BiFeO3 based tunneling magnetoresistance (TMR) device

• Main Author: Zhang, Jiazhen
• Other Authors: Wang Junling
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Materials::Microelectronics and semiconductor materials
• Online Access: http://hdl.handle.net/10356/49012
• Institution: Nanyang Technological University

Tunnelling Magnetoresistance (TMR) has attracted intensive attention these years since 1975. It can provide large signal via small devices. In this project, the CoFe(Fe)/BiFeO3/La2/3Sr1/3MnO magnetic tunnel junctions were fabricated. Their magnetic and electric properties were studied by low temperature probe station. BiFeO3 (BFO) was chosen as the barrier layer because it exhibits ferromagnetism and ferroelectricity at room temperature. It has high Neel temperature (643K) and high Curie temperature (1103K). The bottom electrode La2/3Sr1/3MnO3 (LSMO) and barrier layer BFO were deposited through pulsed laser deposition on (001)-orientated single crystalline SrTiO3. Top electrode was deposited by sputtering. The junctions were patterned through double layer photolithography which makes a T shape of top electrode in each junction. This method enable the top electrode has a contact area of 5umX5um with the barrier layer BFO while has a top contact area of 40um X40um for testing probes to be put on. Good TMR ratios (around 80%) were observed in some of those magnetic tunnel junctions. However, due to the limitation of the external magnetic field applied, the obtained TMR can only be calculated in a rough way. Future investigation of TMR dependence on temperature and bias voltage can be conducted. TMR can be combined with TER and achieve 4 states, which is a promising topic in the future.