JPS5859617A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To easily form a piezoelectric film and, at the same time, improve characteristics at high frequencies of a titled element, by forming a substrate by installing an aluminium nitride single crytal eqitaxial layer on a silicon single crystal layer consisting of (001) crystal planes. CONSTITUTION:A silicon single crystal plate 1 is composed of a silicon crystal cut along crystal planes (001) or equivalent planes. An aluminium nitride (AlN) single crystal epitaxial layer 2 is formed on the silicon single crystal substrate 1 in such a way that the piezoelectric axis becomes perpendicular to the plane of the substrate 1. Then, comb-shaped elastic acoustic wave driving electrodes 3 and detecting electrodes 4 are formed on the layer 2. The phase speed Vp of the surface acoustic wave against the film pressure (h) of the layer 2 rises from about 5,083m/sec to about 5,600m/sec within 0-5.0 range of 2pih/lambda (lambda is the wavelength of the surface acoustic wave). The variation is one maintaining a high phase speed and the dispersion to the film pressure is small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a new structure of surface acoustic waves (Surface Acoustic Waves) with excellent characteristics.
Conventionally, structures (substrates) constituting surface acoustic wave elements for handling various electrical signals by using ave) have been conventionally used. ), 2. Structure 3 in which a piezoelectric film is formed on a non-piezoelectric substrate, structure 3 in which a piezoelectric film is formed on a semiconductor substrate, etc. are known.

Among these, the monolithic structure of No. 3, in which a surface acoustic wave element can be formed together with an integrated circuit on the same semiconductor substrate, is advantageous in terms of applications and is expected to be further developed in the future.

By the way, 3 above. At present, a well-known monolithic structure is a structure in which a zinc oxide (ZnO) film is formed by sputtering or other methods on a silicon (Si) single crystal substrate. Due to these drawbacks, there are problems in practical use.

1. Electrical instability occurs due to voltage application.

2. Because it is difficult to form a high-quality film, it is difficult to obtain a film with sufficient reproducibility in terms of resistivity, piezoelectricity, etc.

3. A protective film (8i0z) is required on the silicon single crystal substrate.

4. Surface acoustic wave propagation loss is large in the high frequency region.

5゜ Large distribution in surface acoustic wave propagation characteristics.

6. It does not match the normal Sirien IC process.

The present invention has been made to address these problems, and its fundamental feature is to use an elastic structure (substrate) in which an aluminum nitride single crystal epitaxial layer is formed on a silicon single crystal layer. Specifically, it is an object of the present invention to provide a surface acoustic wave device using a silicon single crystal layer having a (001) crystal plane. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a surface acoustic wave device according to an embodiment of the present invention, where l is a silicon single crystal substrate cut on the (001) crystal plane or an equivalent plane, and 2 is a silicon single crystal substrate cut on the (001) crystal plane or an equivalent plane. The piezoelectric axis of the aluminum nitride (AlN) single crystal epitaxial layer thus formed is perpendicular to the surface of the silicon single crystal substrate. No. 4 is a comb-shaped surface acoustic wave generation electrode and detection electrode formed on the surface of the aluminum nitride single crystal epitaxial layer 2, and is the film thickness of the hH aluminum nitride single crystal epitaxial layer 2.

When a surface acoustic wave element having the above structure is excited (propagated) in a direction equivalent to the (110) axis direction of the silicon single crystal substrate 1, the surface acoustic wave as shown in FIG. Velocity dispersion characteristics were obtained.

In the figure, the horizontal @ indicates the standardized thickness of the aluminum nitride single crystal epitaxial film 2 in 2πh/λ (here, λ is the wavelength of the surface acoustic wave), and the vertical axis indicates the phase of the surface acoustic wave. This shows the speed Vp. As is clear from the figure, when 2πh/λ was approximately 5.01, the surface acoustic wave mode did not disappear.

However, Vp corresponding to the range of 2πh/λ from O to 5,0 is approximately 5083 In/sec to approximately 5600 m/sec.
It rose to the right up to sec, and this change maintained a large phase velocity, and the dispersion with respect to the film thickness was small.

Figure 6 shows the characteristic curve of the electromechanical coupling coefficient, where the horizontal axis shows 2πh/λ as in Figure 5, and the vertical axis shows the square value K of the electromechanical coupling coefficient as a percentage. . In the same figure, curve A has a characteristic corresponding to the structure of FIG. 1, and K[about 0.5% was obtained near 31 of the normalized film thickness 2πh/λ. This value is usually sufficient to generate and detect surface acoustic waves.

FIG. 2 (al, bl'ld) is a sectional view showing another embodiment of the present invention, in which (al) shows a surface acoustic wave generation electrode 3 and a fabrication detection electrode 4 on the surface of a silicon single crystal substrate 1. Formed□
After that, an aluminum nitride single crystal epitaxial layer 2 is formed to cover these. After comb-shaped surface acoustic wave generation electrodes 5 and detection electrodes 6 made of low-resistance silicon are embedded in the layer, an aluminum nitride single crystal is placed to cover them.

In the surface acoustic wave element having the above structure, surface acoustic waves are excited in a direction equivalent to the C110) axis direction of the silicon single crystal substrate 1 in the same manner as in the structure shown in FIG. 1, as shown in FIG. It was found that such velocity dispersion characteristics were obtained, and the dispersion was small with respect to the normalized film thickness 2πh/λ of the aluminum nitride single-crystal layer 2. .

Further, since the curve B in FIG. 6 is sensitive to the square value of the electromechanical coupling coefficient, a K value of about 0.61% was obtained in the vicinity of 3.1 of the normalized film thickness 2πh/λ. This value is usually sufficient to generate and detect surface acoustic waves.

FIG. 3 (al, (bl) shows other embodiments of the present invention, after a pair of thin electrodes 8 are partially formed as second electrodes on the surface of the acid silicon single crystal substrate 10. , shows a structure in which an aluminum nitride single crystal epitaxial layer 2 is formed so as to cover these, and a surface acoustic wave detection electrode 3 and a machining detection electrode 4 are formed on this surface as a vcw1 electrode, and (b) shows a structure in which an aluminum nitride single crystal epitaxial layer 2 is formed on this surface as a vcw1 electrode. After forming a low-resistance silicon layer 9 partially on the surface of the substrate 1, a silicon nitride single crystal epitaxial layer 2 is formed to cover these layers, and the generation electrode 3 is used as a first electrode on this different surface to detect the production. This figure shows the structure in which the electrode 4 is formed.

Similar to the structure shown in FIG. 1, the surface acoustic wave element having the above structure was designed to excite surface acoustic waves in a direction equivalent to the [110] axis direction of the silicon single crystal substrate 1, and as shown in FIG. It was found that the velocity dispersion characteristics as shown were obtained, and the dispersion was small with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

Curve C in FIG. 6 shows the square r[K characteristic of the electromechanical coupling coefficient, and K is about 0.34% near 0.29 of the normalized film thickness 2πh/λ, and further, vc2πh/
In the vicinity of λ of 41, K was about 0.44%, and a so-called double peak characteristic was obtained.

In particular, it was found that at a thin film thickness that gives the first peak of the former, dispersion is very small, and the film has excellent ultra-high frequency and low dispersion characteristics. These two values are usually sufficient to generate and detect surface acoustic waves.

FIGS. 4(a) and 4(bl) show other embodiments of the present invention. FIG. 4(a) shows a surface acoustic wave generation electrode 3 and a detection electrode 4 as first electrodes on the surface of a silicon single crystal substrate 1. After forming these, an aluminum nitride single crystal epitaxial layer 2 is formed on top of these, and a pair of shielding electrodes 8 are partially formed on the surface of the silicon layer as a second electrode. A high/low resistance layer 7 or a depletion layer is partially formed on the surface of the single crystal substrate 1, and the generation electrode 5 and the detection electrode 6 as a comb-shaped first electrode made of low resistance silicon are formed on these layers. After embedding, an aluminum nitride single crystal epitaxial layer 2 is formed in the gills covering these, and a pair of thin electrodes 8 are formed as second electrodes on the surface of the aluminum nitride single crystal epitaxial layer 2.

In the surface acoustic wave device having the above structure, by exciting surface acoustic waves in a direction equivalent to the C110) axis direction of the silicon single crystal substrate l in the same manner as in the structure shown in FIG. Velocity dispersion characteristics were obtained, and it was found that the dispersion was small with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

The curve in Figure 6 shows the characteristics of the square value of the electromechanical coupling coefficient, and in the vicinity of 0.19 of the normalized film thickness 2πh/λ, K is approximately 0.26%, and further, vc2πh/λ
In the vicinity of 3.6, K was approximately 0.54%, and double-beak characteristics were obtained. In particular, it was found that at a thin film thickness giving the first peak of the former, the dispersion was lower than that of non-turnips, and it was found to be excellent in ultra-island frequency and low dispersion. K in these
This value is sufficient to generate and detect normal acoustic waves.

In the structure of FIGS. 1 to 4(a), (bl), the piezoelectric axis of the aluminum nitride single crystal epitaxial layer 2 is parallel to the surface of the silicon single crystal substrate and its (110
) Other embodiments of the present invention will be described below in which they are formed in a direction equivalent to the axis.

(110:] of the silicon single crystal substrate 1)
When a surface acoustic wave is excited in a direction equivalent to the axial direction, the seventh
The velocity dispersion characteristics of surface acoustic waves as shown in the figure were obtained.

In the figure, the horizontal and vertical axes are the same as in FIG. 5, and the normalized film thickness 2πh/λ was about 5.0-1, and the mode did not disappear into a surface acoustic wave mode.

However, the phase velocity Vp corresponding to the range of 0 to 8,0 of 2πh/λ is about 5083 m/sec to about 5570 m/sec.
It rose to the right in sec 1, and this change maintained a large phase velocity, and the dispersion with respect to the film thickness was small. In particular, when 2πh/λ is around 1.0, the dispersion takes a minimum value and becomes very small.

Further, even when 2πh/λ is around 0.2, the dispersion takes a local maximum value and becomes small.

The curve Afi in FIG. 8 shows two characteristics in the square value of the electromechanical coupling coefficient, and K was about 0.95% in the vicinity of 2.5 of the normalized film thickness 2πh/λ. Furthermore, even in the vicinity of 1.0, where velocity dispersion is small, 0.65% was obtained.

These values are usually sufficient to generate and detect surface acoustic waves.

Next, in FIG. 2(a), a surface acoustic wave element formed in the same structure as (bl) is prepared, and the (11
In order to excite the surface acoustic wave in the direction equivalent to the 0"l axis direction, the velocity dispersion characteristics as shown in Fig. 7 are obtained,
It was found that the dispersion was small with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

Curve B in Figure 8 shows the characteristics of the square value of the electromechanical coupling coefficient, and 2 is approximately 0.15% in the vicinity of 0.39 of the normalized film thickness 2πh/λ, and ' 2 [2πh/λ wealth, near 0, K is about 0.5%
was obtained, and a double peak characteristic was obtained. These two values are usually sufficient to generate and detect surface acoustic waves.

Next, in FIG. 3(a), a surface acoustic wave element formed in the same structure as (bl) is prepared, and the (11
0) By exciting the surface acoustic waves in a direction equivalent to the axial direction, the velocity dispersion characteristics shown in Fig. 7 can be obtained, and the normalized film thickness of the aluminum nitride single crystal epitaxial layer 2 is 2πh/λ. It was found that the variance was small.

Curve C in FIG. 8 shows the square of the electromechanical coupling coefficient [K2 characteristic, and K was about 1.1% in the vicinity of 2.0 of the normalized film thickness 2πh/λ.

In particular, in FIG. 7, a K of about 0.8% was obtained where the velocity dispersion was small where 2πh/λ was around 1.0.

These values are usually sufficient to generate and detect surface acoustic waves.

Next, prepare a surface acoustic wave formed in the same structure as FIG.
] Exciting surface acoustic waves in a direction equivalent to the axial direction.

As a result, the velocity distribution characteristics shown in Figure 7 were obtained.
It was found that the dispersion was small with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

Furthermore, the curve in FIG. 8 shows the square 1iK characteristic of the electromechanical coupling coefficient, and approximately 0.56% of the normalized film thickness 2πh/λ was obtained in the vicinity of 2.7.

In particular, 2πh/λ, which has a small velocity dispersion, is around 1.0 and about 0.
A K of 12% was obtained. These values are usually sufficient to generate and detect surface acoustic waves.

The present invention when surface acoustic waves are excited in a direction equivalent to the [100] axis direction of the silicon single crystal substrate 1 in a surface acoustic wave device having the structure shown in FIGS. 1 to 4 (al, (bl). The fourth embodiment will be described below.

First, in the case of a surface acoustic wave bare hand having the same structure as that shown in FIG. 1, the velocity dispersion characteristics of the surface acoustic wave as shown in FIG. 9'f were obtained.

In this figure, the horizontal and vertical axes are the same as in FIG. 5, and the surface acoustic wave mode did not disappear until the normalized film thickness 2πh/λ was approximately 5.0.

However, the phase velocity Vp corresponding to the range of 0 to 5,0 of 2πh/λ is about 4920 m/sec to about 5500 m/sec.
The upper right vvc rose to c, and this change maintained a large phase velocity, and the dispersion with respect to the film thickness was small.

The song 1fMA in FIG. 10 has a square value of electromechanical coupling coefficient of 3.
In the vicinity of 1, K of about 0.49% was obtained. This value is usually sufficient to generate and detect surface acoustic waves.

Next [In the case of a surface acoustic wave device having the same structure as in FIG. 2 (al, lb), the velocity dispersion characteristics shown in FIG. 9 are obtained, and the normalized film thickness of the aluminum nitride single crystal epitaxial layer 2 is 2πh/λ. It was found that the variance was small.

In addition, the square of the electromechanical coupling coefficient (W
3.1 of the normalized film thickness 2πh/λ
K of about 0.57% was obtained in the vicinity.

This value is usually sufficient to generate and detect surface acoustic waves.

Next, in the case of a surface acoustic wave element having the same structure as in Fig. 3 (al, fb), velocity dispersion characteristics as shown in Fig. 9 are obtained,
It was found that the dispersion was small with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

In addition, the curve C in Figure 10 shows the characteristics of the electromechanical coupling coefficient at 2W values, and in the vicinity of 0.25 of the normalized film thickness 2πh/λ, approximately 0.35% of K is obtained, and further l/ (2πh
In the vicinity of /λ of 4.0, K of about 044 was obtained, and a so-called double-bi characteristic was obtained.

In particular, it was found that at a thin film thickness that gives the first peak of the former, dispersion is very small, and the film has excellent ultra-high frequency and low dispersion characteristics. The two values in these are usually one value, which is sufficient to generate and detect surface acoustic waves.

Next, in the case of a surface acoustic wave element having the same structure as in FIGS. 4(al and bl), velocity dispersion characteristics as shown in FIG.
It was found that C had a small dispersion with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

Furthermore, the curve shown in Fig. 10 shows the characteristic of the square value of the electromechanical coupling coefficient, and K is approximately 0.28% in the vicinity of 0.20 of the normalized film thickness 2πh/λ, and furthermore, 2πh/λ
In the vicinity of 3.5, K had a coefficient of about 0.51, and a so-called double peak characteristic was obtained.

In particular, it was found that at a thin film thickness that gives the first peak of the former, dispersion is very small, and the film has excellent ultra-high frequency and low dispersion characteristics. In these cases, 2 m is usually a sufficient value to generate and detect surface acoustic waves.

In the structure shown in FIGS. 1 to 4 (al, (b)), the piezoelectric axis of the aluminum nitride single crystal epitaxial layer 2 is parallel to the surface of the silicon single crystal substrate (100
) Other embodiments of the present invention will be described below in which they are formed in a direction equivalent to the axis.

First, a surface acoustic wave element formed in the same structure as that shown in FIG. 1 is prepared, and when surface acoustic waves are excited in a direction equivalent to the [100] axis direction of the silicon single crystal substrate 1, the result shown in FIG. 11 is obtained. The velocity dispersion characteristics of surface acoustic waves as shown were obtained.

In the figure, the horizontal and vertical axes are the same as in FIG. 5, and the surface acoustic wave mode disappeared when the normalized film thickness 2πh/λ was about 0.51.

However, the phase velocity Vp corresponding to the range of 2πh/λ from O to 5.0 is about 4921 m/Sec to about 5600 m
/sec 1, and this change was a change that maintained a large phase velocity, and the dispersion with respect to the film thickness was small.

Curve A in FIG. 12 shows the characteristics of the square value of the electromechanical coupling coefficient, and a peak of K of about 0.9% was obtained near 2.5 of the normalized film thickness 2πh/λ. Especially 2πh/λ
is around 1.0, approximately 0.6% of 2 is obtained, and the first
As shown in Figure 1, the dispersion is extremely small at the minimum point. These values are usually sufficient to generate and detect surface acoustic waves.

Next, prepare a surface acoustic wave element formed in the same structure as in FIG. 2 (al, (bl),
0] By exciting surface acoustic waves in a direction equivalent to the axial direction, velocity dispersion characteristics as shown in Figure 11 can be obtained,
It was found that the dispersion was unfavorable with respect to the normalized film thickness 2πh/λ of the aluminum nitride single crystal epitaxial layer 2.

Curve B in Figure 12 is the square of the electromechanical coupling coefficient III.
It shows IK2 characteristics, and has a normalized film thickness of 2πh/λ of 0,
In the vicinity of 34, K of about 0.15% was obtained, a relationship was obtained, and a double peak characteristic was obtained. These Klls are usually of sufficient value to generate and detect surface acoustic waves.

Next, a surface acoustic wave element formed in the same structure as in FIG. 3 (al, (bl) is prepared, and the (10
0) - By exciting the surface acoustic waves in a direction equivalent to the axial direction, a velocity dispersion characteristic as shown in FIG. 11 is obtained, and the normalized film thickness of the aluminum nitride single crystal epitaxial layer 2 is 2πh/λ. On the other hand, the dispersion is small! Understood.

Further, in the curve CFs in FIG. 12, which shows the characteristics in the square value of the electromechanical coupling coefficient, K was about 1.0% in the vicinity of 2.0 of the normalized film thickness 2πh/λ.

Special [2πh/λ force around 1.0 1/m$-ite, about 0.7
%) is obtained, and as shown in FIG. 11, the dispersion is very small at the minimum point. These values are usually sufficient to generate and detect surface acoustic waves.

Next, prepare surface acoustic waves formed in the same structure as (al and (bl) in FIG. 4, and (100)
By exciting the surface acoustic waves in a direction equivalent to the axial direction, a velocity distribution characteristic as shown in FIG. 11 is obtained, and the normalized film thickness 2 of the aluminum nitride single crystal epitaxial layer 2 is
It was found that the dispersion was small relative to πh/λ.

In addition, the curve shown in Figure 12 shows two characteristics directly related to the square f of the electromechanical coupling coefficient, and a peak of about 0.55% for K was obtained near 2.7 of the normalized film thickness 2πh/λ. .

This value is usually sufficient to generate and detect surface acoustic waves.

As is clear from the above description, the present invention uses an elastic body structure in which an aluminum nitride single crystal epitaxial layer is formed on a silicon single crystal substrate (layer).
1) Since a silicon single crystal substrate consisting of crystal planes is used to propagate surface acoustic waves, a surface acoustic wave element with excellent characteristics can be obtained.

The optimum range of the film thickness of the aluminum nitride single crystal epitaxial layer in each of the examples in this text is clear from each characteristic diagram, and is shown in the following table for each example.

According to the present invention explained above, the following effects can be obtained.

1. Since an epitaxial aluminum nitride film is used, the film quality is uniform and the propagation loss at high frequencies is small.

2. Surface acoustic waves have a high sound velocity, so the wavelength at high frequencies becomes large, making it easier to manufacture comb-shaped electrodes and the like.

3. Since the frequency dispersion of surface acoustic wave sound velocity is kept small, waveform distortion accompanying signal propagation is reduced.

4. A monolithic structure is possible in which integrated circuits and surface acoustic wave devices are formed on a common semiconductor substrate.

5. The band gap of aluminum nitride film is approximately 6.2.
It is electrically stable because it has a large resistivity of 1016 Ωm or more, and can be easily formed using MO-CVD technology, which is compatible with the silicon IC process.

As described above, the structure according to the present invention can be particularly formed into an elastic surface, so that it can be applied to a wide range of uses.

[Brief explanation of the drawing]

Figure 1, Figure 2 ta), Tb), Figure 3 (a), (bl
Oh [Lil! Figures 4 (al and bl) are cross-sectional views showing examples of the present invention, and Figures 5 to 12 are characteristic diagrams showing the results obtained by the present invention. l...Silicon single crystal Substrate, 2... Aluminum nitride A single crystal epitaxial layer, 3.4.5.6... Comb-shaped electrode, 7... High resistance silicon layer, 8... Shielding electrode, 9... Low resistance Silicon layer. Patent applicant: Nobu Mikoshiba, Oro Uchi, Patent attorney: Nagai 1) Takesanbe 1, Indication of the case Showa Patent Application No. 157594 3, Relationship with the amended person case Patent applicant 4 , Agent 105 Address: Shiba 3-chome Building, 3-2-14 Shiba, Minato-ku, Tokyo February n, 1982 (shipment date)

Claims (1)

[Claims] 1. A silicon single crystal layer consisting of a (001) crystal plane or a plane equivalent thereto, an aluminum nitride single-crystalline epitaxial layer formed on this layer with a piezoelectric axis oriented in VC1, and a predetermined position thereof. A surface acoustic wave element comprising: an electrode formed on the surface of the surface acoustic wave element; 2. The surface acoustic wave device according to claim 1, wherein the piezoelectric axis of the aluminum nitride single crystal epitaxial layer is perpendicular to the silicon single crystal layer. 3. Claim 1, characterized in that the piezoelectric axis of the aluminum nitride single crystal epitaxial layer is formed in a direction parallel to the silicon single crystal layer and in a direction equivalent to its [110] crystal axis. surface acoustic wave device. 4. Claim 1, characterized in that the piezoelectric axis of the aluminum nitride single crystal epitaxial layer is formed in a direction parallel to the silicon single crystal layer and in a direction equivalent to the 7 (100) crystal axis. The surface acoustic wave device described above. 5. The surface acoustic wave device according to claim 2 or 3, characterized in that the surface acoustic wave is propagated in a direction equivalent to the (110) axis on the plane of the silicon single crystal layer. 6. The surface acoustic wave device according to claim 2 or 4, characterized in that surface acoustic waves are propagated in a direction equivalent to the (100) axis on the plane of the silicon single crystal layer. 7. Claims characterized in that the film thickness of the aluminum nitride single crystal epitaxial layer belongs to the range of 2πh/λ (5,0 (where λ represents the growth of surface acoustic waves 'T) The surface acoustic wave device according to any one of items 2 to 6. 8. Claims 1 to 6, characterized in that the electrode is formed on a surface portion of an aluminum nitride single crystal epitaxial layer. 9. The bottom acoustic wave device according to any one of claims 1 to 7, wherein the electrode is formed between a silicon single crystal layer and an aluminum nitride single crystal epitaxial layer. 10. The surface acoustic wave device according to claim 10, wherein the electrodes are formed as a pair of first electrodes on the surface of the aluminum nitride single crystal epitaxial layer, and a second electrode is formed between the silicon single crystal layer and the aluminum nitride single crystal epitaxial layer. A surface acoustic wave device 0-11 according to any one of claims 1 to 7, characterized in that a pair of thin electrodes are formed, the electrodes being a silicon single crystal layer and a nitrided silicon layer. A pair of first electrodes are formed between the aluminum single crystal epitaxial layers, and a pair of thin electrodes are formed as second electrodes on the surface of the aluminum nitride epitaxial layer. A surface acoustic wave device according to any one of the ranges 1 to 7.