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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/6537

Title: Inelastic electron tunneling spectroscopy of magnetic tunnel junctions
Other Titles: Ci sui dao jie de fei tan xing dian zi sui chuan pu
磁隧道結的非彈性電子隧穿譜
Authors: Leung, Ming Wai ( 梁明蕙)
Department: Department of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 2011
Publisher: City University of Hong Kong
Subjects: Tunneling spectroscopy.
Notes: CityU Call Number: QC454.T75 L48 2011
xviii, 89 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2011.
Includes bibliographical references (leaves 71-80)
Type: thesis
Abstract: Magnetic tunnel junction (MTJ), which consists of an insulator of nano-size thickness sandwiched with two ferromagnetic electrodes, has become one of the most successful technologies applied to the read head in hard disk drive recording. MTJ can also be used as magnetic logic, and magnetoresistive random access memory (MRAM). Electrons, which tunnel through a MTJ, are determined by many parameters of a MTJ, such as the materials used in the stack, the crystallinity of the materials, the integrity of the layers and the interfaces between ferromagnetic electrodes and the insulating barrier. In other words, these parameters help us to understand the physics in electron tunneling mechanism in the MTJ which would help to generate some insights in the improvement in MTJ fabrication technique. In this project, a cryogenic (low temperature) electrical characterization technique known as inelastic electron tunneling spectroscopy (IETS) was set up to study the interface properties of the MTJ with 10Å magnesia (MgO) insulating barrier and 1.1-1.3Ωµm2 resistance-area (RA). After the successful set up of the IETS instrument, various tests were conducted to confirm its capability. Thereafter, the IETS was used to obtain and compare the IET spectra of two groups of industrial read head samples. From the IET spectra, the group with a complicated material content in the ferromagnetic layer was shown to contain slightly more impurities than the group with a simpler material content in ferromagnetic layer by observing the IETS peak intensities at around ±0-15mV. Besides, the crystallinity of MgO barrier of each read head was deduced from the IET spectra by observing the IETS peaks at around ±80mV. IETS spectra of the two groups of read head samples showed similar peak location and intensities when compared with results of past investigators. The results from this work indicated that although read heads from the same group were manufactured from the same wafer, different IET spectra were obtained. While the present instrument was able to distinguish their differences, it was also explained that the difference in the spectra in the form of different magnitudes of peak was due to the variation of back-end process. All the IETS expected peaks were present in our MgO barrier MTJ samples, which were the zero-bias anomaly (ZBA) at around ±0-15mV. It was also found that the magnon excitation at the ferromagnetic-barrier interface occurred at ±25 and ±50mV. The presence of phonon excitation was attributable to MgO barrier at around ±80mV.
Online Catalog Link: http://lib.cityu.edu.hk/record=b4086289
Appears in Collections:AP - Master of Philosophy

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