Yasuhiro Uemoto

Gate Injection Transistor (GIT)—A Normally-Off AlGaN/GaN Power Transistor Using Conductivity Modulation

We have developed a normally-off GaN-based transistor using conductivity modulation, which we call a gate injection transistor (GIT). This new device principle utilizes hole-injection from the p-AlGaN to the AlGaN/GaN heterojunction, which simultaneously increases the electron density in the channel, resulting in a dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits a threshold voltage of 1.0 V with a maximum drain current of 200 mA/mm, in which a forward gate voltage of up to 6 V can be applied. The obtained specific ON-state resistance (RON . A) and the OFF-state breakdown voltage (BV ds) are 2.6 mOmega . cm2 and 800 V, respectively. The developed GIT is advantageous for power switching applications.

99.3% Efficiency of three-phase inverter for motor drive using GaN-based Gate Injection Transistors

In this paper, we present a successful operation of Gallium Nitride(GaN)-based three-phase inverter with high efficiency of 99.3% for driving motor at 900W under the carrier frequency of 6kHz. This efficiency well exceeds the value by IGBT (Insulated Gate Bipolar Transistor). This demonstrates that GaN has a great potential for power switching application competing with SiC. Fully reduced on-state resistance in a new normally-off GaN transistor called Gate Injection Transistor (GIT) greatly helps to increase the efficiency. In addition, use of the bidirectional operation of the lateral and compact GITs with synchronous gate driving, the inverter is operated free from fly-wheel diodes which have been connected in parallel with IGBTs in a conventional inverter system.

8300V Blocking Voltage AlGaN/GaN Power HFET with Thick Poly-AlN Passivation

We report ultra high voltage AlGaN/GaN heterojunction transistors (HFETs) on sapphire with thick poly-AlN passivation. Extremely high blocking voltage of 8300 V is achieved while maintaining relative low specific on-state resistance (Ron*A) of 186 mOmegaldrcm2. Via-holes through sapphire at the drain electrodes enable very efficient layout of the lateral HFET array as well as better heat dissipation.

AlGaN/GaN power HFET on silicon substrate with source-via grounding (SVG) structure

We have developed a high-power AlGaN/GaN HFET fabricated on 4-in conductive Si substrate with a source-via grounding (SVG) structure. The SVG structure enables efficient chip layout and high packing density by the vertical configuration. By establishing a high-quality epitaxial technology on a Si substrate and by significantly reducing the parasitic resistance, a very low specific on-state resistance of 1.9 m/spl Omega//spl middot/cm/sup 2/ is achieved. The breakdown voltage is as high as 350 V, which is attributed to the Si substrate acting as a backside field plate. Because of reduction of the parasitic inductance, very high level of current (2.0 kA/cm/sup 2/) transients, i.e., a turn-on time of 98 ps and a turn-off time of 96 ps, are successfully measured for the first time.

A high-power RF switch IC using AlGaN/GaN HFETs with single-stage configuration

A high-power single-pole double throw (SPDT) switch IC using AlGaN/GaN heterojunction field-effect transistors (HFETs) is demonstrated for the first time. The reduction of on-resistance (R/sub on/) and off-capacitance (C/sub off/) for AlGaN/GaN HFETs enables the GaN-based switch IC that can be applied for practical RF applications. A novel Si-doping technique is employed to reduce ohmic contact resistance, which successfully reduces the R/sub on/. The C/sub off/ of the HFETs on a sapphire substrate is found to be smaller than that on a SiC substrate, together with low cost fabrication. The GaN-based SPDT switch IC with single-stage configuration is designed by using a circuit simulator based on the extracted device parameters. The fabricated SPDT switch IC achieves insertion loss of 0.26 dB and isolation of 27 dB at 1 GHz, as well as an extremely high-power handling capability of 43 W. This value is 10 times higher than that of typical GaAs-based switch ICs. In addition, the switch IC exhibits low distortion characteristics, where the third-order intercept point of 41 dBm is achieved. The chip size is reduced to 40% as compared with conventional four stage GaAs-based switch ICs by using the single-stage circuit configuration.

Current-collapse-free operations up to 850 V by GaN-GIT utilizing hole injection from drain

Current collapse at high drain voltage in a GaN-based transistor is successfully suppressed by the introduction of p-GaN region which is placed beside the drain of a Gate Injection Transistor (GIT). The additional p-GaN region enables hole injection which effectively releases trapped electrons at around drain region after the application of high drain voltages. The p-GaN region is electrically connected to the drain electrode so that this is named as Hybrid Drain-embedded GIT (HD-GIT). The fabricated HD-GITs are free from current collapse at 850 V of the drain voltage or over, which significantly helps to achieve stable system operations and is very promising for future switching power supply applications.

GaN monolithic inverter IC using normally-off gate injection transistors with planar isolation on Si substrate

We present a GaN monolithic inverter IC on Si substrate and successful motor-drive by it for the first time. Taking advantages of the bi-directional operation free from the forward voltage off-set [1], the inverter can be operated just by the integrated six GaN-based normally-off gate injection transistors (GITs) without any external fast recovery diodes (FRDs) to flow the fly-wheel current. The IC enables the efficiency as high as 93% at low power operation where so far that of conventional Si-based inverters has remained lower value owing to the forward voltage off-set. The key processing technology is the newly introduced planar isolation using Fe ion implantation which fully isolates the GaN-based lateral devices each other.

Analysis of solid phase crystallization in amorphized polycrystalline Si films on quartz substrates

The solid phase crystallization of amorphized Si films on quartz substances is studied by means of the transmission electron microscope observation of grain growth. The amorphous Si films are prepared by Si ion implantation into polycrystalline Si films deposited by low‐pressure chemical vapor deposition. It has been found that the twin formation in grains at the early stage of the crystallization accelerates the growth rate preferentially in a 〈112〉 direction. During the twin growth about a given 〈112〉 direction, other twins also grow from the twin boundary dendritically in some other 〈112〉 directions, leading to the formation of a large grain of dendritic structure.

GaN-on-Si Power Technology: Devices and Applications

In this paper, we present a comprehensive reviewand discussion of the state-of-the-art device technology and application development of GaN-on-Si power electronics. Several device technologies for realizing normally off operation that is highly desirable for power switching applications are presented. In addition, the examples of circuit applications that can greatly benefit from the superior performance of GaN power devices are demonstrated. Comparisonwith other competingpower device technology, such as Si superjunction-MOSFET and SiC MOSFET, is also presented and analyzed. Critical issues for commercialization of GaN-on-Si power devices are discussed with regard to cost, reliability, and ease of use.

GaN power switching devices

State-of-the-art device technologies of GaN power switching transistors are reviewed. The presented technologies solve the technical issues on GaN transistors for practical use replacing currently used Si-based power devices. Thick epitaxial growth over 6-inch Si substrates enables low cost fabrication of GaN devices with high breakdown voltages. A new operating principle for the normally-off GaN transistor called Gate Injection Transistor (GIT) is proposed in which hole injection from the p-type AlGaN gate increases the drain current by conductivity modulation. Six GITs are integrated onto a single chip on silicon as the world first GaN-based monolithic inverter IC. The inverter IC successfully drives a motor with low operating loss which is 42% reduced from that of the conventional IGBT (Insulated Gate Bipolar Transistor)-based one. These technologies are indispensable for wide-spread use of GaN power switching transistors in the future.