Micromachining of Electret Materials , Advantages and Possibilities

In this pa er we describe a process for the micromachining of materials like Teflon-FEP. We have used photolithography and plasma etching, by which electrets can be etched selemvely. The advantages of, in such a way micromachined electrets are numerous. Miniature sensors like microphones and pressure sensors, containi6 local areas with Teflon, have been realized in our laboratones. The process can also be used for electret research. An example is the overall reduction of electret film thickness, by which we have determined the average penetration depth of accelerated electrons in Teflon-FEP. INTRODUCTION organic eectret P The application of carbon-fluor polymerj, for electrets is well known. Teflon-FEP has a resistivity of 10 k m and a reported charge-deca time of more than 10 years [l]. The use of TeflonFTF6 for electret and piezoelectric applications is also well known. The electret properties of such polymers appear to depend on the film thickness. Useful values, and commercially available are 12.5 and 25 pm [l]. In many applications the thickness of the foil and the size of the structures to be realized are not very critical. However, in the Biosensor Research Grou of Twente in the development of microtransducers with submillimeter dimensions [2]-[6]. In that case the lateral dimensions of the foil as well as its thickness are very important and should be controlled in a well-defined way. A very useful tool in the realization of microsensors is hotolithography. This technique enables us to pattern thin ilms in many different profiles. The process consists of several steps, as schematically drawn in figure 1 and described below. University we are considering the application o P Teflon foils CH2593-2/ 88/ 0000-0582601 .OO Copyright 1988 IEEE