Temperature dependent conversion from digital to analog resistive switching behavior of rf sputtered TiO2−x thin-film-based metal–oxide–semiconductor devices

Abstract

Substrate temperature driven digital to analog resistive switching behavior is observed in metal–oxide–semiconductor device in which TiO${}_2$ and Si act as gate oxide and substrate, respectively where 10-nm-thick TiO${}_2$ thin-films were deposited on $n$-type Si (100) substrates by rf sputtering of TiO${}_2$ target at room temperature. Earlier, TiO${}_2$ deposition rate was calibrated using grazing incidence X-ray reflectivity (GIXRR) technique. In situ temperature dependent X-ray photoelectron spectroscopy (XPS) and room temperature photoluminescence techniques were employed to get concentration of oxygen vacancies and Ti${}^{3+}$. Current–voltage ($I-V$) and high frequency (HF) capacitance–voltage ($C-V$) properties were studied from room temperature to 200 °C. The $I-V$ data shows a change in nature of resistive switching behavior of the devices from its abrupt/digital to analog nature with increasing measurement temperature. It is observed that the digital switching appears beyond a certain temperature due to alignment of energized oxygen vacancies up to 150 °C. With further rise in temperature, a redistribution of vacancies takes place, responsible for creation of multiple conducting pathways leading to change the nature into analog one. A model is also proposed to explain such a change in its resistive switching nature. The HF $C-V$ data shows highest accumulation capacitance at RT due to the presence of maximum number of oxygen vacancies. The capacitance lowers down significantly at 50 °C and again starts increasing at 100 °C and maintains the rising trend up to 200 °C. This phenomena may be explained on the basis of temperature dependent reaction of oxygen vacancy with carbon impurities present in the device.