Electrostatic actuation is highly efficient at micro and nanoscale. However, large deflection in common electrostatically driven MEMS requires large electrode separation and thus high driving voltages. To offer a solution to this problem we developed a novel electrostatic actuator class, which is based on a force-to-stress transformation in the periodically patterned upper layer of a silicon cantilever beam. We report on advances in the development of such electrostatic bending actuators. Several variants of a CMOS compatible and RoHS-directive compliant fabrication processes to fabricate vertical deflecting beams with a thickness of 30 μm are presented. A concept to extend the actuation space towards lateral deflecting elements is introduced. The fabricated and characterized vertical deflecting cantilever beam variants make use of a 0.2 μm electrode gap and achieve deflections of up to multiples of this value. Simulation results based on an FE-model applied to calculate the voltage dependent curvature for various actuator cell designs are presented. The calculated values show very good agreement with the experimentally determined voltage controlled actuation curvatures. Particular attention was paid to parasitic effects induced by small, sub micrometer, electrode gaps. This includes parasitic currents between the two electrode layers. No experimental hint was found that such effects significantly influence the curvature for a control voltage up to 45 V. The paper provides an outlook for the applicability of the technology based on specifically designed and fabricated actuators which allow for a large variety of motion patterns including out-of-plane and in-plane motion as well as membrane deformation and linear motion.
We have been developing a piezoresistive position detection for scanning micro mirrors in order to combine high
position resolution with the capability of monolithic integration. In comparison to our formerly published results,
the sensor sensitivity was strongly enhanced by implanting a 1 μm thick p-doped layer of NA ≈ 1017 cm-3 into
the lowly p-doped SOI device layer of NA ≈ 1015 cm-3. This sensitivity was even further improved by at least
a factor of 3 by a novel sensor design, allowing to couple more mechanical stress into the sensor structure.
Aluminum nitride (AlN) is a promising piezoelectric material suitable for full CMOS compatible MEMS processes. Due
to the transversal inverse piezoelectric effect the use of AlN enables quasistatic deformable mirrors by actively coupling
lateral strain in micro machined membranes. In this work a fast and reliable way for reactive magnetron rf-sputtered aluminum
nitride thin films with piezoelectric properties is shown. The thin AlN films were deposited on amorphous TiAl,
SiO2 and silicon substrates using an industrial PVD cluster system. The morphologies of the deposited polycrystalline
AlN films are characterized by X-ray diffraction measurements and SEM images of the layer surfaces. An enhanced
texture coefficient is used to demonstrate the correlation between the X-ray diffraction pattern and the surface topology.
High values of this enhanced texture coefficient will guarantee piezoelectric properties. Virtual powder X-ray diffraction
experiments are used to determine the relative powder intensities required for texture coefficient evaluation. The transversal
inverse piezoelectric coupling coefficient d31 is measured for tempered and untreated aluminum nitride thin films
with high enhanced texture coefficients by quasistatic deflected wafer cantilevers.
Position feedback of resonant scanning micromirrors plays a key role for various applications like portable laser
projection displays or scanning grating spectrometers. The SOI device layer without an additional surface implantation
is used for the piezoresistive sensor design. It assures the full compatibility to microscanner technology
and requires no additional technological efforts. The necessary asymmetry of the current field density is achieved
by the geometrical design of the sensor and its contacting. Integrated 2D position sensors with amplitude sensitivities
of 0.42mV/V° were fabricated. FEA simulation and measured data correlates well with variations of