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Four types of WO3 particles, spherical, disk, cuboid, and hexagonal, were prepared and WO3 film sensors were deposited on Au comb-type microelectrodes by dropping suspension using the various WO3 powders obtained. The sensing properties to dilute NO2 revealed that the cuboid WO3 film sensor had the best response-recovery characteristics with the 90% response and 90% recovery times of 1.3 and 0.9 min to 0.05 ppm NO2 at 200°C, respectively. On the other hand, the hexagonal WO3 film sensor showed extremely high sensor response of 41.1 even to 0.01 ppm NO2 at 200°C, but the sensor response fluctuates widely with the operating temperature ranging from 80 to 300 °C. The adsorption-desorption behaviours of NO2 on various surfaces of WO3 particles with different morphologies were investigated using temperature programmed desorption (TPD) technique, which suggesting that NO2 molecules were adsorbed easily on the WO3 surface. The desorbed amount of NO decreased in the order of hexagonal, cuboid, disk and spherical, which agreed with the respective sensor response of the four WO3 film sensors.

Piezoelectric microdevices using lead zirconate titanate (PZT) bulk ceramics are desired for use in actuators requiring a large driving force. We have designed a fabrication process for microdevices using PZT bulk ceramics together with Si single crystals. The key techniques of the process are the bonding of PZT bulk ceramics to Si single crystals, the thinning of bulk ceramics, and the micromachining of bulk ceramics. PZT ceramics were bonded to Si using a gold thin film as an intermediate layer. The tensile strength of the PZT-Si bonded wafers depended on the PZT poling process. A dicer or a KrF excimer laser was used to cut the PZT ceramics along the designed pattern. A PZT-Si diaphragm was fabricated as an example of a basic structure that can be used in a device such as a piezoelectric micropump.