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INDUSTRY GaN DEVICES


Increasing the availability of GaN HEMTs


A robust, reliable foundry process will spur a proliferation of GaN applications


BY WALTER WOHLMUTH, WEI-CHOU WANG, I-TE CHO AND WEN-KAI WANG FROM WIN SEMICONDUCTORS


Figure 1. WIN has a GaN


process involving damascene T-gates with


overlying source- coupled field plates to control the electric field distribution. A thick 4 μm air- bridge enhances current handling capabilities and provides high-Q inductors.


THE TREMENDOUS AMOUNT OF MONEY poured into the development of GaN RF and power devices is enabling new markets and driving an upheaval in existing ones. Thanks in part to governments around the world funding a variety of projects – including US initiatives such as DARPA’s Wide Bandgap Semiconductors for RF and AFRL’s title III GaN-on-SiC programme, plus the European effort KORRIGAN and the Japanese project NEDO – this technology has matured significantly.


GaN technology is now at a comparable maturity level to the GaAs technologies of the late 1990s, prior to the explosive growth in that industry. This was driven by commercial opportunities requiring higher data transmission and better efficiency.


The commercial opportunities for GaN include wireless communication. The traditional transistor deployed in base stations is silicon LDMOS, but migration to 4G LTE and HSPA networks sporting higher bandwidths has triggered a move to GaN HEMTs combining higher efficiency, higher bandwidth and reduced cooling requirements with a comparable price at the system level. This trend is set to continue, as base station products formed with GaN deliver the requirements for 4G communications while offering excellent reliability.


Other opportunities for GaN in the RF arena include a class of satellite communication known as VSAT, which is moving towards a more complicated, data- intense transmission technology referred to as the 4096 QAM format.


There are also changes in cable TV transmission technologies that are playing into the hands of GaN, as operators move to OFDM transmission on both up and downstream paths, due to the implementation of DOCSIS3.1 specifications that have a higher bandwidth in order to serve video-on-demand and HDTV.


And it is not just silicon LDMOS that is under threat from GaN – this material could also displace archaic, staid technologies such as travelling-wave tubes and magnetrons used for microwave heating and phased array radar. In today’s microwave ovens, heating is extremely inefficient, imprecise, and bulky, and introducing GaN could address all these weaknesses. Meanwhile, a switch to GaN in radar system architecture could trim weight and cooling


54 www.compoundsemiconductor.net October 2014 Copyright Compound Semiconductor


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