Modelling and Experimental Verification of Step Response Overshoot Removal in Electrothermally-Actuated MEMS Mirrors

Abstract

Micro-electro-mechanical system (MEMS) mirrors are widely used for optical modulation, attenuation, steering, switching and tracking. In most cases, MEMS mirrors are packaged in air, resulting in overshoot and ringing upon actuation. In this paper, an electrothermal bimorph MEMS mirror that does not generate overshoot in step response, even operating in air, is reported. This is achieved by properly designing the thermal response time and the mechanical resonance without using any open-loop or closed-loop control. Electrothermal and thermomechanical lumped-element models are established. According to the analysis, when setting the product of the thermal response time and the fundamental resonance frequency to be greater than Q/2π, the mechanical overshoot and oscillation caused by a step signal can be eliminated effectively. This method is verified experimentally with fabricated electrothermal bimorph MEMS mirrors.

A Customized Two Photon Fluorescence Imaging Probe Based on 2D scanning MEMS Mirror Including Electrothermal Two-Level-Ladder Dual S-Shaped Actuators

“…Factually, the response time of the actuators depends on the type of materials that compose the thermal bimorph actuator and their thermal expansion coefficients (TEC). The two materials that are widely used to fabricate the bimorph thermal actuators are Copper (Cu) with tungsten [ 29 , 30 ] and Aluminium (Al) with silicon dioxide (SiO2) [ 25 , 31 ]. Thus, due to their larger TEC difference (23.1 × 10 −6 /K for Al and 0.5 × 10 −6 /K for SiO2) comparing Cu/W actuators [ 30 ], the use of Al/SiO2 bimorph actuators was favored.…”

“…A number of electrothermal MEMS mirror-based probes have been reported in the literature, with most of them deploying single-level S-shaped bimorph actuators [ 15 , 16 , 25 ]. This type (single level architecture) can achieve ~ ±12° as optical scan range [ 15 ] using a low voltage with a fast response time (~4 ms) [ 25 ]. However, it suffers from a short stable frequency range before reaching the resonance regime [ 15 ], while the use of a high voltage (>5 V) may damage the actuators.…”

Editorial for the Special Issue on MEMS Mirrors

“…There are 15 papers published in this special issue, covering MEMS mirrors based on all of the commonly used actuation mechanisms including electrostatic [1,2,3,4,5], electromagnetic [6,7,8], piezoelectric [9], and electrothermal [10,11,12,13,14]. Half of these papers explore various aspects of MEMS mirrors, such as working in harsh environments [1], spring hardening compensation [3], optimal packaging conditions for resonance operation [5], input saturation control [8], extremely large scan angle [9], overshoot suppression [10], electrothermal actuator modeling [13], and design optimization [14].…”

“…Half of these papers explore various aspects of MEMS mirrors, such as working in harsh environments [1], spring hardening compensation [3], optimal packaging conditions for resonance operation [5], input saturation control [8], extremely large scan angle [9], overshoot suppression [10], electrothermal actuator modeling [13], and design optimization [14]. There is also a paper reporting a passive micromirror [15].…”

“…Gu-Stoppel et al presented a lead zirconate titanate (PZT)-actuated micromirror that achieves an extremely large scan angle of up to 106° and a high frequency of 45 kHz simultaneously [9]. M. Li et al effectively eliminated the overshoot and oscillation of electrothermally-actuated micromirrors simply by setting the product of the thermal response time and the fundamental resonance frequency to be greater than Q/2π [10]. Torres et al reported the modeling of a MEMS mirror structure with four actuators driven by the phase-change of VO 2 thin film [13].…”