Electrostatic and electromagnetic microactuation technology for medical and MEMS applications

This research is part of the development of the auditory micro-electro machine system (AMEMS) which is a totally implantable hearing device that is suitable for patients with sensorineural and/or conductive hearing losses. AMEMS integrates a microsensor and a microactuator in the middle ear with an ASIC signal processor (this ASIC consists of preamplifier, graphic equalizer, power amplifier and remote control) and a power source.; This dissertation focused on the development of the microactuator. In this research, electrostatic and electromagnetic actuation methods were utilized. To achieve this method of actuation, electrostatic microactuators with 1.0 {dollar}mu{dollar}m suspended polyimide circular diaphragms were fabricated on (100) silicon wafers. Diaphragms with diameters of 0.5, 1.0 and 1.5 mm were utilized. The wafer surface acted as the bottom plate of a capacitor, and the polyimide diaphragm constituted the top plate which deformed under applied voltage. The entire electrostatic microactuator design required a minimum of five photomasks. The main feature is the use of a sacrificial layer technique to define an air-gap capacitor, in which aluminum was used as the sacrificial layer. Reactive Ion Etching (RIE) using SF{dollar}sb6{dollar}/O{dollar}sb2{dollar} was utilized to etch an access hole through the Si wafer. Finite Element Modeling (FEM) analysis of the diaphragm deflection was carried out using I-DEAS software. A central deflection of 0.1 {dollar}mu{dollar}m was achieved at 2.5 and 3.5 V DC for the 1.0 mm and 0.5 mm polyimide diaphragms, respectively. The frequency response of the device under an AC signal was tested up to 4.0 KHz for the peak-to-peak displacement of the diaphragm. Slopes between {dollar}-{dollar}10 and {dollar}-{dollar}15 dB/decade were calculated for the curves of the peak-to-peak displacement of the diaphragm as a function of frequency. The frequency response of the devices showed a behavior similar to the actual stapes peak-to-peak displacement as a function of frequency.; The alternative method was to achieve electromagnetic actuation by employing 3 x 3 multilevel microsolenoid arrays on a silicon substrate. The electromagnetic device was capable of converting the electromagnetic energy of current signals in the solenoid to mechanical motion of a thin magnetizable plunger placed in a hole at the center of the device. A minimum of seven photomasks were required to design and fabricate the electromagnetic microactuator. Standard IC and bulk (wet/dry) micromachining fabrication processes were used to fabricate the devices. Four layers of Al metal were used to construct the planar spiral coil. Polyimide PI2611 was used as a dielectric isolation and planarization layer between the metal layers. A 15 mil diameter mumetal plunger was used to guide the magnetic field and to sense the magnetic force of the microactuator. A maximum deflection of 92 {dollar}mu{dollar}m was obtained with a 15 mA DC current. Interpolation from the deflection data showed that for a deflection of 0.1 {dollar}mu{dollar}m, a current of 40 {dollar}mu{dollar}A (which was determined to be too much for the AMEMS application) would be required. Forces in the range of 10{dollar}sp{lcub}-6{rcub}{dollar}N were obtained. Hence, a technique for large z-axis deflection for microelectromechanical systems (MEMS) was demonstrated. (Abstract shortened by UMI.)...