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Microelectromechanical Systems, Journal of

Issue 2 • Date Apr 2003

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Displaying Results 1 - 12 of 12
  • Integrated micro-heat-pipe fabrication technology

    Publication Year: 2003 , Page(s): 138 - 146
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1522 KB)  

    This paper presents the design and fabrication of an integrated micro-heat-pipe system consisting of a heater, an array of heat pipes, temperature and capacitive sensors. Taking advantage of the large difference between the dielectric constants of liquid and vapor, the integrated capacitor can be used for void-fraction measurements in two-phase flows. Both CMOS-compatible and glass-based fabrication technologies are reported. In the CMOS-compatible technology, the heat pipes are capped by a thin nitride layer utilizing wafer bonding and etch back technique. In the glass-based technology, the heat pipes are covered by a glass substrate using die-by-die anodic bonding to allow visualization of the two-phase flow patterns. This approach also results in a significant reduction of the parasitic capacitance, thus enhancing the sensitivity of the capacitance sensor. A few particular problems related to this technology are discussed and proper solutions are proposed. View full abstract»

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  • Air-channel fabrication for microelectromechanical systems via sacrificial photosensitive polycarbonates

    Publication Year: 2003 , Page(s): 147 - 159
    Cited by:  Papers (39)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1161 KB)  

    This research involves the fabrication of encapsulated air-channels via acid-catalyzed degradation of photosensitive polycarbonates (PCs). There is a need for lower-temperature, degradable polymeric materials to fabricate buried air-channels for microelectromechanical systems (MEMS), microfluidic devices, and micro-reactors. Some polycarbonates undergo thermolytic degradation in the temperature range of 200 to 350°C. These polycarbonates are also known to undergo acid-catalyzed decomposition in the presence of catalytic amounts of acid. A small percentage of an acid in the polycarbonate formulation can greatly reduce the onset of decomposition temperature to the 100 to 180°C temperature range. The photoacid and thermal acid induced degradation behavior of PCs and its use as a sacrificial material for the formation of air-gaps have been studied in this work. The decomposition of several polycarbonates with the aid of in situ generated photo-acid has been demonstrated and applied to the fabrication of micro air-channels. Based on FT-IR, mass spectrometry, and thermogravimetric analysis (TGA), a degradation mechanism was proposed. View full abstract»

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  • Soft-magnetic rotational microwings in an alternating magnetic field applicable to microflight mechanisms

    Publication Year: 2003 , Page(s): 221 - 227
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (751 KB) |  | HTML iconHTML  

    This paper presents microsized soft-magnetic rotational wings in an alternating magnetic field. The wireless power supply as well as control of magnetic microwings are readily applicable to microflight mechanisms. As a magnetic material, soft magnetic material, such as nickel-iron alloy was deposited via electroplating, which is a well-developed MEMS batch process. The magnetization of the soft-magnetic device, however, changes its direction and magnitude during rotation, where the shape magnetic anisotropy of the wings plays a vital role. The principle of the wing rotation in an alternating magnetic field was elucidated theoretically and showed favorable agreement with the experimental results with large-sized models. The aerodynamic performances of soft magnetic rotational wings were evaluated, including the microrotational wings 165 μg in weight consisting of 0.9-mm-long magnetic wings made of electroplated nickel-iron alloy and an axis of wing rotation made of a sharpened glass tube. The micromagnetic rotational wings presented here were utilized for microflight mechanisms, which achieved successful flights. View full abstract»

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  • A high-flow thermopneumatic microvalve with improved efficiency and integrated state sensing

    Publication Year: 2003 , Page(s): 201 - 208
    Cited by:  Papers (37)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (870 KB)  

    This paper reports a thermopneumatic microvalve featuring a corrugated diaphragm. A sealed cavity below the diaphragm contains a volatile fluid, the vapor pressure of which can be increased by resistive heating to deflect the diaphragm, thus closing the valve. Silicon heater grids are elevated 9 μm above the cavity floor, and the cavity is only partially filled with fluid, to increase thermal efficiency. A vacuum-sealed, capacitive pressure sensor on the floor allows direct monitoring of the cavity pressure. Pentane-filled actuators sustain a 2070 torr pressure rise above atmospheric with 500 mW input power. A device tested in situ closes with 350 mW at 1000 torr inlet pressure (venting to vacuum) and maintains closure with 30 mW input. Valves conduct 400 sccm under 1500 torr differential pressure, while maintaining leak rates as low as 10-3 sccm, yielding a dynamic range of 105. A thermodynamic model has been developed that matches experimental power, pressure, and transient response data to within a few percent. This model is used to suggest an optimized structure capable of a 2000 torr pressure rise with 50 mW input and a 1 s response time. The glass-and-silicon valve structure is suitable for integration into complete microfluidic systems. View full abstract»

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  • Fabricating capacitive micromachined ultrasonic transducers with wafer-bonding technology

    Publication Year: 2003 , Page(s): 128 - 137
    Cited by:  Papers (85)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1347 KB)  

    Introduces a new method for fabricating capacitive micromachined ultrasonic transducers (CMUTs) that uses a wafer bonding technique. The transducer membrane and cavity are defined on an SOI (silicon-on-insulator) wafer and on a prime wafer, respectively. Then, using silicon direct bonding in a vacuum environment, the two wafers are bonded together to form a transducer. This new technique, capable of fabricating large CMUTs, offers advantages over the traditionally micromachined CMUTs. First, forming a vacuum-sealed cavity is relatively easy since the wafer bonding is performed in a vacuum chamber. Second, this process enables better control over the gap height, making it possible to fabricate very small gaps (less than 0.1 μm). Third, since the membrane is made of single crystal silicon, it is possible to predict and control the mechanical properties of the membrane to within 5%. Finally, the number of process steps involved in making a CMUT has been reduced from 22 to 15, shortening the device turn-around time. All of these advantages provide repeatable fabrication of CMUTs featuring predictable center frequency, bandwidth, and collapse voltage. View full abstract»

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  • Polycrystalline silicon-germanium films for integrated microsystems

    Publication Year: 2003 , Page(s): 160 - 171
    Cited by:  Papers (47)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1704 KB) |  | HTML iconHTML  

    Two approaches were demonstrated for fabricating microstructures after completion of CMOS circuits with aluminum metallization. The first approach employed n-type poly-Ge deposited at 400°C as a structural material with an SiO2 sacrificial layer and an HF release. The CMOS circuits were protected from the release etchant with an amorphous Si layer. Clamped-clamped lateral resonator test structures had quality factors in vacuum as high as ∼30000. Following a 500°C, 30 s RTA the poly-Ge stress was 200 MPa (tensile) and the resistivity was 5.3 mΩ-cm. In the second integration approach, p-type poly-Si0.35Ge0.65 deposited at 450°C was the structural material with poly-Ge as the sacrificial material and H2O2 as the release etchant. The H2O2 did not significantly etch the p-type poly-SiGe structural layer and no protection of the underlying CMOS layers was needed. For the first time, the fabrication of LPCVD surface microstructures directly on top of standard electronics was demonstrated, providing dramatic reductions in both MEMS-CMOS interconnect parasitics and device area. A folded flexure lateral resonator had a quality factor in vacuum as high as ∼15000. No stress or dopant-activation anneal was needed, since the in situ boron-doped poly-SiGe was found to have an as-deposited stress of only -10 MPa (compressive) and a resistivity of only 1.8 mΩ-cm. View full abstract»

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  • Characterization of selective polysilicon deposition for MEMS resonator tuning

    Publication Year: 2003 , Page(s): 193 - 200
    Cited by:  Papers (18)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1197 KB) |  | HTML iconHTML  

    Variations in micromachining processes cause submicron differences in the size of MEMS devices, which leads to frequency scatter in resonators. A new method of compensating for fabrication process variations is to add material to MEMS structures by the selective deposition of polysilicon. It is performed by electrically heating the MEMS in a 25°C silane environment to activate the local decomposition of the gas. On a (1.0×1.5×100) μm3, clamped-clamped, polysilicon beam, at a power dissipation of 2.38 mW (peak temperature of 699°C), a new layer of polysilicon (up to 1 μm thick) was deposited in 10 min. The deposition rate was three times faster than conventional LPCVD rates for polysilicon. When selective polysilicon deposition (SPD) was applied to the frequency tuning of specially-designed, comb-drive resonators, a correlation was found between the change in resonant frequency and the length of the newly deposited material (the hotspot) on the resonator's suspension beams. A second correlation linked the length of the hotspot to the magnitude of the power fluctuation during the deposition trial. The mechanisms for changing resonant frequency by the SPD process include increasing mass and stiffness and altering residual stress. The effects of localized heating are presented. The experiments and simulations in this work yield guidelines for tuning resonators to a target frequency. View full abstract»

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  • A servo-controlled capacitive pressure sensor using a capped-cylinder structure microfabricated by a three-mask process

    Publication Year: 2003 , Page(s): 209 - 220
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1010 KB) |  | HTML iconHTML  

    A silicon-micromachined servo-controlled capacitive pressure sensor is described. The use of a capped-cylinder shape with pick-off electrodes external to a sealed cavity permits this device to be fabricated in only three masking steps. Device behavior is evaluated experimentally and by finite element analysis. A fabricated device with 2 mm diameter, 9.7 μm structural thickness and 10 μm cavity height provides a measured sensitivity of 0.516 V/kPa over a dynamic range of 20-100 kPa gauge pressure, with a nonlinearity of <3.22% of full scale. The open-loop sensitivity of this device averaged over a dynamic range of 0-250 kPa is -408 ppm/kPa. A voltage bias applied to the servo-electrode can be used to tune both the open-loop and servo-controlled sensitivity by more than 30%. An alternative design in which the Si electrode is segmented to relieve residual stress provides 10-20% more open-loop sensitivity with similar structural dimensions. Fabricated devices are sealed within a metal package filled with an inert dielectric liquid. This enhanced open-loop sensitivity by a factor of about 1.7, and in servo-controlled operation, reduced restoring voltage by a similar factor. Measurements and analysis of temperature responses of these devices are presented. View full abstract»

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  • Controlled multibatch self-assembly of microdevices

    Publication Year: 2003 , Page(s): 117 - 127
    Cited by:  Papers (75)  |  Patents (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1258 KB)  

    A technique is described for assembly of multiple batches of micro components onto a single substrate. The substrate is prepared with hydrophobic alkanethiol-coated gold binding sites. To perform assembly, a hydrocarbon oil, which is applied to the substrate, wets exclusively the hydrophobic binding sites in water. Micro components are then added to the water, and assembled on the oil-wetted binding sites. Moreover, assembly can be controlled to take place on desired binding sites by using an electrochemical method to deactivate specific substrate binding sites. By repeatedly applying this technique, different batches of micro components can be sequentially assembled to a single substrate. As a post assembly procedure, electroplating is incorporated into the technique to establish electrical connections for assembled components. Important issues presented are: substrate fabrication techniques, electrochemical modulation by using a suitable alkanethiol (dodecanethiol), electroplating of tin and lead alloy and binding site design simulations. Finally, we demonstrate a two-batch assembly of silicon square parts, and establishing electrical connectivity for assembled surface-mount light emitting diodes (LEDs) by electroplating. View full abstract»

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  • Novel fabrication method for surface micromachined thin single-crystal silicon cantilever beams

    Publication Year: 2003 , Page(s): 185 - 192
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (802 KB)  

    This paper describes a novel technique for the fabrication of surface micromachined thin silicon cantilever beams using merged epitaxial lateral overgrowth (MELO) of silicon and chemical-mechanical polishing (CMP). The objective is to demonstrate the feasibility of using this novel technique for the fabrication of arrays of ultrathin, low-stress, single-crystal silicon cantilever beams for use in ultrahigh sensitivity surface-stress or resonant-frequency-based chemical or biological detection schemes. The process flow used in this work is described in detail and the issues that were faced during the fabrication are discussed. Cantilever beams with thickness of 0.3-0.5 μm that were 10-25-μm wide and 75-130-μm long were fabricated. Mechanical characterization of the cantilever beams were performed by measuring their spring constant using the "added mass" method, which also demonstrated the use of these initial structures to detect masses as low as 10-100 pg. Further work is underway to scale the thickness of these beams down to the sub-100-nm regime. View full abstract»

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  • Implantable multichannel electrode array based on SOI technology

    Publication Year: 2003 , Page(s): 179 - 184
    Cited by:  Papers (27)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (627 KB) |  | HTML iconHTML  

    This work presents a new method of fabricating implantable multielectrode arrays on lightly doped single-crystal silicon. Such arrays are essential tools for electrical stimulation and recording of nerve signals. Our new microfabrication process, based on silicon-on-insulator (SOI) technology, inherently has excellent control over the final probe thickness without wet etching. The needle shanks are 6 mm long and 80 μm wide. Here the thickness of the probe, 25 μm, is defined by the device layer thickness on the SOI wafer. Our new sprinkler fluidic channel, which has holes spaced 50 μm apart along its 6 mm length, permits the perfusion of a large area of tissue with any desired neurotransmitter or other drug. The probes fabricated here are tested in the cat primary visual cortex; data recorded from adjacent neurons was used to characterize their orientation tuning. The sprinkler channel was characterized, and flowrate through the channel is a linear function of the applied pressure. View full abstract»

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  • Cubic millimeter power inductor fabricated in batch-type wafer technology

    Publication Year: 2003 , Page(s): 172 - 178
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (765 KB)  

    A hybrid technology for the realization of three-dimensional (3-D) miniaturized power inductors is presented. Our devices consist of planar Cu coils on polyimide substrates, and mm-size ferrite magnetic cores, obtained by three-dimensional micro-patterning of ferrite wafers using powder blasting. The coils are realized using an in-house developed high-resolution polyimide spinning and Cu electroplating process. Winding widths down to 5 μm have been obtained and total device volumes are ranging between 1.5 and 10 mm3. Inductive and resistive properties are characterized as a function of frequency; inductance values in the 100 μH range have been obtained. View full abstract»

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Aims & Scope

The topics of interest include, but are not limited to: devices ranging in size from microns to millimeters, IC-compatible fabrication techniques, other fabrication techniques, measurement of micro phenomena, theoretical results, new materials and designs, micro actuators, micro robots, micro batteries, bearings, wear, reliability, electrical interconnections, micro telemanipulation, and standards appropriate to MEMS. Application examples and application oriented devices in fluidics, optics, bio-medical engineering, etc., are also of central interest.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Christofer Hierold
ETH Zürich, Micro and Nanosystems