Mark G. Allen
School of Elec. Eng., Microelectron. Res. Ctr., Georgia Inst. of Technol., Atlanta, GA 30332-0250
There is currently application in micromachining technology for a spin-on, organic piezoelectric material that could be used for microactuation. One material that possesses these properties and is currently being studied actively is the copolymer of vinylidene fluoride and triflouroethylene, PVDF-TrFE. It has been found that this material also exhibits a strong electrothermal effect; i.e., it can be locally heated by application of voltage in the MHz frequency range. This heating is sufficient to allow electrothermal actuation of released micromachined structures fabricated using this material. Using bulk micromachining, several released bridges and cantilever beam structures have been fabricated, ranging in length from tens of microns to a few millimeters. The structures are bimorphs, consisting of a layer of PVDF-TrFE (sandwiched between two metal electrodes) on top of a layer of polyimide. The structures were tested by applying 0-16-V peak rf signal with frequencies up to 50 MHz and observing the resultant deflection. The deflection was a function of both frequency and amplitude of the applied signal. To verify that the heating of the sample was due to the dielectric loss of PVDF-TrFE, the induced temperature change was measured by measuring the IR radiation of the structures. These measurements clearly show the expected linear dependence of the film temperature with the square of rf signal amplitude (i.e., the applied power). Deflections exceeding 900 (mu)m have been observed. The structures can also be made to vibrate up to about 50 Hz by gating the input rf signal.