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ISPSD 2013 – Big Picture Problems, High Voltage Solutions

Contributed by: Dr. St.J. Dixon-Warren

The 25th International Symposium on Power Semiconductor Devices & ICs (ISPSD 2013) conference is being held this year in the historic city of Kanazawa, on the north-west coast of Japan.  As mentioned in my previous blog posting, the conference covers the following technical areas:

  • High Voltage Power Devices
  • New Material Power Devices
  • Power ICs
  • Low Voltage Power Devices
  • Module and Package Technologies

The conference began with three plenary talks. The first, by Masazumi Yamamoto of Mitsubishi, was a fairly high level discussion of the energy challenges facing Japan.  The main challenge is the shutdown of all Japan’s nuclear reactors after the earthquake two years ago. In 2009 29% of Japan’s electricity was nuclear and this was projected to grow to 41% by 2019, as part of Japan’s goal to become a low carbon society. He discussed a number of challenges, not the least of which is the demographic trend that projects a decline in the working age population that is expected to accelerate in the near future. This talk demonstrated something that has always been striking about power technology events. They are always grounded (pun intended) in “real world” issues rather than the more flashy consumer events that talk about the latest apps. or gaming benchmarks.

The second plenary was more technical. It was presented by Stefan Linder of ABB who discussed the power electronics as a key enabler for a future with more than 20% wind and solar energy.  Two of the major difficulties with wind and solar energy are their intermittent nature and their relative geographic distance from areas of high energy use.  Intermittence drives the need for sophisticated power management electronics to maintain grid stability, which include complex data networks which provide the data necessary for managing the grid. The long transmission distanced required to make renewable sources feasible will depend on the implementation of high voltage DC (HVDC) electricity grids.

The capacity of a HVAC grid apparently drops for long distances, while DC grids are less affected by distance.  In addition energy storage is required, and presently it appears that hydroelectric storage is the most technologically mature option.  He ended the talk with a discussion of power electronics requirements of using hydroelectric energy storage in conjunction with renewable energy sources and he argued that Integrated Gate Commutated Thyristors (IGCTs) would be a critical component.

The third plenary, by Don Tan, President of the IEEE Power Electronics Society, was delivered in two parts. The first part concerned the Power Electronics Society, which is also celebrating its 25th anniversary, and its relationship to the ISPSD community.  He then turned to a technical discussion of the bus architecture required to manage digital and RF loads with ever decreasing voltage levels.

Once the plenary talks were over, it was time to head over to the technical sessions.

The first technical session centered on an Integrated Gate Bipolar Transistors (IGBTs). IGBTs have been an area of interest to this community for their entire 25 year history. Jun Hu of Alpha & Omega gave the first talk which discussed a new IGBT that combined features from both trench and planar devices. They call it a trench shielded planar gate IGBT (TSPG-IGBT). The modifications were all on the top side of the devices, with the backside being the same as for standard Alpha & Omega IGBT products. He presented experimental and simulation results and they claim lower conductive losses, lower turn on losses and a robust short circuit capacity, when compared to both planar and trench devices.

The first session continued with three more IGBT papers (we aren’t covering them here) and was followed by the second session on New Materials Power Devices. This was led off by Toyota Motor Corporation and presented by Hidefuni Takaya. He discussed a SiC trench MOSFET which used a thick bottom oxide to improve the characteristics. The thick bottom oxide reduces the electric field strength. The devices achieved 1400 V breakdown voltage and 4.4 mOhm cm2 for the specific on-state resistance.

The second talk in the session was presented by Lin Cheng of CREE. She discussed a 1600 V 4H-SiC DMOSFET that was able to operate at 150 A. She claimed 3X higher power density and 20% lower switching losses as compared to an equivalent silicon IGBT device. CREE already has this technology on the commercial market as the C2M0080120D 2nd-Generation, Z-FET™, which is rated for 1200 and 80mΩ, silicon carbide MOSFET.

The final paper of the day was presented by Don Disney of Avogy, a California-based start-up company. The title was Vertical Power Diodes in Bulk GaN. He claimed it was the first bulk GaN paper ever to be presented at ISPSD. The devices are formed using N- GaN epi on an N+ GaN substrate.  A layer of in situ Mg doped P-GaN for the anode of the diode structure. Pd metal is used for the anode metal, while Al is used for the cathode.

GaN Diode Construction

GaN Diode Construction

The author claimed that the diode devices exceeded the SiC limit and were very close to meeting reaching the theoretical limits for GaN technology. He also claimed that yield optimization and preliminary reliability testing showed the devices to be commercially viable.

The first day of the conference ended with a reception at the Kanazawa Castle.  Japanese beer, sake and snacks were served in this splendid, traditional wooden castle. ISPSD has always been one of the premier events in terms of technical presentations, focus, and choice of venues and 2013 is no exception.