Technologies for RF power LDMOSFETs beyond 2 GHz: metal/poly-Si damascene gates and low-loss substrates

Studies technologies to extend the frequency range of RF power LDMOSFETs. A metal/poly-Si damascene gate with a very low resistance was developed in an effort to reduce gate loss. Using this technology, three alternatives for reducing RF substrate loss were critically examined: high-resistivity bulk Si, SOI, and high-resistivity SOI. LDMOSFETs on all three low-loss substrates are shown to have higher PAE than LDMOSFETs on bulk silicon. The effectiveness, of high resistivity SOI, however, was found to be limited by the formation of an inversion layer at the buried oxide/handle wafer interface. The combination of metal/damascene gates and low-loss substrates enables high PAE with long gate fingers at frequencies up to 4 GHz.