Ovonic threshold switching in polycrystalline zinc telluride thin films deposited by RF sputtering

• Published in: Nanotechnology 2019-03, Vol.30 (13), p.13LT01-13LT01
• Main Authors: Kim, Taeho, Kim, Youngjae, Lee, Ingwan, Lee, Dayoon, Sohn, Hyunchul
• Format: Article
• Language: English
• Subjects: crystalline; ovonic threshold switching; selection device; thermal stability; zinc telluride
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/1361-6528/aafe13

Chalcogenide materials of the amorphous phase with low band gaps were reported to show Ovonic threshold switching (OTS), making them suitable for selection devices in cross-point memory arrays. Herein, we report that ZnTe films with polycrystalline structures show OTS behavior. Nearly stoichiometric ZnTe thin films were deposited by an RF sputtering method. X-ray diffraction analysis indicated that the films were polycrystalline. The optical band gaps of the ZnTe films were estimated as 2.2 eV from UV-visible spectroscopy transmittance measurements. Photoluminescence measurements indicated the existence of deep-level defects in the ZnTe thin films. Although these ZnTe films have a polycrystalline structure with a relatively high band gap, I-V profiles show OTS characteristics, with a selectivity of over 104, fast threshold switching time in the sub-10 ns scale, and thermal stability up to 400 °C. ZnTe also shows switching endurance for more than 109 cycles without Vth drift, maintaining its selectivity of 104. Thus, we improved the threshold switching characteristics by using a wide band-gap and polycrystalline-structured ZnTe-based chalcogenide material. Post-annealing experiments indicated that the thermal budget of the ZnTe thin film was sufficient for stacked cross-point array structures, thereby overcoming a previous limitation of chalcogenide switching materials. This material is promising for application in high-density cross-point memory arrays as the selection device.