RRAM electronics and Switching Mechanism
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RRAM electronics and Switching Mechanism Sheng Teng Hsu, and TingKai Li Department 5, Sharp Laboratories of America, 5700 NW Pacific Rim Blvd, Camas, WA, 98607 ABSTRACT The property of PCMO RRAM memory devices have been studied in terms of electrical pulse width, Pulse polarity, voltage ramping, film thickness, resistivity distribution, and temperature dependent of resistance. The PCMO material is deposited using MOD, PVD, or PLD process. The experimental results clearly indicated the resistance increase is due to localization of valence electrons. The narrow pulse induced resistance increase near the cathode indicated the localization of valence electrons is the effect of high density of excessive nonequilibrium electrons through the well known Jahn-Teller effect. High density of nonequilibrium electrons may also be induced by any other means such as displacement current, space charge limited current, SCLC, and radiation. High field intensity collapses the localized valence electrons and returns the device to the low resistance state. This is the intrinsic property of transition metal oxides. We expect all doped and un-doped transition metal oxides to exhibit resistance switching property. INTRODUCTION The binary transition metal oxide, MIM memory devices were discovered decades ago [1-7]. This device had not been a serious contender for large scale memory array application. After the publication of electric-pulse-induced reversible (EPIR) resistance non-volatile memory by Liu et al in 2000 [8, 9] the ternary MIM memory devices have attracted considerable interest [10 to 17]. Since the MIM memory resistor is suitable for high density random access memory (RAM) application the device is named RRAM. The ratio of the resistance at the high resistance state to the resistance at the low resistance state of a RRAM memory device can be larger than four orders of magnitude. The material Liu et al used is Pr0.7Ca0.3MnO3 other material such as SrTiO3 [10], Cr doped SrTiO3 [11], ZnxCd1-x S [12], and other doped and un-doped transition metal oxide also exhibit EPIR property. Beck et al [10] observed there is no crystalline-amorphous phase transition and metallic filaments do no occur in the low resistance state. They concluded it is a generic property of oxide in the presence of intrinsic defects. Consists partly on impurities having different oxidation states and vacancies and can form a series of states at various levels within the energy gap. Watanabe et al [11] attributed the resistance switching to carrier-injectioninduced degradation and carrier-emission-induced recovery of a Schottky barrier that is more resistive than the other. Liu et al [13] showed that the temperature dependent of the Au/PCMO/Pt/LAO RRAM resistance at high resistance state and that at the low resistance state is practically parallel in the temperature range of 23∞C to 100∞C. Baikalov et al studied the nonvolatile property of Ag/PCMO/YBCO memory devices [14]. They concluded that the switch takes place at the Ag-PCMO interface. The electr
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