AlN Barriers for Capacitance Reduction in Phase-Change RF Switches

We demonstrate four-terminal GeTe-based RF switches with independent thermal actuation (switching). These devices incorporate an AlN-based dielectric separating high-conductivity W micro-heaters from the RF signal path. With dc, pulsed, and RF testing, we show that an AlN barrier decreases the switch parasitic capacitance with minimal increases in the switching power. Decoupling these design variables, with the high thermal conductivity of the AlN, makes it possible to increase the electrical separation with a thicker AlN film for lower parasitic capacitance with minimal decrease in desirable thermal coupling. Increasing the AlN thickness from 105 to 170 nm results in switches with an improvement in cutoff frequency, f
_CO
from 5.3 to 8 THz, a C
_OFF
improvement from 15 to 10 fF, while maintaining the R
_ON
at 2 Ω. This improvement was accompanied by normalized minimum power to amorphize increases of only 14% (from 1.5 to 1.7 W) for a 100-ns heater pulse.