Comparison of MESFET and HEMT MMIC technologies using a compact Kaband voltage-controlled oscillator

To compare the capability of MESFET and HEMT technologies for monolithic microwave integrated circuit (MMIC) implementation we have fabricated and tested discrete field-effect transistors (FETs) and a novel Ka-band monolithic voltage controlled oscillator (VCO). We implemented the circuit with three different active devices: moderate- and high-doped ion-implanted MESFETs (metal-semiconductor FETs) and AlGaAs/GaAs HEMTs (high electron mobility transistors). A comparison of the measured oscillator phase-noise and an independent comparison of the temperature dependence of MESFET and HEMT RF equivalent circuits yields two general guidelines: MESFETs are preferred over HEMTs for applications requiring low phase-noise and temperature insensitive operation.