JPH04135019U - surface acoustic wave filter - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a surface acoustic wave filter with low loss and good frequency characteristics. [Structure] An input surface acoustic wave transducer 20 and an output surface acoustic wave transducer 30 formed on a piezoelectric substrate 11 are formed using a low-density electrode metal film 21 made of aluminum or the like that has low resistance characteristics and can reduce propagation loss. This electrode metal film 2
1 and the piezoelectric substrate 11, the bonding pad portions 60, 70 have a two-layer structure made of chromium, aluminum, etc.
was connected. As a result, resistance loss and propagation loss are reduced, and the bonding pad portions 60 and 70 are firmly adhered to the surface of the piezoelectric substrate 11 by a metal film such as chromium for reinforcing adhesion, thereby preventing deterioration of bonding performance.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention generates a desired frequency using surface acoustic waves propagating along the surface of a piezoelectric substrate. Extracting surface acoustic wave filters, especially input elastic surfaces for excitation and reception of surface acoustic waves Improved material properties of wave transducer and output surface acoustic wave transducer to achieve low loss and good frequency The present invention relates to a surface acoustic wave filter designed to obtain characteristics.

0002

[Conventional technology]

Conventionally, as this type of surface acoustic wave filter, for example, the one shown in Fig. 2 has been used. was there. The configuration will be explained below using figures.

0003 FIG. 2 is a schematic plan view showing an example of the configuration of a conventional surface acoustic wave filter, and FIG. FIG. 3 is a sectional view taken along the line x-y in FIG. 2;

0004 This surface acoustic wave filter can be used, for example, as a communication signal filter, etc. It extracts the frequency of , and has a piezoelectric substrate 1. on this piezoelectric substrate 1 In this case, three input surface acoustic wave transducers 2 and two output surface acoustic wave transducers 3 are arranged alternately. is placed opposite to. Each input surface acoustic wave transducer 2 has a comb-shaped It is composed of multiple pairs of electrode fingers 2a and 2b formed on the The surface wave transducer 3 also includes a plurality of pairs of electrode fingers 3a and 3b formed in a comb shape. ing.

[0005] Electrode fingers 2a, 3a of each input surface acoustic wave transducer 2 and each output surface acoustic wave transducer 3 is a bonding pad 6 for input electrical signals via the extraction electrode parts 4 and 5; They are respectively connected to bonding pads 7 for output electrical signals. Electrode finger 2b , grounding bonding pads 8 and 9 are connected to the electrode fingers 3b, respectively. Ru. Further, on the piezoelectric substrate 1, an input surface acoustic wave transducer 2 and an output surface acoustic wave transducer 2 are provided. For example, a wiring pattern 10 for grounding is formed on the outer periphery of the device 3.

[0006] As shown in FIG. 3, the input surface acoustic wave transducer 2 is made of chromium (Cr) for the base electrode. Two-layer structure of film A and metal film B of aluminum (Al) or aluminum alloy It is formed of. Similarly, for the output surface acoustic wave transducer 3, the input surface acoustic wave It is formed of a two-layer structure made of the same material as the converter 2. The extraction electrode parts 4, 5 and the button The landing pads 6 and 7 are connected to each input surface acoustic wave transducer 2 and each output surface acoustic wave transducer. After forming the converter 3, a chromium film C and aluminum or aluminum alloy or gold are coated. Since it is formed by depositing a metal film D of (Au), the extraction electrode parts 4, 5 and Each of the bonding pads 6 and 7 has a four-layer structure. Also, the grounding button As for the landing pads 8 and 9, a chromium film C is also applied to the connecting portions of the electrode fingers 2b and 3b. and a metal film D such as aluminum, so it has a four-layer structure. ing.

[0007] This surface acoustic wave filter includes a bonding pad 6, a bonding pad 7, And each grounding bonding pad 8, 9 is shown via a bonding wire. connected to the input terminal, output terminal, and ground wiring pattern 10. It is.

[0008] Next, the operation of this surface acoustic wave filter will be explained.

[0009] When an electrical signal is input to an input terminal (not shown), the input electrical signal is The input signal is supplied to each surface acoustic wave transducer 2 via the input pad 6. Each input surface acoustic wave The transducer 2 generates surface acoustic waves in a direction perpendicular to the electrode fingers 2a and 2b (in the direction of the arrow in the figure). Excite. At that time, each output surface acoustic wave transducer 3 converts the propagated surface acoustic wave into The electrode fingers 3a and 3b receive the signal, convert it into an electrical signal, and transfer the electrical signal to the bonding pad. The signal is output to an output terminal (not shown) via the cable 7.

0010 In this way, it is excited between the electrode fingers 2a and 2b of each input surface acoustic wave transducer 2. A high output is obtained at a frequency that matches the surface acoustic wave output, and conversely, a high output is obtained when the surface acoustic wave output does not match. becomes low and functions as a filter.

[0011] Here, the insertion loss of this type of surface acoustic wave filter is the input surface acoustic wave transducer 2 When the number of output surface acoustic wave transducers 3 is N and M, respectively, the following equation (1) is given. available. 10 Log(N/M) dB…(1) According to equation (1), the number of input surface acoustic wave transducers 2 and output surface acoustic wave transducers 3 is Increasing N and M reduces the insertion loss of the surface acoustic wave filter.

0012

[Problem that the idea aims to solve]

However, the prior art has the following problems.

[0013] (i) In addition to the theoretical insertion loss expressed in equation (1) above, Therefore, it is desired to reduce resistance loss and propagation loss. However, the metal material for electrodes Due to its characteristics, trying to reduce resistance loss will result in an increase in propagation loss. cause problems.

[0014] (ii) Although the chromium film A shown in Figure 3 has a relatively high specific resistance, First, in the piezoelectric substrate 1, an input surface acoustic wave transducer 2, an output surface acoustic wave transducer 3, Close contact with electrode metals such as extraction electrode parts 4 and 5 and bonding pads 6 and 7 It is used to prevent metal peeling to strengthen the strength of the film, and is usually used with a film thickness of around 100 Å. I'm tired. If chromium films A and C are removed to reduce resistance loss, the wire When performing bonding, separation occurs between the material of the piezoelectric substrate 1 and the electrode metal, and the bond The problem arises that it is no longer possible to perform

[0015] The present invention solves the problems that the prior art had, without increasing propagation loss. It is difficult to reduce resistance loss and prevent peeling of the piezoelectric substrate and electrode metal. A surface acoustic wave filter that solves the need to take into account the need to reduce resistance loss. It provides routers.

[0016]

[Means to solve the problem]

The first idea was to solve the above problem by propagating surface acoustic waves along the surface. an input surface acoustic wave transducer that converts an input electrical signal into the surface acoustic wave; is arranged opposite to the input surface acoustic wave transducer and converts the surface acoustic wave into an output electric signal. an output surface acoustic wave transducer that converts and outputs the input surface acoustic wave transducer; The extraction electrode parts connected to the output surface acoustic wave transducers and the extraction electrode parts connected to the output surface acoustic wave transducers, respectively, and The bonding pad connected to the pole part connects to the provided surface acoustic wave filter. the input surface acoustic wave transducer, the output surface acoustic wave transducer, and the drawer; The electrode section and the bonding pad section are constructed as follows.

[0017] That is, the input surface acoustic wave transducer and the output surface acoustic wave transducer have low resistance characteristics. It is composed of a single layer of low-density electrode metal film that has high properties and can reduce propagation loss. The extraction electrode portion is formed on the piezoelectric substrate and extends to the electrode metal film. A first wiring metal film and a second wiring metal film for reinforcing adhesion formed on the first wiring metal film. A three-layered wiring metal film and a third wiring metal film formed on the second wiring metal film. It consists of The bonding pad portion is formed on the piezoelectric substrate and is connected to the first bonding pad portion. a first bonding metal film for reinforcing adhesion extended to the second wiring metal film; a wire formed on the first bonding metal film and extending to the third wiring metal film; It is composed of two layers including a second bonding metal film for bonding.

[0018] The second invention is a method in which the electrode metal film and the first wiring metal film of the first invention are The second wiring metal film and the first wiring metal film are formed of aluminum or aluminum alloy. A bonding metal film is formed of chromium, and the third wiring metal film and the first bonding metal film are formed of chromium. The second bonding metal film is formed of aluminum, aluminum alloy, or gold. It was completed.

[0019]

[Effect]

In the first idea, since the surface acoustic wave filter is configured as described above, When a signal is input through the bonding pad section, the input surface acoustic wave transducer It works to excite surface acoustic waves through electric effects. The output surface acoustic wave transducer is Receives surface acoustic waves propagating on the surface of the electrical board, converts them into electrical signals, and transmits the electrical signals. It works to output the signal as an output electrical signal. Here, input surface acoustic wave transducer and The output surface acoustic wave transducer is a low-density transducer that has low resistance characteristics and can reduce propagation loss. Formed with a single layer of electrode metal film, it does not become a load against periodic vibrations. , even if the adhesion strength to the piezoelectric substrate does not decrease, resistance loss and propagation loss decrease. It works as it should.

[0020] On the other hand, a first wiring metal film and a third wiring metal film are formed on the piezoelectric substrate to strengthen their adhesion. A firmly attached extraction electrode part is formed by the second wiring metal film. , the second bonding metal film for bonding is in close contact with the bonding pad part. The first bonding metal film for strength reinforcement firmly adheres to the surface of the piezoelectric substrate. Deterioration of bonding properties is prevented.

[0021] The second idea reduces resistance loss, reduces propagation loss, and stabilizes the first idea. It is possible to realize bonding properties with high reliability and reproducibility. Therefore, the above problem can be solved. You can decide.

[0022]

【Example】

FIG. 1 is a schematic plan view of a surface acoustic wave filter showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line X-Y in FIG. 1. FIG.

As shown in FIG. 1, this surface acoustic wave filter is used, for example, as a signal filter for communication, and is used for surface acoustic wave elements made of, for example, lithium niobate (LiNbO ₃ ) single crystal. It has a piezoelectric substrate 11. On this piezoelectric substrate 11, there are three input surface acoustic wave transducers 20 having a plurality of pairs of electrode fingers 20a and 20b formed in a comb shape, and electrode fingers 30a and 30a having the same shape as the electrode fingers 20a and 20b. Two output surface acoustic wave transducers 30 having an output of 30b are arranged opposite to each other alternately.

[0024] Further, on the piezoelectric substrate 11, electrode fingers 20a and 20a of each input surface acoustic wave transducer 20 are provided. and the lead-out voltages connected to the electrode fingers 30b of each output surface acoustic wave transducer 30. The pole parts 40, 50 and the bonders connected to the lead electrode parts 40, 50, respectively. the electrode fingers 20b of each input surface acoustic wave transducer 20 and each A grounding bonder is connected to each electrode finger 30a of the output surface acoustic wave transducer 30. pad portions 80 and 90 are formed.

[0025] Further, on the piezoelectric substrate 11, for example, an input surface acoustic wave transducer 20, an output surface acoustic wave transducer 20, and an output surface acoustic wave transducer 20, A predetermined ground wiring pattern 100 is formed around the outer periphery of the wave converter 30. Then, the bonding pad section 60, the bonding pad section 70, and each ground The bonding pad portions 80 and 90 are connected via bonding wires (not shown). Connected to the input terminal, output terminal, and ground wiring pattern 100, respectively. There is.

[0026] As shown in FIG. 4, each input surface acoustic wave transducer 20 and output surface acoustic wave transducer 3 0 uses sputtering vapor deposition technology etc. on the piezoelectric substrate 11, for example, aluminum is deposited on the piezoelectric substrate 11. After forming the film, an electrode metal film 21 is formed using photolithography technology. . This electrode metal film 21 becomes electrode fingers 20a, 20b and electrode fingers 30a, 30b. ing. In addition, together with the electrode metal film 21, a first wiring metal film 41 for an extraction electrode, 51 are patterned at the same time. Each electrode metal film 21 is formed in one layer on the piezoelectric substrate 11. is provided, and its film thickness is about 500 Å to 1000 Å. Here, aluminum is selected as one of the low density metals that have low resistance properties and can reduce propagation loss. It is.

[0027] The extraction electrode section 40 is made of a first wiring metal film 41 made of the same material as the electrode metal film 21. , a second wiring metal film 42 formed in a layered manner on this first wiring metal film 41; 3 and a wiring metal film 43. Similarly, the extraction electrode section 50 has an electrode A first wiring metal film 51 made of the same material as the metal film 21, and a top of this first wiring metal film 51. It is composed of a second wiring metal film 52 and a third wiring metal film 53 formed in a layered manner. It is.

[0028] The second wiring metal films 42 and 52 and the third wiring metal films 43 and 53 are Sputtering vapor deposition technology, photolithography technology, etc. are applied on the metal films 41 and 51. First, a second wiring metal film made of chromium, etc., which is one of the metals for reinforcing adhesion, is formed. 42 and 52, respectively, and further on the second wiring metal films 42 and 52, Third wiring metal films 43 and 53 made of aluminum or the like are each patterned. It is something that was given. On the first wiring metal films 41 and 51, chromium and aluminum are coated. A two-layer film will be formed, and the film thickness will be approximately 3000 Å to 1 μm. The ROM film thickness is approximately 100 Å). Therefore, the shaded area in Figure 1 has a three-layer structure. The electrode film thickness is approximately 3500 Å to 1.1 μm.

[0029] The bonding pad parts 60 and 70 are formed at the same time as the extraction electrode parts 40 and 50. It is made of the same material as the second wiring metal films 42 and 52 and is in close contact with the surface of the piezoelectric substrate 11. The first bonding metal films 61 and 71 formed at the same time and the first bonding metal films 61 and 71 formed at the same time, The same material as the third wiring metal films 43 and 53 is simultaneously applied on the wiring metal films 61 and 71. The second bonding metal films 62 and 72 are formed. bondi The contact pad portions 60 and 70 are made of a two-layer film of chromium and aluminum on the piezoelectric substrate 11. is formed, and its film thickness is about 3000 Å to 1 μm.

[0030] The grounding bonding pad parts 80 and 90 are respectively provided on the surface of the piezoelectric substrate 11. The electrode fingers 20b of each input surface acoustic wave transducer 20 and each output surface acoustic wave transducer are in close contact with each other. The first bonding metal film 8 is formed over the connection portions of the 30 electrode fingers 30b. 1, 91 and the wire bonds formed on the first bonding metal films 81, 91. and second bonding metal films 82 and 92 for bonding. stop Similarly to the bonding pad parts 60 and 70, chromium and alumina are placed on the piezoelectric substrate 11. A two-layer film of aluminum will be formed, with a thickness of approximately 3000 Å to 1 μm. It is m.

[0031] The operation of the surface acoustic wave filter configured as above will be explained.

[0032] When an input electrical signal is input to an input terminal (not shown), the input electrical signal is is supplied to each input surface acoustic wave transducer 20 via the pad section 60. input bullet In the surface wave transducer 20, distortion occurs between the electrode fingers 20a and 20b due to the piezoelectric effect. At the same time, it is elasticized in a direction perpendicular to the electrode fingers 20a and 20b (in both directions perpendicularly indicated by the arrows in the figure). Excite sexual surface waves. When the surface acoustic waves reach the output surface acoustic wave transducer 30, each output The surface acoustic wave transducer 30 converts surface acoustic waves into electric signals using electrode fingers 30a and 30b. and converts the electrical signal into an output electrical signal through the bonding pad section 70. output to an output terminal (not shown).

[0033] In this way, the spacing between the electrode fingers 20a and 20b can be adjusted to correspond to the desired frequency. By setting a frequency that matches the excited surface acoustic wave output, high output is obtained, and conversely, when there is a mismatch, the output becomes low, and the function as a filter is obtained. .

[0034] This embodiment has the following advantages.

[0035] (a) The input surface acoustic wave transducer 20 and the output surface acoustic wave transducer 30 are connected to an electrode metal film. 21, and is formed on the piezoelectric substrate 11. This allows surface acoustic waves to Filter resistance and propagation losses are reduced. The reason for this will be explained next.

[0036] Resistance loss is determined by the specific resistance of the electrode metal. On the other hand, the propagation loss is It is determined by the density of For example, the specific resistance is aluminum: 2.6 μΩ-m, gold: 2 ．． 1 μΩ-m, chromium; 12.9 μΩ-m. Density is aluminum;2. 7 g/cm3, gold: 19.3 g/cm3, and chromium: 7.2 g/cm3.

[0037] For example, in aluminum, gold, and chromium, it is necessary to Gold is best because of its low resistance, followed by aluminum. Reduce propagation loss For example, among aluminum, gold, and chromium, aluminum has a lower density. The best. Thus, a metal selected for its resistivity and density, e.g. The input surface acoustic wave transducer 20 and the output surface acoustic wave transducer 30 are formed using one layer of aluminum. If this is done, the electrical resistance and mass will be increased by chromium compared to the conventional one using chromium. It is clear that the electrode fingers 20a, 20b and the electrode fingers 30a, 3 Since the load can be removed for periodic vibrations of 0b, the resistance can be reduced without increasing propagation loss. Can reduce losses.

[0038] (b) The electrode materials of the bonding pad portions 60 and 70 are usually reliable and reproducible. It is formed with a two-layer structure of chromium and aluminum or chromium and gold, taking into account . The thickness of chromium is approximately 100 Å in order to strengthen the adhesion with the piezoelectric substrate 11 (prevent peeling). used in Also in this example, since chromium is used as the base electrode material, Bonding pad parts 60, 70 and ground bonding pad parts 80, 90 Here, the two-layer structure is used to increase the adhesion strength with the piezoelectric substrate 11, and the extraction electrode part 40, 50 has a three-layer structure that increases the adhesion between the metal films, so the electrode gold The problem of metal peeling does not occur, and the same bonding properties as before can be obtained.

[0039] Note that the present invention is not limited to the embodiments described above, and various modifications are possible. Variations For example, there are the following:

(I) In the embodiment described above, the piezoelectric substrate 11 is made of a piezoelectric material made of LiNbO ₃ single crystal, but may be made of a piezoelectric material such as LiTaO ₃ single crystal. Alternatively, a glass substrate with a piezoelectric material film formed thereon may be used.

[0041] (II) In FIG. 1, the input surface acoustic wave transducer 20 and the output surface acoustic wave transducer 30 Although the total number of installed electrodes is five, it is not limited to this. Surface acoustic waves of 5 or more It may also be configured using a converter.

[0042] (III) In the above embodiment, each input surface acoustic wave transducer 20 and each output surface acoustic wave transducer 20 Aluminum was used as the electrode material of the wave converter 30, but in keeping with the spirit of the present invention, If so, electrode materials other than aluminum may be used. For example, aluminum Using aluminum alloys such as aluminum and copper (Cu), aluminum and silicon (Si), etc. It's okay. Further, the electrode material of the bonding pad portions 60 and 70 is The bonding metal film is made of chromium, and the second bonding metal film is made of aluminum alloy or gold. A two-layer structure using, for example, may be used.

[0043] (IV) In FIG. 1, a grounding wiring pattern 100 is formed on the piezoelectric substrate 11. The grounding bonding pad parts 80 and 90 were connected respectively, but the For example, connect the ground bonding pad parts 80 and 90 to a ground such as the outside of the piezoelectric substrate 11. It may also be configured to connect to a terminal.

[0044]

[Effect of the idea]

As explained in detail above, according to the first invention, the input device formed on the piezoelectric substrate The power surface acoustic wave transducer and the output surface acoustic wave transducer have low resistance characteristics and low propagation loss. It has a single-layer structure of a low-density electrode metal film that can reduce loss, and this electrode metal film and piezoelectric substrate The bonding pad is made of a two-layer metal film that firmly adheres to the As a result, resistance loss and propagation loss are reduced without impairing electrical characteristics, and bonding is improved. This can solve the problem of metal peeling during cleaning. This provides low loss and good frequency characteristics. It is possible to obtain a surface acoustic wave filter with

[0045] According to the second invention, the reduction in resistance loss, the reduction in propagation loss and A surface acoustic wave filter that can achieve stable bonding with good reliability and reproducibility. can be provided easily and inexpensively.

[Brief explanation of drawings]

FIG. 1 is a plan view of a surface acoustic wave filter according to an embodiment of the present invention.

FIG. 2 is a plan view of a conventional surface acoustic wave filter.

FIG. 3 is a sectional view taken along the line x-y in FIG. 2;

FIG. 4 is a sectional view taken along the line X-Y in FIG. 1;

[Explanation of symbols]

11 Piezoelectric substrate 20 Input surface acoustic wave transducer 30 Output surface acoustic wave transducer 40, 50 Extraction electrode portions 60, 70 Bonding pad portion 21 Electrode metal film 41, 42, 43, 51, 52, 53 First, second, Third wiring metal film 61, 62, 71, 72 First, second bonding metal film

Claims (2)

[Scope of utility model registration request] 1. A piezoelectric substrate on which surface acoustic waves propagate along the surface thereof, an input surface acoustic wave transducer for converting an input electric signal into the surface acoustic wave, and an input surface acoustic wave transducer disposed opposite to the input surface acoustic wave transducer. an output surface acoustic wave transducer that converts a surface acoustic wave into an output electric signal and outputs it; an extraction electrode section connected to the input surface acoustic wave transducer and the output surface acoustic wave transducer, respectively; and the extraction electrode section. In the surface acoustic wave filter, the input surface acoustic wave transducer and the output surface acoustic wave transducer are provided with a bonding pad portion connected to the The lead-out electrode portion includes a first interconnect metal film formed on the piezoelectric substrate and extended to the electrode metal film, and a first interconnect metal film formed on the first interconnect metal film. The bonding pad portion is composed of three layers: a second wiring metal film for reinforcing adhesion and a third wiring metal film formed on the second wiring metal film, and the bonding pad portion is connected to the piezoelectric substrate. a first bonding metal film for reinforcing adhesion formed above and extending to the second wiring metal film; and a first bonding metal film formed on the first bonding metal film and extending to the third wiring metal film. 1. A surface acoustic wave filter comprising two layers: a second bonding metal film for wire bonding; and a second bonding metal film for wire bonding. 2. The surface acoustic wave filter according to claim 1, wherein the electrode metal film and the first wiring metal film are formed of aluminum or an aluminum alloy, and the second wiring metal film and the first bonding film are formed of aluminum or an aluminum alloy. A surface acoustic wave filter in which a metal film is made of chromium, and the third wiring metal film and the second bonding metal film are made of aluminum, an aluminum alloy, or gold.