Slow-wave distributed MEMS phase shifter in CMOS for millimeter-wave applications

This paper presents the first experimental results of a distributed-MEMS phase shifter for millimeter waves applications. It is based on a tunable shielded coplanar waveguide (S-CPW) fabricated using the back-end-of-line (BEOL) of AMS 0.35 μm CMOS technology. A simple maskless post-CMOS etch was used to remove the BEOL silicon dioxide and release the ribbons of the S-CPW that can be electrostatically displaced, changing the capacitance of the S-CPW, altering the phase of the propagating signal. A phase shift of 25.1° with an insertion loss of 0.7 dB was measured in an 1120 μm-long S-CPW at 60 GHz, under a 60 V bias voltage, resulting in a Figure of Merit of 36°/dB. The developed approach also leads to a small insertion loss variation of ±0.1 dB. These first results should be further improved by optimizing the mechanical design.