Manabu Yanagihara

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.

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.

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.

A Normally-off AlGaN/GaN Transistor with R on A=2.6mΩcm 2 and BV ds =640V Using Conductivity Modulation

We report a normally-off GaN-based transistor using conductivity modulation, which we call GIT (gate injection transistor). This new device principle utilizes hole-injection from p-AlGaN to AlGaN/GaN heterojunction, which increases electron density in the depleted channel resulting in dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits the threshold voltage of 1.0V with high maximum drain current of 200mA/mm. The obtained on-state resistance (Ron·A) and off-state breakdown voltage (BVds) are 2.6mΩ·cm2 and 640V, respectively. These values are the best ones ever reported for GaN-based normally-off transistors

Unlimited High Breakdown Voltage by Natural Super Junction of Polarized Semiconductor

A breakdown mechanism of polarized semiconductors represented by GaN-based materials is presented, based on the concept of a natural super junction, which is established by the inherent material polarization. In this concept, owing to the precise matching of positive and negative polarizations of both sides of GaN and AlGaN materials, average charge concentration in the material becomes nearly zero under reverse bias condition, which realizes extremely high breakdown voltage. This model is confirmed by device simulation taking all polarization charges of GaN-based materials into account. Furthermore, experimentally fabricated GaN-based Schottky barrier diodes showed a linear increase of breakdown voltage along the anode-cathode spacing, achieving a record breakdown voltage over 9000 V.

AlGaAs/GaAs heterojunction bipolar transistors with small size fabricated by a multiple self-alignment process using one mask

A multiple self-alignment process for HBTs using one mask is developed to form emitters, emitter contacts, emitter contact leads, buried small collectors, base contacts, and base contact leads. This process makes it possible to produce HBTs of very small size and to reduce parasitic elements. An AlGaAs/GaAs HBT fabricated by the process, with an emitter 1 × 20/µm2in size and a buried collector by O+implantation gives a good performance of ft= 54 GHz and fmax= 42 GHz. The performance may be explained by the reduction of parasitic elements, base transit time, and collector depletion layer transit time.

Suppression of current collapse by hole injection from drain in a normally-off GaN-based hybrid-drain-embedded gate injection transistor

Current collapse is suppressed up to 800 V of drain voltage in our proposed device, Hybrid-Drain-embedded Gate Injection Transistor (HD-GIT), where an additional p-GaN layer is grown on the AlGaN barrier layer and is connected to the drain electrode. We present, based on a device simulation and electroluminescence study, that the hole injection from the additional drain-side p-GaN at the OFF state compensates the hole emission in the epilayer. As a result, the gate-drain access region is not negatively charged at the OFF state, resulting in the drastic suppression of current collapse in HD-GIT.

650 V 3.1 mΩcm 2 GaN-based monolithic bidirectional switch using normally-off gate injection transistor

We report a normally-off GaN-based monolithic bidirectional switch for the first time. The switch consists of a double-gate AlGaN/GaN gate injection transistor (GIT) which serves normally-off operation with high drain current utilizing the hole injection from the p-type gate. The fabricated bidirectional switch exhibits high breakdown voltage of 650 V for both polarities and low on-state resistance (Ron .A) of 3.1 mΩcm2 . The GaN-based bidirectional switch can be applied to AC-AC matrix converters with high efficiency.