Titanium Oxynitride Thin Films And Their Applications In On-chip Microsupercapacitors

On chip microsupercapacitors(on-chip MSCs)have great value in application of various sensor systems embedded into the wireless Internet of Things(IoT),and therefore become one of the hot topics in the cutting-edge research of micro-energy technologies.For on-chip MSCs reported so far,their energy and power densities can be hardly improved simultaneously;and these two key indicators benchmarking the performance of devices are significantly lower than the requirements for practical applications.At the same time,their preparation techniques are incompatible with the processes of microelectronic integrated circuit and micro-electro-mechanical system(MEMs).It is unable to achieve the wafer-scale collective fabrication and monolithic integration with the other modules in microsystems.It is therefore desirable to develop a novel approach for on-chip MSCs,which should be fully compatible with the processes of microelectronic integrated circuit and has great potential to optimize the energy and power densities simultaneously.This thesis focuses on the study of on-chip MSCs.Firstly,according to the optimized Structure Zone Model(SZM),the microstructure and content of active materials in the thin-film electrodes were optimized by tailoring the nucleation and growth mechanism of thin films.The effects of deposition parameters on the chemical composition,crystal structure,microstructure,electrical and electrochemical properties of current collectors and electrodes were investigated systematically.It was established a relationship among the chemical composition,microstructure and macroscopic electrical and electrochemical properties of the films,which provides an important theory support for the preparation of high performance current collector and electrode materials.Secondly,based on the unique properties of TiOxNy thin films,a new method was designed for in-situ growing TiN current collector/TiOxNy electrode,which provides a new technical scheme for the preparation of high performance on-chip MSCs.Finally,based on the above results,sandwiched and interdigitated on-chip MSCs were fabricated.The electrochemical performances of the series and parallel arrays of on-chip MSCs were investigated systematically.The main conclusions are listed as follows:(1)TiN thin films with high density,low surface roughness and resistivity were grown by direct current reactive magnetron sputtering on Si substrates.The effects of deposition parameters such as substrate negative bias voltage,working pressure and substrate temperature on the microstructure and properties of thin films were studied in detail.The results show that when an optimized negative bias voltage was applied to the substrate,the abilities of atom diffusion,migration and nucleation on the film surface were improved.TiN films with a surface roughness of ?0.66 nm and resistivity of ?53.2 ?? cm can be grown over a wide range of working pressures and substrate temperatures.These superior performances can meet the critical conductivity requirement for the current collectors of on-chip MSC devices.(2)High performance TiOxNy film electrodes were prepared by direct current reactive magnetron sputtering on Si substrates.The chemical composition,microstructure,and properties of TiOxNy electrodes were investigated in detail as functions of the nitrogen flow rate,working pressure,substrate temperature,and deposition time.The results indicate that the increasing nitrogen flow rate was beneficial for enhancing the mass loading of film electrodes.The higher working pressure and the lower substrate temperature led to more porosity in film electrodes.While,the resistivity of the film electrodes increased significantly(>1000 ?? cm).The deposition time increased to obtain the required thickness for further improving the mass loading and porosity of electrodes.After optimizing the deposition parameters,the specific capacitance was two orders of magnitude higher than before.Power law dependence of the peak current on sweep rate in CV curves was introduced to analyze the charge-storage mechanism of film electrodes,and it was mainly dominated by the pseudocapacitive faradaic reaction.The faradaic reaction was possibly attributed to the continuous chemisorption of electrolyte cations on the surface of TiOxNy.Solid-state symmetric microsupercapacitors were fabricated by sandwiching PVA/KOH electrolyte between two TiOxNy electrodes.The energy and power densities of MSCs were 36.8 mWh cm-3 and 20 W cm-3,respectivity.After 10 000 cycles of continuous charge/discharge,the device showed excellent durability with negligible decay in capacitance.MSCs connected in series and parallel exhibited excellent performance for potential use in the electronic circuits.(3)The TiN current collector/TiOxNy electrode double-layer films were in-situ grown successfully on Si substrates by direct current reactive magnetron sputtering.The interdigitated on-chip MSCs were prepared via shadow masks.The results show that the resistivity of in-situ grown TiN current collector/TiOxNy electrode double-layer films were two orders of magnitude lower than the corresponding values for the single TiOxNy film electrodes.The specific capacitances between the two electrodes changed slightly.The highest scan rate of maintaining the capacitive characteristic of the CV curves was improved by two orders of magnitude.The RC time constant decreased from 4.65 s to 82.6 ms.It can be seen that the specific capacitance and charge-discharge response time of the film electrodes were synergistically optimized by using the in-situ growth process.The TiN current collector/TiOxNy film electrode MSCs with different interdigital width were prepared via shadow masks.With decrease in interdigital width,the highest scan rate of maintaining the capacitive characteristic of the CV curves increased from 300 to 1000 V s-1.The specific capacitance decreased with decreasing interdigital width.After 10 000 cycles of continuous charge/discharge,the interdigitated MSCs exhibited good cycling stability with negligible decay in capacitance.The highest energy and power densities of MSCs were 3.1 mWh cm-3 and 852 W cm-3,respectivity.The potential window of two devices connected in series increased to 2.0 V.The aforementioned superior performances show that the method of in-situ growth of TiN current collector/TiOxNy electrode films is sample and easy to operate which has important application values.It provides a new way to solve the problem that the energy and power densities of on-chip MSCs cannot be improved simultaneously.