Posted: May 14, 2015

Contributed by: St.J. Dixon-Warren

The formal sessions of the 27th International Symposium on Power Semiconductor Devices and ICs (ISPSD 2015) is being held this week at the Shangri-La Hotel in Hong Kong, China. Based on the weather outside my hotel room, I think we must be in the middle of Monsoon Season. Fortunately, the hotels provide umbrellas to patrons.

The ISPSD Conference runs May 10-14, 2015. Short courses were held yesterday. This is the first time the conference has been held outside the triad of Europe, North America, and Japan. The motivation for expanding the territory was the increasing activity in power electronics, especially in Asia. 

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Focusing on power electronics

The focus of ISPSD, naturally, is power electronics, which is divided into high voltage devices (mostly IGBTs), low voltage devices (mostly discrete MOSFETs), wide bandgap devices (GaN and SiC MOSFETs and diodes), and integrated power (also sometimes known as smart power). The conference also includes sessions on packaging. It’s the major annual international gathering for serious researchers in this field, both from industry and academia, in approximately equal proportions. Chipworks has participated in this conference as an exhibitor and for the past several years as a vendor.

Attendance

The conference has 415 registered attendees with the majority being from Asia, as might be expected given the location. According to the Conference General Chair, Johnny K.O. Sin, 218 abstracts were submitted, 98 of which were accepted, corresponding to a 45% acceptance rate. There are 43 oral presentations and 56 posters scheduled. Apparently, 31% of the 218 total submissions came from Europe, 20% from North America, 16% from Japan, and 33% from other regions (mainly China).

GaN transistors with CEO of Efficient Power Conversion

The conference began with four plenary talks. The first was given by Alex Lidow, CEO of Efficient Power Conversion Corporation on the subject of GaN transistors, which he claimed were “Giving New Life to Moore’s Law.” Chipworks has analyzed a number of EPC devices, including the EPC2012 GaN HEMT. Mr. Lidow disclosed that EPC fabricates their GaN HEMT devices at Episil using GaN-on-silicon wafers. He persuasively argued that GaN transistors, at least for certain applications, now exceed the performance capabilities of silicon power MOSFETs.

Due to its larger bandgap and higher electron mobility, GaN has been known for many years to theoretically support higher switching speeds and higher blocking voltages with lower on-state resistance. However, achieving these theoretical capabilities was not possible due to the difficulty in making high quality crystalline GaN material. An additional benefit of the EPC devices, according to the speaker, is that they are produced in a chip scale format, with solder bars that directly bond to the PCB. This results in much lower inductance and improved thermal performance.

Much of the presentation concerned reliability. EPC has documented 10 billion device hours and only 73 device failures. Mr. Lidow concluded his presentation with an announcement of the compact 0.9 mm x 0.9 mm EPC2035 – an enhancement node power transistor. He then held up a bright red AC power adaptor and announced that GaN technology would soon be dominating this application space. GaN is certainly a major area of focus for the conference.

Rail transportation and power electronic devices

The second plenary was given by Jiaxi Hu of the CSR Electrical Technology and Material Engineering Research Institute in Zhuzhou, China on the subject of “Power Electronic Devices in Rail Transportation Traction Systems.” Much progress has been made in recent years on the extraordinary expansion of rail transportation in China and Mr. Hu reiterated the statistics: In the period from 2008 to 2014, China has been investing over $100 billion per year in rail infrastructure. They have built 16,000 km of high speed rail lines, corresponding to more than half the global total. During his presentation, Mr. Hu pointed out that the electrical requirements of high speed rail, main line rail, and metro rail are different. While a high speed rail locomotive uses 100 IGBT modules, a metro rail car uses only 50.

Expanding LED lighting

The third plenary talk was given by Shohei Yamamoto of Panasonic Eco Solutions on the expansion of LED lighting and the expectations for power semiconductors. He began his lecture with a short video from Hiroshi Amano of Nagoya University. Hiroshi Amano shared the Nobel Prize with two others for the invention of the GaN blue LED, which has made the white LED revolution possible.

He claimed that white LEDs have the potential to save 217 TWh of electricity in the US, and as a result, they have been the subject of a tremendous research effort in both academia and industry. Current white LEDs consist of a blue GaN LED and a yellow phosphor, which is excited by the blue light and then emits yellow light.

The combination looks white to the eye. He talked quite a bit about improvements to the color of white LEDs, and cited several studies that show that varying the color (or temperature) of the light throughout the day can result in increased productivity, due to synchronization with human circadian physiology. He also discussed efforts at Panasonic to optimize the spectrum of white LED light to improve the appearance of human skin. The Bikoshoku LED lights are optimized for Japanese skin, showing that human vanity has a never ending value in the marketplace. 

 

21st Century landscape of power electronics

The final plenary talk was given by Pierric Gueguen of Yole Development who discussed the landscape of power electronics in the 21st century.

Technical session overview

The technical sessions began in the afternoon with a session on high voltage devices, followed by a session on GaN devices. The first technical talk was given by Marina Antonio of Cambridge University. She discussed a new design for a trench gate IGBT that incorporated a “P-ring” boron implant at the bottom of the trench gates. She claimed that the P-ring increases the threshold voltage and that they obtained a 1.7 kV breakdown, with a 20% reduction in on-state losses.

      

The conference continues until Thursday and the location of ISPSD 2016 has announced. It will be held June 12-16, 2016 in Prague, Czech Republic.

Chipworks and power electronics

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