Sadao Matsumura

Elastic and Dielectric Properties of LiNbO3

Elastic constants C 11 , C 33 , C 44 , and C 66 , and dielectric susceptibilities χ 11 and χ 33 in LiNbO 3 , were determined over the temperature range from 300 to above 1030 K. The elastic-constant difference between constant polarization and constant field \(C^{P}_{\imath\imath}-C^{E}_{{\imath}i}\), and the inverse-susceptibility difference between constant strain and constant stress\((\chi^{x}_{i{\imath}})^{-1}-(\chi^{X}_{\imath\imath})^{-1}\) are interpreted in terms of both electrostrictive and higher-order interaction between strain and polarization. The results for χ 33 indicate that LiNbO 3 undergoes nearly second-order phase transition at T C =1410 K. Above T C , χ 33 showed dispersion in the frequency range between 1 and 13 MHz. A comparison of these results with soft-mode frequency implies that the soft mode couples with a low frequency relaxation process near T C .

Growth and Properties of Li2B4O7 Single Crystal for SAW Device Applications

Large Li2B4O7 single crystals, up to 45 mm in diameter, have been successfully grown along the X- and Z-axis by Czochralski technique. Fundamental phsyical and chemical properties were determined, and basic SAW properties were studied for the various surface orientations and SAW propagation directions from theoretical and experimental points of view. It was found that there were useful substrate orientations for SAW resonators and narrow bandpass SAW filters around the rotated X-cut, Z-propagation, where SAW propagation delay time was a parabolic function of temperature and SAW coupling factor k2 was approximately 1%. When a SAW propagates along the Z-direction on the 28° rotated X-cut substrate, the temperature coefficient of delay time (TCD) is zero at 20°C and the second order TCD is 0.27 ppm/°C2, k2 is 0.8% and SAW velocity vs is 3470 m/s. The bulk wave spurious signal response level is lower by -20 dB than the SAW fundamental response level.

Growth of LiTaO3 single crystal for saw device applications

Abstract A large “SAW grade” LiTaO3 single crystal, up to 2.5-3.0 inch in diameter and 4–5 inch long, could be successfully grown by the Czochralski technique using an economic Pt-Rh crucible instead of an expensive Ir crucible. Grown crystals have a deep brown to pale yellow color due to Rh impurity from the crucible. The relations among optical absorption, Rh impurity concentration and growth conditions were examined and discussed, compared with those of crystals grown from an Ir crucible. Compositional variation, reproducibility of SAW properties and durableness for the device fabrications of large crystals grown economically, were examined and the crystals were found to have quality suitable to match SAW device applications.

SAW Propagation Characteristics on Li2B4O7

Lithium tetraborate (Li2B4O7) was reported as a new piezoelectric material which has zero temperature coefficient of delay (TCD) and moderately high coupling coefficient (k2). This paper estimates SAW propagation properties (k2 and TCD) on Li2B4O7 over the full cuts and propagation directions. Further, the TCD dependency on aluminum layer is also assessed, considering construction of a SAW device with aluminum electrodes. As a result, it is found that there is a region of zero TCD and high coupling coefficient (1%).

Growth conditions for large diameter X-axis LiTaO3 crystals

Abstract Suitable thermal environment, crystal rotation rate and growth rate have been established for the growth of large diameter X -axis LiTaO 3 crystals having a 65 mm diameter. The relations between the optimum growth conditions and the grown crystal diameter have been determined quantitatively. The relations are consistent with theoretical considerations based on the temperature distribution and thermal balance in the growth furnace. From these results, it can be concluded that the optimum growth conditions become limited to a narrow region as crystal diameter becomes larger.

Effect of Li/Nb Ratio on the SAW Velocity of 128°Y–X LiNbO3 Wafers

The effects of the composition on the SAW velocity and the electro-mechanical coupling constant (k2) of 128°-rotated Y-cut X-propagating (128°Y–X) LiNbO3 wafers have been quantitatively investigated. The composition of the wafer was determined from the Curie temperature detected by DTA measurements and the SAW velocity from the measurements on a 70 MHz band SAW Comb filter. From the experiments, both the SAW velocity and the k2 obviously depended on the composition of the wafer. Variations of the SAW velocity and the k2 per 1 Li2O mol% were 43.4 m/sec and 0.43%. At the composition of 48.6 Li2O mol% which was reported as the congruent melt composition by Carruthers et al.,1) the SAW velocity and the k2 were 3986 m/sec and 5.8%, respectively.

Piezoelectric and Elastic Properties of Li2GeO3 Single Crystal

The main components of the elastic, piezoelectric and dielectric constant tensors of Li2GeO3 single crystal are measured in the temperature range between 20°C and 200°C. The temperature coefficients of these constants are determined at room temperature. The c-cut plate of this crystal has a large coupling factor (0.31~0.32) and small dielectric constant (9.8~10.9) in this temperature range. The mechanical impedance of this plate (22×106 kg/sm2) is nearly equal to that of typical elastic material such as PbMoO4 crystal. These deta have been used to evaluate this material for use as a transducer of ultrasonic devices by using the Meitzler model. It has been shown that this crystal has very attractive properties for this application.