Stability Study of an Electrothermally-Actuated MEMS Mirror with Al/SiO2 Bimorphs

Peng Wang,Huikai Xie,Yabing Liu,Huan Liu,Weiguo Liu,Donglin Wang

doi:10.3390/mi10100693

Peng Wang, Huikai Xie + Show 4 more

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https://doi.org/10.3390/mi10100693

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Abstract

Electrothermal actuation is one of the main actuation mechanisms and has been employed to make scanning microelectromechanical systems (MEMS) mirrors with large scan range, high fill factor, and low driving voltage, but there exist long-term drifting issues in electrothermal bimorph actuators whose causes are not well understood. In this paper, the stability of an bimorph electrothermal MEMS mirror operated in both static and dynamic scan mode has been studied. Particularly, the angular drifts of the MEMS mirror plate were measured over 90 h at different temperatures in the range of – °C. The experiments show that the temporal drift of the mirror plate orientation largely depends on the temperature of the electrothermal bimorph actuators. Interestingly, it is found that the angular drift changes from falling to rising as the temperature increases. An optimal operating temperature between °C to °C for the MEMS mirror is identified. At this temperature, the MEMS mirror exhibited stable scanning with an angular drift of less than °/h.

Highlights

Electrothermal actuation based on thermal bimorphs has been widely applied on scanning microelectromechanical systems (MEMS) mirrors due to its advantages of large displacement, high fill factor, and economical fabrication process [1]
Feedback control is often needed for electrothermal MEMS mirrors in high-precision applications because of the relatively low repeatability and stability of Al/SiO2 bimorph actuators [4]
It should be noticed that 0.1◦ of the mirror tilt angle corresponded to a 2.2 μm displacement of the bimorph actuators

Summary

Introduction

Electrothermal actuation based on thermal bimorphs has been widely applied on scanning microelectromechanical systems (MEMS) mirrors due to its advantages of large displacement, high fill factor, and economical fabrication process [1]. Al/SiO2 electrothermal bimorph-based MEMS mirrors have been extensively studied [2], and have been used in many applications, such as endoscopic optical imaging [3] and microspectrometers [1]. Feedback control is often needed for electrothermal MEMS mirrors in high-precision applications because of the relatively low repeatability and stability of Al/SiO2 bimorph actuators [4]. To compensate the instability of the electrothermal MEMS mirrors, closed-loop control with additional optical position sensing mechanisms is generally required, which increases the complexity and the size and cost. Improving stability of the electrothermal MEMS mirrors is critical for them to be used in high-precision applications

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