SiC microwave power devices

Mesfet power RF / Microwave transistors based on SiC substrates and epitaxy are now trying to emerge as commercial products. Impressive power emission results ill have already been published. Initial predictions [2,3,4] about the higher voltage handling and output impedance level have now been experimentally confirmed. Moreover, linearity of SiC Mesfets seems goad, at least as good as for silicon LD-MOS, which is crucial for any amplifier to be used in the next generations of telecommunications systems with complex modulation schemes.. Thermal management does not seem to be as simple as expected, due to: (1) the very high dissipated power density, (2) the non-linear thermal conductivity of SiC, and (3) the rapid decrease of electron mobility with temperature. Some device samples have already been delivered to a few selected potential customers, at feast in USA and Europe. However, it seems that there are still technical issues to be solved before they can be established as "normal" products. One major issue is the stability of the device electrical characteristics [4,5]. A second one is the power density, still too low, lower than 2 W/mm for 30 W devices. Both seem to be strongly related to the substrate and epitaxy quality, and it is now clear that the requirements on the SIC semi-insulating substrates and the epitaxy used for making the SiC Mesfets are extremely severe. Some improvement can be obtained using adequate buffering structures, but it seems that the decisive step forward will come from the use of purer semi-insulating substrates. If those problems cannot be solved rapidly, there is a significant chance/risk that the availability of III-N/SiC HEMT can eliminate the interest for SIC R;Mesfet, as a consequence of the higher gain of III-N HEMT and due to the fact that III-N materials and technology experience rapid progress as a spin-off of the efforts devoted to III-N optoelectronics. However, III-N microwave and III-N optoelectronics technologies are not so similar; and there are still many problems to be solved before the III-N devices can meet the performance even of the imperfect SIC Mesfets demonstrated today.