Thermal Transport in GaN HEMTs on Diamond Substrates

The emergence of Gallium Nitride-based High Electron   Mobility Transistor (HEMT) technology has proven to be a

significant enabler of next generation RF systems. However,

thermal considerations currently prevent exploitation of the

full electromagnetic potential of GaN in most applications,

limiting HEMT areal power density (W/mm2

) to a small

fraction of electrically limited performance. GaN on Diamond

technology has been developed to reduce near junction

thermal resistance in GaN HEMTs. However, optimal

implementation of GaN on Diamond requires thorough

understanding of thermal transport in GaN, CVD diamond and

interfacial layers in GaN on Diamond substrates, which has

not been thoroughly previously addressed.

To meet this need, our study pursued characterization of

constituent thermal properties in GaN on Diamond substrates

and temperature measurement of operational GaN on

Diamond HEMTs, employing electro-thermal modeling of the

HEMT devices to interpret and relate data. Strong agreement

was obtained between simulations and HEMT operational

temperature measurements made using two independent

thermal metrology techniques, enabling confident assessment

of peak junction temperature. The results support the potential

of GaN on Diamond to enable a 3X increase in HEMT areal

dissipation density without significantly increasing operational

temperature. Such increases in HEMT power density will

enable smaller, higher power density Monolithic Microwave

Integrated Circuits (MMICs).