This article was downloaded by: [Northeastern University]On: 03 November 2014, At: 08:58Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

International Journal ofOptomechatronicsPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/uopt20

Piston Motion Performance Analysis of a3DOF Electrothermal MEMS Scanner forMedical ApplicationsA. Espinosa a , K. Rabenorosoa a , C. Clévy a , B. Komati a , P. Lutz a ,X. Zhang b , S. R. Samuelson b & H. Xie ba FEMTO-ST Institute, UMR CNRS/ENSMM/UFC/UTBM , Besancon ,Franceb Interdisciplinary Microsystems Group, University of Florida ,Gainesville , Florida , USAPublished online: 10 Jun 2014.

To cite this article: A. Espinosa , K. Rabenorosoa , C. Clévy , B. Komati , P. Lutz , X. Zhang , S.R. Samuelson & H. Xie (2014) Piston Motion Performance Analysis of a 3DOF Electrothermal MEMSScanner for Medical Applications, International Journal of Optomechatronics, 8:3, 179-194, DOI:10.1080/15599612.2014.916581

To link to this article: http://dx.doi.org/10.1080/15599612.2014.916581

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

PISTON MOTION PERFORMANCE ANALYSIS OFA 3DOF ELECTROTHERMAL MEMS SCANNERFOR MEDICAL APPLICATIONS

A. Espinosa,1 K. Rabenorosoa,1 C. Clevy,1 B. Komati,1

P. Lutz,1 X. Zhang,2 S. R. Samuelson,2 and H. Xie21FEMTO-ST Institute, UMR CNRS=ENSMM=UFC=UTBM,Besancon, France2Interdisciplinary Microsystems Group, University of Florida,Gainesville, Florida, USA

MEMS scanners are useful for medical applications as optical coherence tomography and

laser microsurgery. Although widespread design of MEMS scanners have been presented,

their behavior is not well known, and thus, their motions are not easily and efficiently

controlled. This deficiency induces several difficulties (limited resolution, accuracy, cycle time,

etc.), and to tackle this problem, this article presents the modeling of an ISC electrothermally

actuated MEMS mirror and the experimental characterization for the piston motion.

Modeling and characterization are important to implement the control. A multiphysic model

is proposed, and an experimental validation is performed with a good correspondence for

a voltage range from 0V to 3.5Vwith amaximum displacement up to 200lmand with a relative

tilting difference of 0.1�. The article also presents a simple and efficient experimental setup

to measure a displacement in dynamic and static mode, or a mirror plane tilting in static mode.

Keywords: electrothermal actuator, MEMS, modeling, OCT scanner, tip-tilt-piston motion

1 INTRODUCTION

The increasing use of micro electro-mechanical-systems (MEMS) and micro-opto-electro-mechanical-systems (MOE-MS) is observed in many fields, such asmedical applications.[1] There are some applications based on optical microsystemswhich are under investigation as microspectrometers,[2,3] confocal microscopefor sample analysis,[4] optical coherence tomography (OCT) for in-vivo cancerdetection,[5–8] and laser microsurgery.[9] It is observed that most optical microsystemsare based on MEMS scanners. The design and fabrication of MEMS scanners arewidely investigated by considering the degrees of freedom (DoFs) number, kinematics,and micro-actuator integration. Generally, we can classify MEMS scanners into twomain categories according to the type of motion generated.

Address correspondence to K. Rabenorosoa, AS2M, 24 rue Alain Savary, Besancon 25000, France.

E-mail: rkanty@femto-st.fr

Color versions of one or more of the figures in the article can be found online at www.tandfonline.

com/uopt.

International Journal of Optomechatronics, 8: 179–194, 2014

Copyright # Taylor & Francis Group, LLC

ISSN: 1559-9612 print=1559-9620 online

DOI: 10.1080/15599612.2014.916581

179

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

. In-plane displacement presented in Refs.[2,3,10–12] for 1 DoF, and Refs.[4,13] for2DoF (X-Y).

. Out-of-plane displacement which can be 2DoF (Tip-Tilt) presented in Refs.[14–17],and 3DoF (Tip-Tilt-Piston Motion) presented in Refs.[5,18,19]

In-plane motion is usually used for confocal microscopes and spectrometerswhere the displacement is observed in the substrate plane. Out-of-plane motion isrequired to deflect a laser beam in order to scan a sample surface like laser micro-surgeries and OCT. There are several characteristics (response time, hysteresis, anglevariations, mirror flatness, etc.) which are important for scanner performances. Conse-quently, they will define the working performance of each optical microsystems. Twoimportant working modes are often considered: static and dynamic. In addition, thereare some parameters to be characterized as linearity, response, resolution, andcross-axis coupling. Indeed, these parameters directly determine the specifications ofthe optical systems, e.g., the image frame rate, distortion for OCT, and precision ofmicrosurgery. It is observed that the characterization of MEMS performances is verydifficult according to Ref.[20] due to the lack of sensors and procedures. At the micro-scale, the physical properties of material and the obtained behavior from microma-chining are difficult to characterize. Few works can be found about the procedure inthe literature, such as Refs.[21,22] In addition, the results obtained through the charac-terization can be used to check if the micromachining provides the expected behavior,to obtain a feedback on the design (thus can be employed as inputs for re-engineering),and to work on the control aspects in order to improve the performances.

This article is focused on scanner performance analysis of a 3DoF electrother-mal MEMS for OCT. In section 2, the MEMS micromirror is presented through itsdesign and fabrication processes. In section 3, a modeling of the MEMS micromirroris proposed based on kinematic and physical considerations. Afterwards, perfor-mance analysis of piston motion through experiments are presented in section 4.Finally, section 5 concludes the article.

2. PRESENTATION OF THE MEMS MICROMIRROR

MEMS micromirrors are important in the development of optical micro-systems. Several kinds of actuator have been used in the literature with various

NOMENCLATURE

dplatform displacement of the mirror platform

(m)

dISC, dt Displacement of one ISC (m)

dNI Deflection of the non inverted bimorph

(m)

dIV Deflection of the inverted bimorph (m)

dOL Deflection of the overlap (m)

aAl CTE of aluminium (1=K)

aSiO2CTE of dioxyde of silicon (1=K)

bb Curvature coefficient

hIV Angle of the the inverted bimorph

(Rad)

hNI Angle the non inverted bimorph (Rad)

qNI Curvature of the non inverted bimorph

(m)

qIV Curvature of the inverted bimorph (m)

n Thermal coefficient of resistance (1=K)

Da Difference of the CTE of the two

bimorph materials (1=K)

DT Temperature variation (K)

180 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

kinematics, number of DoF, and design. A 3DoF electrothermal MEMS scannerdesign and fabrication is detailed in the following.

2.1. Design

The actuation mechanism used for the micromirror is the inverted-series-connected (ISC) bimorph design comparable to Ref.[18], which can solve therotation-axis shift problems during actuation. Also, large displacements can beachieved using the ISC bimorph design for actuation at relatively low drive voltage.

The concept of the ISC actuator is shown in Figure 1. For a basic bimorph,when the temperature is changed, it will bend because of the different coefficientsof thermal expansion (CTEs) of the two materials in the bimorph. There will bea tangential tilt generated at the tip of the bimorph beam (Figure 1(a)). If two basicbimorphs are inverted and connected in the series, the tangential tilt can be canceled,but there still exists a lateral shift (Figure 1(b)). To achieve pure displacement in they-direction, two ISC bimorphs are connected to cancel the lateral shift, as shown in(Figure 1(c)). A properly-designed ISC actuator can achieve vertical displacement iny-axis with zero tip-tilt and zero lateral shift. In addition, the overlap part at the mid-dle of each S-shaped bimorph is designed to improve the robustness of the actuator.The two layers in the bimorph are Al and SiO2 because of their large CTE differenceand the ease for fabrication. An embedded Pt layer is used to provide uniform heatthrough the entire bimorph beam.

The schematic of the ISC micromirror design is shown in Figure 2, where fourISC actuators are connected to the central mirror plate. The connections between theISC actuators and the mirror plate are pure SiO2 to isolate the heat generated inthe actuators from the mirror plate. Also, the thermal isolation can prevent thecross-talk through the mirror plate among the actuators. The actuators can be

Figure 1. The concept of ISC actuator with undeformed shape in solid and deformed in dashed. (a) Basic

bimorph; (b) half ISC bimorph: zero tangential tip tilt but still lateral shift, and (c) ISC bimorph of the

micromirror: zero tip tilt and zero lateral shift.

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 181

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

controlled together or individually to achieve piston (pure motion along Z) or tiltmotion (rotation of the mirror plate around X and Y). It has been proven[18] that thisdesign can generate large vertical displacements with small lateral shift or tilt.

Figure 3. Flowchart of the ISC bimorph MEMS mirror. (a) SiO2 deposition, (b) RIE etching, (c) Pt depo-

sition, (d) insulation layer deposition followed by Al sputtering, (e) SiO2 deposition and etching, (f) DRIE

etching of the handle layer, (g) buried oxyde etching, and (h) Si etching to release the ISC bimorphs.

Figure 2. Top view of the ISC micro mirror design, including eight ISC bimorphs.

182 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

2.2. Fabrication

The fabrication process of the micromirror is a combination of both thin-filmand bulk processes. The mirror plate is a 1 mm-thick Al layer coated on a 50 mm-thicklayer of silicon to achieve good flatness. A silicon on insulator (SOI) wafer is chosenfor better control of the fabrication process. The thin-film layers for bimorphs aredeposited using plasma-enhanced chemical vapor deposition (PECVD) or sputtering.Six photomasks are needed to form the entire structure.

The process flow is shown in Figure 3. The fabrication process starts with anSOI wafer. First, a 1 mm layer of SiO2 is deposited using PECVD as the structurelayer for the non-inverted bimorph (Figure 3(a)), followed by SiO2 RIE (ReactiveIon Etching) etching (Figure 3(b)). Then, a 0.2 mm thick Pt is sputtered as the heater,followed by lift-off (Figure 3(c)). After the formation of the heater, a thin SiO2 layeris deposited and followed by SiO2 RIE etching as the insulation layer between Pt andAl. The next step is Al sputtering and lift-off to form the mirror plate and part of thestructure for bimorphs (Figure 3(d)). Then, the second SiO2 PECVD deposition and

Figure 4. SEM pictures of the fabricated MEMS mirror. (a) Top view and (b) side view.

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 183

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

SiO2 RIE etching are performed to form the structural layer for inverted bimorphs(Figure 3(e)). After the front side process, deep reactive ion etching (DRIE) is used toetch through the silicon handle layer of the SOI wafer to the buried oxide layer(Figure 3(f)). Then, the buried oxide is etched, resulting in a uniform silicon layerformed underneath the Al layer (Figure 3(g)). The last step is isotropic Si etchingto release the bimorphs (Figure 3(h)).

After the release step, the mirror plate will pop up because of the initial stressbetween Al and SiO2, as shown in Figure 4. The initial pop-up displacement is about220 mm.

3. PISTON MOTION MODELING

The modeling of the electrothermal actuated mirror is based on Refs.[23,24]

Figure 5 shows the sketch of the steps followed for modeling the ISC bimorphs.The model assumes that the deflection of the ISC dISC bimorphs is equivalent tothe displacement of the mirror platform dplatform when the same voltage is appliedto the four actuators (see Equation (1)). The obtained motion is named pistonmotion. The displacement of the half ISC dt is considered to be the sum (Equation(2)) of the deflections of one inverted bimorph dIV, a straight multi-bimorph dOL oroverlap and a non-inverted bimorph dNI, as illustrated in (Figure 6).[18]

dplatform ¼ dISCðV1 ¼ V2 ¼ V3 ¼ V4Þ ð1Þ

dt ¼ dNI þ dIV þ dOL ð2Þ

First, a single bimorph is modeled and the average temperature variationaccording to the voltage input is derived in Equation (3). Note, that in the followingsome equations of the electrothermal model have been already reported inbibliography are given again to clarify the modeling. The increase of temperatureon the bimorph is derived from Ref.[24] and it is available for other bimorphs.

DT ¼ V 2

R0ð1þ nDTÞRT ð3Þ

Figure 5. Followed steps to model ISC bimorph with db the bimorph deflection, V the applied voltage, dISCthe deflection of the ISC bimorph, LNI and dNI the length and deflection of non-inverted part, LOL and dOL

the length and deflection of the overlap part, and LIV and dIV the length and deflection of the inverted part.

184 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

where R0 is the initial electrical resistance at ambient temperature, V the applied

voltage, n is the thermal coefficient of resistance, and RT is the equivalent average

effective thermal resistance. Due to the complexity of the calculation of RT becauseof the ICS actuator geometry and the difficulties to quantify the thermal loses bymean of convection and conduction along the bimorph and the substrate and mirrorisolation regions, this parameter has been identified using an experimental data. Solving

Equation (3) gives the average temperature change DT due to a voltage input V andderived in Equation (4).

DT ¼ 1

2n

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi4nRT

R0V 2 þ 1

s� 1

!ð4Þ

The vertical tip deflection db can be obtained by analyzing Figure 6. Equation (5)gives the bimorph deflection as a function of the radius of curvature q and angle h.

db ¼ 2qsin2h2

� �ð5Þ

with1

q¼ bb

tbDaDT ð6Þ

and

h ¼ lbq¼ bblb

tbDaDT ð7Þ

The inverse of the bimorph radius of curvature, given in Equation (6) is derivedin Ref.[25] where bb is the curvature coefficient, tb is the thickness of the bimorph, Dais the difference of the CTE of the two bimorph materials, and DT is the temperaturevariation. The curvature coefficient depends on the layer thickness ratio of thebimorph layers on the physical properties of the materials, whose range is from0 to 1.5. Ideally the bimorph is designed to maximize it. Thus, its value is expectedto be close to 1.5 according to Ref.[26]

Figure 6. Description of half ISC bimorph with the three parts and three layers (SiO2, Al, and Pt).

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 185

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

Merging Equations (2) and (5)–(7), the displacement of half of an half ICSbimorph is obtained as follows:

dt ¼ qNI 1� coslNI

qNI

� �� �|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

dNI

þ qIV ð1� cosð lIVqIV

ÞÞ|fflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflffl}dIV

þLOLsinðhNI Þ|fflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflffl}dOL

ð8Þ

In order to obtain the total displacement of the whole bimorph it is needed tomultiply Equation (8) by 2. Finally, considering the effect of embedded Pt layer, theoverlap portion and the difference in the behaviors of the inverted bimorph andnon-inverted bimorph explained in Ref.[24], the deflection of the entire ISC bimorphis given by Equation (9) where K¼ 0.921. Table 1 gives parameter values ofthe electrothermal actuators.

dISC ¼ 2Kdt ð9Þ

4. PERFORMANCE ANALYSIS

The aim of this section is to characterize the performance of the mirror whenthe piston motion is performed, and thus enables an experimental validation of themodel. The working voltage range goes from 0 to 3.5V, with a maximum powerconsumption of 35mW=actuator.

4.1. Experimental Setup

The experimental setup used for the performance characterization of theMEMS mirror, includes a Keyence LC-2420 laser and an XY nanopositioningplatform apart from manual positionners and an optical table. The Keyence Laserhas a working range from �250 mm to 250 mm with 10 nm resolution while the XYplatform has a total displacement of 200 mm for each axis. This experimentalsetup shown in Figure 7 can provide single point characterization as well as planar

Table 1. Parameter values of the electrothermal actuators

Parameter Symbol Value

Non-inverted bimorph lenght LNI 250mmInverted bimorph lenght LIN 125mmOverlap length LOL 120mmBimorph total thickness tb 2.4mmCurvature coefficient bb 1.5

Al CTE aAl 23� 106K�1

SiO2 CTE aSiO20.7� 1 06K�1

Initial electrical resistance R0 360� 15XPlatinumthermal resistance coefficient n 3.92� 10�3K�1

CTE materials variation Da 2.22� 10�5K�1

Equivalent thermal coefficient of resistance RT To be identified

186 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

scanning. The control of the experimental setup is performed through an RT 1104Dspace board in order to ensure a real time motion control and data acquisition.

This developed experimental setup is able to perform two measurementprocedures:

. Procedure 1. Measurement of the relative z position on the center of the mirrorplate in static or dynamic mode.

. Procedure 2. Scanningmeasurement of the mirror surface during a static mode. Thistest consists of the scanning of a 100mm squared area of the mirror surface. Whilethe XY platform performs five squares at a speed of 20mm=s the Keyence laser pro-vides a distance to the mirror for each position, obtaining at the end a cloud ofpoints. The data obtained is processed using the Principal Component Analysis(PCA) presented in Ref.[21], which uses the maximum dispersion criterion to obtainthe best fitting plane. Thus, the two inclination angles of the plane are derived.

4.2. Identification of RT

Equivalent average thermal resistance is difficult to calculate due to the uncer-tainties on the obtained dimensions of each layer (Pt, Al, and SiO2) and the physical

parameters. We propose to identify RT based on measurement displacement for3.5V applied voltage and with the parameter values given in Table 1. The calculationgives 5.7� 103 K=W which will be used for the model validation.

Figure 7. Experimental setup for performance characterization. (a) Frame orientation, (b) mirror detail,

and (c) setup description.

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 187

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

4.3. Model Validation

The objective of this section is to validate the modeling presented before withthe results obtained experimentally in static mode of procedure 1. The experimen-tation is performed in the setup described before and provides the displacementamplitude of the mirror for its working voltage range.

The initial position is considered at 0V where the mirror is situated around220 mm over the substrate. As steps of 0.1V are applied, the mirror approaches tothe substrate. Figure 8 shows the comparison between the displacement of the mirrorgiven by the analytical model and the one provided by the experimentation.

Results show two curves with similar shape but with a slight amplitude differ-ence between them. The experimental maximum displacement is obtained for 3.5Vand has a value of 173.7 mm. The maximum absolute error between the two curvesis about 9.2 mm at 1.9V which corresponds to 12.4% of relative error. The differencebetween both can be due to several reasons; among them, fabrication tolerances,model initial assumptions as the negligibility of convection, actuator asymmetriesthat can introduce some torques in the joints between the actuators and the mirrorplate, and some residual tangential tip tilts.

4.4. Piston Motion Characterization

Piston motion characterization aims to measure the behavior of the MEMSmirror when the same DC voltage is applied to all of its actuators. For this, differentexperiments have been carried out; among them, dynamic step response, hysteresismeasurement, and static mirror plane scanning. They will be presented in thefollowing.

Figure 8. Absolute displacement comparison between model and experimentation and absolute error.

188 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

Figure 9. Step responses of the ISC actuated MEMS mirror. (a) Repeating responses, (b) zoom in

the upward transient part, and (c) zoom in the downward transient part compared to the

reference frame.

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 189

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

4.4.1. Dynamic step response. Step response is measured through thedeveloped experimental setup in real time. The presented results is based on onepoint of mirror plate measurement (procedure 1). The transient part can be observedwith some oscillations for the upward (Figure 9(b)) and downward motion(Figure 9(c)) compared to the reference frame. A creep is observed in the static partand continued up to 30 s, afterwards, the position is stable. The response time t95%corresponds to the time when the measured displacement reaches 95% of its finalvalue, which is measured to be 563ms.

4.4.2. Hysteresis measurement. Hysteresis tests (procedure 1) have beendone at 1V� 0.5V for four frequencies. Figure 10 shows that the MEMSmirror response is affected by hysteresis. The hysteresis is around 1.6 mm at0.1Hz, 4 mm at 1Hz, 5.9 mm at 20Hz, and 9.5 mm at 100Hz. As the frequency ofthe input increases, hysteresis becomes higher and the displacement range becomessmaller.

Figure 10. Hysteresis results with four frequencies of sinusoidal input voltage.

Figure 11. Mirror plane positions for different applied voltages.

190 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

4.4.3. Mirror plane scanning. With procedure 2, the experimentationprovides the relative position of the mirror surface for each applied voltage. Theresult is presented in Figure 11 with 3-D representation of the mirror plate. Takingas a reference the position of the mirror when a 2V offset is applied (in order to bein the middle of the entire actuation range), the two residual tilting angles arecharacterized.

Figure 12 shows the angle variations hX and hY for different applied voltages.The tests has been repeated in order to prove if the variation on the tilting ischanging during piston motion. The results show that the mirror plane orientation

Figure 12. Angle variation for different applied voltage. (a) Variation around X axis and (b) variation

around Y axis.

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 191

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

is slightly changing during the piston motion. The mean variation of hX and hY is,respectively, about 0.09� and 0.01�. In the same way, the standard deviation for bothangles is around 0.12� or hX and 0.09� for hY. This variations can be explainedbecause of the slight differences among the electrical resistances, the thermalcoefficients of the resistance, and the dimensions of the four actuators due tofabrication variations.

5. CONCLUSION

This article presents modeling and experimental characterization of the pistonmotion for a 3DoF electrothermal MEMS mirror. It has been demonstrated thata simple and effective setup experimentation is able to measure motions of somehundreds of mm in size of mobile platform in both static and dynamic modes.Experimentation shows that the modeling developed fits within 9.2 mm of absoluteerror. The piston motion is achieved within a range close to 175 mm for 0 to 3.5Vapplied voltages with some tilting variations of the mirror plate less than 0.09�.The step response has been characterized with a response time of t95% of 563ms.It was observed that the presence of oscillations on the transient part and creepon the static part. The hysteresis variation and the maximum displacement wereobserved according to frequency changes for the same applied voltage. The resultsare useful for understanding the MEMS mirror behavior, for validating the design,and the fabrication processes. The obtained results will enable open loop controlto increase the performances and provide inputs for the future designs. Furthermore,investigations in tip-tilt motion and in control domain are ongoing.

FUNDING

This work is partially supported by the French RENATECH and itsFEMTO-ST technological facility under the Labex ACTION project (contractANR-11-LABX 01-01). This is also partially supported by FP7=IRSES Net4M,Region Franche Comte by MIOP project, and by the U.S. National ScienceFoundation under award #0901711.

REFERENCES

1. Tolfree, D.; Jackson, M.J. (eds.). Commercializing Micro-Nanotechnology Products.CRC Press: Boca Raton, FL, 2007.

2. Manzardo, O. Micro-sized Fourier Spectrometers. PhD thesis, Ecole PolytechniqueFederale de Lausanne, Lausanne, Switzerland, 2002.

3. Wallrabe, U.; Solf, C.; Mohr, J.; Korvink, J.G. Miniaturized Fourier transformspectrometer for the near infrared wavelength regime incorporating an electromagneticlinear actuator. Sensor. Actuat. A: Phys. 2005, 123–124, 459–467.

4. Gorecki, C.; Bargiel, S.; Laszczyk, K.; Albero, J.; Krezel, J.; Kujawinska, M. Lookingfor a new generation of mems-type confocal microscopes. In Fringe 2009, Springer: Berlin,2009, pp. 1–4.

5. Singh, J.; Teo, J.H.S.; Xu, Y.; Premachandran, C.S.; Chen, N.; Kotlanka, R.; Olivo, M.;Sheppard, C.J.R. A two axes scanning soi mems micromirror for endoscopic bioimaging.J. Micromech. Microeng. 2008, 18, 1–9.

192 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

6. Sun, J.; Xie, H. Mems based endoscopic optical coherence tomography. InternationalJournal of Optics 2011, 2011, 1–12.

7. Aljasem, K.; Froehly, L.; Zappe, H.; Seifer, A. Integrated three-dimensional scannerfor endoscopic optical coherence tomography. In SPIE Photonics Europe. InternationalSociety for Optics and Photonics: Bellingham, WA, 2012; pp. 77162P–77162P.

8. Can-Jun, M.; Fei-Ling, Z.; Wuya-Ming. High-speed and large-scale electromagneticallyactuated resonant mems optical scanner. Chinese Phys. Lett. 2007, 24, 3574–3577.

9. Hoy, C.L.; Everett, W.N.; Yildirim, M.; Kobler, J.; Zeitels, S.M.; Ben-Yakar, A. Towardsendoscopic ultrafast laser microsurgery of vocal folds. J. Biomed. Opt. 2012, 17(3),0380021–0380028.

10. Das, A.N.; Sin, J.; Popa, D.O.; Stephanou, H.E. On the precision alignment andhybrid assembly aspects in manufacturing of a microspectrometer. In IEEE Conferenceon Automation Science and Engineering (CASE), Washington, DC, August 23–26; IEEE:Piscataway, NJ, 2008; pp. 959–966.

11. Yu, K.; Lee, D.; Krishnamoorthy, U.; Park, N.; Solgaard, O. Micromachined fouriertransform spectrometer on silicon optical bench platform. Sensor. Actuat. A: Phys.2006, 130, 523–530.

12. Peterson, B.A.; Patterson, W.C.; Herrault, F.; Arnold, D.P.; Allen, M.G. Laser-micromachined permanent magnet arrays with spatially alternating magnetic field distri-bution. In PowerMEMS, Atlanta, GA, December 2–5; IEEE: New Brunswick, NJ, 2012.

13. Takahashi, K.; Mita, M.; Fujita, H.; Toshiyoshi, H. A high fill-factor comb-drivenxy-stage with topological layer switch architecture. IEICE Electronics Express 2006,3, 197–202.

14. Chong, C.; Isamoto, K.; Toshiyoshi, H. Optically modulated mems scanning endoscope.IEEE Photon. Technol. Lett. 2006, 18(1), 133–135.

15. Jain, A.; Kopa, A.; Pan, Y.; Fedder, G.K.; Xie, H. Two-axis electrothermal micromirrorfor endoscopic optical coherence tomography. IEEE J. Sel. Top. Quant. Electron. 2004, 10,636–642.

16. Jung, W.; Zhang, J.; Wang, L.; Wilder-Smith, P.; Chen, Z.; McCormick, D.T.; Tien, N.C.Three-dimensional optical coherence tomography employing a 2-axis microelectro-mechanical scanning mirror. IEEE J. Sel. Top. Quant. Electron. 2005, 11, 806–810.

17. Kim, K.H.; Park, B.H.; Maguluri, G.N.; Lee, T.W.; Rogomentich, F.J.; Bancu, M.G.;Bouma, B.E.; de Boer, J.F.; Bernstein, J.J. Two-axis magnetically-driven mems scanningcatheter for endoscopic high-speed optical coherence tomography. Opt. Exp. 2007, 15,18130–18140.

18. Jia, K.; Pal, S.; Xie, H. An electrothermal tip-tilt-piston micromirror based on folded duals-shaped bimorphs. J. Microelectromech. Syst. 2009, 19, 1004–1015.

19. Liao, W.; Liu, W.; Zhu, Y.; Tang, Y.; Wang, B.; Xie, H. A tip-tilt-piston micromirrorwith symmetrical lateral-shift-free piezoelectric actuators. Sensors J. 2013, 13,2873–2881.

20. Clevy, C.; Rakotondrabe, M.; Chaillet, N. (eds.). Signal Measurement and EstimationTechnique for Micro and Nanotechnology. Springer: New York, 2011.

21. Rabenorosoa, K.; Clevy, C.; Bargiel, S.; Mascaro, J.P.; Lutz, P.; Gorecki, C. Modular andreconfigurable 3d micro-optical benches: Concept, validation, and characterization.In Proceedings of the 6th ASME 2011 International Manufacturing Science and EngineeringConference (MSEC), Corvallis, OR, June 13–17; ASME: New York, 2011; pp. 479–485.

22. Zea, J.G.; Sandozy, P.; Laurent, G.; Lemos, L.L.; Clvy, C. Twin-scale vernier micro-pattern for visual measurement of 1d in-plane absolute displacements with increasedrange-to-resolution ratio. Int. J. Optomechatronics 2013, 7, 222–234.

23. Todd, S.T.; Xie, H. Steady-state 1d electrothermal modeling of an electrothermaltransducer. J. Micromech. Microeng. 2005, 15, 2264–2276.

PISTON MOTION PERFORMANCE OF 3DOF MEMS SCANNER 193

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014

24. Todd, S.T.; Jain, A.; Qu, H.; Xie, H. A multi-degree-of-freedom micromirror utilizinginverted-series-connected bimorph actuators. J. Opt. A, Pure Appl. Opt. 2006, 8, 352–359.

25. Peng, W.; Xiao, Z.; Famer, K.R. MEMS design and application. In Technical Proceedingsof the 2003 Nanotechnology Conference and Trade Show, San Francisco, CA, August12–14; Nano Science and Technology Institute: Danville, CA, 2003.

26. Jia, K.; Samuelson, S.R.; Xie, H. High-fill-factor micromirror array with hidden bimorphactuators and tip-tilt-piston capability. J. Microelectromech. Syst. 2011, 20, 573–582.

194 A. ESPINOSA ET AL.

Dow

nloa

ded

by [

Nor

thea

ster

n U

nive

rsity

] at

08:

58 0

3 N

ovem

ber

2014