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Microelectromechanical Systems, Journal of

Issue 4 • Date Dec 1995

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Displaying Results 1 - 10 of 10
  • High-aspect-ratio photolithography for MEMS applications

    Publication Year: 1995 , Page(s): 220 - 229
    Cited by:  Papers (12)  |  Patents (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2332 KB)  

    High-aspect-ratio photolithography using a commercially available positive photoresist and a conventional contact mask aligner with standard UV light source is described. A multiple coating process is developed to obtain a photoresist thickness up to 23 μm while maintaining a smooth photoresist surface. Intimate contact between the mask and wafer is found to be most critical for high-resolution photolithography. Vacuum contact is found to be well-suited for this purpose. Additionally, edge bead removal is found to be of significant importance for intimate contact between the mask and the substrate. Prebake, exposure, and development conditions are optimized for resolution and aspect ratio. Maximum prebake temperature still allowing the photoresist to be developed is found to be the optimal temperature for obtaining high resolution. Prebake time distribution is optimized for avoiding residual stress in the photoresist, as well as maintaining high resolution, when multiple coating is applied. Minimum linewidth and spacing of 3.5 μm and 2.5 μm, respectively, and a maximum aspect ratio of 7.7 have been achieved in a photoresist thickness of 23 μm. Postbake improves the chemical resistance to subsequent processes, for example, electroless nickel plating using the photoresist as a mold. However, postbake also causes pattern distortion, which can be severe at times. Therefore, optimal process and design conditions for minimizing the pattern distortion have been studied View full abstract»

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  • Demonstration of three-dimensional microstructure self-assembly

    Publication Year: 1995 , Page(s): 170 - 176
    Cited by:  Papers (21)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1532 KB)  

    Self-assembly of three-dimensional microstructures using the surface tension force of molten solder to produce out-of-plane rotation is demonstrated. The generic nature of the technique is illustrated by reconfiguring structures formed in both Ni metal and single crystal Si. The structures do not have a hinge to constrain the rotation. This considerably simplifies fabrication and eliminates problems associated with the compatibility of a suitable hinge material. Details of the fabrication processes are given and results are presented for rotated structures View full abstract»

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  • Fabrication of 45° mirrors together with well-defined v-grooves using wet anisotropic etching of silicon

    Publication Year: 1995 , Page(s): 213 - 219
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1660 KB)  

    The most commonly used microstructure for passive fiber alignment is the ordinary v-groove, defined by {111} planes on a (100) silicon wafer. The plane at the end of the groove, having a 54.7° angle to the surface, can be used as a reflecting mirror. For single-mode fiber applications, a 45° mirror is advantageous together with high accuracy in the position of the fiber, i.e. a smooth mirror and good control of the groove geometry is needed. Two techniques are presented to form 45° mirrors along with well-defined grooves in silicon, using the wet anisotropic etchants EDP and KOH. These techniques are used: (1) to reveal {110} planes on (100) silicon and (2) to make {111} mirrors on wafers that are cut 9.7° off the [100] axis. On (100) silicon, EDP without pyrazine gave the best result. The best mirror and groove reproducibility was found on off-axis cut silicon, using 36 wt.% KOH, with isopropyl alcohol added View full abstract»

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  • Equilibrium of hinged and hingeless structures rotated using surface tension forces

    Publication Year: 1995 , Page(s): 177 - 184
    Cited by:  Papers (9)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (940 KB)  

    Two different geometries for the rotation of microstructures by the surface tension force of molten solder are investigated theoretically and experimentally. The geometries are based on structures with and without a hinge acting to constrain the motion of a flap to pure rotation. The equilibrium geometry of a hinged structure is first found analytically by considering the surface energy of the solder. An analysis of hingeless structures is then performed that shows a hinge to be unnecessary under certain conditions. Macroscopic experiments performed using printed circuit board parts are then described; the results show that the behaviors of hinged and hingeless structures are similar View full abstract»

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  • TiNi (shape memory) films silicon for MEMS applications

    Publication Year: 1995 , Page(s): 206 - 212
    Cited by:  Papers (9)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (764 KB)  

    TiNi shape memory alloy in thin film form is an excellent candidate for MEMS microactuation. Using RF sputter deposition, thin films of TiNi (51.7 at% Ti-48.3 at% Ni) have been formed on silicon substrates and produced shape memory behavior at approximately 60°C. Films were amorphous when deposited and were subsequently annealed at 515°C for 30 min. to crystallize the shape memory microstructure. Excellent adherence was achieved onto silicon, SiO2 and poly-silicon surfaces. Microfabrication was used to create TiNi diaphragms, which exhibited useful shape memory microactuation and other desirable mechanical properties. The diaphragms recovered greater than 2% strain when heated through the phase transformation temperature, providing a maximum work density of at least 5×106 J/m 3. This work density is higher than that of any other type of microactuation View full abstract»

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  • Modeling of a three-layer piezoelectric bimorph beam with hysteresis

    Publication Year: 1995 , Page(s): 230 - 237
    Cited by:  Papers (58)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    Piezoelectric actuators are usually stacked or bimorph in configuration. In this paper the mechanics of a three-layer piezoelectric bimorph is discussed and its dynamic model with hysteresis is presented. The results can be used to analyze piezoelectric actuators constructed with three-layer piezoelectric bimorphs. A piezoelectric bimorph actuator has been fabricated and experiments have been carried out to verify the model. The calculated results of this model closely matched the tested results. This model can also be used with other types of piezoelectric actuators with a slight modification View full abstract»

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  • A new analytical solution for the load-deflection of square membranes

    Publication Year: 1995 , Page(s): 238 - 241
    Cited by:  Papers (30)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    Accurate models are essential for the determination of the elastic properties of thin films from load-deflection experiments. Although finite element method (FEM) models have the potential to be very accurate, analytical models are desirable because of their simplicity. In this paper we present a new analytical solution for the load-deflection of membranes. Our solution yields the same relationship between the load and the deflection as the known analytical solution. However, the values of two constants are up to 35% higher and correspond well with the results from FEM analysis. In addition, the new solution yields analytical forms of the bending lines, which agree well with experimental measurements carried out with silicon nitride membranes View full abstract»

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  • The anharmonic Casimir oscillator (ACO)-the Casimir effect in a model microelectromechanical system

    Publication Year: 1995 , Page(s): 193 - 205
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB)  

    The Casimir effect is the attractive pressure between two flat parallel plates of solids that arises from quantum fluctuations in the ground state of the electromagnetic field. The magnitude of this pressure varies as the inverse fourth power of the separation between the plates. At a 20 nm separation between two metallic plates, the attraction is approximately 0.08 atmosphere. If one or both plates are nonconducting the pressure is smaller, roughly by an order of magnitude. As an idealized MEMS component that takes account of the Casimir effect, the anharmonic Casimir oscillator (ACO) is introduced and shown to be a bi-stable system for certain values of the dimensionless parameter, C, which characterizes the system. The phenomenon of “stiction” in MEMS is then explained as analogous to an ACO energetically descending to and settling in an equilibrium state that is very stable against perturbations for all values of C. A micromechanical switch based on the bistable ACO is proposed and modeled. The dynamics of an ACO, executing undamped periodic motion, are studied using numerical and analytical solutions of the differential equation of motion. Frequencies and amplitudes vary with C. C, in turn, is inversely proportional to the fifth power of the parallel plate separation. This extreme sensitivity makes the ACO an attractive platform for designing rather sensitive sensors and detector systems, such as submicrometer proximity sensors and microlever deflection detectors for scanning probe microscopes View full abstract»

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  • Adhesion release and yield enhancement of microstructures using pulsed Lorentz forces

    Publication Year: 1995 , Page(s): 185 - 192
    Cited by:  Papers (8)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1196 KB)  

    Adhesion of microstructures is an important failure mechanism in surface-micromachined devices. In this paper, a simple and effective method for releasing pinned microstructures is presented. The method uses the Lorentz force due to the interaction of a current with an external magnetic field to generate an upward force that frees the microstructures. The static and transient behavior of beams under the Lorentz force is examined. Critical values of current and pulse durations needed to release the microstructures are determined and verified with experimental data. Using this technique, previously pinned beams and rectangular plates have been released. The release technique is suitable for mass production environments since it is easily applied during the electrical testing of the device, thereby increasing the manufacturing yield View full abstract»

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  • Magnetic microactuation of polysilicon flexure structures

    Publication Year: 1995 , Page(s): 162 - 169
    Cited by:  Papers (34)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1388 KB)  

    A microactuator technology that combines magnetic thin films with polysilicon flexural structures is described. Devices are constructed in a batch-fabrication process that combines electroplating with conventional lithography, materials, and equipment. A microactuator consisting of a 400×(47-40)×7 μm3 rectangular plate of NiFe attached to a 400×(0.9-1.4)×2.25 μm3 polysilicon cantilever beam has been displaced over 1.2 mm, rotated over 180°, and actuated with over 0.185 nNm of torque. The microactuator is capable of motion both in and out of the wafer plane and has been operated in a conductive fluid environment. Theoretical expressions for the displacement and torque are developed and compared to experimental results 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