Mechanical, electrical and magnetic properties of IrMn exchange-biased CoFeB/AlOx/Co magnetic tunnel junctions

• Main Authors: Yuan-Tsung Chen, 陳元宗
• Other Authors: Jenn-Ming Wu
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/71250740064011628245

博士 === 國立清華大學 === 材料科學工程學系 === 95 === Co60Fe20B20/AlOx/Co is a typical device used as a magnetic tunneling junction (MTJ), because Co60Fe20B20 has a high polarization characterization, which means the high tunneling magnetoresistance (TMR). This kind of MTJ system has been studied extensively. However, many researches downplayed the mechanical properties, such as magnetostriction and straining effect of MTJ. In this study, I concentrated on the studies of the crystal structure, magnetic, mechanical, electrical, and nanoscale properties of this MTJ. DC-magnetron sputtering was employed to fabricate various magnetic layers and RF-magnetron sputtering AlOx tunneling layer. First, the single Co and Co60Fe20B20 layer were investigated respectively in order to understand the properties of each single layer. Next, Co60Fe20B20/AlOx/Co device was fabricated to observe the interfacial effect on magnetostriction of MTJ; nanobeam energy dispersive X-ray (EDX) device was incorporated in high-resolution cross-sectional Transmission Electron Microscopy (HR X-TEM). Furthermore, the exchange-biasing phenomenon of the Co(Ferromagnet)/Ir20Mn80(Antiferromagnet) system was studied. Finally, the TMR of the IrMn exchange-biased MTJs was investigated: including the variations of TMR, resistance (R), and exchange-biasing field (Hex) as a function of AlOx thickness ( ) . From the Auger-depth profile analysis, it was found that there is one CoOx or (CoFeB)Ox oxide layer, lying on top surface of the Co or CoFeB film, and another CoOx or (CoFeB)Ox oxide layer, lying near the glass interface. Due to the proximity effect, the CoOx or (CoFeB)Ox oxide layer is weak ferromagnet, not paramagnet or antiferromagnet as expressed. In addition, the atomic concentrations of Fe, Al, and O as a function of in the laminated CoFeB/AlOx( )/Co can affect the trend of its net magnetostriction. The Ir20Mn80 texture plays an important role on the magnetic properties in the Co/Ir20Mn80 system. Eventually, all the MTJs could sustain the external stress effect without failing. Based on my studies, the optimal candidate of this MTJ system is: Si(100)/Ta(30 Å)/CoFeB(75 Å)/AlOx(30 Å)/Co (75 Å)/IrMn(90 Å)/Ta(100 Å), because it has the high TMR, large Hex, and the smallest magnetostriction. Moreover, in the 25 × 10-6 real environment this type of MTJ is stable in the recording head and MRAM application; because it is less sensitive to the external stresses.