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.
This paper discusses the fracture strength study of torsion springs in MEMS microscanners, which are fabricated in
silicon-on-insulator (SOI) with deep-reactive-ion-etch (DRIE) process. High performance microscanners are of particular
interest for scanning laser projection displays. To produce high resolution images, scanners are required to rotate with
large actuation angles (>10 degrees mechanical angle) at designated resonant frequencies. While the designs are pushed
closer to material limits, it is essential to acquire knowledge of single-crystal-silicon's fracture strength. We have
designed samples for fracture strength tests, which reach failure angle (> 20 degrees) with low driving voltage (< 50
volts) under vacuum. The tests are performed with real-time optical feedback to ensure resonance operations. A voltage
ramp is applied to scanners until fractures occur; the ramp-rate and starting angle are chosen such that failures occur
within thirty minutes of operation. Torsional stresses at fracture are calculated from failure angles via an ANSYS(R)
model. In the experiment, forty samples from two spring designs with a cross-section of 14x30 um and a length of 240
um are tested. Because fracture angles scatter around a mean value, Weibull statistics is used to treat the characteristic
behaviors of the tested samples to better interpret the test results. The Weibull characteristic fracture strengths are 2.97
GPa and 2.58 GPa. With a stress limit of less than 2 GPa, we can achieve a 86% reliability SVGA microscanner design
with a 1 mm diameter, a 32 KHz resonance frequency, and a single-side mechanical scan angle of 13 degrees.
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.