Fabrication And Properties Of Transparent Flexible ZnO-based ReRAM

With the continuous development of semiconductor technology,especially after entering the 22 nm process,the development of traditional memory such as Si-based flash has been limited because of a series of problems caused by the device scaling down,so new non-volatile memory was investigated to find a way out.ReRAM plays an important role in non-volatile memory because of its simple structure,fast switching speed and better information retention.As a common semiconductor material,ZnO has received extensive attention because of its good performance in optics,electricity and piezoelectricity,etc.Meanwhile,ZnO-based ReRAM has been developed rapidly in recent years.In this paper,we will focus on transparent,flexible ZnO-based ReRAM research,and study the piezoelectric effect on the performance of the device.In this paper,ZnO thin films were deposited by DC magnetron sputtering.The amorphous TiO2 thin films were deposited by atomic layer deposition,the A1 and Au electrodes were prepared by thermal evaporation.X-ray diffraction analysis was used to study the crystal structure of the film,Fourier transform infrared spectrometer was used to infer the compound structure,scanning electron microscopy and atomic force microscopy were used to analyze of the surface topography,the transmission spectra of the films were measured by UV-visible spectroscopy,valence state of elements on the surface of thin film was analyzed by X-ray electron spectrum analyzer,I-V characteristic tester,combined with self-made simple piezoelectric device to analyze the electrical properties.The main conclusions are as follows:(1)The Si/SiO2/Al/ZnO/Al structure was fabricated.ZnO nano-films grow along c-axis orientation and have a smooth and dense surface.The asymmetrical peak of O 1s indicates that the sputtered ZnO thin film leads to a nonstoichiometric ratio due to oxygen vacancies.I-V characteristics of Si/SiO2/Al/ZnO/Al were investigated.The resistive switching mechanism is explained by the filament model based on the LRS and HRS.The resistance ratio between the HRS and LRS is more than 104,which has good information retention characteristics,and no degradations occurred in 300 cycles.(2)PET/ITO/ZnO and PET/ITO/ZnO/TiO2(ZnO as a barrier layers)were fabricated.The two devices are more flexible,transmittance was above 84%and 56%in visible light,respectively.Both ZnO and TiO2 films have good crystallinity.The XPS depth profile analysis of Ti 2p and O 1s shows that the oxygen vacancies in the TiO2 film are homogeneously distributed.PET/ITO/ZnO/TiO2 device has bipolar switching characteristics.TiO2 film determines the conductive mechanism.The number of switching cycles of the two devices is low,but the device information retention characteristics are better.(3)The effect of piezoelectric effect on the resistive switching characteristics was investigated by self-made simple piezoelectric device.Positive and negative 0.5%strain within the device show stable resistive characteristics.The tensile strain increases the switching voltage of the device,while the compressive strain reduces the switching voltage of the device.The internal mechanism of switching voltage variation under piezoelectric is analyzed by using contact potential barrier.