Kah How Koh

A 1-V Operated MEMS Variable Optical Attenuator Using Piezoelectric PZT Thin-Film Actuators

A rotational Si mirror driven by PZT actuators has been investigated for variable optical attenuator (VOA) applications. The PZT actuators deploy 3.1-mum PZT layer. The developed PZT-driven microelectromechanical systems VOA comprising a large Si reflection mirror integrated with a dual core fiber collimator in 3-D light attenuation arrangement. The curve of the attenuation versus driving voltage shows rather uniform changing rate taking the advantage of the linear relation between the optical angle and the driving voltage. Dynamic range of 40-50 dB is achieved at 1 and 1.2 dc driving voltages, respectively.

Ultra-wide frequency broadening mechanism for micro-scale electromagnetic energy harvester

This work proposed a hybrid frequency broadening (HFB) mechanism in micro-scale for vibration energy harvesting with ultra-wide bandwidth. A strong HFB behavior is induced by the Duffing stiffening of the clamped-clamped beam stretching and further stimulated continuously by three distributed resonances including out-of-plane mode I at 62.9 Hz, torsion mode II at 82.1 Hz, and twist mode III at 150 Hz. At the acceleration of 1.0g, the microfabricated device with a small area of 6 × 6 mm2 is able to broaden the operating bandwidth from 62.9 Hz to be as wide as 383.7 Hz. This design methodology can be implemented for efficient electromagnetic energy harvesting.

A 2-D MEMS scanning mirror based on dynamic mixed mode excitation of a piezoelectric PZT thin film S-shaped actuator

A novel dynamic excitation of an S-shaped PZT piezoelectric actuator, which is conceptualized by having two superimposed AC voltages, is characterized in this paper through the evaluation of the 2-D scanning characteristics of an integrated silicon micromirror. The device is micromachined from a SOI wafer with a 5 μm thick Si device layer and multilayers of Pt/Ti/PZT//Pt/Ti deposited as electrode and actuation materials. A large mirror (1.65 mm x 2mm) and an S-shaped PZT actuator are formed after the backside release process. Three modes of operation are investigated: bending, torsional and mixed. The resonant frequencies obtained for bending and torsional modes are 27Hz and 70Hz respectively. The maximum measured optical deflection angles obtained at 3Vpp are ± 38.9° and ± 2.1° respectively for bending and torsional modes. Various 2-D Lissajous patterns are demonstrated by superimposing two ac sinusoidal electrical signals of different frequencies (27 Hz and 70 Hz) into one signal to be used to actuate the mirror.

Novel piezoelectric actuation mechanism for a gimbal-less mirror in 2D raster scanning applications

In this paper, we present the design, fabrication and measurement results of a 2D scanning mirror actuated by 1 × 10 piezoelectric Pb(Zr,Ti)O3 (PZT) cantilever actuators integrated on a thin silicon beam. A combination of bulk silicon micromachining based on a silicon-on-insulator (SOI) substrate and thin-film surface micromachining on a 5 µm thick Si device layer is used to fabricate the device. Multi-layers of Pt/Ti/PZT/Pt/Ti are deposited as electrode materials. A large silicon mirror plate (5 mm × 5 mm) and a 1 × 10 PZT cantilever array arranged in parallel are formed after the backside release process. The ten PZT cantilever actuators are electrically isolated from one another. The device can operate in three modes: bending, torsional and mixed (or combinational) modes. In bending mode, the first resonant frequency was measured to be 30 Hz and an optical deflection angle of ±8° was obtained when all ten cantilevers were actuated at 9 Vpp. In torsional mode, the resonant frequency was measured to be 89 Hz and an optical deflection angle of ±4.6° was obtained by applying a gradually declining ac voltage started at 8 Vpp to two sets of actuators, where each set comprises five cantilever actuators of the said 1 × 10 array, i.e. 1–5 and 6–10. A 2D raster scanning pattern was achieved in the mixed mode when the bending mode was carried out by cantilever actuators of 4–7 and the torsional modes were exercised by two different sets of cantilever actuators, i.e. 1–3 and 8–10, under opposite biasing direction. This mixed mode operation mechanism demonstrates the first 2D raster scanning mirror-driven beam actuators.

A Piezoelectric-Driven Three-Dimensional MEMS VOA Using Attenuation Mechanism With Combination of Rotational and Translational Effects

A gold-coated silicon mirror (5 mm 5 mm) actuated by piezoelectric (PZT) cantilever beams has been investigated for variable optical attenuator applications. The device is micromachined from a SOI substrate with a 5 μm thick Si device layer, with multilayers of Pt/Ti/PZT/Pt/Ti deposited as electrode materials. A large Si mirror plate and 110 arrayed PZT cantilevers arranged in parallel are formed after the release process. The ten cantilevers are designed to be electrically isolated from one another. A dual-core fiber collimator is aligned perpendicularly to the mirror in a 3-D light attenuation arrangement. Thus, three modes of attenuation mechanisms were investigated based on rotational and translational effects. A dynamic attenuation range of 40 dB is achieved at 1 V and 1.8 V for bending and torsional mode, respectively.

Fabry–Perot filter using grating structures

Grating structures are designed at the inner wall of the Fabry-Perot (FP) resonator to enhance the performance of an FP optical filter. The rectangular grating or triangular grating (TG) structures allows the light to be propagated effectively through the FP resonator. Attributed to the grating structures, the spectrum intensity of a FP resonator with grating structures is calculated to be 4.5-fold higher than that of a FP resonator with slot. In addition, the Q-factor of the resonant peak for a FP resonator with hybrid TG structure and two slots is 9.5-fold and 4.7-fold higher than that of a FP resonator with one slot and TG configurations, respectively.

A Two-Dimensional MEMS Scanning Mirror Using Hybrid Actuation Mechanisms With Low Operation Voltage

This paper presents the design, fabrication, and characterization of a novel CMOS-compatible 2-D MEMS scanning mirror based on hybrid actuation mechanisms. Both electrothermal and electromagnetic (EM) actuations have been integrated in the same device for slow and fast scanning purposes, respectively. The added advantage of a CMOS-compatible fabrication process allows our device to be monolithically integrated with CMOS integrated circuits. Optical deflection angles of ±1.5° for a 74-Hz vertical scan at 12 mW by electrothermal actuation and ±10° for a horizontal scan frequency of 202 Hz at 1.26 mA and 1 Vac by EM actuation are reported. Our unique design of utilizing both electrothermal and EM actuation mechanisms is the first demonstration of such hybrid-driven CMOS-compatible MEMS mirror. Various Lissajous patterns have been demonstrated at low-power biasing condition, making our proposed hybrid actuation design approach suitable for mobile 2-D raster scanning applications powered by batteries with limited capacity.

Study of hybrid driven micromirrors for 3-D variable optical attenuator applications

Aluminium-coated micromirrors driven by electrothermal and electromagnetic actuations have been demonstrated for 3-D variable optical attenuation applications. Three types of attenuation schemes based on electrothermal, electromagnetic and hybrid, i.e. combination of electrothermal and electromagnetic, actuations have been developed. In addition, two different designs have been fabricated and characterized to investigate the effects of the variations made to both the actuators on the optical attenuation performances of the micromirror. Our unique design of using both ET and EM actuators simultaneously to achieve attenuation is the first demonstration of such hybrid driven CMOS compatible MEMS VOA device.

Low-Voltage Driven MEMS VOA Using Torsional Attenuation Mechanism Based on Piezoelectric Beam Actuators

A gold-coated silicon mirror (5 mm × 5 mm) driven by a piezoelectric Pb(Zr,Ti)O3 (PZT) beam with 1 × 10 cantilever actuators has been demonstrated for variable optical attenuator application. A dual-core-fiber collimator is aligned perpendicularly to the mirror in a three-dimensional light attenuation arrangement. Torsional attenuation based on the difference in the dc biasing voltage applied to the ten piezoelectric cantilevers was investigated. The attenuation curve under dc bias follows that of a Gaussian distribution, with dynamic attenuation range of 40 dB achieved at 1.8 V.

Development of CMOS MEMS thermal bimorph actuator for driving microlens

A CMOS MEMS based thermal actuator is developed by using bimorph with embedded SiO<inf>2</inf> and inverted-connected metal line adopted from CMOS materials. Vertical displacement of 47µm and power consumption of 139mW is obtained at 3V<inf>dc</inf>.