Microstrip resonators on anisotropic substrates

The spectral domain method is applied to study shielded microstrip resonators printed on anisotropic substrates. A Green's function that takes into account the dielectric anisotropy effects is derived through a fourth-order formulation. Galerkin's method is then applied to form the characteristic equation from which the resonant frequency of the microstrip resonator is numerically obtained. Results for a microstrip situated on an isotropic substrate are used to validate the theory     

Patch antennas on ferromagnetic substrates

Patch antennas on ferrite substrates allow for pattern control, frequency shifting, and scattering reduction. This is achieved by external magnetic field biasing coupled with the inherent magnetization of the ferrite substrate. Measurements and analytical studies based on the method of moments (MoM) have verified these attractive properties of ferrite substrates. However, verification of the analysis is difficult and, furthermore, previous models have relied on uniform biasing across the substrate. We present a hybrid finite element-boundary integral (FE-BI) method, which permits modeling of the true nonuniform bias fields within the substrate for a more accurate prediction of the ferrite patch performance. After validation of the proposed simulation and a demonstration of the inherent properties of the ferrite patch, it is shown that nonuniform biasing is responsible for additional frequency shifts. We also identify the poor condition of the resulting matrix systems and relate this situation to the predictable occurrence of nonpropagating substrate modes. A more robust iterative solver with preconditioning is, therefore, proposed and applied to handle these situations     

Micromachined filters on synthesized substrates

Effective high-frequency spectrum usage requires high-performance filters to have a sharp cutoff frequency and high stopband attenuation. Stepped-impedance low-pass designs achieve this function best with large ratios of high-to-low-impedance values. In high-index materials, such as Si (11.7) and GaAs (12.9), however these high-to-low-impedance ratios are around five, thereby significantly limiting optimum filter performance. This paper characterizes the use of Si micromachining for the development of synthesized substrates, which, when utilized appropriately, can further reduce the low-impedance value or increase the high-impedance value. Both designs have demonstrated high-to-low-impedance ratios that are 1.5-2 times larger than conventional techniques     

Polysilicon thin-film transistors on polymer substrates

Different approaches to fabricate low-temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) on polymer substrates are reviewed and the two main routes are discussed: (1) standard fabrication of LTPS TFTs on glass substrates followed by a transfer process of the devices on the polymeric substrate; (2) direct fabrication of the devices on the polymeric substrate. Among the different techniques we have described in more detail the process we have recently developed for the fabrication of LTPS TFTs directly on ultra-thin polyimide (PI) substrate. LTPS TFT technology is particularly suited for high performance flexible electronics applications, due to the excellent device characteristics, good electrical stability and CMOS technology. Flexible display application remains the most attractive application for LTPS technology, especially for AMOLED displays, where device stability and the possibility to integrate the driving circuits make LTPS technology superior to all the other competitive TFT technologies. Among the other applications, particularly promising is also the application to flexible smart sensors, where integration of a front-end electronics is essential. Some examples of flexible gas sensors and pressure sensors, integrated with simple readout electronics based on LTPS TFTs and fabricated on ultra-thin PI substrate, are presented.     

Poly-Si thin-film transistors on steel substrates

We report the successful fabrication of poly-Si thin-film transistors (TFTs) on stainless steel substrates. The TFTs were fabricated on a 500 μm thick polished stainless steel substrate using furnace crystallized amorphous Si deposited by PECVD. These devices typically have threshold voltages of 8.6 V, linear effective mobilities of 6.2 cm²/V·s and subthreshold slopes of 0.93 decade/V. This work demonstrates the feasibility of poly-Si TFTs on stainless steel substrates and identifies some critical issues involved in poly Si processing on stainless steel. This will enable the fabrication of arrays with integrated drivers on a cheap, flexible and durable substrate for various displays and other large area array microelectronic applications     

GaAs MESFET's fabricated on InP substrates

This paper reports the first successful MESFET fabrication in GaAs layers grown directly on InP substrates by molecular beam epitaxy (MBE). The fabricated GaAs MESFET's exhibit good I-V curves with complete pinch-off and saturation characteristics. About 100-mS/ mm transconductance was obtained for a 1.2-µm gate length device.     

Crystalline oxide-based devices on silicon substrates

We have developed a process to grow epitaxial SrTiO₃ (STO) on Si. This STO/Si substrate can then be used as a pseudo substrate for the further deposition of many other oxides that are closely lattice matched to STO. The STO is grown by molecular-beam epitaxy (MBE) with a subsequent oxide layer deposited either by MBE or sol-gel deposition. The pseudo substrate has been used to demonstrate ferroelectric devices and piezoelectric devices. Ferroelectric capacitors using epitaxial BaTiO₃ (BTO) show a memory window of 0.5 V; however, the retention time for these devices is short because of the depolarization field caused by the silicon-oxide interface layer used to improve the band alignment of the BTO/Si interface. Surface acoustic wave (SAW) resonators using epitaxial Pb(Zr,Ti)O₃ show excellent response with a coupling coefficient of 4.6% and a velocity of 2,844 m/s.     

GaAs-GaAlAs heterostructure lasers on semi-insulating substrates

Two structures of GaAs-GaAlAs heterostructures were fabricated on semi-insulating substrates. Low-threshold single-mode operation was achieved. The integration of a laser with an active electronic device (Gunn oscillator) on the same chip of GaAs was demonstrated.     

Characteristic-impedance measurement error on lossy substrates

This paper examines error caused by parasitic inductance in the characteristic impedance measured by the calibration comparison method on lossy silicon substrates     

MOSFET's on Au-diffused high-resistivity Si substrates

Si MOSFET's on Au-diffused high-resistivity substrates were fabricated and their electrical properties were investigated. At 80 K, the current leakage between the source and drain of both n- and p-channel devices decreased below 10^-10A, and the devices exhibited normally-off behaviors. Au concentrations (N) in Si substrates as a function of diffusion temperature Tdiffwas determined from the change in the threshold voltage.Nversus Tdiffthus obtained is in fairly good agreement with that obtained by other methods. Dependence of effective mobility on Tdiffwas investigated in the form of a MOS device. The effective mobility decreased with increasing Tdiff, and it became clear that the diffusion temperature must be lower than about 700°C to obtain semi-insulating substrates with reasonably high carrier mobility. A C-MOS inverter was fabricated using an Au-diffused Si substrate, where no isolation wells were needed, in operation at low temperatures.     

High-performance TFTs fabricated on plastic substrates

Poly-Si thin-film transistors (TFTs) have recently been introduced to commercial glass flat-panel displays. This letter presents a manufacturable process for fabricating poly-Si TFTs directly on plastic substrates that exceed TFT parameter requirements for active-matrix displays. Plastic sheets are laminated onto carrier wafers, to allow use of automated tools for manufacturing. In order to maintain adhesion through the whole process, the wafer temperature is kept below 105/spl deg/C. Laser crystallization is used to grow poly-Si, and a quarter-wavelength stack layer is deposited to protect plastic from the laser processing. In order to achieve state-of-the-art poly-Si TFTs on plastic, the gate oxide is optimized. Using a higher temperature anneal after delamination minimizes leakage currents.     

Microstrip dipoles on electrically thick substrates

Certain basic radiation properties of microstrip dipoles on electrically thick substrates are investigated, and a comparison is made with the case of dipoles printed on a dielectric half-space. It is concluded that the microstrip dipole radiation properties become sensitive to substrate loss as the substrate thickness increases, with the half-space properties obtained for an adequate amount of loss. Asymptotic formulas for radiated power and efficiency are given for both the thick substrate and half-space problems, showing the behavior with increasing dielectric constant. The method of moments is used to extend the analysis to center-fed strip dipoles, and a method of improving both the efficiency and gain of a printed antenna by using a superstrate layer is discussed.     

Microstrip rectangular resonators on ferrimagnetic substrates

The resonant frequency, bandwidth, efficiency and resonant length of a rectangular microstrip resonator on a ferrimagnetic substrate are derived theoretically and are computed for a typical ferrite substrate. The computed values are compared with those of a similar microstrip antenna on a dielectric substrate.     

Dipole arrays printed on ferrite substrates

The authors report on the radiation from infinite dipole arrays printed on ferrite substrates. Ferrite materials offer unique design capabilities at microwave frequencies because some of their properties depend on the DC magnetic field applied to them. The performance of an array of printed elements depends strongly on, among other things, the modes supported by the substrate. The nature of grounded ferrite substrate modes and their relation to the scan performance of dipole arrays printed on such ferrite substrates are described. Both in-plane and perpendicular bias are considered, and a scheme of dynamic ferrite biasing is outlined resulting in unique scan performance and a 16% frequency agility of ferrite substrate dipole arrays     

基于蓝宝石纳米图形衬底上氮化镓生长的研究

利用两步生长法在蓝宝石纳米图形衬底（NPSS）上生长得到高质量的氮化镓薄膜。通过XRD和SEM对薄膜质量的表征和研究发现,为得到高质量的氮化镓（GaN）薄膜,在NPSS上生长时得到的最优缓冲层厚度为15nm,而在微米级尺寸的图形衬底（MPSS）上得到的最优缓冲层厚度远大于15nm。同时,在NPSS上生长氮化镓薄膜的过程中观察到一个有趣的现象,即GaN在NPSS上生长的初始阶段,氮化镓晶粒主要在图形之间的平面区域生长,极少量的GaN在衬底图形的侧面上聚集生长。这一有趣的现象明显不同于GaN在MPSS上的生长过程。接着,又在NPSS上生长了GaN基LED结构,并对其光电性能进行了研究。     

Bibliography on communicating technical research information

The technical communication literature contains many articles and books providing advice on how scientists and engineers can improve their skills at communicating research results. The journal articles and book chapters the authors felt offered sound advice on fifteen topics relevant to writing original research results for publication are briefly discussed     

文献与摘要(123)

互连技术在迅速变化The Rapidly Changing Interconnect新技术推动新的应用,电子行业变化莫测,电子互连和印制板技术也在变化前沿。作者认为随着基础电子制造业向亚洲转移,使美国经济发展缓慢。印制板技术实现HDI是电子互连走向高水平,现在3维安装连接和HDI板3维化–埋置元件印制板是使电子互连和印制板     

Fully elastic interconnects on nanopatterned elastomeric substrates

Elastically stretchable metal interconnects are required for electronic skin. To date, the resistance of such thin-film interconnects has been found to increase much more with mechanical strain than expected from purely geometrical deformation of the conductor. It has been discovered that the resistance change due to fully elastic deformation is minimal when the metal films are deposited on pyramidal nanopatterned surfaces. The nanopattern constrains the film to purely elastic deformation by localizing the microcracks that are formed in the conductor during stretching. Between 0% and 25% mechanical strain, the electrical resistance increases by only 60%, which is in close agreement with purely geometric deformation.     

基于砷化镓衬底的RF MEMS膜开关

射频微机械开关由于其优越的高频特性在微波和毫米波电路中表现出巨大的应用前景。但是目前的微机械开关都是制作在硅基衬底上的 ,难于与后面的高频砷化镓处理电路相集成。本文介绍了基于砷化镓衬底的RFMEMS膜开关 ,着重介绍了开关的工作原理、制作过程和测试结果