Nariaki Ikeda

GaN Power Transistors on Si Substrates for Switching Applications

In this paper, GaN power transistors on Si substrates for power switching application are reported. GaN heterojunction field-effect transistor (HFET) structure on Si is an important configuration in order to realize a low loss and high power devices as well as one of the cost-effective solutions. Current collapse phenomena are discussed for GaN-HFETs on Si substrate, resulting in suppression of the current collapse due to using the conducting Si substrate. Furthermore, attempts for normally off GaN-FETs were examined. A hybrid metal-oxide-semiconductor HFET structure is a promising candidate for obtaining devices with a lower on-resistance (Ron) and a high breakdown voltage (Vb).

High power AlGaN/GaN HFET with a high breakdown voltage of over 1.8 kV on 4 inch Si substrates and the suppression of current collapse

In this paper, we successfully demonstrate an AlGaN HFET with a high breakdown voltage of over 1.8 kV on 4 inch Si substrates. In order to obtain the high breakdown voltage and to improve the crystalline quality of GaN layers, a thick GaN epitaxial layer including a buffer layer with a total thickness of over 6 mum was grown. The breakdown voltage and the maximum drain current were achieved to be over 1.8 kV and 120 A, respectively. Furthermore, the suppression of the current collapse phenomenon is examined. The on-resistance is not so significantly increased up to the high drain off-bias-stress of 1.0 kV.

Switching Characteristics of GaN HFETs in a Half Bridge Package for High Temperature Applications

AlGaN/GaN heterojunction field effect transistors (HFETs) are expected to be a good candidate for power switching application at high temperatures. We designed and fabricated a discrete HFET package and a half bridge module using the AlGaN/GaN HFETs and SiC Schottky barrier diodes (SBDs) for high temperature applications. The half bridge module exhibited good reliability after 250 C and 400 h high temperature storage. Switching characteristics of the AlGaN/GaN HFET were investigated. Qg x Ron, which shows a figure of merit of switching operation, was more than 10 times better than commercial Si MOSFETs. The switching characteristics of the HFET showed no significant degradation up to 225 C.

High-power AlGaN/GaN MIS-HFETs with field-plates on Si substrates

In this paper, GaN-based MIS-HFET devices on 4-inch Si substrates were fabricated, and the device characteristics were examined. As a result, the breakdown voltage was improved to be over 2.45 kV using high-resistive carbon doped buffer layers with a larger thickness of over 7.3 µm. The maximum drain current was estimated to be over 115 A using MIS-structures. A trade-off between the specific on-resistance (RonA) and the breakdown voltage (Vb) was improved using carbon doped buffer layers, resulting in obtaining RonA = 5.9 mΩcm2 and Vb = 1730 V simultaneously with the gate-width of a 340 mm. Furthermore, the field-plate structure was introduced into MIS-HFET structures. We have examined the suppression of a current collapse phenomenon owing to the combination of the gate field-plate structure and a conductive Si substrate with MIS-HFET devices.

High-Temperature Operation of AlGaN/GaN HFET With a Low on -State Resistance, High Breakdown Voltage, and Fast Switching

Improved characteristics of an AlGaN/GaN HFET are reported. In this paper, the authors introduce a new ohmic electrode of Ti/AlSi/Mo and a low refractive index SiNx to decrease the contact resistance and gate leakage current. The AlGaN/GaN HFET showed a low specific resistance of 6.3 mOmega middot cm2 and a high breakdown voltage of 750 V. The switching characteristics of an AlGaN/GaN HFET are investigated. The small turn-on delay of 7.2 ns, which was one-tenth of Si MOSFETs, was measured. The switching operation of the HFET showed no significant degradation up to 225 degC

Over 1.7 kV normally-off GaN hybrid MOS-HFETs with a lower on-resistance on a Si substrate

In this study, normally-off GaN hybrid MOS-HFET devices on 4-inch Si substrates were fabricated, and the device characteristics were examined. As a result, the breakdown voltage (Vb) was improved using a combination of a high-resistive carbon-doped back barrier layer and a thin channel layer of 50 nm. The specific on-resistance (RonA) was estimated to be less than 7.1 mΩcm2 for Lgd = 12 μm, and Vb was estimated to be over 1.71 kV for Lgd = 18 μm. To our knowledge, these values are the best results ever reported for normally-off GaN-based MOSFETs.

Low On-Voltage Operation AlGaN/GaN Schottky Barrier Diode with a Dual Schottky Structure

We propose a novel Schottky barrier diode with a dual Schodky structure combined with an AlGaN/GaN heterostructure. The purpose of this diode was to lower the on-state voltage and to maintain the high reverse breakdown voltage. An AlGaN/GaN heterostructure was grown using a metalorganic chemical vapor deposition (MOCVD). The Schottky barrier diode with a dual Schottky structure was fabricated on the AlGaN/GaN heterostructure. As a result, the on-voltage of the diode was below 0.1 V and the reverse breakdown voltage was over 350 V.

288 V-10 V DC- DC Converter Application Using AlGaN/GaN HFETs

We report on the 288 V-10 V DC- DC converter circuit using AlGaN/GaN HFETs for the first time. The AlGaN/GaN HFET with a large current and a high breakdown voltage operation was fabricated. That is, the maximum drain current was over 50 A, and the minimum on-resistance was 70 mohm. The breakdown voltage was over 600 V. A DC-DC down-converter from input DC 288 V to output DC 10 V was fabricated using these HFETs. It was confirmed that the switching speed of the AlGaN/GaN HFET was faster than that of Si MOSFET. The DC-DC down-converter was fabricated using these HFETs. This converter was composed of a full bridge circuit using four n-channel AlGaN/GaN HFETs. In the case of AlGaN/GaN HFET, a gate switching wave (Vgs) and source-drain wave (Vds) were abrupt compared with those of using Si MOSFETs. In both cases, a stable and constant output DC 10V was also obtained and the conversion efficiency of the converters with AlGaN/GaN HFETs was 84%.

Soft Switching Controlled AlGaN Based Power Transistors for Induction Heating Applications

This paper reports on our first and series trial to apply the AlGaN heterojunction field effect transistors (HFETs) for in substitution for Si transistors in the induction heating (IH) applications. The on-resistance of the 800 V/50 A AlGaN HFET was 0.11 ohm, and the turn-on and turn-off times were less than 20 ns, respectively, which are lower than that of conventional Si based metal-oxide-semiconductor field effect transitors (MOSFETs). The input capacitance of the AlGaN HFET of up to 350 V was one digit smaller than that of the conventional Si MOSFETs. We fabricated the IH system with a soft switching circuit driven by the AlGaN HFETs. We realized the operation of this IH cookers at an operation voltage of 280 V and current of 8 A at a frequency of 29.6 kHz.

Fabrication of AlGaN/GaN HFET with a High Breakdown Voltage on 4-inch Si (111) Substrate by MOVPE

We investigated an AlGaN/GaN heterostructure field effect transistor (HFET) on Si substrates using a multi-wafer metalorganic vapor phase epitaxy (MOVPE) system. It was confirmed that a GaN film with smooth surface and without any crack was obtained. To increase a resistance of a GaN buffer layer, the carbon (C) -doping was carried out by controlling the V/III ratio and the growth pressure. The breakdown voltage of the buffer layer was dramatically improved by introducing the C. As a result, the breakdown voltage was about 900 V when the C concentration was about ∼8×10 18 cm −3 . After while, an AlGaN/GaN heterojunction FET (HFET) on a C-doped GaN buffer layer was fabricated. We achieved the breakdown voltage of over 1000 V and the maximum drain current of over 150 mA/mm, respectively. It was found that the C doped buffer layer is very effective for improving the breakdown voltage of AlGaN/GaN HFETs.