September 3, 2008

Sanken Develops Ultra-low Loss (1/50 of Conventional On-Resistance), High Breakdown Voltage (800 V)
Silicon Substrate Normally-Off GaN FET
- First in Industry Successfully Operated in Actual Inverter -

Sanken Electric Co., Ltd. today announced the successful development of a normally-off GaN (gallium nitride) FET (field effect transistor) using Sanken proprietary epitaxial technology for high-quality GaN crystals on a Si substrate and adopting a new device structure. Sanken has proven its operation in an actual power supply circuit—an achievement that is an industry first. Applications for 41 patents have been filed. The device has a normally-off design, which makes it easy to use because it operates in the same way as traditional silicon MOSFETs. It was up to now difficult to realize with a conventional structure of GaN FET.
   
1. Development Background
  GaN has breakdown electric field about ten times higher than that of silicon, allowing thinner layers with lower resistance, thereby reducing element loss. GaN is expected to take over as the main material used in next-generation high-breakdown-voltage power devices. Usually, sapphire substrate or SiC (silicon carbide) substrate are used for GaN devices. However, these substrates are extremely expensive and significantly raise device costs.

Sanken conducted lengthy research into technology to enable this new material—GaN—to be formed on a silicon substrate, which is low cost and can be fabricated easily on large-diameter wafers. In spite of the extreme difficulty of forming a thick layer of GaN crystals on a silicon substrate, Sanken has succeeded in doing just that through the use of an original, innovative epitaxial technology. The result is a normally-off, ultra-low loss, high breakdown voltage (800 V) GaN FET—proven in operation on an inverter circuit.

Looking at this achievement as just an initial step, Sanken plans to continue improving the performance of the new FET and developing application technologies, with the aim of commercializing the product at an early stage.

Alongside the successful development of this new GaN FET, Sanken has also completed development of a high-breakdown-voltage (800 V) GaN Schottky barrier diode (SBD), which has been proven to operate in an actual PFC (power factor correction) circuit.              
 
2. Features
  <GaN FET>
• Low On-resistance of 3 mΩcm2 (1/50 that of silicon MOS FETs)
• High efficiency, low noise
• Reduced chip size
<GaN SBD>
• High breakdown voltage (800 V)
• Low VF
• Low conduction loss, low switching loss
   
3. Ideal Applications
  • Wide-screen FPD-TVs  
• Switching power supplies
• Inverters (in air conditioners, industrial motors)
• UPS (uninterruptible power supply) units 
• DC power supply equipments
• Electric vehicles, hybrid vehicles, etc.
   
4.  Feature Summary
  <GaN FET>
• Normally-off type realized by adopting a new device structure (gate-electrode p-type semiconductors are formed in excavations made in the substrate).
• Breakdown voltage: 800 V; threshold voltage: 1.0 V; On-resistance: 3 mΩcm2
• A GaN SBD can be formed on the same chip.
• When housed in a TO-3PF–equivalent package, a breakdown voltage of 800 V and on-resistance of 10 mΩ or lower is possible.
<GaN SBD>
• VF is 0.5 V lower than previous devices, achieved by adopting a new device structure (a barrier metal and two-dimensional electron gas are brought into direct contact in excavations made in the substrate).
• Breakdown voltage: 800 V
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