|Budget Amount *help
¥33,500,000 (Direct Cost : ¥33,500,000)
Fiscal Year 1998 : ¥7,400,000 (Direct Cost : ¥7,400,000)
Fiscal Year 1997 : ¥12,300,000 (Direct Cost : ¥12,300,000)
Fiscal Year 1996 : ¥13,800,000 (Direct Cost : ¥13,800,000)
In order to fabricate spin devices using tunnel magnetoresistant effect, we carried out the research on fundamental physical mechanism for tunnel junctions, on the development a measuring instrument for the interfacial structure and on the micro-fabricating process for microstructured junctions. The main results are summarized as follows.
1. Fundamental physical properties
The tunnel magnetoresistance (TMR) effect in the Ferro/Insulator/Ferro junctions depends not only the spin-polarizations of electrodes (ferromagnets) but also on the barrier height and width of insulator. These dependences were confirmed by systematic experiments and by comparison with theoretical treatments reported by other groups. Also, the temperature and applied voltage dependence of TMR ratio were investigated in detail. Spin-valve type junctions with exchange-biasing one of the magnetic layers using a thin antiferromagnetic FeMn or IrMn layer were prepared. These junctions exhibited an well defined switching fie
ld, temperature insensitive TMR ratio and improved the applied voltage dependence of the TMR ratio.2. Fabrication of measuring apparatus In order to analyze the interfacial structure of the tunnel junctions, inelastic electron tunnel spectroscopy (IETS) apparatus was developed. By using the apparatus IET spectrum for many kind of the junctions were examined and the usefulness of the analysis was proved. Furthermore, a Kerr hysteresis apparatus for measuring a small area of the tunnel junction was made. By using the apparatus it was shown that the magnetization process of 40*40 mum^2 junction area corresponds well to the magnetoresistance curve of the junction.
3. Micro-fabrication process and microstructured tunnel junction
By using photolithography and Ar ion milling, the process to fabricate a small tunnel junction was investigated. A redeposited free junction was made by choosing the optimum incident angle of Ar ions and milling depth. A small contact hole at the center of active junction area was well made by plasma etching with CF_4 gases. By using the processes, a junction with 3*3mum2 active area, 500OMEGA tunnel resistance and 15% TMR ratio was successfully made. The tunnel junction possesses a high potential for magnetic reading head for high density magnetic recording and/or magnetic random access memory.