Origin and Optimization of RF Power Handling Limitations in Inline Phase-Change Switches

Abstract

The power handling capabilities of inline phase-change switches (IPCS’s) at radio frequencies (RF) have been correlated with the dc threshold voltage ( ${V}_{{\text {th}}}$ ) of the devices. The dependence of ${V}_{{\text {th}}}$ on microheater pulsing parameters and device layout has been characterized, accompanied by observation of the size of the amorphous chalcogenide region through scanning transmission electron microscopy. All observations are consistent with threshold field ( ${F}_{{\text {th}}}$ ) of nominally 50:50 GeTe of 12.6 V/ $\mu \text{m}$ . Use of W-based microheaters in the IPCS processes has improved device performance and reliability, with increases in the product of cutoff-frequency ( ${F}_{{\text {co}}}$ ) and ${V}_{{\text {th}}}$ over previous IPCS devices using NiCrSi microheaters. The improved devices demonstrated power handling capabilities up to 29 dBm in a 50- $\Omega $ system for a switch with submicrometer dimensions, where the improvement is attributed to the larger amorphous zone created at the minimum power to amorphize. These improved devicesdemonstrate the feasibility of these switches in both transmit and receivewireless applications. A correlation between the maximum allowed RF voltage across the OFF-state switch and the dc ${V}_{{\text {th}}}$ of the OFF device was observed, indicating the dc ${V}_{{\text {th}}}$ is an accurate predictor of RF power handling.