Study Of The Resistance Switching Effect Based On The Schottky Barrier

The current memory technology based on a floating gate structure, so called Flash, its sizedecreasing year by year following the Moore’s law, is viral to semiconductor integrated circuitand information technology. However, Flash memory is rapidly approaching to its physicallimit due to the tradeoffs between the high speed, low power operation and long time retention.In order to extend Moore’s law for memory applications, several emerging nonvolatile memorytechnologies have attracted extensive attentions in the academy and industry. One of them,based on the resistance switching（RS） effect, due to simply structure, excellent scalability, lowpower operation, fast speed and compatibility with standard CMOS process, is considered thegood candidate as the next generation random access memory. But because of the various kindsof resistance switching materials and several conductive models, the mechanism has notinterpreted theoretically.This paper has fabricated metal （Ti, Ag and Au）/Nb:SrTiO₃（NSTO） device structures bylithography as well as magnetic controlled sputtering and investigated the resistanceswitching（RS） effect mechanism based on the Schottky barrier through the methods of electricfield induced and thermal treatment substrates. The main results achieved in this dissertation arelisted as follow:First, the measure instruments are linked with computer by the virtual instrument （VI）technology. With the low temperature equipment, the RS characteristics test system is designed.And the LabVIEW software is employed to program operating panel of test system, includingCurrent-Voltage （I-V） test, Temperature dependence of resistance （R-T） test, SET&RESET test,P/E pulses test and multilevel memory pulses test.Second, the two commercially available0.7wt%Nb-doped SrTiO₃（NSTO） single crystals,as substrates, are employed and deposited Ti, Ag and Au thin films by lithography and magneticcontrolled sputtering technique to fabricate the Ag/NSTO/Ti and Au/NSTO/Ti structures. With the RS characteristics test result and referred to the papers reported, the RS effect originatesfrom the Schottky barrier at the interface of Ag/NSTO and Au/NSTO.For the Ag/NSTO/Ti device, there were a lot of oxygen vacancies （Vo2+） assembling at theinterface of Ag and NSTO as the trap site. Applying with the forword and reverse voltages, thetrap site traps or releases the electrons, which change the depletion layer width in the Schottkybarrier and result HRS and LRS. In addition, with the multilevel memory pulses induced, thejunction of Ag and NSTO has the multi-switch resistance states effect. Considering the R-Tcharacteristics of HRS and LRS with both semiconductor-like behavior, the mechanism ofmulti-swith memory may be explained by the change of depletion layer width of Schottkybarrier due to the different number of electrons trapped or detrapped by oxygen vacancy （Vo2+）in depletion region.For the Au/NSTO/Ti device, there are a lot of oxygen vacancies assembling at the interfaceof Au and NSTO as the trap site, much like the Ag/NSTO interface. However, the Au/NSTO inthe HRS has the metallic behavior and no multi-switch resistance effect. The phenomenon isdescribed as that, in the LRS, oxygen vacancies （Vo2+） as the trap site at the Au/NSTO interfacereleases the electrons, resulting the reduction of Schottky barrier height and electron tunnelingeasily. In the HRS, the trap site traps electrons in saturation.At last, the NSTO substrates are annealed with different thermal treatment and the interfaceof metal Ag and NSTO are measured by the RS characteristics test system. The results showthat the interfaces of Ag and NSTO, with nonannealed and annealed treatment in air under the400oC and700oC, all have the large hysteresis. And with the temperature of thermal treatmentincreasing, the rectifying ratio of I-V curve is larger. In P/E pulses test, compared with theinterface of Ag and NSTO substrate annealing under400oC, the ratio of HRS and LRS under700oC is larger. Besides that, the stabilization is obtained in the LRS with the thermal treatmentunder700oC.