A polydimethylsiloxane diaphragm integrated with a sputtered thin film NdFeB magnet

In this paper we propose a MEMS fabrication process that enables a polydimethylsiloxane (PDMS) diaphragm to be integrated with a sputtered thin film permanent magnet (TFPM), which can be used for micro pumps, energy harvesters, tactile display devices and so on. The magnetic performance of the 14.8 μm thick TFPM, consisting of multilayers of 300 nm thick NdFeB and 10 nm thick Ta deposited sequentially, is as high as a conventional bulk NdFeB magnet. However, the high sputtering temperature makes it impossible to deposit the TFPM directly onto the PDMS diaphragm without damaging the PDMS material. The process proposed here involves, firstly, sputtering the TFPM onto a silicon substrate, then coating this with PDMS, and finally etching silicon using XeF₂ gas. The high substrate temperature during the XeF₂ etching process degraded the magnetic performance of the TFPM and also caused part of the TFPM to become detached from the PDMS layer. The variation in temperature of the substrate during the XeF₂ etching process with respect to etching pressure, and the magnetic properties of the TFPM as well as the mechanical ones of the PDMS diaphragm were evaluated experimentally. The substrate temperature can be decreased by reducing the XeF₂ etching pressure, thus avoiding both degradation of the magnetic performance of the TFPM and delamination of the TFPM. The results of the evaluation show that the PDMS diaphragm and the TFPM not only remained attached, but also retained their mechanical and magnetic properties.