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Firing voltage reduction in thermally annealed Gea??Asa??Te thin film with ovonic threshold switching
摘要： Recently, chalcogenide materials have exhibited ovonic threshold switching characteristics, improving their suitability as selector devices to effectively depress the sneak current in the cross-point array (CPA) structures. However, chalcogenides must be subjected to a firing process before they can exhibit the threshold switching behavior. The firing process causes operation problems with respect to the memory operation process in the case of the CPA structure. Although the firing process is expected to be related to Joule heating with a high electric current, the physical nature of the changes during the firing process remains unclear. In this study, selector devices are fabricated by sandwiching amorphous Ge–As–Te thin films between the TiN and W layers. Furthermore, the authors examine the microstructure of the Ge–As–Te thin films before and after the electric firing process using transmittance electron microscopy (TEM, JEOL JEM-F200). The TEM analysis of the pristine Ge–As–Te thin films denotes the uniform contrast of the image, which implies the uniform chemical composition of the film. However, the Ge–As–Te thin films exhibit nonuniform contrast due to the effects of Joule heating after the electric firing process. The Ge–As–Te thin films were thermally annealed at 150 and 250 °C for 1 min via the rapid thermal annealing process to verify the effects of thermal treatment on the firing process in chalcogenide thin films. The effect of thermal annealing on the threshold switching behavior was also investigated by studying the compositional stability. Their results showed that the thermal annealing process caused the uniform compositions on the pristine Ge–As–Te films to be fluctuated with decreasing firing voltage for threshold switching.
关键词： Ge–As–Te thin films,chalcogenide materials,thermal annealing,ovonic threshold switching,firing process
更新于2025-09-23 15:21:01
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Trap-controlled space-charge-limited conduction in amorphous As <i> <sub/>x</sub></i> Te <sub/> 1a?? <i>x</i> </sub> thin films with ovonic threshold switching
摘要： Ovonic threshold switching (OTS) in chalcogenide materials has attracted considerable interest for application in electronic devices to suppress leakage current in cross-point array structures. Although OTS appears to originate from an electronic process, the exact mechanism of OTS remains unclear with respect to sub-threshold conduction and threshold switching. In this study, we demonstrated that the sub-threshold conduction characteristics is affected by the structures of the exponentially distributed trap states in amorphous chalcogenide materials. Using binary AsxTe1?x thin films, we investigated the effects of trap distribution on OTS characteristics, analyzed the band structures, and developed a trap-controlled space-charge-limited conduction model.
关键词： Ovonic threshold switching,space-charge-limited conduction,amorphous AsxTe1?x thin films,chalcogenide materials
更新于2025-09-23 15:19:57
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Ovonic threshold switching in polycrystalline zinc telluride thin films deposited by RF sputtering
摘要： 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.
关键词： crystalline,ovonic threshold switching,selection device,thermal stability,zinc telluride
更新于2025-09-19 17:15:36