August 19, 2022
8 mins
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GaN: The Wonder Material - Wafers to Amplifier Modules, Gallium-Nitride (GaN) on diamond Field-Effect

Side view of a cleaved 100-μm GaN-on-diamond wafer Photo credit: Dubravko Babic, Quentin Diduck, others,

This piece deals with the development and issues related to fabrication, die processing and packaging GaN-on-diamond high-electron mobility transistors into X-band amplifier modules. This is a short excerpt. The detailed article can be read here

Thermal resistance measurements using liquid-crystal thermography confirm agreement with theory and previously published measurements on GaN-on-diamond devices.

Over more than the past decade, the commercial availability of Gallium-Nitride (GaN) electronic components such as field-effect transistors, Schottky diodes, light-emitting diodes and lasers has had a significant impact on consumer, professional and military electronics sectors.

Manufacturers and organisations involved directly as well as indirectly with radar, deep-space and military communication equipment are seeking to enhance or replace travelling-wave tube amplifiers using solid-state components where GaN is the most preferred choice. The reason for such high and multi-sectoral interest in GaN is because of its electrical properties and related components (AlGaN, InAlN). 

These demonstrate a combination of key material parameters that is superior to any other material used in RF power and switching. Mainly those of higher breakdown field, electron channel density, and mobility.

GaN is truly a wonder-material. GaN HEMTs can exhibit output powers greater than 10 W/mm of gate periphery (at X-band) which is higher than that of GaAs pHEMT. This is possible owing to its high maximum drain current and operating voltages. Furthermore, relative to the GaAs pHEMTs, GaN HEMTs exhibit lower input capacitance and higher output impedance for the same power, while higher output power per unit gate periphery reduces the need for on-chip power combining – a source of reduced amplifier efficiency. 

There is however a downside. Heat conductivity of GaN and related compounds are lower than that of silicon. Furthermore, the substrates on which the GaN devices are commonly grown, sapphire and silicon have much lower thermal conductivity than that of SiC and chemical vapor deposited (CVD) diamond.  

GaN-on-diamond wafers. Photo credit: Dubravko Babic, Quentin Diduck,others,

Although some RF power devices are indeed commercially fabricated on SiC substrates, their output power and efficiency can be improved further by placing GaN epilayers on CVD diamond. This is particularly important for devices that have inherently small features yet process large power densities, such as high-power RF and millimeter-wave transistors and single-mode visible semiconductor lasers. 

Side view of a cleaved 100-μm GaN-on-diamond wafer. Photo credit: Dubravko Babic, Quentin Diduck,others,

The big difference lies in heat spreading properties. The reduced thermal resistance in GaN-on-diamond electronic devices stems from highly efficient heat spreading: the device active region (i.e., field-effect transistor conductive channel) is placed in the immediate proximity of a highly thermally conductive substrate. This key aspect of diamond substrates: that of efficient heat spreading, is a crucial aspect in vastly improving the thermal properties of HEMTs.

Diamond heat-spreading and lower thermal-conductance packaging will give a designer of GaN-based high-power microwave components thermal management solutions that are vastly superior to other available technologies.

Source: ResearchGate and IEEE Xplore

For full publication, click here:

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