| Owing to its rich structure,electrical,magnetic and optical characteristics,functional oxides have always been a hot issue of material science,physics and chemistry,and have shown broad application prospects in electronic information industry.The functionality of functional oxides is reflected not only in its unique electrical,optical,and magnetic properties,but also in the controllability of these physical properties.The control of physical properties of functional oxides can not only improve its performance,but also help us to understand the relationship between its physical properties and lattice structure or electronic configuration.Electric field control of physical properties,that is to change the electrical,magnetic and optical properties of materials via the electric field generated by an applied voltage,can realize continuous and reversible control of physical properties of functional oxide films.It's a premise for functional oxides to realize functional devices.The electric field can affect materials' physical properties by modulating their carrier concentration through electrostatic induction,which can not only change the electrical resistance of most materials but also affect the carrier-mediated magnetic and optical properties of some materials.The electric field can also realize non-volatile control of physical properties by driving ion migration,which is an electrochemical redox process.The electric field control based on ion migration greatly enriches the control of physical properties of functional oxides,and achieves significant modulation of electrical,magnetic and optical properties in many materials.The structural phase change,metal-insulator transition,ferromagnetic-antiferromagnetic transition,and changes in light transmittance that accompanied with ion migration not only demonstrate the high efficiency of the ion-migration-based control,but also spawn many functional devices,such as resistive(magnetic)switching transistors,resistive switching random access memories(RRAM),electrochromic devices,artificial synapses,etc.In this thesis,we prepared several functional devices with different types of oxide films.Ion-migration-induced significant modulation of the films' physical properties was demonstrated.The main results are summarized as follows:(1)Electric field control of ferromagnetic metal-antiferromagnetic insulator transition of SrCoO2.5 film via O2-migration.Electric-field modulation of the oxygen nonstoichiometry in strontium cobaltite has been realized using a flexible solid-state electrolyte at room temperature,which allow a reversible phase transition between insulator-antiferromagnetic brownmillerite-SrCoO2.5 and metal-ferromagnetic perovskite-SrCoO3-?.Based on the results obtained from a variety of comparative experiment performed in different atmosphere,it can be concluded that the variation of oxygen content in strontium cobaltite film is caused by the electrochemical redox reaction between the trace water in electrolyte and strontium cobaltite.In addition,thin film self-powered ultraviolet(UV)photodectectors based on ZnO/SrCoOx heterojunction were fabricated on flexible polyimide substrate at room temperature Amorphous SrCoOx film,for the first time,was used as the p-type semiconductor to construct p-n junction with n-type ZnO.This device exhibits a prominent performance for UV light detection.Moreover,a long-term stability and a good flexibility were demonstrated.These results indicate that this room-temperature processed flexible UV detector can be a promising candidate for energy-efficient and wearable optoelectronic devices.(2)Electric field control of tri-state phase transition of VO2 film via H+migration.Electric-field modulation of the H+concentration in VO2 film has been realized using a flexible solid-state electrolyte at room temperature,which allow a reversible tri-state phase transition from insulator VO2 to metal HVO2 and to insulator HVO2.The strong electric field induced at the interface is sufficient to extract and reinsert H+ into the underlying VO2 film depending on gating voltage polarity.We further explored the dynamic extraction process of H+in VO2 film by cycling R-T test,which confirmed the key role of H+in the phase transition process.Based on the results obtained from structure,morphology,and electrical transport measurement,the repeatable structure and conductivity transitions accompanied with H+migration were demonstrated.Moreover,the cumulative resistance modulation and nonvolatile memory effect under impulse gate voltage were observed.(3)Electrochromism of transparent conductive film induced by electric field driven Li+ migration.Based on a typical lithium-ion half battery structure,an electrochromic cell with fluorine-doped tin oxide film as electrochromic layer was fabricated.The light transmittance of FTO was controlled via guided motion of Li ions.The device can be reversibly switched between a deeply colored state and an uncolored state via the inserting/extracting of Li ions in the FTO film.Based on the results obtained from structure,morphology,electrochemistry and in-situ UV-visible measurement,the proper operating voltage window was obtained and the reversible and stable light transmittance modulation was demonstrated.Our results indicate that FTO is a promising electrochromic active material with high color efficiency and low cost(4)Multifunctional phototransistor controlled by electric field regulation of F-distribution.ZnO film was deposited on LaF3 single crystal substrate to construct a phototransistor with source,drain,and gate three-terminal electrodes.The LaF3 substrate is used as dielectric layer.Owing to the regulation of F-distribution at the interface between ZnO and LaF3 driven by gate voltage,the strong electric field induced at the interface is sufficient to realize huge adjustment of optical and electrical properties of ZnO film.By employing electrical transport and photoresponse measurements,the performance of the device as a non-volatile field effect transistor,an artificial synapse device with controllable cumulative resistance modulation,and a voltage controllable UV detector were demonstrated.More than four orders of resistance modulation was achieved reversibly.Light impulses induced resistive memory effect can be controlled by gate voltage.Photoresponsivity of 25 mA/W was obtained at a gate voltage of-5 V for UV detection. |
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