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 GexSe1–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 Ge0.6Se0.4 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.