| Summary: | 博士 === 國立臺灣科技大學 === 材料科學與工程系 === 102 === Resistive switching random access memory (RRAM) has attracted great interest for the application in next generation nonvolatile memory. RRAM has gained significant interest in the past decade as one of the most promising candidates as a nonvolatile memory device due to its potential for high density integration, low operating power, fast switching speed, long data retention time, simple structure and compatibility with conventional CMOS process. However, the resistive switching (RS) mechanism is still under debate, and the devices have to be optimized before they can be used commercially.
In this work, RS characteristics and mechanism of multicomponent oxide (MCO) (ZrCuAlNi)Ox, Zr1-yCuyO2-3y/2 (ZCO), Zr1-rNirO2-r (ZNO) and amorphous ZrCuOk (a-ZCO) thin film-based memory devices are studied. MCO-based on an amorphous active layer with a thin thickness of ~15nm is sputter deposited without substrate heating or post-annealing. The device shows forming-free unipolar RS properties of low operation voltage (<1.7V), long retention time, good endurance and resistance ratio of 22. The RS property is considered to be dominated by the filamentary conduction due to the presence of oxygen vacancies in the grain boundary-free structure.
To further investigate the dominant substances for the RS behavior and mechanism in the MCO film, we reduce the composition of the target to binary metals. Then, the thin oxygen deficient ZCO films are investigated for nonvolatile memory applications. Both the as-deposited ZCO and rapid thermal annealed (RTA) A-ZCO samples show unipolar resistive switching, good retention time, forming free, low voltage (<1.9V) and thin thickness (~11 nm). The high vacuum RTA treatment at 150°C for 30 minutes is beneficial to improve the switching cycles from 286 to ~6.4x103 and the resistance ratio from 13 to 25. The improved characteristics of the RTA`ed-samples are achieved due to appropriate defect concentration and film quality improvement. The current images in the low resistance state (LRS) and high resistance state (HRS) of the device observed using CAFM. The current density of LRS and HRS are ~3.0x102 nA/μm2 and ~3.3x10-2 nA/μm2, respectively. The RS mechanism of the device is attributed to the formation and rupture of conduction filaments (CFs) based on defects (oxygen vacancies).
Also, this work includes the fabrication and characterization of ZNO thin film-based RRAM devices. The RS behaviours and mechanism of Pt/Zr1-rNirO2-r/Pt memory device are studied. Zr1-rNirO2-r active layer with a thin thickness of ~7nm is sputter deposited without substrate heating or post-annealing. The device shows forming-free unipolar RS properties of low operation voltage (<1.9V), long retention time, good endurance and more than two-order resistance ratio. The analysis shows that the RS property initiates from the formation and rupture of CFs due to the presence of defects (oxygen vacancies) in the oxide films. In addition, a-ZCO films were prepared from oxide target to compare the result with ZCO samples which were prepared from binary metal target. The a-ZCO-based devices show forming-free unipolar RS properties of low operation voltage (<1.8V), good retention time and endurance.
Therefore, RS properties and switching parameters of emerging ZrOx-based RRAM devices for forming-free, low power, longer data retention and thinner thickness nonvolatile memory devices are studied. A potential application of ZrOx-based thin films in future low power, nanoscale microelectronic device applications is realized from this study.
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