A review of fabrication processes for vertical comb drives

Gallagher, Else; Moussa, Walied A.; McDermott, Mark T.

doi:10.1007/s00542-011-1406-8

“…The electrostatic attractive force generated between the two arrays of combs is independent of the displacement [62]. However vertical comb-drive actuators suffer from the side "pull-in" instability if the fingers are not properly aligned in the transverse direction due to the imperfection in fabrication or external vibration [39].…”

Section: K Gmentioning

confidence: 99%

Development of electrostatic actuators with large out-of-plane deflection and its application in scanning display

Chen¹

2021

Preprint

0

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Electrostatic out-of-plane microactuators have been widely used in applications of variable capacitors, optical attenuators, optical switches and scanning displays due to their small size, low cost, simple and diverse structure, low power consumption and high compatibility with semiconductor process. The large out-of-plane displacement of the microactuator with high reliability is preferred in order to increase the tuning range, tunability and the display size. However, the “pull-in” instability associated with conventional attractive-force electrostatic microactuators significantly limits the out-of-plane displacement and lowers the operation stability. A repulsive-force microactuator has been previously developed which can achieve large out-of-plane rotation and does not suffer from the “pull-in” instability. However, a larger rotation angle of the repulsive-force actuator is highly desired in order to improve its performance in the applications such as increasing the tunability and the scanning angle. In this thesis two novel repulsive-force actuators, i.e., two-row interdigitating-finger and two-width-finger (TWF) actuators are developed which output much larger out-of-plane rotation than the previous repulsive-force actuator without suffering from the “pull-in” instability. The mathematical models are established for both actuators using a hybrid approach. The actuators require only two thin layers and are suitable for surface micromachining process. The measured results show that the two microactuators can achieve rotation angles of 11.5° and 7.5° at 150 V respectively. The improvements are 100% and 35% in comparison to the previous repulsive-force actuator with the same size, stiffness and driving voltage. A 2D scanning micromirror has been developed and fabricated based on the two-row-finger (TRF) actuator. Experimental results show the micromirror has larger rotation angle and faster response speed than those of the micromirror driven by the previous repulsive-force microactuator. The vector scanning display based on the micromirror is demonstrated. An advanced display approach is developed to generate displays with less distortion and higher refreshing rate compared to the previous generic display approach. The automotive Head-up Display (HUD) based on the micromirror and advanced display approach has been constructed for both real and virtual image configurations, which has advantages of small size, low cost, large viewing angle and good visibility over those HUDs in the market.

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“…Consequently, the "pull-in" effect is avoided and the movable plate is mainly driven by the electric fields between it and the side electrodes. The offset-drive configuration has similar structure to vertical comb-drive which is usually fabricated using bulk micromachining process [36], [39].…”

Section: K Gmentioning

confidence: 99%

“…Bulk micromachining is more popular in fabricating the vertical comb-drives which is able to provide large travel range to the actuator and the driven microstructures [39]. One challenge of the bulk micromachining is the alignment of the fingers.…”

Section: K Gmentioning

confidence: 99%

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Development of electrostatic actuators with large out-of-plane deflection and its application in scanning display

Chen¹

2021

Preprint

0

View full text Add to dashboard Cite

Electrostatic out-of-plane microactuators have been widely used in applications of variable capacitors, optical attenuators, optical switches and scanning displays due to their small size, low cost, simple and diverse structure, low power consumption and high compatibility with semiconductor process. The large out-of-plane displacement of the microactuator with high reliability is preferred in order to increase the tuning range, tunability and the display size. However, the “pull-in” instability associated with conventional attractive-force electrostatic microactuators significantly limits the out-of-plane displacement and lowers the operation stability. A repulsive-force microactuator has been previously developed which can achieve large out-of-plane rotation and does not suffer from the “pull-in” instability. However, a larger rotation angle of the repulsive-force actuator is highly desired in order to improve its performance in the applications such as increasing the tunability and the scanning angle. In this thesis two novel repulsive-force actuators, i.e., two-row interdigitating-finger and two-width-finger (TWF) actuators are developed which output much larger out-of-plane rotation than the previous repulsive-force actuator without suffering from the “pull-in” instability. The mathematical models are established for both actuators using a hybrid approach. The actuators require only two thin layers and are suitable for surface micromachining process. The measured results show that the two microactuators can achieve rotation angles of 11.5° and 7.5° at 150 V respectively. The improvements are 100% and 35% in comparison to the previous repulsive-force actuator with the same size, stiffness and driving voltage. A 2D scanning micromirror has been developed and fabricated based on the two-row-finger (TRF) actuator. Experimental results show the micromirror has larger rotation angle and faster response speed than those of the micromirror driven by the previous repulsive-force microactuator. The vector scanning display based on the micromirror is demonstrated. An advanced display approach is developed to generate displays with less distortion and higher refreshing rate compared to the previous generic display approach. The automotive Head-up Display (HUD) based on the micromirror and advanced display approach has been constructed for both real and virtual image configurations, which has advantages of small size, low cost, large viewing angle and good visibility over those HUDs in the market.

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“…The proposed scanner is also of a compact size, which will be justified in section 2. The tilted angle (vertical offset) of the comb electrodes can be easily controlled by using the proposed microassembly process, which contrasts with the case of other fabrication methods [20]. The maximum rotational angle of the mirror is determined by the effective tilted angle (ETA), which can be theoretically derived from the geometric model of comb electrodes.…”

Section: Introductionmentioning

confidence: 99%

A gimbal-less two-axis electrostatic scanner with tilted stationary vertical combs and serially connected springs via a microassembly process

Jun

¹

,

Moon

²

,

Lee

³

et al. 2014

J. Micromech. Microeng.

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We propose a gimbal-less two-axis electrostatic microelectromechanical system (MEMS) scanner with tilted stationary vertical combs (TSVCs) fabricated via a microassembly process. The gimbal-less two-axis scanner has the advantage of being of a compact size and also does not need any additional fabrication sequence for electrical isolation. The TSVCs and coupled springs (T-shaped springs and folded springs) allow the mirror scanner to rotate around two axes with a large scanning angle. The fabrication steps for the proposed scanner can be remarkably reduced by employing a microassembly process, as there is no need to conduct a multistep etching process for height offset between two vertical combs. It was found that the width of the folded spring and the T-shaped spring dominated the resonant frequency of the fast axis and the slow axis, respectively. By modeling the capacitance change of TSVCs with respect to the rotational angle (θ), the effective tilted angle (ETA), as a new design criterion, was introduced to determine an adequate operation range. The optical scanning angle of the fabricated scanner was up to 7.8° at 90 V for the slow axis in quasistatic mode and up to 17.3° at 100 V for the fast axis in resonant mode at 2.84 kHz. The fabricated scanner can be used for various endoscopic optical applications.

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A review of fabrication processes for vertical comb drives

Cited by 7 publications

References 37 publications

Development of electrostatic actuators with large out-of-plane deflection and its application in scanning display

Development of electrostatic actuators with large out-of-plane deflection and its application in scanning display

Development of electrostatic actuators with large out-of-plane deflection and its application in scanning display

A gimbal-less two-axis electrostatic scanner with tilted stationary vertical combs and serially connected springs via a microassembly process

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