direction of these two actuators, the stage can perform 2-axis in-plane motions. ... Silicon-based micro positioning stages can find various applications in micro ...
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Procedia Engineering 25 (2011) 689 – 692
Proc. Eurosensors XXV, September 4-7, 2011, Athens, Greece
Development of a Novel Dual-axis Large-displacement Microstage Using Lorentz Force Actuators and Curved-beam Springs Feng-Yu Leea, Tsung-Lin Tanga, Weileun Fanga,b a Power Mechanical Eng. Department MEMS Inst., National Tsing Hua University, Hsinchu, Taiwan
b
Abstract This study demonstrates the design, fabrication and characteristics of a novel dual-axis microstage. The stage is supported by curved-beam springs and driven by two Lorentz force actuators. By modulating the magnitude and direction of these two actuators, the stage can perform 2-axis in-plane motions. The microstage has two merits: (1) Lorentz force actuator with thermal buckling characteristic to enlarge the microstage displacement, (2) curved-beam spring to enable the 2-axis positioning. The typical microstage has a planar size of 3mmu3mm with output displacements of ±13 ȝP in X and Y-axis. © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Keywords: microstage; dual-axis; large displacement; Lorentz force
1. Introduction Silicon-based micro positioning stages can find various applications in micro systems, such as micro optical switches [1], micro optical lens scanners [2], scanning probe microscope (SPM) [3] and high density data storage [4].In general, the chip size, stroke and resolution, motion decoupling in different directions, and natural frequency are several critical considerations to design the micro positioning stage. Presently, various actuating methods have been reported for different operating conditions, such as piezoelectric (PZT) actuators [5], shape memory alloy (SMA) actuators [6], electro-thermal actuators [7], electromagnetic actuators [4] and electrostatic comb-drive actuators [1-3, 8]. Among these methods, the PZT actuators have excellent E-İ efficiency and the SMA actuators can perform large displacement, but both of them suffer from the difficulty of fabrication. Electro-thermal and electromagnetic actuators can induce large displacement, but the temperature issue and the thick coils need to be considered. The comb-
1877-7058 © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2011.12.170
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drive actuators, which are most commonly used, have low power consumption and easy fabrication. However, the applications are limited by the small displacement and the side pull-in effect. This study introduces a novel actuating method for dual-axis microstage application. The Lorentz force actuators combined with curved-beam springs enable decoupled 2D motion with large displacements. 2. Concept And Design This study presents the novel micro positioning stage in Fig.1. The design employs the curved-beam +I1 -I1 Y B field Curved-beam springs
Stage
-I2
+I2
Lorentz force actuators
Current direction
X
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Fig. 1 Concept and design of the dual-axis microstage.
springs and the Lorentz force actuators to respectively support and drive the stage. The Lorentz forces induced by the input currents will cause the in-plane displacements of the actuators. The curved-beam springs design enable the decoupled 2D motions of the microstage through the actuating of two linear actuators. Figure 2a shows the concept of dual-axis motion for the position stage. As two actuators have the same displacement in the same (opposite) direction, the stage will travel in the ±Y-axis (±X-axis)
+I2
Y
+I1 (x, y) (i1,i2)
-Y direction
+Y direction
X
-I2
-I1 -X direction
+X direction (a)
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Fig. 2 (a)The operating concept of dual-axis positioning, and (b) the relation between microstage position and the input currents.
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direction. Otherwise, the microstage will move in both X-axis and Y-axis directions. In other words, the in-plane position (x, y) of microstage can be controlled by specifying the input currents (i1, i2) on actuators. Fig. 2b schematically shows the relationship between the microstage position (on the X-Y plane) and the input currents of the two actuators (on the I1-I2 plane). 3. Fabrication And Results Figure 3a shows the fabrication process steps. First, the LPCVD nitride was patterned as the mask for (1)
Aluminium
Epi wafer
Silicon
Nitride
(2)
Aluminium (3)
Oxide Lorentz force actuator
(4) (a)
(b)
Fig. 3 (a) Fabrication process steps, and (b) typical fabrication results of the dual-axis microstage.
electrochemical etching on an epitaxy (epi) wafer (Fig.3a-1). After Al-film was deposited and patterned as wires, the PECVD oxide was deposited and patterned as hard mask for the following DRIE (Fig.3a-2). After the back-side electrochemical Si etching and front-side Si DRIE (Fig.3a-3), the remaining PECVD oxide was removed (Fig.3a-4). Fig.3b shows the SEM micrographs of typical fabrication results. It indicates the device area is 3mm×3mm with the stage size of 500ȝPîȝP 7Ke Al wires are patterned on top of the Lorentz force actuators with a WKLFNQHVV RI ȝP The zoom-in SEM micrographs also show the curved-beam springs, which have a radius of curvature of 1mm, support the stage and connect it to the Lorentz force actuators. 4. Experiments And Discussions The measured microstage displacements versus driving-currents in Fig.4a and Fig.4b show the microstage has large displacements of ȝP in X and Y-axis. The coupling of X-Y displacements is less than 1% for Y-axis actuation and less than 10% for X-axis actuation. Due to the thermal buckling of the Lorentz force actuators [9] and the design of the curved-beam springs, the output displacement is increased nonlinearly with the input current. Thus, the traveling distance of the stage is improved. Note that the output displacement of Lorentz force actuators will be restricted by the maximum tolerable current of conducting wires. Fig.4c further shows the positioning range of microstage as the input currents are ±150mA. By varying the input currents of I1 and I2 on actuators, the position stage will travel within the rhombus area in the X-Y plane, as indicated in Fig.4c.
Feng-Yu Lee et al. / Procedia Engineering 25 (2011) 689 – 692
14
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Fig. 4 Dual-axis displacement when (a) actuating along X, (b) actuating along Y, and (c) input currents restricted below f150 mA.
5. Conclusion This study demonstrates a novel dual-axis microstage driven by two Lorentz force actuators and supported by curved-beam springs. The Lorentz force actuators enable large displacement due to the thermal buckling of beams. The curved-beam springs design enable the decoupled 2D motions of the microstage through the actuating of two Lorentz force linear actuators. In applications, the typical fabricated microstage has the size of 3mmu3mm with output displacements of ±13 ȝP in X and Y-axis. Acknowledgements This study is based (in part) upon work supported by the National Science Council, Taiwan under Grant NSC 99-2221-E-007-040-MY3. The authors would like to express his appreciation to the Nano Science and Tech. Center of National Tsing Hua University, and Nano Facility Center of National Chiao Tung University in providing the fabrication facilities. References [1] Li J, Zhang Q X, Liu A Q. Advanced fiber optical switches using deep RIE (DRIE) fabrication. Sensors Actuators. A 102 286 95, 2003. [2] Kim C-H, Kim Y-K. Integration of a micro lens on a micro XY-stage. Proc. SPIE Int. Soc. Opt. Eng. 3892 109 17, 1999. [3] Indermuhle P-F, Jaecklin V P, Brugger J, Linder C, de Rooij N F, Binggeli M. AFM imaging with anxy-micropositioner with integrated tip. Sensors Actuators A 47 562 65, 1995. [4] Choi J-J, Park H, Kyu Y K, Jong U J. Electromagnetic micro x y stage with very thick Cu coil for probe-based mass data storage device. Proc. SPIE Int. Soc. Opt. Eng. 4334 363 71, 2001. [5] Yao Q, Ferreira P M, Mukhopadhyay D. Development of a novel piezo-driven parallel-kinematics single crystal silicon micropositioning XY stage. Proc. SPIE Int. Soc. Opt. Eng. 5836 56 66, 2005. [6] Yigui L, Minoru S, Kazihiro H. A two-dimensional self-aligning system driven by shape memory alloy actuators. Opt. Laser Technol. 37 147 9, 2005. [7] Wu C-T, Hsu W. An electro-thermally driven microactuator with two dimensional motion. Microsystem Techonoledgy, 8 47 50, 2002. [8] Epitaux M, Verdeil J-M, Petremand Y, Noell W, De Rooij N F. Micro-machined XY stage for fiber optics module alignment. IEEE Conf. on Optical Fiber Communication (Anaheim, CA) pp 131 3, 2005. [9] Andrew Cao, Phyllis Yuen, Liwei Lin. Microrelays with bidirectional electrothermal electromagnetic actuators and liquid metal wetted contacts. J. Microelectromechanical Systems, 16 700 708, 2007.
