Shinji Taniguchi

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.

Development of an X-Band Filter Using Air-Gap-Type Film Bulk Acoustic Resonators

We have developed an X-band filter utilizing air-gap-type film bulk acoustic resonators (FBARs). The air-gap structure is simple and cost-effective. Results from both simulations and experiments demonstrate that a dome-shaped air gap was formed between the substrate surface and the bottom electrode and that an air-gap-type FBAR structure was possible. The air gap can be formed on the flat substrate using stress control of piezoelectric and metal films without using a thick sacrificial layer. As a result, the fabricated X-band FBAR operated successfully with a keff2 of 6.30%, a resonance Q of 246, and an antiresonance Q of 462. The fabricated filter had a center frequency of 9.07 GHz, a fractional bandwidth of 3.1% and a minimum insertion loss of 1.7 dB.

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.

Driver-less 40 Gb/s LiNbO/sub 3/ modulator with sub-1 V drive voltage

We have succeeded in reducing the drive voltage of a 40Gb/s LiNbO/sub 3/ modulator to 0.9 V, which is the lowest-drive-voltage 40Gb/s LiNbO/sub 3/ modulator in the world. The modulator can be driven within the break down voltage of a SiGe transistor. This result was achieved using a new design concept that featured a wide-gap, long CPW (coplanar waveguide) electrode.

BAW/SAW/IPD hybrid type duplexer with Rx balanced output for WCDMA Band I

This paper describes a 3.0 ° 2.5 ° 0.7 mm3 wideband code division multiple access (WCDMA) Band I duplexer with receiver (Rx) balanced output we developed. The low-loss and power-durable film bulk acoustic resonator (FBAR) and the single-to-balanced double mode SAW (DMS) were utilized for the transmitter (Tx) and the Rx filter respectively. It was experimentally confirmed that the 2nd distortion of FBAR was significantly worse than that of the surface acoustic wave (SAW). In order to suppress the 2nd harmonic due to the nonlinear distortion of the duplexer and the power amplifier (PA), a notch circuit was implemented at the antenna port using our high-Q Integrated Passive Devices (IPD) technology. As a result, we realized the duplexer with suppressed nonlinear distortion as well as excellent filter response.

7E-1 An Air-Gap Type FBAR Filter Fabricated Using a Thin Sacrificed Layer on a Flat Substrate

We describe the development of an air-gap type film bulk acoustic resonator (FBAR) filter fabricated using a thin sacrificed layer on a flat substrate. In the development process we focused on reducing the cost of the wafer process. Results from both simulations and experiments demonstrate that a dome- shaped air gap was formed between the substrate surface and the bottom electrode and that an air-gap type FBAR structure was possible. Even if a thin sacrificed layer is used, the air gap can be formed on the flat substrate using stress control. Consequently, the Q-factor at resonance and anti-resonance and effective k2 were found to be 1500, 1100, and 7.2% in the 2-GHz range, respectively. The wideband code division multiple access (W- CDMA) band I duplexer was designed using the proposed air- gap type FBAR filters in a 3.0 times 2.5 times 0.7-mm ceramic package. The insertion losses were as small as 1.2 dB and 1.5 dB in the Tx and Rx bands respectively.

Film Bulk Acoustic Resonator using High-Acoustic-Impedance Electrodes

A 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. A high-Q factor and low loss are big advantages for a film bulk acoustic resonator (FBAR). The electrode material that is selected is very important for maintaining a high-Q and appropriate coupling factor. An analysis of the effects of acoustic impedance on AlN-based FBAR performance is described. The electromechanical coupling factor (k2) and filter loss were found to be influenced by acoustic impedance and to be mainly dominated by Youngs modulus. Ru was found by analysis and experiments to be a suitable material for the electrode. Finally, a 2 GHz wide band code division multiple access (WCDMA) filter was demonstrated to have a good performance.

Super-High-Frequency Band Filters Configured with Air-Gap-Type Thin-Film Bulk Acoustic Resonators

The first 24 and 30 GHz band thin-film bulk acoustic resonator (FBAR) filters are reported in this paper. The filters were configured with air-gap-type FBARs on a flat silicon substrate. They were designed using a Butterworth–Van-Dyke (BVD) equivalent circuit considering the linear relationship between resonant frequency, capacitance ratio, and loss in the FBAR. The measured characteristics corresponded with those of the simulation using the equivalent circuit in the pass-band. The center frequency, fractional bandwidth, minimum insertion loss, and out-of-band suppression were 23.8 GHz, 3.4%, -3.8 dB, and -13 dB in the 24 GHz band filter, and 29.2 GHz, 3.4%, -3.8 dB, and -11 dB in the 30 GHz band filter, respectively.

X-Ray Analysis of the Structure of Premelted Layers at Ice Interfaces

X-ray diffraction patterns of a premelted layer of ice and liquid water were obtained by a glancing-incidence method. Diffuse intensity patterns due to the premelted layer exhibited variation with temperature. Fourier transformation of the intensity curves gave pair-correlation functions, where the first, second and third peaks were observed in the premelted layer and liquid water. This suggests that there is a short range order in their molecular distribution. The average intermolecular distances between the nearest neighbors were 1–2% smaller in the premelted layer than in liquid water.

10-Gb/s polarization-independent Ti:LiNbO/sub 3/ modulator

A 10-Gb/s polarization-independent LiNbO/sub 3/ modulator with a tandem electrode and a half-wave plate was developed. An insertion loss of 5.1 dB and 10-Gb/s optical modulation can be achieved with any polarized input light.