GaN-on-Diamond wafer Power Amplifiers and Satellite Radios

GaN-on-diamond wafers are prepared by the direct diamond formation (DDF) process [3]. The diamond is typically between 100 and 200 microns thick. In its final form, the wafer consists of a 750nm GaN epitaxial layer on a free-standing CVD diamond substrate. The CVD diamond has thermal conductivity of greater than 1,600 W/mK.The diamond wafer is polished to reduce back-side roughness and TTV both of which are necessary for processing of the HEMTs. 

The HEMT fabrication uses Ti/Al/Ni/Au Ohmics, a trunk etch in SiN for the gate formation, and a Tcap metallization. The devices are a result of multiple process runs. The gate length and sourcedrain spacing vary according to the target device performance, from a minimum gate length of 150nm to a maximum of 500nm. S-D spacing similarly vary from 2 to 6 microns. 

The Akash PA Module is built based on this GaN-on-Diamond substrate. The proximity of the GaN to the diamond enables a rapid/efficient heat extraction during RF operation. The ensuing reduction in the gate’s thermal rise (i.e., the difference between the gate and the baseplate temperatures) of a GaN-on-Diamond device leads directly to extended lifetimes, greater RF output power, improved linearity at high saturated power, and it enables CW operation where pulsed-mode is otherwise needed to prevent selfheating. In a space operating environment characterized by vacuum, limited power supply, size and weight constraints, GaNon-Diamond enables increased design flexibility for boosting .

We compare the thermal properties of GaN-on-diamond with a GaN/SiC multi-finger FET. Both devices have 10 fingers and 40 um gate to gate spacing. GaN-on-diamond thermal measurements and thermal extracted models can be seen in figure 2. GaN-onDiamond shows a ~65- 700C lower channel temperature. 

We have demonstrated GaN-on-diamond amplifiers Noise Power Ratios of 20dB at a 3dB back off from Psat, and a space ready radio capable of transmitting 650 Mbits/second at X-band, all operating in CW mode without active cooling. Crucially, this paper represents the first report of the radiation resilience of GaN-onDiamond power amplifiers. These results demonstrate how GaNon-diamond RF power amplifiers can assist in building the most capable space ready radio systems. 

As we send components into space, critical parameters are the items size, weight, and power (SWAP). The diamond substrate in GaN-on-diamond gives the radio a high level of flexibility in designing the component’s SWAP. Comparing the GaN-ondiamond radio to competing radios, competitors are typically three times the size and weight or a fraction of the power and data rate of GaN-on-Diamond radios. The differentiator is the efficient heat extraction of diamond.

CSMH has been committed to the research and development and production of diamond materials. Now it has products such as diamond heat sink sheet,diamond wafer, diamond window to provide customers with a comprehensive thermal management solution.