Osamu Kawachi

Optimum leaky-SAW cut of LiTaO/sub 3/ for minimised insertion loss devices

The paper describes how the propagation loss /spl alpha/ of leaky surface acoustic wave (LSAW) is dependent upon the Al thickness h of grating electrodes and rotation angle /spl theta/ for rotated Y-X LiTaO/sub 3/. Since the energy leak of LSAW originates from the coupling of the slow-shear field component with other components through the surface boundary conditions, zero /spl alpha/ can be realised when the slow-shear component is decoupled. This means that the optimal /spl theta/ giving zero /spl alpha/ should change with h as well as the surface electrical boundary conditions. Since relatively large h of 0.07-0.1 wavelengths is needed for present LSAW devices, the optimal /spl theta/ shifts to 40-42/spl deg/ from the conventional value of 36/spl deg/. Thanks to the minimised propagation loss, experimental results showed that device performances are markedly improved only by increasing /spl theta/ to circa 42/spl deg/ from 36/spl deg/. We also describe the state-of-the-art of the performances obtainable in commercially available LSAW devices based on 42/spl deg/YX-LiTaO/sub 3/.

Optimal cut for leaky SAW on LiTaO/sub 3/ for high performance resonators and filters

The paper describes how the characteristics of leaky surface acoustic wave (LSAW) propagation depend on the thickness of Al grating electrodes on rotated Y-X LiTaO/sub 3/. It is shown that the propagation loss arising from leaky nature changes parabolically with both the grating electrode thickness and rotation angle and becomes zero when electrode thickness and rotation angle are properly determined. This means that even when thick grating electrodes are needed in device design, zero propagation loss is always realized by properly determining the rotation angle. When the grating electrode thickness is 0.07 to 0.1 in wavelength for example, LSAWs on 40-42/spl deg/Y-X LiTaO/sub 3/ give zero propagation loss without deteriorating other characteristics. Ladder-type filters for the 800-MHz range were fabricated, which essentially need thick Al grating electrodes of about 0.1 wavelength thickness. As predicted by theoretical calculation, experimental results showed that if the rotation angle is increased to circa 42/spl deg/ from a conventional value of 38/spl deg/, the insertion loss and shape factor are markedly improved compared with devices based on 36/spl deg/Y-X LiTaO/sub 3/. This is essentially a result of the minimized propagation loss.

Optimum cut of LiTaO/sub 3/ for high performance leaky surface acoustic wave filters

The paper describes how leaky surface acoustic wave (LSAW) propagation characteristics on LiTaO/sub 3/ depend upon its rotation angle when the Al electrode thickness is increased. It is shown that the propagation loss arising from the leaky nature changes parabolically with both the film thickness and rotation angle, and becomes zero when they are properly chosen. This means that even when relatively thick electrodes are needed, zero propagation loss is always achieved by properly determining the rotation angle for LiTO/sub 3/. When the electrode thickness is 0.07/spl sim/0.1 wavelengths, for example, LSAWs on the 40/spl sim/42/spl deg/ Y-X LiTaO/sub 3/ offer zero propagation loss without deteriorating other characteristics. Ladder filters for 800 MHz range were fabricated, which essentially need thick Al electrodes. As is predicted by theoretical calculation, experimental results showed that if the rotation angle a is increased to circa 42/spl deg/ from the conventional value of 36/spl deg/, the insertion loss and shape factor are improved by 0.7 dB and 0.26, respectively. The result gives a valuable guideline for determining the optimal rotation angle of LiTaO/sub 3/ to be used for high performance LSAW filters, which are one of the key components in RF sections of mobile communication systems.

High performance balanced type SAW filters in the range of 900 MHz and 1.9 GHz

This paper describes balanced SAW filters with low insertion loss and high stopband rejection, which are applicable to 900 MHz and 1.9 GHz range portable telephone. The longitudinal coupled type double mode SAW design is suitable for balanced filter design. The 42 degree Y-X LiTaO/sub 3/ substrate is chosen to get low insertion loss and high Q factor performances. The design and evaluation method are studied and the effect of phase difference between balanced terminal signals is shown. The new filter design makes it possible to convert input/output impedance in order to match to an IC impedance.

Analysis and optimal SAW ladder filter design including bonding wire and package impedance

This paper describes analysis and optimal design of SAW ladder filter, which includes effect of bonding wire and package impedance. Attenuation performance of SAW filter is influenced by not only their design conditions but also bonding wire effect and package design structure. To confirm their effect, theoretical and experimental analysis were studied, and it was found that electrical resonance generated by SAW element capacitance including capacitance of electrode fingers and stray capacitance, bonding wire and package inductance influence an attenuation characteristics. By using their characteristics effectively, we propose new improvement method of stop-band rejection.

A low-loss and wide-band DMS filter using pitch-modulated IDT and reflector structures

This paper proposes the use of pitch-modulated IDTs and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode SAW (DMS) filters. This technique offers drastic improvement of the device performance through the introduction of a sufficient number of DoF in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional un-modulated structure, and device performances are compared both theoretically and experimentally. Then it is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.

Low-Loss and Wide-Band Double-Mode Surface Acoustic Wave Filters Using Pitch-Modulated Interdigital Transducers and Reflectors

This paper proposes use of pitch-modulated interdigital transducers (IDTs) and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode surface acoustic wave (DMS) filters. This technique offers drastic improvement of the device performances through the introduction of a sufficient number of degrees of freedom in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional unmodulated structure, and device performances are compared both theoretically and experimentally. It then is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.

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

Realization of small and low profile Duplexer using a CSSD packaging technology

This paper presents the realization of Duplexer with small size, high reliability and excellent performance. Good heat radiation, hermetic performance and small frequency drift against temperature shift are essential to achieve small size and highly reliable Duplexers. In this paper, we will report on the advantage of the Chip Size SAW Devices (CSSD) structure for miniaturization and high reliability. In addition, we will discuss the possibility of further miniaturization.

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.