Metamorphic HEMT technology for submillimeter-wave MMIC applications

Metamorphic high electron mobility transistor (mHEMT) technologies with 50 and 35 nm gate length were developed for the fabrication of submillimeter-wave monolithic integrated circuits (S-MMICs) operating at 300 GHz and beyond. Heterostructures with very high electron sheet density of 6.1×10¹² cm^-2 and 9800 cm²/Vs electron mobility were grown on 4” GaAs substrates using a graded quaternary InAlGaAs buffer layer. For proper device scaling channel-gate distance and source resistance were reduced. Maximum transconductance of 2500 mS/mm and a transit frequency of 515 GHz were achieved for the 35 nm mHEMT with 2 × 10 μm gate-width. Already the 50 nm technology allows the realization of S-MMIC operation frequencies up to 320 GHz, the current limit of on-wafer probe availability. A compact four-stage H-band amplifier circuit based on a grounded coplanar waveguide (GCPW) layout is presented in 50 and 35 nm technology, respectively. The 50 nm mHEMT amplifier has a linear gain of 19.5 dB at 320 GHz and more than 15 dB between 240 and 320 GHz. The same amplifier utilizing 35 nm gate-length transistors achieves more than 20 dB gain within the entire H-band from 220 to 320 GHz.