Low-noise SiGe pMODFETs on sapphire with 116 GHz f/sub max/

Recent advances in SiGe MODFET technology indicate that these devices may have promise for future high-speed analog communications applications (Adesida et al, 1997; Konig et al, 1998). However, losses and isolation problems due to the conducting Si substrate represent a serious disadvantage compared to III-V devices that utilize semi-insulating substrates. The use of insulating substrates such as sapphire is a potential solution to this problem, and previous results on Si and pseudomorphic SiGe-channel MOSFETs fabricated on silicon-on-sapphire (SOS) wafers have been encouraging (Johnson et al, 1998; Mathew et al, 1999). However, SiGe MODFETs require relaxed SiGe buffer layers, and the growth of high-quality relaxed SiGe on sapphire or SOS substrates has not previously been demonstrated. In this paper, we present the results of 0.1 /spl mu/m gate length pMODFETs fabricated on high-mobility Si/sub 0.2/Ge/sub 0.8/-Si/sub 0.7/Ge/sub 0.3/ quantum wells grown on SOS wafers. These devices displayed a power gain cut-off frequency (f/sub max/) of 116 GHz, and minimum noise figure (F/sub mm/) of 2.5 dB at 20 GHz. To our knowledge, these values are the best reported to date for pFETs in any material system.