Tsutomu Miyashita

Surface acoustic wave filter

A surface acoustic wave (SAW) filter includes a plurality of interdigital transducers located on a piezoelectric substrate along a surface wave propagation direction, at least a single one-port SAW resonator connected in series with an output side of the SAW filter, while the resonance frequency of the SAW resonator is set at a level which is higher than the passband of the SAW filter.

Development of low-loss band-pass filters using SAW resonators for portable telephones

A bandpass filter using surface acoustic wave (SAW) resonators in a ladder circuit structure for portable telephone systems is reported. For filter design, a simulation tool is used to consider the effects of electrodes (their apertures, the number of paired elements, thickness, and bulk wave radiation). Filter input and output impedance conditions are designed by the resonator capacitance to match the line impedance. The insertion loss and stopband rejection values are traded off against each other and are controlled by the ratio of capacitances between the parallel arm and series arm resonators, 800-MHz and 1.9-GHz band filters mounted in 3.8 mm*3.8-mm*1.5-mm ceramic packages were fabricated. They are suitable for surface mount technology (SMT). Typical frequency response characteristics are 2.5-dB maximum insertion loss in the 25-MHz passband and a stopband rejection of 25 dB.<<ETX>>

Development of Piezoelectric Thin Film Resonator and Its Impact on Future Wireless Communication Systems

The bulk acoustic wave filter composed of piezoelectric thin film resonators has many features superior to those of other small filters such as a surface acoustic wave (SAW) filter and a ceramic filter. As it has no fine structure in its electrode design, it has a high Q factor that leads to low-loss and sharp-cut off characteristics and a high power durability particularly in the high-frequency range. Furthermore, it has the potentiality of integrated devices on a Si substrate. In this paper, we review the recent developments of piezoelectric thin film resonator filters in the world, including our development for mobile communication applications. After describing the feature and history of the piezoelectric thin film resonator filters, our technologies are introduced in focusing on the resonator structures, the piezoelectric thin film and electrode film materials, the cavity structures, the filter structure and its design rules and characteristics, comparing with SAW filters. The competition and coexistence between the piezoelectric thin film resonator filters and the SAW filters are also described. In this paper, we describe the development of a piezoelectric thin film resonator from the standpoint of researchers who have a long experience of SAW filter development.

High performance and miniature thin film bulk acoustic wave filters for 5 GHz

Fujitsu has developed high-performance, miniature aluminum nitride (AlN) thin Film Bulk Acoustic Resonators (FBAR) filters for 5-GHz Wireless Local Area Network (WLAN) applications. Filters with higher frequencies of around 5 GHz and wider bandwidths will be needed in future mobile communication systems. Therefore, we developed filters using thin-film Bulk Acoustic Wave (BAW) technology, which shows promise as a possible solution to these higher frequency applications. There are two issues related to the development of FBAR filters. The first has been the need for miniaturization. To achieve this, we developed a new resonator configuration that employs bulk micromachining techniques. The second issue has been to increase the bandwidth. Five-GHz WLAN applications require a 200-MHz bandwidth at 5250 MHz, which corresponds to a fractional bandwidth of 3.8%. However, the piezoelectric coupling coefficient (k/sup 2/) of AlN cannot satisfy this requirement. To achieve wider filter bandwidth, we developed two approaches. They utilize epitaxial AlN film-growth and reactance-controlled flip-chip package design technologies. The packaging technology also enabled us to miniaturize the filters.

New electrode material for low-loss and high-Q FBAR filters

We have developed a new electrode material, suitable for AlN-based FBARs. The necessary conditions for FBAR electrode materials are low density, low resistivity, and high acoustic impedance. We investigated the influence of electrode materials on the resonant characteristics of FBAR in FEM simulations and experiments. We found the properties of ruthenium (Ru) to be suitable for use as electrode materials for AlN-based FBARs. In addition, by smoothing the surface of the electrodes, full width at half-maximum (FWHM) of the X-ray rocking curves of the AlN films is found to be 2.9/spl deg/ on Ru electrodes. The resonant characteristics of FBAR using Ru electrodes were an unloaded resonant quality factor, Q/sub r/, of 3585 and an effective electromechanical coupling coefficient, k/sup 2/, of 6.6% at 5 GHz. Furthermore, we applied these resonators to ladder-type FBAR filters for 5 and 2 GHz. As a result, we achieved low-loss and high-Q FBAR filters with Ru electrodes.

High-Q Resonators using FBAR/SAW Technology and their Applications

This paper describes FBAR and SAW resonators which have high-Q factor using unique technology, and their applications. A new electrode material suitable for AIN-based FBARs have been developed in order to realize high-Q factor for low loss. The necessary conditions for FBAR electrode materials are low resistivity and high acoustic impedance. It is found the properties of ruthenium (Ru) to be suitable for use as electrode materials for AIN-based FBARs. The resonant characteristics of FBAR using Ru electrodes indicates Q r of 1200 and an effective electromechanical coupling coefficient k 2 of 6.7% at 2 GHz. On the contrary, SAW resonator with narrow finger electrode, which can suppress transverse leakage of SAW, shows Q r of 670 and k 2 of 7.1%. Furthermore, we applied these resonators to ladder-type FBAR filter for 2-GHz WCDMA and SAW duplexer for US-PCS, respectively, and achieved low-loss and step cut-off filters as a result.

Development of 800 MHz band SAW filters using weighting for the number of finger pairs

A surface acoustic wave (SAW) bandpass filter has been developed for pocket and mobile telephones for 800-MHz-band cellular radio systems. In developing this filter, it was found that the number of finger pairs suppressed the sidelobe. The number of finger pairs was varied for each input and output transducer which composed an interdigitated interdigital transducer (IIDT) structure. The proportion of weighting for the number of finger pairs was optimized using computer simulation. A transmitting filter for AMPS was constructed using this method. Sidelobe suppression improved to above 8 dB compared to no weighting. Absolute suppression was less than -24 dB. This filter has properties suitable for practical use in a temperature range from -30 to +70 degrees C.<<ETX>>

Magnetization, strain, and anisotropy field of Ne+ and H+ ion‐implanted layers in bubble garnet films

The effects of the implantation dose and annealing on magnetization (4πMs), lattice constant strain (Δd/d), and change in the anisotropy field (ΔHK) of a layer implanted with Ne+ or H+ ions in bubble garnet films have been investigated using a vibrating sample magnetometer (VSM), the double crystal x‐ray technique, and ferromagnetic resonance measurements. The magnetic and crystalline properties of Ne+ or H+ ion‐implanted layers were quite different. Saturation magnetization of the H+ ion‐implanted layer decreased gradually with Δd/d beyond 1%, while that of the Ne+ ion‐implanted layer decreased abruptly above 1%. ΔHK of the Ne+ ion‐implanted layer was proportional to Δd/d up to a saturation point of about 1%; however, ΔHK of the H+ ion‐implanted layer continued to increase after Δd/d passed 1%. The other distinct difference between the H+ and Ne+ ion‐implanted specimens was the temperature necessary to obtain annealing effects. In the H+ ion‐implanted layer, annealing in the lower (around 200 °C) tempera...

Effects of Plasma Exposure on Magnetization of Ion-implanted Bubble Garnet

Exposure to plasma results in an increase in the change in induced anisotropy field ¿H<inf>k</inf> of ion-implanted garnet film. In this work, the change in saturation magnetization was also studied. Ne⁺ ions were implanted into (YSmLuCa)<inf>3</inf> (GeFe)<inf>5</inf> O<inf>12</inf> film and then exposed to plasma. Whereas a linear decrease in saturation magnetization 4¿M<inf>s</inf> with implantation dose was seen, plasma exposure caused an increase which was also proportional to the dose. The temperature dependence of 4¿M<inf>s</inf> indicated that plasma exposure raised the T<inf>c</inf>, which had fallen from 246°C to 180°C with implantation, back to 198°C. Occlusion of hydrogen in the plasma may be partially responsible for this behavior.

Design consideration for a 2‐μm‐period ion‐implanted propagation track (abstract)

We report on the design of ion‐implanted propagation tracks with a 2‐μm period. Reducing cell size causes increased drive field and margin degradation due to adjacent loop interaction. We investigated the effect of ion‐implanted layer properties on these problems. Using conventional photolithography, we fabricated propagation tracks on YSmLuCaGeFeO films with 0.5–0.7 μm bubble diameters by triple implantation of hydrogen and neon ions. After implantation, we exposed the wafers to argon plasma to increase the implantation‐induced anisotropy field change (ΔHk), then coated them with rf‐sputtered SiO2 film. We next annealed the coated wafers at temperatures ranging from 350 °C to 450 °C. To investigate the effect of the implanted layer thickness and its ratio to LPE film thickness, we proportionally varied the energies of triple implantation at a constant dose. The interaction between adjacent loops and the minimum drive field decreased as the implanted layer thickness decreased. Furthermore, we found that w...