The switches play an important role in making the multifunctional radio communication circuit and therefore, the high-performance microminiaturized high-frequency switches are urgently expected. RF-MEMS switch with mechanical switching structure is hoped to improve both high-frequency signal loss and isolation quality simultaneously and to provide better linearity on the performance and compatibility to silicon-based circuit elements. But considering the applications, such as cellular phone and wireless-LAN, lower driving voltage and smaller switch dimensions are required.
In order to solve these requirements, a novel electrostatic actuator with a unique structure of movable electrodes which enables the stable contact resistance is developed for RF-MEMS switches. This actuator has slits between the movable electrodes and the restoring spring. The electrostatic actuator with a movable electrode area of 0.5mm² was driven at low voltage of 9-11V. And no defect due to restoration shortage is observed during switching test up to 400million cycles.
In this paper, the results of mechanical design of the electrostatic actuator, the simulation, the experiments, and the reliability test are described

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We have designed a prototype microfluidic device to mix suspended particles with isotonic saline by use of electrically induced swirling flow in the microchannel. However, the principles underlying microfluidic rotation induced by AC electrodes are not well understood, and the characteristics of the rotation velocity are unpredictable. Furthermore, these properties have not been studied using a highly conductive liquid like isotonic saline, which is an important fluid in the medical and biological fields. The lack of such studies causes uncertainty in the design required for high-performance microfluidic devices. We have examined the electrical rotational properties of the microfluid at an isotonic concentration of saline using computer simulation, and here we show that buoyant flow, which has previously been largely ignored, has a significant effect in channels of 100-μm depth or deeper, and that AC electroosmotic flow is not induced at isotonic saline concentrations.

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Piezoelectric thin film transduced micro resonator offers competitive potential applications in mass sensing technology because of its low driving-voltage, self-actuation self-sensation capability and better impedance-matching with electronics. In this paper, the authors fabricated PZT cantilevers with different geometries and PZT thicknesses. Then the authors investigated the essential aspects of the PZT cantilever for mass-detection sensitivity from the viewpoint of mechanical quality factor of the cantilever and piezoelectric induced output of the PZT film. It was found that the mass-detection sensitivity of the cantilever was improved at thicker PZT film under atmospheric conditions by taking advantage of quality factor. The sensitivity can be further improved several times when pressure was reduced into the molecular flow region and the intrinsic region. For a given material properties and structural layer thickness, the cantilever with thicker PZT film was expected to exhibit high open circuit voltage output, while the cantilever with thinner PZT film was expected to show high piezoelectric charge output. In addition, the residual stress of PZT film was found decreased at thicker film. The effects of residual stress in PZT film on cantilever's sensitivity were therefore discussed in this paper.

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In this paper, a visible light blind ultraviolet sensor of a Schottky barrier photodiode using a ZnO single crystal is described. The sensor consists of a semitransparent Pt film for the Schottky electrode and Al thin film for the ohmic electrode on an n-type ZnO single crystal substrate grown by the hydrothermal method. The responsivity was 0.12 A/W at the wavelength of 365 nm and the photoresponse time was 12 μs.

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A thin film Pirani vacuum sensor having a single microheater and two diode-thermistors (Th-A and Th-B) composed of pn junction diodes on the micro-air-bridge (MAB) is fabricated by micromachining technologies. A method to eliminate the ambient temperature effects based on double pulse-heating (pulse duration: 125ms) up to two different temperatures, T_h and T_l, above the room temperature in vacuum sensing is proposed. Pulse-heating has also a merit to prevent temperature increase of the sensor chip. It is demonstrated that the Pirani gauge with a cantilever type MAB structure can almost compensate the ambient temperature effects by double pulse-heating. A method to correct the errors due to the non-linearity in the I-T relationship of the diode-thermistor as a very sensitive temperature sensor is also described.

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A new type absolute temperature-sensor with the measurable temperature range between 77 K and 400 K based on the forward voltage change due to the ambient temperature is proposed and demonstrated. In this temperature-sensor the forward ac voltage change or the forward ac current change at the pn junction diode due to the temperature change is measured for a constant amplitude of superimposed ac small signal of current δI or voltage δV, respectively, on the constant forward dc current I₀. This sensor has merits that it can be calibrated at only one temperature point, that output voltage is proportional to the absolute temperature T and that the measurement can be done independent of the ground point, since the ac signal circuits can be isolated from dc bias voltage circuits.

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Reliability of surface MEMS fabricated with standard CMOS back-end-of-line (BEOL) processes was investigated by several film analyses and by monitoring change in MEMS properties after standard pressure cooker test (PCT). A significant change in MEMS characteristics was observed after PCT for samples with SiN passivation layer thinner than 100nm, while for passivation layer thicker than 150nm, no change was observed. A large shift in film stress after PCT and results from TDS (Thermal Desorption Spectroscopy) and XRR (X-ray reflectometry) suggested that this is due to water release from SiO₂ film used in the structure.

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The displacement measurement device using a comb-drive actuator is described. The comb-drive actuator is driven in its mechanical resonance by the same manner as the crystal oscillator widely used in modern electronics. The key feature of our comb-drive actuator is to show the clear nonlinear mechanical immitance near its resonance, by which the comb-drive actuator can be vibrated using a simple positive feedback circuit. Since the self-oscillation frequency is changed when a probe formed with the comb-drive actuator contacts with an opposing object, displace mesurement like a stylus meter is possible by measuring the frequency. In our experiment, 0.23 μm step is succesfully measured using the self-oscillated comb-drive actuator.

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A capacitive MOSFET sensor using a SOI wafer for detecting vertical force applied to its floating gate is herein proposed. A MOSFET is fabricated on a SOI wafer, and the box oxide under the gate is removed to release the gate structure. This sensor detects the displacement of the movable gate electrode from changes in drain current, and this current can be amplified electrically by adding voltage to the gate, i.e., the MOSFET itself serves as a mechanical sensor structure. By using a SOI wafer having a thick active silicon layer, a thick gate structure is made possible, which increases the mechanical stiffness and durability, and increases the sensitivity in accelerometer application by weighting a proof mass. During the fabrication process of this sensor, it is necessary that photoresist be coated on the top-surface and sidewall of the vertical pillar structure with a high aspect ratio. To address this problem, photoresist is applied using spray coating. The uniform coating is successfully realized by adjusting the moving speed of the substrate, and the substrate temperature. A practical test device is under development using this method, and aluminum electrodes for drain, source and gate areas are successfully patterned.

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A high-sensitivity, compact set-up, which bases on a photonic bandgap fiber (PBG) and enables the precise measurement of low concentration of gas was designed. Besides high sensitivity, the priority was put on a low cost, portability and simplicity. Proposed technique allows reducing gas sample volume to 0.01 cc. The micro-capillary gas flow inside photonic crystal fiber was estimated. Darcy - Weisbach equation for non-compressible flow and quasi - Panhandle equation for compressible gas flow were used for the calculation of gas flow rate and gas velocity. During the experimental work several types of PBG fibers of various parameters were specially designed, produced and used. The core diameters ranged from 10.9 μm to 700 μm.

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Odor sensing system using quartz crystal microbalance (QCM) sensor array and pattern recognition technique has been for a long time an important research topic. Research of novel sensing materials for QCM odor sensors is vital for realization of artificial olfaction and related devices such as odor recorder. Herein we study quartz crystal microbalance (QCM, 20 MHz, AT-cut) sensors coated with lipopolymers with polyethylene glycol (PEG) as a tether. The tether's molecular weights were 1000, 2000 and 5000. In addition, we fabricated QCM sensors coated with PEGs of molecular weights 1000, 2000 and 4000. The fabricated sensors' properties were evaluated during experiments of exposures to vapors of alcohols, esters and acids. From the obtained results it is clear that the tether's length (molecular weight) is an important factor influencing the resulting material's sensing properties. Sensititivity patterns of the lipopolymeric sensors were clealrly different from the ones for respective polymers. The obtained sensors seem to have a good capability to discriminate among odor samples according to the functional group of an odorant.

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A recent study of carbon nanotube (CNT)-field emission display (FED) was described, and luminance uniformity of the experimental panel and the results of the life test of the CNT emitters were revealed. Furthermore, a high-resolution CNT-FED was investigated for graphic-displays. The sub-pixel size was 0.2 mm × 0.6 mm. The configuration of the display was a metal-backed color-phosphor screen, tall-spacer of 0.5-1.0 mm height for individual phosphor line, a metal gate-substrate with tall spacer and chemical vapor deposition (CVD)-grown-CNT on a metal-electrode. In order to improve field-emission characteristics of the CNT cathode, we developed two kinds of new CNT emitters by thermal-CVD. One is an emitter with thin CNTs which were grown on an alumina layer. The emission was extremely increased at lower voltage, compared to our conventional CNT emitter. Another is an emitter with secondary thin CNTs grown on thick CNTs. The emission showed an improvement in emission distribution uniformity.

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This paper presents the design, fabrication and characterization of a 3-DOF (3-degree of freedom) highly sensitive soft-contact tactile (SCT) sensor, which utilizes micro force moment sensing (MFMS) chip. The MFMS chip is working based on the piezoresistive effect in silicon. The MFMS chip has been packaged to produce 3-DOF SCT sensor, which has the contact part is made of silicone rubber. The sensor can independently detect three components of force (Fx', Fy', Fz') acting on the soft contact part of the sensor. The MFMS chip and the SCT sensor have been calibrated. The outputs were linear and the crosstalk was small.

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This paper proposes a new composition of the multi-probe using optical interference patterns for a parallel nano imaging in a large area scanning. We achieved large-scale integration with 50,000 probes fabricated with MEMS technology, and measured the optical interference patterns with CCD, which was difficult in a conventional single scanning probe. In this research, the multi-probes are made of Si3N4 by MEMS process, and, the multi-probes are joined with a Pyrex glass by an anodic bonding. We designed, fabricated, and evaluated the characteristics of the probe. In addition, we changed the probe shape to decrease the warpage of the Si3N4 probe. We used the supercritical drying to avoid stiction of the Si3N4 probe with the glass surface and fabricated 4 types of the probe shapes without stiction. We took some interference patterns by CCD and measured the position of them. We calculate the probe height using the interference displacement and compared the result with the theoretical deflection curve. As a result, these interference patterns matched the theoretical deflection curve. We found that this multi-probe chip using interference patterns is effective in measurement for a parallel nano imaging.

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In this paper, we propose a fabrication and characterization of silicon mold for PMMA hot embossing process. Silicon molds were fabricated from silicon wafer with thickness of 500μm. First, DRIE technique was performed after optimized etching time and deposition (passivation) time to obtain a depth of 30μm with positive tapered sidewall of 1°. This is very important for de-molding process while hot embossing. Second, in order to reduce scalloping steps on the sidewall after DRIE, silicon molds were soaked in the TMAH solution 20% at 80°C for 10 minutes without magnetic stirrer. Third, to further reduce the friction coefficient between sidewall surface and PMMA substrate while de-molding, the post-passivation technique was applied to create a thin layer of Teflon-like material on the surface of the sidewall of silicon mold. These smooth silicon molds were used to emboss several models of PMMA patterns and comb-drive actuators, as well as applications in Micro Conveyer System. The PMMA patterns obtained after hot embossing process had very sharp edge and aspect ratio of 15 with minimum feature sized of 2μm.

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An optical tactile pressure sensor using surface plasmon resonance is reported. A colloidal crystalline membrane of elastic polymer particles (n = 1.59) is pressed against a surface of Au film on a glass prism (n = 1.51) where SPR is excited. At the contact area between the particle and Au film, excitation condition of SPR is broken and the incident light internally reflects. Since the contact area changes reversibly according to the loaded pressure, optical measurement of pressure is realized by monitoring the intensity of reflection light. Measurement of 5 MPa was achieved by the proposed method.

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