Powdec 600 V GaN Schottky Diode Breaks Barriers
Japanese firm Powdec K.K. has successfully developed a Schottky diode with a high breakdown voltage of over 600 V using next generation Gallium Nitride (GaN) technology.
In addition to the vertical Schottky diodes being made on low-cost, large diameter sapphire wafers, a proprietary method was developed where the sapphire substrate is removed, further improving the thermal conductance of the device.
The on-resistance of this GaN diode is over 100 times smaller than existing silicon power diodes, resulting in the reduction of power losses by more than 50%. Powdec plans volume shipments of the Schottky diodes by 2012.
Figure 1. SEM Image of GaN vertical Schottky diode after separation from substrate
Powdec’s new GaN Schottky diode can be used in the power conditioning of solar power systems, motor drive circuits, as well as in inverter and power factor correction (PFC) circuits that are key in the power supply unit of servers and other equipment. The use of these GaN diodes, will dramatically lower the DC/AC conversion power losses.
The replacement of the existing silicon power diodes by these GaN power diodes, results in a 15 to 30% reduction in emitted CO2. Powdec’s products will enable an accelerated adoption of smart grids throughout our societies (where power and information networks are tied together, and where individually generated electricity from solar power etc. is smoothly connected to the main power grid).
As large diameter sapphire substrates are used, devices can be manufactured at very low cost like LEDs. At 620 V, a leak current of less than 1 mA/cm2 was achieved. So for a 10 A diode, leak current will be on the order of 20 microamps, which is one-tenth that of than other GaN devices.
Figure 2. Comparison of vertical Schottky diode device structure using conventional technology and Pwerdec’s technology
The diode has a vertical structure and it doesn’t suffer current collapse as in lateral devices. The thickness of the diode is extremely thin at approximately 20 microns, which gives very low conduction resistance and thermal resistance. This provides the device with low power losses and higher operating temperatures as well as allowing reduced system size as less thermal components are needed.
The GaN Schottky diode provides high-speed performance so high frequency operation is possible. This allows for a reduction in capacitors and inductors needed in the system, thus leading to smaller and lower cost systems.
According to Powdec, it has previously been said that to create a GaN diode with a vertical structure like a silicon diode would not be possible unless expensive GaN wafers are used. Sapphire and silicon wafers are lower cost than GaN wafers. However, until now, their use has led to lower quality GaN crystal growth on top, reducing the voltage limits of the diode.
Powdec has developed an innovative epitaxial lateral overgrowth (ELO) technology and succeeded in realizing very high quality GaN crystal growth on sapphire wafers with numbers of dislocations being several 100 times less than that produced by conventional growth technologies.
While this Schottky diode has achieved a breakdown voltage of 620 V, Powdec’s proprietary technology also allows the possibility to create 1,200 V diodes. Powdec has been granted patents for this technology. To accelerate the market adoption of these innovative, low-power GaN devices, Powdec is actively expanding its partnerships worldwide.
Powdec develops and produces high quality Gallium Nitride (GaN) semiconductor wafers and devices. The firm, based in Oyama City, Japan, focuses on delivering next-generation semiconductor power devices to create an energy efficient, green future.