錳氧化物和矽奈米針異質結構 之電場輔助磁傳輸以及電阻切換特性

Electric-Field-Assisted Magneto-Transport and Resistance Switching in La0.7Sr0.3MnO3/Si Nanotips Heterojunction

張昌偉(Cheong-Wei Chong)

指導教授 ： 陳永芳

共同指導教授 ： 林麗瓊 ； 林昭吟 ； 陳貴賢(Kuei-Hsien Chen)

國立臺灣大學/理學院/物理研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.00251

摘要

無資料

關鍵字

矽奈米針 ； La0.7Sr0.3MnO3 ； 磁阻 ； 電阻切換 ； 電場增強

並列摘要

In this thesis, the quasi-array of Si-nanotips (SiNTs) is used as a template for depositing the La0.7Sr0.3MnO3 (LSMO) layer. SiNTs template is prepared using electron cyclotron resonance microwave plasma enhanced chemical vapor deposition method, while LSMO layer is coated by pulse-laser deposition techniques. The purpose of utilization of this nano-tips structure is to achieve the nanoscale-controlled electronic and magnetic properties using its high local electric field. The combined effects of electric and magnetic field are expected to generate a sensitive resistance-modulation in this system. Transport mechanism in this nano-heterojunction is studied via the measurements of current vs. voltage (I-V) and magnetoresistance (MR) as functions of temperature, external bias and magnetic field on the samples with different aspect ratio of n-SiNTs. In addition, resistance switching (RS) effect is also investigated using DC bias voltage sweeping technique and electric-pulse system. In this RS study, LSMO was prepared on n-SiNTs and heavy-doped n-type SiNTs (n+-SiNTs).
The unique nanostructured LSMO/SiNTs arrays are ferromagnetic above room temperature. In this work, an enhanced magnetoresistance effect and well-controlled resistance switching properties of LSMO/SiNTs heterostructures have been realized.
Enhancement of room temperature magnetoresistance (up to 20% under 0.5 Tesla and a bias current of 20 µA) is demonstrated in LSMO/n-SiNTs heterojunctions, which increases with increasing external bias and the aspect ratios of the nanotips. It is suggested that the filamentary current induced spin alignment under the strong local electric field has generated a giant negative magnetoresistance in nanoheterojunctions. Interestingly, a giant positive MR (PMR) of ~200 % (at 40 K under 5 Tesla magnetic field) in LSMO/NTs junction is unexpectedly observed for the first time. It is proposed that in the presence of magnetic field, the coupling between electron-electron interaction (EEI) and electron-magnon scattering in LSMO could be greatly enhanced, which is the origin for this giant PMR. Furthermore, this effect is triggered by using n-Si nanotips as an electron injector based on the metal-insulator semiconductor (MIS) structure, in which Fowler-Norheim high-field tunneling dominates the junction conduction mechanism.
The enhancement of RS ratios in LSMO using n+-SiNTs as n-type substrate is achieved with lower switching voltage and read voltage, in comparison with the planar wafer device. The switching mechanism is found tunable using different SiNTs morphologies. Switching ratio in pyramid-based device exhibits one order of magnitude enhancement compared with other samples (

並列關鍵字

silicon nanotips ； La0.7Sr0.3MnO3 ； magnetoresistance ； resistance switching；field enhancement

參考文獻

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