Narrow Results

This paper reports a successful improvement of the low breakdown voltages in short gate-length metamorphic high electron-mobility transistors. The technical approach includes both the optimization of the epitaxial layer design and the selection of the proper gate recess scheme. By employing a novel epitaxial design (including a high indium composite channel and the double-sided doping) and an asymmetric gate recess, both the off-state and on-state breakdown voltages have been improved for 50-nm high-performance metamorphic high electron-mobility transistors. The results reported herein demonstrate that these devices are excellent candidates for ultra-high-frequency power applications.

We review our state-of-the-art GaN-based device technologies for power switching at low frequencies and for future millimeter-wave communication systems. These two applications are emerging in addition to the power amplifiers at microwave frequencies which have been already commercialized for cellular base stations. Technical issues of the power switching GaN device include lowering the fabrication cost, normally-off operation and further increase of the breakdown voltages extracting full potential of GaN-based materials. We establish flat and crack-free epitaxial growth of GaN on Si which can reduce the chip cost. Our novel device structure called Gate Injection Transistor (GIT) achieves normally-off operation with high enough drain current utilizing conductivity modulation. Here we also present the world highest breakdown voltage of 10400V in AlGaN/GaN HFETs. In this paper, we also present high frequency GaN-based devices for millimeter-wave applications. Short-gate MIS-HFETs using in-situ SiN as gate insulators achieve high f_max up to 203GHz. Successful integration of low-loss microstrip lines with via-holes onto sapphire enables compact 3-stage K-band amplifier MMIC of which the small-signal gain is as high as 22dB at 26GHz. The presented devices are promising for the two future emerging applications demonstrating high enough potential of GaN-based transistors.

Power semiconductor devices are important for numerous applications with power conversion being an important one. Wide energy gap semiconductors SiC and GaN have properties that make them attractive for such applications. Among these properties are high thermal conductivity, high breakdown electric field, wide energy gap, low intrinsic carrier concentration, high thermal stability, high saturation velocity and chemical inertness. These lead to low on-resistance, high breakdown voltage, high frequencies, small volume, and small passive inductors and capacitors. These desirable properties are offset by the higher material costs and higher defect densities. Although wide energy gap devices have been in development for many years, only recently have they become available commercially. Their main competition is silicon power devices with breakdown voltages up to 8000 V and very high surge current capacity. However, silicon power devices are approaching their material limits and wide energy gap devices are beginning to have an impact in the power electronics space. SiC has the advantage of substrates with diameters approaching 150 mm and the ability to grow thermal SiO₂. GaN has the heterojunction advantage, but no viable substrate technology. In fact, a large portion of SiC production is used for GaN substrates. GaN material development has also benefited significantly from the development of optical devices, e.g., light-emitting diodes and lasers.

This paper focuses on testing the reliability of a Strained Superjunction Vertical Single diffused MOS (s-SJVSDMOS) at high-temperature. It provides an in-depth study of the device behavior at high-temperatures specifically at 300, 350 and 400 K. The s-SJVSDMOS is simulated in 2D T-CAD simulator and the outcomes are extracted. The variation of the extracted parameters with temperature is explored. The electrical and channel characteristics of the device are analyzed here. From the discussion, it was deduced that at high-temperature the device exhibits analogous characteristics as at room-temperature condition.

Natural ester is currently used as an insulating oil and coolant for medium-power transformers. The biodegradability of insulating natural ester makes it a preferable insulation liquid to mineral oils. In this work, Fe₃O₄ nanoparticles were used along with oleic acid to improve the performance of insulating natural ester. The micro-morphology of Fe₃O₄ nanoparticles before and after surface modification was observed through transmission electron microscopy. Attenuated total reflection-Fourier transform infrared spectroscopy, thermal gravimetric analysis, and differential thermal analysis were employed to investigate functional groups and their thermal stability on the surface-modified Fe₃O₄ nanoparticles. Basic dielectric properties of natural ester-based insulating nanofluid were measured. The electrodynamic process in the natural ester-based insulating nanofluid is also presented.

This paper contains experimental results of the direct current breakdown voltage curves in nitrogen, hydrogen, oxygen and dry air discharges formed between parallel-plane electrodes placed at distances ranging from 2.5 μm to 100 μm. Experimental results presented here clearly show that electrical breakdown across micron size gap may occur at voltages below the minimum predicted by the conventional scaling law. The observed breakdown voltage reduction maybe attributed to the long path breakdown. Experimental results satisfactorily agree with the available simulation results and can be useful for microelectronic devices in localized diagnostics of ICs during their manufacture, in choosing appropriate conditions for electromechanical micro systems which may eventually lead to nano-machining in localized treatment of materials and assembly of nano-structures and in micro- and nano-biological processing and diagnostics.

The influence of pressure and $\beta$-radiation (1 kGy $\beta$ doses) on the charge transport mechanism, charge trapping effects in porous zeolite surfaces and breakdown voltage $(U_B)$ are discussed in atmospheric microplasmas for the first time. This is due to exposure the zeolite cathode (ZC) to $\beta$-radiation resulting in substantial decreases in the $U_B$, discharge currents and conductivity due to increase in porosity of the material. Results indicated that the enhancement of plasma light intensity and electron emission from the ZC surface with the release of trapped electrons which are captured by the defect centers following $\beta$-irradiation. The porosity of the ZC and radiation defect centers has significant influence on the charge transport of the microstructure and optical properties of the devices manufactured on its base. Thus, we confirm that the ${\mathrm{\text{ZC}}}_{\mathrm{\text{ir}}}$ is a suitable cathode material for plasma light source, field emission displays, energy storage devices and low power gas discharge electronic devices.

A novel silicon-on-insulator (SOI) high voltage device with a composite dielectric buried layer (CD SOI) is proposed in this paper. In the proposed structure, the composite dielectric buried layer consists of Si₃N₄ dielectric and low-k (relative permittivity) dielectric. The electric field strength in the buried layer is enhanced by the low-k dielectric. The Si₃N₄ dielectric in the buried layer not only modulates the electric field distribution in the drift region, but also provides a heat conduction path for the SOI layer and alleviates the self-heating effect (SHE). The breakdown voltage (BV) = 362 V for CD SOI is obtained by simulation on a 1 μm SOI layer over 2 μm buried layer, which is enhanced by 26% compared with that of conventional SOI.

Dielectric behavior of aluminum oxide (Al₂O₃) thin film under high DC electric field is presented and discussed. Aluminum oxide thin films were prepared starting from aluminum isopropoxide as a precursor via a wet chemistry route. Silicon substrates and silica glass substrates were used to deposit the films via spin-coating technique. The deposited films were then annealed under 450°C–700°C for 2–3 h. Dense, crack-free and uniform films were obtained. The thickness of the films is in the range of 200–800 nm. The films obtained are in amorphous state as revealed by the X-ray diffraction patterns. Voltage–Current (V–I) characteristics of the films were used to study the dielectric behavior of the films. Very low leakage current density J under high DC electric field E can be obtained. The breakdown electric field of the films is around 1.2 MV/cm. The V–I characteristics of the films are slightly nonlinear. With platinum as bottom electrode and gold as top electrode, successive breakdown phenomena of the films under high DC electric field were observed. Each breakdown event of the film corresponds to a sharp spike at the V–I plot of the sample. The shape of the breakdown spots of the films are in crater-like with a breakdown channel of diameter around a few micrometers as revealed by SEM images. The top gold electrode at the breakdown spots either splashed out or ripped off from the breakdown spots, which isolated the breakdown spots from rest of the electrode, and made the successive breakdown of the sample possible. The breakdown spots of the sample are concentrated at the edge of the electrode with proportional spacing, which can be easily understood as the edge effect of the parallel capacitor configuration, while the uniform distribution of the breakdown spots signifies that the uniformity of the films thus prepared are satisfied. Breakdown spots apart from the electrode edge can also be observed. Most of such spots associated with ripped-off gold film electrode in large area. We suppose such breakdown took place at higher electric field after the successive breakdown at the electrode edge and the isolation of the edge part from rest of the sample. Higher energy is needed to tear off larger section of the electrode. The breakdown characteristics of the films reported in this work are useful for the further study to enhance the breakdown strength of the film.

This paper reports a successful improvement of the low breakdown voltages in short gate-length metamorphic high electron-mobility transistors. The technical approach includes both the optimization of the epitaxial layer design and the selection of the proper gate recess scheme. By employing a novel epitaxial design (including a high indium composite channel and the double-sided doping) and an asymmetric gate recess, both the off-state and on-state breakdown voltages have been improved for 50-nm high-performance metamorphic high electron-mobility transistors. The results reported herein demonstrate that these devices are excellent candidates for ultra-high-frequency power applications.

We review our state-of-the-art GaN-based device technologies for power switching at low frequencies and for future millimeter-wave communication systems. These two applications are emerging in addition to the power amplifiers at microwave frequencies which have been already commercialized for cellular base stations. Technical issues of the power switching GaN device include lowering the fabrication cost, normally-off operation and further increase of the breakdown voltages extracting full potential of GaN-based materials. We establish flat and crack-free epitaxial growth of GaN on Si which can reduce the chip cost. Our novel device structure called Gate Injection Transistor (GIT) achieves normally-off operation with high enough drain current utilizing conductivity modulation. Here we also present the world highest breakdown voltage of 10400V in AlGaN/GaN HFETs. In this paper, we also present high frequency GaN-based devices for millimeter-wave applications. Short-gate MIS-HFETs using in-situ SiN as gate insulators achieve high f_max up to 203GHz. Successful integration of low-loss microstrip lines with via-holes onto sapphire enables compact 3-stage K-band amplifier MMIC of which the small-signal gain is as high as 22dB at 26GHz. The presented devices are promising for the two future emerging applications demonstrating high enough potential of GaN-based transistors.

Power semiconductor devices are important for numerous applications with power conversion being an important one. Wide energy gap semiconductors SiC and GaN have properties that make them attractive for such applications. Among these properties are high thermal conductivity, high breakdown electric field, wide energy gap, low intrinsic carrier concentration, high thermal stability, high saturation velocity and chemical inertness. These lead to low on-resistance, high breakdown voltage, high frequencies, small volume, and small passive inductors and capacitors. These desirable properties are offset by the higher material costs and higher defect densities. Although wide energy gap devices have been in development for many years, only recently have they become available commercially. Their main competition is silicon power devices with breakdown voltages up to 8000 V and very high surge current capacity. However, silicon power devices are approaching their material limits and wide energy gap devices are beginning to have an impact in the power electronics space. SiC has the advantage of substrates with diameters approaching 150 mm and the ability to grow thermal SiO₂. GaN has the heterojunction advantage, but no viable substrate technology. In fact, a large portion of SiC production is used for GaN substrates. GaN material development has also benefited significantly from the development of optical devices, e.g., light-emitting diodes and lasers.