Coating processes – Electrical product produced – Piezoelectric properties
Reexamination Certificate
2002-10-07
2004-04-06
Barr, Michael (Department: 1762)
Coating processes
Electrical product produced
Piezoelectric properties
C427S255280, C427S596000, C204S192100
Reexamination Certificate
active
06716479
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the use of Mg
x
Zn
1-x
O based materials and structures for acoustic devices, and more particularly, to the tailoring of the piezoelectric properties to achieve flexibility in the Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) design and fabrication for applications in telecommunications and various sensors.
BACKGROUND OF THE INVENTION
Currently, several technologies exist that provide modifying the piezoelectric properties in ZnO based multilayer structures. Theoretical analysis was reported for multilayers of two different materials (see E. K. Sittig “Transmission Parameters of Thickness-Driven Piezoelectric Transducers Arranged in Multilayer Configurations”,
IEEE Trans. SU
, SU-14 (4), 167, October 1967), and for off-axis ZnO multilayers (see E. Akcakaya, E. L. Adler, G. W. Farnell, “Apodization of Multilayer Bulk-Wave Transducers”,
IEEE Trans. UFFC,
36(6), 628, November 1989 and E. Akcakaya, E. L. Adler, G. W. Farnell, “Anisotropic Superlattice Transducers: Characteristics and Models”,
Proc. IEEE
1988
International Ultrasonics Symposium,
333, 1988). E. K. Sittig shows individual transducers consisting of multiplicity of piezoelectrically active layers electrically connected with conductive or non-conductive layers of different characteristics acoustic impedances. Akcakaya et al discloses calculating electromechanical characteristics of transducers consisting of multilayers of ZnO with alternating crystal orientation. BAW thin film resonators (TFRs) using sputter deposited off-axis ZnO multilayers with alternating crystal structure were demonstrated by J. S. Wang, K. M. Lakin, (“Sputtered C-axis Inclined ZnO Films for Shear Wave Resonators”,
Proc. IEEE
1982
International Ultrasonics Symposium,
480, 1982) and by B. Hadimioglu, L. J. La Comb, Jr., L. C. Goddard, B. T. Khuri-Yajub, C. F. Quate, E. L. Ginzton, (“Multilayer ZnO Acoustic Transducers at Millimeter-Wave Frequencies”,
Proc. IEEE
1987
International Ultrasonics Symposium,
717, 1987.) BAW TFRs using alternating multilayers of ZnO and non-piezoelectric materials were demonstrated by W. S. Hu, Z. G. Liu, R. X. Wu, Y. F. Chen, W. Ji, T. Yu, D. Feng, (“Preparation of Piezoelectric-Coefficient Modulated Multilayer Film ZnO/Al
2
O
3
and its Ultrahigh Frequency Response”,
Appl. Phys. Lett.,
71(4), p. 548, July 1997). Piezoelectric property tailoring in the ternary compound Al
x
Ga
1-x
N, was demonstrated by C. Deger, E. Born, H. Angerer, O. Ambacher, M. Stutzmann, J. Hornsteiner, E. Riha, G. Fischerauer, (“Sound velocity of Al
x
Ga
1-x
N thin films obtained by surface acoustic wave measurements”,
Appl. Phys. Lett.,
72(19), p. 2400, May 1998). Deger et al shows determining SAW and BAW velocities in Al
x
Ga
1-x
N thin films by tailoring the piezoelectric properties of Al
x
Ga
1-x
N films. Y. F. Chen, S. N. Zhu, Y. Y. Zhu, N. B. Ming, B. B. Jin, R. X. Wu, “High-frequency Resonance in Acoustic Superlattice of Periodically Poled LiTaO
3
”, Appl. Phys. Lett.,
70(5), 592, February 1997 and H. Gnewuch, N. K. Zayer, C. N. Pannell, “Crossed-Field Excitation of an Acoustic Superlattice with Matched Boundaries: Theory and Experiment”,
IEEE Trans, UFFC,
47(6), 1619, November 2000 describe a piezoelectric property tailoring method suitable only for those piezoelectric materials which are also ferroelectric materials facilitating construction of acoustic superlattice (ASL) and optic superlattice (OSL) devices.
Piezoelectric ZnO thin films have been used for multilayer SAW and BAW devices due to the high electromechanical coupling coefficients (see F. Moeller, T. Vandahl, D. C. Malocha, N. Schwesinger, W. Buff, “Properties of thick ZnO layers on oxidized silicon”,
Proc.
1994
IEEE Int. Ultrasonics Symp.
, pp. 403-406; Kim, Hunt, Hickernell, Higgins, Jen, “ZnO Films on {011}-Cut<110>-Propagating GaAs Substrates for Surface Acoustic Wave Device Applications”,
IEEE Trans. Ultrasonics, Ferroelectrics and Frequency Control
, v. 42, no3, pp. 351-361, May 1995; H. Ieki, H. Tanaka, J. Koike, T. Nishikawa, “Microwave Low Insertion Loss SAW Filter by Using ZnO/Sapphire Substrate with Ni Dopant”, 1996
IEEE MTT
-
S Digest
, pp. 409-412; and H. Nakahata, H. Kitabayashi, S. Fujii, K. Higaki, K. Tanabe, Y. Seki, S. Shikata, “Fabrication of 2.5 GHz Retiming Filter with SiO
2
/ZnO/Diamond Structure”,
Proc.
1996
IEEE Int. Ultrasonics Symp.
, pp. 285-288). Recently, the ternary compound magnesium zinc oxide (Mg
x
Zn
1-x
O), formed by alloying ZnO with MgO, has attracted increasing interest for UV optoelectronic applications (see A. Ohtomo, M. Kawasaki, T. Koida, K. Masubuchi, H. Koinuma, Y. Sakurai, Y. Yoshida, T. Yasuda, Y. Segawa, “Mg
x
Zn
1-x
O as a II-VI widegap semiconductor alloy”,
Appl. Phys. Lett.
, vol. 72, n. 19, pp. 2466-2468, May 11, 1998; A. K. Sharma, J. Narayan, J. F. Muth, C. W. Teng, C. Jin, A. Kvit, R. M. Kolbas, O. W. Holland, “Optical and structural properties of epitaxial Mg
x
Zn
1-x
O alloys”,
Appl. Phys. Lett.
, vol. 75, n.21, pp. 3327-3329; and T. Minemoto, T. Negami, S. Nishiwaki, H. Takakura, Y. Hamakawa, “Preparation of Zn
1-x
Mg
x
O films by radio frequency magnetron sputtering”,
Thin Solid Films
, vo. 372, pp. 173-176, Sep. 1, 2000). Its energy bandgap can be extended from 3.3 eV (ZnO) to 4.05 eV (Mg
0.35
Zn
0 65
O). Although the solid solubility limit of MgO in ZnO is less than 5% in equilibrium conditions, a higher range of Mg composition can be achieved using non-equilibrium growth methods.
Currently, the ZnO film thickness and the dimensions of the devices (such as SAW filters) were the only parameters available for modification, limiting the design flexibility, as well as the processing latitude. It would be useful to provide a SAW or a BAW device in which their characteristics can be tuned using other parameters.
SUMMARY OF THE INVENTION
The present invention provides a method of controlling piezoelectric properties in various acoustic devices. The method involves using Mg
x
Zn
1-x
O film as a new piezoelectric material and adjusting Mg mole percent in the Mg
x
Zn
1-x
O film to tailor piezoelectric properties in the Mg
x
Zn
1-x
O film. Similarly, the method further involves using Mg
x
Zn
1-x
O/ZnO as a new piezoelectric multilayer structure and adjusting Mg mole percent in the Mg
x
Zn
1-x
O to tailor piezoelectric properties in the acoustic devices. Thus, the piezoelectric properties in ZnO based devices can be tailored by using Mg
x
Zn
1-x
O/ZnO multiplayer structures as well as by using Mg
x
Zn
1-x
O single layer with controlled Mg composition.
In addition to being piezoelectric, both ZnO and Mg
x
Zn
1-x
O are wide-bandgap semiconductors. Thus piezoelectric and semiconductor devices can be integrated on the same material system. This leads to new classes of devices with integrated features and tunability.
REFERENCES:
patent: 6593679 (2003-07-01), Higuchi et al.
Emanetoglu et al., “MgxZn1-xO: A New Piezoelectric Material”, 2001 IEEE Ultrasonics Symposium, Oct. 7, 2001, pp. 253-256.*
Emanetoglu, et al. “Analysis of SAW Properties of Epitaxial ZnO Films Grown on R-Al2O3Substrates ”. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 48, No. 5, Sep. 2001, pp. 1389-1394.
Wu, et al. “Temperature Compensation of SAW in ZnO/SiO2/Si Structure”. 2001 IEEE Ultrasonics Symposium, pp. 211-214.
Gorla, et al. “Structural, optical, and surface acoustic wave properties of epitaxial ZnO films grown on (0112) sapphire by metalorganic chemical vapor deposition”. Journal of Applied Physics, vol. 85, No. 5, Mar. 1, 1999, pp. 2595-2602.
Muthukumar, et al. “Control of morphology and orientation of ZnO thin films grown on SiO2/Si substrates”. Journal of Crystal Growth 225 (2001), pp. 197-201.
Emanetoglu, et al. “MgxZn1-xO: A New Piezoelectric Material”. 2001 IEEE Ultrasonics Symposium, pp. 253-256.
Zhu, et al. “A Multi-IDT Input Tunable Surface Acoustic Wave Filter”. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 48, No. 5, Sep. 2001, pp. 1383-1388.
Wittstruck, et al. “Analysis of B
Emanetoglu Nuri William
Lu Yicheng
Barr Michael
Hoffmann & Baron , LLP
Rutgers The State University of New Jersey
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