Improved Gradual Resistive Switching Range and 1000x On/Off Ratio in HfOx RRAM Achieved with a $G{e}_{2}S{b}_{2}T{e}_5$ Thermal Barrier

Abstract

Gradual switching between multiple resistance levels is desirable for analog in-memory computing using resistive random-access memory (RRAM). However, the filamentary switching of $Hf{O}_x$-based conventional RRAM often yields only two stable memory states instead of gradual switching between multiple resistance states. Here, we demonstrate that a thermal barrier of $G{e}_{2}S{b}_{2}T{e}_5$ (GST) between $Hf{O}_x$ and the bottom electrode (TiN) enables wider and weaker filaments, by promoting heat spreading laterally inside the $Hf{O}_x$. Scanning thermal microscopy suggests that $Hf{O}_x+GST$ devices have a wider heating region than control devices with only $Hf{O}_x$, indicating the formation of a wider filament. Such wider filaments can have multiple stable conduction paths, resulting in a memory device with more gradual and linear switching. The thermally-enhanced $Hf{O}_x+GST$ devices also have higher on/off ratio ($>10^3$) than control devices ($<10^2$), and a median set voltage lower by approximately 1 V (~35%), with a corresponding reduction of the switching power. Our $Hf{O}_x+GST$ RRAM shows 2x gradual switching range using fast (~ns) identical pulse trains with amplitude less than 2 V.