Anantram, ManjeriDarling, Robert BWan, Zhenni2018-04-242018-04-242018Wan_washington_0250E_18352.pdfhttp://hdl.handle.net/1773/41711Thesis (Ph.D.)--University of Washington, 2018In this Ph.D. work, the resistive switching effects of vanadium pentoxide (V2O5) thin films are extensively explored and investigated. Contrary to conventional Flash memory devices where the information is stored by the electrons in the floating gate (FG), emerging memory devices employs the resistive switching effects of metal-insulator-metal (MIM) devices in which the information is stored in the location of atoms, which determines the high or low resistance state. Both reversible and irreversible resistive switching are discovered for the first time in V2O5 based MIM devices and the switching effects are studied as a function of metal contacts and environment, which play an important role in determining the device characteristics. Two conductor materials, chromium and indium tin oxide (ITO), are mainly investigated and the mechanisms for both irreversible and reversible switching are addressed. The dependence of switching effects on testing environment is enabled by building a vacuum test chamber. The devices are tested in a variety of gases environment and the role of intercalated H2O molecules in enabling the resistive switching is established. Resistance change is attributed to reduction of valence states of vanadium at electrode/V2O5 interface resulting from the electrochemical reactions when a voltage bias is applied. Reversibility of the switching is determined by whether the electrode material has the capability of temporarily storing oxygen ions. V2O5 xerogel film synthesized by sol-gel process experiences drastic atomic structural change during post annealing process, resulting in significant impact on resistive switching characteristics. X-ray diffraction analysis reveals that -phase V2O5 forms at bottom V2O5/ITO interface while -phase V2O5 forms at top V2O5/ITO interface. The presence of intercalated H2O molecules is essential for the reversible switching to occur. Ab initio calculations prove that the enlarged interlayer spacing in V2O5 xerogel significantly reduces the formation energies of oxygen vacancies, thus enabling the creation of mobile oxygen ions. In order to make the synthesis of V¬2O5 thin film more compatible with modern IC fabrication processes, thermal evaporation is employed for V2O5 deposition. Reversible bipolar switching is preserved and the stability of I-V characteristics over annealing temperature has been improved. DFT calculations are performed to simulate the amorphous V2O5 structure generated by melt-quench process using ab initio molecular dynamics technique. Formation energies of oxygen vacancy is also reduced in amorphous V2O5. Degradation of V2O5 film due to spontaneous reduction of vanadium oxide with presence of intercalated water molecules has been suppressed.application/pdfen-USnoneBipolar SwitchingOxygen VacanciesReRAMsVanadium PentoxideElectrical engineeringMaterials SciencePhysicsEngineeringThesis