Atomic Layer Deposition of Ge _xSe_{1- x} Thin Films for Endurable Ovonic Threshold Selectors with a Low Threshold Voltage

An ovonic threshold switch (OTS) based on amorphous chalcogenide materials possesses several desirable characteristics, including high selectivity and fast switching speed, enabling the fabrication of one selector-one resistor (1S-1R) crossbar array (CBA) for random access memory. Among the several chalcogenide materials, GeSe offers high selectivity and a strong glass-forming ability with environment-friendly, simple binary composition. In this report, the GeSe thin films were deposited via atomic layer deposition (ALD) using Ge(N(Si(CH₃)₃)₂)₂ and ((CH₃)₃Si)₂Se for its envisioned application in fabricating three-dimensional vertical-type phase-change memory. Highly conformal Ge_xSe_1-x films were obtained at a substrate temperature ranging from 70 to 160 °C. The unique deposition mechanism that involves Ge intermediates provided a way to modulate the composition of the Ge-Se films from 5:5 to 7:3. Low threshold voltages ranging from 1.2 to 1.4 V were observed depending on the composition. A cycling endurance of more than 10⁶ was achieved with the Ge_0.6Se_0.4 composition with 10⁴ half-bias nonlinearity. This work presents the foundations for the future development of vertical-type 1S-1R arrays when combined with the ALD technique for Ge₂Sb₂Te₅ phase-change materials.