Yasumi Kobayashi

Characteristics of AlN Thin Films Deposited by Electron Cyclotron Resonance Dual-Ion-Beam Sputtering and Their Application to GHz-Band Surface Acoustic Wave Devices

A (001) plane of hexagonal aluminum nitride (AlN) has been deposited on R-plane sapphire ((1 2)Al2O3) with inclination of about 26° against the substrate by electron cyclotron resonance (ECR) dual-ion-beam sputtering. A shear horizon (SH) wave as well as a modified Rayleigh wave could be excited on this AlN film. The phase velocities of the SH wave (V SH) and Rayleigh wave (V R) were 6000~6730 m/s and 5600~5950 m/s, respectively. V R has no effect on the propagation direction. However, V SH has considerable influence on the propagation direction, and becomes maximum at the propagation direction of 45 degrees against [120]AlN. The insertion loss and temperature coefficient of delay time (TCD) of the 1.21-GHz-band two-port-type resonator using SH waves were 7.5 dB and 35.4 ppm/°C, respectively. These values are acceptable for practical use.

1.9-GHz-Band Surface Acoustic Wave Device Using Second Leaky Mode on LiTaO3

The propagation characteristics of a new high-phase-velocity leaky surface acoustic wave (SAW) mode, which is called the second leaky mode, in a periodic structure on LiTaO 3 (90°, 90°, 31°) are analyzed experimentally. The propagation loss is the lowest when the KH (K=wave number, H=Al electrode thickness) parameter is about 0.5. The higher mode of the second leaky mode is excited when the KH parameter is larger than 0.7. A ladder type band-pass SAW filter utilizing the second leaky mode on LiTaO 3 was designed and fabricated by applying the analysis results to the periodical structure. The pitch of the electrode fingers is 0.8 μm. The center frequency of the pass band is 1.938 GHz. The minimum insertion loss is 3.3dB. The attenuation at the center frequency ±100 MHz is 25dB. The measured characteristics of this filter can be sufficient for practical mobile communication systems.

Characteristics of Surface Acoustic Wave on AlN Thin Films.

A surface acoustic wave (SAW) on a (001) plane of hexagonal aluminum nitride (AlN) deposited on R-plane sapphire ( (1\bar12)Al2O3) with an inclination of about 26 degrees to the substrate was analyzed. A Rayleigh wave and shear-horizontal-type (SH-type) wave were found. The phase velocity of these was 5400-5800 m/s and 6100-6600 m/s, respectively. To confirm this results, the propagating characteristics of both SAW modes were measured by input admittance of single interdigital transducers (IDT) and by transmission characteristics between two IDTs. The phase velocity of the Rayleigh wave and the SH-type wave was 5600 m/s and 6500 m/s, respectively, and the propagation loss was 0 dB/λ and 0.04 dB/λ, respectively. These measured characteristics approximately agree with the results of the simulation.

GHz-band surface acoustic wave devices using the second leaky mode on LiTaO3 and LiNbO3

The propagation characteristics of a new high-phase-velocity leaky surface acoustic wave (SAW) mode, which is called the second leaky mode, were analyzed experimentally in a periodic structure on LiTaO3 (90°, 90°, 31°) and LiNbO3 (90°, 90°, 37°). As regards the mode on LiTaO3, the propagation loss is lowest when KH ( K=wave number, H=Al electrode thickness) is about 0.5. The higher mode of the second leaky mode is excited when KH is more than 0.7. As regards the mode on LiNbO3, the propagation loss exhibits no distinct minimum when plotted against KH. The higher mode of the second leaky mode is excited when KH is more than 0.6. A ladder-type band-pass SAW filter utilizing the second leaky mode on LiTaO3 was designed and fabricated by applying the analysis extended results to the periodic structure. The pitch of the electrode fingers is 0.8 µ m. The center frequency of the pass band is 1.866 GHz. The minimum insertion loss is 3.3 dB. The width of the 1 dB pass band is 32 MHz. The attenuation at a center frequency of ±60 MHz is 25 dB. The measured characteristics of this filter are sufficient for practical mobile communication systems.

New High-Phase-Velocity Leaky Surface Acoustic Wave Mode on LiTaO3 and LiNbO3

A new high-phase-velocity leaky surface acoustic wave (SAW) mode, which was predicted by computer simulation, was confirmed experimentally to exist on both LiTaO3 and LiNbO3. The Euler angles of the propagation direction are (90°, 90°, 31°) on LiTaO3 and (90°, 90°, 37°) on LiNbO3. One-port SAW resonators were produced to confirm these modes. The phase velocity of the mode on LiTaO3 (90°, 90°, 31°) is 6250 m/s, and that on LiNbO3 (90°, 90°, 37°) is 7170 m/s. The temperature coefficient of the resonance frequency on LiTaO3 (90°, 90°, 31°) is -30 ppm/°C, and that on LiNbO3 (90°, 90°, 37°) is -30 ppm/°C.

Small SAW filters using optimized high-reflection-coefficient reflectors

The dependence of the reflection coefficient on grating reflector parameters, such as electrode thickness, the reflector metallization ratio and Pi/Pr, was studied in detail. Pi and Pr are the electrode finger periods of interdigital transducers (IDTs) and reflectors, respectively. The maximum value of the reflection coefficient occurred at a metallization ratio of 75% and Pi/Pr of 0.990. Intermediate frequency (IF) surface acoustic wave (SAW) filters for the Advanced Mobile Phone Service (AMPS) system were made using these high-reflection-coefficient reflectors. As a result, package size was reduced from 11 mm/spl times/5 mm to 7 mm/spl times/5 mm. Their characteristics include a center frequency of 85.38 MHz, an insertion loss of 2.5 dB and a 3 dB-passband width of 54 kHz.

Epitaxial growth of aluminum nitride thin films on (111) si by ecr dual ion beam sputtering

Abstract Aluminum nitride (AIN) thin films grown on silicon substrates are very promising materials for GHz-band bulk and surface acoustic wave (SAW) devices with monolithic circuits because of their high acoustic velocity and piezoelectricity, as well as their passivation and insulating properties. Epitaxial growth techniques for AIN films with high crystallinity and a smooth surface are very important for these applications.