Y. Aota

Tohoku University, Japan

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Publications (9)2.13 Total impact

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    ABSTRACT: We discuss millimeter-wave film bulk acoustic resonator (FBAR) with very thin aluminium nitride (AlN) film fabricated using metal organic chemical vapor deposition (MOCVD) method. In previous works, we have successfully grown c-axis oriented AlN film using MOCVD method on Ru/Ta/SiO<sub>2</sub>/Si substrate. In this paper, we grew excellent orientation films of AlN and Ru electrodes in MOCVD, although their film thickness were very thin. Experimental results show that full width at half maximum (FWHM) is 1.3° at AlN thickness of 30 nm. In calculating analysis, when both top and bottom electrode thicknesses were 20 nm and AlN thickness was 30 nm, we obtained that resonant frequency was higher than 50 GHz. Therefore, FBAR is possible to apply to millimeter-wave bands devices, also contribute to small-size, low power consumption and low cost for millimeter-wave terminals.
    Ultrasonics Symposium (IUS), 2009 IEEE International; 10/2009
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    ABSTRACT: We have successfully fabricated 5 GHz band FBAR using aluminium nitride (AlN) film by metal organic chemical vapor deposition (MOCVD) method on SiO<sub>2</sub>/Si substrate. However, large spurious existed between resonant frequency and antiresonant frequency on admittance characteristics of prototype FBAR. We analyzed spurious vibration mechanism using three-dimensional (3-D) simulation. Spurious vibration mode was longitudinal thickness mode by simulation results. Therefore, we completely suppressed the spurious vibration by designing film thickness.
    Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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    ABSTRACT: Film bulk acoustic resonator (FBAR) was fabricated using AlN(0002) film. We achieved the high oriented AlN(0002) film through the metal-organic chemical vapor deposition (MOCVD) method on Ru/Ta bottom electrode. But thermal stress of AlN film was a problem in the high temperature MOCVD process over 1000degC. To reduce the thermal stress of AlN film, the low temperature AlN film growth was needed. We investigated the influence of H2 and N2 carrier gas in the MOCVD process to the AlN film quality. The full width at half maximum (FWHM) of the AlN(0002) using the N2 carrier gas was better than that of the H2 gas at the low temperature. Then the AlN cracks was reduced by the low temperature AlN growth. Furthermore, the FWHM of AlN(0002) using H2 and N2 gases at the MOCVD method were excellent value of under 1.5deg at less than 0.5 mum thickness.
    01/2008;
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    ABSTRACT: Film bulk acoustic resonator (FBAR) was fabricated using high oriented AlN(0002) film obtained through the metal-organic chemical vapor deposition (MOCVD) method. We used the Ru/Ta bottom electrode to improve the FBAR resonant characteristics because Ru has a high acoustic impedance and a hexagonal crystalline that is effective to obtaine the high oriented AlN(0002) film. The Ru/Ta electrode had good characteristics under 1100degC in points of the full width at half maximum (FWHM) of Ru(0002), the surface roughness and the electrode resistivity. The evaluated FWHM of AlN(0002) on Ru/Ta at 1050degC was exellent value of 1.2deg. The resonant frequency and anti-resonant frequency of the fabricated FBAR using the Ru/Ta bottom electrode were 5.217 GHz and 5.479 GHz, respectively. The resistance of the FBAR electrodes and of the series-resonance part in modified Butterworth Van Dyke (MBVD) equivalent circuit were improved to 4.3 Omega from 7.0 Omega and to 0.5 Omega from 3.0 Omega compared to the results of previous Mo bottom electrode, respectively. The effective electro-mechanical coupling coefficient (k<sub>eff</sub> <sup>2</sup>) of the fabricated FBAR was exellent value of 7.0 % and the evaluated Q<sub>r</sub> was 329. We successfully fabricated the FBAR with the small insertion loss and the large k<sub>eff</sub> <sup>2</sup> using the Ru/Ta bottom electrode and high oriented AlN(0002) film.
    Ultrasonics Symposium, 2007. IEEE; 12/2007
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    ABSTRACT: Film bulk acoustic resonator (FBAR) using AlN film was fabricated. Metal-organic chemical vapor deposition (MOCVD) was used to obtain high oriented AlN (0002) film. The unloaded Q factor (Qscrr) of fabricated FBAR was improved by reduction of Mo electrode resistance and optimization of cavity etching process. Since Mo nitridation degraded Mo resistance, reaction time between Mo and NH3 became shorter than conventional process to suppress the nitridation during AlN deposition. As a result, Mo resistance was improved to be 12.3 muOmegacm from 26.4 muOmegacm. In conventional process using Bosch process to fabricate cavities, insufficient etching selection ratio between Si/SiO2 of 200 brought incomplete structure of cavities. The etching selection ratio between Si/SiO2 was improved to be 650 by change of the etching process. The evaluated Qscrr of the fabricated FBAR was as high as 1557 at 3.698 GHz. We achieved the high Qscrr value FBAR using high oriented AlN (0002) film by the MOCVD method
    Proceedings of the IEEE Ultrasonics Symposium 01/2006;
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    ABSTRACT: Not Available
    Ultrasonics Symposium, 2005 IEEE; 10/2005
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    ABSTRACT: A high c-axis-oriented and atomically flat-surface aluminum nitride (AlN) film has been successfully deposited on a (0001)sapphire substrate by metalorganic chemical vapor deposition. We evaluated the dependences of surface roughness, tilted mosaicity and twisted mosaicity on the conditions of AlN deposition. It was found that the atomically flat-surface AlN film was deposited under the diffusion-limited area with suppression of vapor phase reaction at a substrate temperature of 1200°C and a V/III ratio of 800. It was also recognized that surface roughness was controlled by gas flow velocity, which is determined by both gas flow rate and pressure in reactor. Mean surface roughness (Ra) of the deposited AlN films was approximately 1 Å. The full width at half maximum of X-ray rocking curve for (0002) and (10\bar{1}2)AlN were approximately 100 and 2300 arcsec, respectively.
    Japanese Journal of Applied Physics 01/2005; 44:2987-2992. · 1.07 Impact Factor
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    ABSTRACT: We have investigated the surface acoustic wave (SAW) properties of atomically flat-surface (0001)aluminum nitride on a (0001)sapphire (AlN/alpha-Al2O3) combination. SAW propagated along [1\bar{2}10]AlN/[1\bar{1}00]alpha-Al2O3 and [10\bar{1}0]AlN/[11\bar{2}0]alpha-Al2O3. SAW velocity was measured to be approximately 1.0% higher than that of a conventionally calculated curve. The dispersion of SAW velocity as a function of normalized thickness (kH) was as low as 1.3%. The measured temperature coefficient of delay was 9 ppm/°C at kH values of 5.9 and 9.9. The propagation loss in the case of using an atomically flat-surface AlN film was lower by one order of magnitude than that using a conventional AlN film. The propagation loss at 5.172 GHz was measured to be 0.0053 dB/lambda.
    Japanese Journal of Applied Physics 01/2005; 44:4512-4515. · 1.07 Impact Factor
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    ABSTRACT: We fabricated a film-bulk-acoustic resonator with high c-axis oriented AlN film on Mo/SiO<sub>2</sub>/Si (100) using metalorganic chemical vapor deposition. The resonant frequency and anti-resonant frequency of the fabricated resonator were 3.189 GHz and 3.224 GHz, respectively. The quality factor and the effective electromechanical coupling coefficient were 24.7 and 2.65%, respectively. The conditions of AlN deposition were substrate temperature of 950°C, pressure of 20 torr, and V-III ratio of 25000. We have successfully grown high c-axis oriented AlN film with 4×10<sup>-5</sup> Ωcm resistivity of the Mo bottom electrode. The full width at half maximum (FWHM) of the AlN (0002) on Mo/SiO<sub>2</sub>/Si (100) and Mo/SiO<sub>2</sub>/Si (111) were 4° and 3.8°, respectively. The FWHM values of the deposited AlN film satisfy the RF band pass filter specification for GHz-band wireless local area network.
    Ultrasonics Symposium, 2004 IEEE; 09/2004