Phase transformation properties and stress changes in V1-xMx(W, Cr)O2 thin-film libraries
Xiao Wang, Ruhr-Universität Bochum, Bochum, GermanyDetlef Rogalla, Ruhr-Universität Bochum, Bochum, GermanyAlfred Ludwig, Ruhr-Universität Bochum, Bochum, Germany
VO2 film undergoes a semiconductor-to-metal transformation at a critical temperature Tc, which is accompanied by crystallographic structure change from the monoclinic phase (M1) to rutile phase (R). Due to the strain change of up to 1% along the rutile axis and high Young’s modulus of about 140 GPa, high stress change in the thin film-substrate combination is associated with the phase transformation, which make the VO2 promising in application of micro/nano-actuators. In present study, V1-xWxO2 and V1-xCrxO2 thin film libraries were fabricated by reactive co-sputtering, and high-throughput characterizations of their compositions, crystalline structures, transformation properties and stress changes were performed. In the V1-xWxO2 library, the evolution of crystalline structure from M1 phase to R phase was observed at room temperature as the W amount increases from x=0.007 to 0.044. Stress changes across the phase transformation decrease from ~700 MPa to ~250. In V1-xCrxO2 libraries, the crystalline structure evolves from M1 to T then to M2 phase as Cr amount increases from x= 0.008 to 0.128. The stress changes increase from ~900 MPa to ~1250 MPa with addition of Cr. In addition, the effect of microstructure of the thin films on the stress change was studied. Tc decreases with W in V1-xWxO2, while it increases with Cr amount in V1-xCrxO2. A phase diagram of V1-xMx (W, Cr)O2 was assessed in dependence of temperature and concentration of W and Cr.