High-density crossbar arrays based on storage class memory (SCM) are ideally suited to handle an exponential increase in data storage and processing as a central hardware unit in the era of AI-based technologies. To achieve this, selector devices are required to be co-integrated with SCM to address the sneak-path current issue that indispensably arises in such crossbar-type architecture. In this perspective, we first summarize the current state of tellurium-based threshold-switching devices and recent advances in the material, processing, and device aspects. We thoroughly review the physicochemical properties of elemental tellurium (Te) and representative binary tellurides, their tailored deposition techniques, and operating mechanisms when implemented in two-terminal threshold switching devices. Lastly, we discuss the promising research direction of Te-based selectors and possible issues that need to be considered in advance.

In this work, the effect of sputtering working pressure for the tellurium film and its thin-film transistor was investigated. The transfer characteristics of tellurium thin-film transistors were improved by increasing the working pressure during sputtering process. As increasing working pressure, physical and optical properties of Te films such as crystallinity, transmittance, and surface roughness were improved. Therefore, the improved transfer characteristics of Te thin-film transistors may originate from both improved interface properties between the silicon oxide gate dielectric layer and the tellurium active layer with an improved quality of Te film. In conclusion, the control of working pressure during sputtering would be important for obtaining highperformance tellurium-based thin film transistor.

TeO_x thin films were deposited at various O₂/Ar gas-flow ratios by a reactive RFmagneton sputtering technique from TeO₂ and Te targets. X-ray diffraction (XRD) results revealed that the TeO_x thin films were amorphous. The structure and chemical composition of the TeO_x thin films were investigated by fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The optical characteristics of the TeO_x thin films were investigated by an Ellipsometer and a UV-VIS-NIR spectrophotometer. According to the O₂/Ar gas-flow ratios, the atomic composition ratio of TeO_x thin films was divided into two regions(x=1-2, 2-3). Different optical characteristics were shown in each region. With an increasing O₂/Ar gas-flow ratio, the refractive index of the TeO_x thin films decreased and the optical bandgap of the films increased.

One-dimensional (1D) photonic crystals (PCs) were prepared by TeOx(2＜x＜3)/SiO2 with thedifference refractive index, and fabricated by sputtering technique from a TeO2 and SiO2 target. TheTeOx(2＜x＜3) layers were fabricated by using the sputtering gas ratio (Ar:O2=40:10). A 10-pair TeOx(2＜x＜3)/SiO2 1D PCs were fabricated with the structure parameters of filling factor=0.5185, and period=410nm. The properties of 1D PCs with and without a defect layer were evaluated by UV-VIS-NIR. Anormal mode 1D PC have a photonic band gap (PBG) in the near infrared (NIR) region from 1,203 to1,421 nm. In the case of 1D PC containing a defect layer, a defect level appears at 1,291 nm. Themeasured transmittance (T) spectra are nearly corresponding to calculated results. After He-Cd laserexposure, the defect level is shifted from 1,291 nm to 1,304 nm.