Research On Transparent Capacitor Electrode Based On Transition Metal Compound

With the rapid development of science and technology,the transparent electronic field are required to update,such as transparent,flexible and wearable electronic products.Displays account for a large proportion of transparent electronic devices.Traditional displays rely on a backlight that consumes a lot of power.When technology comes into reality,the application of fully transparent displays brings a new human-computer interaction.Transparent display using the environment as a backlight,not only can reduce energy consumption,but also can bring convenience to life.Thin film transistors（TFT）and thin film capacitors（TFC）are important components in the pixel drive circuit of the display.Research and development of transparent and high-performance capacitors has become a problem facing the current,and has a certain commercial value.Therefore,this paper studies the electrode materials of transparent capacitors,mainly focusing on the following three parts:（1）Research has been carried out on the electrode materials of transition metal compounds nickel nitride（NiN）,titanium nitride（TiN）,nickel oxide（NiO）and aluminum-doped zinc oxide（AZO）.The basic optical and electrical properties of the films were studied by reactive magnetron sputtering and atomic layer deposition with different working gas ratios.Through characterization and analysis,it is found that different reaction gas contents have certain effects on the resistivity,growth rate,transmittance,crystal structure and composition of the film.The optimum sputtering conditions were found through the demand of transparent conductive film.The deposition conditions of NiN films are as follows:gas pressure is 3 mTorr,sputtering power is 100 W,nitrogen content ratio is 47%.The deposition conditions of TiN films are as follows:gas pressure is 0.85 mTorr,sputtering power is 75 W,nitrogen content ratio is 8%.The deposition conditions of NiO films are as follows:gas pressure is 2 mTorr,sputtering power is 75 W,oxygen content ratio is 65%.（2）Based on the optimal sputtering conditions of the deposited films,the corresponding transparent flat capacitor structures were prepared.ITO material was selected as the bottom electrode and Al₂O₃material was selected as the medium dielectric layer.Firstly,when TiN is used as the upper electrode,the capacitance density is stable at both low and high frequencies.The capacitance density is almost constant in the range of 1 k Hz to 1 MHz,and the capacitance density is 4.6 fF/μm².The leakage current density is 2.4×10^-6A/cm²at the voltage of 1 V.The results of the variable temperature experiment show that when the temperature rises from room temperature to 240℃,the capacitance density is not affected at low frequency,and only part of the loss occurs at high frequency,which means that the performance of the capacitor is not significantly degraded at the temperature below 240℃,and the high temperature resistance is good.Secondly,NiO is used as the top electrode material.The transmission of the capacitor in the visible light range is more than 70%,and the capacitance density has a good low-frequency stability.The capacitance density is about 4.2 fF/μm²,but the leakage current performance is good.Finally,when AZO is used as the upper electrode,its transmittance in the visible light range reaches more than 80%,which is the best choice for transparent capacitors electrode.The capacitance density is about 8.1 fF/μm²,and the low frequency and medium frequency stability is good.At 300k Hz,the leakage current density is as low as 3.06×10^-7A/cm².（3）The electrode layer and dielectric layer of transparent flat capacitor were optimized.The effects of two composite electrodes,AZO/AgNWs/AZO and NiO/AgNWs/NiO were studied on the performance of the capacitor.the results show that composite electrode reduces the sheet resistance of the electrode,which significantly improve the high frequency stability of the device.The capacitance density of the NiO/AgNWs/NiO composite electrode capacitor decreases only when the frequency is 300 k Hz,the capacitance density of the capacitor with the AZO/AgNWs/AZO compound electrode hardly changes in the frequency of 1 k Hz to 1 MHz,and the device still maintains a low leakage current level of 10^-7orders of magnitude.By using Al₂O₃and Al N double dielectric layer,the results show that the double dielectric layer significantly improves the medium-high frequency stability of the capacitor,with no decrease in the capacitance density between 1 k Hz to 2 MHz until it slowly attenuate at 2 MHz,and reduced the leakage current by an order of magnitude to 3.4×10^-7A/cm² at 1V.