Indirect Electrical-Control Through Heating of a GeTe Phase Change Switch and Its Application to Reflexion Type Phase Shifting

This paper presents a switch based on GeTe (Germanium-Telluride) phase-change material (PCM) suitable for millimeter-wave applications. A shunt configuration with indirect excitation through heating is proposed to facilitate the implementation process in integrated circuits and to reduce impact on RF signal. Electromagnetic simulations, from 50 GHz up to 70 GHz, of two parallel switches shunted a CPW transmission line (TL) show an overall ON-state resistance (RON) of 3 $\Omega$ with an OFF-state capacitance (COFF) of 7.1 $\mathbf{fF}$. This leads to a high Figure-of-Merit with a cutoff frequency of 7.5 THz. The demonstrated performance is validated through the design of a reflection-type phase shifter (RTPS), where a 3-dB branch-line coupler is loaded with tunable-length lines using those shunt-switches. Simulation results of the RTPS show great precision in terms of phase tunability with an insertion loss (IL) less than 2.7 dB at 60 GHz.