Study Of Threshold Selector Element For Memristor Array Application

Memristor possesses the advantages of high integration,high speed and low power consumption,which makes high-density crossbar memristor array promising in the non-volatile memory,in-memory computing and neuromorphic computing.Nonetheless,sneak-path current coexisting in the crossbar array prohibits the realization of large scale array,which is one of the bottle-neck for memristor application.In order to break through the bottle-neck,this paper aims at the threshold switching selector and carries out study on device theory,design,fabrication and characterization to provide a high-performance threshold switching selector scheme.The contents include:Chapter 2 gives a thorough literature review of various selectors based on the research status and analyzes the merit and demerit of each kind.Firstly,crossbar memristor array,sneak-path current and solution are briefly introducted to elicit the significance of selector.Meanwhile,the ideal properties of selectors are proposed to guide the subsequent research.Secondly,continuous current selector and is reviewed.Thirdly,threshold switching selector is reviewed.Lastly,and there exists bottle-neck according to the simulation results,which is not suitable for large scale memristor array.Meanwhile,threshold switching selector is comparing with continuous current selector and is chosen as the study direction.Chapter 3 proposed a design rule for threshold switching selector by simulating the crossbar array integrating memristor and threshold switching selector.It can realize the selection method of selector parameters on account of specific memristor.Firstly,array architecture and simulation frame are discussed in detail.The voltage scheme is ordinary1/2 or 1/3 and the worst scenario in crossbar is considered in simulation,which is implemented with matrix manipulation in matlab.Secondly,the device model of 1S1 R cell is discussed,including memristor model,selector model and 1S1 R model.Lastly,the design rule is proposed.Under ideal condition,the OFF-and ON-resistance of selector is determined to assure the minimum impact of sneak-path current and accurate operation.Then,regarding to the variation of threshold voltage in actual devices,the adverse impact is analyzed and approriate range is determined in different cases of resistance.Chapter 4 studied the design and fabrication process of programmable metallization cell with threshold switching characteristics based on SiTe material.It foucsed on the influence of annealing process and multi-structure on the device perfomance improvement.Firstly,the design scheme is demonstrated in detail,including choice of material,structure design.Secondly,it introduced the fabrication process flow and process control.The representation is utilized to check if it conforms to the design.Thirdly,PMC selector devices are tested and compared.It revealed that the PMC selectors with volatile threshold switching are realized based on SiTe material.Meanwhile,it helped increase the selectivity and endurance with annealing process by traps annihilation or reduction.Furtherly,the selectivity is increased more with multi-layer structure and the variation decreases as well.The reason for performance improvement is fully analyzed.Finally,it is compared with other PMC selectors published before.Chapter 5 studied the design and fabrication process of ovonic threshold switches with threshold switching characteristics based on Se-rich GeSe material.It foucsed on the influence of annealing process and Nitrogen doping on the device perfomance improvement.Firstly,the design scheme is demonstrated.From the theory of OTS deivces,the atom structure stability is enhanced by adjusting the element ratio.Meanwhile,the device structure and process is brief introduced.Secondly,it briefly introduced the fabrication process flow and test setup.Thirdly,OTS selector are electrically tested.It revealed that the OTS selectors with volatile threshold switching are realized based on GeSe material.Meanwhile,it helped increase the selectivity and endurance with annealing process by traps annihilation or reduction.Furtherly,the variation decreases by doping N into GeSe to increase the atom structure stability.Finally,it is compared with other OTS selectors published before.