Threshold Switching by Bipolar Avalanche Multiplication in Ovonic Chalcogenide Glasses

Abstract

Abstract An ovonic threshold switch (OTS) based on chalcogenide glasses finds application as a selecting device in storage class memory (SCM) arrays. The OTS operation relies on the threshold switching, where the device switches from the off to the on state without phase transition, then the device turns off almost immediately as the voltage is reduced below a certain holding value. The physics behind the switching phenomenon has attracted wide interest due to the complicated interplay between electronic transport, joule heating and phase transition. In this work, it is shown that the current‐voltage characteristic close to the switching point carries the fingerprint of carrier multiplication. The physical mechanism of threshold switching is then explained by bipolar impact ionization leading to avalanche multiplication, which in turn gives rise to the typical S‐shaped characteristic. Numerical simulations by this physics‐based model account for the measured switching properties, namely threshold voltage and current, at various chalcogenide thicknesses and compositions. These results provide the theoretical framework for future design and optimization of OTS in memory and computing applications.

Keywords

• cross‐point memory
• device modeling
• impact ionization
• Poole Frenkel
• ovonic threshold switching