S2-T4: Low-temperature substrate bonding technology for high power GaN-on-diamond HEMTs

Abstract

We report the first demonstration of GaN-ondiamond RF power transistors produced by low-temperature substrate bonding technology. GaN high-electron-mobility transistors (HEMTs) are lifted from the original SiC substrate post fabrication and transferred onto high-quality polycrystalline diamond with thermal conductivity of 1,800 -2,000 W/mK. Resulting GaN-on-diamond HEMTs demonstrated DC current density of 1.0A/mm, transconductance of 330mS/mm, and RF output power density of 6.0W/mm at 10GHz (CW). Finiteelement thermal modeling indicates GaN-on-diamond technology based on low-temperature substrate bonding is capable of 3X increased power per area compared to conventional GaN-on-SiC devices.

Diamond/GaN HEMTs: Where from and Where to?

“…The generic process flow is schematically represented in Figure 6. In 2014, functional GaN HEMTs originally fabricated in a SiC substrate were bonded to a 1″ PCD wafer at a temperature lower than 150 °C [109] by means of a 35 nm-thick layer of Si-containing bonding material [110]. The experimental value of TBRGaN/diamond was 34 m 2 K/GW and the yield of the bonding process was 70% (Figure 7a).…”

“…The RF characteristics of the GaN-on-diamond devices also degraded in comparison with GaN-on-SiC ones: at 10 GHz and for VD = 20 V PAE/PD were 38%/3.4 W/mm and 48%/4.6 W/mm for both devices, respectively, when tuned for maximum power, and 42%/3.0 W/mm and 57%/4.1 W/mm (when tuned for efficiency). According to the authors, this was primarily due to the omission of air-bridge structures in the In 2014, functional GaN HEMTs originally fabricated in a SiC substrate were bonded to a 1" PCD wafer at a temperature lower than 150 • C [109] by means of a 35 nm-thick layer of Si-containing bonding material [110]. The experimental value of TBR GaN/diamond was 34 m 2 •K/GW and the yield of the bonding process was ≈70% (Figure 7a).…”