Design and Optimization of Tunneling Nanoelectromechanical Switches

Abstract

As silicon complementary metal-oxide-semiconductor (CMOS) technology nears its scaling limits, nanoelectromechanical (NEM) switch relays have emerged as promising candidates for complementing CMOS technology due to their superior characteristics, including zero leakage, steep subthreshold swings, high on-of current ratios, and robustness in harsh environments. However, the practical integration of NEM switches still faces challenges such as high actuation voltages, stiction, and slower switching speeds compared to CMOS. One promising strategy to mitigate these issues is the integration of a self-assembled monolayer (SAM) to create tunneling NEM switches. Such switches could achieve nanometer-scale mechanical modulation of gaps between electrodes, showing the potential to overcome the limitations of a conventional NEM switch by exhibiting low actuation voltages, high switching speeds, and minimizing stiction. Nevertheless, the tunneling NEM switches reported to date still show limited performance and require intricate fabrication processes. Additionally, functional tunneling NEM switches demonstrated are limited to two-terminal architectures. This thesis explores innovative designs, fabrication techniques, and material choices to address these limitations and to develop tunneling NEM switches with enhanced performance and reliability for next-generation NEM logic applications. To this end, switches with various structures have been fabricated and investigated, and their respective characteristics are analyzed. In a three-terminal lateral structure fabricated using entirely conventional nanofabrication techniques, switching is demonstrated in both contact and tunneling modes. While operation in direct contact mode shows a high on-of ratio, the integration of the SAM leads to a significantly reduced actuation voltage of 2 V and a lower hysteresis. Further, two-terminal vertical structured devices are studied in tunneling mode, and they consistently demonstrate operation cycles exceeding 100, with a maximum of over 7000, which manifests the reliability prospects of SAM. The trends in IV characteristics indicate that the SAM might have experienced physical deformation due to compression, highlighting a potential area for future research in the molecular engineering of the self-assembly monolayer.