Magnetic Properties and Growth Behavior of Nd–Fe–B Films on Si(111)

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NdFeB films were prepared by dc-magnetron sputter-depositiononto Si(111) at 600 to 700°C. Anisotropic films with remanence ratiolarger than 0.67 and intrinsic coercivity greater than 7 kOe wereobtainable at a substrate temperature of 650°C on Si(111) using one ofW, Mo, or Pt as the underlayer. The mechanical polishing can reducethe film thickness from about 850 nm to 150 nm, and the coercivityremains 2–5 kOe. The coercivity of being strongly dependent on filmthickness can be explained by the domain-wall motion in films throughsuitable modeling. The depth-profile and microstructure of the filmson different underlayers were explored by secondary ion massspectroscopy (SIMS) and high resolution transmission electronmicroscopy. The Pt underlayer, being in fact a Pt/Ti/SiO2/Si(111), isa sound barrier layer between the NdFeB film and Si(111) so that thereis negligible interdiffusion as evidenced by SIMS depth profile. Theformation of silicide was found in films with Mo or W underlayersputtered at 650°C. This can be observed from the overlap regionbetween the underlayer and Si(111) in the SIMS depthprofile. Diffusion coefficients of the Nd, Fe, B in Si(111) were alsoquantitatively estimated.
1999-07-15