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.
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.
This paper describes the design, fabrication, and characterization of the first MEMS scanning mirror with performance
matching the polygon mirrors currently used for high-speed consumer laser printing. It has reflector dimensions of 8mm
X 0.75mm, and achieves 80<sup>o</sup> total optical scan angle at an oscillation frequency of 5kHz. This performance enables the
placement of approximately 14,000 individually resolvable dots per line at a rate of 10,000 lines per second, a record-setting
speed and resolution combination for a MEMS scanner. The scanning mirror is formed in a simple
microfabrication process by gold reflector deposition and patterning, and through-wafer deep reactive-ion etching. The
scanner is actuated by off-the-shelf piezo-ceramic stacks mounted to the silicon structure in a steel package. Device
characteristics predicted by a mathematical model are compared to measurements.
A novel MEMS actuation technique has been developed for scanned beam display and imaging applications that allows driving a two-axes scanning mirror to wide angles at high frequency. This actuation technique delivers sufficient torque to allow non-resonant operation as low as DC in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies great enough to support SXGA resolutions. Several display and imaging products have been developed employing this new MEMS actuation technique. Exceptionally good displays can be made by scanning laser beams much the same way a CRT scans electron beams. The display applications can be as diverse as an automotive head up display, where the laser beams are scanned onto the inside of the car’s windshield to be reflected into the driver’s eyes, and a head-worn display where the light beams are scanned directly over the viewer’s vision. For high performance displays the design challenges for a MEMS scanner are great. The scanner represents the system’s limiting aperture so it must be of sufficient size; it must remain flat to fractions of a wavelength so as to not distort the beam’s wave front; it must scan fast enough to handle the many millions of pixels written every second; and it must scan in two axes over significant angles in order to “paint” a wide angle, two-dimensional image. Using the new actuation method described, several MEMS scanner designs have been fabricated which meet the requirements of a variety of display and imaging applications.