Improved Gradual Resistive Switching Range and 1000x On/Off Ratio in HfOx RRAM Achieved with a $Ge_2Sb_2Te_5$ Thermal Barrier

TL;DR

This paper demonstrates that adding a Ge2Sb2Te5 thermal barrier in HfOx RRAM devices enhances filament width, enabling more gradual resistance switching, higher on/off ratios (>1000), and lower set voltages, improving analog memory performance.

Contribution

The study introduces a thermal barrier of Ge2Sb2Te5 to HfOx RRAM, resulting in wider filaments, improved gradual switching, and significantly higher on/off ratios compared to conventional devices.

Findings

Wider filaments observed with Ge2Sb2Te5 barrier.

Achieved >1000 on/off ratio in RRAM devices.

Demonstrated 2x gradual switching range with low-voltage pulses.

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 $HfO_x$-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 $Ge_2Sb_2Te_5$ (GST) between $HfO_x$ and the bottom electrode (TiN) enables wider and weaker filaments, by promoting heat spreading laterally inside the $HfO_x$. Scanning thermal microscopy suggests that $HfO_x+GST$ devices have a wider heating region than control devices with only $HfO_x$, 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 $HfO_x+GST$ 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 $HfO_x+GST$ RRAM shows 2x gradual switching range using fast (~ns) identical pulse trains with amplitude less than 2 V.