| Summary: | 博士 === 國立交通大學 === 材料科學與工程學系 === 98 === This dissertation is devoted to study the magneto impedance effect of magneto resistive elements, and tungsten oxide resistive memory extensively for providing in-depth their physical understanding.
The magneto resistive elements such as pseudo spin valve (PSV) and magneto tunneling junction (MTJ) play a role for magneto random access memory (MRAM). The DC behaviors for magneto resistive elements have been widely studied, but the AC behaviors are still rare. Thus, in the first half of this dissertation we focus on the AC behaviors of magneto resistive elements.
By using AC characteristics, we provide a new non-destructive analysis method to study the nano-oxide layer effects of PSV. Besides, the equivalent circuit model is used to describe the AC behaviors for MTJ. For Ru (5nm) /Cu (10nm) /Ru(5nm) /IrMn(10nm) /CoFeB(4nm) /Al(1.2nm)-oxide /CoFeB (4nm) /Ru (5nm) system, a huge imaginary part of magneto impedance ratio more than 17000% is observed at high frequency 17.7MHz. Magneto impedance effect of the MTJ is potentially a sensitive sensor for high frequencies.
In the second half of this dissertation, tungsten oxide resistive random access memory is studied extensively. Although resistive random access memory (RRAM) is forecasted to be the promising solutions to replace the electron storage memory due to its excellent scalability and 3D possibility, up to now, the fundamental understanding is still very limited and device performance is required to improve. Thus, we proposed a novel WOX for the RRAM system, because it requires only one extra mask under standard CMOS process. By using rapid thermal oxidation (RTO) for the WOX RRAM, we have demonstrated its good performance such as low switching current, fast programming speed, good thermal stability, and high endurance > 1M times for nonvolatile memory.
Under this study, we further find the work function (WF) of the electrode is a key element determining the conduction mechanism for WOX RRAM. SCLC (space charge limit current) mechanism and thermionic emission mechanism are identified for low WF and high WF electrodes, respectively. These studies imply that the device performance may be significantly improved by selecting the proper electrode. With this guideline, Ni/WOX/W device is investigated. The new Ni/WOX/W device shows very good performance that operates at <200uA switching current, a 100X resistance ratio window, and extremely good data retention of > 300 years at 85 C.
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