Epitaxial VO₂ on Si 100 via TiN Buffer Layer for CMOS Applications

Vanadium oxide (VO₂) exhibits an insulator-to-metal (IMT) transition at 68 °C from a low-temperature insulating phase (P2₁/c) to a high-temperature metallic phase (P4₂/mnm). The optical or electrical excitation can trigger the IMT resulting in an abrupt change in resistance (x10⁴) of VO₂. Due to IMT, VO₂ is used in bolometers, electro-optic modulators, and infrared photodetectors [1]. VO₂ films are grown on single crystalline substrates like Al₂O_3, which severely limits its applications. Integrating epitaxial VO₂ films on Si (100) (complementary metal-oxide-semiconductor) platform enables integrated electro-optic devices and temperature sensors. Moreover, preserving the symmetry of the substrate in some form would pave the way for integrating further oxides epitaxially on top of the VO₂ film. Yun et al.[2] had seen superior performance of UV detector by integrating ZnO on VO₂. The formation of amorphous SiO₂ at the VO₂/Si interface limits its heteroepitaxial integration on Si (100). An epitaxial TiN interlayer layer deposited by reactive pulsed laser deposition (RPLD) [3] is introduced between Si and VO₂ to overcome the same. This work focuses on the growth, crystallography, and IMT characteristics of VO₂/TiN/Si.<br/>Epitaxial VO₂ films on TiN buffered Si is achieved through pulsed laser deposition (PLD) using a V₂O₅ target in oxygen ambient. The deposition pressure is finely tuned to find the narrow growth window for the VO₂ phase [4]. Dual-stage growth is employed, in which an initial few layers (2-5 nm) of deposition at low pressure is followed by high-pressure deposition. The VO₂ film growth is monitored in situ using reflection high energy electron diffraction (RHEED) and shows clear diffraction spots confirming the epitaxial growth of VO₂ on TiN/Si. The VO₂ films grow on TiN/Si in a 3D growth mode in which islands of films nucleate and merge to form continuous films. The high-resolution X-ray diffraction (HRXRD) pattern shows only VO₂ (011) and (022) peaks which indicate the films are phase pure with (011) orientation in the out-of-plane. The symmetric rocking curve FWHM is 1.8^o, which reveals the mosaic nature of the films in the out-of-plane direction. For (200) VO₂ Bragg condition, 8-Bragg reflections were seen, vs. (111) TiN 4-Bragg reflections in the merged pole figure of TiN(111) and VO₂(200), suggesting the presence of in-plane rotation variants [5]. Temperature-dependent XRD and electrical measurements were done to confirm IMT behavior. A comprehensive study on the epitaxial orientation relationship between these variants investigated by X-ray diffraction and electron microscopy (HREM and SAED) and IMT characteristics will be discussed at the conference.<br/>[1] A. Joushaghani, “Micro-and nano-scale optoelectronic devices using vanadium dioxide,” 2014.<br/>[2] Xin, Yun, et al. "Phase-transition-induced superior ultraviolet photodetection of a ZnO/VO 2 bilayer." <i>Journal of Materials Chemistry C</i> 8.33 (2020): 11399-11406.<br/>[3] Vura, Sandeep, et al.<i> ACS Applied Electronic Materials</i> 3.2 (2021): 687-695.<br/>[4] Lee, Shinbuhm, et al. <i>Applied Physics Letters</i> 105.22 (2014): 223515.<br/>[5] Grundmann, et al. <i>Physical review letters</i> 105.14 (2010): 146102.