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In GaN Schottky barrier diodes (SBD), there is a trade-off between the turn-on voltage and the leakage current. In this study, recess-free 4 nm-thin-barrier AlGaN/GaN SBDs with minimal leakage current as well as excellent turn-on voltage homogeneity are developed, which enable better electrical control to pinch off the 2DEG channel under the anode region and avoids trap introduced in the barrier etching process. In detail, the effect of reverse stress on the SBD performance is initially explored by using differential conductance, and then, the anode-to-cathode distances and temperatures dependence of SBDs output characteristics are systematically studied. The fabricated thin-barrier GaN SBDs show a turn-on voltage of ∼0.75 V and a low level leakage current of 9.66 × 10−10 (1.91 × 10−8) A/mm at 300 (423) K, which is among the lowest reported values at the comparable reverse bias voltage and temperature. Moreover, structure parameters of the thin-barrier AlGaN/GaN SBD are systematically modeled and optimized by the TCAD simulations, including anode metal work function, Al mole fraction, the anode-to-cathode distance, and slanted anode angle. The introduction of slanted anode is found to have significant effect on the improvement of reverse breakdown voltage and leakage current characteristics. [ABSTRACT FROM AUTHOR]

A high-performance AlGaN/GaN-based ultraviolet photodetector with a field-enhanced mechanism for photocurrent collection is designed and fabricated in this work. In addition to the inherent polarization field, two additional sets of collection fields are formed from a 2DEG layer to a ITO thin film and from the 2DEG layer to a cathode electrode sinker. The effectiveness in the collection of photogenerated carriers is remarkably enhanced, which leads to a photocurrent of 6.6 mA/mm under the illumination of 365 nm-centered ultraviolet light at an intensity of 1.8 mW/cm2. With an in-built shallow isolation trench, the dark current is suppressed below 40 pA/mm under a device bias of 5.0 V. A photo-to-dark current ratio as high as 1.7 × 108, a record high photo-responsivity over 4.3 × 106 A/W, and a high gain of 1.46 × 107 under 365-nm light are demonstrated by the fabricated prototype, showing great competitiveness in state-of-the-art AlGaN/GaN-based ultraviolet photodetectors. [ABSTRACT FROM AUTHOR]

The superjunction MOSFET power devices, such as p-n column superjunction (named SJ or CoolMOS) devices and oxide-bypassed (OB) devices, are highly recognized for their higher blocking capability and lower on-state resistance. However, the performance of SJ devices is greatly handicapped due to difficulties in formation of perfect charge-balanced SJ p-n columns by the current process technology, especially for devices with small widths and voltage ratings below 180 V. OB devices can be an alternative in this voltage region, which utilize the well established oxide thickness control in fabrication instead of the difficult doping control as in SJ devices. However, OB drift region electric field distribution is not as optimal as that in SJ devices. Gradient oxide-bypassed (GOB) structure enhances the performance of OB devices so that it can achieve a performance comparable to that of an ideal p-n column SJ device in the medium voltage range, and at the same time, requires simple process technology. Complete descriptions on the GOB device and related design issues are presented in this paper. Fabrication issues are also discussed with possible sacrificial materials and etchants for making the vertical graded oxide sidewalls. Design cases for 80, 120, and 180 V GOB devices are also illustrated for better understanding in the device. Index Terms--Breakdown voltage, gradient oxide-bypassed (GOB), ideal unipolar silicon limit, oxide-bypassed (OB), power MOSFETs, specific on-state resistance, superjunction.

This paper describes research work on the design and fabrication of current sensor suitable for smart power integration in lateral insulated-gate bipolar transistor (LIGBT) structure. In general, the proposed design can also be used for various types of MOS- controlled bipolar transistor structures. Both the electron and hole current sensor layers are integrated in a concise form within the device structure. The sensing performance was further refined with the proposed flat-top doping profile achievable through a double-implantation, single-anneal and post-anneal-oxidation approach. The integrated structure was fabricated on silicon wafer with laboratory measurements performed to verify its electrical performance. The sensing ratio is maintained at a relatively constant level with a variation of within [+ or -] 0.46% and [+ or -] 1.2% (as a switching device), and [+ or -] 0.85% and [+ or -] 1.73% (as an amplifier device), respectively, when anode current and gate voltage vary. For operating temperature range of 300 K to 400 K, the sensor is able to maintain a sensing ratio within [+ or -] 5.2% variation. Index Terms--IGBT, integrated current sensor, smart power integration.

A new partial silicon-on-insulator (SOI) formation technology and the associated RF LDMOSFET device structure on silicon bulk substrate are described. The technology assists in the reduction of drain/substrate parasitics and leakage current for devices fabricated on bulk substrate.

A good magnetic field sensor should exhibit high sensitivity, low power consumption, and low output offset to accurately detect small fields. In this work, the high sensitivity in magnetoresistance variation (ΔR) is achieved by the AlGaN/GaN fin-shaped high electron mobility structure, in comparison to that of planar structures. A physical based analysis is presented to describe the influence of the fin width dimension on the ΔR dependency under magnetic fields. The sensitivity is expressed as a function of geometric parameters, electron mobility, and two-dimensional electron sheet density, with relaxation of polarization, shoulder density distribution, and sidewall trapped charges considered. Devices were fabricated, and a high sensitivity is observed in laboratory measurements on devices at narrower fin widths. At the fin width of 50 nm, the measured device has a sensitivity of 0.76 Ω/μΤ2 at the magnetic flux of 85 μΤ. The sensor's power consumption is as low as 48 μW, and the minimum magnetic flux detectable is at 20 μΤ. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) high-temperature Hall sensors are strongly required in various applications such as in the automotive and aircraft engines and in the diagnostic system of the thermonuclear reactors. In this paper, we propose a novel Hall sensor based on the wide-bandgap GaN-based materials on a single chip with greatly reduced area which can simultaneously detect 3D magnetic fields at high temperature up to 650 K. The device is analysed and demonstrated by performing the technology computer-aided design simulations, and significantly improved performances are achieved by employing space isolation and passivation scheme to effectively reduce the carrier interference from each dimension. Finally, high current-related magnetic sensitivities are found and the typical values are 128.6, 88.1, and 49.9 V A−1 T−1 on x, y and z axes, respectively, at room temperature. And the temperature coefficients are as low as −286.4, −366.8, and −202.9 ppm K−1, respectively. Moreover, dramatically improved cross-sensitivities are revealed and the maximum value is less than 1.0% at B ≤ 1.0 T which is much lower compared with other currently reported data. The work provides a new technical approach to realize a single-chip 3D magnetic sensor which is promising especially for high-temperature applications. [ABSTRACT FROM AUTHOR]

In this paper, a new actuation scheme for the push-pull electrostatic microelectromechanical systems comb drive actuators is proposed. The displacement amplitude excited by the new form of driving voltages can be more than three times as large as that which is achievable using the conventional form for the same applied system voltage. Index Terms--Microactuation, microelectromechanical systems (MEMS) comb drive.

In this letter, the suppression of dynamic on-state resistance (RON) degradation for faster dynamic RON recovery is achieved by the multimesa-channel (MMC) structure in AlGaN/GaN high electron mobility transistors. The measurement results are discussed with the physical mechanisms investigated. The initial transient RON degradation is reduced in the MMC structure, resulting from the lower peak electric field around the drain-side gate edge in the trigate structure compared to that in a planar device. The faster dynamic RON recovery in MMC devices is attributed to the quick emission of electrons at sidewall traps of shallower energy levels. The energy levels of dominant traps at the sidewall and top interfaces are found to be 0.26 eV and 0.37 eV below the conduction band edge, respectively, verified by Technology Computer Aided Design simulations in agreement with the measurement data. [ABSTRACT FROM AUTHOR]

Photovoltaic responses, including photovoltage, photocurrent, illuminated J-V curve, and light-to-electricity power conversion efficiency, were investigated in chemical-solution-derived polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLZT) thin films sandwiched between different metal and oxide electrodes. The epitaxial PLZT films with Au/PLZT/Nb-doped SrTiO3 structure exhibited about one order of magnitude larger photocurrent and efficiency over the randomly oriented polycrystalline PLZT films with Au/PLZT/Pt structure due to the high crystalline quality with the reduced defects and enhanced depolarization field. The illuminated J-V curve was approximately linear for both polycrystalline and epitaxial PLZT thin films. The nonzero photovoltaic outputs in the unpoled films were induced by asymmetric interfacial Schottky barriers. The illuminated J-V curve shifted toward the positive voltage direction after positive poling and toward the negative voltage direction after negative poling, and the enhancement of efficiency only occurred when the polarization direction accorded with the direction of Schottky barrier difference at the two electrode interfaces. Thickness dependences of photovoltage, photocurrent, and light-to-electricity conversion efficiency were also examined. It was observed that photovoltage linearly increased with film thickness while both photocurrent and efficiency exponentially increased with the decrease in thickness. Furthermore, at a fixed small film thickness, efficiency was also found to increase reciprocally with the decrease of incident UV intensity. [ABSTRACT FROM AUTHOR]

Ferroelectric (Pb0.97,La0.03)(Zr0.52,Ti0.48)O3 thin films in different thicknesses were fabricated on Pt/Ti/SiO2/Si substrates through a sol-gel process. Film thickness dependence of photoinduced current was investigated under the illumination of ultraviolet light. A theoretical model was developed to describe the thickness-dependent photocurrent. Both the theoretical model and experimental results showed that the photocurrent increases exponentially with the decrease in film thickness. However, photocurrent may drop in the films with the very small thickness of tens of nanometers and below in which the small size effect of ferroelectricity is considered. This model also reveals the relationship between the photocurrent and the internal electric field or remnant polarization and predicts a small diffusion current in the opposite direction at very low field or polarization region. These results provide useful guides for the design of ferroelectric film photovoltaic devices. [ABSTRACT FROM AUTHOR]

Byline: Yee Win Shwe, Yung C. Liang Piezoelectric materials can be used to convert mechanical energy, such as vibration into electrical energy which can be used to power up devices in a smart dust sensing network. This piezoelectric mechanism exhibits great potentials to resolve many energy supply problems in sensor network to supply energy to radio frequency (RF) circuits, microcontroller, microelectromechanical systems (MEMS) and sensors placed in remote locations. This paper presents the detailed development work of a self-powered wireless sensor node which harvests the power energy from surrounding machinery vibration by the piezoelectric generator. The detailed design on a temperature sensing system is described in this paper. This approach is very useful in application in real-time remote monitoring of the machine temperature by sensor network in industries.

AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) have become a promising candidate for use in efficient power conversion applications. In order to realize converter circuit control function and overcurrent protection of device itself, we have designed, fabricated, and experimentallymeasured the Au-free AlGaN/GaN MIS-HEMTs with embedded current sensing structure. A floating ohmic current sensing electrode is inserted between source and gate electrode of which the sensing voltage signal can represent the drain current. We have achieved stable current sensing ratios at various operating conditions including quasi-static, transient state, and under high temperature. The proposed structure is highly useful in monolithic power integrated circuit on CMOS-compatible AlGaN/GaN technologies. [ABSTRACT FROM PUBLISHER]

In order to examine the feasibility of full wide-bandgap GaN-based converters in aerospace power conversion applications, this paper proposes a monolithic DC-DC buck converter design with integrated high-side gate driver, over-current protection, and pulse-width-modulation feedback control circuits based on full AlGaN/GaN MIS-HEMT configuration. After model calibration of the DC and transient behaviors with fabricated normally-ON and normally-OFF AlGaN/GaN MIS-HEMT devices, the DC-DC buck converter is simulated. The circuit converts the input 100 V down to an adjustable range at 1 MHz switching frequency. The over-current protection function can properly protect the converter at a preset over-current threshold. The converter can respond to the load current and line input voltage fluctuations due to the integrated feedback control. These results illustrate the performance of proposed all-GaN DC-DC power converter design. [ABSTRACT FROM AUTHOR]

In this paper, a normally-off AlGaN/GaN MIS-HEMT with improved threshold voltage (VTH) thermal stability is reported with investigations on its physical mechanism. The normally-off operation of the device is achieved from novel short argon plasma treatment (APT) prior to the fluorine plasma treatment (FPT) on Al2O3 gate dielectrics. For the MIS-HEMT with FPT only, its VTH drops from 4.2V at room temperature to 0.5V at 200 °C. Alternatively, for the device with APT-then-FPT process, its VTH can retain at 2.5V at 200 °C due to the increased amount of deep-level traps that do not emit electrons at 200 °C. This thermally stable VTH makes this device suitable for high power applications. The depth profile of the F atoms in Al2O3, measured by the secondary ion mass spectroscopy, reveals a significant increase in the F concentration when APT is conducted prior to FPT. The X-ray photoelectron spectroscopy (XPS) analysis on the plasma-treated Al2O3 surfaces observes higher composition of Al-F bonds if APT was applied before FPT. The enhanced breaking of Al-O bonds due to Ar bombardment assisted in the increased incorporation of F radicals at the surface during the subsequent FPT process. The Schrödinger equation of Al2OxFy cells, with the same Al-F compositions as obtained from XPS, was solved by Gaussian 09 molecular simulations to extract electron state distribution as a function of energy. The simulation results show creation of the deeper trap states in the Al2O3 bandgap when APT is used before FPT. Finally, the trap distribution extracted from the simulations is verified by the gate-stress experimental characterization to confirm the physical mechanism described. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT), which employs the principle of electromagnetic induction, is widely applied to wireless charging applications. The efficiency of an IPT system is highly dependent on the quality factor (Q) of the power resonant tank. In this paper, a novel design on the structure of the resonant coil is used in the resonant tank to achieve a significantly high Q above 1000 for the IPT system. Compensating capacitors are used in both primary and secondary circuits to align the resonant frequencies in order for the system resonant status to be maintained by a frequency tracking circuit. The experimental results show that with a primary coil Q of 1200, the proposed IPT system allows power to be transferred at a maximum air gap distance to coil diameter ratio of 1.46 for a highest efficiency of 87% at the resonant frequency of 106 kHz. [ABSTRACT FROM AUTHOR]

In this paper, an observation of drain current instability on p-GaN gate AlGaN/GaN HEMTs is reported. Contrary to the Schottky gate AlGaN/GaN HEMTs, which show stable and consistent Id – Vd curves under different pulsed conditions, the Id – Vd curves for p-GaN gate AlGaN/GaN HEMTs show a dispersion in the saturation region under the same pulse conditions, which cannot be explained by the trapping of electrons in the material. A model considering the trapping of holes in the p-GaN gate under different gate and drain biases is proposed to explain this new phenomenon. [ABSTRACT FROM AUTHOR]