High-Power Transistors Emerge at CEATEC
Sanken, Fujitsu Laboratories, and other Japanese companies introduced high-power transistors, some of them aimed at the growing market for electric vehicles. The SiC- and GaN-based devices were on display at the CEATEC Japan 2009 show.
Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 10/14/2009
Higher-power semiconductor devices using SiC or GaN materials emerged at the CEATEC Japan 2009 show, held last week at Makuhari Messe near Tokyo.
The higher-power devices feature not only lower on-resistance and higher breakdown voltages, but also higher switching speeds, supporting smaller inductors in switch-mode power supplies and DC-DC converters. The market is a growing one, as high-power transistors are used in electric vehicles and other motors that operate at high temperatures.
GaN is well known for its use in light-emitting diodes (LEDs), but its wider bandgap also allows high-temperature operation. Sanken Electric Co. Ltd. (Niiza, Japan) demonstrated GaN FETs using GaN on a silicon substrate. The GaN layer is deposited epitaxially on the silicon substrate through a buffer layer to mitigate lattice mismatch.
Sanken prototyped three kinds of power devices — a Schottky barrier diode (SBD), normally-on type GaN FET, and a GaN FET integrated with an SBD — that are produced in the GaN layer on a 5 in. silicon substrate. The FET features a 600 V breakdown voltage, a gate threshold voltage of 1 V, an on-resistance of 10 mΩ encapsulated in a TO-3P package, and a drain current of 15-20 A. The company also demonstrated 200 V/2.2 kW three-phase motor drivers.
The FET consists of an AlGaN on InGaN layer on the substrate. The gate region of a p-material is formed at a recessed gate. The JFET-like structure, similar to the HEMT (high electron mobility transistor) structure invented by Fujitsu Laboratories Ltd. (Kawasaki, Japan), uses a 2-D electron gas to provide higher mobility.
Fujitsu Labs also demonstrated a newly structured HEMT, designed for higher-temperature applications. The recessed gate oxide is intruded into the n-AlGaN layer and the oxide is produced by atomic layer deposition (ALD) to reduce the drain leakage current at zero-gate voltage. The device was detailed at the Device Research Conference held in June, according to Fujitsu Labs. The transistor features a 600 V breakdown voltage, 40-50 A current, and 3 V gate threshold. The substrate is a 3 in. SiC wafer.
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Fujitsu Laboratories developed a HEMT device for high-power applications. |
Rohm Co. Ltd. (Kyoto, Japan) has developed two kinds of SiC power MOSFETs — a planar DMOS type and a trench DMOS type. The company earlier prototyped a planar DMOS FET designed for three-phase motor drive. The chip measures 5 × 5 mm with handling current of 40 A. In cooperation with the University of Arkansas, the company made a prototype of a 200 kHz, 70 A DC-DC converter using the SiC DMOSFETs. The inductor of the DC-DC converter measures one-tenth the size of conventional silicon IGBT converters, due to the higher operation frequency of 200 kHz, supporting smaller motor drivers.
The company also showed a prototype of a trench DMOS FET using a 3 in. SiC wafer. It delivers 300 A of current with 790 V breakdown voltage with 1.7 mΩ at 4.8 × 4.8 mm chip size.
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