JPS58156216A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To obtain a surface acoustic wave element with which the production of a comb-shaped electrode, etc. is facilitated with small delay time of a surface acoustic wave, by using an elastic matter structure in which an aluminum nitride film having orientation of a piezoelectric axis is formed on an elastic substrate made mainly of a silicon single crystal. CONSTITUTION:A silicon single crystal substrate 1 having positive delay time temperature coefficient to a surfaceacoustic wave is cut at a surface equivalent to a crystalline face (111), (110) or (001). An aluminum nitride film 2 is formed on the substrate 1 so that the piezoelectric axis of the film 2 is set vertical or horizontal to the substrate 1. Then a surface acoustic wave generating electrode 3 and a surface acoustic wave detecting electrode 4 are formed with comb- shaped electrodes on the surface of the film 2. Thus the surface acoustic wave is transmitted in the direction vertical or horizontal to the piezoelectric axis of the film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a surface acoustic wave device (4#) which is applied to a surface acoustic wave device having a new structure with excellent buttock properties.

Elastic table @@ (5surface Acoustic V
A structure (base 41[) that constitutes an elastic am liquid element for handling various electrical signals by utilizing
Conventionally, L is a structure with only a piezoelectric substrate (piezoelectric single crystal substrate, piezoelectric ceramic substrate, etc.), L is a structure with a piezoelectric layer formed on a non-piezoelectric substrate, 1 is a structure with a piezoelectric layer formed on a semiconductor substrate, etc. are known.

By the way, as the above-mentioned multilayer structure of λ, a structure in which a zinc oxide film (ZnO) is formed on a sapphire substrate or a glass substrate by sputtering method etc. is currently known, but this ZnO film has the following structure. There are gaps because there are defects.

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

λ　There is a lot of surface acoustic wave propagation loss in the high frequency region.

3. Dispersion of surface acoustic wave propagation characteristics is large.

46 Temperature change rate (1/τ
)・(aτ/#T) is difficult to control. (T: Ambient Temperature) The present invention has been made to address these problems, and is an elastic body in which aluminum is formed on aluminum nitride on an elastic substrate that has a positive air-time temperature coefficient for surface acoustic waves. The fundamental feature is the use of the structure (41[), and 41
The object of the present invention is to provide an elastic Table II#L element using a silicon single crystal substrate.゛Hereinafter, refer to I1m and sound the present invention JII#l.

Figure 1 is a section I showing an acoustic wave surface element according to an embodiment of the present invention.
In 1 wJ, 1 consists of a silicon single crystal substrate cut in the (III) crystal direction and with an image equivalent to the (11G) crystal plane or the (001) crystal plane, and 2 consists of this silicon single crystal substrate 4[1] The aluminum nitride film is formed such that its piezoelectric axis (C axis or (oool) axis) is perpendicular or parallel to the silicon single crystal substrate IK. 3 and 4 are the above aluminum nitride 112! The elastic surface line generating electrode and the calibration electrode are formed in a comb-shape I-, and H is the thickness of the aluminum nitride film.

For the surface acoustic wave device having the above structure, when the elastic table [Ial is propagated in a direction perpendicular to the piezoelectric axis (C axis or (0001) axis) direction of the aluminum nitride film 2, the result is as shown in Figure 4. The velocity error of surface acoustic waves was obtained as follows. 1
jll! 1, the horizontal axis shows the standardized thickness H of the aluminum nitride film 2 in 2πH/λ (here, λ is the wavelength of the surface acoustic wave), and the vertical axis shows the phase velocity Vp of the surface acoustic wave.
This shows that. In the same figure, when a surface acoustic wave is propagated on the (111) plane of a silicon single crystal group [1 in a direction equivalent to the (112) axis direction, b is a silicon single crystal group #1.
When a surface acoustic wave is propagated on the (110) Ni of i1 in a direction equivalent to the (001) axis direction, C is a direction equivalent to the (031) axis direction on the (100) plane of the silicon single crystal substrate 1. This shows the characteristics of an elastic surface when waves are propagated.

As is clear from the fj1 diagram, the dispersion of the phase velocity ■p is small, and a very large value of the phase velocity ■p can be obtained.

In addition, Figure lI6 shows the characteristic curve of the electromechanical coupling coefficient obtained from it, and the horizontal axis is denoted by 2I'λ,
The vertical axis indicates the square K of the electromechanical coupling coefficient as a percentage. In fjlgec, element A exhibits characteristics corresponding to the structure shown in Figure 1, and normally has elasticity I! ! This shows that sufficient K is obtained to generate and detect plane waves, and that the piezoelectricity is excellent.

Furthermore, the 7th all (6) to plow show the characteristic curve of the delayed temperature coefficient i11 (TCD) for surface acoustic waves obtained thereby, the horizontal axis is 2πH/λ, and the vertical axis is the elasticity coefficient m Temperature change rate of luck time τ of #l ('/r)・
(aτ/aT) is expressed in pyn/C units. In the same 111, ^ is (111) of silicon single crystal substrate 1
- When a surface acoustic wave is propagated in a direction equivalent to the (112) axis direction above, @ is (0
01) When propagating in a direction equivalent to the axial direction, (q is (0
01') When propagating in a direction equivalent to the (10G) axis on II, I show the characteristics when propagating in a direction equivalent to the (110) axis on a (001) plane. . Here, the silicon single crystal substrate 1 has a positive temperature coefficient of delay time (on the other hand, the aluminum nitride film 2 has the opposite (negative temperature coefficient of delay time), so the overall characteristics of each are different from those of both. is a value that compensates for each other, and changes according to changes in the film thickness H of the aluminum nitride film 2. By selecting the film thickness H appropriately, the temperature change rate during the delay time can be made closer to zero than K. .

Next, when a surface acoustic wave is propagated in a direction parallel to the piezoelectric axis (C axis or (0001) axis) of aluminum nitride@2 in a surface acoustic wave element having the structure shown in Fig. K111, in the 59th review, The velocity dispersion characteristics of surface acoustic waves as shown were obtained.

In the figure, d is 9 o'clock when the surface acoustic wave is propagated on the (001) plane of the silicon single crystal substrate 1 in a direction equivalent to the (lOO) axis direction, and similarly Ke is on the (110) plane with the (001) axis. It shows each characteristic when propagated in a direction equivalent to the direction of the wave. As is clear from the figure, the dispersion of the phase velocity vp is small, and a phase velocity of a very large value can be obtained.

In addition, Fig. 6 (Q, η shows the characteristic curves of the electromechanical coupling coefficients obtained at that time. Element A has characteristics corresponding to the structure shown in Fig. 1, and Fig. 6 0 shows the characteristic curves of the electromechanical coupling coefficient obtained at that time. 1 (
Similarly, when a surface acoustic wave is propagated in a direction equivalent to the (001) axis direction on the (001) plane, the 6th Ii2 (IN is (00
1) It shows each characteristic when propagating on a plane in a direction equivalent to the (10G) axial direction.

As is clear from the figure, surface acoustic waves are normally generated.
2 was obtained sufficiently for detection, indicating excellent piezoelectricity.

Furthermore, in FIG. 7 (to), (P5 shows the characteristic curve of the temperature coefficient of delay time (TCD) for the surface acoustic wave obtained at that time, and the (001) II
Similarly, when a surface acoustic wave is propagated in a direction equivalent to the (1oe) axis direction, K (g) is (001) on the (110) plane.
Each characteristic when propagated in a direction equivalent to the axial direction is shown. As is clear from FIGS. 7(5) to (g), the film thickness H of the aluminum nitride film 2 is 0, 2 < 2πH/λ
By selecting a value in the range of <3.0, the rate of temperature change during the delay time can be brought close to zero.

*ZWJ to FIG. 4 are cross-sectional views showing other embodiments of the present invention, and FIG. 2 is a surface sK elasticity table I of the silicon single crystal substrate 1.
11 shows a structure in which an aluminum nitride film 2 is formed to cover the electrodes 3 and 4i14 for detection after forming them. FIG. 3 shows that after a pair of thin electrodes 7 are partially formed as second electrodes on the surface of a silicon single crystal substrate 1, an aluminum nitride film 2 is formed on these surfaces. This shows a structure in which a surface acoustic wave generating electrode &3:td and a detection electrode 4 are formed as the first @ pole.

Further, FIG. 4 shows that after forming an elastic surface electrode 4ii3 for mIIL generation and an IE electrode 4 for detection as electrodes on the surface of the silicon single crystal substrate 1, an aluminum nitride layer 2 is formed on the surface 5 to cover them. This figure shows a structure in which a pair of thin electrodes 7 are partially formed as second electrodes on this surface.

When a surface acoustic wave is propagated in a direction perpendicular to the piezoelectric axis direction of the aluminum nitride film 2 for the surface acoustic wave element having each of the above structures, the % characteristics as shown in (b) are obtained. Obtained.

In the figure, element B has characteristics corresponding to the structure in Figure 2.
Element C has characteristics corresponding to the structure shown in Fig. 3, and element C has characteristics corresponding to the structure shown in Fig. 14. It shows that you are sexually superior.

Similarly, when a surface acoustic wave is propagated in a direction parallel to the piezoelectric axis direction of the aluminum nitride film 2 for the surface acoustic wave elements having the structures No. 211 to No. 4811, Fig. 6 (q, a#
As shown in c, 4I properties were obtained.

In Oka WJ, 1lL6tlJIQ is the (00
1) - Direction equivalent to the (100) axial direction above (shows each characteristic of the propagated sound, and 2 is usually sufficient to generate and detect surface acoustic waves, and has excellent piezoelectricity) It is shown that.

As is clear from Figure 6 (4) No'211, it is possible to obtain a practically sufficient value from K by keeping the normalized film thickness 2πH/λ in the range of 0.2 to 6.0. This shows that it has excellent piezoelectricity.

The aluminum nitride film used in each example has a large band gap of approximately 6.2 eV, and exhibits good insulating properties because it can easily be obtained with a specific resistance of 1.0 or 1 O1eas or more. Although this aluminum nitride film is preferably JINm crystal, it can be easily formed into a single-crystal "epitaxial layer" by using the well-known MO-CVD technique.

Furthermore, compared to the conventional zinc oxide film formed by sputtering, the aluminum nitride film has superior reproducibility and can provide a uniform film quality, making it possible to suppress propagation loss particularly in high-rise waves.

Since the aluminum nitride film mentioned above has a negative temperature coefficient of delay time for surface acoustic waves, it has a property that the temperature coefficient of delay time is positive, like a silicon single crystal substrate. (If formed on a substrate with a resonator, the delay time temperature coefficients will be mutually compensated, and stable characteristics against temperature changes can be obtained. This is the most important performance in narrowband signal processing elements such as oscillators, and the structures of each of the above embodiments allow for stable operation against temperature changes, as well as 44-frequency and low-loss performance. They can be measured together.

The substrate on which the aluminum nitride film is formed is not limited to silicon single crystal, but any material having a negative temperature coefficient of delay time can be selected. For example, it is possible to use an IIIi temporary film in which a silicon surface barrier such as a silicon dioxide film is formed on a silicon single crystal.

As is clear from the above description, according to the #IC invention, an elastic body structure is used in which an aluminum nitride film is formed on a silicon substrate with a positive delay time temperature coefficient for elastic surface wi waves. , a surface acoustic wave device with excellent characteristics can be obtained.

According to the Honjitsu Wi4 described above, the following effects can be obtained.

1. Since the surface acoustic wave velocity is high, the wavelength at high frequency becomes large, making it easy to manufacture a comb-shaped electrode ring.

2. Since the rate of frequency variation due to film thickness variation is small, it becomes easy to manufacture elements that match the designed operating Ji1 wave number, and thus it is possible to reduce costs by improving yield.

3. The delay time of the surface acoustic wave element can be brought close to zero.

4. An aluminum nitride film with high insulating properties can be easily obtained, and its single crystal epitaxial film can be easily formed using MO-CVD technology.

Note that the crystal plane of the aluminum nitride film formed on the substrate and T-plate shown in the examples of the main text and the crystal direction for exciting (propagating) surface acoustic waves may be the same even if appropriate selections are made other than in the examples. It is possible to obtain the effect.

[Brief explanation of the drawing]

Figures 1 to 4 are all cross-sectional views showing embodiments of the present invention, and Figures 5 (At, (c), Figures 6 and 75, It is a characteristic diagram showing the obtained results. 1... Silicon single crystal, 2... Aluminum nitride film, 3... Electrode for surface acoustic wave generation, 4... Electrode for surface acoustic wave detection, 7 ...Shiyahei electrode. Patent applicant: Nobu Mikoshiba, Kazuo Uchi, agent: Eiji Benkashi 1) Takesanbe Figure 7 (A) Figure 7 (Reference Figure 7 (C) Figure 7 ( 0) Figure 7 (E) Figure 7 (F) Before procedural amendment (method/spontaneous) April 9, 1980 Commissioner of the Patent Office, hEB Haruki Tono, Katana 3,
Person making amendment 4, agent 〒105

Claims (1)

[Claims] L Elasticity Table - An aluminum nitride film mainly composed of a silicon single crystal with a positive delay time temperature coefficient for IIL; KJit is formed on the body substrate and presses at the position KJit.
1. A surface acoustic wave element comprising 11 poles. λ The elastic wrist according to claim 111 of the patent, characterized in that the elastic substrate is made of silicon single crystal.
element. λ The silicon single crystal is made of a (111) crystal box, and the piezoelectric axis of aluminum nitride is perpendicular or horizontal to the silicon single crystal, and the piezoelectric axis direction of the aluminum nitride film is parallel to the piezoelectric axis of the aluminum nitride film. 2. The elastic table III wave element according to claim 2, wherein the surface acoustic wave is propagated in a vertical or horizontal direction. 4. The thickness H of the aluminum nitride film is 0.2〈21H
/λ〈z5 (However, λ is elastic!! Indicates the internal wave wavelength)
Claim 1!1 characterized in that it belongs to the scope of
The elastic lIr7IA wave device according to item 113. 5. The silicon single crystal consists of a plane equivalent to a (11G) crystal picture, and the piezoelectric axis of the aluminum nitride film is formed perpendicularly or horizontally to the silicon single crystal,
Claim 1 characterized in that the elasticity table 1riIjll is propagated in a direction perpendicular or horizontal to the piezoelectric axis direction of the aluminum nitride film! 2] The surface acoustic wave device according to J. 6. The thickness H of the aluminum nitride film is 1<2πH/λ
Claim I characterized by belonging to category 3 @!
The surface acoustic wave device according to item 5. 7. The silicon single crystal is made of a (001) crystal equivalent to a (001) crystal, and the piezoelectric axis of the aluminum nitride film is perpendicular or horizontal to the silicon single crystal, and the piezoelectric axis direction of the aluminum nitride is parallel to the piezoelectric axis of the aluminum nitride film. A surface acoustic wave device according to Patent No. 11/12, characterized in that it propagates surface acoustic m-waves in the vertical or horizontal direction. & The film thickness H of the above aluminum nitride film is 1<2πH/λ
``Claims characterized by belonging to category 2■
7. The surface acoustic wave device according to item 7. 9. The surface acoustic wave device according to any one of claims 11111 to ms, wherein the aluminum nitride film is made of a single crystal epitaxial material.