Outstanding Scientific Results

NiFe Biaxial Magnetic Scanner for 2D Imaging

Arda D. Yalcinkaya*, Hakan Urey, Sven Holmstrom *Earlier on Koc University, Istanbul, Turkey. Now on Bogazici University, Istanbul, Turkey. Koc University, Istanbul, Turkey. Microvision, Seattle, USA

tel: +90-212-338-1709; fax: +90-212-338-1548

e-mail: arda.yalcinkaya@boun.edu.tr

The first biaxial soft magnetic biaxial microscanner is presented The device is operated via a  magnetostatic torque produced by the combination of a AC flux from a custom made electro coil and a NiFe layer deposited on the movable part. The device is in atmospheric pressure capable of full optical scan angles of 88° (at 100 mA RMS coil current) and 1.8° for slow and fast scan directions, respectively. In combination with a mirror size of 1.5 mm, resulting µoptD products are 132 deg·mm and 2.7 deg·mm for slow and fast axis, respectively. As a result an display or part of a display with the present device with 2000×50 resolution can be achieved in ambient pressure, eliminating the need for expensive vacuum sealed packaging.

The Device

The device makes use of an earlier scanner, tested, fabricated and published by the Optical Microsystem Laboratory (Koc University) in cooperation with Microvision (Seattle, USA). The earlier device is a Lorentz type device, driven by a moving copper coil placed on the outer frame, encircling the mirror. When placed in a static magnetic field this allows for a world leading scanning performance among comparable microscanners. The device is composed of a circular mirror, gimbal mounted to an outer frame. The outer frame is anchored to a fixed substrate through a set of springs. To be able to instead make use of an external coil the flat copper coils on the outer were electroplated with NiFe alloy. Due to the high mechanical quality factors inherent in the structure the device works as a multi band pass filter and make the two vibration modes well separated. This allows for actuation of the two orthogonal scanning modes using only one coil fed with two super positioned sinus signals.

Magnetostatic Actuator Operation

When an alternating current is passed between the ports 1 and 2, (see figure) a frequency dependent magnetic field (and flux) is created in the direction normal to the scanner plane. The slow scan, consisting of rocking of the outer frame around its hinges, has a resonance frequency at 367Hz. The fast scan resonance occurs at 22230Hz and is due to the high quality factor of the fast scan. The outer frame makes a small rocking motion parallel with its own hinges, the amplitude of which is multiplied with the quality factor of the mirror to create its much larger deflection. It is worth remembering that the high quality factor of each mode separates the slow and fast scan motions by suppressing all the other spurious drive components because of the strong built in mechanical band-pass filters.

Conclusions

A novel microscanner actuation mechanism is presented to satisfy the performance requirements of the raster scanning mirrors. Several advantages are inherent in the design: Vacuum packaging is not necessary, enhancing cost as well as productivity yield. Resonant operation of the scanner allows filtering out the nonlinearities and hysteresis in the excitation torque. Fabricated using bulk micromachining process, the present device is immune to the dynamic deformation and surface quality problems. There are a number of applications where the present device can directly be used and there is also room for improvement, since the silicon scanner used was originally fabricated for a different actuation method.