Flexible Temperature Sensor Based On Multicomponent Doped Vanadium Dioxide Thin Film

Wearable and pliant temperature sensors are extensively employed for continuous and long-term health monitoring due to their flexibility,exceptional biocompatibility,lightness,and heightened sensitivity.The sensitivity of temperature sensors is contingent on the resistance temperature coefficient（TCR）of the sensitive layer.Vanadium dioxide（VO₂）thin films have been extensively used in temperature sensing domains due to their high TCR and metal-insulator transition（MIT）characteristics.However,the current VO₂thin film utilized in the realm of flexible wearables still faces certain unresolved issues.Firstly,the TCR of the membrane phase transition temperature stage is considerably high,yet significantly different from the human body temperature.Secondly,the VO₂ film exhibits thermal lag during the temperature rise and temperature drop process,leading to inaccurate sensor measurements.Moreover,the existing flexible method of VO₂ thin film has high complexity and low repeatability,thereby making it challenging to achieve large-scale production.In order to solve the above problems,a multi-component doped VO₂ thin film with phase transition temperature close to human body temperature and zero thermal hysteresis was prepared on fluoropolymica by co-doping tungsten（W）and titanium（Ti）ions.By using fluoropolymica with layered structure as the substrate,the flexibility of VO2 film was realized,and a flexible temperature sensor with high sensitivity was prepared.Firstly,undoped VO₂ films with resistance mutations of nearly 5 orders of magnitude were prepared by optimizing polymer-assisted deposition（PAD）.On this basis,tungsten（W）and titanium（Ti）co-doped VO₂ films with different concentrations were prepared on fluoropolymica substrate,and the phase morphology of the films was analyzed.The results show that W and Ti ions in the form of W⁶⁺and Ti⁴⁺are successfully doped into VO₂ film lattice to form solid solution,and the grain size of co-doped film decreases.The electrical performance test results show that the thermal hysteresis loop width decreases with the change of phase transition temperature.In addition,the effect of different doping concentrations of W and Ti ions on the phase transition temperature,thermal hysteretic and TCR of VO₂ thin films were discussed.The doping changes the crystal structure and electronic structure of the film.Specifically,the V-V bond of the low-temperature monoclinic VO₂ film is greatly changed by W doping,and the high-temperature rutile phase is stabilized.Ti doping significantly changes the V-V bond of the rutile VO₂ film and stabilizes the monoclinic phase.The energy barrier between codoped monocline phase and rutile phase decreases and the number of defect nucleation increases,which significantly reduces the change of phase transition temperature and the width of hysteresis loop.In this work,multicomponent doped VO₂ films with high TCR（5.74%/K）,zero thermal hysteresis and phase transition temperature close to human body temperature were obtained.A flexible temperature sensor based on multi-component doped VO₂ films was successfully fabricated by mask technology and water-assisted method using the special lamellar structure of fluoropolymica substrate which can be peeled and thinnable.The linearity of the sensor is 99.7%,the human temperature response time is 8 s,the recovery time is 40 s,has a good temperature cycling stability and bending stability.