Hisayoshi Matsuo

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.

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.

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.

GaN-based natural super junction diodes with multi-channel structures

We propose a new breakdown mechanism of GaN-based electron devices called ldquonatural super junctionrdquo. The junction model is supported by device simulations and experiments for newly developed multi-channel diodes with a dual-recessed structure. Based on the model, the on-resistance of the diodes can be reduced keeping high breakdown voltages. The fabricated diode achieves extremely high breakdown voltage of 9300 V with low on-state resistance RonA of 176 mOmegacm2, which is the record low value for GaN-based SBDs with the breakdown voltage over 9000 V.

Through recessed and regrowth gate technology for realizing process stability of GaN-GITs

A new gate recess process technology has been implemented in normally off GaN based gate injection transistors (GITs) on Si substrate, in order to realize the process stability. In this process, compared to conventional recessed gate structure, the AlGaN barrier is fully removed in the gate region and then AlGaN is reproduced by epitaxial regrowth for the first time. By using this technology, standard deviation of Vth improves drastically from 229 mV to 63 mV on 6-inch substrate. And Vth is easily controlled from 1.0 to 2.3 V by changing the regrowth AlGaN thickness, without changing other DC characteristics and their distributions.

Depth profiles of strain in AlGaN/GaN heterostructures grown on Si characterized by electron backscatter diffraction technique

Electron backscatter diffraction (EBSD) technique has been applied to the strain distribution measurements for GaN based heterostructures for the first time. From the results for the simple AlGaN/GaN structures on GaN substrates, it was confirmed that this method has high spatial resolution of about 80nm and gives quantitatively reasonable strain values. The EBSD technique was then applied to the heterostructures grown on Si substrates to study the role of an AlN/GaN multilayer prior to the growth of a thick GaN layer. It was clarified that there exists a compressive strain in the GaN layer, especially near the interface to the AlN/GaN multilayer. This compressive strain will be relevant to the suppression of the crack generation in the thick GaN layer.

Status of GaN-Based Power Switching Devices

State-of-the-art technologies of GaN-based power switching transistors are reviewed, in which normally-off operation and heat spreading as technical issues. We demonstrate a new operation principle of GaN-based normally-off transistor called Gate Injection Transistor (GIT). The GIT utilizes hole-injection from p-AlGaN to AlGaN/GaN hetero-junction which increases electron density in the depleted channel resulting in dramatic increase of the drain current owing to conductivity modulation. The fabricated GIT on Si substrate 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 800V, respectively. These values are the best ones ever reported for GaN-based normally-off transistors. In addition, we propose the use of poly-AlN as surface passivation. The AlN has at least 200 times higher thermal conductivity than conventional SiN so that it can effectively reduce the channel temperature.