Rare Earth Thick Film Magnets Deposited on Glass Substrates for MEMS Application

Abstract

Rare earth permanent magnet films thicker than $10\mu \mathrm{m}$ were hopeful materials applied for MEMS, however almost all the samples have been deposited on Si or glass substrates with a metal buffer layer [1] [2]. In this study, the preparation of Pr-Fe-B thick films on glass substrates without a buffer layer was carried out. This contribution reports the evaluation on the magnetic and mechanical properties in each film with different Pr contents. Each film was deposited on a glass substrate by using a YAG pulse laser ( $\lambda$ : 355 nm, frequency: 30 Hz) in the vacuum atmosphere of $2\times 10^{-5}$ Pa. The laser beam was focused on the surface of a Pr X Fe 14 B(X=1.8, 2.0, 2.2, 2.4) target under the deposition rate higher than $10\mu \mathrm{m}/\mathrm{h}$ . A pulse annealing (PA) method enabled us to crystallize hard magnetic phase. Figure 1 shows the magnetic properties as a function of Pr contents in each film thicker than $10\mu \mathrm{m}$ . As the amount of Pr increased, coercivity increased and residual magnetic polarization decreased. We have already reported that Nd(or Pr)-Fe-B thick films with rare-earth amount less than 15 at. % deposited on Si substrates were broken after a post annealing process [3], however the Pr amounts could be reduced down to approximately 13 at. % without the deterioration of mechanical properties on glass substrates. It was also confirmed that an approximately $100\mu \mathrm{m}$ -thick Pr-Fe-B thick film with $(BH)_{\max}$ of about 80 kJ/m3 could be deposited on a glass substrate.