The applicability of MOEMS scanning mirrors towards the creation of "flying spot" scanned laser displays is well
established. The extension of this concept towards compact embedded pico-projectors has required an evolution of
scanners and packaging to accommodate the needs of the consumer electronics space. This paper describes the
progression of the biaxial MOEMS scanning mirrors developed by Microvision over recent years. Various aspects of the
individual designs are compared. Early devices used a combination of magnetic quasistatic actuation and resonant
electrostatic operation in an evacuated atmosphere to create a projection engine for retinal scanned displays. Subsequent
designs realized the elimination of both the high voltage electrostatic drive and the vacuum package, and a simplification
of the actuation scheme through proprietary technical advances. Additional advances have doubled the scan angle
capability and greatly miniaturized the MOEMS component while not incurring significant increase in power
consumption, making it an excellent fit for the consumer pico-projector application.
The simplicity of the scanned laser-based pico-projector optical design enables high resolution and a large effective
image size in a thin projection engine, all of which become critical both to the viability of the technology and adoption
by consumers. Microvision's first scanned laser pico-projector is built around a MOEMS scanning mirror capable of
projecting 16:9 aspect ratio, WVGA display within a 6.6 mm high package. Further evolution on this path promises
continued improvement in resolution, size, and power.
In this paper, a nonlinear mathematic model for Microvision's MOEMS scanning mirror is presented. The pixel
placement accuracy requirement for scanned laser spot displays translates into a roughly 80dB signal to noise ratio, noise
being a departure from the ideal trajectory. To provide a tool for understanding subtle nonidealities, a detailed nonlinear
mathematical model is derived, using coefficients derived from physics, finite element analysis, and experiments.
Twelve degrees of freedom parameterize the motion of a gimbal plate and a suspended micromirror; a thirteenth is the
device temperature. Illustrations of the application of the model to capture subtleties about the device dynamics and
transfer functions are presented.
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