Kazuyuki Nagatsuma

Temperature‐compensated PbTiO3 ceramics for surface acoustic wave applications

Lead titanate PbTiO3 ceramics with a zero temperature coefficient of surface wave delay time are developed by addition of Nd2O3, In2O3, and MnO2. These ceramics have very small temperature coefficients of less than 1 ppm/ °C over a wide temperature range (−10–+60 °C). They have a large electromechanical coupling factor and low dielectric constant. The propagation loss is 4 dB/cm at 57 MHz. These modified PbTiO3 ceramics have high potential for use in surface wave applications, e.g., filters.

Surface acoustic wave and piezoelectric properties of (Pb, Ln) (Ti, Mn)O3 ceramics (Ln = rare earths)

The surface acoustic wave (SAW) and piezoelectric properties of PbTi03 ceramics modified by the partial substitution of rare earths for Pb, particularly (Pb, Ln) (Ti, Mn)03 (Ln = La, Ce, Pr, Nd, Sm, or Gd) ceramics, are examined. The effects of the rare earths introduced on these properties are noted. Properties, such as velocities and electromechanical coupling factors, for bulk wave and SAW vary monotonically with the ionic sizes of the rare earths. On the other hand, the temperature coefficient of SAW delay time takes a minimum value when the Ln is Nd. It is shown that the variation of the temperature coefficient with rare earths corresponds well with those of the temperature coefficients of elastic constants CE33 and CE44.

Surface acoustic wave properties of (Pb,Ln)(Ti, Mn, In)O3 ceramics (Ln = La and Nd)

The surface acoustic wave properties of PbTiO3 ceramics are improved. The ceramic systems investigated are (Pb,Ln)(Ti,Mn,In)O3(Ln = La,Nd). The temperature coefficients of delay time are lowered to 46×10−6/ °C, when Ln is La. A zero temperature coefficient of delay can be achieved when Ln is Nd. The Nd and In substitution also cause the electromechanical coupling factor to increase and the dielectric constant to decrease.

SAW propagation loss mechanism in piezoelectric ceramics

The surface acoustic wave (SAW) propagation loss mechanism of piezoelectric ceramics is examined using lead titanate (PbTiO3) ceramics modified with additives of Nd2O3, MnO2, and In2O3, which have zero temperature coefficients of SAW delay time. The propagation loss L in the frequency range 30 to 300 MHz consists of two parts. One is the Rayleigh scattering loss LS caused by grain, and the other is the true dissipative loss LF caused by internal friction. Thus, total loss results in L(dB/cm) = LS+LF = 3.2×103D3f4+6.8×10−4f2 (where D and f denote average grain size in cm and frequency in MHz, respectively). It is also revealed experimentally that the internal friction causing the latter loss has a close correlation with the dielectric loss through piezoelectric combination. Therefore, materials with fine grain (<0.5 μm) and low dielectric loss (<10−3) must be developed to reduce SAW propagation losses which prevent the piezoelectric ceramics from being used in higher frequency (≳100 MHz) SAW applications. ...

Rare-earth substituted piezoelectric PbTiO3 ceramics for acoustic wave applications

Electromechanical and surface acoustic wave (SAW) properties of PbTiO3, ceramics modified by partial substitution of rare-earth for the Pb, specifically (Pb, Ln) (Ti, Mn)O3 (Ln=La, Ce, Pr, Nd, Sm, Eu, or Gd) ceramics, are extensively investigated. The SAW delay time temperature coefficient is found to be minimum when Ln=Nd. A zero temperature coefficient can be achieved in the (Pb, Nd) (Ti, In, Mn)O3 system with appropriate compositions. High frequency SAW filters are fabricated using these ceramics. It is also found that (Pb, Sm) (Ti, Mn)O3 ceramics have exceptionally large electromechanical anisotropy (ratio of electromechanical coupling factor for thickness vibration to that for planar vibration is above 15). A 7.5MHz linear array ultrasonic probe employing these ceramics is developed for medical use.

Surface acoustic wave characteristics of (Ba2−xSrx)TiSi2O8 crystals

The surface acoustic wave characteristics of fresnoite (Ba2TiSi2O8) crystals are improved. The temperature coefficients of delay time are greatly lowered, with almost no change in the electromechanical coupling factor, as the result of partial substitution of Sr for Ba, particularly in (Ba2−xSrx)TiSi2O8 crystals. These crystals have temperature coefficients of delay comparable to LiTaO3, while their electromechanical coupling factors are twice as large.

New Piezoelectric Ceramics with Zero Temperature Coefficients for Acoustic Wait Applications

Lead titanate (PbTi03) ceramics having zero temperature coefficients in various acoustic wave modes are developed by addition of Nd2O3, and Mn02. The chemical formulae of these ceramics are generally expressed by (Pbl 3,+lZNd,) (Til-y-zM”yInz)03. These ceramics have very small surface wave delay time temperature coefficients (less than 1 x 10-6/OC) over a wide temperature range (-loo to +6OoC) with appropriate compositions. Furthermore, it is possible to reduce the resonance frequency temperature coefficients in bulk wave modes (radial mode, thickness mode, flexure mode) to the same order as for surface waves by appropriately changing the combination of Nd, Mn, In concentrations. These modified PbTi03 ceramics are thus potential materials for acoustic wave applications. As application examples, SAW filters (60, ~OOMHZ), tuning fork resonators (3OkHz), and thickness mode resonators (4wz) are fabricated using these ceramics. In203

High-performance PIN photodiodes with an integrated aspheric microlens

We describe an aspheric-microlens-integrated high-performance PIN photodiode, which exhibits high speed (35 GHz), high responsivity (0.8 A/W), and large alignment tolerance (26 µm) for direct coupling to a flat-ended standard single-mode fiber.

Elastic properties of modified pbtio3 ceramics with zero temperature coefficients

Abstract Lead titanate PbTiO3 ceramics, with a zero temperature coefficient of surface acoustic wave delay time (TCD), have been developed by substituting appropriate amounts of Nd, Mn and In. The elastic, piezoelectric and dielectric constants, and their temperature coefficients, are measured for these ceramics using resonance methods. The TCD is numerically analyzed using the measured data. It is found that their temperature coefficients of elastic stiffness constants, C E 11 C E 12, C E 13, and C E 33 are all positive, though that of C E 44 is a small negative value. It is also found that these unusual temperature characteristics cause the TCD to reduce to zero.

4-channel/spl times/10-Gbit/s parallel laser-diode module for high-capacity optical interconnects

A 4-channel/spl times/10-Gbit/s parallel LD module for next-generation high-capacity optical interconnects was developed. To suppress the inter-channel crosstalk, a PPLC platform with a channel-pitch conversion function was also developed. Four un-cooled 1.3-/spl mu/m InGaAlAs FP-LDs were mounted on separated electrodes of the PPLC platform by passive alignment; thus, the module is compact and low cost. Crosstalk is as low as -40 dB. The module has a total throughput of 40 Gbit/s over 300-m transmission without suffering any degradation caused by inter-channel crosstalk. Our proposed 4-channel/spl times/10 Gbit/s parallel LD module can be applied to next-generation high-capacity optical interconnects.