GB2181917A

GB2181917A - Surface acoustic wave device

Info

Publication number: GB2181917A
Application number: GB08624225A
Authority: GB
Inventors: Nobuo Mikoshiba; Kazuo Tsubouchi; Kazuyoshi Sugai
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-11
Filing date: 1986-10-09
Publication date: 1987-04-29
Also published as: GB8624225D0; GB2181917B

Abstract

A SAW device comprises an elastic silicon single-crystal substrate 11 having a major surface with a given crystal orientation and having a positive delay time temperature co- efficient, an AIN film 12 deposited on the elastic substrate so that piezoelectric axis of the AIN film is perpendicular or parallel to the major surface of the elastic substrate, and electrodes 13-14 provided on the AIN film or between the elastic substrate and the AIN film. <IMAGE>

Description

SPECIFICATION Surface acoustic wave device This invention relates to a surface acoustic wave device.

Known surface acoustic wave devices have substrates of the following forms: 1. A single structure consisting of only a piezoelectric substrate (piezoelectric singlecrystal substrate, piezoelectric ceramic substrate, etc.) 2. A laminated structure comprising a piezoelectric film deposited on a non-piezoelectric substrate.

3. A laminated structure comprising a piezoelectric film deposited on a semiconductive substrate; and others.

A known structure of the second type above comprises a sapphire substrate or a glass substrate with a zinc oxide film (ZnO) deposited thereon by sputtering.

However, a zinc oxide film has the following drawbacks: 1. It is difficult to obtain a good quality film whereby the devices are often inferior in piezoelectricity, etc.

2. Propagation loss of a surface acoustic wave is large in the high frequency range.

3. Dispersion of the propagation characteristic of the surface acoustic wave is large.

4. It is difficult to control variation of the delay time temperature coefficient (1/r).(Dr/T) of the delay time (T) of the surface acoustic wave depending on variation of temperature (T is ambient temperature).

According to this invention there is provided a surface acoustic wave device comprising an elastic substrate; an aluminum nitride (AIN) film deposited on said substrate; and electrodes for converting an electric signal to a surface acoustic wave and vice versa, said substrate having a positive delay time temperature coefficient to a surface acoustic wave, and said aluminum nitride film having an orientation of the piezoelectric axis thereof such that its delay time temperature coefficient to the surface acoustic wave is negative.

This invention will now be described by way of examplse with reference to the drawings, in which: Figure 1 is a sectional view through a device according to the invention; Figures 2 to 10 show the characteristics obtained with the device of Fig. 1; Figures 11 to 14 are sectional views through further devices according to the invention; Figures 15A, 15B, 16A to 16D and 17A to 17F show the characteristics obtained with the devices of Figs. 11 to 14; Figures 18 to 2 1 are sectional views through further devices according to the invention; Figures 22A, 22B, 23A, 23B, 24A and 24B show characteristics obtained with the devices of Figs. 18 to 21; and Figure 25 is a block diagram of a MO-CVD (metal organic-chemical vapor deposition) system for expitaxial processing.

Fig. 1 is a sectional view through a surface acoustic wave device according to the present invention. Reference numeral 1 designates a sapphire substrate having a major surface (Csurface) which is substantially the (0001)-crystal-surface. Reference numeral 2 denotes an AIN film which is deposited on the sapphire substrate 1 so that the piezoelectric axis (Caxis or [0001]-axis) of the film is perpendicular or parallel to the surface of the sapphire substrate 1. Reference numerals 3 and 4 denote comb-shaped electrodes for generating a surface acoustic wave and comb-shaped electrodes for detecting the surface acoustic wave, respectively, and reference symbol H indicates the thickness of the AIN film 2.

First there will be described a device in which the major surface of the sapphire substrate 1 is the (0001)-crystal-surface, and the AIN film 2 is deposited so that the C-axis thereof is perpendicular to the surface of the sapphire substrate 1. A surface acoustic wave is made to propagate in the perpendicular direction to the piezoelectric axis (C-axis) of the Aln film 2 and in the direction eqivalent to the [1 100]-axis (Y-axis) on the (0001)-surface of the sapphire substrate 1.

Fig. 2 shows a velocity dispersion characteristic for the surface acoustic wave which is obtained in such device. In this figure, the abscissa is normalized thickness 27sH/A (A is the wavelength of the surface acoustic wave) when the thickness of the AIN film 2 is H, while the ordinate is the phase velocity Vp of the surface acoustic wave. The phase velocity does not disperse much but is very large.

Fig. 3 shows a characteristic curve of the electromechanical coupling coefficient which is obtained with such device. The abscissa is the normalized thickness 2H/A, while the ordinate is the electromechanical coupling coefficient K2. When the normalized thickness 2H/A is 2.0 to 6.0, K2 is 0.22% to 0.27%. This value is in general suitable for generation and detection of a surface acoustic wave, and leads to excellent piezoelectricity.

Fig. 4 shows a characteristic curve of the delay time temperature coefficient (TCD) for a surface acoustic wave which is obtained with such device. The abscissa is the normalized thickness 27lH/A while the ordinate shows the coefficient (1/.(T/JT) in ppm/ C unit. Since the delay time temperature coefficient of the sapphire substrate 1 is positive while that of the AIN film 2 is negative, the two temperature coefficients compensate each other, and the resulting characteristic varies in accordance with the thickness H of the AIN film 2.

When the thickness H is in the range to satisfy the relation 3.02H/A < 5.0, delay time temperature coefficient approaches zero.

The first device, therefore, is excellent in its delay time temperature coefficient characteristic as well as velocity dispersion characteristic and K2 characteristic.

A second device will now be described, which is different from the first device merely in that the surface acoustic wave is a made to propagate in the direction equivalent to the [1120]-axis (X-axis) on the (0001)-surface of the sapphire substrate instead of the direction equivalent to [1100]-axis (Y-axis).

Fig. 5 shows a velocity dispersion characteristic for the surface acoustic wave which is obtained with the second device. Phase velocity V,p does not disperse much but is very large.

Fig. 6 shows a characteristic curve of the electromechanical coupling coefficient (K2 characteristic) which is obtained with the second device. When the normalized thickness is 2.0 to 8.0, K2 is 0.2% to 0.28%. This value is in general suitable for generation and detection of a surface acoustic wave, and leads to excellent piezoelectricity.

Fig. 7 shows a characteristic curve of the delay time temperature coefficient (TCD) for the surface acoustic wave which is obtained with the second device. When the thickness H of the AIN film 2 is in the range to satisfy the relation 3.0t27cHlt6.0, the delay time temperature coefficient approaches zero.

The second device, therefore, is excellent in delay time temperature coefficient characteristic as well as velocity dispersion characteristic and K2 characteristic.

A third device will now be described wherein the sapphire substrate 1 is cut by Rsurface which is substantially the (0112)-crystal-surface, and the AIN film 2 is deposited so that the C-axis thereof is parallel to the [0111 ]-axis of the sapphire substrate 1. A surface acoustic wave is made to propagate in the direction parallel to the piezoelectric axis (C-axis) of the AIN film 2 and in the direction which is substantially the [Olll]-axis on the (0112)-surface (R-surface) of the sapphire substrate 1.

Fig. 8 shows a velocity dispersion characteristic of a surface acoustic wave which is obtained with the third device. Phase velocity Vp does not disperse much but is very large.

Fig. 9 shows a characteristic curve of the electromechanical coupling coefficient which is obtained with the third device. When the normalized thickness 27rH/A is 1.0 to 8.0, K2 is 0.75% to 0.8%. This value is in general suitable for generation and detection of a surface acoustic wave, and leads to excellent piezoelectricity.

Fig. 10 shows a characteristic curve of the delay time temperature coefficient (TCD) of a surface acoustic wave which is obtained with the third device. When the thickness H of the AIN film 2 is in the range to satisfy the relation 2.0 < 71H/A5.0, the delay time temperature coefficient approaches zero.

The third device, therefore, is excellent in its delay time temperature coefficient characteristic as well as velocity dispersion characteristic and K2 characteristic.

Figs. 11 to 14 show further embodiments of the present invention wherein a silicon single-crystal substrate having a positive delay time temperature coefficient to a surface acoustic wave is used as the elastic substrate.

In the embodiment of Fig. 11, reference numeral 11 designates a silicon single-crystal substrate which has a major surface which is substantially the (111)-crystal-surface, (110)crystal-surface or (001)-crystal-surface. Reference number 12 denotes an AIN film which is deposited on the silicon single-crystal substrate 11 so that the piezoelectric axis (C-axis or [0001]-axis) of the film is perpendicular or parallel to the silicon single-crystal substrate 11. Reference numerals 13 and 14 denote comb-shaped electrodes for generating a surface acoustic wave and comb-shaped electrodes for detecting the surface wave, respectively. Reference symbol H is the thickness of the AIN film 12.

Fig. 15A shows velocity dispersion characteristics which are obtained when the devices of Figs. 11 to 14 are used and a surface acoustic wave propagates in the direction perpendicular to the piezoelectric axis (C-axis or [0001]-axis) of the AIN film 12. In Fig. 11, the abscissa is normalized thickness 27rH/A while the ordinate is the phase velocity Vp of the surface acoustic wave.Curve (a) is obtained when the surface acoustic wave propagates in the direction which is substantially the [112]axis on the (111)-surface of the silicon singlecrystal substrate 11, curve (b) is obtained when the surface acoustic wave propagates in the direction which is substantially the [001]axis on the (110)-surface of the silicon singlecrystal substrate 11, and curve (c) is obtained when the surface acoustic wave propagates in the direction which is substantially the [011]axis on the (100)-surface of the silicon single: crystal substrate 11. As is apparent from the drawing, the phase velocity Vp does not disperse much but is very large.

Fig. 16A shows characteristic curves of electromechanical coupling coefficients which are obtained with the same devices. The abscissa is the normalized thickness 2nH/1 while the ordinate is the electromechanical coupling coefficient K2. In this figure, device A has the structure of Fig. 11. These curves show that electromechanical coupling coefficients K2 suitable for generation and detection of surface acoustic waves and excellent piezoelectricities can be obtained.

Fig. 1 7A to 1 7D show characteristic curves of delay time temperature coefficients (TCD) which are obtained with the same devices.

The abscissa is the normalized thickness 27rH/R while the ordinate shows the delay time temperature coefficient (1 /T).(T/) in ppm/ C units. The curve of Fig. 1 7A is obtained when the surface acoustic wave progagates in the direction which is substantially the [112]-axis on the (111)-surface of the silicon single-crystal substrate 11; the curve of Fig. 17B is obtained when the surface acoustic wave propagates in the direction which is substantially the [001]-axis of the (1 10)-sur- face; the curve of Fig. 1 7C is obtained when the surface acoustic wave propagates in the direction which is substantially the [100]-axis on the (001)-surface; and the curve of Fig.

1 7D is obtained when the surface acoustic wave propagates in the direction which is substantially the (110)-axis on the (001)-surface.

Since the delay time temperature coefficient of the silicon single-crystal substrate 11 is positive while that of the AIN film 12 is negative, the two temperature coefficients compensate each other, and the resulting characteristic varies in accordance the thickness H of the AIN film 12. The thickness H may be determined so that the delay time temperature coefficient approaches zero.

Fig. 15B shows velocity dispersion characteristics of a surface acoustic wave which are obtained when the surface acoustic wave propagates in the direction parallel to the piezoelectric axis (C-axis or [0001]-axis). The curve (d) is obtained when the surface acoustic wave propagates in the direction whcih is substantially the [001]-axis on the (100)-surface of the silicon single-crystal substrate 11 while the curve (e) is obtained when the surface acoustic wave propagates in the direction which is substantially the [001]-axis on the (110)-surface of the silicon single-crystal substrate 11. The phase velocity Vp does not disperse much and is very large.

Figs. 16C and 16D show characteristic curves of the electromechanical coupling coefficient which are obtained with the same device and with the same propagating directions.

Device A has the structure of Fig. 11. The curve of Fig. 16C is obtained when the surface acoustic wave propagates in the direction which is substantially the [001]-axis on the (110)-surface of the silicon single-crystal substrate 11, while the curve of Fig. 1 6D is obtained when the surface acoustic wave propagates in the direction which is substantially the [001]-axis on the (100)-surface of the substrate 11. These figures show that electromechanical coupling coefficients K2 suitable for generation and detection of surface acoustic waves and excellent piezoelectricities can be obtained.

Figs. 17E and 17F show delay time temperature coefficients (TCD) of a surface acoustic wave under the same conditions. The curve of Fig. 1 7E is obtained when the surface acoustic wave propagates in the direction which is substantially the [100]-axis on the (001)-surface of the silicon single-crystal substrate 11, while the curve of Fig. 1 7F is obtained when the surface acoutic wave propagates in the direction which is substantially the [001]-axis on the (110)-surface of the substrate 11. As understood from Figs. 1 7A to 17f, when the thickness H of the AIN film 12 in the range to satisfy the relation 0.2 < 27lH/23.0, the delay time temperature coefficient approaches zero.

An AIN film thickness in the range 0.2 < 27rH/A < 2.5 on a (111)-oriented silicon substrate, a thickness in the range of lt2nHIIZt3 on a (110)-oriented silicon substrate and a thickness in the range of lt2aHllt2 on a (001)-oriented silicon substrate are preferable.

The embodiment of Fig. 12 has a structure comprising a silicon single-crystal silicon substrate 11, SAW generating electrodes 13, and SAW detecting electrodes 14, provided on the surface of the substrate 11, and on AIN film 12 deposited on the substrate 11 so as to cover the electrodes 13 and 14.

The embodiment of Fig. 13 has a structure comprising a silicon single-crystal substrate 11, a pair of screen electrodes 17 provided on the substrate 11 to serve as second electodes, an AIN film 12 provided on the substrate 11 so as to cover the screen electrodes 17, and SAW generating electrodes 13 and SAW detecting electrodes 14 provided on the AIN film 12.

The embodiment of Fig. 14 has a structure comprising a silicon single-crystal substrate 11, SAW generating electrodes 13 and SAW detecting electrodes 14 provided on the surface of the substrate 11 to serve as first electrodes, an AIN film 12 provided on the substrate 11 so as to cover the electrodes 13 and 14, and a pair of screen electrodes 17 provided on the AIN film 12.

Figs. 16A and 16B show K2 characteristics which are obtained when a surface acoustic wave propagates in the direction perpendicular to the piezoelectric axis of the AIN film 12 in devices with the structures of Figs. 12 to 14.

In these figures, device B corresponds to Fig.

12, device C to Fig. 13 and device D to Fig.

14, respectively. These Figures show that electromechanical coefficients K2 suitable for generation and detection of a surface acoustic wave and excellent piezoelectricities can be obtained.

Figs. 1 6C and 1 6D show K2 characteristics which are obtained when a surface acoustic wave propagates in the direction parallel to the piezoelectric axis of the AIN film 12 in devices as shown in Figs. 12 to 14. The curve of Fig. 16C is obtained when a surface acoustic wave propagates in the direction which is substantially the (001)-axis on the (110)-surface of the substrate 11, while the curve of Fig 16D is obtained when a surface acoustic wave propagates in the direction which is substantially the [100]-axis on the (001)-surface of the substrate 11. These figures show that electromechanical coupling coefficients K2 suitable for generation and detection of a surface acoustic wave and excellent piezoelectricities can be obtained.

As apparent from Figs. 1 6A to 16D, when the normalized thickness 2nH/ is in the range from 0.2 to 6.0, K2 values suitable for practical use and excellent piezoelectricities can be obtained.

The AIN film may be an AIN single-crystal epitaxial film. In this case, the surface acoustic wave device can be made by the system as shown in Fig. 25.

Fig. 25 is a block diagram of a MO-CVD (metal organic-chemical vapor deposition) system for epitaxial processing. Reference numeral 31 designates a standing-type reaction tube in which a silicon single-crystal substrate 32 to be processed is put on a rotatable support plate 3. Reference numeral 34 is a hydrogen (H2) gas source, 35 is an ammonia (NH3) gas source, 36 is a source of an aluminium compound which may be trimethylaluminium (TMA, Al(CH3)3: liquid at ordinary temperature), for example, 37A and 37B are pipes, 38 is a valve, 39 is a flowmeter, 40 is a purifier, 41 is a high-frequency coil, 42 is a vacuum suction pipe, and 43 is a discharge pipe.

While rotating the silicon single-crystal substrate 32 within the stand-type reaction tube 31 by the rotatable support plate 33 and applying heat to the substrate 32 by the highfrequency coil 41, trimethylaluminium which is bubbled by hydrogen gas is supplied to the reaction tube 31 through the pipe 37A, and ammonia gas is supplied to the reaction tube 31 through the pipe 37B. Trimethylaluminium and ammonia react on each other within the reaction tube 31, resulting in formation and epitaxial growth of AIN film on the silicon single-crystal substrate 32.

A film growth velocity of 3pm/h for the AIN film was obtained under the following epitaxial processing conditions:heat applied to the silicon single-crystal substrate 32: 1,260"C; hydrogen gas flow: SQImin; ammonia gas flow: 3Q/min; and trimethylaluminium flow: 13.6x10-6 moQ/min. Further, silicon single-crystal substrates with (111)-crystal-surface, (110)-crystal-surface and (100)-crystal-surface, (100)-crystal-surface, respectively, are used and are processed in the same manner. As the result, in each case, the AIN film grew into (0001)-crystal-surface.

Figs. 18 to 21 show still further devices according to the present invention wherein an SOS (silicon-on-sapphire) substrate is used as the elastic substrate with a positive delay time temperature coefficient to a surface acoustic wave.

In Fig. 18, reference numer 21 designates an SOS substrate which comprises a sapphire substrate 25 and a silicon film 26 deposited on the sapphire substrate 25. Reference numeral 22 denotes an AIN film which is deposited on the SOS substrate 21 so that the piezoelectric axis (C-axis or [0001]-axis) of the film is perpendicular or parallel to the surface of the SOS substrate 21. Reference numeral 23 and 24 denote comb-shaped electrodes for generation of a surface acoustic wave and comb-shaped electrodes for detection of the surface acoustic wave, both provided on the surface of the AIN film 22. H is the thickness of the AIN film 22, and T is the thickness of the silicon film 26.

Fig. 22A shows a velocity dispersion characteristic to a surface acoustic wave which is obtained when using the device of Fig. 18, and having the surface acoustic wave propagate in the direction perpendicular to the pie electric axis (C-axis or [0001]-axis) of the AIN film 22. The abscissa is normalized thickness 27rH/A while the ordinate is the phase velocity Vp of the surface acoustic wave. As apparent from this figure, the phase velocity Vp does not disperse much and is very large.

Fig. 23A shows a characteristic curve of the electromechanical coefficient which is obtained under the same conditions. The abscissa is normalized thickness 27rH/A while the ordinate is electromechanical coupling coefficient K2.

Device A corresponds to the structure of Fig.

18. When the normalized thickness 2xH/A is near 3.0, the value of K2 is 0.39% approximately. This value is suitable for the generation and detection of surface acoustic waves.

Fig. 24A shows characteristic curves of delay time temperature coefficient (TCD) for a surface acoustic wave which is obtained under the same conditions. The abscissa is normalized thickness 2n H/l while the ordinate shows delay time temperature coefficient (1/l).(bT/bT) in ppm/ C units. Since the delay time temperature coefficient of the SOS substrate 21 is positive while that of the AIN film 22 is negative, the time temperature coefficients compensate each other and the resulting characteristic varies in accordance with the thickness H of the AIN film 22. When the thickness H is determined to satisfy the relation 1.0 < 27sH/A4.0, the delay time temperature coefficient approaches zero.

Fig. 22B shows a velocity dispersion characteristic of a surface acoustic wave which is obtained when using the device of Fig. 18, and having a surface acoustic wave propagate in the direction parallel to the piezoelectric axis (C-axis or [0001]-axis) of the AIN film 22.

As apparent from this figure, the phase velocity Vp does not disperse much and is very large.

Fig. 23B shows characteristic curves of electromechanical coupling coefficient which is obtained under the same conditions. The curve A is the characteristic of the device of Fig. 18. When the normalized thickness is near 2.9, K2 is 0.88% approximately. This value is suitable for generation and detection of a surface acoustic wave.

Fig. 24B shows a characteristic curve of delay time temperature coefficient (TCD) for a surface acoustic wave which is obtained by the same conditions. When the tickness H of the AIN film 22 is determined to satisfy the relation 1 .0 < 2nH/ < 4.0, the delay time temperature coefficient approaches zero.

The embodiment of Fig. 19 has a structure wherein the SAW generating electrodes 23 and the SAW detecting electroes 24 are provided on the surface of the SOS substrate 21 and the AIN film 22 is thereafter deposited on the SOS substrate 21 so as to cover the electrodes 23 and 24.

In the embodiment of Fig. 20, a pair of screen electrodes 27 to serve as second electrodes are provided on parts of the surface of the SOS substrate 21, the AIN film 22 is thereafter provided on the substrate 21 so as to cover the screen electrodes 27, and the SAW generating electrodes 23 and the SAW detecting electrodes 24 are provided on the AIN film 22.

In the embodiment of Fig. 21, the SAW generating electrodes 23 and the SAW detecting electrodes 24 are provided on the surface of the SOS substrate 21. The AIN film 22 is thereafter deposited on the substrate 21 so as to cover the electrodes 23 and 24. The pair of screen electrodes 27 are provided on the surface of the AIN film 22.

When the devices of Figs. 19 to 21 are used and surface acoustic wave propagates in the direction perpendicular to the piezoelectric axis of the AIN film 22, the velocity dispersion characteristics obtained are substantially the same as that of Fig. 22A, and the delay time temperature coefficients (TCD) are substantially the same as that of Fig. 24A. Further, K2 characteristics are shown in Fig. 23A in which device B corresponds to the structure of Fig.

19, device C to Fig. 20, and device D to Fig.

21, respectively. In the case of device B, when the normalized thickness 27rH/A is near 3.1., K2 represents a double peak characteristic of 0.35%. In the case of device 3, when the normalized thickness 27rH/A is 0.27 and 3.6, K2 reaches two peaks of 0.27% and 0.45%, respectively. These values are suitable for generation and detection of a surface acoustic wave.

When the devices of Figs. 19 to 21 are used and a surface acoustic wave propagates in the direction parallel to the piezoelectric axis of the AIN film 22, the velocity dispersion characteristics obtained are substantially the same as that of Fig. 22B, and the delay time temperature coefficients (TCD) are substantially the same as that of Fig. 24B. K2 characteristics which are obtained under the same conditions are shown in Fig. 23B wherein device B corresponds to the structure of Fig. 19, device C to Fig. 20 and device D to Fig. 21, respectively. In the case of device B, when the normalized thickness 27rH/A is 0.4 and 2.9, K2 reaches the peaks 0.15% and 0.62% respectively.In the case of device C, when the normalized thickness 2z H/A is near 1.9, K2 is 0.97%, and in the case of D, when the normalized thickness 27rH/R is near 2.8, K2 is 0.7%. These values are suitable for generation and detection of surface acoustic wave.

As shown in Figs. 23A and 23B, by selecting a normalized thickness 27rH/R of 0. 1 to 6.0, it is possible to obtain K2 values suitable for practical use and excellent piezoelectricities.

Since the AIN film has a large energy gap of 6.2 eV and may easily be designed to have a specific resistance larger than 1016Q cm, it is excellent in insulation.

Further, the AIN film is superior to zinc oxide film which is made by sputtering, because film with an even and constant quality can be obtained. This makes it possible to maintain the propagation loss small even in the high frequency band.

Particularly because the delay time temperature coefficient for the surface acoustic wave, of the AIN film is negative, when it is deposited on a substrate such as a sapphire substrate whose delay time temperature coefficient is in turn positive, the two temperature coefficients compensate each other, and the resulting characteristic is stable to variation of temperature. Stability of the surface acoustic wave device against a temperature variation is the most important factor in a narrow band signal processing device such as a resonator, an oscillator, etc. From this point of view, each of the above-mentioned devices ensures stable action against temperature variation.

Suitability to high frequency band and low propagation loss are also assured by the same devices.

The devices described above have the following advantages: 1. Due to the high velocity of the surface acoustic wave, the wavelength in the high frequency band is large, thereby facilitating fabrication of the comb-shaped electrodes.

2. Due to the small frequency variation ratio depending on variation of film thickness, it is easy to fabricate devices suitable for a desired frequency band, resulting in good yield and cost reduction.

3. It is possible to keep the delay time of the surface acoustic wave device near zero.

4. An AIN film with good insulation can be easily made. Further, an AIN single-crystal epitaxial film can easily be provided by the MO-CVD method.

Claims

1. A surface acoustic wave device comprising an elastic substrate; an aluminum nitride (AIN) film deposited on said substrate; and electrodes for converting an electric signal to a surface acoustic wave and vice versa, said substrate having a positive delay time temperature coefficient to a surface acoustic wave, and said aluminum nitride film having an orientation of the piezoelectric axis thereof such that its delay time temperature coefficient to the surface acoustic wave is negative.

2. A surface acoustic wave device as claimed in Claim 1, in which the substrate is made of sapphire and said electrodes are provided on said AIN film, said substrate having a major surface which is substantially the (0001)-crystal-surface, the piezoelectric axis of said AIN film being perpendicular or parallel to said major surface, and said electrodes providing propagation of the surface acoustic wave substantially in the direction of the [1100]-axis on said major surface.

3. A device as claimed in Claim 2, wherein the thickness (H) of said AIN film is in the range to satisfy the relation of 22nH/ < 6 where A is the wavelength of the surface acoustic wave.

4. A surface acoustic wave device as claimed in Claim 1, in which said substrate is made of sapphire and said electrodes are provided on said AIN film, said substrate having a major surface which is substantially the (0001)-crystal-surface, the piezoelectric axis of said AIN film being perpendicular or parallel to said major surface, and said electrodes providing propagation of the surface acoustic wave substantially in the direction of the [1120]-axis on said major surface.

5. A device as claimed in Claim 4, wherein the thickness (H) of said AIN film is in the range to satisfy the relation 2t2nHlt8 where A is the wavelength of the surface acoustic wave.

6. A surface acoustic wave device as claimed in Claim 1, in which said substrate is made of sapphire and said electrodes are provided on said AIN film, said substrate having a major surface which is substantially the (0112)-crystal-surface, the piezoelectric axis of said AIN film being perpendicular or parallel to said major surface, and said electrodes providing propagation of the surface acoustic wave substantially in the direction of the [Olll]-axis on said major surface.

7. A device as claimed in Claim 6, wherein the thickness (H) of said AIN flm is in the range to satisfy the relation lt2aH/1 < 8 where A is the wavelength of the surface acoustic wave.

8. A device as claimed in any preceding claim, wherein said AIN film is a single-crystal epitaxial AIN film.

9. A surface acoustic wave device substantially as hereinbefofe described with reference to the drawings.

9. A surface acoustic wave device as claimed in Claim 1, in which said substrate consists of a silicon single-crystal and said electrodes are provided between said substrate and said AIN film; said substrate having a major surface which is substantially the (111 )-crystal-surface,, the piezoelectric axis of the AIN film being perpendicular or parallel to said major surface, and said surface acoustic wave propagation electrodes providing propagation of the surface acoustic wave substantially in the direction perpendicular or parallel to the piezoelectric axis of the AIN film.

10. A device as claimed in Claim 9, wherein screen electrodes are provided on said AIN film at positions aligned with said surface acoustic wave propagation electrodes.

11. A device as claimed in Claim 9, wherein the thickness (H) of said AIN film is in the range to satisfy the relation 0.2 < 27rH/A2.5 where A is the wavelength of the surface acoustic wave.

12. A surface acoustic wave device as claimed in Claim 1, in which said substrate consists of a silicon single-crystal and said electrodes are provided between said substrate and said AIN film, said substrate having a major surface which is substantially the (110)-crystal-surface, the piezoelectric axis of the AIN film being perpendicular or parallel to said major surface, and said surface acoustic wave propagation electrodes providing propagation of the wave substantially in the direction perpendicular or parallel to the piezoelectric axis of the AIN film.

13. A device as claimed in Claim 12, wherein the thickness (H) of said AIN film is in the range to satisfy the relation 1 2nH/ < 3 where A is the wavelength of the acoustic wave.

14. A surface acoustic wave device as claimed in Claim 1, in which said substrate consists of a silicon single-crystal and said electrodes are provided between said substrate and said AIN film, said substrate having a major surface which is substantially the (001)-crystal-surface, the piezoelectric axis of the AIN film being perpendicular or parallel to said major surface, and said surface acoustic wave propagation electrodes providing propagation of the surface acoustic wave substantially in the direction perpendicular or parallel to the piezoelectric axis of the AIN film.

15. A device as claimed in Claim 14, wherein the thickness (H) of said AIN film is in the range to satisfy the relation lt2nHl;lt2 where A is the wavelength of the surface acoustic wave.

16. A device as claimed in Claim 12, 13, 14 or 15, wherein said AIN film is a singlecrystal epitaxial AIN film.

17. A surface acoustic wave device as claimed in Claim 1, in which said substrate consists of a sapphire substrate with a silicon film deposited thereon (SOS substrate) and said electrodes are provided between said SOS substrate and said AIN film, the piezoelectric axis of the AIN film being perpendicular to a major surface of said SOS substrate.

18. A surface acoustic wave device as claimed in Claim 1, in which said substrate consists of a sapphire substrate with a silicon film deposited therein (SOS substrate) and said electrodes are provided between said SOS substrate and said AIN film, the piezoelectric axis of the AIN film being parallel to a major surface of said SOS substrate.

19. A device as claimed in Claim 17 or 18, wherein screen electrodes are provided on said AIN film at positions aligned with said surface acoustic wave propagation electrodes.

20. A surface acoustic wave device substantially as hereinbefore described with reference to the drawings.

CLAIMS New claims or amendments to claims filed on 13-10-86 Superseded claims 1-20 New or amended claims:

1. A surface acoustic wave device comprising an elastic substrate consisting of a silicon single-crystal whose delay time temperature coefficient to a surface wave is positive; an AIN film having a negative delay time temperature coefficient to the surface acoustic wave deposited on the surface of said elastic substrate; and surface acoustic wave propagation electrodes provided on said AIN film or between said substrate and said AIN film; said silicon single-crystal substrate having a major surface which is substantially the (111)-crystalsurface, fthe piezoelectric axis of the AIN film being perpendicular or parallel to said major surface, and said surface acoustic wave propagation electrodes providing propagation of the surface acoustic wave substantially in the direction perpendicular or parallel to the piezoelectric axis of the AIN film.

2. A device as claimed in Claim 1, wherein screen electrodes are provided between said substrate and said AIN film at positions aligned with said surface acoustic wave propagation electrodes provided on said AIN film.

3. A device as claimed in Claim 1, wherein the thickness H of said AIN film is in the range to satisfy the relation 0.2 < 27sH/A < 2.5 where 2 is the wavelength of the surface acoustic wave.

4. A surface acoustic wave device comprising an elastic substrate consisting of a silicon single-crystal whose delay time temperature coefficient to a surface acoustic wave is positive; an AIN film having a negative delay time temperature coefficient to the surface acoustic wave deposited on the surface of said elastic substrate; and surface acoustic wave propagation electrodes provided on said AIN film or between said substrate and said AIN film; said silicon single-crystal substrate having a major surface which is substantially the (110)-crystal-surface, the piezoelectric axis of the AIN film being perpendicular or parallel to said major surface, and said surface acoustic wave propagation electrodes providing propagation of the wave substantially in the direction perpendicular or parallel to the piezoelectric axis of the AIN film.

5. A devide as claimed in Claim 4, wherein the thickness H of said AIN film is in the range to satisfy the relation 1 2nH/23 where 2 is the wavelength of the acoustic wave.

6. A surface acoustic wave device comprising an elastic substrate consisting of a silicon single-crystal whose delay time temperature coefficient to a surface acoustic wave is positive; an AIN film having a negative delay time temperature coefficient to the surface acoustic wave deposited on the surface of said elastic substrate; and surface acoustic wave propagation electrodes provided on said AIN film or between said substrate and said AIN film; said silicon single-crystal substrate having a major surface which is substantially the (001)-crystal-surface, the piezoelectric axis of the AIN film being perpendicular or parallel to said major surface, and said surface acoustic wave propagation electrodes providing propagation of the surface acoustic wave substantially in the direction perpendicular or parallel to the piezoelectric axis of the AIN film.

7. A device as claimed in Claim 6, wherein the thickness H of said AIN film is in the range to satisfy the relation 1 2n;H/22 where A is the wavelength of the surface acoustic wave.

8. A device as claimed in Claim 4, 5, 6 or 7, wherein said AIN film is a single-crystal epitaxial AIN film.