Polarity-Induced Threshold Voltage Shift in Ovonic Threshold Switching Chalcogenides and the Impact of Material Composition

Amorphous chalcogenide-based ovonic threshold switch (OTS) selectors are an important part of the crosspoint memory arrays. It is known that the threshold voltage (V-th) of the OTS device can be affected by operating conditions, such as pulse amplitude and ramp rate. Herein, the impact of pulse polarity on OTS parameters is investigated. Recent findings on the polarity-induced V-th shift observed in SiGeAsTe and SiGeAsSe materials are summarized. This effect is manifested as a stable and reversible change in V-th resulting from the reversal of applied pulse polarity, thus allowing V-th to be electrically controlled. Herein, for the first time exceptionally large polarity-induced V-th shift in GeSe OTS is reported. The behavior observed in binary GeSe and quaternary SiGeAs(Te/Se) material systems is compared and the dependence of polarity effects on the composition of OTS devices is discussed. The impact of film thickness, interface, and stoichiometry in GeSe OTS is investigated.