Haruki Kyoya

Incredible high performance SAW resonator on novel multi-layerd substrate

High Q and low TCF are elemental characteristics for SAW resonator, in order to realize high performance filters and duplexers coping with new LTE frequency bands. Authors focus on the acoustic energy confinement in SAW propagation surface and electrical characteristics have been investigated theoretically and experimentally. A new multi-layered structure substrate have realized incredible high performances such as both three times Q and one fifth TCF compared with conventional structure. Band25 duplexer using the new structure has been developed successfully with low loss and good temperature stability.

Study on generation mechanisms of second-order nonlinear signals in surface acoustic wave devices and their suppression

In this study, we examine the generation mechanisms of the second-order nonlinear signals in surface acoustic wave resonators/duplexers fabricated on a 42°YX-LiTaO3 substrate. It is shown that the crystal asymmetry of the substrate can generate the second-order nonlinear signals. The following two mechanisms mainly contribute to their generation: (a) self-mixing of the electrostatic field and (b) mixing of the electrostatic field with the strain field associated with laterally propagating modes. Both of them occur at the gaps between the electrode tip and the dummy electrode. In addition, an interdigital transducer design that cancels this asymmetry is proposed. The design is applied to a one-port resonator and a duplexer, and the effectiveness of this technique is demonstrated.

Influence of electrode structure on generation of third-order nonlinearity in surface acoustic wave devices

In this paper we describe the influence of the electrode material on the generation of the third-order nonlinearity in surface acoustic wave (SAW) devices fabricated on a 42°YX-LiTaO3 substrate. It is shown that the crystallinity of the Al layer in the electrode considerably influences the intensity of the third-order nonlinearity. Surprisingly, electrodes with better crystallinity generate stronger third-order nonlinearity. This indicates that the Al layer is one of the major reasons behind its generation. It is also shown that the third-order nonlinearity can be reduced by properly designing the layer stack of the electrodes such that acoustic strain is not concentrated in the Al layer. This means that the acoustic strain in the electrode is one of the main causes of the third-order nonlinearity.

Discussion about generation mechanisms of third-order nonlinear signals in surface acoustic wave resonators based on simulation

In this paper, we discuss the generation mechanisms of third-order nonlinearity in surface acoustic wave (SAW) devices on the basis of simulation results, which are obtained by a proposed method for this discussion. First, eight nonlinear terms are introduced to the piezoelectric constitutive equations, and nonlinear stress and electric flux fields are estimated using linear strain and electric fields calculated by a linear analysis, i.e., the coupling of mode simulation. Then, their contributions are embedded as voltage and current sources, respectively, in an equivalent circuit model, and nonlinear signals appearing at external ports are estimated. It is shown that eight coefficients of the nonlinear terms can be determined from a series of experiments carried out at various driving and resulting frequencies. This is because the effect of each nonlinear term on the nonlinear signal outputs changes markedly with the conditions. When the coefficients are determined properly, the simulations agree well with some measurement results under various conditions.

Effective suppression method for 2 nd nonlinear signals of SAW devices

Linearity performances are getting one of the most important characteristics of surface acoustic wave (SAW) duplexers because nonlinear signals generated in RF front-end of cellar phone handsets deteriorate the receiver sensitivities significantly. In this paper, the generation mechanisms of the 2nd order nonlinear signals of SAW resonators/duplexers on a 42°Y-X LiTaO3 substrate and an effective suppression method for them are discussed. The crystalline asymmetry properties of substrates are focused on as the one possibility of the occurrence factor of the 2nd order nonlinear signals. Additionally, based on this hypothesis, an interdigital transducer (IDT) design which realizes the cancellation of the crystalline asymmetry effect is proposed to improve the linearity. As the result, the 2nd order harmonics level of the one-port SAWresonators and the 2nd order intermodulation distortion (IMD2) levels of the SAW duplexers have been improved up to about 25dBm and 20dBm, respectively.

High-Performance SAW Resonator on New Multilayered Substrate Using LiTaO 3 Crystal

To develop the high-performance filters and duplexers required for recent long-term evolution frequency bands in mobile handsets, a surface acoustic wave (SAW) resonator is needed that has a higher quality (Q) and a lower temperature coefficient of frequency (TCF). To achieve this, the authors focused on acoustic energy confinement in the depth direction for a rotated Y-X LiTaO3 (LT) substrate. Characteristics of multilayered substrates with low-impedance and high-impedance layers under LT layer were studied numerically in terms of acoustic energy distribution, phase velocity, coupling coefficient, and temperature characteristics employing a finite-element method simulation. After several calculations, a novel multilayered structure was developed that uses SiO2 for a low-impedance layer and AlN for a high-impedance layer under the thin LT layer. A one-port resonator using the new substrate was fabricated, and its experimental results showed that the developed resonator had a Bode-Q over 4000 and TCF of −8 ppm/°C, which are four times higher than and one-fifth as small as those of a conventional 4° YX-LT SAW resonator, respectively. By applying this technology, a band 25 duplexer with very narrow duplex gap was successfully developed, which shows extremely low insertion loss, steep cutoff characteristics, and stable temperature characteristics.

Influence of electrode materials and structural design on third-order nonlinear signals of SAW devices

In this paper, we investigate influence of the electrode on the third-order nonlinearity of SAW devices. First, some one-port resonators are fabricated on 42°YX-LiTaO3 substrates with different electrode material or electrode crystallinity, and their nonlinear signal levels are estimated. As the result, nonlinear signal levels change markedly with electrode material and crystallinity of electrode. Next, the electrode metal stack is redesigned not to change the linear characteristics of resonators, and its impact to the nonlinearity is estimated. From the results of these discussions, it is concluded that electrode fingers in IDT are one of the major sources of the third-order nonlinearity.

Study on generation mechanisms of third-oder nonlinearity in SAW devices

In this paper, generation mechanisms of third-order nonlinearity in surface acoustic wave (SAW) devices are discussed. For this discussion, a simulation technique, in which all conceivable generation mechanisms are taken into account, is proposed. In the simulation procedure, nonlinear stress and electric flux at each electrode finger are estimated by using results of linear analysis and eight nonlinear terms. Then, their contributions are embedded as the voltage and current sources, respectively, in an equivalent circuit model, and nonlinear signals appearing at an external port are estimated. It is shown that each nonlinear coefficient can be determined from a series of experiment carried out in various driving frequencies. This is because influence of each nonlinear term to the nonlinear output changes markedly with the driving conditions.

Considerations on nonlinearity measurement with high signal-to-noise ratio for RF surface and bulk acoustic wave devices

This paper discusses the measurement setup of non-linearity caused in radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices with high signal-to-noise ratio (SNR). It is shown that when some important points are considered, the background level can be suppressed better than −135 dBm, and the non-linearity signals can be measured in high SNR. Finally, measured results are compared with those measured independently by Murata Manufacturing, and validity of the measurement is cross-checked.