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Temperature elevation due to global warming increases the risks of dehydration, which can induce heat-related illness. Proper rehydration with appropriate amounts of water and electrolytes is essential to aid body fluid homeostasis. Wearable sweat sensors which can monitor both the sweat rate and sweat electrolyte concentration may be an effective tool for determining appropriate rehydration. Here, we developed a novel potentially wearable sensor that can monitor both the local sweat rate and sweat electrolyte concentration continuously. The new device includes a system with a short microfluidic pathway that guides the sweat appearing on the skin to a small space in the device to form a quantifiable droplet. The sweat rate is assessed from the time for the droplet to appear and droplet volume, while an integrated electric sensor detects the sodium chloride concentration in each sweat droplet. We demonstrated that this new device could record both the flow rates of artificial sweat and its sodium chloride concentration in ranges of human sweating with an accuracy within ±10%. This is equivalent to the accuracy of commercially available sweat rate meters and sweat ion sensors. The present study provides a new perspective for the design of wearable sensors that can continuously monitor sweat rates and sweat electrolyte concentrations for potential application to a healthcare device. [ABSTRACT FROM AUTHOR]

This paper describes an analysis and a performance limit of a vibrational energy harvester with a novel slit-and-slider structure. This structure has a separable electret and microelectromechanical systems (MEMS) parts. In the MEMS parts, movable electrodes slide due to external vibration and receive electrical field that is periodically modulated by slits of fixed electrodes. The structure was fabricated based on MEMS technology and produced an ac current of 170 pA with an external vibration of amplitude of 1 \m/s^2 at a frequency of 1166 Hz. Since the structure is separable, individual characterization of the electret and movable electrodes was performed. On the basis of their quantitative analyses, a structural model was constructed and validated. The model showed a way to optimize structural and material parameters for enhancement of output power and predicted a performance limit of 2.5 \times 10^-3\ \mu\W and 6.1% as output power and harvester effectiveness, respectively. This value of effectiveness is comparable to that of conventional non-MEMS-based large energy harvester around 1 \cm^3, which indicates feasibility of MEMS-based small energy harvesters around 0.01 \cm^3 by appropriate designing.\hfill[2011-0347] [ABSTRACT FROM AUTHOR]

Reduction of the size and cost of optical receivers is important to the proliferation of optical communications technology for short-distance communications. In the present research, an integrated optical receiver is fabricated with a standard 0.35-µm CMOS process targeting the POF optical transmission system. A photodiode, a trans-impedance amplifier, a limiting amplifier, and a buffer are integrated in this optical receiver. The photodiode is formed with an N-well and a P-diffused layer of stripe configuration and has an optical receiving surface area of 150 × 150 µm and a response sensitivity of about 0.04 A/W (at a wavelength of 650 nm). In the CMOS process, the large junction capacitance of the photodiode is problematic. Therefore, the input impedance of the circuit is lowered by means of an RGC-type trans-impedance amplifier and LC resonance is suppressed by optimization of the package and circuit. The chip is mounted in a small ceramic package for measurement. Excellent eye patterns are obtained. The minimum receiving sensitivity for a bit error rate of less than 10-9 is -10 dBm at 600 Mbit/s and -4.5 dBm at 1 Gbit/s. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(12): 10–18, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20099 [ABSTRACT FROM AUTHOR]

A selective removal of dry-etching residue using hydrofluoric acid (HF) vapor is described in relation to the fabrication of microelectromechanical-system (MEMS) devices. Auger electron spectroscopy (AES) analysis of residue after dry etching of polymer sacrificial layers reveals that the residue is mainly composed of silicon oxides. HF vapor removes the dry-etching residue, and raising the vapor temperature enables the selective removal of the residue without damaging silicon dioxide (SiO2), which is often used as the insulator for MEMS devices. Direct-contact-type MEMS switches with SiO2 insulators fabricated using polymer sacrificial layers demonstrate the effectiveness of removing the dry-etching residue selectively. [ABSTRACT FROM AUTHOR]

A technique for cleaning a gold surface with a dry process is described for the fabrication of microelectromechanical system (MEMS) devices. Thermal desorption spectroscopy (TDS) analysis of a gold surface exposed to reactive oxygen revealed that annealing causes oxygen to desorb from the gold oxide. To examine the effectiveness of dry-process surface cleaning, the surfaces were annealed in a vacuum, with nitrogen as an inert ambient, and hydrogen as a reductive ambient. For the annealing in a vacuum and nitrogen ambient, a temperature of over 260 °C is necessary for the oxide removal. Annealing in hydrogen ambient drastically lowers the cleaning temperature from 260 to 60 °C. [ABSTRACT FROM AUTHOR]

We describe a technique for cleaning a gold surface using a dry process during the fabrication of microelectromechanical system (MEMS) devices. After exposure to oxygen plasma for ashing of the organic contaminants or etching of a sacrificial-layer film, the gold surface is oxidized. On such an oxidized surface, there are different incubation periods at different places, which give rise to nonuniform thickness in electroplating as well as in electrodeposition. A surface analysis by X-ray photoelectron spectroscopy (XPS) revealed that annealing at a temperature of over 260 °C causes oxygen to desorb from the gold oxide. The application of this cleaning technique before electroplating or electrodeposition leads to uniform growth. [ABSTRACT FROM AUTHOR]

In this paper, we describe a new capacitive-sensing scheme that detects the displacement of a movable structure for the control of a microelectoromechanical-systems (MEMS) device stacked on a complementary metal–oxide–semiconductor (CMOS) LSI. The problem is that the small capacitance of the air gap between the movable element and a sensor plate needs to be detected in spite of the large parasitic capacitance caused by LSI interconnections. The solution is a sensing circuit that features a shield plate and a ramp detection circuit. The shield plate separates the sensed capacitance from the parasitic capacitance. A ramp detection circuit enhances the detection sensitivity using a gradient signal generated by the parasitic capacitance. To check the effectiveness of the scheme, a sensing circuit and a MEMS variable capacitor were fabricated in a 0.6-µm CMOS process and a MEMS process. This scheme enhanced the sensitivity, which is the ratio of the output voltage to the sensed capacitance, by a factor of six. These results demonstrate that this scheme is suitable for the control of a CMOS-MEMS device. [ABSTRACT FROM AUTHOR]

We have developed a lightweight heartbeat detection algorithm for electrocardiogram (ECG) measurement in consumer-grade wearable devices. Based on a principle of calculating the clearance height in the inverted time differential of an ECG, the algorithm has a sensitivity specific to the QRS complex in an ECG. Because this algorithm is simple and lightweight, an efficient implementation form has been established for porting the algorithm to consumer-grade devices. We experimentally confirmed that the algorithm runs in an actual commercialized wearable device and provides improvement of heart rate measurement with noise caused by body motion.