Electrode structure, piezoelectric vibration piece, piezoelectric device, and intermediate wafer for manufacturing piezoelectric device

Abstract

To provide a piezoelectric vibration piece 10 which includes a crystal piece 11 and an excitation electrode 13 comprising a titanium film 13a provided on the front and back of the crystal piece 11, as a lower layer, and a gold film 13b laminated on the titanium film, the excitation electrode 13 being improved in specific resistance and stress as compared with the conventional ones.SOLUTION: A titanium film has a film thickness of 0.5 nm or more and less than 3 nm, preferably 0.5 nm or more and 2 nm or less, and more preferably 0.5 nm or more and 1 nm or less, and a gold film has a film thickness of 10 nm or more and 100 nm or less, and preferably 10 nm or more and less than 40 nm. A crystal piece 11 is an AT-cut crystal piece.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrode structure consisting of a titanium (Ti) film as an underlayer and a gold (Au) film laminated on this titanium film, a piezoelectric vibrating piece using this electrode structure, a piezoelectric device using this piezoelectric vibrating piece, and an intermediate wafer suitable for use in manufacturing piezoelectric devices. [Background technology]

[0002] As communication speeds become higher, there is an increasing demand for higher frequencies in piezoelectric devices, which are the reference signal sources for communication devices. One type of piezoelectric device vibrates in thickness shear mode. In order to achieve higher frequencies in piezoelectric devices that vibrate in thickness shear mode and at the fundamental wave, the thickness of the piezoelectric vibrating reed becomes thinner and thinner. However, this leads to problems with the effect of the excitation electrodes provided on the front and back of the piezoelectric vibrating reed on the characteristics of the piezoelectric device.

[0003] As a specific example, Patent Document 1 describes a problem related to the conductive resistance of the excitation electrodes (e.g., paragraphs 6 and 7 of Patent Document 1). Also, Patent Document 2 describes a problem related to the conductive resistance of the excitation electrodes and a problem of thermal stress (e.g., paragraphs 6 and 7 of Patent Document 2). As a solution to the above problem, Patent Document 1 and Patent Document 2 each describe an electrode structure consisting of a titanium film as a lower layer and a gold film laminated on this titanium film. Patent Document 1 also describes that it is preferable to set the thickness of the gold film to 400 to 800 Å (e.g., claim 2 of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-214838 A [Patent Document 2] JP 2006-311337 A Summary of the Invention [Problem to be solved by the invention]

[0005] The electrode structure consisting of a titanium film as a lower layer and a gold film laminated on this titanium film is considered to be preferable as an excitation electrode for a high-frequency piezoelectric vibrating piece that vibrates in a thickness shear mode. However, according to the research of the inventor of this application, it has been found that there is still room for improvement. This application has been made in consideration of the above points, and therefore, an object of this application is to provide an electrode structure consisting of a titanium film and a gold film laminated on this titanium film, which has improved characteristics. Another object of this application is to provide a piezoelectric vibrating reed having the above-mentioned new electrode structure. Another object of this application is to provide a piezoelectric device using the above-mentioned piezoelectric vibrating reed. Another object of this application is to provide an intermediate wafer that can be used to mass-produce the above-mentioned piezoelectric device. [Means for solving the problem]

[0006] In order to achieve the above objects, the inventors of this application have conducted extensive research into an electrode structure consisting of a titanium film as a lower layer and a gold film laminated on the titanium film, focusing in particular on the structure of the titanium film. As a result, they have found facts about titanium films and facts about gold films that are useful for achieving the above objects. Therefore, according to the electrode structure of the first invention of this application, in an electrode structure consisting of a titanium film as a lower layer and a gold film laminated on this titanium film, the thickness of the titanium film is 0.5 nm or more and less than 3 nm. In carrying out this invention, the thickness of the titanium film is preferably 0.5 nm or more and 2 nm or less, more preferably 0.5 nm or more and 1.5 nm or less, and even more preferably 0.5 nm or more and 1 nm or less.

[0007] From another point of view, the first invention may be characterized in that, in an electrode structure consisting of a titanium film as a lower layer and a gold film laminated on the titanium film, the thickness of the titanium film is 0.5 nm or more and 28% or less of the thickness of the gold film. In this case, it is preferable to characterize the thickness of the titanium film as 0.5 nm or more and 15% or less of the thickness of the gold film. In carrying out the first aspect of the invention, the thickness of the gold film is preferably 10 nm or more and 100 nm or less, and more preferably 10 nm or more and less than 40 nm.

[0008] As described later, the electrode structure of the first invention is superior to the conventional Ti / Au electrode structure in terms of resistivity, stress, etc., and can be used in various fields. For example, it can be used as an excitation electrode for a piezoelectric vibrating reed, thereby providing a piezoelectric vibrating reed with superior characteristics compared to the conventional one. Therefore, according to the piezoelectric vibrating reed which is the second invention of this application, in a piezoelectric vibrating reed which has a substrate having piezoelectricity, and an excitation electrode which is composed of a titanium film as a lower layer provided on the substrate and a gold film laminated on the titanium film, the excitation electrode is characterized in that it is composed of the electrode structure of the first invention described above.

[0009] Furthermore, the piezoelectric device according to the third invention of this application is characterized by comprising the piezoelectric vibrating piece according to the second invention and a container that contains the piezoelectric vibrating piece. Here, the piezoelectric device refers to a piezoelectric vibrator, a piezoelectric oscillator, a piezoelectric vibrator with a temperature sensor, a piezoelectric oscillator with a temperature compensation function, etc., and typical examples are a quartz crystal vibrator (including one with a temperature sensor) that vibrates in a thickness shear mode, such as an AT-cut quartz crystal vibrator, and a quartz crystal oscillator (including one with a temperature compensation function).

[0010] According to a fourth aspect of the present invention, there is provided an intermediate wafer for manufacturing a piezoelectric device, which is a wafer having piezoelectricity and which includes a large number of the piezoelectric vibrating pieces according to the second aspect of the present invention in a matrix form. In the fourth aspect of the present invention, the wafer having piezoelectricity is a wafer made of a material having piezoelectricity such as quartz crystal, lithium niobate, or lithium tantalate, and is typically a quartz crystal wafer for quartz crystal resonators that vibrate in a thickness shear mode, such as an AT-cut quartz crystal wafer.

[0011] In carrying out the first and second aspects of the invention, it is preferable to carry out the following manufacturing method in order to manufacture the above-mentioned electrode structure and piezoelectric vibrating reed. That is, it is preferable to carry out a manufacturing method including the steps of forming a titanium film on the front and back sides of a piezoelectric substrate with a thickness of 0.5 nm or more and less than 3 nm, preferably 0.5 nm or more and less than 2 nm, more preferably 0.5 nm or more and less than 1.5 nm, and even more preferably 0.5 nm or more and less than 1 nm, and forming a gold film on each of the titanium films of the substrate on which the titanium film has been formed with a thickness of 10 nm or more and less than 100 nm, more preferably 30 nm or more and less than 100 nm, and more preferably 10 nm or more and less than 40 nm. From another point of view, it is preferable to carry out a manufacturing method including the steps of forming a titanium film on the front and back of a piezoelectric substrate with a thickness of 0.5 nm or more and 28% or less of the thickness of the gold film planned in the subsequent gold film forming step, more preferably 0.5 nm or more and 15% or less of the thickness of the gold film planned in the subsequent gold film forming step, and forming a gold film with the planned thickness on each of the titanium films of the substrate on which the titanium film has been formed. When carrying out these manufacturing methods, the planned thickness of the gold film is preferably 10 nm or more and 100 nm or less, more preferably 10 nm or more and less than 40 nm. According to the above-mentioned manufacturing method, since it includes the step of forming the titanium film and the gold film under predetermined conditions, the piezoelectric vibrating reed of the second invention can be manufactured with good reproducibility. Effect of the Invention

[0012] According to the electrode structure which is the first invention of this application, in an electrode structure composed of a titanium film as a lower layer and a gold film laminated on this titanium film, the thickness of the titanium film is set to be within the specified thickness range as described above, so that the resistivity and stress of the electrode structure can be set to desired values, thereby providing an electrode structure with improved characteristics compared to conventional ones. Furthermore, according to the piezoelectric vibrating reed which is the second invention of this application, since it is provided with the electrode structure of the first invention, it is possible to provide a piezoelectric vibrating reed with improved characteristics compared to conventional ones. Furthermore, according to the piezoelectric device which is the third invention of this application, since the piezoelectric vibrating piece of the second invention is used, it is possible to provide a piezoelectric device with improved characteristics compared to conventional devices, such as a high frequency piezoelectric device. In addition, the intermediate wafer for manufacturing piezoelectric devices, which is the fourth invention of this application, has a large number of piezoelectric vibrating pieces of the second invention arranged in a matrix, so that the piezoelectric devices of the third invention can be mass-produced by mounting individual piezoelectric vibrating pieces cut from this wafer in a container. [Brief description of the drawings]

[0013] [Figure 1] 1A to 1C are diagrams for explaining an electrode structure and a piezoelectric vibrating reed according to embodiments of the present invention; [Diagram 2] 1A to 1C are diagrams for explaining an experiment for discovering the requirements for each of the electrode structure and the piezoelectric vibrating reed of the present invention and the results thereof. [Diagram 3] 2 for explaining the experiment for discovering the requirements for the electrode structure and the piezoelectric vibrating reed and the results thereof. FIG. [Figure 4] 1A to 1C are diagrams illustrating a piezoelectric device according to an embodiment of the present invention. [Diagram 5] 1A to 1C are diagrams for explaining an example of a method for manufacturing a piezoelectric vibrating piece and an intermediate wafer for manufacturing a piezoelectric device. [Figure 6] 13A and 13B are diagrams illustrating a piezoelectric vibrating reed according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments of the inventions of this application will be described with reference to the drawings. Note that each drawing used in the description is merely a schematic illustration to the extent that these inventions can be understood. In addition, in each drawing used in the description, similar components are indicated by the same numbers, and their description may be omitted. Furthermore, the shapes, dimensions, materials, etc. described in the following description are merely preferred examples within the scope of this invention. Therefore, the present invention is not limited to only the following embodiments.

[0015] 1. Electrode structure and piezoelectric vibrating piece 1-1.Configuration Fig. 1 is an explanatory diagram of a piezoelectric vibrating reed 10 as an embodiment of the electrode structure of the first invention and the piezoelectric vibrating reed of the second invention. In particular, Fig. 1(A) is a plan view of the piezoelectric vibrating reed 10, and Fig. 1(B) is a cross-sectional view of the piezoelectric vibrating reed 10 taken along line PP in Fig. 1(A). Fig. 1(B) also shows an enlarged view of a portion of the excitation electrode. The piezoelectric vibrating piece 10 of the embodiment is an example in which the present invention is applied to an AT-cut quartz crystal piece. The coordinate axes X, Y', and Z' in Fig. 1(A) are axes derived from the crystal axes of quartz crystal. The piezoelectric vibrating piece 10 of the embodiment includes an AT-cut crystal blank 11 as a substrate having piezoelectricity, and an excitation electrode 13 having an electrode structure including a titanium film 13a as a lower layer provided on each of the front and back main surfaces of the crystal blank 11 and a gold film 13b laminated on the titanium film. The titanium film 13a as the lower layer functions as an adhesive layer between the crystal blank 11 and the gold film 13b. In the present invention, the thickness of the titanium film 13a is preferably 0.5 nm or more and less than 3 nm, more preferably 0.5 nm or more and 2 nm or less, even more preferably 0.5 nm or more and 1.5 nm or less, and even more preferably 0.5 nm or more and 1 nm or less. The thickness of the gold film 13b is preferably 10 nm or more and 100 nm or less, and more preferably 10 to 60 nm, more preferably 10 to less than 40 nm, in order to reduce the amount of gold used. From another point of view, the thickness of titanium film 13a may be 0.5 nm or more and 28% or less of the thickness of gold film 13b, and preferably 0.5 nm or more and 15% or less of the thickness of gold film 13b. The reason why it is preferable to set the thickness of the titanium film 13a and the thickness of the gold film 13b to the above values ​​will be explained in the experimental section described later.

[0016] In the case of the piezoelectric vibrating piece 10 of the embodiment, the crystal blank 11 has a square planar shape, and in this case, a rectangular shape. The thickness (dimension in the Y' direction) of the crystal blank 11 is a predetermined thickness according to the oscillation frequency required of the piezoelectric vibrating piece 10. Therefore, the higher the frequency of the piezoelectric vibrating piece 10, the thinner the crystal blank 11. And, as the piezoelectric vibrating piece 10 becomes higher frequency and the thickness of the piezoelectric vibrating piece becomes thinner, the configuration of the titanium film 13a and gold film 13b of the excitation electrode 13 becomes more important, and the above-mentioned numerical values ​​of the film thickness, etc. become effective. In this embodiment, the planar shape of the excitation electrode 13 is also rectangular, similar to the crystal blank 11. An extraction electrode 15 is extracted from a part of the excitation electrode 13 to one end of the crystal blank 11. However, the planar shapes of the crystal blank and the excitation electrodes are not limited to a rectangle, and may be changed according to the design of the piezoelectric vibrating piece 10, and may be circular or elliptical. The planar shapes of the crystal blank and the excitation electrodes may be different.

[0017] 1-2.Experiment The reason why the thicknesses of the titanium film 13a and the gold film 13b are set to the above values ​​is based on the experiments conducted by the inventor of this application, which will be described below with reference to FIGS. 1-2-1. Study of resistivity The inventors of this application prepared a large number of substrates, specifically AT-cut quartz crystal substrates, divided them into groups, and formed titanium films on the substrates of each group by evaporation so that the thicknesses were different, specifically 0.5 nm, 1 nm, 3 nm, and 5 nm. After the titanium film had been formed on the substrates of each group, a gold film was formed by evaporation at multiple levels between 10 nm and 200 nm. After the gold film had been formed, each substrate was heat-treated at 300°C in a nitrogen atmosphere, simulating the heat of a curing furnace used when fixing the piezoelectric vibrating reed to a piezoelectric device container with a conductive adhesive during the manufacture of the piezoelectric device. Also, a sample having only a titanium film was prepared by the same procedure as above, except that only a titanium film was formed on the substrate. Next, the resistivity of the film was measured for each of the sample having the titanium film and the gold film formed thereon, and the sample having only the titanium film formed thereon.

[0018] Next, a parallel resistance model was assumed for a sample with both titanium and gold films and a sample with only titanium film, and the resistivity of the gold film was calculated using the resistivity of both samples. The reason for calculating the resistivity of the gold film is to understand whether the resistivity of the gold film has changed due to the diffusion of the titanium film into the gold film, and the degree of influence if it has changed. In addition, as comparative samples, a chromium film was formed on the substrate instead of the titanium film, with a film thickness of 3 nm and 5 nm, and the other steps were the same as those for the titanium and gold film samples and the titanium film only sample. The resistivity of the gold film in the comparative sample was also calculated using the same parallel resistance model as above. Furthermore, as a reference, a gold film alone was formed on the substrate at multiple levels of thickness from 10 nm to 200 nm, and the resistivity of each was measured.

[0019] FIG. 2(A) shows the relationship between the ratio of the titanium film thickness to the gold film thickness, i.e., the Ti / Au ratio (%), and the resistivity of the gold film for various experimental samples formed as described above using a titanium film. FIG. 2(B) shows the relationship between the titanium film thickness and the gold film resistivity in a Ti / Au film, i.e., the distribution of the gold film resistivity relative to the titanium film thickness. Fig. 3(A) is a characteristic diagram summarizing the tendency of the gold film resistivity against the titanium film thickness and gold film thickness for various experimental samples formed as described above using a titanium film, a comparative sample formed using a chromium film, and a reference sample using only a gold film. In Fig. 3(A), the dashed line (Bulk Au) represents the characteristic of the reference sample. In addition, since the resistivity of the gold film of the sample with a titanium film thickness of 0.5 nm was essentially the same as that of the sample with a titanium film thickness of 1 nm, the plots of the resistivity of the sample with a titanium film thickness of 0.5 nm are omitted in Figures 2(A) and (B) and Figure 3(A). From FIG. 2(A), it can be seen that there is an almost linear and strong correlation between the titanium film thickness / gold film thickness and the resistivity of the gold film. Also, from Fig. 2(B), when a titanium film is used as the lower layer (adhesive film), the smaller the thickness of the titanium film, the smaller the resistivity of the gold film and the smaller the variation in resistivity of the gold film. Explaining Fig. 2(B) in detail, when the titanium film is 1 nm thick, the average resistivity of the gold film is 3.7μΩcm and the standard deviation is 1.53, when the titanium film is 3 nm thick, the average resistivity of the gold film is 7.2μΩcm and the standard deviation is 6.93, and when the titanium film is 5 nm thick, the average resistivity of the gold film is 11.2μΩcm and the standard deviation is 10.58. It can be seen that when the titanium film is less than 3 nm, 2 nm or less, or even 1 nm or 0.5 nm thick, the average resistivity and standard deviation of the gold film become smaller. Also, from FIG. 3(A), it can be seen that the resistivity of the gold film can be made smaller when a titanium film is used as the lower layer (adhesive film) than when a chromium film is used.

[0020] Here, in the case of a quartz crystal unit as a piezoelectric device, if we consider an example of a quartz crystal unit with a frequency of, for example, 48 MHz, which is often used as a reference clock source, the resistivity of the gold film is about 20 μΩcm. Furthermore, it is preferable that the resistivity of the gold film included in the excitation electrode of a high-frequency quartz crystal unit is 20 μΩcm or less. From this perspective, when considering the characteristic diagrams of Figures 2(A) and (B) and Figure 3(A), the following points (a) to (d) can be said. (a) When a titanium film is used as the underlayer (adhesive film), an electrode film with a lower resistivity is obtained than when a chromium film is used (see FIG. 3(A) in particular). (b) If the resistivity of the gold film is desired to be 20 μΩcm, the ratio of titanium film thickness / gold film thickness should be 28% or less. If the resistivity of the gold film is desired to be 10 μΩcm, which is half of 20 μΩcm, the ratio of titanium film thickness / gold film thickness should be 15% or less (see Figure 2(A) in particular). (c) The smaller the thickness of the titanium film, the smaller the resistivity of the gold film and the smaller the variation in resistivity of the gold film (see FIG. 2(B) in particular). Moreover, from FIG. 3(A), it can be estimated that even if the gold film is as thin as 10 nm, if the titanium film is as thin as 2 nm or less, the resistivity of the gold film can be made smaller than 20 μΩcm. Similarly, even if the gold film is as thin as 10 nm, if the titanium film is thinner than 1.5 nm, the resistivity of the gold film can be made smaller than 20 μΩcm. Therefore, it can be said that the thickness of the titanium film is preferably 0.5 nm or more and less than 3 nm, more preferably 0.5 nm or more and less than 2 nm, and even more preferably 0.5 nm or more and less than 1.5 nm or less, or 1 nm or less. The reason why the lower limit of the thickness of the titanium film 13a is set to 0.5 nm is that if the thickness of the titanium film 13a is smaller than this, it is considered that the film has low viability and does not provide adhesion to the substrate as an underlying film. (d) On the other hand, in this experiment, the gold film showed a reasonable resistivity when its thickness was 10 nm to 200 nm, but if it was 30 nm or more, the gold resistivity could be made smaller than 10 μΩcm, regardless of whether the titanium film was 1 nm, 3 nm, or 5 nm thick. On the other hand, since a thick gold film increases the material cost and is not preferable, it is considered that the gold film should be 10 to 100 nm thick, and preferably 10 to 100 nm thick. Considering the need to further reduce the material cost of gold and the fact that the mass of the electrode is preferably small in the case of high-frequency piezoelectric devices, it is considered that the gold film may be 10 to 60 nm thick, and more preferably less than 10 to 40 nm thick.

[0021] 1-2-2. Consideration of stress Next, the relationship between the thickness of the titanium film in the electrode structure of the present invention and the stress of the electrode structure will be considered. Figure 3(B) is a diagram summarizing the relationship between the thickness of the titanium film and the stress in the electrode structure of the above embodiment, with the horizontal axis representing the thickness of the gold film and the vertical axis representing the stress in the electrode structure of the embodiment. The positive direction of the vertical axis represents tensile stress, and the negative direction represents compressive stress. In the case of a piezoelectric vibrating piece, if stress is generated in the electrode structure, the oscillation frequency may vary due to stress relaxation over time, so it is preferable that the stress in the electrode structure is small. When the characteristic diagram of Figure 3(B) is considered from this perspective, the following can be said. It can be seen that the absolute value of stress decreases with decreasing titanium film thickness, for thicknesses of 1, 3, 5 nm, and 0.5 nm (not shown). In particular, when the titanium film thickness is 1 nm (including the case of 0.5 nm (not shown)), the stress approaches zero. It can also be seen that the tendency of stress caused by the titanium film thickness is counteracted as the gold film thickness increases. From these facts, it can be said that when the gold film thickness shown in this experiment is 10 to 200 nm, the titanium film thickness should be less than 3 nm, preferably 2 nm or less, more preferably 1.5 nm or less, and even more preferably 1 nm or less. This tendency coincides with the above-mentioned tendency to improve the resistivity. In addition, in each of the inventions of the electrode structure and the piezoelectric vibrating piece, the titanium film has a thin thickness of several nm, with a minimum of 0.5 nm. Examples of methods for identifying such film thickness include XPS depth profile analysis, XRR (X-ray reflectance method), and cross-sectional TEM.

[0022] 2. Piezoelectric Device Embodiments Next, an embodiment of the piezoelectric device of the present invention will be described. Here, an example of a quartz crystal resonator will be described as the piezoelectric device. FIG. 4 is an explanatory diagram for this purpose. In particular, FIG. 4(A) is a plan view of a piezoelectric device 20 of the embodiment, and FIG. 4(B) is a cross-sectional view of the piezoelectric device 20 taken along line QQ in FIG. 4(A). In FIG. 4(A), the illustration of the cover member 25 provided on the piezoelectric device 20 is omitted. A quartz crystal resonator 20 as a piezoelectric device 20 of the embodiment includes the piezoelectric vibrating piece 10 according to the first aspect of the invention and a container 21 that houses the piezoelectric vibrating piece 10. In this example, the container 21 includes a recess 21a having a rectangular shape in a plan view for accommodating the piezoelectric vibrating piece 10, a bank portion 21b surrounding the recess 21a, an adhesive pad 21c to which the piezoelectric vibrating piece 10 is fixed and bonded, and an external connection terminal 21d provided on the outer bottom surface of the container 21 for connecting the piezoelectric device 20 to an arbitrary electronic device. The adhesive pad 21c and the external connection terminal 21d are electrically connected by via wiring or castellation (not shown). The container 21 can be formed of a known ceramic package. In this case, the piezoelectric vibrating piece 10 has a cantilever support structure. Therefore, the piezoelectric vibrating piece 10 is connected and fixed to the adhesive pad 21c of the container 21 at the position of the extraction electrode 15 by a conductive adhesive 23. A lid member 25 is bonded to the top surface of the bank portion 21b of the container 21 in a structure according to the sealing method, and the piezoelectric vibrating piece 10 is sealed in the container 21.

[0023] In the above embodiment of the piezoelectric device, a quartz crystal resonator is shown as an example of the piezoelectric device, but the electronic device of the present invention also includes a piezoelectric device in which a quartz crystal resonator piece and other electronic components such as a temperature sensor and an oscillation circuit are mounted inside the container 21, that is, a quartz crystal resonator or a quartz crystal oscillator with a temperature sensor (including those having a temperature compensation function). Also, the structure of the container 21 described above is merely one example, and the container may have any other suitable structure.

[0024] 3. Example of manufacturing method for piezoelectric vibrating piece and intermediate wafer for forming piezoelectric device Next, an example of a manufacturing method of the electrode structure of the first invention and the piezoelectric vibrating piece of the second invention, and an embodiment of an intermediate wafer for a piezoelectric device of the fourth invention will be described. Figures 5(A) to (D) are manufacturing process diagrams for this purpose. Figures 5(B) and (C) are cross-sectional views of the wafer during the manufacturing process, and are cross-sectional views taken along line RR in Figure 5(A). In this example, a quartz crystal vibrating piece will be used as the piezoelectric vibrating piece for the description. First, an AT-cut crystal wafer 30 is prepared (FIG. 5(A)). Next, this crystal wafer 30 is processed using known photolithography and wet etching techniques to create the contours of the piezoelectric vibrating pieces, forming a wafer having a large number of crystal pieces 11, each of which is connected at one end to a frame 30a (FIG. 5(A)). Next, titanium films 31 are formed on the front and back of the quartz crystal wafer 30 on which the quartz crystal piece 10 has been formed, using any suitable film-forming method, so as to have a thickness within the range required by the first aspect of the invention, for example a thickness of 1 nm (FIG. 5(B)). Next, a gold film 33 is formed on this titanium film 31 by any suitable film formation method so as to have a thickness within the range of the requirements of the first invention, for example, a thickness of 60 nm (FIG. 5(C)). Next, the titanium film 31 and the gold film 33 are patterned into the shape of the excitation electrode 13 by known photolithography and metal etching techniques (FIG. 5(D)). By these steps, the piezoelectric vibrating piece 10 can be manufactured, and an intermediate wafer 30x for forming piezoelectric devices (see FIG. 5(D)) can be obtained which has a large number of piezoelectric vibrating pieces 10 for manufacturing piezoelectric devices arranged in a matrix.

[0025] This invention can be modified in any suitable manner. In the above embodiment, the planar shape of the quartz crystal wafer is circular, but the planar shape of the quartz crystal wafer may be other shapes, such as a square. Furthermore, the quartz crystal wafer is not limited to an AT cut, and may be a twice-rotated quartz crystal wafer, such as an SC cut. In the above-described embodiment, the piezoelectric vibrating piece uses a flat crystal piece as shown in Fig. 1, but the shape of the piezoelectric vibrating piece is not limited to this. For example, the piezoelectric vibrating piece 40 may be as shown in the plan view and the cross-sectional view along the line SS in Fig. 6(A). That is, the piezoelectric vibrating piece 40 may include a thick portion 41a having a thick portion, a vibrating portion 41b having a predetermined thickness according to the frequency, and excitation electrodes 43 according to the present invention provided on the front and back of the vibrating portion 41b. Also, for example, a piezoelectric vibrating piece 50 as shown in the plan view and the cross-sectional view along the line SS in Fig. 6(B) may be used. That is, the piezoelectric vibrating piece 50 may include a vibrating portion 51a having a predetermined thickness according to the frequency, thick portions 51b surrounding the vibrating portion 51a on all four sides, and excitation electrodes 53 according to the present invention provided on the front and back of the vibrating portion 51a. [Explanation of symbols]

[0026] 10: Piezoelectric vibrating piece (quartz crystal vibrating piece) of embodiment 11: Piezoelectric piece (quartz crystal piece) 13: Electrode structure (excitation electrode) 13a: Titanium film 13b: Gold film 20: Piezoelectric device (quartz crystal unit) according to an embodiment 21: Container 23: Conductive adhesive 25: Lid component 30: Wafer (quartz crystal wafer) 30a: Frame 31: Titanium film 33: Gold film 30x: Intermediate wafer for manufacturing piezoelectric vibrating pieces

Claims

1. In an electrode structure consisting of a titanium film as a lower layer and a gold film laminated on the titanium film, An electrode structure, characterized in that the thickness of the titanium film is 0.5 nm or more and less than 3 nm.

2. 2. The electrode structure according to claim 1, wherein the thickness of the titanium film is set to 0.5 nm or more and 2 nm or less.

3. 2. The electrode structure according to claim 1, wherein the thickness of the titanium film is set to 0.5 nm or more and 1 nm or less.

4. In an electrode structure consisting of a titanium film as a lower layer and a gold film laminated on the titanium film, 11. An electrode structure comprising: a titanium film having a thickness of 0.5 nm or more and 28% or less of the thickness of the gold film.

5. 5. The electrode structure according to claim 4, wherein the thickness of said titanium film is set to be 0.5 nm or more and 15% or less of the thickness of the gold film.

6. 6. The electrode structure according to claim 1, wherein the gold film has a thickness of 10 nm or more and 100 nm or less.

7. 6. The electrode structure according to claim 1, wherein the gold film has a thickness of 10 nm or more and less than 40 nm.

8. A piezoelectric vibrating piece including a substrate having piezoelectricity, a titanium film as a lower layer provided on the substrate, and an excitation electrode formed of a gold film laminated on the titanium film, The piezoelectric vibrating piece has a thickness of the titanium film that is equal to or greater than 0.5 nm and less than 3 nm.

9. 9. The piezoelectric vibrating piece according to claim 8, wherein the thickness of the titanium film is 0.5 nm or more and 2 nm or less.

10. 9. The piezoelectric vibrating piece according to claim 8, wherein the thickness of the titanium film is 0.5 nm or more and 1 nm or less.

11. A piezoelectric vibrating piece including a substrate having piezoelectricity, a titanium film as a lower layer provided on the substrate, and an excitation electrode formed of a gold film laminated on the titanium film, A piezoelectric vibrating piece, characterized in that the thickness of the titanium film is 0.5 nm or more and 28% or less of the thickness of the gold film.

12. 12. The piezoelectric vibrating piece according to claim 11, wherein the thickness of the titanium film is 0.5 nm or more and 15% or less of the thickness of the gold film.

13. 13. The piezoelectric vibrating piece according to claim 8, wherein the gold film has a thickness of 10 nm or more and 100 nm or less.

14. 13. The piezoelectric vibrating piece according to claim 8, wherein the gold film has a thickness of 10 nm or more and less than 40 nm.

15. 15. The piezoelectric vibrating piece according to claim 8, wherein the piezoelectric vibrating piece is an AT-cut quartz crystal piece.

16. A piezoelectric device comprising: the piezoelectric vibrating piece according to any one of claims 8 to 15; and a container that contains the piezoelectric vibrating piece.

17. 17. The piezoelectric device according to claim 16, wherein the piezoelectric device is a quartz crystal resonator, a quartz crystal resonator with a temperature sensor, a quartz crystal oscillator, or a quartz crystal oscillator with a temperature compensation function.

18. 16. An intermediate wafer for manufacturing a piezoelectric device, comprising a piezoelectric substrate having a large number of the piezoelectric vibrating pieces according to claim 8 in a matrix form.

19. 20. The intermediate wafer for manufacturing a piezoelectric device according to claim 18, wherein the piezoelectric vibrating piece is a quartz vibrating piece, and the intermediate wafer is a quartz wafer.

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