センサ・マイクロマシン部門誌（論文誌E）では一昨年度（平成25年度）から，総合研究会で講演された論文に関する特集号を企画しています。第2回目の今回は本誌2015年5月号にて発刊の運びとなりました。掲載されている論文は「平成26年度センサ・マイクロマシン部門総合研究会」

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MEMS ultrasonic sensor was fabricated using the poly(vinylidene fluoride-trifluoroethylene)[P(VDF/TrFE)] copolymer thin films having multilayer diaphragm structures. It was shown that the P(VDF/TrFE) thin film on MEMS ultrasonic sensor exhibit a remanent polarization P_r of 72 mC/m² and a coercive field E_c of 59 MV/m. The resonant frequency, Q-value and sensitivity of the MEMS ultrasonic sensors are estimated to be on the order of 178 kHz, 24 and 45 µV/Pa, respectively. The P(VDF/TrFE) thin film was shown to be useful for piezoelectric material of MEMS ultrasonic sensor.

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Aiming at developing a portable and speedy blood test device, a microfluidic system is designed and developed. Blood is injected into a hole with a diameter of 3.0 mm and a height of 3.0 mm. When the blood sample is transported from the bottom to the top of the hole, blood cells sediment at the bottom and plasma is separated at the upper side. Using this system, approximately 1 µL pure plasma can be obtained when blood is injected at a flow rate of 0.70 µL/min for 15 minutes. Moreover, by retaining the blood in the hole for seven minutes, pure plasma can be obtained 11 minutes later.

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We have developed the tactile sensor using micro-cantilevers embedded in the elastomer which can measure both the normal and shear forces by piezoresistance. In this work, a piezoelectric tactile sensor using micro-cantilevers embedded in the elastomer has been proposed and fabricated for realizing lower power consumption than the conventional sensor using piezoresistor. The BiFeO₃ thin film (thickness: 400 nm) deposited by rf sputtering at substrate temperature of 520°C and gas pressure of 0.6 Pa has a good piezoelectric property because output voltage of 300 mV is obtained for strain induced by vibration of the cantilever. Therefore, it is demonstrated that the BiFeO₃ can be used to detect the micro-cantilever deflection by external force applied on the tactile sensor.

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Electrostatically actuated resonant varifocal mirrors were developed by bonding a silicon-on-insulator wafer and a glass wafer. Three different types of supporting fringes for the mirrors were tested to study the mirror's surface profiles by using the optical interference images. The surface profile deviation from the ideal parabolic shape was supported to 70 nm or less when the mirror's supporting fringe was made to be mechanically compliant.

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This paper proposes a new electret with high surface potential and high thermal resistance, which is made of nano-porous silicon dioxide (SiO₂). Electrical charge density in the nano-porous SiO₂ is higher than that in a normal (i.e., nonporous) SiO₂ because there are many voids in the nano-porous SiO₂ and the interface between void and SiO₂ traps electrical charges strongly. Therefore, decrease rate of the trapped charge density in the nano-porous SiO₂ is lower than that of normal SiO_2. Since SiO₂ is thermally stable, thermal stability of the electrical charge in nano-porous SiO₂ electret is better than that in a polymer electret. Output power generated by vibration energy harvesting using the nano-porous SiO₂ electret is also larger than that using the normal SiO₂ or polymer electret.

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We designed and evaluated low power ASIC (Application Specific Integrated Circuits) for the human activity and health monitoring systems to reduce the total power consumption. The ASIC extracts walking and running steps and holds the maximum and minimum values from raw data of acceleration sensor. To realize ultra-low power consumption, the algorithm is designed to reduce the amount of the data calculation for pedometer. Power consumption was reduced to 15% from previous prototype system by using the designed ASIC.

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Subwavelength structures are attracting scientific interests as a novel mean of thermal radiation control. In our previous work, we proposed emissivity control through the coupling between the surface polariton and the guided mode in resonant gratings. In this paper, we analytically investigate the emissivity of the thermal emitter that consists of slightly doped silicon gratings and a heavily doped silicon layer. The modal analysis is used to evaluate the active modulation capability. Fabrication process to manufacture the device and challenges encountered on the fabrication are discussed. The actuation of the grating height is also simulated.

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