Kazushi Hashimoto

Low loss ladder type SAW filter in the range of 300 to 400 MHz

Low loss SAW filters in the range of 300 to 400 MHz for communication systems have been developed, which have ladder circuit structure using 36° rotated Y-cut LiTaO3. This type of filter has low loss and high stop band rejection, however, a spurious mode appears, which depends on electrode thickness and a reflectors electrode pitch of a resonator. Low frequency range filters need thick Al electrodes more than 7% of wave length to shift the resonant frequency of spurious mode to a frequency range higher than the pass-band frequency range. To reduce the spurious response, the design of an electrode pattern and electrode material having more mass effect than Al were investigated by simulation and experiment. The spurious response can be suppressed by optimizing a reflectors electrode pitch. By using Au film, thin film of about 1.5% of wave length can be applied to a filter. SAW filters in the range of 300 to 400 MHz with fractional band width from 2 to 4% were manufactured and mounted in SMD type 5×7×1.4 mm ceramic packages, which have 2 dB minimum insertion loss and attenuation characteristics of about 40 dB. Input and output impedance of filter are 50 Ω

Development of ladder type SAW RF filter with high shape factor

The paper presents ion implantation technology to improve the shape factor of a ladder-type SAW RF filters for mobile communication systems. The improvement of the shape factor was confirmed experimentally. However we found that the SAW phase velocity is decreased by ion implantation. To stabilize and recover the SAW phase velocity, several annealing conditions were investigated. At the annealing condition of over 450/spl deg/C/spl times/1 hour, SAW phase velocity was recovered to almost the same as the initial velocity. In the past, the shape factor values of ladder-type SAW filters using a LiTaO/sub 3/ substrate have been almost 1.7. The ion implantation technology has been applied to a PDC (personal digital cellular) -1.5 GHz SAW band pass filter using a LiTaO/sub 3/ substrate. We have obtained the shape factor value of 1.4 under the following conditions; ion: double charge Ar/sup ++/, dose: 5/spl times/10/sup 13//cm/sup 2/, acceleration voltage: 180 keV.

SiO2/36° Y-X LiTaO3 surface acoustic wave resonator

SiO2/36° Y-X LiTaO3 substrate which has an excellent characteristic of temperature and a high electro-mechanical coupling coefficient is realized. Temperature coefficient of frequency (TCF) is zero and electro-mechanical coupling coefficient (K2) is 5.2% when thickness of SiO2(H/λ) is 21%. Using this resonator, a voltage controlled oscillator (VCO) with excellent temperature characteristic and wide frequency deviation larger than 800 ppm/V is obtained.

Wide frequency deviation and temperature stable VCO using SiO/sub 2//36 degrees Y-X LiTaO/sub 3/ resonator

An SiO/sub 2//36 degrees Y-X LiTaO/sub 3/ substrate which has an excellent temperature characteristic and a high electromechanical coupling coefficient has been prepared. The temperature coefficient of frequency (TCF) is zero, and the electromechanical coupling coefficient is 5.2% when the thickness of SiO/sub 2/(H/ lambda ) is 21%. An energy-trapped structure which is a one-port-type resonator connects a loading capacitance in series to a transducer. Using this resonator, a voltage-controlled oscillator (VCO) with an excellent temperature characteristic and a wide frequency deviation larger than 800 ppm/V is obtained.<<ETX>>