A novel optic sensor using platinum-loaded tungsten oxide (Pt/WO3) and a silicon microring resonator for detection of hydrogen gas at room temperature was developed and tested. The sensing principle is mainly based on the resonant wavelength shift caused by the catalytic combustion reaction of hydrogen. In a previous study, it was found that Pt/WO3 film could not be deposited uniformly on the surface of the microring. To solve this problem, acetylene glycol surfactant was used and mixed with Pt/WO3 precursor solution. Electron probe microanalyzer images of the device surface showed that the Pt/WO3 layer successfully covered the target part of the microring. When this device was tested, a 580-pm resonant wavelength shift was observed after 20-min exposure to pure hydrogen gas at room temperature. When the previous device was tested under the same condition, a 160-pm resonant wavelength shift was observed, so the sensitivity (defined by the wavelength shift after 20-min exposure to sample gas) of the developed device was approximately four times larger than that of the previous one.
A gelatinized ionic liquid of [TMPA]+[TFSI]- suspended in a polymer is proposed for the first time as a dielectric material for micro-electromechanical systems (MEMS) vibrational energy harvesters. Owing to the high-density charges in the electrical double layer (EDL) formed at the gel/electrode interface, a high contrast of capacitance modulation is realized, thereby enhancing the electrostatic induction current. A typical current of 4.6 µArms cm-2 is experimentally confirmed for a 10 kΩ load resistance connected to a DC voltage of 1.5 V, which is thought to be 86-fold greater than that produced by an energy harvester with a simple air-gap.
This paper describes the fabrication and characterization of a shape memory alloy (SMA) thick film actuator array for MEMS-type tactile displays that present information to a human finger with mechanical stimulation. A planar SMA thick film actuator array (5×5 array, 1 mm pitch) is proposed as a core component of tactile displays. A prototype of the MEMS-type SMA actuator array device with planar meandering SMA actuators and Pt thin film micro-heaters was successfully fabricated from a 10 µm thick SMA flash-evaporated film through a novel fabrication processes. The basic force generation properties of the completed SMA actuator were evaluated by heating the Pt micro-heater. When the device initially deflected to 100 µm, it was able to generate 33 mN and 16 mN of force by heating with 15 mA of DC current and without heating, respectively. In the combination with a bias spring, reversible force generation and displacement were estimated to be 5 mN and 20 µm when driven with a DC current, respectively. The force generated by the SMA actuator during vibrational motion at 20-40 Hz decreased to half the force generated during static motion. However, the output force was expected to be large enough to mechanically stimulate a human finger at 20-40 Hz.
A novel magnetic sensor composed of a silicon mechanical resonator and a magnetostrictive material is proposed, fabricated, and theoretically and experimentally evaluated. The sensor's measurement principle relies on the resonant-frequency change caused by a magnetically-induced compressive load resulting from a change in the size of the magnetostrictive material; the material expands upon application of an external magnetic field, and the resulting compressive load on the resonator changes its resonant frequency. The theoretical magnetic sensitivity and magnetic response are calculated based on material mechanics and thermomechanical noise. In our experiments, we evaluate the frequency response and fluctuation. The resonant frequency of the sensor linearly decreases as the magnetic field increases, which corresponds to a theoretical equation. The experimental magnetic resolution is 1.56×10-4 T, while the theoretical one is 4.62×10-10 T. This difference between theory and experiment is due to the low frequency stability of the device. The device sensitivity is improved by reducing the frequency fluctuation and sensor size. Our results indicate the feasibility of performing high-sensitivity measurements using the proposed mechanical resonant magnetic sensor.
A nano-gap electrode array is batch-fabricated based on photolithography. A high resolution is obtained by using an over-hanging resist cover on the under-etched metal film. The process includes two-time mask-patterning. The first photoresist is UV-cured, allowing second patterning without degrading the first pattern. A nano-gap width of 237±63 nm is obtained from a 704-electrode array with an yield of 97%.