SciCombinator

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Concept: Dry etching

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Heavily boron-doped silicon layers and boron etch-stop techniques have been widely used in the fabrication of microelectromechanical systems (MEMS). This paper provides an introduction to the fabrication process of nanoscale silicon thermoelectric devices. Low-dimensional structures such as silicon nanowire (SiNW) have been considered as a promising alternative for thermoelectric applications in order to achieve a higher thermoelectric figure of merit (ZT) than bulk silicon. Here, heavily boron-doped silicon layers and boron etch-stop processes for the fabrication of suspended SiNWs will be discussed in detail, including boron diffusion, electron beam lithography, inductively coupled plasma (ICP) etching and tetramethylammonium hydroxide (TMAH) etch-stop processes. A 7 μm long nanowire structure with a height of 280 nm and a width of 55 nm was achieved, indicating that the proposed technique is useful for nanoscale fabrication. Furthermore, a SiNW thermoelectric device has also been demonstrated, and its performance shows an obvious reduction in thermal conductivity.

Concepts: Nanotechnology, Microelectromechanical systems, Photolithography, Thermoelectric effect, Electron beam lithography, Tetramethylammonium hydroxide, Thermoelectric cooling, Dry etching

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The efficacy of pharmaceutical treatments can be greatly enhanced by physiological feedback from the patient using biosensors, though this is often invasive or infeasible. By adapting microelectromechanical systems (MEMS) technology to miniaturize such biosensors, previously inaccessible signals can be obtained, often from inside the patient. This is enabled by the device’s extremely small footprint which minimizes both power consumption and implantation trauma, as well as the transport time for chemical analytes, in turn decreasing the sensor’s response time. MEMS fabrication also allows mass production which can be easily scaled without sacrificing its high reproducibility and reliability, and allows seamless integration with control circuitry and telemetry which is already produced using the same materials and fabrication steps. By integrating these systems drug delivery devices, many of which are also MEMS-based, closed loop drug delivery can be achieved. This paper surveys the types of signal transduction devices available for biosensing-primarily electrochemical, optical, and mechanical-looking at their implementation via MEMS technology. The impact of MEMS technology on the challenges of biosensor development, particularly safety, power consumption, degradation, fouling, and foreign body response, are also discussed.

Concepts: Microelectromechanical systems, Electrical engineering, Sensor, Biosensor, Dry etching

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The purpose of this paper is to show the feasibility of grasping force control by feeding back signals of the developed micro-laser Doppler velocimeter (μ-LDV) and by discriminating whether a grasped object is slipping or not. LDV is well known as a high response surface velocity sensor which can measure various surfaces-such as metal, paper, film, and so on-thus suggesting the potential application of LDV as a slip sensor for grasping various objects. However, the use of LDV as a slip sensor has not yet been reported because the size of LDVs is too large to be installed on a robotic fingertip. We have solved the size problem and enabled the performance of a feasibility test with a few-millimeter-scale LDV referred to as micro-LDV (μ-LDV) by modifying the design which was adopted from MEMS (microelectromechanical systems) fabrication process. In this paper, by applying our developed μ-LDV as a slip sensor, we have successfully demonstrated grasping force control with three target objects-aluminum block, wood block, and white acrylic block-considering that various objects made of these materials can be found in homes and factories, without grasping force feedback. We provide proofs that LDV is a new promising candidate slip sensor for grasping force control to execute target grasping.

Concepts: Control theory, Object, Microelectromechanical systems, Electrical engineering, Sensor, Laser Doppler velocimetry, Dry etching

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Photolithography based on optical mask is widely used in academic research laboratories due to its low-cost, simple mechanism, and ability to pattern in micron sized features on a wafer scale area. Since the resolution is bound by diffraction limits of the light source, nano-scale patterning using photolithography requires short wavelength light source combined with sophisticated optical elements, adding complexity and cost. In this paper, a novel method of sub-wavelength patterning process using conventional i-line mercury lamp is introduced, without the use of such advanced optical tools. The method utilizes the re-entrant geometry of image reversal photoresist produced from the developing process, where a secondary mask is generated by isotropically depositing a metal layer to cover the re-entrant profile of the photoresist. Removing the photoresist by applying ultrasonic vibrations in acetone bath uniformly cracks the metal layer at the sidewalls of the re-entrant profile, exposing the substrate with a reduced feature size. The width of the initial mask pattern can be reduced down by 400 nm in a controlled manner, regardless of the original width choice. As a result, the method is shown to achieve sub-100 nm scale linear patterns compatible for both subsequent deposition process and dry etching process. Our approach is applicable to various shapes of the patterns, and can be used in electronic device fabrication requiring nanoscale lithography patterning, such as the gate fabrication of AlGaN/GaN high electron mobility transistor (HEMT).

Concepts: Light, Integrated circuit, Semiconductor, Pattern, Photolithography, Semiconductor device fabrication, Mercury-vapor lamp, Dry etching

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Carbon nanotube thin film transistors (CNT-TFTs) have been regarded as strong competitors to currently commercialized TFT technologies. Though much progress has been achieved recently, CNT-TFT research is still in the stage of laboratory research. One critical challenge for commercializing CNT-TFT technology is that the commonly used device fabrication method is a lift-off based process, which is not suitable for mass production. In this paper, we report an etching based fabrication process for CNT-TFTs, which is fully manufacturing compatible. In our process, the CNT thin film channel was patterned by dry etching, while wet etching was used for patterning the layers of metal and insulator. The CNT-TFTs were successfully fabricated on a 4 inch wafer in both top-gate and buried-gate geometries with low Schottky barrier contact and pretty uniform performance. High output current (>1.2 μA μm(-1)), high on/off current ratio (>10(5)) and high mobility (>30 cm(2) V(-1) s(-1)) were obtained. Though the fabrication process still needs to be optimized, we believe our research on the etching fabrication process pushes CNT-TFT technology a step forward towards real applications in the near future.

Concepts: Semiconductor, Carbon nanotube, Chemical vapor deposition, Semiconductor device fabrication, Thin-film transistor, Ion implantation, Microfabrication, Dry etching

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When the dimensions of polycrystalline structures become comparable to the average grain size, some reliability issues can be reported for the moving parts of inertial microelectromechanical systems (MEMS). Not only the overall behavior of the device turns out to be affected by a large scattering, but also the sensitivity to imperfections gets enhanced. In this work, through on-chip tests, we experimentally investigate the behavior of thin polysilicon samples using standard electrostatic actuation/sensing. The discrepancy between the target and actual responses of each sample has then been exploited to identify: (i) the overall stiffness of the film and, according to standard continuum elasticity, a morphology-based value of its Young’s modulus; (ii) the relevant over-etch induced by the fabrication process. To properly account for the aforementioned stochastic features at the micro-scale, the identification procedure has been based on particle filtering. A simple analytical reduced-order model of the moving structure has been also developed to account for the nonlinearities in the electrical field, up to pull-in. Results are reported for a set of ten film samples of constant slenderness, and the effects of different actuation mechanisms on the identified micromechanical features are thoroughly discussed.

Concepts: Young's modulus, Elasticity, Microelectromechanical systems, Electrical engineering, Elastic modulus, Stiffness, Hooke's law, Dry etching

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Stretchable microelectromechanical systems (MEMS) possess higher mechanical deformability and adaptability than devices based on conventional solid and flexible substrates, hence they are particularly desirable for biomedical, optoelectronic, textile and other innovative applications. The stretchability performance can be evaluated by the failure strain of the embedded routing and the strain applied to the elastomeric substrate. The routings are divided into five forms according to their geometry: straight; wavy; wrinkly; island-bridge; and conductive-elastomeric. These designs are reviewed and their resistance-to-failure performance is investigated. The failure modeling, numerical analysis, and fabrication of routings are presented. The current review concludes with the essential factors of the stretchable electrical routing for achieving high performance, including routing angle, width and thickness. The future challenges of device integration and reliability assessment of the stretchable routings are addressed.

Concepts: Mathematics, Failure, Design, Microelectromechanical systems, Electrical engineering, Reliability engineering, Information appliance, Dry etching

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Although recently developed bio-inspired nanostructures exhibit superior optic performance, their practical applications are limited due to cost issues. We present highly transparent glasses with grassy surface fabricated with self-masked dry etch process. Simultaneously generated nanoclusters during reactive ion etch process with simple gas mixture (i.e., CF4/O2) enables lithography-free, one-step nanostructure fabrication. The resulting grassy surfaces, composed of tapered subwavelength structures, exhibit antireflective (AR) properties in 300 to 1,800-nm wavelength ranges as well as improved hydrophilicity for antifogging. Rigorous coupled-wave analysis calculation provides design guidelines for AR surface on glass substrates.

Concepts: Light, Nanomaterials, Lens, Glass, Book of Optics, Glasses, Anti-reflective coating, Dry etching

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Abstract Intracortical microprobes allow the precise monitoring of electrical and chemical signaling and are widely used in neuroscience. Microelectromechanical system (MEMS) technologies have greatly enhanced the integration of multifunctional probes by facilitating the combination of multiple recording electrodes and drug delivery channels in a single probe. Depending on the neuroscientific application, various assembly strategies are required in addition to the microprobe fabrication itself. This paper summarizes recent advances in the fabrication and assembly of micromachined silicon probes for drug delivery achieved within the EU-funded research project NeuroProbes. The described fabrication process combines a two-wafer silicon bonding process with deep reactive ion etching, wafer grinding, and thin film patterning and offers a maximum in design flexibility. By applying this process, three general comb-like microprobe designs featuring up to four 8-mm-long shafts, cross sections from 150×200 to 250×250 µm², and different electrode and fluidic channel configurations are realized. Furthermore, we discuss the development and application of different probe assemblies for acute, semichronic, and chronic applications, including comb and array assemblies, floating microprobe arrays, as well as the complete drug delivery system NeuroMedicator for small animal research.

Concepts: Semiconductor, Microelectromechanical systems, Semiconductor device fabrication, Plasma ashing, Deep reactive-ion etching, Ion implantation, Microfabrication, Dry etching

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Signal-to-noise ratio (SNR) is a critical parameter in the adoption of small scale (~1 mm) microphones for use in hearing aids. As a result, electret microphones have dominated the market since their invention in the 1960’s. Significant effort is being invested to increase the SNR of microelectromechanical (MEMs) microphones near that of electrets. This work covers the approach of using multiple microphone elements to increase SNR. It explores the theory, examines the dependence of the SNR improvement on the matching of the microphone elements, and compares measurements on a single element microphone versus a multiple element microphone. Finally, it examines why the MEMs fabrication process lends itself to this usage and compares the trade-offs in scaling elements versus scaling size.

Concepts: Ratio, Sound, Signal-to-noise ratio, Piezoelectricity, Telephone, Microphone, ITU-R 468 noise weighting, Dry etching