MEMS Micromirror Actuation Techniques: A Comprehensive Review of Trends, Innovations, and Future Prospects

Abstract

Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation of these mirrors is critical in determining their performance, as it contributes to factors such as response time, scanning angle, and power consumption. This article aims to provide a thorough exploration of the actuation techniques used to drive micromirrors, describing the fundamental operating principles. The four primary actuation modalities-electrostatic, electrothermal, electromagnetic, and piezoelectric-are thoroughly investigated. Each type of actuator's operational principles, key advantages, and their limitations are discussed. Additionally, the discussion extends to hybrid micromirror designs that combine two types of actuation in a single device. A total of 208 closely related papers indexed in Web of Science were reviewed. The findings indicate ongoing advancements in the field, particularly in terms of size, controllability, and field of view, making micromirrors ideal candidates for applications in medical imaging, display projections, and optical communication. With a comprehensive overview of micromirror actuation strategies, this manuscript serves as a compelling resource for researchers and engineers aiming to utilize the appropriate type of micromirror in the field of optical scanning technology.

Keywords: MEMSs; MEMSs mirrors; microactuators; microelectromechanical systems; micromirrors; optical scanning.

Figure 2

(a) Illustration of the first ESA micromirror exhibiting four-leaf clover shape; (b) cross-sectional view of single element. Lateral motion micromirror: (c) schematic diagram; (d) optical photo of the fabricated device. Adapted with permission from Ref. [34]. Copyright 1995, IOP Science. (e) Micromirror design with pedestal and auxiliary fixed-free beams. Adapted with permission from Ref. [45]. Copyright 2018, Springer Nature.; Bending arm based micromirrors: (f) schematic diagram of interdigitated cantilevers; (g) operational mechanism. Adapted with permission from Ref. [46]. Copyright 2009, IEEE. (h) L-shaped arm based micromirror. Adapted from Ref. [47], Available under a CC-BY license. Copyright 2020, MDPI. (i) Double-bridge micromirror. Adapted with permission from Ref. [21]. Copyright 2020, IEEE.

Figure 7

Inverted series connector bimorph (a) Concept of ISCB. (b) An illustration of the modified ISCB showing the overlapped region. (c) Top view of the device design. (d) SEM image of the fabricated mirror. Adapted with permission from Ref. [127]. Copyright 2009, IEEE. Three stacked FDS bimorphs proposed by Ref. [129]. (e) Composite image of the actuation mechanism. (f) Optical image of the final device. (g) The actuation motions of the proposed device. Adapted from Ref. [129]. Available under a CC-BY license. Copyright 2021, MDPI. Concept of LSF actuation (h) Two bimorph displays LVD with lateral shift. (i) A three-bimorph system demonstrates LVD without lateral shift. Adapted with permission from Ref. [130]. Copyright 2008, Elsevier. (j) SEM image of the fabricated array device with a detailed single cell and single actuator. Adapted with permission from Ref. [131]. Copyright 2010, IEEE.

Figure 1

Block diagram of MEMSs micromirror actuation methods.

Figure 3

Electrostatic combdrive: (a) schematic diagram with electrical connections; (b) SEM image of combdrive connected to linear resonant plate. Adapted with permission from Ref. [66]. Copyright 1990, Elsevier. (c) 3D polysilicon micromirror-based tunable laser diode. Adapted with permission from Ref. [68]. Copyright 2001, IEEE. 2D vertical combdrive micromirrors: (d) Schematic diagram; (e) SEM image with some magnified parts. Adapted with permission from Ref. [71]. Copyright 2004, IOP Science. (f) Schematic structure of the motion-amplifying levers based two-axis mirror. Adapted with permission from Ref. [72]. Copyright 2006, IEEE. (g) (left): High fill factor micromirror illustration with transparent mirror for better visualization. (right): Bonding pads to connect to the electrodes. Adapted with permission from Ref. [73]. Copyright 2006, IEEE.

Figure 4

A 2D vertical combdrive micromirror: (a) SEM images of the diamond shaped diaphragm. The mirrored surface of the device is shown in the bottom left small image. Adapted with permission from Ref. [93]. Copyright 2006, IOP Science. (b) VOA device using rotary CDA. Adapted with permission from Ref. [95]. Copyright 2006, IEEE. (c) Schematic of the repulsive actuators micromirror. (d) top and bottom plates. Adapted with permission from Ref. [96]. Copyright 2012, Elsevier. (e) Schematic of two-row repulsive torque single actuator. (f) SEM image of fabricated micromirror. Adapted with permission from Ref. [60]. Copyright 2015, IEEE.

Figure 5

Monomorphic electrothermal actuators: (a) Configuration of a U-shaped actuator. (b) Illustration of Chevron electrothermal actuator. (c) A 1D Chevron actuator micromirror. Presented by [108]. (d) Conversion of lateral motion to torsional motion. (e) A 2D micromirror actuator. Adapted with permission from Ref. [108]. Copyright 2009, IOP Science. (f) Illustration of a bimorphic contilever in pre-actuation and under-actuation state. (g) conceptual diagram of the 1D micromirror presented by [109] and its (h) SEM image. Adapted with permission from Ref. [109]. Copyright 2002, IEEE. (i) Illustration of 2D micromirror proposed by [110]. (j) SEM image of the fabricated 2D micromirror.Adapted with permission from Ref. [110]. Copyright 2004, IEEE. (k) Top view of the paired actuators mirror by [111]. (l) SEM image of the fabricated mirror. Adapted with permission from Ref. [111]. Copyright 2006, Elsevier.

Figure 6

(a) Optical image of the micromirror employing linear actuator (b) SEM image of the fabricated device. (c) Image of the micromirror with curved actuator. (d) Corresponding SEM photographs of the device. Adapted with permission from Ref. [24]. Copyright 2007, IOP Science. (e) SEM image depicting a circular micromirror. (f) Simulated micromirror with initial tilt upon release. The color bar illustrates the out−of−plane displacement from its unreleased position. (g) Cross-section illustration of the multimorph actuator. Adapted with permission from Ref. [124]. Copyright 2011, Elsevier. (h) SEM image of piston only micromirror presented by [125]. (i) SEM image of TTP micromirror. Adapted with permission from Ref. [125]. Copyright 2012, Elsevier.

Figure 8

(a) Schematic of the aluminium spring based EMAM clamped under ES force. (b) Under electromagnetic actuation. Adapted with permission from Ref. [149]. Copyright 2003, IEEE. (c) Vertical EMAM in switched-off status. (d) Vertical EMAM when switched ON. Adapted with permission from Ref. [155]. Copyright 2005, IEEE. (e) Schematic of the optical scanner for OCT imaging with optical image of the fabricated EMAM. Adapted with permission from Ref. [156]. Copyright 2006, IOPScience. (f) Schematic of 2D double gimbal micromirror. Adapted with permission from Ref. [5]. Copyright 2018, IEEE. (g) Illustration of dual-axis micromirror moving-magnet actuation; (h) Integration of the sequence of the components (top); cross-section of the integrated system (bottom). Adapted with permission from Ref. [157]. Copyright 2012, IOPScience. (i) Design of the mirror with mechanical amplification (left); SEM image of the fabricated mirror (right). Adapted from Ref. [158]. Available under a CC-BY license. Copyright 2015, Optica.

Figure 9

(a) Prototype of FR4-based scanning EMAM enclosed in a plexiglass package; (b) frontal copper coils for sensing; and (c) back-side of the FR4 platform for driving and sensing. Adapted from Ref. [167]. Available under a CC-BY license. Copyright 2018, MDPI. (d) Structure of flexible PCB EMAM and (e) the assembled flexible PCB. Adapted with permission from Ref. [169]. Copyright 2019, IOPScience. Shown are 3D-printed mechanical structures-based micromirrors (f) Operation principal of mirror described in [173]. (g) Structure with mirror and magnets. (h) Final assembled scanning device. Adapted with permission from Ref. [173]. Copyright 2022, Elsevier. (i) Upper coil assembly of the biaxial scanning mirror presented by Ref. [174]. (j) Lower coil assembly; (k) structure of the coil bonded mirror; (l) laser-patterned coils made of copper foil; (m) the final packaged mirror. Adapted with permission from Ref. [174]. Copyright 2022, Elsevier.

Figure 10

(a) Schematic of the 2D scanner with SEM image of the fabricated scanner. (b) Actuation mechanism. Adapted with permission from Ref. [176]. Copyright 2007, IEEE. (c) Schematic of MEMS scanner actuated by an array of PZT actuators and photograph of the packaged device. Adapted with permission from Ref. [177]. Copyright 2010, Elsevier. (d) Gimble-mounted piezoelectric 2D micromirrors. Adapted with permission from Ref. [179]. Copyright 2015, IEEE. (e) cantilever-type actuator based micromirror. Adapted with permission from Ref. [182]. Copyright 2024, IEEE. (f) Fabricated circular arc beam structured micromirror with a bell-shaped connection to the X axis actuator and U-shaped connection to the Y axis actuator. Adapted with permission from Ref. [183]. Copyright 2024, IEEE. Steel plate based 1D micromirror: (g) Schematic of structure #1. (h) Assembled structure #1. (i) Schematic of structure #2. (j) Assembled structure #2. Adapted with permission from Ref. [184]. Copyright 2024, Elsevier.

Figure 11

Hybrid electrothermal–electromagnetic micromirrors: (a) Hybrid mirror with zoomed images of buckle beams and torsion bar. Adapted with permission from Ref. [191]. Copyright 2009, IOPScience. (b) Schematic and optical image hybrid micromirror proposed by [192]. Adapted with permission, Copyright 2012, IEEE. Hybrid electrothermal–electrostatic micromirrors: (c) Presented by Ref. [193] and adapted with permission, Copyright 2011, IEEE. (d) Presented by Ref. [194] and adapted with permission, Copyright 2013, IEEE.

Figure 12

Design and validation methodology for MEMS micromirrors.