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
≤ 20.4%.
We present two designs of two-dimensional gimbal microscanners with low vertical-scan frequencies of 70 Hz and
330 Hz and a high horizontal scan frequency of 30 kHz. The scanners are fabricated in a 30 μm silicon-on-insulator
with backside structures for both mirror and gimbal-frame. The backside structure under the frame increases the
frame weight and effectively reduces the resonant frequency of the rotation springs. The slow vertical scan can
thus be achieved without reducing the spring width dramatically. A patterned backside structure also reinforces
the mirror plate during actuation such that the root-mean-square dynamic deformation of the 1 mm diameter
mirror is less than 44 nm (λ/10 for blue) at 10 degrees mechanical scan angle. A microscanner is installed into
a prototype laser projector to demonstrate its capability of producing high quality images.
A new two-dimensional and resonantly driven scanning micro mirror has been simulated, fabricated and characterized.
Features are a small chip size of 2900 μm x 2350 μm with a frame oscillating at frequencies in the range of 1 kHz. The
frame carries a mirror of 500 μm diameter in a gimbal mounting oscillating at frequencies in the range of 16 kHz. The
characteristic mechanical amplitudes are 21o and 28o respectively. Voltages of 60 V and less than 140 V were necessary
to accomplish this. Much higher amplitudes have been achieved on the mirror axis without breaking the torsion bars.
Initial difficulties in realizing the high amplitudes have been overcome by improving the geometry of the suspension.
The initial design is presented as well as the measurement results of the initial and improved design. The device was
used to develop a micro laser camera with high depth of focus. Pictures taken with the system are presented revealing
the excellent resolution.
A novel translational micro mirror with a circular shape of 3 mm diameter and oscillation frequencies of 500 Hz and 1000 Hz is presented including a design study based on analytical and numerical calculations. The study takes mechanical limits like stress and shock resistivity into account as well as fabrication issues resulting in the design points presented. Considerations and results of this study including stress limits for single crystalline silicon and a FE analysis of the main oscillation mode of the resonant structure will be illustrated. Based on an SOI process with 30 μm thick and highly doped single crystalline silicon several devices were fabricated. For the characterization of the devices a Michelson interferometer set-up was used which allows determining the voltage-deflection curves as a function of the air pressure. Deflections of more than ± 50 μm for the 500 Hz device and ± 85 μm for the 1000 Hz have been achieved at a pressure of 10 Pa. The target is at ± 250 μm and ± 180 μm amplitude. In the outlook packaging requirements and approaches will be shown.
We present a scanning micromirror with 5x better flatness of the mirror plate compared to our previous devices. The devices are designed for a laser scanning displays with VGA resolution. Scanning laser displays are certainly the most demanding application for scanning micromirrors. The fast axis must provide a large mirror plate that remains flat, when deflected to large angles at high frequency. The presented devices meet the specifications for VGA-resolution (640x480 pixels). Oscillation frequency is 16kHz. The mirror-plate has 1mm diameter and can be deflected by +/-10°. Dynamic deformation is below lamba/10 under these conditions. The devices are fabricated in the established SOI process of Fraunhofer IPMS Dresden. Mirror plate and springs are made of 30um of crystalline silicon. Operation is resonant with lateral out-of-plane comb-drives. In this article we present the design, simulation results and measurement results.
KEYWORDS: Electrodes, Finite element methods, Micromirrors, 3D modeling, Capacitance, Mirrors, Electroluminescence, Data modeling, Microsystems, Microelectromechanical systems
Since damping is the limiting factor for the reachable maximum deflection, it is a very important issue in the context of resonant microsystems. In this paper, we present an optimized comb design and an extended damping model for out-of-plane scanning micromirrors. It bases on the compact analytical model published by Sandner et al. (at the SPIE conference Photonics Europe in 2004). The basic concept of this model is to attribute viscous damping in the comb gaps as the dominant contributor of damping moments. The model is extended by findings from a fluidmechanical FEM model of an electrode finger. It also considers the effects from pressure and temperature changes. The extended model is verified and discussed in the context of experimental results. The primary goal of damping analysis and optimization is to minimize power consumption and to reduce driving voltage. To consider that, the damping of the out-of-plane electrode comb is discussed in the context of its capacitance. One of the results presented in this paper is a out-of-plane comb-drive with optimized drive efficiency.
In this paper we present the analytical and experimental investigation of the air damping of micromachined scanning mirrors with out-of-plane comb drive actuation. A simple, compact model for the damping torque is derived by estimating the orders of magnitude of certain damping contributors. Viscous damping in comb finger gaps is estimated to be the dominant contributor. Because the comb fingers disengage as the scan amplitude increases, the damping coefficient is dependent on the amplitude of angular vibrations. Experimental measurements are presented for a variety of comb-finger geometries. The comb finger length, width, and the gap between comb fingers are varied, and the damping behaviour for single-axis scanning is characterised by measuring the decay rate of free oscillations. The damping is characterised by the exponential decay constant δ, found by fitting to the decaying oscillation amplitude. The predictions of the analytical model are compared to these experimental damping measurements.
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