Development Of Power Devices Research Articles

Epitaxial Growth and Defect Control of SiC for High-Voltage Power Devices

Recent progress in fast epitaxial growth and defect control of silicon carbide (SiC) toward development of high-voltage power devices is reviewed. In chemical vapor deposition of 4H-SiC on off-axis (0001), a high growth rate of 85 µm/h and a low background doping of 1×1013 cm−3 are achieved. Conversion of basal-plane dislocations to threading edge dislocations and generation of stacking faults during epitaxial growth are discussed. Deep levels in as-grown n-type and p-type 4H-SiC epitaxial layers have been investigated. A lifetime-killing defect, Z1/2 center, can be almost eliminated by thermal oxidation, which leads to significant increase in carrier lifetimes. The obtained carrier lifetimes are long enough to fabricate 10 kV-class bipolar devices. Control of carrier lifetimes by low-energy electron irradiation is demonstrated.

SiC Power Devices for Microgrids

Microgrids with distributed generation sources are critical for reduction of greenhouse gas emissions and imported energy. However, power converters and circuit breakers built with silicon (Si) switches are too bulky and inefficient to be used in the microgrid system. The development of high-voltage power devices based on silicon carbide (SiC) will be a critical component in building the microgrid with distributed and fluctuating sources of power generation. In this paper, the physics and technology of high-voltage (>10 kV) 4H-SiC power devices, namely MOSFETs and insulated gate bipolar transistors are discussed. A detailed review of the current status and future trends in these devices is given with respect to materials growth, device design, and fabrication processing.

RF power performance evaluation of surface channel diamond MESFETs

We experimentally investigate the large-signal radio frequency performances of surface-channel p-type diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination have a coplanar layout with two gate fingers, total gate periphery of 100 μm; in DC they exhibit a hole accumulation behavior with threshold voltage V t ≈ 0–0.5 V and maximum drain current density of 120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency f T and oscillation frequency f max) were obtained close to the threshold and were of the order of 6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load impedance at a bias point V DS = −14 V, V GS = −1 V. To the best of our knowledge, these are the first large signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential of such technology for the development of microwave power devices.

Development of YBCO power devices in Japan

A new Japanese national project, called M-PACC, to develop high temperature superconducting electric power devices started in June last year (FY2008–FY2012). This project aims to develop three different types of electric power devices that are expected to provide stable power supplies with large capacity and small size by using YBCO coated conductors. The first program is the development of a 2GJ class superconducting magnetic energy storage system to control stable electric power systems. It is planned to develop several sets of element coils for a 20MJ class system as a technological feasibility study for a 2GJ class coil. The second program is the development of two different types of power cables with higher performance than existing power cables; one is a three-core 66kV–5kA class large current cable and the other is a single-phase 275kV–3kA class high voltage cable. These cable were required several technological developments, namely, large current and low AC loss, high voltage insulation and low dielectric loss, and power and heat balance for both cables. The third program is the development of a 20MVA class power transformer with 66kV/6.9kV as a distribution transformer. In this project, power transformer systematization technology including 2kA class large current coil technology, anti short-circuit wire winding technology, AC loss reduction technology, and winding technology will be developed.

Remnants of Early Hydraulic Power Systems

This paper briefly outlines the development of water hydraulic power systems and devices during the 19th century, and then describes a range of extant system elements from Australia and New Zealand. The significance of this early motive power technology is underlined by the many end-use applications that evolved, and further work in identifying, recording and, where practicable, conserving extant remnants is advocated.

Light extraction from GaN‐based LED structures on silicon‐on‐insulator substrates

AbstractNano‐patterning of GaN‐based devices is a promising technology in the development of high output power devices. Recent researches have been focused on the realization of two‐dimensional (2D) photonic crystal (PhC) structure to improve light extraction efficiency and to control the direction of emission. In this study, we have demonstrated improved light extraction from green light emitting diode (LED) structures on thin silicon‐on‐insulator (SOI) substrates using surface nanopatterning. Scanning electron microscopy (SEM) is used to probe the size, shape, and etch depth of nano‐patterns on the LED surfaces. Different types of nanopatterns were created by e‐beam lithography and inductively coupled plasma etching. The LED structures after post processing are studied by photoluminescence (PL) measurements. The GaN nanophotonic structures formed by ICP etching led to more than five‐fold increase in the intensity of the green emission. The improved light extraction is due to the combination of SOI substrate reflectivity and photonic structures on top GaN LED surfaces. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Japanese efforts on coated conductor processing and its power applications: New 5 year project for materials and power applications of coated conductors (M-PACC)

Five years of Japanese national project (FY2003–FY2007) was ended last spring with remarkable success. The national project was originally aimed for development of coated conductors which have high superconductivity performance and long length enough to fabricate high temperature superconducting (HTS) electric power devices. Preliminary research and development of HTS electric power devices were carried out as well. A series of R&D results will be summarized and reviewed in this paper. The new 5 years Japanese national project has started last June (FY2008–FY2012) to develop HTS electric power applications including SMES, cables and transformers and to develop/produce coated conductors satisfying the requirements from the respective power devices. Collaborative R&D efforts by national laboratories, universities and private companies have been started with the supports of NEDO and METI. The accomplishment of the previous project will be summarized and the plans and goals of the new project will be presented in this paper.

Suitability of 4H-SiC Homoepitaxy for the Production and Development of Power Devices

ABSTRACTIn this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 6×100mm wafers per run. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm runs will be shown and compared to results of the former 7×3″ setup. The characteristic of the run-to-run reproducibility for the 6×100mm setup will be discussed. To demonstrate the suitability of the reactor for device production results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3″, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.

Advances in 4H-SiC Homoepitaxy for Production and Development of Power Devices

AbstractIn this paper we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system. This equipment exhibits a capacity of 7x3” wafers per run and can be upgraded to a 6x4” setup. Characteristics of epilayers and reproducibility of the proc-esses are reported. Furthermore, we show recent results of p-type SiC homoepitaxial growth on 3” 4° off-oriented substrates using a single-wafer hot-wall CVD. The dependence of layer prop-erties on growth parameters, doping and thickness uniformity as well as doping memory effects are discussed. For the characterization of epitaxially grown pn-junctions first research grade pin-diodes were fabricated. The p-type emitters were either deposited in the same growth run to-gether with the n-type buffer and drift layers (continuous growth) or the n- and p-layers were grown in two different growth runs (separate growth).

Status and Prospects of SiC Power Devices

Silicon Carbide (SiC) power devices offer significant benefits of improved efficiency, dynamic performance and reliability of electronic and electric systems. The challenges and prospects of SiC power device development are reviewed considering different device types. A close correlation between an exponential increase of current handling capability during the last ten years and improvement in substrate quality is demonstrated. The voltage range of silicon and SiC unipolar and bipolar power devices with respect to the on-state voltage is determined based on device simulations. 4H-SiC unipolar devices are potentially superior to all silicon devices up to 5kV design voltage and to all SiC bipolar devices up to 5-6kV design voltage for temperatures up to 150°C. The low end of SiC unipolar devices is determined to be around 200V design voltage provided substrate resistance is reduced by reducing the thickness of the substrate down to 100μm. The influence of reduced channel mobility on the specific on-resistance of 4H-SiC and 3C-SiC DMOSFETs is shown. It has been demonstrated that 3C-SiC DMOSFETs could be a better choice compared to 4H-SiC DMOSFETs in the voltage range below 1.2kV utilising better channel mobility and larger substrate size obtainable in the near future in 3C-SiC polytype. An impact of the super junction (SJ) concept on silicon and SiC MOSFET specific on-resistance limits is demonstrated.

Comparison of SOI Power Device Structures in Power Converters for High-Voltage, Low-Charge Electrostatic Microgenerators

An inertial generator based on a moving-plate capacitor can provide energy for medical sensors from low-frequency (human body) motion. The energy exists as a very small charge (4 nC) at high voltage (300 V). An initial proposal for power processing used a carefully scaled lateral power MOSFET-diode pair, which results in a low, but sufficient, energy yield. It was found that increasing the area of the MOSFET to reduce conduction loss is highly detrimental to the energy yield because of capacitive loading of the generator. This paper examines alternative device topologies which may greatly increase the energy yield for a given system size by increasing both the generation efficiency and the conversion efficiency. An insulated gate bipolar transistors (IGBT) and a MOS-triggered thyristor, both based on previous silicon-on-insulator MOSFET designs, are examined for their switching speed and losses using physics-based finite-element simulation. The scaling criteria to achieve optimum system effectiveness are discussed. The small charge available from the generator results in a brief conduction period which does not allow the devices to reach their steady-state carrier distributions. Nevertheless the IGBT, and especially the MOS-triggered thyristor, switch on faster than the MOSFET, run at higher current densities, and provide improved efficiency. This allows the devices to be reduced in area leading to less capacitive loading on the generator. It also allows a reduction in the value and volume of the circuit inductor without a conduction loss penalty. We describe the device behavior in detail for the various phases of the conversion cycle and illustrate device/circuit tradeoffs graphically. Requirements are outlined for the development of power devices for microgenerators in implanted medical sensors.

High Speed and High Functional Inverter Power Supplies for Plasma Generation and Control, and their Performance

The Rapid development of high power and high speed semiconductor switching devices has led to their various applications in related plasma fields. Especially, a high speed inverter power supply can be used as an RF power source instead of conventional linear amplifiers and a power supply to control the magnetic field in a fusion plasma device. In this paper, RF thermal plasma production and plasma heating experiments are described emphasis placed on using a static induction transistor inverter at a frequency range between 200 kHz and 2.5 MHz as an RF power supply. Efficient thermal plasma production is achieved experimentally by using a flexible and easily operated high power semiconductor inverter power supply. Insulated gate bipolar transistor (IGBT) inverter power supplies driven by a high speed digital signal processor are applied as tokamak joule coil and vertical coil power supplies to control plasma current waveform and plasma equilibrium. Output characteristics, such as the arbitrary bipolar waveform generation of a pulse width modulation (PWM) inverter using digital signal processor (DSP) can be successfully applied to tokamak power supplies for flexible plasma current operation and fast position control of a small tokamak.

Ge semiconductor devices for cryogenic power electronics - II

We have begun investigation and development of cryogenic semiconductor power devices (diodes, bipolar transistors and field-effect transistors) based on germanium. The motivation is NASA's interest in electronics that can operate down to deep cryogenic temperatures (as low as 30-40 K) for exploration of the outer planets and other Solar System bodies that present cold environments as well as for future space observatories. There are also potential applications related to cryogenic/superconducting motors and generators and power distribution and storage. We have characterized available Ge diodes and bipolar transistors at cryogenic temperatures and have begun examining MIS (metal-insulator-semiconductor) capacitors on Ge. Our investigations show that all these types of devices can operate from room temperature down to 20 K or lower.

The impact of surface states on the DC and RF characteristics of AlGaN/GaN HFETs

GaN based HFETs are of tremendous interest in applications requiring high power at microwave frequencies. Although excellent current-voltage (I-V) characteristics and record high output power densities at microwave frequencies have been achieved, the origin of the 2DEG and the factors limiting the output power and reliability of the devices under high power operation remain uncertain. Drain current collapse has been the major obstacle in the development of reliable high power devices. We show that the cause of current collapse is a charging up of a second virtual gate, physically located in the gate drain access region. Due to the large bias voltages present on the device during a microwave power measurement, surface states in the vicinity of the gate trap electrons, thus acting as a negatively charged virtual gate. The maximum current available from a device during a microwave power measurement is limited by the discharging of this virtual gate. Passivated devices located adjacent to unpassivated devices on the same wafer show almost no current collapse, thus demonstrating that proper surface passivation prevents the formation of the virtual gate. The possible mechanisms by which a surface passivant reduces current collapse and the factors affecting reliability and stability of such a passivant are discussed.

Morphology Of Silicon Oxides On Silicon Carbide

AbstractThe development of high power devices based on silicon carbide requires a more complete understanding of the oxide formation process and interface characteristics. By using an integrated UHV system, samples were cleaned and oxides deposited in situ. The approach of the oxide formation process was to form the initial insulator, a few angstroms thick, and then deposit an oxide. Various deposition techniques are used in the oxide growth process; both thermal and plasma enhanced chemical vapor deposition were employed with two different precursors (oxygen and nitrous oxide), and the results were compared with thermal oxidation. The morphology of each of the deposited oxides was compared to the bare substrate and the thermal oxide wafers. This study focuses on the morphology of the different deposition processes using AFM. Examination of the morphology of the initial insulator growth process and the oxide deposition process gives insight into the physical characteristics of the silicon dioxide deposited on silicon carbide. The RMS values of the initial insulator formation and the control wafers are 0.93 and 0.95 nm respectively. Meanwhile, the RMS values for PECVD (200–400°C) and thermal CVD (400–600°C for oxygen-silane and 800–1000°C for nitrous oxide-silane) range from 1.43 to 1.93 nm.

Section X-ray topography applied to power device materials problems

X-ray section topographs contain much information about the position of defects inside single crystal slices of silicon. In this paper, the type of information which can be obtained without recourse to the complex dynamic diffraction theory is described. Some examples where section topographs have provided useful information concerning problems in development of power devices are given: bulk defects in silicon starting materials have been studied and shown to be a direct cause of premature electrical breakdown in high power devices. Other examples include determination of the depth of process-induced dislocations and revelation of copper decorated swirls on the crystal growth front.

Bistable noise in p-n junctions : S. T. Hsu. Solid State Electron.14 (1971), p. 487

We experimentally investigate the large-signal radio frequency performances of surface-channel p-type diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination have a coplanar layout with two gate fingers, total gate periphery of 100 μm; in DC they exhibit a hole accumulation behavior with threshold voltage Vt ≈ 0–0.5 V and maximum drain current density of 120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency fT and oscillation frequency fmax) were obtained close to the threshold and were of the order of 6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load impedance at a bias point VDS = −14 V, VGS = −1 V. To the best of our knowledge, these are the first large signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential of such technology for the development of microwave power devices.