Monolithic integration of RF-MEMS and semiconductor devices for the K-band

Abstract

In this paper a process for complete monolithic integration of semiconductor devices and radio-frequency micro-electro-mechanical systems (RF-MEMS) on a single substrate is presented. Our attempt was to combine RF-Schottky-Diodes to form sub-harmonic mixer and RF-MEMS-phaseshifters on a single chip. The diodes were etched from a molecular beam epitaxy grown silicon stack using two mesa etching steps. Nickel forms a nickel-silicon alloy (nickel silicide) during a rapid thermal processing step acting as Schottky-metallisation. On this stack, the RF-MEMS-fabrication starts with its metallisation layers as a back-end process. To insulate the relatively high actuation voltage (20-40 V) from the RF circuitry, a new concept for bias decoupling is presented. To demonstrate the functionality of the semiconductor integration approach, a mixer for 24 GHz has been designed in coplanar waveguide technology, the local oscillator frequency is at 12 GHz . Fabricated within the same run, switched line phaseshifters are used to show the MEMS capabilities. First tests of diodes revealed good results in their DC- and RF characteristics, the conversion loss of the subharmonic zero biased mixer reached 20 dB for 6 dBm power of the local oscillator. Fabricated teststructures of the phaseshifters achieved good results showing that transmission losses lower than 3 dB at a phaseshift of 180° can be reached.