Study On Asymmetric Switching Speed Of Ferroelectric And Conventional Schottky Junction Bipolar Resistors

In today's society,people's demand for high-speed,high-density and non-volatile new high-performance memory is becoming stronger.Currently used flash memory is close to the physical and technical limits.The next generation of new memory includes ferroelectric memory,magnetic memory,phase change memory,and resistive memory.Among them,ferroelectric memory has been commercially applied,but the destructive readout and storage density are difficult to significantly improve,making it difficult to mass-produce.As an important candidate for non-volatile memory-resistive memory,resistance storage requires less area and is easy to achieve ultra-high density storage,and has the advantages of low power consumption,high speed and non-destructive readout.However,in general,the two main microscopic mechanisms of metal oxide resistive phenomena involve imperfections and chemical changes in the material,which will cause reliability problems such as data retention and fatigue.In recent years,researchers have discovered that the transition of ferroelectric polarization is accompanied by changes in the high and low conductance.This kind of iron-resistor change effect based on polarization flipping is particularly favored because the polarization reversal does not cause chemical changes and the resistance at low voltage Read-out is non-destructive without the need for recovery circuits and reduced power consumption.With ultra-high switching speeds and high switching ratios,it is easy to achieve high-density storage and is expected to be the next generation of non-volatile memory materials.We have successfully fabricated Au/Nb:SrTiO₃/In and Au/BaTiO₃/Nb:SrTiO₃/In devices on a0.7%wt doped monocrystalline Nb:SrTiO₃ substrate using sputtering and laser pulse deposition techniques,and passed X-ray diffractometers and atomic force microscopy were used to characterize the Crystal structure and surface topography of the BTO films.The electrical properties of the device were characterized using a Keithley Model 2400 SourceMeter,an impedance analyzer Aglient 4294A,an Aglient33250 function signal generator,and an oscilloscope.There are many interesting phenomena,such as large on/off ratios,bipolar resistance switches,and continuously adjustable resistance states.We focused on the research and analysis of the asymmetrical resistance phenomenon.Generally,the resistive switching based on electronic processis supposed to be much faster than those based on ionic process.On a particular device,the speed for SET?high resistance state to low resistance state transition?and RESET?low resistance state to high resistance state transition?operations is similar.However,asymmetric resistive switching effectsare observed in Au/NSTO/Insystem.The process of electron trapping/detrapping is much faster than the drift of oxygen vacancies,so the SET transition?HRS to LRS?caused by positive bias is much faster than RESET transition?LRS to HRS?caused by negative bias.This fast SET and slow RESET switching is promising for some special application.Asymmetrical resistance switching is also observed in the BaTiO₃/Nb:SrTiO₃ Schottky junction.Specifically,the SET transition from high to low resistance state is in 10 ns under+8 V bias,while the RESET transition from low to high resistance state is in the range 10⁵ ns under-8 V.The process of electron screening is much faster than that of oxygen vacancies,so the SET transition?HRS to LRS?induced by positive bias is much faster than RESET transition?LRS to HRS?induced by negative bias.Furthermore,this switch exhibits fast SET and slow RESET transition,which may have potential applications in some special regions.