A novel 24-kHz resonant scanner for high-resolution laser display

Abstract

This contribution deals with design, fabrication and test of a micromachined resonant scanner usable for horizontal deflection of the laser beam in a projection display. The electrostatically driven plate is separated from the mirror in order to reduce air damping and electrostatic non linearity. The device consists of a circularly shaped mirror which is suspended by torsion beams in the center of an elastically suspended driving plate. A resonator with two rotational degrees of freedom is arranged in this way. The rotation axes of mirror and driving plate are the same. A suitable design of the properties of the two degrees of freedom resonator leads to a significant amplification of the oscillation of the mirror compared to the oscillation of the driving plate. The first resonant mode is a rotation of both plates with nearly the same magnitude at a frequency of approx. 5 kHz. The second mode with paraphase deflection at 24 kHz shows a deflection amplification by a ratio of 53 and is used for scanning operation. A supporting part made of glass carries two electrodes in the region of the driving plate and has a micro sandblasted hole beneath the mirror. Bulk micromachining, KOH wet etching of the electrode gap size on the back side of the driving plate, reactive ion etching for contour shaping of the mirror, of the driving plate and of the torsion beams and anodic bonding have been used for fabrication of the mechanical structure. The mirror is evaporated by an aluminum layer. Applying a voltage of 380V results in a mechanical deflection of ± 5.5 degrees at 24 kHz at atmosphere pressure. The device shows very small dynamic warp (<100nm) of the mirror plate even though the relatively large size of 2.2 mm diameter because of the thickness of 280 µm. The measured mechanical Q-factor is 5100.

Invited Review Article: Imaging techniques for harmonic and multiphoton absorption fluorescence microscopy

“…They produce a sinusoidal scanning pattern at frequencies as high as 24 kHz. 65 In order to take advantage of the full sinusoidal scan, data must be acquired in both, the forward and backward directions. Also, due to the variation in data rate acquisition when using a sinusoidal oscillation, in practical implementations, one typically acquires data only during the "linear" part of the sine wave.…”

Comb-Actuated Resonant Torsional Microscanner With Mechanical Amplification

“…EM scanners require the placement of magnets close to the scanning device, while ES comb-drive scanners have a fairly simple fabrication and arrangement of the actuator, with the tradeoff of requiring high voltage. ES-actuated scanners have been demonstrated by many groups [9], [11], [13], [14], [16], [18]- [20], [24]- [26], [32].…”

“…1(a) compares published scanner performances [10]- [26], [32] according to θ OPT · Dproduct and horizontal scan frequency f . The product θ OPT · D · f can be considered as a new figure of merit indicating [26], [32]. Only high-performance scanners are reported and numbers in the plot area correspond to the reference listed below the figure.…”

“…The solid lines indicate requirements for different display formats assuming 60-Hz refresh rate and bidirectional scanning, except for the HDTV line in the second chart, which assumes bidirectional scanning with two separate laser beams to reduce the frequency requirements. (b) Performance comparison of ES scanners according to two metrics: θ OPT · D · f and θ OPT · D · f/V [11], [18], [20] [21], [25], [26], [32]. The former indicates the number of pixels per second, while the latter is an efficiency metric.…”

High-Q MEMS Resonators for Laser Beam Scanning Displays

“…It so far has been tried to shift the resolution limits only by increasing the driving power in order to increase the torque acting on the MEMS mirror axes. Consequently, driving circuits for electrostatically actuated MEMS mirrors have to handle disadvantageously high driving voltages [6,7] or, in the case of electromagnetically actuated mirrors, driving currents and power consumption are disadvantageously high [4]. Thus, the MEMS mirror concept proposed in this paper is to reduce gas damping instead of further increasing power consumption.…”