Study On Preparation And Properties Of Vanadium Dioxide Ferroelectric Field Effect Transistor

The semiconductor industry is developing rapidly,and the characteristic dimensions of transistors follow exponentially decreasing according to Moore's Law,from the micron order to the current nanometer scale,but further development is inherently limited.Due to the reversible phase transition property of vanadium dioxide?VO₂?,the conductivity can be mutated by 4-5 orders of magnitude in phase transition.In recent years,researchers have proposed a VO₂-based Mott transition field effect transistor.At present,some researches have been made on VO₂ FET,but there are still many disadvantages.For example,devices using SiO₂,TiO₂,etc.as gate insulating layers have poor modulation,and ionic liquids have good gate modulation but are easily disabled in air and not good for device applications.In order to solve the above problems,this thesis attempts to use VO₂ as the channel material,and introduce a high dielectric and polarized lead zirconate titanate?PZT?ferroelectric thin film as the gate insulating material to construct the FET device structure and research on the output performance and phase transition regulation of the device.The indirect transfer method was used to construct VO₂ devices for the previous results.When the VO₂ film was prepared by pulsed laser deposition method on silicon wafer,the effects of deposition atmosphere and annealing process on VO₂ film were studied.The phase change performance of VO₂ film obtained by characterization test was good,and the phase transition property and cycle stability were good too.On this basis,the transfer of VO₂ film to PZT substrate was carried out,and the results showed that the feasibility was poor.Therefore,the direct growth method was studied.The phase structure,phase transition property,film morphology and safety of the VO₂ film deposited directly on PZT by three methods were compared.The results show that the VO₂ film with dense structure,excellent phase transition property and good cycle stability is prepared by pulsed laser deposition method for the first time,which lays a foundation for the device construction.And this experimental method is also suitable for the development of other thin film devices.Subsequently,VO₂/PZT/Nb-STO based field effect devices were successfully developed by electron beam exposure and metal evaporation,and the modulation performance and phase transition regulation performance of the device were tested.The experimental results show that the output characteristics of the VO₂ device are good and have obvious gate-voltage modulation effect.The modulation ratio of the device is over 80%under the lower gate bias,and the response is fast and there is no time lag effect.On this basis,the effect of the thickness of the gate insulating layer PZT film on the device performance is studied.The PZT with a thickness of 200 nm has a small leakage current and the best modulation performance.Then the effect of field effect modulation on the phase transition temperature of VO₂ material is studied.In the insulation phase,the resistance decreases obviously,the temperature hysteresis narrows,but the change of phase transition temperature point is less affected.At the same time,the phase change mechanism is also explained.The main reason is that the gate bias affects the ion movement in the crystal structure,which leads to an increase in electron concentration and thus affects the conductivity change of VO₂.By using a high dielectric constant PZT material as the gate insulating layer,a stronger electric field effect can be provided at a lower voltage,so that the modulation effect of the final device is superior to that of other materials,and avoided the shortcomings which ionic liquid gate is prone to failure,and laid the foundation for deviceization of VO₂ FET.