Surface roughness control of the Al and Al 2 O 3 thin films deposited by using pulsed DC magnetron sputtering
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Surface roughness control of the Al and Al2O3 thin films deposited by using pulsed DC magnetron sputtering Jinjun Qiu, Kebin Li, Guchang Han, Zaibing Guo, and Yihong Wu1 Data Storage Institute, DSI Building, 5 Engineering Drive 1, Singapore 117608) 1 Department of Electrical and Computer Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 ABSTRACT The thickness of the Al2O3 layer used in the magnetic tunneling junctions FM1/Al2O3/FM2 is less than 2 nm, here FM1 is for the ferromagnetic layer 1 and FM2 is for ferromagnetic layer 2. In order to obtain ultra-thin Al2O3 layer with higher breakdown voltage and pinhole free, extremely smooth surface roughness of this layer is required. The influence of the sputtering gas pressure, DC pulsed frequency, DC pulsed power, substrate bias and buffer layer on surface roughness and properties of Al thin films were studied. The single layer Al films are usually amorphous, texture (111) Al films can be obtained while using thin Ta 5 nm or Ta5/NiFe2 as underlayer. Very smooth Al thin film can be sputtered on Si/SiO2 (100) wafer with Ta/NiFe buffer layer at f=15 kHz (DC pulsed frequency) and with RF substrate biasing (Vpp is about 21 V). High quality MTJs with high MR ratio up to 44.6% and high field sensitivity up to 19.3%/Oe were finally demonstrated after optimization of thin film deposition process. INTRODUCTION Recently the magnetic tunnel junctions (MTJ) which compose of two ferromagnetic layers separated by an ultra-thin insulating barrier layer (FM/I/FM) are of great interest since large tunneling magnetoresistance (TMR) in relative low magnetic fields was observed at room temperature [1-3]. However, one of the challenges is to fabricate an extremely thin (
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