Thomas S. Hickernell

The elastic properties of thin-film silicon nitride

The elastic properties of thin-film silicon nitride (Si/sub 3/N/sub 4/) were investigated using surface-acoustic-wave (SAW) propagation data for plasma-enhanced chemical-vapor-deposition (PECVD) grown Si/sub 3/N/sub 4/ on gallium arsenide. For three films with thicknesses of 102 nm, 250 nm, and 497 nm, elastic constants were calculated from least-squares fits of theoretical dispersion curves to phase velocity data at different film thickness-to-wavelength ratios. The measured film density decreased from 2800 to 2500 kg/m/sup 3/ with increasing film thickness. Within this density range the longitudinal elastic modulus averaged near 1.83*10/sup 11/ N/m/sup 2/ and the shear elastic modulus decreased from 0.918*10/sup 11/ N/m/sup 2/ to 0.561*10/sup 11/ N/m/sup 2/ as the film density decreased. The elastic moduli of thin-film silicon nitride are comparable to those of Si/sub 3/N/sub 4/ ceramics at similar densities.<<ETX>>

The surface acoustic wave propagation characteristics of 64° Y-X LiNbO 3 and 36° Y-X LiTaO 3 substrates with thin-film SiO 2

The SAW characteristics of thin-film sputtered silicon dioxide (SiO/sub 2/) on substrates of 64/spl deg/ Y-X lithium niobate (LiNbO/sub 3/) and 36/spl deg/ Y-X lithium tantalate (LiTaO/sub 3/) have been measured in the frequency range from 30 MHz to above 1.0 GHz. Silicon dioxide films in the 500 nm to 2000 nm thickness range were deposited by RF diode sputtering. The SAW velocity, propagation loss, capacitance ratio (C/sub m//C/sub 0/), and temperature coefficient of frequency (TCF), were measured using thin-film aluminum interdigital electrodes patterned on the upper film surface. The presence of the SiO/sub 2/ initially stiffened the substrate surfaces before softening the surface with increasing thickness. The SAW propagation loss values showed a minimum at film-thickness to acoustic-wavelength ratios (t//spl lambda/) in the 0.02 to 0.08 region. The TCF improved but C/sub m//C/sub 0/ decreased with increasing t//spl lambda/ ratio.

Surface acoustic wave characterization of PECVD films on gallium arsenide

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given.<<ETX>>

The surface acoustic wave propagation characteristics of 41/spl deg/ lithium niobate with thin-film SiO/sub 2/

The surface acoustic wave (SAW) propagation properties of 41/spl deg/ Y-X lithium niobate (LiNbO/sub 3/) with SiO/sub 2/ film layers have been investigated using interdigital transducer structures. Different thicknesses of SiO/sub 2/ from 500 nm to 1500 nm were deposited on the 41/spl deg/ LiNbO/sub 3/ by RF diode sputtering from a glass target. An arrayed transducer pattern of aluminum interdigital transducer electrodes on the upper SiO/sub 2/ film surface facilitated the excitation of a wide frequency band of harmonic waves and permitted delineation of SAW velocity and propagation loss characteristics for several values of film-thickness to acoustic-wavelength (t//spl lambda/) ratio. With resonator patterns at the substrate/film interface, the capacitance ratio (C/sub m//C/sub 0/), related to coupling factor, and the temperature coefficient of frequency (TCF) were determined.

The elastic properties of PECVD silicon oxynitride films on gallium arsenide

The elastic constants of low-stress plasma-enhanced chemical vapor deposition (PECVD) grown silicon oxynitride on GaAs are calculated from surface acoustic wave (SAW) measurements. Films from 1000 to 4000 nm in thickness are shown to have very consistent densities and SAW velocity dispersion characteristics. The density of the films is below that of bulk fused quartz, but the elastic moduli are similar to those of fused quartz. The low density indicates that low-temperature PECVD silicon oxynitride is inherently porous compared to an equivalent bulk material.<<ETX>>

Surface acoustic wave propagation on piezoelectric substrates with thin-film PECVD silicon nitride

The SAW characteristics of thin-film silicon nitride (Si/sub 3/N/sub 4/) on piezoelectric substrates of Y-Z and 64/spl deg/ Y-X lithium niobate, and 36/spl deg/ Y-X lithium tantalate have been measured in the frequency range from 30 MHz to above 1.0 GHz. Silicon nitride films 250, 500, and 1000 nm thick were deposited by plasma enhanced chemical vapor deposition (PECVD). The SAW velocity and propagation loss properties were measured using linear arrays of thin-film aluminum interdigital electrodes patterned on the upper film surface. The elastic constants of the films could be determined by fitting a theoretical velocity dispersion curve to the measured velocities for Rayleigh wave propagation. The SAW propagation loss values for the films on the different substrates were compared to the loss characteristics without the film layers. Temperature coefficient of frequency (TCF) measurements of the SAW velocity characteristics for the various film/substrate combinations were also made. The results of these measurements, comparative data on acoustic constants, and the performance enhancements for SAW devices which could be realized by the use of silicon nitride on piezoelectric substrates are discussed.

The surface acoustic wave propagation characteristics of 64° Y-X LiNbO/sub 3/ and 36° Y-X LiTaO/sub 3/ substrates with thin-film SiO/sub 2/

The SAW characteristics of thin-film sputtered silicon dioxide (SiO/sub 2/) on substrates of 64/spl deg/ Y-X lithium niobate (LiNbO/sub 3/) and 36/spl deg/ Y-X lithium tantalate (LiTaO/sub 3/) have been measured in the frequency range from 30 MHz to above 1.0 GHz. Silicon dioxide films in the 500 nm to 2000 nm thickness range were deposited by RF diode sputtering. The SAW velocity, propagation loss, capacitance ratio (C/sub m//C/sub 0/), and temperature coefficient of frequency (TCF), were measured using thin-film aluminum interdigital electrodes patterned on the upper film surface. The presence of the SiO/sub 2/ initially stiffened the substrate surfaces before softening the surface with increasing thickness. The SAW propagation loss values showed a minimum at film-thickness to acoustic-wavelength ratios (t//spl lambda/) in the 0.02 to 0.08 region. The TCF improved but C/sub m//C/sub 0/ decreased with increasing t//spl lambda/ ratio.

P6H-9 Discerning the Quality of ZnO Films from Their Etch Properties

Several tests have been used over the years to determine the quality of thin film zinc oxide. These tests have included coupling factor measurement, acoustic and optical loss, surface roughness, and grain size. One such test, which is especially useful when establishing the best ZnO deposition condition, is chemical etching. Chemical etching reveals considerable information about the density of the fiber grain structure, the film orientation, film strain, and can be related to coupling factor. Etching ZnO films or crystals is highly anisotropic depending upon whether the acid attacks its zinc face, its oxygen face, or laterally to its c-axis orientation. By controlling the percentage of the acid etchant in water, direct comparisons can be made of the film properties under different deposition conditions. Etch times extend as low as 100 Angstroms per second for ZnO films with dense uniform fiber grains and as high as 1000 Angstroms per second for nonuniform grain structures. This paper will present the results of etching studies on micrometer thick ZnO under a triode system of deposition which can produce very high quality films. Taking into account the etch rates and the etch pit density. Both can be used to predict the quality of the ZnO films for applications.

The dependencies of SAW-transducer equivalent-circuit-model parameters on transducer geometry

A new equivalent-circuit (EC) model for SAW transducers has been developed which incorporates the measured dependencies of model parameters on the number of transducer electrode pairs, N, and the acoustic aperture. W. Three EC parameters that relate the transducer geometry to the circuit-model elements are the electrode-pair capacitance per unit length, C/sub e/, the capacitance ratio, r, and the resonant velocity, V/sub r/, which is proportional to the velocity of the SAW. For conventional transducer EC models these parameters are independent of N and W. Parameter values were extracted from RF waveguide-probe measurements of an array of SAW transducers with resonant frequencies near 900 MHz fabricated on 64/spl deg/ Y-cut X-propagating lithium niobate. The transducers had numbers of electrode pairs ranging from 50 to 150, acoustic apertures ranging from 5 to 20 wavelengths, and bus-bar heights ranging from 5 to 15 wavelengths. Even with a fixed electrode width-to-pitch ratio and thickness-to-wavelength ratio, results showed approximately 25% variation in C/sub e/, 50% variation in r, and 0.4% variation in V/sub r/ due to the variations in N and W. The parameters varied little with bus-bar height. The measured and computer-simulated responses of a SAW ladder filter designed for a GSM receiver application at 947 MHz were compared. The new model which accounts for geometrical variations in the EC parameters shows an improvement in accuracy over previous models.

The surface acoustic wave propagation characteristics of 64/spl deg/ Y-X LiNbO/sub 3/ and 36/spl deg/ Y-X LiTaO/sub 3/ substrates with thin-film SiO/sub 2/

The SAW characteristics of thin-film sputtered silicon dioxide (SiO/sub 2/) on substrates of 64/spl deg/ Y-X lithium niobate (LiNbO/sub 3/) and 36/spl deg/ Y-X lithium tantalate (LiTaO/sub 3/) have been measured in the frequency range from 30 MHz to above 1.0 GHz. Silicon dioxide films in the 500 nm to 2000 nm thickness range were deposited by RF diode sputtering. The SAW velocity, propagation loss, capacitance ratio (C/sub m//C/sub 0/), and temperature coefficient of frequency (TCF), were measured using thin-film aluminum interdigital electrodes patterned on the upper film surface. The presence of the SiO/sub 2/ initially stiffened the substrate surfaces before softening the surface with increasing thickness. The SAW propagation loss values showed a minimum at film-thickness to acoustic-wavelength ratios (t//spl lambda/) in the 0.02 to 0.08 region. The TCF improved but C/sub m//C/sub 0/ decreased with increasing t//spl lambda/ ratio.