Two-axis electromagnetic microscanner for high resolution displays

A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65/spl deg/ and 53/spl deg/ are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting /spl theta//sub opt/D product of 79.5 deg/spl middot/mm for fast axis is obtained. This two-dimensional (2-D) magnetic actuation technique delivers sufficient torque to allow non-resonant operation as low as dc in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies large enough to support SXGA (1280 /spl times/ 1024) resolution scanned beam displays.     

Design and characterization of an electrothermally driven monolithic long-stretch microdrive in compact arrangement

An electrothermally driven long stretch microdrive (LSMD) is presented for planar rectilinear motions in hundreds of micrometers. Design concept is based on connecting several actuation units in series to form a cascaded structure to accumulate relative displacement of each unit, and two cascaded structures are further arranged in parallel by a connection bar to double output force. The proposed area-saving design features monolithic compliant structure in compact arrangement to achieve long stroke. In experiments, the maximum reversible operating voltage is 3 V. In addition, the voltage-displacement relation shows good linearity within /spl plusmn/5% in 0.5-3.0 V. Fabricated nickel LSMD can generate displacement up to 215 /spl mu/m (W=8 /spl mu/m, /spl theta/=0.2/spl deg/, D=34 /spl mu/m) at 3 dc volts (669 mW). The maximum operation temperatures of tested LSMDs at 3 V are below 300 /spl deg/C. Output forces up to 495 /spl mu/N are measured by in situ passive micromechanical test beams. The LSMD can be operated at 100 Hz without degradation on displacement. Two geometrical design parameters, bent angle and constraint bar width, are also investigated analytically and experimentally.     

Electromagnetically actuated mirror arrays for use in 3-D optical switching applications

This paper presents an electromagnetic MEMS mirror technology for use in 3-D optical switching applications. These mirrors may be actuated through large angles at low voltage and low current. Multiple coils on the backs of the mirrors interact with permanent magnetic fields to provide two-axis orthogonal actuation. A custom package brings the MEMS mirror array and magnets into close proximity. Actuation is linear versus drive current on both axes, and displays negligible charging and drift. These mirrors have achieved greater than 10/spl deg/ mechanical rotation per mA in each axis. The mirror rotation angle is hysteresis free to less than the 0.01/spl deg/ measurement accuracy.     

Design, Fabrication, and Characterization of a High Fill-Factor, Large Scan-Angle, Two-Axis Scanner Array Driven by a Leverage Mechanism

We report on the design, fabrication, and characterization of a high fill-factor, large scan-angle, two-axis scanner array. The two-axis microelectromechanical-systems (MEMS) mirror is driven by electrostatic vertical comb-drive actuators through four motion amplifying levers. The maximum mechanical rotation angles are$pm 6.7^circ$at 75 V for both axes, leading to total optical scan angle of 26.8$^circ$. The resonant frequency is 5.9 kHz before metallization. A linear fill factor of 98% is achieved for the one-dimensional (1-D) micromirror array. This 1D array of two-axis micromirrors was designed for$1times N ^2$wavelength-selective switches (WSSs). In addition to two-axis rotation, piston motion with a stroke of 11.7$mu m$is also attained.1731     

The SiOG-based single-crystalline silicon (SCS) RF MEMS switch with uniform characteristics

This paper details single-crystalline silicon (SCS) direct contact radio frequency microelectromechanical systems (RF MEMS) switch designed and fabricated using an SiOG (silicon-on-glass) substrate, so as to obtain higher fabrication and performance uniformity compared with a conventional metal switch. The mechanical and electrical performances of the fabricated silicon switch have been tested. In comparison with a conventional metallic MEMS switch, we can obtain higher productivity and uniformity by using SCS, because it has very low stresses and superior thermal characteristics as a structural material of the switch. Also, by using the SiOG substrate instead of an SOI substrate, fabrication cost can be significantly reduced. The proposed switch is fabricated on a coplanar waveguide (CPW) and actuated by electrostatic force. The designed chip size is 1.05 mm/spl times/0.72 mm. Measured pull-in voltage and actuation voltage were 19 V and 26 V, respectively. Eighteen identical switches taken randomly throughout the wafer showed average and standard deviation of the measured pull-in voltage of 19.1 and 1.5 V, respectively. The RF characteristics of the fabricated switch from dc to 30 GHz have been measured. The isolation and insertion loss measured on the four identical samples were -38 to -39 dB and -0.18 to -0.2 dB at 2 GHz, respectively. Forming damping holes on the upper electrode leads to a relatively fast switching speed. Measured ON and OFF time were 25 and 13 /spl mu/s, respectively. In the switch OFF state, self-actuation does not happen up to the input power of 34 dBm. The measured holding power of the fabricated switch was 31 dBm. Stiction problem was not observed after 10/sup 8/ cycles of repeated actuation, but the contact resistance varied about 0.5-1 /spl Omega/ from the initial value.     

Microfabricated torsional actuators using self-aligned plastic deformation of silicon

In this paper, we describe angular vertical-comb-drive torsional microactuators made in a new process that induces residual plastic deformation of single-crystal-silicon torsion bars. Critical dimensions of the vertically interdigitated moving-and fixed-comb actuators are self-aligned in the fabrication process and processed devices operate stably over a range of actuation voltages. We demonstrate MEMS scanning mirrors that resonate at 2.95kHz and achieve optical scan angles up to 19.2 degrees with driving voltages of 40V/sub dc/ plus 13V/sub pp/. After continuous testing of five billion cycles at the maximum scanning angle, we do not observe any signs of degradation in the plastically deformed silicon torsion bars.     

Self-aligned vertical electrostatic combdrives for micromirror actuation

In this paper, we analyze the effect of misalignment in electrostatic combdrives, and describe a fabrication technology that minimizes misalignment in vertical electrostatic combdrives by creating self-aligned, vertically staggered electrodes. Self-alignment of the interdigitated electrodes simplifies fabrication and minimizes failures due to electrostatic instability, thus enabling fabrication of narrow-gap, high-force actuators with high yield. The process is based on deep-reactive ion etching (DRIE) of buried-patterned silicon-on-insulator (SOI) wafers. Measurements on fabricated combdrives show relative misalignment of less than 0.05 /spl mu/m. This corresponds to less than 0.1% misalignment, which, according to our analysis, results in a travel range of 98% of that for perfectly aligned drives. The validity of the process is demonstrated by fabrication of scanning micromirrors measuring 300 /spl mu/m by 100 /spl mu/m. Optical angular deflections from 4/spl deg/ at low frequency to 40/spl deg/ at resonance were measured for an applied voltage of 75 Vpp. Resonant frequencies ranged from 5 kHz to 15 kHz for these devices, making them suitable for high-speed, high-resolution optical scanning and switching.     

Design and fabrication aspects of an S-shaped film actuator based DC to RF MEMS switch

This paper reports on design and fabrication aspects of a new microelectromechanical series switch for switching dc and RF signals. The switch consists of a flexible S-shaped film with the switching contact, rolling between a top and a bottom electrode in electrostatic touch-mode actuation. This design allows a low actuation voltage independent of the contact distance in the off-state. With a large contact distance, large overlapping switching contact areas are possible by obtaining a high off-state isolation. The RF transmission line and the MEMS part of the switch are fabricated on separate wafers, allowing an implementation of the switch with different RF substrates. The final assembly is done on device level for the first prototypes, even though the design provides the possibility of an assembly by full wafer bonding, leading to a near-hermetic package integrated switch. The measured prototype actuation voltages are 12 V to open and 15.8 V to close the contacts, with a resistance of 275 m/spl Omega/ of each contact at an estimated contact force of 102 /spl mu/N. The measured RF isolation with a contact distance of 14.2 /spl mu/m is better than -45 dB up to 2 GHz and -30 dB at 15 GHz, at a large nominal switching contact area of 3500 /spl mu/m/sup 2/.     

Analog piezoelectric-driven tunable gratings with nanometer resolution

This work presents the design, fabrication, and characterization of a piezoelectrically actuated MEMS diffractive optical grating, whose spatial periodicity can be tuned in analog fashion to within a fraction of a nanometer. The fine control of the diffracted beams permits applications in dense wavelength-division multiplexing (DWDM) optical telecommunications and high-resolution miniaturized spectrometers. The design concept consists of a diffractive grating defined on a deformable membrane, strained in the direction perpendicular to the gratings grooves via thin-film piezoelectric actuators. The tunable angular range for the first diffracted order is up to 400 /spl mu/rad with 0.2% strain (/spl sim/8 nm change in grating periodicity) at 10 V actuation, as predicted by device modeling. The actuators demonstrate a piezoelectric d/sub 31/ coefficient of -100 pC/N and dielectric constant /spl epsiv//sub r/ of 1200. Uniformity across the tunable grating and the out-of-plane deflections are also characterized and discussed.     

Two-axis single-crystal silicon micromirror arrays

This work presents the design, fabrication, and testing of a two-axis 320 pixel micromirror array. The mirror platform is constructed entirely of single-crystal silicon (SCS) minimizing residual and thermal stresses. The 14-/spl mu/m-thick rectangular (750/spl times/800 /spl mu/m/sup 2/) silicon platform is coated with a 0.1-/spl mu/m-thick metallic (Au) reflector. The mirrors are actuated electrostatically with shaped parallel plate electrodes with 86 /spl mu/m gaps. Large area 320-mirror arrays with fabrication yields of 90% per array have been fabricated using a combination of bulk micromachining of SOI wafers, anodic bonding, deep reactive ion etching, and surface micromachining. Several type of micromirror devices have been fabricated with rectangular and triangular electrodes. Triangular electrode devices displayed stable operation within a (/spl plusmn/5/spl deg/, /spl plusmn/5/spl deg/) (mechanical) angular range with voltage drives as low as 60 V.     

Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.     

A MEMS electromagnetic optical scanner for a commercial confocal laser scanning microscope

A MEMS electromagnetic optical scanner for horizontal scanning of a commercial confocal laser scanning microscope has been developed. The purpose is to replace the currently used commercially available scanner with our new MEMS scanner in an existing microscope product, and therefore, the scanner specifications have to be compatible with those of the current one. Electromagnetic actuation is selected because of the millimeter-sized mirror, and a single crystal silicon hinge is used for realizing high-speed scanning with sufficient scan angle. In order to maintain mirror flatness for high quality optics requirement, the whole wafer thickness (300 /spl mu/m) is used as the mirror, resulting in a large moment of inertia, and this has been taken into consideration in the actuator design. Although few MEMS actuators have been commercialized to date, it has successfully satisfied all the specifications including not only the fundamentals such as resonant frequency and scan angle but also those for the commercial product such as scanning stability and reliability. It has been commercialized as a part of our product, Olympus OLS1100 (remodeled as OLS1200 in August 2002).     

Gimbal-less MEMS two-axis optical scanner array with high fill-factor

In this paper, we report on a MEMS-based two-axis optical scanner array with a high fill factor (>96%), large mechanical scan angles (/spl plusmn/4.4/spl deg/ and /spl plusmn/3.4/spl deg/), and high resonant frequencies (20.7 kHz). The devices are fabricated using SUMMiT-V, a five-layer surface-micromachining process. High fill factor, which is important for 1/spl times/N/sup 2/ wavelength-selective switches (WSSs), is achieved by employing crossbar torsion springs underneath the mirror, eliminating the need for gimbal structures. The proposed mirror structure can be readily extended to two-dimensional (2-D) array for adaptive optics applications. In addition to two-axis rotation, piston motion with a stroke of 0.8 /spl mu/m is also achieved. [1496].     

The SOI DAWN process for three-dimensional silicon micromachining and its applications

A DRIE assisted wet anisotropic bulk micromachining (DAWN) process is demonstrated to fabricate various three-dimensional MEMS devices on a silicon-on-insulator (SOI) wafer. This SOI DAWN process can realize thin film structures, reinforced (thin film) structures, and thick structures with totally different mechanical characteristics. Various passive and active mechanical components, including flexible springs, rigid structures, and actuators, have been fabricated using the SOI DAWN process and have been further integrated to create MEMS devices which are flexible as well as movable in both in-plane and out-of-plane directions. This SOI DAWN process has been successfully applied to produce various multi-DOF devices made of single crystal silicon (SCS).     

Low-voltage, large-scan angle MEMS analog micromirror arrays with hidden vertical comb-drive actuators

This paper reports on novel polysilicon surface-micromachined one-dimensional (1-D) analog micromirror arrays fabricated using Sandia's ultraplanar multilevel MEMS technology-V (SUMMiT-V) process. Large continuous DC scan angle (23.6/spl deg/ optical) and low-operating voltage (6 V) have been achieved using vertical comb-drive actuators. The actuators and torsion springs are placed underneath the mirror (137/spl times/120 /spl mu/m/sup 2/) to achieve high fill-factor (91%). The measured resonant frequency of the mirror ranges from 3.4 to 8.1 kHz. The measured DC scanning characteristics and resonant frequencies agree well with theoretical values. The rise time is 120 /spl mu/s and the fall time is 380 /spl mu/s. The static scanning characteristics show good uniformity (相似文献   

A single-layer PDMS-on-silicon hybrid microactuator with multi-axis out-of-plane motion capabilities-part II: fabrication and characterization

This paper reports on fabrication and characterization of a new electrostatic microactuator that achieves out-of-plane multi-axis motion with a single silicon device layer. The multi-axis motion with the simple actuator design is possible by incorporating a three-dimensional (3-D) polydimethylsiloxane (PDMS) microstructure. This paper develops a new device processing method named "Soft-Lithographic Lift-Off and Grafting (SLLOG)" to fabricate the previously designed PDMS-on-silicon hybrid actuator structure. SLLOG is a low-temperature (less than 150/spl deg/C) process that allows replica molded PDMS microstructures to be integrated in silicon micromachined device patterns. The fabricated actuator is characterized using laser vibrometry. The experimental results demonstrate actuation motions achieved in three independent axes with fast dynamic response reaching a bandwidth of about 5 kHz. The fabricated PDMS-on-silicon actuator yields a vertical displacement up to 5 /spl mu/m and rotational motions with a 0.6-/spl deg/ tilting angle at a 40-V peak-to-peak ac actuation voltage.     

A mold and transfer technique for lead-free fluxless soldering and application to MEMS packaging

This paper demonstrates a technique to premold and transfer lead-free solder balls for microelectrocmechanical systems (MEMS)/electronics packaging applications. A reusable bulk micromachined silicon wafer is used to mold a solder paste and remove excess flux prior to transfer to a host wafer that may contain released MEMS. This technique has been used to fabricate low temperature thin film MEMS vacuum packages. Long term (>5 months) reliability of these packages at room temperature and pressure is demonstrated through integrated Pirani gauges. These packages have survived over 600 hours in an autoclave (130/spl deg/C, 85% RH, 2 atm) and more than 1300 temperature cycles (55/spl deg/C to 125/spl deg/C).     

Arrays of monocrystalline silicon micromirrors fabricated using CMOS compatible transfer bonding

In this paper, we present CMOS compatible fabrication of monocrystalline silicon micromirror arrays using membrane transfer bonding. To fabricate the micromirrors, a thin monocrystalline silicon device layer is transferred from a standard silicon-on-insulator (SOI) wafer to a target wafer (e.g., a CMOS wafer) using low-temperature adhesive wafer bonding. In this way, very flat, uniform and low-stress micromirror membranes made of monocrystalline silicon can be directly fabricated on top of CMOS circuits. The mirror fabrication does not contain any bond alignment between the wafers, thus, the mirror dimensions and alignment accuracies are only limited by the photolithographic steps. Micromirror arrays with 4/spl times/4 pixels and a pitch size of 16 /spl mu/m/spl times/16 /spl mu/m have been fabricated. The monocrystalline silicon micromirrors are 0.34 /spl mu/m thick and have feature sizes as small as 0.6 /spl mu/m. The distance between the addressing electrodes and the mirror membranes is 0.8 /spl mu/m. Torsional micromirror arrays are used as spatial light modulators, and have potential applications in projection display systems, pattern generators for maskless lithography systems, optical spectroscopy, and optical communication systems. In principle, the membrane transfer bonding technique can be applied for integration of CMOS circuits with any type of transducer that consists of membranes and that benefits from the use of high temperature annealed or monocrystalline materials. These types of devices include thermal infrared detectors, RF-MEMS devices, tuneable vertical cavity surface emitting lasers (VCSEL) and other optical transducers.     

Low-actuation voltage RF MEMS shunt switch with cold switching lifetime of seven billion cycles

This paper investigates the performance and lifetime of a metal-to-metal shunt RF MEMS switch fabricated on an SI-GaAs substrate. The switch is a shunt bridge design that is compatible with standard microelectronic processing techniques. The RF performance of the switch includes actuation voltages of less than 15 V, isolation better than 20 dB from 0.25 to 40 GHz, and switching speeds of less than 22 /spl mu/s. Varying the geometry of the switch affects both switching voltage and reliability, and the tradeoffs are discussed. We have developed a cold switching test method to identify the root cause of sticking as a failure mechanism. The switch structure includes "separation posts" that eliminate sticking failure and has demonstrated lifetimes as high as 7/spl times/10/sup 9/ cold switching cycles. These results show that good reliability is possible with a metal-to-metal RF MEMS switch operated with a low actuation voltage.     

Surface- and bulk- micromachined two-dimensional scanner driven by angular vertical comb actuators

In this paper, we present the design, fabrication, and measurements of a two-dimensional (2-D) optical scanner with electrostatic angular vertical comb (AVC) actuators. The scanner is realized by combining a foundry-based surface-micromachining process (Multi-User MEMS Processes-MUMPs) with a three-mask deep-reactive ion-etching (DRIE) postfabrication process. The surface-micromachining provides versatile mechanical design and electrical interconnect while the bulk micromachining offers high-aspect ratio structures leading to flat mirrors and high-force, large-displacement actuators. The scanner achieves dc mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The resonant frequencies are 315 and 144 Hz for the inner and the outer axes, respectively. The 1-mm-diameter mirror has a radius of curvature of over 50 cm. [1454].