Design, fabrication and characterization of a high fill-factor micromirror array for wavelength selective switch applications

Sensors and Actuators A 171 (2011) 274–282

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Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna

Design, fabrication and characterization of a high fill-factor micromirror array for wavelength selective switch applications Sihua Li a,b,∗ , Jing Xu a,1 , Shaolong Zhong a,2 , Yaming Wu a,2 a State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, People’s Republic of China b Graduate University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, People’s Republic of China

a r t i c l e

i n f o

Article history: Received 31 January 2011 Received in revised form 5 July 2011 Accepted 7 July 2011 Available online 23 July 2011 Keywords: Micromirror array Wavelength selective switch (WSS) High fill-factor Bumper Terraced electrodes

a b s t r a c t This paper presents the design, fabrication and characterization of a high fill-factor micromirror array in application of wavelength selective switch (WSS). The micromirror array consists of 52 independent micromirrors. Each micromirror is composed of a cantilever-type micromirror plate (800 ␮m × 120 ␮m) with a bumper and an eight-terraced bottom electrode with a limiting plane. A cantilever beam is designed to obtain the rotation angle of micromirror plate and achieve a high fill-factor for the micromirror array. Meanwhile, the bumper and limiting plane are used to prevent the damage possibly caused by the pull-in effect or some vibration instance. An eight-terraced electrode is utilized for reducing the driving voltage. The micromirror array with a high fill-factor in excess of 97% has been successfully achieved using the bulk micromachining technologies. The measured static and dynamic characteristics show that the micromirror can achieve a maximal rotation angle of 0.87◦ with a Direct Current (DC) driving voltage of 156 V. The turn-on responding time is 0.57 ms, and the turn-off responding time is 4.36 ms. Furthermore micromirror plate can be easily released from the pull-in state without damaged due to the novel bumper design. The switching function between the two output ports of a WSS optical system has also been demonstrated. © 2011 Elsevier B.V. All rights reserved.

1. Introduction With the rapid development of optical communications, all-optical switching networks have become more and more important. Wavelength-selective switch (WSS) is one of the key modules in optical network and can mange network at the wavelength level [1]. Various technologies have been explored to implement the wavelength-selective switch function, including liquid crystal [2,3] and Micro-Electro-Mechanical System (MEMS). MEMS WSS has drawn a great attention due to its advantages of lower optical insertion loss and crosstalk, faster switching speed, higher extinction ratio and polarization independent. Free-space Grating-MEMS optical systems [4–8] and hybrid Planar Lightwave Circuit (PLC)MEMS optical systems [9,10] are the two major approaches to

∗ Corresponding author at: State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, People’s Republic of China. Tel.: +86 21 62511070 5467; fax: +86 21 62131744. E-mail addresses: [email protected] (S. Li), [email protected] (J. Xu), [email protected] (S. Zhong), [email protected] (Y. Wu). 1 Tel.: +86 21 62511070 5466; fax: +86 21 62131744. 2 Tel.: +86 21 62511070 5474; fax: +86 21 62131744. 0924-4247/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2011.07.001

implement MEMS WSS, in both of which the micromirror array play a key role. For MEMS based micromirror array, micro-actuation mechanism has the first priority consideration over device structuring and fabrication. Electrostatic actuation has become the most popular approaches for micromirror array, because of its faster speed with low power consumption and easily integrated with electronic control systems. In general, electrostatic actuators contain comb driver actuator and parallel-plate actuator. The comb driver actuator can offer the larger force density resulting in a large torsion angle of the micromirror with a low driving voltage [11–13]. However, the fabrication process is difficult because the arrangement of structure is complicated in order to achieve a high fill-factor array device. On the contrary, the parallel-plate electrostatic actuator has a simpler structure, and the fabrication process of a high fill-factor array structure is easier. Parallel-plate electrostatic actuated micromirror arrays have been reported previously [14–19], in which torsional micromirror plates were built with fixed parallel-plate electrodes on an insulation layer. It requested a high driving voltage to obtain a rotation angle with a large dimension of micromirror plate. A sloping or terraced bottom electrode can be used to reduce the driving voltage. Several micromirror arrays with terraced electrode have been reported [15,18]. However, in the plate electrostatic actuator, a small overvoltage can cause the micromirror to snap abruptly

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into contact with the fixed substrate. This phenomenon is called the pull-in effect. It may result in mechanical or electrical damages, and the two surfaces may also be stuck together permanently. Furthermore, contrasting with bulk micromachining micromirror, a surface micromachining micromirror gives low quality of optical surface, and the stress control of the thin film becomes difficult when multiple film layers are utilized to build the actuator. This paper presents the design, fabrication and characterization of a high fill-factor micromirror array. A novel bumper and limiting plane structure is proposed and successfully implemented to prevent the stick and damage caused by the pull-in effect. The cantilever-type micromirror plate is designed to achieve a high fillfactor for the micromirror array. A multi-terraced-plate structure is analyzed, and the optimized number of terraces is confirmed in order to reduce the driving voltage. The micromirror array is fabricated by using a bulk micromachining technology, and it is characterized with a WSS optical system. The design, simulation and fabrication of the device are described in Sections 2 and 3, respectively. Characterization of the device is studied in Section 4. The conclusions of the paper are summarized and discussed in Section 5. 2. Design and structure simulation As the key switching component, the requirements for a WSS micromirror array include a high fill-factor (>92%), large size micromirror (such as 800 ␮m × 120 ␮m), about 1◦ rotation angle, and a limited driving voltage (<200 V). Meanwhile, the resonant frequency of the micromirror actuator is required to be higher than 3.5 kHz to ensure the good anti-vibration performance. By considering and fulfilling these requirements, a high fill-factor micromirror array has then been proposed. 2.1. Structure design of micromirror array The schematic diagram of a high fill-factor micromirror array is shown in Fig. 1(a). The close-up view of a unit of micromirror is shown in Fig. 1(b), where a cantilever-type micromirror plate with gold film, eight-terraced bottom electrode, a bumper, and limiting plane were designed. The cantilever-type micromirror is selected in order to simplify the device structure relative to the existing design [20,21], and it helps the micromirror array with high fill-factor be easily achieved. The cantilever beam can also be used to realize the transformation from beam deformation to rotation angle of micromirror plate.

Fig. 1. Schematic diagram of a high fill-factor micromirror array (a) micromirror array (b) a unit of micromirror actuator.

275

Fig. 2. Model of micromirror with different bottom electrodes (a) parallel-plate bottom electrodes (b) multi-terraced bottom electrodes.

When a driving voltage is applied between the micromirror plate and the eight-terraced bottom electrode, the cantilever beam is enforced to bend by electrostatic force and thus results in a controllable rotation angle of the micromirror plate. With different driving voltages, micromirror plate can be rotated to desired angle, therefore a desired WDM channel can be chose in a WSS optical system. For preventing the damage caused by the pull-in effect or some vibration instance, the bumper and limiting plane structures have been proposed. The bumper is a silicon salient in 5 ␮m high covered with a 2 ␮m thick silicon dioxide (SiO2 ) film, which can be used as a dielectric layer. The bumper can limit the movement distance of micromirror plate and help the micromirror being back to previous controllable state rapidly even when the bumper contacts with the limiting plate. An eight-terraced structure has been introduced as a bottom electrode, which can reduce the driving voltage significantly for fitting the requirements of a WSS system. 2.2. Analysis of cantilever-type micromirror plate with different bottom electrodes The schematic diagram of the cantilever-type micromirror plate with different bottom electrodes is shown in Fig. 2. Fig. 2(a) shows the parallel-plate bottom electrodes with cantilever-type micromirror plate and Fig. 2(b) shows the multi-terraced bottom electrodes with cantilever-type micromirror plate. In this design, the micromirror plate is much wider, lengthier, and thicker than the rectangular cantilever beam and both ends of the micromirror plate are not clamped, so the deformation of the micromirror plate is negligible. The rotation of the micromirror plate comes from the displacement of the free end of the rectangular cantilever beam. As a result, we can utilize the analysis model of a rectangular cantilever beam with a concentrated end loading, which was generated by the electrostatic force between micromirror plate and bottom electrode. There are two coordinate systems in the model. In the o–x axis as shown in Fig. 2, b, h, and L represents the width, thickness and length of the cantilever beam, respectively, and F is the end loading force caused by the electrostatic force. Because the mass of the beam and micromirror plate is very small, the electrostatic force is much greater than the cantilever-type micromirror plate’s gravity. A simple estimate indicated that the cantilever bending angle due to gravity is smaller than 0.01◦ , so the gravitational force can

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be neglected in our analysis. The force moment caused by the end loading force against the clamped end of the beam is M0 = FL

(1)

As a result, the displacement of the cantilever beam, W(x), is [22] 2F(3L − x)x2 Ebh3

W (x) =

(2)

The maximal bending angle, , at the free end of the cantilever beam is ˙ (L) = ≈W

6FL2 6LM0 = Ebh3 Ebh3

(3)

where E is the Young’s modulus of silicon material. For the parallel-plate bottom electrode at the O –X axis, as shown in Fig. 2(a), while V is the voltage applied between the micromirror plate and bottom electrode, the force torque (for a small ), Te1 , caused by the electrostatic force is [23,24]



ˇa

Te1 =

Bεε0 V 2 x dx 2(d − x )

a



−ln

2



a 1− d

Bεε0 V 2 = 2 2

  ln

ˇa 1− d



1 1 − + 1 − (ˇa/d) 1 − (a/d)

Fig. 3. Relation between number of multi-terraced structure and normalized driving voltage.

 (4)

where B is the width of the bottom electrode, a is the length of cantilever-type micromirror plate (including the length of cantilever beam), d is the gap between the micromirror plate and bottom electrode, ε0 is the permittivity of the vacuum, ε is the relative permittivity of the air,  is the rotation angle of the micromirror plate (the rotation angel is equal to maximal bending angle of the cantilever beam),  and ˇ are percentage of the origin and end of the bottom electrodes in length of cantilever-type micromirror plate, respectively. Their value range of  and ˇ is between 0 and 1. For the multi-terraced bottom electrode as shown in Fig. 2(b), at the O –X axis, the force torque, Ten , is the sum of electrostatic force torque caused by each individual terraced electrode, which can be regarded as a parallel-plate actuator structure. Therefore, the torque caused by the electrostatic force under a driving voltage V is Ten =

n 

Tn =

i=1

n   i=1

ˇi a

i a

n

i=1

+

2(di − x )

 

Bεε0 V 2  ln 2 2

=

Bεε0 V 2 x dx

1−

ˇi a di

1 1 − 1 − (ˇi a/di ) 1 − (i a/di )

 − ln

1−

i a di

3 = Vn

n   

ln

i=1

+

ˇ a 1− i di



 (5)

where n is the number of the terraced electrodes,  i and ˇi are normalized position of the start point and end point of the terraced bottom electrode i, respectively. di is the gap between the micromirror plate and the terraced bottom electrode i. For the cantilever beam, the force moment applied at the free end of the cantilever beam is equal to the force torque caused by the electrostatic force Te1 = M0

(6)

Ten = M0

(7)

So, the relationship between the driving voltage (Vn ) and the rotation angle of the micromirror plate () can be expressed as

3LBεε0

n i=1



− ln

 a 1− i di

1 1 − 1 − ˇi a/di 1 − i a/di



 (9)

A typical relation between Vn and  determined by Eq. (9) is shown in Fig. 3. With reference to this figure, we can choose the optimized number of the terraced electrodes to get a reasonable driving voltage of micromirror. By considering the complexity of the fabrication process, an eight-terraced bottom electrode has been selected for the practical application. As shown in Fig. 3, the voltage would reduce over 50%. The calculated characteristics of the micromirror with different electrodes will be presented later, together with the experimental results.

For a micromirror array for WSS application, the micromirror pitch varies due to the nonlinearity in the grating’s angular dispersion. Uniform micromirror interval and different micromirror size are usually been chose based on the fabrication requirements. The micromirror size is decided by the WSS optical system design. In this FEM simulation, a typical unit of micromirror plate in dimension of 25 ␮m in thickness, 120 ␮m in width and 800 ␮m in length has been analyzed. With the assistance of CoventorWare, the cantilever-type micromirror with eight-terraced structure was simulated. The displacement of micromirror plate under 180 V DC bias is shown in Fig. 4(a). The maximum displacement was recorded as ∼15 ␮m, which is equivalent to about 1 degree rotation angle of the micromirror plate. By adjusting the thickness and length of the cantilever beam, different displacement of micromirror plate and the frequency of fundamental vibration mode were simulated as shown in Fig. 4(b). As expected, the results show that the micromirror performs a



Vn =



2.3. Structure parameters optimization based on finite element analysis

2



According to the relation between Vn and  determined by Eq. (8), by using a normalized driving voltage, Vn = Vn2 3LBεε0 /Ebh3 we have

Ebh3  3 [ln(1 − ˇi a/di ) − ln(1 − i a/di ) + 1/(1 − ˇi a/di ) − 1/(1 − i a/di )]

(8)

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Fig. 5. Simulation maximum displacement of mirror plate under 20 g acceleration vibrations.

Fig. 4. FEA simulation results (a) micromirror plate displacement with a DC bias, (b) calculated displacement and oscillation frequency with difference the thickness and length of cantilever beam.

lower resonant frequency and larger displacement with a lengthier and thinner cantilever beam. The gap between the limiting plane and the bumper is about 24 ␮m, so a maximum displacement is also limited. Combined with all the factors mentioned above, the optimum width, thickness and the length of the cantilever beam is 10 ␮m, 7 ␮m and 60 ␮m, respectively. The width of the bottom electrode is 110 ␮m. 2.4. Vibration analysis With the optimized structure parameters, the fundamental vibration mode is the rotation mode to fulfill our need and the resonant frequency is about 4000 Hz. The maximal vibration displacement of micromirror plate under 20 g acceleration vibrations with frequency range from 10 Hz to 6 kHz is shown in Fig. 5. In general application, we consider the environmental vibration with frequency to be less than 2000 Hz. As shown in Fig. 5, at the frequency about 2000 Hz, the maximal vibration displacement is about 0.4 ␮m, which is equivalent to rotation angle about 0.03◦ . As a result, the vibration displacement would cause the change of optical signal less than 1 dB. So the micromirror array can be recognized having anti-vibration capabilities. 3. Fabrication For the micromirror in capability of high-speed operations, the dynamic deformation of the large mirror plate could be an important issue [25,26]. However, surface micromachining micromirrors give low optical quality in a large size of micromirror plate, and typically the structures may have the robust problems. One possible method to avoid these robust problems is to increase the stiffness of the mirror plate. Therefore, a SOI wafer with a thicker device sili-

con layer has been used to increase the stiffness of the micromirror plate. At the same time, the proposed micromirror array was fabricated using a bulk micromachining process including Si–Si bonding technology. The Si–Si bonding has some obviously merits as follows: (i) large mirror area with a high optical quality; (ii) offering more freedom in selecting mirror thickness and gap spacing between mirrors and electrodes; (iii) allowing the independent fabrication of the mechanical and electrical components of a device; and (iv) simpler mechanical structures. 3.1. Fabrication process flow Fig. 6 shows the proposed processing sequence to fabricate the micromirror array. The device consists of two individually processed wafers: a top wafer with the cantilever-type micromirror plate and a bottom wafer with the eight-terraced structure. The process commenced with the top wafer which is a silicon-oninsulator (SOI) wafer. The device layers is 30 ␮m with a buried silicon dioxide (BOX) layer in thickness about 2 ␮m and a handle layer of 400 ␮m as shown in Fig. 6(a). The wafer is oxidized and then a 5 ␮m gap is defined by a wet etching process with KOH solution as shown in Fig. 6(b) and (c). A 1 ␮m thick thermal silicon oxide film is grown and used as an etch mask in etching top silicon as shown in Fig. 6(d). And then the backside of the cantilever beam is etched with a KOH solution as shown in Fig. 6(e) then the wafer is oxidized again, and 2 ␮m thick silicon oxide film on the top of silicon salient in 5 ␮m high is defined by a wet etching process with HF solution as shown in Fig. 6(f). The bumper is defined as the structure of silicon salient covered with silicon oxide film. The bottom silicon wafer in 500 ␮m thick, shown in Fig. 6(g), is oxidized and etched by HF and KOH solution in sequence as shown in Fig. 6(h). The etched depth by KOH is 20 ␮m. By repeating the process mentioned above, but a difference is the etched depth by KOH solution. The second and third etched depth is 10 ␮m and 5 ␮m, respectively as shown in Fig. 6(i) and (j). As a result, an eight-terraced silicon structure is successfully achieved as shown in Fig. 6(k). Then, thermal oxide of 2 ␮m is grown as shown in Fig. 6(l), and a poly-silicon film in 1.8 ␮m thickness are deposited by Low Pressure Chemical Vapor Deposition (LPCVD). The poly-silicon film is dense boron doped to reduce the resistivity. After that the bottom electrodes and pads are patterned using Deep Reactive Ion Etch-

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Fig. 6. Cross-sectional view of the fabrication process flow (a) start with an SOI wafer, (b) oxide, (c) KOH defines a gap, (d) oxide, (e) KOH defines the cantilever beam’s back position, (f) keep the SiO2 film on the top of the silicon salient, (g) the separate Si wafer, (h) oxide and KOH defines the terraced position, (i–k) repetitious the process mentioned above to obtain a terraced structure, (l) oxide, (m) deposit and pattern poly-silicon bottom terraced electrodes, (n) Si–Si bonding, (o) the handle and buried layer is removed, (p) Au film is deposited and patterned the reflective surface and the region of top pad, (q) DRIE release the micromirror plate and the region of bottom pad, (r) by using a shadow mask to deposit the Au film to bottom pad.

ing (DRIE) technology and HF solution in sequence as shown in Fig. 6(m). After the micro-structure built, the top SOI wafer and bottom silicon wafer are assembled by using the wafer level Si–Si bonding technology as shown in Fig. 6(n). Then the handle layer and the BOX layer of the SOI wafer are all removed as shown in Fig. 6(o). In general the lateral erosion is large by using a gold wet etching. In order to realize a high fill-factor gold reflective micromirror and wire-bonding pads of top electrode, the gold thin film in thickness of 300 nm is deposited and patterned by ion beam etching method (OXFORD, Ionfab 300plus) as shown in Fig. 6(p). Both the micromir-

ror plates and cantilever beams are defined and released through the DRIE process as shown in Fig. 6(q). At last, additional gold thin film was only deposited on the wire-bonding pads in regions of poly-silicon bottom electrodes by using a shadow mask as shown in Fig. 6(r). 3.2. Fabrication results Micromirror arrays were successfully fabricated using the mentioned fabrication process flow as shown in Fig. 6. The surface roughness of the micromirror plate has been measured using a

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structure in the back-side of the micromirror plate is shown in Fig. 8(d). 4. Characterization In order to verify its electromechanical performance and compare the real measurements with the results of analysis modeling, the micromirror array was characterized in the static and the dynamic operating modes. 4.1. Static test

Fig. 7. Roughness of the micromirror plate.

3D interferometer (Veeco® , WYKO) as shown in Fig. 7. The root mean square (RMS) of the surface profile is about 11 nm which are adequate for the optical wavelengths application. Fig. 8 shows the SEM images of the fabricated micromirror array. The micromirror array with a high fill-factor in excess of 97% is shown in Fig. 8(a). Fig. 8(b) shows the cantilever beam image. The cross-sectional view of the micromirror is illustrated in Fig. 8(c), which shows the cantilever-type micromirror plate, eight-terraced bottom electrodes, a bumper as well as limiting plane. The bumper

In static test, the rotation angle of the micromirror has been measured using a 3D interferometer (Veeco® , WYKO) and DC power supply. The picture of the test system is shown in Fig. 9. The DC power supply generates a high voltage in the range of 0–300 V. When a desired DC voltage is applied to a micromirror by using a control circuit, the micromirror rotated to a desired angle. Utilizing the interferometer, the rotation angle of the micromirror plate has obtained and recorded. After a series of DC voltages are applied to the micromirror, static deflection characteristics of the micromirror plate can be achieved. The test results and the theoretical curve determined by Eq. (8) are shown in Fig. 10. The test results show that the maximal optical rotation angle is 0.87◦ with an applied bias of 156 V. The rotation angle can meet the requirement of WSS system, and the test result also shows the validity of this equation and calculation. In comparison with the theoretical calculation, the measured driving voltages are a little bit lower than theoreti-

Fig. 8. SEM images of the fabricated micromirror array (a) close-up view of micromirror array, (b) cantilever beam image, (c) cross-sectional view of the micromirror, (d) a bumper array in back-side of micromirror plate.

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Fig. 11. Optical system of WSS assembly scheme. Fig. 9. Picture of static test the micromirror array.

design, the micromirror plate could be easily released from the pull-in state when the driving voltage was reduced to 138 V. The test results show that the bumper design can prevent the stick and damage caused by the pull-in effect. 4.2. Dynamic test

Fig. 10. Static deflection characteristics of the micromirror.

cal curve. The slight discrepancy may be caused by the fabrication imperfections. Furthermore we applied an overvoltage about 178 V on the micromirror to illustrate a pull-in effect. Owing to the bumper

A WSS assembly scheme has been proposed to test the dynamic characteristics of the fabricated micromirror array. The schematic configuration of the free-space Grating-MEMS optical systems is shown in Fig. 11. It is composed of three major subassemblies, including a cylindrical optics, a transmission grating and the fabricated micromirror array. The cylindrical optics is utilized to collimate the input and output optical beam. The transmission grating spatially disperses the input optical beam, which consists of the WDM channels, onto the fabricated micromirror array. The micromirror array is designed to rotate an expected angle, and input light is reflected to a desired output direction. As a result, WSS can achieve the function of switch operation. The transient responses of the micromirror for step input voltages are measured by an oscilloscope (YOKOGAWA AQ6370B). When a small voltage is applied between micromirror plate and bottom electrode, the turn-on responding time of micromirror plate, which has been defined as the time from mark a to mark b as shown in Fig. 12(a), is recorded as 0.57 ms without considering the small fluctuations from mark b to mark c. When the applied voltage is then released, the turn-off responding time is recorded

Fig. 12. Transient responses of the micromirror (a) turn-on responding time and (b) turn-off responding time.

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2008AA03Z406 and No. 2009AA03Z443) and National Natural Science Foundation of China (Grant No. 60877066). The author would like to thank the Accelink Company for the characterization collaboration.

References

Fig. 13. Switching times of micromirror.

as 4.36 ms from mark a to b as shown in Fig. 12(b). The reason for turn-off responding time being longer than the turn-on responding time might be that there is a difference between capacitor charging and discharging time of the micromirror. In addition, the switching function between two optical outputports was successfully demonstrated using the WSS optical system. Through the photoelectric conversion, output-ports one and output-ports two were simultaneous inputted to oscilloscopes. When the driving voltage was not applied, only output-ports one had the optical signal corresponding to blue line as shown in Fig. 13. When the micromirror switched from the output-port one to the output-port two, the output-ports one was blocked, and the signal of output-ports two were captured corresponding to red line as shown in Fig. 13. The measured transient responses of switching time, which has been defined as the time from mark a to b as shown in Fig. 13, is 0.53 ms. The switching time is almost consistent with the turn-on responding time. A small oscillation shown in Fig. 13 appeared from the temporary free vibration of the cantilever beam when it switched to the output-ports two position. 5. Conclusion A high fill-factor micromirror array was designed and successfully fabricated by using the bulk micromachining technology. Novel bumper and limiting plane structure was proposed and validated to prevent the stick and damage caused by the pull-in effect. A cantilever-type micromirror plate was selected in order to simplify the device structure and realize the transformation from beam deformation to rotation of micromirror plate. An eight-terraced bottom electrode was introduced to further reduce the driving voltage. Comparing to the traditional parallel-plate bottom electrodes, the voltage is reduced more than 50%. High fill-factor in excess of 97% was achieved in an array with 52 micromirrors. Due to the device silicon layer of SOI being used for the micromirror plate, the fabricated reflector has a high quality optical surface with RMS about 11 nm. The static and dynamic characteristics of the fabricated micromirror array have been tested. The maximal optical rotation angle is 0.87◦ with an applied bias of 156 V. Meanwhile, the measured turn-on responding time of micromirror is 0.57 ms and the turn-off responding time is 4.36 ms. The switching function between two optical output-ports was successfully demonstrated using a WSS optical system as well. Acknowledgments This work was supported by the National High Technology Research and Development Program of China (Grant No.

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Biographies Sihua Li was born in Jiangxi, China in the year of 1979. He received his Bachelor degree in optoelectronics from Shanghai University, Shanghai, China, in 2001. Since 2006 he has been studying in the State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystems and Information Technology, Chinese Academy of Sciences, Shanghai, China, to pursue his Ph.D. degree in Microelectronics. His current research interest includes micromachining technology and Optical MEMS devices. Jing Xu was born in Gansu, China in 1977. She received her Bachelor and Master degrees in opto-electronic engineering from Wuhan University, Wuhan, China, in 1998 and 2001, respectively. Then she received her PhD degree in optical engineering from Zhejiang University, Hangzhou, China, in 2004. Her doctoral work involved

the optical waveguide devices baced on polymide material including arrayed waveguide grating and Mach-Zender inference sensor. She worked as a post-doctor in State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, from 2004 to 2007, and she currently works there as an associate professor. Dr. Xu’s research interests include the development of the Optical MEMS actuators and sensors and the related technologies. Shaolong Zhong graduated with the Bachelor’s degree in mechanical and electronic engineering from Nanjing University of Science and Technology, China, in 1997. As a communication product system engineer, he worked in Huawei Technologies for 4 years. His research interests include: high speed digital circuits design, fiber and MEMS sensors. Yaming Wu was born in Hubei, China in 1966. He received the M.S. degree in Optics from Huazhong University of Science and Technology, Hubei, China, in 1989 and a Ph.D. degree in Optical Engineering from Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, in 1993. He worked as a post-doctor in Shanghai Institute of Technical physics of the Chinese Academy of Sciences, from 1993 to 1995. From 2000 to now, he has been a professor of the State Key Lab of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences. His research interests have been in the fields of devices and system of optical communications, optics sensors, MOMES devices, micro-optics and integrated optics technologies.