Inline phase-change switch material optimizations for increased reliability, RF power handling, and integration

Abstract

The power handling capabilities of inline phasechange switches (IPCS's) at radio frequencies (RF) has been correlated to the DC threshold voltage (Vth) of the devices. The dependence of Vth 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 (STEM). Use of W-based microheaters in the IPCS processes has improved device performance and reliability, with increases in the product of cutoff-frequency (Fco) and Vth over previous IPCS devices using NiCrSi microheaters. A correlation between the peak allowed RF voltage across the OFF-state switch and the DC Vth of the OFF-device was observed, indicating the DC Vth is an accurate predictor of RF power handling. Inline phase-change switch (IPCS) devices were also fabricated on top of an AlN heat spreading layer deposited on a thick SiO2 layer. The thick SiO2 properly emulates the interlayer dielectric (ILD) thermal properties that prevent direct integration of IPCS devices at the end of a back-end-of-line (BEOL) CMOS process. The AlN acts as a heat spreading layer, enabling the proper thermal quench rate despite the poor low thermal quality conductivity of the oxide underneath such that IPCS devices can be integrated at the end of any microfabrication process — regardless of the substrate or materials underneath. This is attractive for many CMOS applications where wafer real estate is expensive, or in III-V applications where the wafer thermal properties are poor and variable vary among different technologies.