GaN-on-diamond technology platform: Bonding-free membrane manufacturing process

GaN-on-diamond samples were demonstrated using a membrane-based technology. This was achieved by selective area Si substrate removal of areas of up to 1 cm × 1 cm from a GaN-on-Si wafer, followed by direct growth of a polycrystalline diamond using microwave plasma chemical vapor deposition on etch exposed N-polar AlN epitaxial nucleation layers. Atomic force microscopy and transmission electron microscopy were used to confirm the formation of high quality, void-free AlN/diamond interfaces. The bond between the III-nitride layers and the diamond was validated by strain measurements of the GaN buffer layer. Demonstration of this technology platform is an important step forward for the creation of next generation high power electronic devices.

Transistors created on a GaN-on-diamond material system have attracted significant interest in recent years due to their increased high frequency and high power handling potential when compared to commercially established GaN-on-SiC technologies. The high thermal conductivity of polycrystalline diamond substrates significantly improves thermal transistor management, increasing by up to ∼3× the power density handling capability of GaN-based radio-frequency (RF) devices.1 This performance benefit can be utilized to increase RF transmitter output power as required for next generation (5G and beyond) wireless communication systems with enhanced reliability. The current GaN-on-diamond state-of-the-art fabrication process uses amorphous dielectric interlayers as seed layers for diamond growth,1–6 following wafer bonding to a temporary carrier wafer4,7–9 and additional processing. The inclusion of a wafer bonding stage increases manufacturing complexity and potentially compromises the device surface, negatively impacting device performance.

In this work, we describe a membrane-based GaN-on-diamond production methodology which obviates the need for bonding to a carrier wafer. A polycrystalline diamond is deposited directly on membranes formed from GaN-on-Si wafers by selective area substrate removal, enabling the growth of a 50 μm thick crack-free diamond directly on the exposed back-side (N-polar face) of AlN epitaxial nucleation layers. The simplified production method provides a route to GaN-on-diamond devices and circuits with improved performance and manufacturability.