In this paper, a new way of actively tuning the resonant frequency of vibrating microelectromechanical devices by electrostatically adjusting the length of the resonating structure is explored. Variations in micromachining processes cause submicron differences in the size of fabricated micromachined devices, which lead to frequency variations in resonators. For radio frequency (RF) applications where high frequency selectivity and low noise frequency manipulation are key performance issues, micromachined resonators need to output a fixed frequency if they are to replace current off-chip, passive devices. This motivates the investigation of post-fabrication techniques that compensate for fabrication defects and errors, and shift the resonant frequency to its designed value. A simple universal analytical model has been developed to investigate the different states a cantilever undergoes during pull-in due to an applied voltage. The beam's natural frequencies throughout these states have been plotted. It is shown that the frequency can be changed by a factor of 4 during pull down, and thereafter increased proportionally with actuation provided an initial minimum voltage was applied.

Purpose -The processing techniques and materials utilized in the fabrication of a two-terminal electrostatically actuated micro-electro-mechanical cantilever-arrayed device used for radio frequency tuning applications are presented in this work. The paper aims to discuss these issues. Design/methodology/approach -The process, which is based on silicon surface micromachining, uses spin-coated photoresist as the sacrificial layer underneath the electroplated gold structural material and an insulating layer of silicon dioxide, deposited using plasma enhanced chemical vapour deposition (PECVD), to avoid a short circuit between the cantilever and the bottom electrode in a total of six major fabrication steps. These included the PECVD of the silicon dioxide insulating layer, optical lithography to transfer photomask layer patterns, vacuum evaporation to deposit thin films of titanium (Ti) and gold (Au), electroplating of Au, the dry release of the cantilever beam arrays, and finally the wafer dicing to split the different micro devices. These process steps were each sub-detailed to give a total of 14 micro-fabrication processes. Findings -Scanning electron microscope images taken on the final fabricated device that was dry released using oxygen plasma ashing to avoid stiction showed 12 freely suspended micro-cantilevered beams suspended with an average electrostatic gap of 2.29^0.17 mm above a 4,934^3 Å thick silicon dioxide layer. Preliminary dimensional measurements on the fabricated devices revealed that the cantilevers were at least 52.06^1.93 mm wide with lengths varying from 377.97^0.01 to 1,491.89^0.01 mm and were at least 2.21^0.05 mm thick. Originality/value -The cantilever beams used in this work were manufactured using electroplated gold, and photoresist was used as a sacrificial layer underneath the beams. Plasma ashing was used to release the beams. The beams were anchored to a central electrode and each beam was designed with varying length.