Harnessing Unipolar Threshold Switches for Enhanced Rectification

Abstract: Phase transition materials (PTM) have drawn significant attention in recent years due to their abrupt threshold switching characteristics and hysteretic behavior. Augmentation of the PTM with a transistor has been shown to provide enhanced selectivity (as high as ~107 for Ag/HfO2/Pt) leading to unique circuit-level advantages. Previously, a unipolar PTM, Ag-HfO2-Pt, was reported as a replacement for diodes due to its polaritydependent high selectivity and hysteretic properties. It was shown to achieve ~50% higher DC output compared to a diode-based design in a Cockcroft-Walton multiplier circuit. In this paper, we take a deeper dive into this design. We augment two different PTMs (unipolar Ag-HfO2-Pt and bipolar VO2) with diodeconnected MOSFETs to retain the benefits of hysteretic rectification. Our proposed hysteretic diodes (Hyperdiodes) exhibit a low forward voltage drop owing to their volatile hysteretic characteristics. However, augmenting a hysteretic PTM with a transistor brings an additional stability concern due to their complex interplay. Hence, we perform a comprehensive stability analysis for a range of threshold voltages (-0.2 < Vth < 0.8) and transistor sizes to ensure operational stability and to choose the most optimum design parameters. We then test a standalone AgHfO2-Pt and an Ag-HfO2-Pt-based Hyperdiode in two different types of voltage multipliers and report ~500 and ~20 times lower settling time, respectively.