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Microelectromechanical Systems, Journal of

Issue 3 • Date June 2014

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Displaying Results 1 - 25 of 35
  • Table of contents

    Publication Year: 2014 , Page(s): C1 - C4
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  • Journal of Microelectromechanical Systems publication information

    Publication Year: 2014 , Page(s): C2
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  • Editorial

    Publication Year: 2014 , Page(s): 501
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  • Displacement Sensing With Silicon Flexures in MEMS Nanopositioners

    Publication Year: 2014 , Page(s): 502 - 504
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    We report a novel piezoresistive microelectromechanical system (MEMS) differential displacement sensing technique with a minimal footprint realized through a standard MEMS fabrication process, whereby no additional doping is required to build the piezoresistors. The design is based on configuring a pair of suspension beams attached to a movable stage so that they experience opposite axial forces when the stage moves. The resulting difference between the beam resistances is transduced into a sensor output voltage using a halfbridge readout circuit and differential amplifier. Compared with a single piezoresistive flexure sensor, the design approximately achieves 2, 22, and 200 times improvement in sensitivity, linearity, and resolution, respectively, with 1.5-nm resolution over a large travel range exceeding 12 μm. View full abstract»

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  • Fabrication process for thick-film micromachined multi-pole electromagnets

    Publication Year: 2014 , Page(s): 505 - 507
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    This letter introduces a fabrication process for thick (>50 μm) multipole electromagnets that produce fields exceeding 20 mT across 0.2-mm3 free-space volumes. The novelty of the process involves the multistep thick-film electroplating of a magnetic alloy inside a high-density high-aspect-ratio solenoidal coil, producing high intensity fields across a larger volume than previous microelectromechanical systems electromagnets. To demonstrate an application enabled by this process, a 600-μm-gap four-pole electromagnet is fabricated, packaged, and used to steer a 34-keV electron beam. View full abstract»

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  • Self-Aligned Electrodes on SU-8 Negative Photoresist Pedestals

    Publication Year: 2014 , Page(s): 508 - 510
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    We report a novel technique by which self-aligned thin-film electrodes are fabricated on SU-8 negative photoresist pedestals. A bilayer aluminum and titanium structure is used to align the thin-film electrode and to serve as the optical mask for the UV exposure of the SU-8. The SU-8 developer is used to remove both the unexposed SU-8 and the bilayer structure of aluminum and titanium. The result is a thin-film electrode aligned on an SU-8 pedestal with a minimal undercut beneath the thin-film electrode. View full abstract»

    Open Access
  • Displacement Measurement With a Self-Sensing MEMS Electrostatic Drive

    Publication Year: 2014 , Page(s): 511 - 513
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    This letter outlines a simultaneous actuation and displacement sensing technique applied to a microelectromechanical system (MEMS) electrostatic drive. Using the same electrostatic drive for both actuation and sensing allows more die space to be dedicated to the electrostatic drive, increasing the effective transduction efficiency of both functions and simplifying the mechanical design. Displacement sensing is performed with capacitive measurement implemented by incorporating the drive into an LC oscillator. This provides the mapping from displacement-to-capacitance to frequency-to-voltage. The technique was applied to a MEMS nanopositioner and the sensor exhibited no dynamics over the bandwidth of the device. The sensitivity of the sensor was 0.7551 V μm-1 and had a displacement noise floor of 0.00836 nmrms/√Hz. View full abstract»

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  • A Micromachined Acoustic Multiplexer for Ultrasound and Photoacoustic Imaging Applications

    Publication Year: 2014 , Page(s): 514 - 516
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    In this letter, we report the design, fabrication, and testing of a novel micromachined silicon-based acoustic multiplexer. The acoustic multiplexer is capable of selectively transmitting ultrasound signals traveling in multiple acoustic channels one at a time. This makes it possible to send and/or receive multiple channels of ultrasound signals in a serial manner with only one single-element ultrasound transducer, followed by single channel of data acquisition electronics. An eight-channel acoustic multiplexer was constructed and the switching performance of the multiplexer was tested with ultrasound transmission experiment. An excellent signal ON/OFF ratio of 6.5 was achieved between two adjacent acoustic channels. The functionality of acoustic multiplexer in ultrasound imaging system was demonstrated by conducting photoacoustic imaging on an optically absorptive target inside an optical phantom. The micromachined acoustic multiplexer could be a useful component in designing new ultrasound transceiver systems for imaging applications. View full abstract»

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  • Optical MEMS: From Micromirrors to Complex Systems

    Publication Year: 2014 , Page(s): 517 - 538
    Cited by:  Papers (3)
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    Microelectromechanical system (MEMS) technology, and surface micromachining in particular, have led to the development of miniaturized optical devices with a substantial impact in a large number of application areas. The reason is the unique MEMS characteristics that are advantageous in fabrication, systems integration, and operation of micro-optical systems. The precision mechanics of MEMS, microfabrication techniques, and optical functionality all make possible a wide variety of movable and tunable mirrors, lenses, filters, and other optical structures. In these systems, electrostatic, magnetic, thermal, and pneumatic actuators provide mechanical precision and control. The large number of electromagnetic modes that can be accommodated by beam-steering micromirrors and diffractive optical MEMS, combined with the precision of these types of elements, is utilized in fiber-optical switches and filters, including dispersion compensators. The potential to integrate optics with electronics and mechanics is a great advantage in biomedical instrumentation, where the integration of miniaturized optical detection systems with microfluidics enables smaller, faster, more-functional, and cheaper systems. The precise dimensions and alignment of MEMS devices, combined with the mechanical stability that comes with miniaturization, make optical MEMS sensors well suited to a variety of challenging measurements. Micro-optical systems also benefit from the addition of nanostructures to the MEMS toolbox. Photonic crystals and microcavities, which represent the ultimate in miniaturized optical components, enable further scaling of optical MEMS. View full abstract»

    Open Access
  • Shock Reliability of Vacuum-Packaged Piezoelectric Vibration Harvester for Automotive Application

    Publication Year: 2014 , Page(s): 539 - 548
    Cited by:  Papers (1)
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    This paper reports for the first time the shock reliability of vacuum-packaged piezoelectric vibration harvesters for automotive application. Experimental study on >80 devices shows that the failure is induced by the impact between seismic mass and glass package. The statistical results obtained for various types of harvesters have shown a trend of higher shock reliability for a higher resonance frequency. The influence of beam thickness on the shock reliability is then discussed. The trade-off between the power output and shock reliability is elaborated. To further improve the reliability to the level of automotive application, the idea of stepped cavity is discussed and implemented. The experimental results confirmed a significantly enhanced reliability increased by ~50%, up to maximum 2000 g, for the same type of device under shock excitations. View full abstract»

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  • Effective Area Formulation for Thermal Detector Characterization

    Publication Year: 2014 , Page(s): 549 - 554
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    We have derived an expression for the effective absorbing area for thermal infrared detectors having non-zero absorption in the support legs, which is different from the geometric areas of the constituent detector elements. This technique is particularly applicable to devices where sensitivity is more important than fill-factor, as opposed to standard imaging arrays. The effective area can simply be substituted in standard equations to obtain a good estimate of the detector performance under uniform flood illumination conditions. The formalism can also be used for estimating the contributions of the individual signal generating elements to the total measured signal. This approximation has been tested for MEMS infrared detectors with thermoelectric readout operating under vacuum. The responsivity of the same device calculated using the effective area approximation and measured using a tightly constrained absorbing area are found to match very closely, within 5% over the most wavelengths and within 15% at the shortest thermal infrared wavelengths. View full abstract»

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  • Dynamic Response of an Electrostatically Actuated Micro-Beam in an Incompressible Viscous Fluid Cavity

    Publication Year: 2014 , Page(s): 555 - 562
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    This paper studies the dynamic instability of cantilever micro-beam submerged in an incompressible viscous fluid cavity and actuated by electrostatic force. Equivalent squeeze film damping is incorporated in the vibrational equation of the micro-beam to obtain the natural frequencies of the coupled system. Then, imposing various step voltages, dynamic responses, and pull-in conditions of the micro-beam are studied. A parametric study is conducted to evaluate the effect of fluidic confinement on the instability voltage. Dielectric constant of the fluid proves dominantly influential compared with viscosity and density. In addition, values of pull-in voltage are seen to be highly dependent on the vertical position as well as the length of the micro-beam. View full abstract»

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  • Optically Induced Self-Excited Oscillations in an On-Fiber Optomechanical Cavity

    Publication Year: 2014 , Page(s): 563 - 569
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    Optically induced self-excited oscillations of suspended mirror of a fully on-fiber optomechanical cavity are experimentally demonstrated. The cavity is fabricated by patterning a suspended metallic mirror on the tip of an optical fiber and by introducing a static reflector in the fiber. We discuss the use of on-fiber optomechanical cavities for sensing applications. A theoretical analysis evaluates the sensitivity of the proposed sensor operating in the region of the self-excited oscillations. The results are compared with the experimental data and with the sensitivity that is achievable when the oscillations are driven by an external oscillatory force. View full abstract»

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  • Thermomechanical Actuator-Based Three-Axis Optical Scanner for High-Speed Two-Photon Endomicroscope Imaging

    Publication Year: 2014 , Page(s): 570 - 578
    Cited by:  Papers (2)
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    This paper presents the design and characterization of a three-axis thermomechanical actuator-based endoscopic scanner for obtaining ex vivo two-photon images. The scanner consisted of two sub-systems: 1) an optical system (prism, gradient index lens, and optical fiber) that was used to deliver and collect light during imaging and 2) a small-scale silicon electromechanical scanner that could raster scan the focal point of the optics through a specimen. The scanner can be housed within a 7 mm Ø endoscope port and can scan at the speed of 3 kHz x 100 Hz × 30 Hz along three axes throughout a 125 × 125 × 100 μm3 volume. The high-speed thermomechanical actuation was achieved through the use of geometric contouring, pulsing technique, and mechanical frequency multiplication (MFM), where MFM is a new method for increasing the device cycling speed by pairing actuators of unequal forward and returning stroke speeds. Sample cross-sectional images of 15-μm fluorescent beads are presented to demonstrate the resolution and optical cross-sectioning capability of the two-photon imaging system. View full abstract»

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  • 3D Integration Using Self-Assembly at Air-Water-Solid Interface

    Publication Year: 2014 , Page(s): 579 - 584
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    This paper presents the first proof-of-concept 3D integration using fluidic self-assembly of chip-scale parts (2000 × 2000 ×100 μm3 ) at an air-water-solid interface. Four-layer 3D integration is achieved by assembling new parts over previously assembled parts. Assembly proceeds as an assembly substrate is pulled up through an air-water interface and electrical and mechanical bonding are achieved by solder reflow. Magnetic fields and temporary Faraday waves are introduced for one-to-one part-to-site registration in proper orientation. The alignment accuracy degrades with increasing number of layers due to weaker magnetic force. The maximum number of layers that can be achieved is simulated and analyzed. Via resistance including the effect of degradation of solder over repeated reflow process is measured. View full abstract»

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  • Deep Wet-Etched Silicon Cavities for Micro-Optical Sensors: Influence of Masking on {111} Sidewalls Surface Quality

    Publication Year: 2014 , Page(s): 585 - 591
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    In this paper, we investigate the influence of different masking parameters onto the surface quality of the {111} sidewalls in order to generate specifically deep cavities by wet-anisotropic-etching of bulk silicon, for optical sensors using cavity sidewalls as reflectors. Mask alignment with crystal planes prior to wet-etching is found to be essential in order to avoid the appearance of additional planes during long etching. Mask deposition processes have been also evaluated. Among the different employed mask materials, Cr/Au gives the best results. It is then shown that cavities as deep as 1 mm with low roughness sidewalls can be simply produced with potassium hydroxide solution with periodic piranha cleaning. View full abstract»

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  • Estimating Damping in Microresonators by Measuring Thermomechanical Noise Using Laser Doppler Vibrometry

    Publication Year: 2014 , Page(s): 592 - 599
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    The fluctuation-dissipation theorem establishes the fundamental links between thermomechanical noise and damping. In this paper, we bridge the gap between theory and practice by developing protocols for estimating dissipation in low-loss microresonators by measuring thermomechanical noise using laser Doppler vibrometry. The measurement does not require external actuation of the device and damping can be estimated without relying upon knowledge of material properties, device dimensions, or structural stiffness. The power spectral density of velocity and displacement noise is computed using a direct method that avoids segmenting the measurements in the time domain, thereby avoiding any bias in the estimation of the quality factor. We demonstrate the implementation of the protocol by measuring damping at room temperature and low pressure in four silicon-based microcantilever resonators with natural frequencies ranging from 17.6 to 26.7 kHz and quality factors ranging from 2×104 to 2×105 . The accuracy of noise-based estimates is evaluated by comparison with values of the log decrement measured under free decay. View full abstract»

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  • Tunable Properties of Hydrogenated Amorphous/Nanocrystalline Silicon Thin-Films for Enhanced MEMS Resonators Performance

    Publication Year: 2014 , Page(s): 600 - 609
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    Thin-film silicon allows the fabrication of MEMS at low processing temperatures, including on large-area, low-cost, and flexible substrates. For MEMS applications, the main film properties to consider are the deposition rate, electrical conductivity, and mechanical stress. In this paper, n+-doped hydrogenated amorphous/nanocrystalline silicon thin-films are deposited by RF-PECVD. A systematic study of deposition conditions led to the identification of four different characteristic silicon thin-films, corresponding to different microstructures, with very distinct mechanical and electrical properties. These silicon thin-films are used as structural layers of electrostatically actuated thin-film MEMS bridges and cantilevers microresonators, fabricated on glass substrates at temperatures below 200 °C, using surface micromachining and thin-film technology. The effect of the mechanical stress of the structural layer (from tensile to highly compressive) on the device resonance frequency, quality factor, and required actuation forces is studied and interpreted with detailed electromechanical models. View full abstract»

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  • A Feedback Controlled MEMS Nanopositioner for On-Chip High-Speed AFM

    Publication Year: 2014 , Page(s): 610 - 619
    Cited by:  Papers (5)
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    We report the design of a two-degree-of-freedom microelectromechanical systems nanopositioner for on-chip atomic force microscopy (AFM). The device is fabricated using a silicon-on-insulator-based process to function as the scanning stage of a miniaturized AFM. It is a highly resonant system with its lateral resonance frequency at ~850 Hz. The incorporated electrostatic actuators achieve a travel range of 16 μm in each direction. Lateral displacements of the scan table are measured using a pair of electrothermal position sensors. These sensors are used, together with a positive position feedback controller, in a feedback loop, to damp the highly resonant dynamics of the stage. The feedback controlled nanopositioner is used, successfully, to generate high-quality AFM images at scan rates as fast as 100 Hz. View full abstract»

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  • Frequency Trimming of Aluminum Nitride Microresonators Using Rapid Thermal Annealing

    Publication Year: 2014 , Page(s): 620 - 627
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    To transition aluminum nitride (AlN) microresonator filters into a manufacturable technology, accurate control of the resonator frequency across a wafer is required. This paper describes a postfabrication rapid thermal anneal approach to trim resonator frequency over 27000 ppm with an accuracy of 500 ppm. Measurements made on 22.4 MHz resonators indicate that the effect of annealing on the resonators saturates in 5 min and upshift the resonator frequency super linearly with temperature. We replicate the frequency trimming effect on hermetically sealed wafer level packaged devices to reduce the across-wafer frequency distribution from 22000 to 4000 ppm. We confirm that this postannealing technique is permanent by temperature cycling the resonators from 50°C to 125°C. This technique provides a method to trim AlN microresonator frequency overcoming effects such as thin film variations, which are inherent to microsystems fabrication. View full abstract»

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  • Super Hydrophobic Parylene-C Produced by Consecutive {\rm O}_{2} and {\rm SF}_{6} Plasma Treatment

    Publication Year: 2014 , Page(s): 628 - 635
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    The wetting behavior of polymeric biomaterials is of great importance for biomedical research and pharmaceutical applications. Tailoring of polymer surface wettability is particularly effective to address biomedical issues such as biofouling control and biocompatibility improvement. In this paper, we conducted comprehensive experiments and analytical modeling to understand the effects of a consecutive-O2-SF6 plasma treatment on the super hydrophobicity of parylene-C. Experimentally, super hydrophobic parylene-C surfaces with a maximum water contact angle of ~169° have been successfully achieved. Atomic force microscopy and X-ray photoelectron spectroscopy results strongly suggest that the modification of surface wettability can be attributed to the variation in surface roughness and the plasma-induced surface chemistry. Analytically, a transition of droplet status from the Wenzel state to the Cassie state on hydrophobic parylene-C surfaces has been demonstrated after sufficient roughening by O2 plasma pre-treatment. The surface morphology of plasma-treated parylene-C films has also been analyzed and the hexagonal-close-packed model of downward crowns shows the best agreement with experimental results. Our simple and time-efficient treatment eliminates the need for creating well-defined patterns, is completely compatible with conventional microfabrication techniques, and can also be applied to curved parylene surfaces. View full abstract»

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  • Resonant Body Transistors in IBM's 32 nm SOI CMOS Technology

    Publication Year: 2014 , Page(s): 636 - 650
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2011 KB) |  | HTML iconHTML  

    This paper presents unreleased CMOS-integrated MEMS resonators fabricated at the transistor level of IBM's 32SOI technology and realized without the need for any postprocessing or packaging. In this technology, resonant body transistors (RBTs) are driven capacitively and sensed piezoresistively using an n-channel field effect transistor (FET). Acoustic Bragg Reflectors (ABRs) are used to localize acoustic vibrations in the unreleased resonators completely buried under the CMOS metal stack and surrounded by low-κ dielectric. FET sensing is analytically compared with alternative active and passive sensing mechanisms to benchmark CMOS-MEMS resonator performance with frequency scaling. Experimental results from the first generation hybrid CMOS-MEMS RBTs show RBTs operating above 11 GHz with Qs of 24-30 and footprints of 5 × 3 μm. Comparative behavior of devices with design variations is used to demonstrate the effect of ABRs on spurious mode suppression. In addition, the performance of the RBTs is compared with passive electrostatic resonators, which show no discernible peak. Finally, temperature stability of <;3 ppm/K due to complimentary materials in the CMOS stack is analytically and experimentally verified. View full abstract»

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  • Micro Blood Pressure Energy Harvester for Intracardiac Pacemaker

    Publication Year: 2014 , Page(s): 651 - 660
    Cited by:  Papers (1)
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    This paper presents the design, fabrication, and tests of a microspiral-shaped piezoelectric energy harvester and its associated microfabricated packaging that collects energy from ordinary blood pressure variations in the cardiac environment. This device could become a life-lasting, miniaturized energy source for active implantable medical devices such as leadless pacemakers. We present the concept and tested prototypes of 10 μm thin and ultra-flexible electrodeposited microbellows (6mm diameter, 21mm3 volume) as a new type of implant packaging. It enables direct blood pressure harvesting and permits a high efficiency of energy transfer to a transducer operating in quasi-static mode and hence adaptable and unaffected by frequent heartbeat frequency changes. Spiral-shaped piezoelectric transducers are introduced for their flexibility and large incoming mechanical energy. Non-trivial optimal electrodes placement and best spiral design parameters are studied and discussed. Three types of spiral prototypes (11mm3 volume each) with doubled-sided microstructured electrode patterns are presented and characterized. A power of 3 μJ/cm3/heartbeat and a transduction efficiency of 5.7×10-3 have been obtained for the best designs at 1.5Hz and we predict that twice as much could be obtained using similar design process and material. Through implementing smart adapted electronic circuits, a potential additional tenfold increase in power output could be achieved, which would be sufficient to power a leadless pacemaker. View full abstract»

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  • A Compliant MEMS Device for Out-of-Plane Displacements With Thermo-Electric Actuation

    Publication Year: 2014 , Page(s): 661 - 671
    Cited by:  Papers (1)
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    A MEMS actuator for micrometric displacements in the out-of-plane direction is proposed in this paper. The device is based on a compliant micromechanism composed of a thick layer of nickel and two thin layers of silicon nitride ensuring displacements in the out-of-plane direction. Its actuation is thermo-electrically performed, the polysilicon resistor encapsulated between the two thin silicon nitride layers is heated by Joule effect; the obtained thermo-mechanical deformation is therefore converted into an out of plane displacement thanks to the compliant mechanism realized in the device structure. The behavior of the device has been analytically modeled through the pseudo-rigid body model methodology and simulated with finite elements models in order to study and optimize its performance. The results coming from the presented models and the device operation have been experimentally validated by characterizing a prototype of this device micro-fabricated in the MetalMUMPs process from MEMSCAP. The maximum displacement of the device is ~16 μm with a maximum actuation voltage of 90 V and the maximum exerted force is ~17 mN. View full abstract»

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  • Bulk-Like Laminated Nitride Metal/Semiconductor Superlattices for Thermoelectric Devices

    Publication Year: 2014 , Page(s): 672 - 680
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    Bulk-like thermionic energy conversion devices have been fabricated from nanostructured nitride metal/semiconductor superlattices using a novel lamination process. 5-μm thick (Hf0.5Zr0.5)N (6-nm)/ScN (6-nm) metal/semiconductor superlattices with a 12 nm period were deposited on 100-silicon substrates by reactive magnetron sputtering followed by a selective tetra methyl ammonium hydroxide substrate etching and a gold-gold lamination process to yield 300 μm × 300 μm × 290 μm microscale thermionic energy conversion elements with 16,640 superlattice periods. The thermionic element had a Seebeck coefficient of -120 μV/K at 800 K, an electrical conductivity of ~2500 Ω-1 m-1 at 800 K, and a thermal conductivity of 2.9 and 4.3 W/m-K at 300 and 625 K, respectively. The temperature dependence of the Seebeck coefficient from 300 to 800 K suggests a parallel parasitic conduction path that is dominant at low temperature, and the temperature independent electrical conductivity indicates that the (Hf0.5Zr0.5)N/gold interface contact resistivity currently dominates the device. The thermal conductivity of the laminate was significantly lower than the thermal conductivity of the individual metal or semiconductor layers, indicating the beneficial effect of the metal/semiconductor interfaces toward lowering the thermal conductivity. The described lamination process effectively bridges the gap between the nanoscale requirements needed to enhance the thermoelectric figure of merit ZT and the microscale requirements of real-world devices. 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