Sheraton Frankfurt Airport Hotel 04 March R & D Award


New Generation 50V GaN HEMT Technology


Cree has a range of 50V GaN HEMT devices which offer a significant reduction in the energy needed to power cellular networks. Radio base station power amplifiers have demonstrated performance improvements of more than 20 percent over incumbent technology at 2.6 GHz operating under the latest 4G LTE signals. This increased power amplifier efficiency could save an estimated 10 TWh per year the equivalent power output of two nuclear power plants.


What industry challenge does this address? The world’s cellular network is estimated to consume more than 100TWh of electricity per year: (approximate value of $12 Billion US Dollars) and 50-80 percent of the networks’ power is consumed by the systems’ power amplifiers and feed infrastructure.


How does it solve the problem?


Cree’s new 50V GaN HEMT products can have a large impact in not only helping cellular network operators and OEMs reduce operational and capital expenses but also in reducing global energy consumption.


allow today's standard unit cell devices to operate at significantly lower junction temperatures. TriQuint is using extensive epitaxial characterization to ensure device quality, material and thermal modelling and micro-Raman thermography to verify results.


Near Junction Thermal Transport Program


The $2.7 million Near Junction Thermal Transport (NJTT) program funded by the Defence Advanced Research Projects Agency (DARPA) seeks to triple the power handling performance of high power gallium nitride (GaN) transistors. TriQuint's NJTT approach is based on developing GaN transistors on polycrystalline diamond substrates prepared by chemical vapour deposition (CVD). The CVD diamond substrate shows over five times better thermal conductivity than standard SiC.


TriQuint extracts less than 1µm-thick active AlGaN/GaN heterostructure layers originally grown on Si substrates and attaches them to 100µm thick CVD diamond substrates using an advanced wafer bonding technique. This enables the most effective thermal spreader material to be placed very close to the device junction. TriQuint uses a proven AlGaN/GaN heterostructure to achieve 6 W/mm of RF power comparable to today's standard GaN devices.


Thermal simulations predict that TriQuint can achieve 3x power handling goal for the output power level, which can enable reduction of today's active device size by one third, or alternately,


What industry challenge does this address? A key challenge is to prepare GaN-on-Diamond wafers for 100mm manufacturing lines while maintaining the thermal boundary resistance at the GaN and diamond interface below a critical level and simultaneously keeping GaN surface quality suitable for good RF performance.


This is being achieved through innovative methods of lifting AlGaN/GaN epitaxial layers from proven high RF performance GaN-on-Si wafers, identifying / eliminating poor thermal conductivity layers of the AlGaN/GaN films, and preparing high thermal conductivity diamond substrates using chemical vapour deposition (CVD). Other challenges include attaching AlGaN/GaN films to the diamond substrates by precisely controlled adhesive bonding and developing necessary new processes to fabricate high performance devices and circuits in GaN-on-Diamond material.


How does it solve the problem? Thermal simulations performed before TriQuint began the NJTT program clearly indicated that 3x or greater power handling improvements of GaN-on-Diamond transistors could be achieved through this approach. During the course of the program, TriQuint has shown improvement of thermal boundary resistance of the material and negligible change in the electronic properties of the AlGaN/GaN heterostructure before and after the epitaxial transfer on diamond substrate.


January / February 2013 www.compoundsemiconductor.net 53


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