JPS59210716A - Substrate for surface wave device - Google Patents

Abstract

PURPOSE:To obtain a high-precision elastic surface wave device by limiting the thickness of a film formed in a mismatching lattice array on a layered-structure substrate whose surface is covered with the thin film in the mismatching lattice array, to a specified range. CONSTITUTION:The elastic surface wave device 10 has the layered structure formed by vapor-depositing the thin film 13 in the mismatching lattice array on the substrate 12 to a 10Angstrom -0.03lambda (lambda: the wavelength of elastic surface wave) thickness. The center frequency f0 of a elastic surface wave filter is determined by f0=v/lambda (v: propagation speed of elestic surface wave), but variance in f0 due to variance in propagation speed (v) depending upon the substrate material is adjusted only by adjusting the film thickness of the thin film in the mismatching lattice array while the vapor-deposition time is varied. The relation between the film thickness and f0 is as shown by a curve 21. In this case, when the film thickness is <=10Angstrom , the thin film is not continuous and the reproducibility of characteristics is not obtained. When the film thickness is >=0.03lambda, on the other hand, the insertion loss increases as shown by a curve 22 and the practicability is not obtained. This structure is considered to has the relation between the f0 and the film thickness of the SiO2 film as shown by a curve 23. The curve 21 is never inverted when the thin film has a lattice in order.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a substrate for a surface acoustic wave device, and particularly to a substrate for a high precision surface acoustic wave device.

Conventional configurations and their problems Surface acoustic wave devices are said to be useful for high-precision solid-state filters, resonators, delay elements, etc. When producing surface acoustic wave devices, due to variations in the characteristics of the materials used, For example, the variation in the center frequency of the surface acoustic wave fill is 0.05% or more.

On the other hand, in recent information devices, the center frequency fluctuation is
Since it is required to be one order of magnitude smaller than this value, it is generally produced by means of sorting. but,
In this case, since it is impossible to mass-produce highly accurate denomination chairs, there has been a strong demand for the development of materials for highly accurate surface acoustic wave devices.The present invention satisfies this demand. It is something.

Object of the Invention Constitution of the Invention The present invention provides a layered structure substrate in which the surface of the substrate is coated with a thin film with a mismatched lattice arrangement, and the thickness of the thin film with the mismatched lattice arrangement is 1Q8 to 0.032 (λ: the surface of the layered structure substrate). The present invention provides a surface wave device substrate suitable for surface wave devices such as resonators and filters.

Description of examples Hereinafter, the present invention will be explained in detail with reference to figures and examples.

FIG. 1 shows the main structure of a high-precision surface acoustic wave device substrate of the present invention. That is, FIG. 10 shows the main structure of a surface acoustic wave device, in which a thin film 13 with a mismatched lattice arrangement is formed on a substrate 12 on which a surface acoustic wave 11 propagates, with a thickness ranging from 10.8 to 0.80 cm. It has a layered structure deposited in the range o3λ(): wavelength of surface acoustic waves).

That is, the frequency characteristics of a normal surface acoustic wave device, for example, the center frequency f of a surface acoustic wave filter. is fo-v/λ
It is determined by the relationship (■: propagation speed of surface acoustic waves). In this case, λ is determined by, for example, the geometric dimensions of an interdigital electrode for excitation of surface acoustic waves, and it is easy to process the dimension to the designed value. Therefore, when manufacturing this type of device, a problem arises in f due to variations in the propagation velocity V of the surface acoustic wave depending on the substrate material. This is the variation in The variations in fo are complicated because they are caused by variations in the physical constants of the substrate material, such as Young's modulus, density, and Boannon ratio, and in the case of single crystal substrates, variations in the setting of the propagation direction of surface acoustic waves are also added. Therefore, it is not easy to reduce these variations using normal techniques.

On the other hand, two of the present inventions are based on the conventional f. Regarding the variation of 10
This type of thin film has an amorphous structure with a mismatched lattice arrangement, which is a thin film of about 0.08 in thickness and has not progressed in crystallization.
It is often seen during the growth process of the thin film. This thin film exhibits a structure in which thin films having an island-like structure are laminated in layers and the state thereof is frozen. ) is sputter-deposited on the propagation path of a surface acoustic wave after cooling it to room temperature, for example, and then f can be easily obtained by simply adjusting the thickness of the misaligned thin film by changing the deposition time. This is based on the discovery by the present inventors that it is possible to adjust the FIG. 2 shows a concrete example. Film thickness and f when a thin film of SiC2 arranged in irregular paths is formed by sputtering on the propagation path of the surface acoustic wave of a surface acoustic wave filter formed on a quartz substrate. The relationship with is shown in curve 21. Curve 21 shows that the change in fo changes from negative to positive depending on the film thickness, and when this change is used, f changes depending on the film thickness.

In this case, if the film thickness is too thin, for example, it will be deposited /c, and if the thickness of the 1.7 film becomes, for example, 108 or less, it will be deposited /ζ The thin film will be a continuous film. The characteristics are not reproducible.

On the contrary, the film thickness is too thick, for example, the film thickness is 0.03λ (λ:
As shown by curve 22, if the insertion loss exceeds 1 dB (the wavelength of the surface wave), the insertion loss increases to more than 1 dB, which is a problem in ordinary circuit design, and is therefore impractical. In addition, in this structure, fo and St○2
Theoretically, the relationship with the thickness of the thin film is f, as shown by curve 23 in FIG. was thought to increase. Therefore, the transition of fo from negative to positive (existence of a minimum point) in curve 21 in FIG. There is also.

Note that f is determined by the thickness of the thin film 13 having an irregular lattice arrangement.

As mentioned above, the peculiar change in 21 indicates the difference in the physical properties of this type of thin film from that of ordinary bulk materials, and this is -
This can also be inferred from the peculiar change in refractive index depending on the film thickness, as shown by curve 31 in FIG. According to this curve 31,
It can be seen that the refractive index of a thin film is lower than that of the bulk, and approaches the bulk value when the film thickness becomes constant.

In addition, in this type of layered structure, 1. the composition of the thin film with mismatched lattice arrangement should be chemically stable and not significantly hinder the propagation of surface acoustic waves;
In addition to oxides such as, nitrides such as silicon nitride and aluminum nitride, and carbides such as silicon carbide and boron carbide.

Borides such as boron and silicon boronide, A s 2
The present inventors have confirmed that chalcogenites such as Se3 are also effective. However, depending on the thickness of the thin film 13,
In order to obtain unique positive and negative change characteristics in the curve 21 and fo in FIG. For this purpose, for example, when the substrate 12 is a single crystal of quartz, a thin film 13 of S z 02 having the same chemical composition as quartz is used. If a glass material is used for the substrate 12, for example, a substrate with a wide range of sound velocities can be obtained, so it is effective as a substrate with this kind of layered structure. The present inventors have confirmed that the present invention is effective for a wide range of practical applications, such as surface acoustic wave filters and dual delay element oscillators.

FIG. 4 40 shows an interdigital transducer (IDT) 4 that uses a piezoelectric crystal as the substrate 12 as in the example described above, and has a pair of comb-shaped electrodes for excitation of surface acoustic waves for transmission and reception.
This is a back acoustic wave filter having a so-called four-terminal structure in which 7 and 13 are provided in the IDT section.

In addition to crystal, LiNb can be used as the piezoelectric material used for the substrate 12.
O3, LiTaos.

CdS, Zn○, A6N, GaAs, pZT (PbZr
, Ti1-xO), etc. In this case, for example, the crystal is for ultra-high stability, L I N bo3. p Z T is for high coupling (broadband), LiTaos, Z n
O is effective in forming a highly stable surface acoustic wave device. Further, the GaAs crystal is effective for monolithically forming a GaAs semiconductor element and a surface acoustic wave device.

Furthermore, as a thin film material with mismatched lattice arrangement suitable for these piezoelectric substrates, 5102 for quartz and L lNb0
Then, LiNb0 LiTa0 then L z T
The present inventors have confirmed that the same composition as the substrate, such as 3 3, 3 of a Os, is useful.

FIG. 560 shows the structure of a surface acoustic wave delay line in which the substrate 12 has a laminated structure in which a piezoelectric thin film 122 is deposited on a non-piezoelectric substrate 121. In this case, the non-piezoelectric substrate 121 is made of, for example, zero temperature coefficient glass whose propagation velocity of surface acoustic waves changes little with temperature, and the piezoelectric thin film 122 is made of, for example, a C-axis oriented ZnO piezoelectric thin film. Further, a thin film 13 having a sub-array of characteristic frequencies of the delay line is successively deposited, and finally, an IDT section 1 for transmitting and receiving is formed. As this substrate 121,
When insulators such as sapphire, spinel, and magnesia, or semiconductors such as St are used in addition to glass, high-quality piezoelectric thin films are formed on these substrates, allowing monolithic integration of surface acoustic wave devices, semiconductors, optical devices, etc. It is also effective for

Furthermore, the present inventors have confirmed that the use of this type of layered substrate is effective in forming a resonator as shown in FIG. 660. This resonator uses, for example, an ST-cut crystal for the substrate 12, and has a pair of IDTs 61 at the center and a reflector 62 with a grating structure at the ends. In this case, a thin film 13 having a mismatched lattice arrangement with a main component of 5102 is laminated on top of the reflector 62, and the film thickness of this thin film 13 is set to a desired value so that the center frequency f of the resonator is set. to the desired value. In addition to this example, when using the non-piezoelectric substrate 12, for example, the central IDT uses a so-called thin-film transformer structure in which thin-film piezoelectric materials are laminated. In addition, when the reflector is formed on a non-piezoelectric substrate, the grating structure described above is used.
In the case of a piezoelectric substrate, in addition to the grating structure, the anti-#J device can also be formed with an interdigital electrode made of, for example, a vapor-deposited film. In this case, the thin film 13 is formed on the interdigital electrode. Of course, these reflectors may be formed on either side of the thin film 13 after the thin film 13 has been deposited to a suitable thin film.

More specific examples will now be described in order to better understand the present invention.

Example (1) A comb-shaped electrode pair (wire width 0.9 μm, number of logarithms 300, electrode film thickness 500) made of an Al vapor-deposited film was formed on the surface of an ST-cut crystal 120. The center frequency f0 of the surface acoustic wave filter with this electrode as the input/output electrode was 848.2 MH2, but it was deviated from the desired frequency by 0.2 MHz.

Subsequently, a quartz target was sputtered in argon gas using a magnetron batter apparatus, and a thin film 13 whose main component was Sio2 was formed on the propagation path for 1 minute.

The temperature of the device was maintained at 30'C during the deposition. As a result, a center frequency of 848 MHz (desired value) was obtained. The thickness of the thin film 13 was 1,008 mm. Here, if a substrate of the present invention with a layered structure is formed on which a 100-layer thin film 13 having the same film thickness and composition as this is pre-deposited, and a surface acoustic wave filter is formed thereon by a similar process, manufacturing variations in fo was less than ±50KHz during mass production.

Example (2) (0001) Multilayer structure substrate 1 of ZnO thin film/glass substrate
A pair of comb-shaped electrodes (line 115.
47zm, logarithm 20. An electrode film thickness of 1500 mm) was formed. The center frequency f of a surface acoustic wave filter with this electrode as an input/output electrode. The frequency was 145 MHz, 0.05 MHz, and the desired frequency was off by 0.05 MHz.

Subsequently, a quartz target was sputtered in argon gas using a magnetron sputtering device to form a thin film 13 whose main component was 8102 on the propagation path for 1 minute. The humidity of the device was maintained at 30° C. during the vapor deposition. As a result, the center frequency is 145 M
Hz (desired value) was obtained. The thickness of the thin film 13 was 300 mm. Here, if a substrate of the present invention with a layered structure is formed on which a 300-layer thin film 13 having the same film thickness and composition as this is pre-deposited, and a surface acoustic wave filter is formed on this by a similar process, manufacturing variations in fo will be reduced. ±10K during mass production
It was below Hz.

Example (3) A comb-shaped electrode pair (line width 1.271 m, logarithm 30° electrode film N
500 persons) and grating reflectors (line width 1.2 μm, number of gratings 200) were provided at both ends of these electrodes to form a surface acoustic wave resonator. As a result, the resonant frequency was 74.2 MHz, which was deviated from the desired frequency by 0.2 MHz.

Next, the quartz film was sputtered in argon gas using a magnetron sputtering device, and one layer was sputtered onto the grating.
A thin film 13 having a main component of 8102 was formed in minutes. The temperature of the device was maintained at 30° C. during the deposition. .

As a result, a resonant frequency of 674 MHz (desired value) was obtained. The thickness of the thin film 13 was 1,008 mm. Here, a thin film 1 whose main component is Sio2 is added to 100 with the same film thickness.
3 is deposited in advance, and a surface acoustic wave resonator is formed thereon by a similar process, the manufacturing variation in resonance frequency is reduced to ±6 during mass production.
It was below 0 KHz.

Effects of the Invention As is clear from the above explanation, the use of the substrate for an elastic surface acoustic wave chair of the present invention has the advantage that a highly accurate surface acoustic wave device can be easily produced.

This case is characterized by a laminated structure of thin films arranged in a mismatched lattice on the propagation path surface of the surface acoustic wave device. Irregular lattice array n′! In this embodiment, the method of forming the 9th film by sputter deposition has been described, but it is not necessarily necessary to rely on the sputter deposition method, and it is sufficient that the lattice of the deposited thin film is disordered. Since ion beam scattering, electron beam evaporation, chemical vapor deposition (CVD), and plasma CVD can also be used, there are no technical problems in manufacturing. Conventionally, it has been considered undesirable to stack different types of materials on the surface acoustic wave propagation surface, as it is said to increase the propagation loss of the surface acoustic waves and reduce the reliability of the device due to the generation of distortion in the substrate. but,
Select a thin film with a unique structure like the one of the present invention and its film thickness range←
Even if they are laminated on the propagation surface of a surface acoustic wave device, not only will this not have any negative effect on the surface acoustic wave characteristics, but silicon carbide thin films, for example, exhibit water rupture properties, which will lead to improved moisture resistance of the device. -! However, the effects of the present invention are not limited to the filter or the two-delay element oscillator described in the embodiments, but are also applicable to convolvers, all kinds of surface acoustic wave devices, and even acousto-optic devices. Since the present invention is effective for formation, its industrial value is high.

[Brief explanation of drawings]

Yes, 41 D. , to L Chu, □No. FIG. 2 is a structural diagram of main parts of a surface acoustic wave device. 12... Substrate, 13... Thin film with mismatched lattice arrangement, 41... Comb-shaped electrode for surface acoustic wave excitation,
62... Reflector, 121... Non-piezoelectric substrate, 122... Piezoelectric thin film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure R

Claims (12)

[Claims] (1) In a layered structure substrate whose substrate surface is coated with a thin film with an irregular lattice arrangement, the thickness of the thin film with an irregular lattice arrangement is 0.03λ (λ: wavelength of surface wave in the layered structure substrate) from 10 people.
A surface wave device substrate characterized by being in the range of . (2) The substrate for a surface wave device according to claim 1, wherein the thin film with a mismatched lattice arrangement is made of at least one of oxides, nitrides, carbides, borides, and chalcogenites. (3) The thin film with mismatched lattice arrangement is silicon oxide! The surface wave device substrate according to claim 1, which has the #I feature. (4) The substrate for a surface wave device according to claim 1, wherein the substrate is a piezoelectric material. (5) Substrate. 2. The surface wave device substrate according to claim 1, wherein the substrate is a semiconductor or an insulator whose surface is coated with a piezoelectric thin film. (6) Piezoelectric body is crystal, LiNb0 LiTaO3,Z
n0゜3aAIN, GaAs, or p Z T (PbZ
5. The surface wave device substrate according to claim 4, wherein the substrate is rxTil-x○3). (7) The piezoelectric thin film is ZnO, AlN, CdS or p
6. The surface wave device substrate according to claim 5, which is zT (P b Z r xT 11-x○3). (8) Patent m' characterized in that the substrate is made of glass, sapphire, spinel, magnesia, or Si.
The substrate for a surface wave device according to item 1, wherein the range of lJ is desired. (9) The substrate for a surface acoustic wave device according to claim 1, wherein the thin film having the mismatched lattice arrangement and the base material have the same constituent material composition. (10) The substrate for a surface acoustic wave device according to claim 9, wherein the misaligned thin film is made of silicon oxide and the substrate is made of quartz. (11) The substrate for a surface acoustic wave device according to claim 1, further comprising a surface acoustic wave reflector for a resonator provided on the substrate. (12) The substrate for a surface acoustic wave device according to claim 1, characterized in that a comb-shaped electrode for excitation of a surface acoustic wave for a filter is provided on the substrate.