We investigated the effect of process damage induced after capacitor etching procedures in the process of ferroelectric random access memory (FeRAM) fabrication for SrBi 2 Ta 2 O 9 capacitors. We found that this damage was suppressed by postmetallization annealing (400 C, 30 min in O 2 ) and that imprint characteristics were improved by the annealing, because active elements such as hydrogen and water induced during contact hole formation on tungsten plugs and first-metal formation are adsorbed effectively by the annealing before they penetrate into these capacitors.
Ocean acoustic tomography (OAT) is a powerful approach for observation of mesoscale ocean fluctuations. The precise estimation of travel time is required for ocean current measurement. We previously proposed the measurement of travel time using phase information. In this paper, we present the theoretical analysis of phase deviation using the Rice distribution. We then propose a new measurement technique of travel time termed as the complex vector method. We also demonstrate the ability of this method by computer simulation and received signals from OAT experiment in 1999. The preliminary results are promising. We conclude that the proposed estimated method is useful in long-range ocean transmission.
An ocean acoustic tomography experiment was carried out throughout the year 2000 with seven 200 Hz transceivers allocated in the area of 1100×1500 km2 in the central equatorial Pacific Ocean. The arrival time of the signal propagating near a sound-channel axis was selected and the effect of distance fluctuation was eliminated by excluding the elapsed time to travel differential length from the mean ray length of the transceivers calculated on the basis of ray theory. The zonal current velocity of a pair of transceivers and meridional current velocity were estimated from the reciprocal arrival time of the transceivers, which was recorded using hydrophones without any handling. Both the zonal and meridional mean velocities at the sound-channel axis were lower than 20 cm/s. To examine the proper of the obtained results, the obtained zonal current was compared with that of calculated by another method and with the acoustic Doppler current profiler (ADCP) data obtained at the tropical atmosphere ocean (TAO) buoy.
Ocean acoustic tomography (OAT) is a powerful approach for observation of mesoscale ocean fluctuations. A precise estimation of travel time is essential for measuring ocean current using OAT. Generally, a reciprocal propagation sound waveforms that are transmitted at the same time are similar mutually, and it is considered that their correlation is high. However, we found that reciprocal sound waveforms sometimes become different in the continuous estimation of travel time difference. In this paper, we present the estimation results of the correlation between the reciprocal transmissions. The correlation coefficient of signals depends on the signal-to-noise (SN) ratio of the signals. We propose an estimation method for the correlation of the reciprocal signals without the effect of SN ratio. Using the method, we estimate the variation of the correlation of reciprocal propagated sound transmissions for a distance of 500 km. A low correlation between the reciprocal propagated sound waveforms occurs at a certain rate. These phenomena seem to occur at a short periodical time.
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