Interface Dewetting Phenomenon in Germanium Telluride for High Work Density Phase Change Nanoscale Actuator and Control Methods for Better Endurance

The introduction of the metal-oxide-semiconductor field effect transistor (MOS-FET) has sparked a major transformation in the semiconductor industry. It is at the core of complementary metal oxide semiconductor (CMOS) technology and has been continuously improved over the past 50 years, providing better performance and more affordable electronics. Nevertheless, the exponentially decreasing miniaturization trend of the MOSFET has been slowing down recently because of fundamental limitations and fabrication challenges. The off-stage current increases exponentially with decreasing threshold voltage, and a thinner oxide gate results in more electron tunneling behavior, which poses issues in both energy efficiency and device reliability. Many “beyond-CMOS” technologies have been proposed as complementary add-ons that address CMOS limitations in application-specific circuits. These technologies aim to improve computational performance, energy efficiency, and cost-effectiveness while working alongside traditional MOSFET-based designs. Among emerging technologies, nanoelectromechanical (NEM) relays can achieve steeper subthreshold swing with zero leakage current making them outstanding candidates for this support role for CMOS.

A phase change material-based nonvolatile nano electromechanical (NEM) relay with high on-off ratio, low off-state leakage current, and good scalability has been introduced by our group, namely, the phase change nanoelectromechanical relay (PCNR). However, the device suffers from endurance issues that need to be addressed for use in any application. In this dissertation, the phase change material is studied as one of the major sources of failure, especially the rarely investigated dewetting between the phase change material (GeTe) and the encapsulation layer (aluminum oxide) that leads to voiding behavior. The dewetting between GeTe and the encapsulated alumina produces a significant volume change (21.9%) for the actuator, but uncontrolled dewetting produces continuous deformations that eventually lead to breaking of the encapsulation and failure of the device. Therefore, we focused on improving the reliability of the actuator for the PCNR by managing its deformation to harvest the maximum elastic energy while increasing the number of cycles. Two methods are proposed to balance dewetting and elastic energies. One is increasing the thickness of the cap to increase its stiffness and balance the dewetting force. The other is to reduce the temperature gradient and slow the progress of the dewetting generated voiding behavior. Both methods have been proven through simulation and experiment.