JP2009118369A - Surface acoustic wave device, and method of manufacturing surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave (SAW) device capable of preventing troubles such as short-circuiting due to a conductive foreign substance, without damaging resonance property, and a method of manufacturing the SAW device. <P>SOLUTION: A SAW resonator 10 has: an inter-digital transducer (IDT) electrode 12 with an insulating film 20 formed on its surface; and a reflector 13 provided on a piezoelectric substrate 11. The insulating film 20 formed on a surface of each electrode finger 12a, 12b of the IDT electrode 12 is formed on an upper surface and a side surface (sidewall portion) of the other electrode finger 12a, 12b while providing an interval in the sidewall of each electrode finger 12a, 12b in which the surface of the sidewall is exposed with the piezoelectric substrate 11 so as not to be brought into contact with the piezoelectric substrate 11. The insulating film 20 is constituted of an anode oxide film formed by performing anode oxidization on aluminum that is a material for forming each electrode finger 12a, 12b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device and a method for manufacturing the surface acoustic wave device.

Conventionally, in the field of high-frequency devices, an elastic surface configured to excite a surface acoustic wave on a piezoelectric body surface or detect a surface acoustic wave by an IDT (Interdigital Transducer) electrode formed on the surface of a piezoelectric substrate. Wave devices are used in various electronic devices. As a surface acoustic wave device, an elastic surface in which an IDT electrode and a pair of reflectors disposed on both sides of the IDT electrode are provided on a piezoelectric substrate made of a piezoelectric material such as quartz, lithium niobate, or lithium tantalate. A wave device (surface acoustic wave resonator) is disclosed in Patent Document 1, for example.
In the surface acoustic wave device described in Patent Document 1, the IDT electrodes are in contact with each other such that a plurality of electrode fingers connected to one bus bar made of aluminum or the like and a plurality of electrode fingers connected to the other bus bar face each other. It is the structure arranged alternately so that it may not. The IDT electrode is excited by applying an AC voltage between the electrode fingers via the one bus bar and the other bus bar, and the surface acoustic wave that oscillates from the IDT electrode and propagates to the piezoelectric substrate is reflected by the reflector. Thus, by confining the surface acoustic wave energy in the IDT electrode, it is possible to obtain resonance characteristics with low energy loss and high Q value.

  By the way, as one of the major characteristic failure factors in the surface acoustic wave device, there is a short circuit of the IDT electrode due to adhesion of a foreign substance having conductivity between the electrode fingers of the IDT electrode. As a means for preventing the IDT electrode from being short-circuited by such a conductive foreign material, there is a method of forming an insulating film on the surface of the IDT electrode. For example, in Patent Document 1, an oxide film (aluminum oxide) may be formed on the surface of an IDT electrode by a method in which a surface acoustic wave device is placed in oxygen plasma to perform plasma discharge or a method in which the surface acoustic wave device is immersed in an oxidizing solution. This oxide film can be used as an insulating film for preventing a short circuit of the IDT electrode.

JP-A 63-10909

However, when an insulating film is formed on the entire surface of the IDT electrode of the surface acoustic wave device, the insulating film on the side wall portion of each electrode finger of the IDT electrode is in contact with the piezoelectric substrate that is the propagation surface of the surface acoustic wave. As a result, the insulating film inhibits the excitation of the surface acoustic wave and increases the vibration loss. For example, when the surface acoustic wave device is a surface acoustic wave resonator, the Q value is lowered and the CI (Crystal Impedance) value is increased. When the surface acoustic wave device is a surface acoustic wave filter, transmission characteristics are generated. Increase the insertion loss.
Further, when the insulating film comes into contact with the piezoelectric substrate and inhibits the excitation of the surface acoustic wave, the electromechanical coupling coefficient K ^{2 of the} surface acoustic wave device is reduced and the piezoelectric effect is reduced. For example, when the surface acoustic wave device is a surface acoustic wave resonator, the capacitance ratio γ increases, the frequency difference between resonance and anti-resonance narrows, and the impedance of the resonator suddenly changes at narrow frequency intervals. Therefore, it becomes difficult to satisfy the oscillation condition in the oscillation circuit. In addition, when the surface acoustic wave device is a resonator-type surface acoustic wave filter, there is a problem that the vibration characteristics of the surface acoustic wave device may be deteriorated, for example, it is difficult to widen the pass bandwidth. It was.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A surface acoustic wave device according to this application example is a surface acoustic wave device having at least a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and having an insulating film formed on a surface thereof. An insulating film is formed on the upper surface and the side surface of the electrode finger of the IDT electrode so as not to contact the piezoelectric substrate.

According to this configuration, since the insulating film on the side wall portion of the IDT electrode is formed so as not to contact the piezoelectric substrate, the insulating film is formed so as to cover the entire surface of the IDT electrode to insulate the side wall portion of the IDT electrode. Problems that may occur when the film is in contact with the piezoelectric substrate can be avoided. For example, when an insulating film inhibits the propagation of surface acoustic waves and increases vibration loss, the Q value decreases and the CI value increases when the surface acoustic wave device is a surface acoustic wave resonator. An increase in insertion loss of transmission characteristics in the case of a surface acoustic wave filter can be prevented. In addition, since the insulating film is in contact with the piezoelectric substrate and inhibits the excitation of the surface acoustic wave, the electromechanical coupling coefficient K ^{2 of the} surface acoustic wave device is reduced, thereby avoiding a problem that may occur due to the reduction of the piezoelectric effect. it can. For example, when the surface acoustic wave device is a resonator-type surface acoustic wave filter, the capacitance ratio γ increases and the frequency difference between resonance and anti-resonance narrows, and the impedance of the resonator changes rapidly in a narrow frequency interval. As a result, it is possible to avoid difficulty in satisfying the oscillation condition in the oscillation circuit. Further, when the surface acoustic wave device is a resonator type surface acoustic wave filter, it is possible to suppress deterioration of vibration characteristics such as difficulty in widening the passband.
Therefore, it is possible to provide a surface acoustic wave device that can prevent a short circuit of the IDT electrode due to a conductive foreign substance without impairing vibration characteristics.

  Application Example 2 In the surface acoustic wave device according to the application example, the insulating film is an oxide film of the metal material for forming the IDT electrode.

  According to this configuration, since the insulating film can be formed by anodizing the IDT electrode itself, a uniform insulating film can be formed on the surface of the IDT electrode by a relatively simple manufacturing process. Further, the oxide film formed by anodic oxidation has a thicker thickness and is stronger than, for example, a natural oxide film of a metal material for forming an IDT electrode or an oxide film obtained by heat treatment or the like. Since an oxide film can be formed, a surface acoustic wave device including an insulating film having excellent insulating properties can be provided.

  Application Example 3 In the surface acoustic wave device according to the application example, aluminum or an alloy containing aluminum as a main component is used as a material for forming the IDT electrode, and the insulating film is formed by anodizing the IDT electrode. It is a formed anodic oxide film.

  According to this configuration, aluminum or an alloy containing aluminum as a main component has been most frequently used as an IDT electrode material of a surface acoustic wave device from the viewpoint of processing and cost, and a metal that forms anodized by anodization. It is a representative material. Thereby, it is suitable as a material for forming the IDT electrode of the surface acoustic wave device according to the application example described above, and a uniform insulating film can be stably formed on the surface of the IDT electrode under well-known anodic oxidation conditions.

  Application Example 4 A method for manufacturing a surface acoustic wave device according to this application example includes at least a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and having an insulating film formed on the surface. A method of manufacturing a surface acoustic wave device formed on an upper surface and a side surface of an electrode finger of the IDT electrode so as not to contact the piezoelectric substrate, wherein the IDT electrode is formed on the piezoelectric substrate using a photolithography method. Forming and leaving the photoresist on the IDT electrode, and sacrificing at least a thickness of the IDT electrode on the piezoelectric substrate in the region where the IDT electrode is formed A sacrificial layer forming step of forming a layer, a photoresist removing step of removing part of the surface of the IDT electrode by removing the photoresist, and the photoresist After the leaving step, an insulating film forming step for forming the insulating film on at least an upper surface and a side surface of the electrode finger of the IDT electrode, and a sacrificial layer removing step for removing the sacrificial layer after the insulating film forming step, , Including.

According to this configuration, since the photoresist is left on the IDT electrode in the IDT electrode forming step, when the sacrificial layer is formed in the sacrificial layer forming step by, for example, a sputtering method, the sacrificial layer is formed on the IDT electrode. Then, it is laminated on the photoresist as it is, on the region where the IDT electrode is formed and on the surrounding piezoelectric substrate. At this time, since the photoresist serves as a barrier for sputtering, the sacrificial layer is hardly stacked on the exposed side wall of the IDT electrode, and the sacrificial layer formed on the piezoelectric substrate with a thickness smaller than that of the IDT electrode. The side wall portion of the IDT electrode is covered with the sacrificial layer by the thickness. Then, by forming the insulating film in the next insulating film forming step, the insulating film is formed on the surface of the IDT electrode excluding the portion covered with the sacrificial layer among the sidewall portions of the IDT electrode. It can form in the upper surface and side surface of the electrode finger of an IDT electrode in the aspect which does not contact a piezoelectric substrate.
As a result, an increase in vibration loss such as a decrease in Q value and an increase in CI value that can occur when the insulating film is in contact with the piezoelectric substrate, or a decrease in the piezoelectric effect due to a decrease in the electromechanical coupling coefficient K ^2. Problems such as deterioration of vibration characteristics can be suppressed. Therefore, it is possible to manufacture a surface acoustic wave device that can prevent the IDT electrode from being short-circuited by a conductive foreign material without impairing vibration characteristics.

  Application Example 5 In the surface acoustic wave device manufacturing method according to the application example described above, in the step of forming the insulating film, the metal material for forming the IDT electrode is oxidized to form an oxide film. The insulating film is used.

  According to this configuration, the insulating film can be formed by anodizing the IDT electrode itself, and a uniform insulating film can be formed on the surface of the IDT electrode by a simple manufacturing process. Further, by controlling the applied voltage at the time of anodizing, for example, it has a thicker thickness than a natural oxide film of a metal material for forming an IDT electrode or an oxide film obtained by heat treatment or the like. In addition, since a strong oxide film can be formed, a surface acoustic wave device including an insulating film having excellent insulating properties can be manufactured.

  Application Example 6 In the surface acoustic wave device manufacturing method according to the application example described above, in the IDT electrode formation step, aluminum or an alloy containing aluminum as a main component is used as a material for forming the IDT electrode, and the insulating film is formed. In the step, the insulating film made of an anodized film is formed by anodizing the IDT electrode.

  According to this configuration, aluminum or an alloy containing aluminum as a main component has been most frequently used as an IDT electrode material of a surface acoustic wave device because of advantages such as workability and cost, and anodized by anodization. As the metal material to be used, it is a representative metal applied to anodic oxidation. Therefore, a uniform insulating film can be stably formed on the surface of the IDT electrode under known anodic oxidation conditions.

  Application Example 7 In the surface acoustic wave device manufacturing method according to the application example, an inorganic amphoteric oxide is used as a material for forming the sacrificial layer in the sacrificial layer forming step, and in the sacrificial layer removing step, The sacrificial layer is dissolved and removed using dilute acid.

  According to this configuration, the sacrificial layer made of an inorganic amphoteric oxide can be removed with a dilute acid, and when the IDT electrode material is, for example, aluminum or an aluminum alloy, the aluminum or aluminum alloy is formed on the surface. The surface acoustic wave device according to the above application example is obtained by removing the sacrificial layer almost without damaging the IDT electrode on which the insulating film is formed in the sacrificial layer removing step. Can be manufactured.

  Application Example 8 In the surface acoustic wave device manufacturing method according to the application example, zinc oxide is used as a material for forming the sacrificial layer in the sacrificial layer forming step, and dilute hydrochloric acid or dilute in the sacrificial layer removing step. The sacrificial layer is dissolved and removed using nitric acid.

  According to this configuration, zinc oxide can be dissolved and removed relatively easily with dilute hydrochloric acid or dilute nitric acid, and when aluminum or an aluminum alloy is used as the material of the IDT electrode, for example, the aluminum or aluminum alloy is not on the surface. It hardly dissolves in dilute hydrochloric acid or dilute nitric acid due to the action of the natural oxide film formed. As a result, the sacrificial layer can be removed in the sacrificial layer removing step without substantially damaging the IDT electrode on which the insulating film is formed, and the surface acoustic wave device according to the application example can be manufactured.

Hereinafter, a SAW (Surface Acoustic Wave) resonator as an embodiment of a surface acoustic wave device will be described with reference to the drawings.
(First embodiment)
1A and 1B illustrate a SAW resonator 10 according to this embodiment. FIG. 1A is a perspective view, FIG. 1B is a cross-sectional view taken along line AA in FIG. ) Is a partially enlarged cross-sectional view illustrating a cross section in a range B in FIG. 2 (a) to 2 (c) and FIGS. 3 (a) to 3 (d) are partial enlarged cross-sectional views for explaining the manufacturing process of the SAW resonator, and FIG. 1 (c) in each manufacturing process. The same cross section is shown.

[SAW resonator]
First, the structure of the SAW resonator will be described.
As shown in FIG. 1A, the SAW resonator 10 includes an IDT electrode 12 and a reflector 13 on a rectangular piezoelectric substrate 11 made of a piezoelectric material such as quartz. The piezoelectric substrate 11 has main surfaces 14 and 15 on the front and back, and an IDT electrode 12 and a reflector 13 are formed on one main surface 14.

  The IDT electrode 12 has two comb-shaped cross finger electrodes, a plurality of electrode fingers 12a connected to the bus bar of one cross finger electrode, and a plurality of electrode fingers 12b connected to the bus bar of the other cross finger electrode. Are arranged so as not to contact each other. In this embodiment, the IDT electrode 12 is made of aluminum (Al), and a surface acoustic wave can be excited by applying reverse-phase voltages to the electrode fingers 12a and 12b of the two intersecting finger electrodes. It is configured.

  The reflector 13 is disposed and formed so as to sandwich the IDT electrode 12 from both sides. The surface acoustic wave propagated from the IDT electrode 12 is reflected by the reflector 13 and serves to contain energy in the central portion of the piezoelectric substrate 11. In the present embodiment, the reflector 13 is also made of aluminum like the IDT electrode 12.

  As shown in FIG. 1B, the distance between the electrode finger 12a and the electrode finger 12b in the IDT electrode 12 is formed at an equal pitch P, and the wavelength λ of the excited surface acoustic wave has a relationship of λ = 2P. Become. The IDT electrode 12 is formed with a thickness H. Further, the thickness t of the piezoelectric substrate 11 is set to a thickness of 4 wavelengths (4λ) or more of the surface acoustic wave.

  As shown in FIG. 1C, an insulating film 20 is formed on the surface of each electrode finger 12 a, 12 b of the IDT electrode 12. The insulating film 20 is provided with a predetermined gap in which the surface of the side wall portion is exposed between the electrode fingers 12a and 12b so as not to contact the piezoelectric substrate 11 at the side wall portions of the electrode fingers 12a and 12b. It is formed on the upper and side surfaces of 12a and 12b. The insulating film 20 of the present embodiment is made of an anodic oxide film formed by anodizing aluminum that is a material for forming the electrode fingers 12a and 12b.

According to the SAW resonator 10 of the above embodiment, the insulating film 20 is formed on the upper and side surfaces of the electrode fingers 12a and 12b on the electrode fingers 12a and 12b of the IDT electrode 12 so as not to contact the piezoelectric substrate 11. ing. Thereby, the insulating film 20 on the side walls of the electrode fingers 12a and 12b is in contact with the piezoelectric substrate 11 as in the case where the insulating film is formed so as to cover the entire surface of the electrode fingers 12a and 12b of the IDT electrode 12. This inhibits excitation of surface acoustic waves and increases vibration loss, resulting in a decrease in Q value and an increase in CI value, or a decrease in electromechanical coupling coefficient K ² and a decrease in piezoelectric effect. There is no. Therefore, it is possible to provide the SAW resonator 10 that can prevent the electrode fingers 12a and 12b of the IDT electrode 12 from being short-circuited by the conductive foreign matter without impairing the vibration characteristics.
The insulating film 20 is made of an anodized film formed by anodizing aluminum that is a metal material for forming the IDT electrode 12. As a result, it is possible to form a uniform insulating film 20 as compared with a case where a separate insulating film material is applied and the like, and is thicker than an oxide film obtained by, for example, a natural oxide film of aluminum or heat treatment. Since the insulating film 20 has a thickness and can form a strong oxide film, the insulating film 20 is excellent in insulation.

[Method for Manufacturing SAW Resonator]
Next, a method for manufacturing the SAW resonator 10 of the first embodiment will be described with reference to FIGS. 2 and 3, the ratio of the thickness of the piezoelectric substrate 11 and the thickness of the IDT electrode 12 is different from the actual thickness, and the thickness of the piezoelectric substrate 11 is shown thin.
In FIG. 2A, first, an aluminum thin film 12M, which is a metal material for forming IDT electrodes, is laminated on the piezoelectric substrate 11 by vapor deposition or sputtering. Next, a photoresist film 90 for forming the IDT electrode 12 is formed by patterning the aluminum thin film 12M on the aluminum thin film 12M by a photolithography method by a spin coating method or a dipping method.
Next, as shown in FIG. 2B, the photoresist film 90 is exposed to the IDT electrode 12 pattern and developed to form a photoresist pattern 90P of the IDT electrode 12. Then, as shown in FIG. 2C, the aluminum thin film 12M is etched using the photoresist pattern 90P as an etching resist, thereby forming the IDT electrode 12 having a plurality of electrode fingers 12a and 12b. In the present embodiment, although not shown, the reflector 13 made of the same aluminum as the IDT electrode 12 is formed simultaneously with the IDT electrode 12 by the same formation method as the IDT electrode 12 described above.

Next, as shown in FIG. 3A, a sacrificial layer 55, which is a thin film made of an amphoteric inorganic material, is formed to a thickness smaller than the thickness of the IDT electrode 12 by sputtering or the like. In this embodiment, zinc oxide (ZnO), which is an inorganic amphoteric oxide, is used as the sacrificial layer 55.
When the sacrificial layer 55 is laminated by the sputtering method, the sacrificial layer 55 is formed on the photoresist pattern 90P remaining on the upper surface of the IDT electrode 12, between the electrode fingers 12a and 12b of the IDT electrode 12, and the IDT electrode 12. It is laminated on the surface of the piezoelectric substrate 11 exposed to the periphery. At this time, the sacrificial layer 55 is hardly laminated on the side wall portions of the electrode fingers 12a and 12b of the IDT electrode 12 due to the photoresist pattern 90P as a barrier, and only a part of the side wall portion on the piezoelectric substrate 11 side is piezoelectric. The state is covered with the sacrificial layer 55 laminated on the substrate 11. The sacrificial layer 55 laminated on the piezoelectric substrate 11 between the electrode fingers 12a and 12b of the IDT electrode 12 is close to the side wall portions of the electrode fingers 12a and 12b with the photoresist pattern 90P serving as a barrier as described above. Since it becomes difficult to stack as the position increases, it is stacked thickly at the central portion between the electrode fingers 12a and 12b, and is stacked with a substantially arcuate cross-sectional shape that becomes thinner toward the side wall portions of the electrode fingers 12a and 12b. .

  Next, when the photoresist pattern 90P is peeled, as shown in FIG. 3B, the sacrificial layer 55 laminated on the photoresist pattern 90P together with the photoresist pattern 90P is removed, and the IDT electrode is formed on the piezoelectric substrate 11. 12 and the sacrificial layer 55 are left.

Next, as shown in FIG. 3C, an insulating film 20 is formed on the exposed surface of the IDT electrode 12. In the present embodiment, the insulating film 20 is an anodized film formed on the surface of aluminum by anodizing the IDT electrode 12 made of aluminum. As a method for forming an oxide film by anodic oxidation on the surface of the IDT electrode 12, for example, in a state where each electrode finger 12a, 12b constituting the IDT electrode 12 is connected to a power source for anodic oxidation on the anode side, the IDT The piezoelectric substrate 11 on which the electrode 12 and the sacrificial layer 55 are formed is immersed in an anodizing solution. In this anodizing solution, a cathode plate connected to the cathode side of the anodizing power source is immersed. An oxide film is formed on the surface of the IDT electrode 12 by applying a predetermined electrolysis voltage to cause the electrode fingers 12a and 12b constituting the IDT electrode 12 as an anode from a power source for anodization to flow a current and electrolytically oxidize aluminum. An insulating film 20 made of is formed.
As the anodizing solution, for example, an aqueous solution of a phosphate, a mixed solution of an aqueous solution of borate, or an aqueous solution of a neutral salt such as citrate or adipate can be used. The temperature of the anodic oxidation solution is preferably about room temperature in order to avoid the anodic oxidation film formed as the insulating film 20 from being a porous film. About 30 ° C is desirable.

The insulating film 20 made of an oxide film obtained by anodizing under such conditions can be formed on the surface of the IDT electrode 12 by controlling the film thickness to be approximately proportional to the applied voltage when anodizing. Further, it can be formed thicker than alumina (Al ₂ O ₃ ), which is an oxide obtained by heating aluminum, or an oxide film naturally formed on the surface of aluminum in the air. Moreover, it becomes a strong oxide film. As a result, the insulating film 20 made of an oxide film obtained by anodic oxidation of the IDT electrode 12 is more susceptible to electrical troubles such as a short circuit due to adhesion of conductive foreign matter to the electrode fingers 12a and 12b of the IDT electrode 12. The protective film can be effectively prevented.

Then, as shown in FIG. 3D, the SAW resonator 10 is obtained by removing the sacrificial layer 55 with a dilute acid such as 1% hydrochloric acid (HCl) or nitric acid (HNO ₃ ).
Since the sacrificial layer 55 is formed of zinc oxide which is an amphoteric oxide, it acts as a basic oxide with respect to dilute acid and dissolves relatively easily. On the other hand, the piezoelectric film of the electrode fingers 12a and 12b of the insulating film 20 formed on the surface of most of the IDT electrode 12 made of aluminum and the IDT electrode 12 covered with the sacrificial layer 55 and not formed with the insulating film 20 is used. The oxide film formed by naturally oxidizing the side wall portion on the substrate 11 side is hardly dissolved in the diluted acid. Thereby, the sacrificial layer 55 can be removed with almost no attack on the surface of the IDT electrode 12.

According to the method of manufacturing the SAW resonator 10 of the above embodiment, the photoresist pattern 90P is left on the IDT electrode 12 in the process of forming the IDT electrode 12. Thus, when the sacrificial layer 55 is formed by a sputtering method or the like in the step of forming the sacrificial layer 55, the photoresist pattern 90P becomes a barrier for sputtering, and the side walls of the electrode fingers 12a and 12b of the IDT electrode 12 are sacrificed. The layer 55 is hardly laminated and is formed on the piezoelectric substrate 11 with a thickness thinner than that of the electrode fingers 12a and 12b. Then, the side walls of the electrode fingers 12 a and 12 b are covered with the sacrificial layer 55 by the thickness of the sacrificial layer 55. Then, by forming the insulating film 20 in the next step of forming the insulating film 20, the surface of each electrode finger 12a, 12b excluding the portion covered with the sacrificial layer 55 among the side walls of each electrode finger 12a, 12b. Thus, the insulating film 20 can be formed on the upper surface and side surfaces (side wall portions) of the electrode fingers 12a and 12b of the IDT electrode 12 in a manner that does not contact the piezoelectric substrate 11.
Thereby, the SAW resonator 10 capable of preventing the electrode fingers 12a and 12b of the IDT electrode 12 from being short-circuited by the conductive foreign material without impairing the vibration characteristics can be manufactured.

(Second Embodiment)
In the SAW resonator 10 and the manufacturing method thereof according to the first embodiment, the insulating film 20 is an anodized film formed by anodizing the IDT electrode 12 made of aluminum. Thus, the oxide film of the metal material for forming the IDT electrode 12 is not limited to the insulating film 20, but an insulating material can be laminated on the surface of the IDT electrode 12 to form the insulating film.

  FIGS. 4A to 4C illustrate the manufacturing process of the SAW resonator in which the insulating film other than the oxide film of the metal material for forming the IDT electrode is formed. FIG. It is a partial expanded sectional view which shows the same cross-sectional part as c). In the SAW resonator manufacturing method of the present embodiment, the manufacturing process up to FIGS. 2A to 2C and FIGS. 3A and 3B described in the first embodiment is the same. Therefore, the description thereof is omitted, and the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

FIG. 4A shows a state in which the SAW resonator 10 according to the first embodiment has been advanced to the same manufacturing process as that shown in FIG. That is, after forming the IDT electrode 12 on the piezoelectric substrate 11 and further laminating the sacrificial layer 55, the extra sacrificial layer 55 and the like are removed, and between the electrode fingers 12 a and 12 b of the IDT electrode 12 and the IDT electrode 12. In this state, the sacrificial layer 55 is left on the peripheral piezoelectric substrate 11.
Next, as shown in FIG. 4B, an insulating film 20 ′ made of an oxide such as silicon dioxide (SiO ₂ ) or a nitride such as silicon nitride (Si ₃ N ₄ ) is laminated by sputtering or the like. Let

  The insulating film 20 ′ formed by sputtering is stacked on the surface of the IDT electrode 12 and the surface of the sacrificial layer 55. At this time, of the insulating film 20 ′ formed on the surface of the IDT electrode 12, the insulating film 20 ′ is stacked on the upper side of the side wall portion as the side walls of the electrode fingers 12a and 12b are stacked. The insulating film 20 ′ becomes a barrier, and the lamination of the insulating film 20 ′ on the side of the piezoelectric substrate 11 on the side wall portions of the electrode fingers 12a and 12b and the side wall portion side of the electrode fingers 12a and 12b on the sacrificial layer 55 is inhibited. Is done. In particular, the insulating film 20 ′ is hardly laminated near the boundary between the electrode fingers 12 a and 12 b and the portion covered with the sacrificial layer 55 on the piezoelectric substrate 11 side, and the electrode fingers 12 a and 12 b are not laminated. A gap is generated in which the surface of the side wall portion is slightly exposed.

Next, as shown in FIG. 4C, the sacrificial layer 55 is removed by dilute acid such as 1% hydrochloric acid or nitric acid to obtain the SAW resonator 10 ′. At this time, the insulating film 20 ′ laminated on the most part of the IDT electrode 12 and the surface of the sacrificial layer 55 hardly dissolves in dilute acid, but the side wall portions of the electrode fingers 12 a and 12 b of the IDT electrode 12. Among these, in the vicinity of the boundary with the portion covered with the sacrificial layer 55 on the piezoelectric substrate 11 side, as described above, dilute acid enters through the gap formed with the insulating film 20 ′ being hardly stacked, and the sacrificial layer 55 is dissolved, and the insulating film 20 ′ on the sacrificial layer 55 is lifted off and removed. As the sacrificial layer 55 is removed, the aluminum on the side of the piezoelectric substrate 11 on the side walls of the electrode fingers 12a and 12b is exposed, but the oxide film formed by natural oxidation of the aluminum surface is rare. Since the acid is hardly dissolved, the sacrificial layer 55 can be removed with almost no attack on the surface of the IDT electrode 12.
As described above, by removing the sacrificial layer 55 and the unnecessary insulating film 20 ′ laminated on the sacrificial layer 55, the side walls of the electrode fingers 12 a and 12 b of the IDT electrode 12 are in contact with the piezoelectric substrate 11. In such a manner, the SAW resonator 10 ′ having the insulating film 20 ′ formed on the upper surface and the side surface (side wall portion) of each electrode finger 12a, 12b is manufactured.

  According to the manufacturing method of the second embodiment, by having the insulating film 20 ′ formed on the surface of the IDT electrode 12 so as not to contact the piezoelectric substrate 11, the conductive property is maintained while maintaining excellent characteristics. The SAW resonator 10 ′ having a high resistance to troubles such as a short circuit due to the foreign material can be manufactured.

  Although the embodiments of the present invention made by the inventor have been specifically described above, the present invention is not limited to the above-described embodiments and modifications thereof, and various modifications can be made without departing from the spirit of the present invention. It is possible to make changes.

  For example, in the first and second embodiments, the insulating films 20 and 20 ′ are formed on both the electrode fingers 12 a and 12 b of the pair of cross finger electrodes constituting the IDT electrode 12. Not only this but also the structure which forms the insulating films 20 and 20 'only in the electrode finger 12a or the electrode finger 12b of any one of the cross finger electrodes can prevent a short circuit due to adhesion of conductive foreign matter.

  In the first embodiment, the insulating film 20 is an anodic oxide film obtained by anodizing aluminum which is a metal material for forming the IDT electrode 12. However, the insulating film 20 may be made of alumina, which is an oxide obtained by heat treatment of aluminum, for example, if the insulating film is formed to a thickness that can ensure sufficient insulation.

Further, although the crystal is used for the piezoelectric substrate 11 described in the first and second embodiments, the present invention is not limited to this. In addition to quartz, oxides such as aluminum nitride (AlN), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), lead zirconate titanate (PZT), lithium tetraborate (Li ₂ B ₄ O ₇ ) A piezoelectric substrate formed by stacking a thin film piezoelectric material such as aluminum nitride or tantalum pentoxide (Ta ₂ O ₅ ) on a substrate or a glass substrate can also be used.

  Moreover, in the said 1st and 2nd embodiment, although aluminum was used as a metal material for formation of the IDT electrode 12 and the reflector 13, it is not limited to this. For example, in the first embodiment in which the insulating film 20 is formed by anodic oxidation, a metal material such as titanium (Ti), tantalum (Ta), or tungsten (W) can be used. In the second embodiment, a multilayer film of gold (Au) and chromium (Cr), magnesium (Mg), or the like can be used.

  In the first and second embodiments, the 1-port SAW resonators 10 and 10 ′ and the manufacturing method thereof have been described in detail as an example of the surface acoustic wave device. However, the present invention is not limited to this, and a 2-port SAW resonator that can be used in a higher frequency band may be used. In addition, an IDT may be formed on a piezoelectric substrate such as a SAW filter or a SAW delay element such as a sensor or a convolver. Other surface acoustic wave devices in which electrodes are formed may be used.

(A) is a perspective view explaining the SAW resonator which is one Embodiment of a surface acoustic wave device, (b) is the sectional view on the AA line of (a), (c) is a figure of (b). The partial expanded sectional view of the range of middle B. (A)-(c) is the elements on larger scale explaining the manufacturing process in the manufacturing method of the SAW resonator of 1st Embodiment. (A)-(d) is the elements on larger scale explaining the manufacturing process in the manufacturing method of the SAW resonator of 1st Embodiment. (A)-(c) is the elements on larger scale explaining the manufacturing process in the manufacturing method of the SAW resonator of 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,10 '... SAW resonator as a surface acoustic wave device, 11 ... Piezoelectric substrate, 12 ... IDT electrode, 12a, 12b ... Each electrode finger of IDT electrode, 12M ... Aluminum thin film as metal material for formation of IDT electrode, DESCRIPTION OF SYMBOLS 13 ... Reflector, 20, 20 '... Insulating film, 55 ... Sacrificial layer, 90P ... Photoresist pattern as photoresist.

Claims (8)

A surface acoustic wave device having at least a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and having an insulating film formed on a surface thereof,
2. The surface acoustic wave device according to claim 1, wherein the insulating film is formed on an upper surface and a side surface of the electrode finger of the IDT electrode so as not to contact the piezoelectric substrate. The surface acoustic wave device according to claim 1,
2. The surface acoustic wave device according to claim 1, wherein the insulating film is an oxide film of a metal material for forming the IDT electrode. The surface acoustic wave device according to claim 2,
Aluminum or an alloy containing aluminum as a main component is used as a material for forming the IDT electrode,
2. The surface acoustic wave device according to claim 1, wherein the insulating film is an anodized film formed by anodizing the IDT electrode. The piezoelectric substrate and at least an IDT electrode provided on the piezoelectric substrate and having an insulating film formed on the surface thereof, and the insulating film does not contact the piezoelectric substrate. A method of manufacturing a surface acoustic wave device formed in
Forming the IDT electrode on the piezoelectric substrate using a photolithography method and leaving the photoresist on the IDT electrode; and
A sacrificial layer forming step of forming a sacrificial layer with a thickness smaller than the thickness of the IDT electrode on at least the piezoelectric substrate in the region where the IDT electrode is formed;
Removing the photoresist to expose a portion of the surface of the IDT electrode; and
After the photoresist removing step, an insulating film forming step of forming the insulating film on at least the upper surface and the side surface of the electrode finger of the IDT electrode;
And a sacrificial layer removing step of removing the sacrificial layer after the insulating film forming step. In the manufacturing method of the surface acoustic wave device according to claim 4,
In the step of forming the insulating film, the metal material for forming the IDT electrode is oxidized to form an oxide film, and the oxide film is used as the insulating film. In the manufacturing method of the surface acoustic wave device according to claim 4 or 5,
In the IDT electrode forming step, aluminum or an alloy containing aluminum as a main component is used as a metal material for forming the IDT electrode.
A method of manufacturing a surface acoustic wave device, wherein the insulating film made of an anodized film is formed by anodizing the IDT electrode in the insulating film forming step. In the manufacturing method of the surface acoustic wave device according to any one of claims 4 and 5,
In the sacrificial layer forming step, an inorganic amphoteric oxide is used as a material for forming the sacrificial layer,
In the sacrificial layer removing step, the sacrificial layer is dissolved and removed using dilute acid. In the manufacturing method of the surface acoustic wave device according to claim 6,
In the sacrificial layer forming step, zinc oxide is used as a material for forming the sacrificial layer,
In the sacrificial layer removing step, the sacrificial layer is dissolved and removed using dilute hydrochloric acid or dilute nitric acid.

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