Resistive Switching Effect In NiO/Nb:SrTiO₃ Heterostructures

Recently,resistive switching effect has attracted widely attention.Resistive Random Access Memory?RRAM?which is based on the resistive switching effect has been considered as one of the most powerful candidate of next generation non-volatile random access memory.It has advantages of high density of integration,high speed of reading/writing process,low cost of fabrication and compatible with CMOS integrated process.A thorough understanding of its underlying mechanisms helps to get a better design as well as enhance the performance of devices in application.When integrating the resistive switching memory cells into crossbar array structures,sneak current problem is a severe issue.It can cause the misreading of data as well as limit the integration scale so that needed to be solved appropriately.Recently threshold switching-based selective devices have been considered as one of the possible solutions to surpress sneak current.NiO is one of the most promising materials in resistive switching effect field.We studied the threshold switching effect with the potential to solve sneak current problem and the bipolar resistive switching effect in NiO/Nb:SrTiO₃ heterostructure.The main work includes two parts as follows:NiO/Nb:SrTiO₃ heterostructures were fabricated using pulsed laser deposition techenique and magnetron sputtering techenique.By current-voltage measurement,the structures show threshold switching behavior under positive voltage sweeping and no resistance states change under negative voltage sweeping.Unidirectional threshold switching effect was observed on the Au/NiO/Nb:SrTiO₃ structure.We measured the current-voltage and capacitance-voltage characteristics of the fresh samples.Then we triggered the devices to resistive switching states and investigated the dependence of switching characteristics on the preparation parameters during NiO film deposition,the characteristics of capacitance states change and the influence of high tempreture on I-V behavior.After the data analysis,it is demonstrated that the mechanism of such unidirectional threshold swithing effect is due to the Schottky barrier formed between NiO and Nb:SrTiO₃ interface and the formation/rupture of unstable Ni filaments in NiO films.These investigations are useful for future applications to solve sneak current problem.In another aspect,we also observed bipolar resistive switching effect on the same structure of devices with relatively thinner NiO films.We got multiple high resistance states by tuning the amplitudes of negative voltage sweeping.Measurements and data analysis using AC impedance techenique were employed to study the mechanism.The results show that the resistive switching effect is originated from trapping/detrapping of the carriers located in NiO/Nb:SrTiO₃interface and the NiO film makes little contribution.The analysis of current-voltage behavior demonstrats that the conducting mechanism is dominated by the trap-controlled space charge limited current mechanism.The relaxation behavior of the low resistance state is also demonstrated.The relaxation index n increases exponentially with temperature which describes the properties of the traps.