Microfabrication technology for an integrated monolithic electromagnetic microactuator based onpolymer bonded permanent magnet.

Electromagnetic microactuators with permanent magnets have many potential applications such as micro-energy scavengers, microswitches, micromirrors and microfluidics. However, many electromagnetic microactuator designs utilize either external permanent magnet or external coil, which do not allow tight integration to other MEMS components and further miniaturization. Furthermore, all of the available permanent magnet microfabrication technologies have some drawbacks and improvements are required. Thus the integrated monolithic electromagnetic microactuator is investigated in this project.The three main components of the electromagnetic actuator have been investigated separately. A novel microfabrication technology called ‘Template printing’for the fabrication of polymer bonded permanent magnet has been investigated anddeveloped. It is based on ‘Screen printing’ which has its drawbacks on alignment accuracy and poor line definition. This is eliminated in ‘Template printing’ by photolithography of the photoresist template. The shape and location of the permanentmagnet is defined by the template. A new approach based on the filling of dry magnetic powder and vacuum impregnation has been developed to form the polymer bonded permanent magnet. This allows the use of short pot-life matrix material and the elimination of homogenous mixing.A monolithic electromagnetic microactuator has been fabricated successfully. It consists of a 2-layer planar copper microcoil, surface micromachined polyimide beam and Strontium ferrite/EPOFIX permanent magnet (diameter of 460 μm and 30 μm thickness). Large deflection in excess of 100 μm at 35 mA driving current and magnetic force of 0.39 μN/mA have been achieved. It compares favourably with other much larger electromagnetic actuators that have been reported.‘Template printing’ has the potential of being a low temperature batch process for the microfabrication of thick polymer bonded permanent magnets with high magnetic properties and low residual stress. The fabrication consistency and the quality of template printed magnet can be improved in future studies