fabricated on In/sub 0.15/Ga/sub 0.85/As epitaxial layers. These layers are grown by MOCVD on three inch diameter GaAs substrates with the indium mole fraction graded from 15% at the InGaAs/GaAs heterointerface to 0% at the surface. Both devices show excellent DC and microwave performance. From S-parameter measurements, extrinsic current gain cutoff frequencies f/sub t/ of 120 and 61 GHz are obtained for the 0.25 mu m and 0.5 mu m gate MESFETs, respectively. The authors investigate the potential of small-bandgap InGaAs materials for submicron-gate MESFET applications.<>     

Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7/Ba_(0.5)Sr_(0.5)TiO_3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

Epitaxial silicon solar cells with uniformly doped layer

Solar cell structures have been prepared both by successive deposition of p-type and n-type silicon layers on p⁺-type single-crystal silicon. Impurities are uniformly doped at epitaxial layers. Efficiency of 9.0 percent with the epitaxial layer junction structure and 12.8 percent with the diffused 0.3-μm junction depth structure have been achieved.     

High-performance In0.52Al0.48As/In0.53Ga0.47As HFET compatible with optical-detectorintegration

The authors report the successful demonstration of a 1.0-μm gate InAlAs/InGaAs heterojunction FET (HFET) on top of thick InGaAs layers using lattice-matched molecular beam epitaxy (MBE). This scheme is compatible with metal-semiconductor-metal (MSM) photodetector fabrication. The authors measured the performance of InAlAs/InGaAs HFETs from 0 to 40 GHz. Device performance is characterized by peak extrinsic transconductances of 390 mS/mm and as-measured cutoff frequencies up to 30 GHz for a nominal 1.0-μm-gate-length HFET. HFET device measurements are compared for samples growth with and without the thick underlying InGaAs optical-detector absorbing layer     

The Microwave Reflective Properties of Water Surfaces-I: The Reflectivity of Smooth Water at 19.24 and 22.43 GHz as Measured with a Free-Wave Microwave Reflectometer

The reflectivity of smooth water has been measured with a free-wave reflectometer at frequencies of 19.24 and 22.43 GHz and for temperatures between 0/spl deg/ and 40/spl deg/C. Reproducibility of the data for water temperatures below 20/spl deg/C is better than /spl plusmn/ 0.15 percent and the absolute accuracy of the reflectometer is thought to be /spl plusmn/ 0.5 percent. The results deviate significantly from the early reflectivity measurements of Saxton and Lane but agree to within experimental error with values calculated from the absorption cell measurements of Lane and Saxton.     

电磁开腔测量双层介质复介电常数

本文提出了一种利用电磁开腔在微波和毫米波频段测量双层介质复介电常数的新技术。在８ｍｍ频段，利用一套电磁开腔自动测量系统对几种双层介质材料进行了具体测量。最后，对测量误差进行了理论分析，并给出了计算实例。     

A Monolithic Dual 16-Bit D/A Converter

A monolithic dual high-speed 16-bit D/A converter is described. In the binary weighted current network a dynamic current divider is used to obtain the required high accuracy of the six most significant bits without any adjustment procedure or trimming technique. To construct the ten least significant bits a new approach is used to construct the passive divider stage based on emitter sealing of transistors. As the bit switches are optimized for fast-settling and low-glitch current, both converters can be used without extra sample-and-hold or deglitcher circuitry at sampling frequencies up to 200 kHz. The converter has a differential linearity of 0.5 LSB over a temperature range of -20 to +70/spl deg/ C. The high linearity of the converter results in a distortion of 0.001 percent over the audio band. The chip is processed in a standard bipolar process and the die size is 3.8 X 5.5 mm/sup 2/.     

Stress testing of a recrystallizing CaO-B2O3-SiO2 glass-ceramic with Ag electrodes for high frequency electronic packaging

CaO−B₂O₃−SiO₂ recrystallizing glass-ceramics are attractive for use in microelectronics packaging since they can be processed at low temperatures (<950°C) and the resultant material has a low loss tangent. This paper reports on the stability of the Ag electrodes with respect to electromigration. Planer multilayer recrystallizing glass-ceramic/Ag samples were prepared and fired at temperatures from 800–950°C. Buried capacitor structures with Ag plates 10 mm in diameter with a separation distance of 0.1 mm were created. These were stressed with voltages from 50 V to 3 kV at temperatures from 25°C to 200°C to induce failure. Failure modes observed ranged from increased, leakage to catastrophic events. A population was analyzed for mean time to failure characteristics. SEM and EDX were used to try to identify leakage paths and movement of the Ag through the glass ceramic. An activation energy was determined for the most common failure mode.     

InSb,GaSb, and GaInSb grown using trisdimethylaminoantimony

GalnSb alloys as well as the constituent binaries InSb and GaSb have been grown by organometallic vapor phase epitaxy using the new antimony precursor trisdimethylaminoantimony (TDMASb) combined with conventional group III precursors trimethylindium (TMIn) and trimethylgallium (TMGa). InSb layers were grown at temperatures between 275 and 425°C. The low values of V/III ratio required to obtain good morphologies at the lowest temperatures indicate that the pyrolysis temperature is low for TDMASb. In fact, at the lowest temperatures, the InSb growth efficiency is higher than for other antimony precursors, indicating the TDMASb pyrolysis products assist with TMIn pyrolysis. A similar, but less pronounced trend is observed for GaSb growth at temperatures of less than 500°C. No excess carbon contamination is observed for either the InSb or GaSb layers. Ga_1-xIn_xSb layers with excellent morphologies with values of x between 0 and 0.5 were grown on GaSb substrates without the use of graded layers. The growth temperature was 525°C and the values of V/III ratio, optimized for each value of x, ranged between 1.25 and 1.38. Strong photoluminescence (PL) was observed for values of x of less than 0.3, with values of halfwidth ranging from 13 to 16 meV, somewhat smaller than previous reports for layers grown using conventional precursors without the use of graded layers at the interface. The PL intensity was observed to decrease significantly for higher values of x. The PL peak energies were found to track the band gap energy; thus, the luminescence is due to band edge processes. The layers were all p-type with carrier concentrations of approximately 10¹⁷ cm³. Transmission electron diffraction studies indicate that the Ga_0.5In_0.5 Sb layers are ordered. Two variants of the Cu-Pt structure are observed with nearly the same diffracted intensities. This is the first report of ordering in GalnSb alloys.