Large throw magnetic microactuator

The design and fabrication of an electromagnetic MEMS actuator capable of repeatedly switching over a gap length of 100 μm is presented. The device is to be used as a switch for radio-frequency (RF) circuits. It is based on a potcore type electromagnet and a mover suspended on a microbeam. The device was first modelled and optimised using a finite element analysis and then microfabricated. The ultra thick, negative photoresist, SU-8, was used extensively throughout the construction as: (i) an electroplating mould for the copper coils (up to four layers thick at 50 μm per layer), (ii) the magnetic material for the pot core and mover by loading it with various powders to produce a range of magnetic properties and (iii) the actuator beams because of its low elastic modulus. The potcore has a footprint of 0.8 mm2 and for a driving current of 1.4 A (corresponding to a power dissipation of about 80 mW) generates an initial force of 0.11 mN which is sufficient to close a 100 μm gap. In this prototype form, the device could be operated for more than 104 cycles. The maximum switching distance achieved was 200 μm.