Kunio Yamashita

Ba2Si2TiO8 for surface‐acoustic‐wave devices

Characteristics of piezoelectric fresnoite (Ba2Si2TiO8) for surface‐acoustic‐wave (SAW) devices are calculated. In general, the SAW characteristics of this material are located between those of LiNbO3 and LiTaO3. It always has nonzero temperature coefficients of delay (TCD’s). The lowest TCD is approximately 38×10−6/K, corresponding to the Bleustein‐Gulyaev wave on the Z‐axis cylinder cuts. A layered structure of Ba2Si2TiO8 thin film deposited on a fused‐quartz substrate is expected to have excellent SAW characteristics, e.g., k2a (electromechanical coupling factor when the interdigital transducers are formed on the surface of the layer) =0.0158–0.0165, and TCD=0–25×10−6/K for kh (where k is the wave number and h is the layer thickness) =2.0–3.2. A comment is made in the Appendix on an additional contribution to the formula for the power flow, and this contribution is taken into account in the present calculation.

A 4-bit/spl times/4-bit multiplier and 3-bit counter in Josephson threshold logic

A fast Josephson circuit using a threshold logic is developed for application to a multiplier and a binary counter. The former is a typical combinational circuit and the latter is a typical sequential circuit. The junction and barrier materials used were Nb-AlO/SUB X/-Nb. An optimized asymmetric two-junction interferometer maximized the operating margin of the threshold gate. A speed-up junction was introduced to decrease the switching delay without sacrificing the operating margin. A dumping resistor, which was inserted parallel to the input signal line of the threshold gate between its two terminals, decreased the reflection of the input signal caused by the gate inductance, thereby ensuring the margin and speed. To demonstrate the high-speed possibility of the Josephson threshold logic, a high-speed experiment for the circuits was performed. The multiplier demonstrated 210-ps operation.

Surface acoustic wave reflector consisting of a poled and unpoled domain array in piezoelectric ceramics

New surface acoustic wave reflectors were fabricated using modified lead titanate ceramics with the chemical composition (Pb1−(3x/2)+(z/2)Ndx ) (Ti1−y−zMnyInz ) O3 (x = 0.11, y = 0.02, z = 0.04). These reflectors consist of many poled and unpoled domains which are arranged alternatively in piezoelectric ceramics, instead of the usual metal strips or grooves. The frequency of measurements was around 22 MHz. Reflectivities per element for these reflectors were found to be as high as 2.9%, since the difference between surface acoustic wave velocities in these domains was large. This reflectivity was about three times larger than that for a conventional metal strip formed on the ceramics. Total reflectivities can be estimated as 89% for only 50 pairs of poled and unpoled domains.

Measurement using a current-axis-independent Josephson sampler

We have improved measurement of the current‐axis‐independent Josephson sampler. We use a new chopping detection circuit in the feedback system for sampling point control. Two channels of the sampling head are utilized to cancel drift in the time base. Drift is about 3 ps. We have measured the output of a short pulse generating circuit and obtained a transition duration of 15 ps.

Surface acoustic wave characteristics of CuCl

Surface acoustic wave (SAW1) characteristics of CuCl were calculated. It was found that both the electromechanical coupling factor and delay time temperature coefficient of CuCl fall between those of LiNbO3 and LiTaO3. This crystal was also found to have very low SAW velocities (1040–1500 m/s). It is concluded that CuCl is a potential SAW material for low‐frequency filter and delay line applications.

Surface acoustic wave characteristics of a single crystal of potassium lithium niobate

The surface acoustic wave (SAW) characteristics of a single crystal of potassium lithium niobate K2.98Li1.55Nb5.11O15 are calculated using published data. It is found that there are two sets of propagation planes and directions having zero temperature coefficient of SAW delay time. One set has a large electromechanical coupling factor (K2s=0.9%) and a zero power flow angle. The temperature stability of this crystal is located between that of T13TaSe4 and ST‐cut quartz.