A novel sensor system of denture base type was developed for simultaneous monitoring of salivary pH and tissue temperature in the oral cavity. Fundamental components of the monitoring system, sensor devices and sensor configuration are showed in this paper. The sensor units consist of IrO2 electrode and thermistor circuit implanted in the denture base that is tightly fixed in the oral cavity. The signals are transmitted by PFM-FM telemeter system that can be used for health care of the aged people without restraint of their daily behavior while at work, sleeping and even at exercise. Some of results concerning the basic characteristics of the sensor system and continuously monitored physiological data were obtained from the preliminary experiments. Availability of the whole system and monitoring method was discussed.

We prepared alkoxide solutions to fabricate SrBi2Ta2O9 (SBT) ferroelectric capacitors with IrO2 electrodes. In this process, to minimize excess bismuth, the Sr : Bi : Ta mole ratio was kept at 0. 9 : 2. 1 : 2. 0, i. e. , nearly stoichiometric. Three types of solution - mixed-only (MIX), complexed (COMP), and hydrolyzed (HYD) - were used. The HYD capacitor had low absolute leakage current, 10-7 A/cm2 order, and good saturation properties to 6 V. When voltage was applied to each capacitor at 2 to 6 V, MIX and COMP capacitors showed only partial hysteresis loops due to a high leakage current, reflecting the I-V characteristics. These results are probably due to film density caused by metaloxane network bonding. A fatigue endurance test was conducted using cycling of polarization switching at 6 V using the HYD capacitor with IrO2 electrodes. Slight changes were, however, observed in hysteresis loop configuration, but good hysteresis properties were kept up to 1. 04 1012 cycles. We compared SBT ferroelectric thin films fabricated with Pt electrodes and with IrO2 electrodes. Scarcely any difference due to SBT in the XRD pattern was seen, depending on the substrate material. We found that the use of IrO2 electrodes had the effect of decreasing the crystallization temperature. On Pt and IrO2 electrodes, the two films have surface morphology quite different from that of the rod-like structure wellknown for SBT films prepared using a metal 2-ethylhexanate solution. Their surfaces show a similar morphology with relatively large, closely packed grains. A comparison of the I-V characteristics after reannealing showed that the capacitor with IrO2 electrodes had a higher leakage current than that with Pt electrodes. The leakage current was probably due to the density of the film and interface between the SBT film and electrodes.

Degradation of ferroelectricity in PZT (Pb(Zr0. 52, Ti0. 48)O3) thin-film capacitors caused by heat treatment in a reductive ambience is investigated. We have found that the degradation of ferroelectricity depends upon the metal used for the top electrode of the PZT capacitor. The increased degradation in the case of a PZT capacitor with Pt electrodes can be explained by a catalytic reaction on the Pt surface. With the use of an IrO2 non-catalytic top electrode, we have made the ferroelectricity of an IrO2/PZT/Pt capacitor retained even after the H2 annealing at 400, or above.

It is well known that PZT material properties are strongly dependent on the Zr/Ti ratio. The reliability characteristics, such as the retention and imprint properties, of PZT thin film correlate with the reliability of FRAM(R). PZT films with various Zr/Ti ratios, 60/40, 52/48, 45/55, 40/60 and 30/70 were prepared on Pt/IrO2 and Pt/Ti electrodes by a sol-gel process. With lower Zr/Ti ratio, the grain size becomes smaller and the film was highly oriented to (111) crystallographic plane. But, pyrochlore phase in the PZT films on Pt/IrO2 electrode was detected by SEM and XRD. Hysteresis and pulse responses were measured on the capacitors. With lower Zr/Ti ratio, Pr and Vc become larger. It was found that the preferential (111) orientation played an important role in determining Pr. Voltage shifts which are related to imprint are dependent on the Zr/Ti compositional ratio. Increasing the Ti concentration causes the voltage shift to increase due to more oxygen vacancies. But, this tendency was not in accordance with the results of Qos which were measured by capacitor test simulation of imprint properties for FRAM operation, because the results of Qos did not change monotonically with Ti concentration. However, the capacitor for 45/55 film grown on Pt/IrO2 had good imprint property, similar to the capacitor for sputtered PLZT. In addition, H2 degradation of PZT capacitor with Pt/IrO2 was studied. It was found that H2 annealing degraded the PZT capacitors even at temperatures as low as 150. Thus, imprint and H2 degradation are serious problems for PZT capacitors and these will be a key issue in the reliability of FRAM.