Improved gradual resistive switching range and 1000× on/off ratio in HfOx RRAM achieved with a Ge2Sb2Te5 thermal barrier.

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 Ge₂Sb₂Te₅ (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 (>10³) than control devices (<10²) 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 2× gradual switching range using fast (∼ns) identical pulse trains with amplitude less than 2 V. [ABSTRACT FROM AUTHOR]