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Novel Resistance Switching Mechanism in SrCoOx Thin FIlms 원문보기

  • 저자

    Octolia Togibasa Tambunan

  • 학위수여기관

    HANKUK UNIVERSITY OF FOREIGN STUDIES. GRADUATE SCHOOL

  • 학위구분

    국내박사

  • 학과

    물리학과

  • 지도교수

    정창욱

  • 발행년도

    2014

  • 총페이지

    138 p

  • 키워드

    strontium cobaltite SrCOOx thin film topotactic transformation water electrolysis resistance switching novel mechanism;

  • 언어

    eng

  • 원문 URL

    http://www.riss.kr/link?id=T13539056&outLink=K  

  • 초록

    Novel Resistance Switching Mechanism in SrCoOx Thin FIlms The crystal structure of strontium cobaltite (SrCoOx) has been known to undergo topotactic phase transformation between two distinct phases, i.e. insulating brownmillerite (SrCoO2.5) and conducting perovskite (SrCoO3-) depending on the oxygen content. Reversible topotactic phase changes between brownmillerite phase of SrCoO2.5 and perovskite phase of SrCoO3- were reported in bulk samples using a liquid-electrolyte-based electrochemical cell, as well as in thin-film samples via ex-situ chemical oxidation, in-situ high oxygen-pressure annealing, and ex-situ low-temperature annealing under suitable gas conditions. Whereas a reversible change between an insulating (HRS) and a conducting (LRS) have been understood in terms of resistance-switching phenomena. In this work, we study whether the SrCoOx film could undergo a reversible transition from an insulating to a conducting state and vice versa, triggered by an external electrical bias voltage. The resistance-switching behavior has not been reported for SCO materials. The SrCoOx film strongly favors the brownmillerite phase of SrCoO2.5 instead of perovskite phase of SrCoO3- on a SrTiO3 (001) substrate due to its low lattice mismatch. Therefore the phase transformation has its own retention. The phase transformation from brownmillerite SrCoO2.5 film to perovskite SrCoO3- film on SrTiO3 (001) substrate through electrolysis process was clearly observed. The out-of-plane lattice constant of the electrolyzed film was reduced from 0.395 nm to 0.389 nm, which is close to the lattice constant of SrCoO2.9 film. The film resistance reduced from 200 M to 15 k, indicated the film changed from insulator to metal state. The phase transformation successfully overcame the large lattice mismatch. Furthermore, we fabricated the Au/SrCoO2.5/SrRuO3/SrTiO3 (001) devices to study the resistance switching phenomena. The bipolar switching behavior from the Au/SrCoO2.5/SrRuO3 memory cell was clearly observed, together with the observation of forming voltage lower than set voltage (VF


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