Abstract-A resonant piezoelectric scanner is developed for high-resolution laser-scanning displays. A novel actuation scheme combines the principle of mechanical amplification with lead zirconate titanate (PZT) thin-film actuation. Sinusoidal actuation with 24 V at the mechanical resonance frequency of 40 kHz provides an optical scan angle of 38.5• for the 1.4-mm-wide mirror. This scanner is a significant step toward achieving full-highdefinition resolution (1920 × 1080 pixels) in mobile laser projectors without the use of vacuum packaging. The reported piezoscanner requires no bulky components and consumes < 30-mW power at maximum deflection, thus providing significant power and size advantages, compared with reported electromagnetic and electrostatic scanners. Interferometry measurements show that the dynamic deformation is at acceptable levels for a large fraction of the mirror and can be improved further for diffraction-limited performance at full resolution. A design variation with a segmented electrode pair illustrated that reliable angle sensing can be achieved with PZT for closed-loop control of the scanner.[ 2012-0116]Index Terms-High-frequency laser beam scanning, lead zirconate titanate (PZT) thin-film-actuated, microelectromechanical systems (MEMS), MEMS mirror, resonant scanner.

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A comb-actuated torsional microscanner is developed for high-resolution laser-scanning display systems. Typical torsional comb-drive scanners have fingers placed around the perimeter of the scanning mirror. In contrast, the structure in this paper uses cascaded frames, where the comb fingers are placed on an outer drive frame, and the motion is transferred to the inner mirror frame with a mechanical gain. The structure works only in resonant mode without requiring any offset in the comb fingers, keeping the silicon-on-insulator-based process quite simple. The design intent is to improve actuator efficiency by removing the high-drag fingers from the high-velocity scanning mirror. Placing them on the lower velocity drive frame reduces their contribution to the damping torque. Furthermore, placement on the drive frame allows an increase of the number of fingers and their capacity to impart torque. The microscanner exhibits a parametric response, and as such, the maximum deflection is found when actuated at twice its natural frequency. Analytical formulas are given for the coupled-mode equations and frame deflections. A simple formula is derived for the mechanical-gain factor. For a 1-mm × 1.5-mm oblong scanning mirror, a 76 • total optical scan angle is achieved at 21.8 kHz with 196-V peak-to-peak excitation voltages.[2009-0304]

A torsional scan mirror suspended with two flexure beams can be used in various display, imaging and other scanning applications. Using various mirror shapes and flexure dimensions as parameters, a set of analytical formulae is presented to predict the natural frequency of the first five vibration modes, which are torsion, in-plane and out-of-plane sliding modes and in-plane and out-of-plane rocking modes. Mode frequencies are compared with the finite element model (FEM) predictions using ANSYS TM for a wide range of flexure beam dimensions. The formulae include the effective inertia of the flexure beams and orthotropic material anisotropy effects. The analytical formulae are verified for both isotropic (e.g. steel) and orthotropic (e.g. silicon) materials. These formulae work very well when the Euler-Bernoulli beam theory assumptions and the rigid mirror assumption are satisfied. The accuracy of analytical predictions is improved by introducing an empirical correction factor to the analytical predictions using non-dimensional flexure beam ratios. The correction factor reduces the error between analytical formulae and FEM predictions to within a few per cent for all five modes for a large range of flexure dimensions. FEM predictions and analytical formulae are partly verified by experimental results.

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