Multi-user MEMS Processes Research Articles

Compact thermally actuated latching MEMS switch with large contact force

A novel latching microelectromechanical system (MEMS) switch is reported, which uses a compact configuration of thermal actuators. In the proposed latching mechanism, the necessary displacement of one of the contacts can be reduced, allowing the use of a linear thermal actuator. This linear actuator together with a V-shaped actuator can be aligned next to each other, requiring less area than the classical latching switch design. Another advantage of the proposed design is the high contact force of 1.33 mN, ensuring a stable contact resistance. The latching switch was fabricated in the Metal multi-user MEMS processes (MUMPs) technology and its functionality was successfully tested. In the latched state, a switch resistance of 0.6 Ω was measured.

Performance of silicon-on-insulator multiuser MEMS processes–based electrothermally actuated silicon microgrippers

Recently, microgrippers are finding more importance in the field of tissue engineering and microassembly in semiconductor electronics. Large force and, hence, large displacement, low power, and low temperature are the essential features to be considered during the design of the microgrippers. The electrical and mechanical behaviors of electrothermally actuated silicon microgrippers are presented. The effect of increasing the flexure length and the cold arm area to improve the displacement is discussed. These microgrippers are normally of the open type, in which the arms have an initial open gap of 20 μm, and they move away from each other with the applied voltage. The displacement of each arm is observed to be 24 μm for the applied voltage of 10 V. The response time of the device is less than 5 ms, and the maximum power dissipation is 110 mW. The displacement of the microgrippers can be increased with increased flexure length and cold arm length with short extended arms. This structure also shows lower stress.

Air-coupled linear and sparse cMUT array manufactured using MUMPs process

An assessment of the standard fabrication Micro-Electro-Mechanical Systems (MEMS) process Multi-User MEMS Processes (MUMPs) for complex air-coupled capacitive Micromachined Ultrasonic Transducer array aperture manufacture is reported. A 1-D linear array and a 2-D sparse symmetric binned-array have been designed and manufactured, and then characterised experimentally using electrical impedance measurements, laser vibrometry and air-coupled field measurement; the experimental data are supported by simulated data using Finite Element technique and field simulation based on Huygens’ principle. A methodology for the manufacture of the array structures using the MUMPs process is described. Electrical characterisation shows the devices operation at 770 kHz and the existence of large parasitic capacitances and electrical losses. Mechanical crosstalk of array substrate has been measured at −40 dB using laser vibrometry. Moreover, the laser vibrometry measurement and the field characteristics of one element reveal that each element operates as a piston radiator.

Calibration of residual stress difference of MetalMUMPs silicon nitride films

The metal multi-user MEMS processes (MetalMUMPs) provide one nickel film, two silicon nitride films and one polysilicon film for constructing various nickel MEMS devices. The two silicon nitride films are either bonded together as a bi-layered structure or they sandwich the polysilicon film to form a tri-layered structure to support nickel structures. The residual stress difference of the two silicon nitride films causes undesired deformations of suspended MetalMUMPs devices. In this paper, the residual stress difference of the two MetalMUMPs silicon nitride thin films is calibrated and the result is 169 MPa. The Young’s modulus of the MetalMUMPs nitride films is also measured, which is 209 GPa.

Surface Micromachined Adjustable Micro-Concave Mirror for Bio-Detection Applications

We present a bio-detection system integrated with an adjustable micro-concave mirror. The bio-detection system consists of an adjustable micro-concave mirror, micro flow cytometer chip and optical detection module. The adjustable micro-concave mirror can be fabricated with ease using commercially available MEMS foundry services (such as multiuser MEMS processes, MUMPs) and its curvature can be controlled utilizing thermal or electrical effects. Experimental results show that focal lengths of the micro-concave mirror ranging from 313.5 to 2275.0 μm are achieved. The adjustable micro-concave mirror can be used to increase the efficiency of optical detection and provide a high signal-to-noise ratio. The developed micro-concave mirror is integrated with a micro flow cytometer for cell counting applications. Successful counting of fluorescent-labeled beads is demonstrated using the developed method.

Characterization of Young's modulus and residual stress gradient of MetalMUMPs electroplated nickel film

Metal multi-user MEMS processes (MetalMUMPs) offered by MEMSCAP provide a 20 μm thick electroplated nickel film suitable for constructing micro RF tunable capacitors, RF inductors, relays, switches, etc. Currently the Young's modulus and the residual stress gradient of the MetalMUMPs nickel film have not been characterized. In this paper the resonance method is used to characterize the Young's modulus of the MetalMUMPs nickel film. The characterization results show that the nickel film has a Young's modulus of 155–164 GPa with an average of 159 GPa. A stress gradient induced free beam mechanism is proposed in this paper to characterize the residual stress gradient in the MetalMUMPs nickel film. Characterization results show that the residual stress in the electroplated nickel film has a gradient across the film thickness of −5.49 MPa/μm to −4.30 MPa/μm with the average of −4.72 MPa/μm. The residual stress change from the bottom surface to the top surface of the nickel film is −97.7 MPa. The Young's modulus and residual stress gradient of the MetalMUMPs nickel film obtained in this paper provide MetalMUMPs users an important reference for designing, optimizing and analyzing suspended nickel structures. The stress gradient induced free beam mechanism proposed in this paper provides a method of characterizing negative residual stress gradient in thin films without using trenches or through-wafer holes.

Elastic Properties and Representative Volume Element of Polycrystalline Silicon for MEMS

A nanoscale mechanical deformation measurement method was employed to obtain the Young’s modulus and Poisson’s ratio of polycrystalline silicon for Microelectromechanical Systems (MEMS) from different facilities, and to assess the scale at which these effective properties are valid in MEMS design. The method, based on in situ Atomic Force Microscope (AFM) imaging and Digital Image Correlation (DIC) analysis, employed 2–2.5 μm thick freestanding specimens with surface measurement areas varying between 1×2 and 5×15 μm2. The effective mechanical properties were quite invariant with respect to the fabrication facility: the Poisson’s ratio of polycrystalline silicon from the Multi-user MEMS Processes (MUMPs) and from Sandia’s Ultra planar four layer Multilevel MEMS Technology (SUMMiT-IV) was 0.22±0.02, while the elastic moduli for MUMPs and SUMMiT-IV polysilicon were 164±7 and 155±6 GPa, respectively. The AFM/DIC method was used to determine the size of the material domain whose mechanical behavior could be described by the isotropic constants. For SUMMiT polysilicon with columnar grains and 650 nm average grain size, it was found that a 10×10-μm2 specimen area, on average containing 15×15 columnar grains, was a representative volume element. However, the axial displacement fields in 4×4 or 2×2 μm2 areas could be highly inhomogeneous and the effective behavior of these specimen domains could deviate significantly from that described by isotropy. As a consequence, the isotropic material constants are applicable to MEMS components comprised of 15×15 or more grains, corresponding to specimen areas equal to 10×10 μm2 for SUMMiT and 5×5 μm2 for MUMPs, and do not provide an accurate description of the mechanics of smaller MEMS components.

Helical wave-front laser beam generated with a microelectromechanical systems (MEMS)-based device

We report a novel helical wave-front laser beam generator based on microelectromechanical systems (MEMS) technology. The device consists of a circular array of micromirrors; each can be electrostatically actuated to move perpendicular to the substrate to modulate the phase of an incident laser beam. A prototype device has been developed using the polysilicon multiuser MEMS processes. The ability of the device to transform a plane wave into an l=3 helical wave-front laser beam has been experimentally demonstrated. Additionally, the device is faster by two orders of magnitude or more than conventional liquid crystal spatial light modulators. In combination with a rapid optical beam steering system, the proposed device might provide new capabilities for fast-scanned optical tweezer arrays, allowing them to combine optical vortices and conventional traps together to trap, guide, and rotate a wide variety of particles.

An open-loop nano-positioning micromechanical digital-to-analog converter for grating light modulation

We report an open-loop digitally driven precision positioning mechanism, termed micromechanical digital-to-analog converter (MDAC), and its pioneering application in a grating light modulator. A prototype grating light modulator driven by a 6-bit MDAC has been fabricated using the polysilicon multiuser microelectromechanical systems processes, achieving a total stroke of 296 nm (full-scale output) and step size [least significant bit (LSB)] of 4.7 nm in a highly repeatable and stable manner. The grating light modulator demonstrated about 13-dB contrast ratio between maximum and minimum intensity of the zeroth diffraction order. The proposed mechanism can be configured for many promising applications including digital variable optical attenuators for optical fiber communications.

Mechanical Design of Compliant Microsystems—A Perspective and Prospects

The field of microsystems, or microelectromechanical systems (MEMS) as it is popularly known, is a truly multidisciplinary area of research. It combines a wide variety of physical, chemical, and biological phenomena into an integrated system on a chip. This unprecedented integration naturally calls for new systems design approaches as well as efficient ways to analyze a single system or a component that is governed by many types of partial and ordinary differential equations from different physical and chemical domains. The key component of almost all MEMS devices, with the exception of microfluidic systems, is a movable mechanical structure of micron dimensions. Since the early works in this area dating back to the late sixties of the 20th Century, simple mechanical structures such as beams and diaphragms have dominated MEMS. Thus, the mechanical design in MEMS is mainly concerned with the design of such elastically deforming structures subjected to a variety of forces ranging from electrostatic, thermal, magnetic, piezoelectric, radiation pressure, etc. In addition to these unconventional forces and the accompanying complex equations that govern them, micromachining brings additional difficulties in microsystem design.

Recent Progress Toward a Manufacturable Polycrystalline SiC Surface Micromachining Technology

In this paper, we present results of recent research from our laboratory directed toward a manufacturable SiC surface micromachining technology for microelectromechanical systems (MEMS) applications. These include the development of a low-pressure chemical vapor deposition and in situ doping processes for silicon carbide (SiC) films at relatively low temperatures, as well as the development of selective dry etching processes for SiC using nonmetallic masking materials. Doped polycrystalline SiC films are deposited at 800/spl deg/C by using a precursor 1,3-disilabutane and dopant gas NH/sub 3/, with the minimum resistivity of 26 m/spl Omega//spl middot/cm. Dry etching for SiC and its selectivity toward silicon dioxide and silicon nitride masking materials are investigated using SF/sub 6//O/sub 2/, HBr, and HBr/Cl/sub 2/ transformer coupled plasmas. The etch rate, etch selectivity, and etch profile are characterized and compared for each etch chemistry. By combining the LPCVD and dry etching process with conventional microfabrication technologies, a multiuser SiC MEMS process is developed.

Operation of electrothermal and electrostatic MUMPs microactuators underwater

Surface-micromachined actuators made in multi-user MEMS processes (MUMPs) have been operated underwater without modifying the manufacturing process. Such actuators have generally been either electro-thermally or electro-statically actuated and both actuator styles are tested here for suitability underwater. This is believed to be the first time that thermal and electrostatic actuators have been compared for deflection underwater relative to air performance. A high-frequency ac square wave is used to replicate a dc-driven actuator output without the associated problem of electrolysis in water. This method of ac activation, with frequencies far above the mechanical resonance frequencies of the MEMS actuators, has been termed root mean square (RMS) operation. Both thermal and electrostatic actuators have been tested and proved to work using RMS control. Underwater performance has been evaluated by using in-air operation of these actuators as a benchmark. When comparing deflection per volt applied, thermal actuators operate between 5 and 9% of in-air deflection and electrostatic actuators show an improvement in force per volt applied of upwards of 6000%. These results agree with predictions based on the physical properties of the surrounding medium.

Electrostatic micromembrane actuator arrays as motion generator

A rigid-body motion generator based on an array of micromembrane actuators is described. Unlike previous microelectromechanical systems (MEMS) techniques, the architecture employs a large number (typically greater than 1000) of micron-sized (10–200 μm) membrane actuators to simultaneously generate the displacement of a large rigid body, such as a conventional optical mirror. For optical applications, the approach provides optical design freedom of MEMS mirrors by enabling large-aperture mirrors to be driven electrostatically by MEMS actuators. The micromembrane actuator arrays have been built using a stacked architecture similar to that employed in the Multiuser MEMS Process (MUMPS), and the motion transfer from the arrayed micron-sized actuators to macro-sized components was demonstrated.

Fiber Bragg Grating Demodulator Based on Hybrid Optical MEMS

This paper describes the design, experimental evaluation and performance results of a tunable optical filter based on hybrid microoptoelectromechanical systems (MOEMS) technology. The tunable filter can meet the demodulation requirements for Fiber Bragg grating (FBG) sensors. The hybrid system is built using an off-the-shelf 200-GHz dense wavelength-division multiplexing filter and a movable MEMS platform actuated by a thermal microactuator array fabricated with silicon-on-insulator multiuser MEMS processes. Results show a repeatable tuning range of over 400 pm, which satisfies the demodulation requirements for FBG sensors.

Evaluation of MUMPS polysilicon structures for thermal flow sensors

The air flow measurement has been studied for its application in many fields. Among flow sensors, those operated under a thermal principle have occupied an important position. The application of micro–electro mechanical systems (MEMS) technologies for designing such devices will allow reducing its size, response time and to increase the sensitivity.In the community of MEMS’ designers it is well established a multi-user service for prototyping named multi-user MEMS processes (MUMPS). It is a general purpose surface micromachining process which employs polysilicon as structural material and silicon oxide as sacrificial layer. There are no reported, to the best of our knowledge, flow sensors developed using this technology.In this work the linear and quadratic temperature coefficients of polysilicon resistors are experimentally determined in anchored, suspended and stacked microstructures fabricated with this process to study their suitability for flow and temperature sensors. The thermal resistance of the three structures is also calculated, determining that suspended plates characteristics indicate their suitability for constant temperature anemometers.

New design for surface micromachined bistable and multistable switches

Microsystems often require switches or mechanisms to provide two stable states. In answer to this need, we design a novel micromechanical bistable switch based on the locking mechanism commonly used in extension ladders. This switch was designed and fabricated through the multiuser MEMS processes (MUMPs). Actual performance of the switch was videotaped, analyzed, and compared with theory and simulation. This design was fully functional on the first design iteration, and can easily be extended to provide multiple stable states. We outline the design, simulation, and results from the testing of the microfabricated system.

Thermal cycling response of layered gold/polysilicon MEMS structures

Multi-layer material structures in micro-electromechanical systems (MEMS) differ considerably from their micro-electronic counterparts since the thicknesses of the film and substrate are comparable. Due to thermal expansion coefficient mismatch between metallic and polysilicon materials, thermal fluctuations in multi-layer MEMS structures may lead to out of plane displacements several times the structure thickness. In the present study we examine the deformation of a series of gold/polysilicon test structures produced using the commercial multi-user MEMS Process. The test structures are multi-layer plates with a gold layer that is 0.5 μm thick on a polysilicon layer with a thickness that is either 1.5 or 3.5 μm. The structures have varying in-plane dimensions on the order of 50–300 μm. Using an interferometric microscope, we measure the full-field deformed shapes of the Au–Si structures subjected to thermal cycles or hold periods. Depending on the Au–Si plate geometry, the structures deform in a non-linear manner and buckle when the temperature change is large enough. When subjected to temperature holds, the curvature of the plates relaxes. Beam-like plates subjected to repeated thermal cycles demonstrate a cyclic response that depends strongly on the mean (or maximum) temperature. Samples cycled at lower mean temperatures show significant ratcheting toward lower curvatures as the number of cycles approaches 10,000. Samples cycled at higher mean temperatures undergo degradation of surface reflectivity as the number of cycles approaches 1000.

Novel multi-user-MEMS-processes-compatible single-layer out-of-plane electrothermal actuator

Microactuators are regarded as a key component in the field of microelectromechanical systems (MEMS). According to the motion of the actuator, it can be classified as an out-of-plane type or an in-plane type. Most of the existing out-of-plane thermal actuators are multi-layer structures. In this study, a novel electrothermal single-layer out-of-plane actuator is presented. The characteristics of this device are stated as follows: (1) This actuator consists of only a single thin film layer, therefore, it can prevent delaminating after a long-term operation. (2) The fabrication process is multi-user MEMS processes (MUMPs)-compatible, and it has the potential to integrate with many different micromachined components. (3) As demonstrated by the experiment, this device can be operated at a relatively low voltage. For the thermal actuator with beam length 275 μm, its deflection amplitude can reach 3.196 μm when driven at 5 V dc, and 5.316 μm when driven at 8 V dc. This structure offers the potential for application in adaptive optics systems and other optical systems. It also provides an interface to cooperate with integrated circuits and various optical elements to construct an embedded-control optical system.

A frequency tunable half‐wave resonator using a MEMS variable capacitor

A frequency tunable half‐wave resonator at 3 GHz is presented with a microelectromechanical systems (MEMS) variable capacitor as the tuning element. The capacitor is fabricated using the multi‐user MEMS process (MUMPs) technology provided by JDS/Cronos, and transferred to an alumina substrate by an in‐house developed flip‐chip process. This capacitor is electrostatically actuated. The resulting C‐V response is linear with a slope of 0.05 pF/V for a wide range of actuation voltages. The MEMS device has a capacitance ratio of 3:1 for 0‐70 V bias, with a Q‐factor of 140 measured at 1 GHz. A half‐wave tunable microstrip resonator with bias lines is designed to include this MEMS device, which exhibits linear tuning over 180 MHz (6 percent) centered around 3 GHz with a constant 3 dB bandwidth of 160 MHz over the entire tuning range. The power consumption of the MEMS device was measured to be negligible.

Thin Film Material Parameters Derived from Full Field Nanometric Displacement Measurements in Non-uniform MEMS Geometries

ABSTRACTMEMS-scale polycrystalline silicon 2 μm thin film specimens fabricated via the Multi User MEMS Processes (MUMPs) have been employed to obtain the non-uniform nanometric displacement fields in the vicinity of prefabricated circular and elliptical micron-sized perforations. For the hole diameter-to-specimen width ratios considered in this work, and for all practical purposes, the displacement solution for a hole in an infinite plate is applicable. This method requires the ability to reliably and repeatably acquire nanometer level displacements on freestanding thin films. These tensile tests were conducted by a custom microtensile tester with the aid of Atomic Force Microscopy (AFM) and a special gripper that makes use of electrostatically assisted UV adhesion to handle and load miniature MEMS specimens. This non-conventional procedure for material parameter determination relies on Digital Image Correlation (DIC) to compare two AFM images, one before and one after specimen loading, and thus compute the nanometer level displacement fields (<50 nm global displacements) in 15×15-μm2 (or smaller) areas, with better than 2–3 nm resolution in displacements. By posing and solving a non-linear least squares inverse problem where, for known applied loads and measured displacement fields in an infinite plate with either a circular or an elliptical hole, it is possible to recover the elastic modulus (E). The main advantage of this approach is the full utilization of high-resolution displacement measurements over a specific specimen area, using only measurements acquired at one load level. Further statistical measurements of material properties may be obtained at varying load levels.