Unlocking stoichiometry-free threshold voltage control in GeSe-based ovonic threshold switch by Fermi-Level unpinning

초록

Matching the threshold voltage of ovonic threshold switches (OTS) with integrated memory elements is strictly required to ensure reliable operation and minimize power consumption in dense crossbar arrays. Binary germanium selenide (GeSe) has emerged as an exceptionally robust and thermodynamically stable active material for ultra-low power OTS applications; however, precise tuning of its threshold voltage remains a critical challenge. In conventional metal direct contact (MDC) structures, severe Fermi-level (FL) pinning effectively neutralizes the intrinsic work function of the electrodes, severely limiting threshold voltage controllability. While conventional approaches attempt to resolve this by altering the chalcogenide stoichiometry, such compositional tuning frequently degrades material stability and complicates semiconductor manufacturing integration. To overcome this fundamental bottleneck, we propose a stoichiometry-free threshold voltage modulation strategy utilizing a metal-interlayer contact (MIC) structure. By physically inserting an ultrathin dielectric interlayer between the top electrode and the GeSe, FL pinning is profoundly alleviated. This successfully restores the influence of the metal work function, allowing precise modulation of the subthreshold hopping activation energy. Consequently, GeSe OTS devices with MIC exhibit customized threshold voltage reductions, highly dependent on the electrode work function (Ta, TiN, and Pt) and optimal interlayer thickness, without disturbing the intrinsic bulk conduction physics. This study provides a breakthrough interface-engineering guideline to unlock reliable, stoichiometry-free threshold voltage controllability for high-density 3D memory architectures.

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