Study On Energy Storage Performance Of ZrO₂-based Thin Film Dielectric Capacitors

Among the current electric energy storage technologies,dielectric capacitors have the highest power density compared with other energy storage technologies,such as electrochemical capacitors,and batteries.The quickly achieving charge and discharge of dielectric capacitors broaden application prospects,such as pulse power supply and medical equipment.However,low energy density limits its practical application.Dielectric material film formation is an effective method to improve its breakdown strength,which is also the development direction of pulsed power technology development and integrated circuit miniaturization.The dielectric thin film capacitors exhibit unique advantages in storing and releasing pulsed micro energy.At present,the energy storage of dielectric thin films is mainly concentrated in the ferroelectric thin film system of perovskite.Although these systems show excellent energy storage performance,their high deposition temperature is not conducive to device integration.This work selects high dielectric materials ZrO2 thin film as the research object.The main research contents and conclusions are as follow:1.The effects of the preparation process of ZrO2 and electrode materials on the properties of ZrO2 films were studied.The results showed that the ZrO2 films grown by reactive magnetron sputtering exhibited crystalline states when the thickness?50 nm.The breakdown strength of the films on ITO/glass were decreasing trend as the thickness increases.The ZrO2thin films growth by pulsed laser deposition,the polarization and breakdown strength of capacitors were influenced by oxygen flows.The dielectric constant of ZrO2 thin film capacitors decreases with the increase of oxygen flows and then remains unchanged,while the breakdown strength first increases and then decreases.The ITO electrode can make up for the problem that the breakdown strength of the film is too small under low oxygen flows.The 30nm thick ZrO₂ thin film crystallizes when the growth temperature is?300°C.The breakdown voltage decreases with the increase of temperature,especially for the sample at 400°C.Different metal materials Au,Ag,ITO and Al were used as upper electrodes to construct capacitors with various metal/oxide dielectric/metal sandwich structures.The breakdown strength of these devices under different bias polarities was studied.The results showed that:The breakdown electric field of ZrO2-based capacitors with ITO as bottom electrode is slightly larger than that of Pt electrode devices under negative bias.The breakdown strength of the device with Ag as the top electrode has obvious bias polarity dependence regardless of ITO or Pt acting as bottom electrode.And the breakdown electric field of Ag electrode device under positive bias is reduced by an order of magnitude.The different breakdown behaviors of the above devices can be explained by the migration and rearrangement of oxygen between the oxide electrode and the dielectric interface,the dissolution migration and reduction of the electrochemically active metal electrode,and the redox reaction between the chemically active metal electrode and the oxide interface,respectively.2.The ITO/ZrO2/ITO structure capacitor was designed.The effect of different ZrO2thicknesses on the breakdown and polarization of the device was studied.And the energy storage performance of the device with the best thickness was investigated.The results showed that the ZrO2 thin film with a thickness of 470 nm had the best breakdown strength up to 5.82MV/cm and high dielectric constant(polarization)characteristics.Therefore,the ITO/ZrO2(470 nm)/ITO structure device realizes high energy storage density(75.4 J/cm³)and efficiency(?88%),which was comparable to ferroelectric Hf O2/ZrO2 thin films and complex composition linear dielectrics thin films.The highly transparent properties make the device a potential application in invisible,transparent electronic circuits that require energy storage elements.The study found that a Sn Ox interface layer can be formed between the ITO electrode and the ZrO2 film.The interface layer can suppress the electron injection of the electrode and the carrier transport in the dielectric.It can also induce the interface polarization to increase the maximum polarization of the device.Thereby,the simultaneous improvement of breakdown strength and polarization is achieved.The extension of the thickness of ZrO2 film to 470 nm is beneficial to improve the total energy stored in the device.3.(TiO2/ZrO2)N(N is the number of cycles)multilayer film capacitors were designed to further improve the energy storage performance of ZrO2-based capacitors.The total thickness of the multilayer film was constant,and the number of deposition cycles was changed to adjust polarization and breakdown strength proporties of these devices.The experimental results confirmed that the interface of TiO2/ZrO2 can adjust the polarization and breakdown strength at the same time.The changing trend of the two parameters is synchronized.The device achieved the best overall performance when period number of the multilayer films was three,which obtained a breakdown strength of up to 6.7 MV/cm.Furthermore,the device achieved an energy storage density of up to 82.0 J/cm³ and an energy storage efficiency of 84.1%.The above ZrO2-based film capacitors are grown at room temperature.Compared with perovskite film materials,the composition and preparation process are simple and the cost is lower,which is conducive to enhancing the compatibility with semiconductor processes.The process can be well extended to the electronics of flexible polymer substrates,and their energy storage properties are competitive with Hf O2/ZrO2-based antiferroelectric thin films or linear oxide thin films with complex compositions.These capacitors hold great promise in the application of energy storage devices.The ZrO2 film also has a high band gap,which makes it have good transmittance in the visible light range,and the constructed dielectric capacitor has the potential for transparent electronics.