The use of microscanning mirrors in mobile laser projection systems demands for robust fabrication technologies. Dust,
change in humidity and temperature can only be tolerated if the fragile devices are enclosed in a hermetic package. A
novel fabrication process is presented based on two 30 micron thick epitaxially deposited silicon layers and a buried
interconnection layer. This technology allows the fabrication of stacked combdrives for electrostatic mirror actuation and
lateral feedthroughs needed for hermetic encapsulation with standard wafer bonding processes. High display resolution
requires large scan angles of the mirror plate. Therefore, a fabrication technology for structured glass wafers is presented
to provide deep cavities for large mirror plate movements. A solution for effective laser spot reflex suppression is
presented based on a static tilt of the mirror plate in relation to the glass cover wafer during eutectic bonding. By doing
so, the reflex generated at the glass surfaces is shifted out of the image area. The cavity pressure of packaged devices has
been measured showing the necessity of a getter layer in order to provide cavity pressures below 1 mbar. The
performance of a packaged device with integrated getter layer has been evaluated. A driving amplitude of only 6 V is
needed to achieve scan angles of above 50 deg. White light interferometric measurements showed excellent planarity of
the mirror plate with a radius of curvature of about 18 m.
Ulrich Hofmann, Marten Oldsen, Hans-Joachim Quenzer, Joachim Janes, Martin Heller, Manfred Weiss, Georgios Fakas, Lars Ratzmann, Eleonora Marchetti, Francesco D'Ascoli, Massimiliano Melani, Luca Bacciarelli, Emilio Volpi, Francesco Battini, Luca Mostardini, Francesco Sechi, Marco De Marinis, Bernd Wagner
Scanning laser projection using resonant actuated MEMS scanning mirrors is expected to overcome the current
limitation of small display size of mobile devices like cell phones, digital cameras and PDAs. Recent progress in the
development of compact modulated RGB laser sources enables to set up very small laser projection systems that become
attractive not only for consumer products but also for automotive applications like head-up and dash-board displays.
Within the last years continuous progress was made in increasing MEMS scanner performance. However, only little is
reported on how mass-produceability of these devices and stable functionality even under harsh environmental
conditions can be guaranteed. Automotive application requires stable MEMS scanner operation over a wide temperature
range from -40° to +85°Celsius. Therefore, hermetic packaging of electrostatically actuated MEMS scanning mirrors
becomes essential to protect the sensitive device against particle contamination and condensing moisture. This paper
reports on design, fabrication and test of a resonant actuated two-dimensional micro scanning mirror that is hermetically
sealed on wafer level. With resonant frequencies of 30kHz and 1kHz, an achievable Theta-D-product of 13mm.deg and
low dynamic deformation <20nm RMS it targets Lissajous projection with SVGA-resolution. Inevitable reflexes at the
vacuum package surface can be seperated from the projection field by permanent inclination of the micromirror.
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