Crystal oscillator, crystal device

Abstract

The present invention provides an AT-cut quartz crystal vibrator equipped with comb-shaped electrodes as the capacitive electrode portion, and having a structure that easily suppresses the generation of unwanted vibrations caused by the comb-shaped electrodes. [Solution] The quartz crystal vibrator 11 is a comb-shaped electrode 11g, and is provided on at least one of the main surfaces of the front and back of the quartz crystal vibrator such that the repeating direction of the comb teeth is aligned with the Z' axis of the quartz crystal vibrator. The space dimension S in the line and space of the comb-shaped electrode is set with respect to the thickness T of the quartz crystal vibrator, S

Description

Technical Field

[0001] The present invention particularly relates to an AT-cut crystal vibrating piece having a capacitance-added structure and a crystal device using the same.

Background Art

[0002] With the miniaturization of electronic devices, the demand for miniaturization of crystal devices incorporated in electronic devices has been increasing more and more. As the miniaturization of crystal devices progresses, the crystal vibrating pieces used for them become smaller and are more likely to be affected by parasitic capacitance and the like, so the frequency stability of crystal devices tends to decrease. In particular, in the case of AT-cut crystal vibrating pieces, since the capacitance ratio cannot be made larger than that of SC-cut crystal vibrating pieces, countermeasures against the above are necessary. As an example of such a countermeasure, there is one described in FIG. 3 of Patent Document 1. In this example, excitation electrodes (resonance electrode portions referred to in Patent Document 1) are provided on both main surfaces of a piezoelectric substrate, and comb-shaped electrodes as capacitive electrode portions connected in parallel to the excitation electrodes are provided on one surface of the piezoelectric substrate. In this example, since the inter-electrode capacitance can be increased (since the capacitance ratio can be made larger) by providing the capacitive electrode portions, the frequency stability can be increased as compared with the case where it is not provided.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, according to the research of the inventors related to this application, it has been found that when comb-shaped electrodes as capacitive electrode portions are carelessly provided on AT-cut crystal vibrating pieces, unnecessary vibrations may occur due to the comb-shaped electrodes. Since unnecessary vibrations often deteriorate the characteristics of the main vibration of the crystal vibrating piece, it is desirable to suppress them as much as possible. This application has been made in view of the above points, and therefore the object of this application is to provide an AT-cut quartz crystal vibrator equipped with a comb-shaped electrode as a capacitive electrode portion, having a structure that easily suppresses the generation of unwanted vibrations caused by the comb-shaped electrode, and a quartz device using the same. [Means for solving the problem]

[0005] To achieve this objective, according to the first invention of this application, in an AT-cut quartz oscillating element comprising an excitation electrode and a comb-shaped electrode as a capacitive electrode portion, The comb-shaped electrode is provided on at least one of the front and back main surfaces of the quartz crystal vibrator such that the repeating direction of the comb teeth is aligned with the Z' axis of the quartz crystal vibrator. However, the Z' axis of the quartz crystal is the axis that is offset from the Z axis of the crystal axis of the quartz crystal due to the cutting angle of the AT-cut quartz crystal vibrator.

[0006] In this invention, the phrase "in a direction along the Z' axis of the crystal" means not only that the repeating direction of the comb teeth is directly parallel to the Z' axis, but also that the repeating direction is slightly deviated from the Z' axis within the scope of the purpose of this invention, and that the deviation in angle between the repeating direction and the Z' axis is, for example, within a range of plus or minus 10 degrees, preferably within a range of plus or minus 5 degrees. Furthermore, the phrase "provided on at least one main surface" above means that one comb-shaped electrode may be provided on one main surface, two or more may be provided, and one comb-shaped electrode may be provided on each of the front and back main surfaces of the quartz crystal vibrator, or two or more may be provided on each. The number and type of comb-shaped electrodes provided on each main surface can be selected according to the required inter-electrode capacitance.

[0007] Furthermore, the crystal device of the second invention of this application is characterized by comprising a crystal oscillator of the first invention and a container for mounting it. The crystal device of the second invention also includes a crystal oscillator with a temperature sensor, which comprises a crystal oscillator of the first invention and a temperature sensor such as a thermisophane inside the container. In addition, it also includes a crystal oscillator (including temperature-compensated crystal oscillators (so-called TCXOs) and oven-temperature crystal oscillators (so-called OCXOs)) comprising a crystal oscillator of the first invention, its oscillation circuit and a container for mounting them. [Effects of the Invention]

[0008] According to the first and second inventions of this application, as can be seen from the experimental results described later, it is possible to suppress some of the unwanted vibrations caused by the comb-shaped electrodes. Therefore, it is possible to provide an AT-cut quartz oscillator equipped with comb-shaped electrodes as the capacitive electrode portion, having a structure that easily suppresses the generation of unwanted vibrations caused by the comb-shaped electrodes, and a quartz device using the same. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram illustrating a quartz crystal vibrator 10 and a quartz device 30 (quartz oscillator 30) using the same, according to a first embodiment of the first invention. [Figure 2] This is a plan view illustrating the comb-shaped electrode, which is the capacitive electrode section. [Figure 3] Figure 1 is a perspective view showing an example of the external shape of a quartz device (junction-type quartz oscillator). [Figure 4] This is a diagram illustrating an example of a quartz crystal oscillator to which the present invention can be applied. [Figure 5] This figure, following Figure 4, illustrates an example of a quartz crystal oscillator to which the present invention may be applied. [Figure 6] This figure, following Figure 5, illustrates an example of a quartz crystal oscillator to which the present invention may be applied. [Modes for carrying out the invention]

[0010] Embodiments of the first and second inventions of this application will be described below with reference to the drawings. Note that the drawings used in this description are only schematic representations sufficient to understand these inventions. Furthermore, in the drawings used in this description, similar components are indicated with the same number, and their descriptions may be omitted. Also, the structural examples and materials used described below are merely preferred examples within the scope of this invention. Therefore, the present invention is not limited to the embodiments described below.

[0011] 1. Crystal oscillator and crystal device according to an embodiment As an embodiment, an example of applying the present invention to a bonded quartz oscillator will be described. Figure 1 is a diagram for this purpose and is an exploded perspective view of a quartz device, i.e., a bonded quartz oscillator 30, comprising a quartz oscillating element 11 of the embodiment and a base plate 13 and a lid plate 15 laminated so as to sandwich it from both sides. Note that the coordinate axes indicated by X, Y', and Z' in Figure 1 and other explanatory diagrams represent the crystal axes of the quartz. Furthermore, the Y' and Z' axes in the coordinate axes indicate that they are deviated from the true crystal axes of the quartz, the Y and Z axes, due to the cutting angle of the AT-cut quartz oscillating element. The AT-cut quartz crystal oscillating element 11 of this embodiment comprises a vibrating portion 11a, a frame portion 11b surrounding the vibrating portion 11a, a through portion 11c provided between the vibrating portion 11a and the frame portion 11b, and a connecting portion 11d partially connecting the vibrating portion 11a and the frame portion 11b. Furthermore, excitation electrodes 11e are provided on both main surfaces of the vibrating portion 11a, and wiring electrodes 11f are provided from the excitation electrodes 11e to the frame portion 11b. In addition, in this example, two comb-shaped electrodes 11g as capacitive electrodes are provided on the surface of the frame portion 11b facing the lid plate 15. The quartz crystal oscillating element 11, the base plate 13, and the lid plate 15 are joined to each other by a seal path 19. The specific structure of each component will be described below.

[0012] In this example, the vibrating part 11a is rectangular in shape when viewed from above. Of course, the planar shape of the vibrating part 11a may be any other shape, such as a circle or an ellipse. The frame portion 11b encloses the vibrating portion 11a, separated by the through portion 11c. The through portion 11c isolates the vibrating portion 11a from the outside, thereby reducing the deterioration of its vibration characteristics. A portion of the vibrating portion 11a and a portion of the frame portion 11b are connected by a connecting portion 11d. In this case, the excitation electrode 11e is rectangular in shape when viewed from above. Of course, the planar shape of the excitation electrode 11e may be any other shape, such as circular or elliptical, depending on the shape of the vibrating part 11a, etc. The wiring electrode 11f is connected from the excitation electrode 11e via the frame portion 11b, and through through holes 17 provided in the frame portion 11b and the base plate 13 to the external connection wiring 21 provided on the bottom surface of the base plate 13. Both the excitation electrode 11e and the wiring electrode 11f are formed from desired metal wiring.

[0013] Furthermore, the comb-shaped electrode 11g, which is a feature of the present invention as a capacitive electrode, is provided on at least one of the main surfaces of the front and back of the quartz crystal vibrator 11 such that the repeating direction of the comb teeth is aligned with the Z' axis of the quartz crystal vibrator 11. In this example, one main surface of the frame portion 11b of the quartz crystal vibrator 11 is used, and a total of two comb-shaped electrodes 11g are provided on two opposing frames of the frame portion 11b. These comb-shaped electrodes 11g are provided in parallel with the excitation electrode 11e. Here, regarding the details of the comb-shaped electrode 11g, as shown in Figure 2, a first comb tooth 11ga for one electrode and a second comb tooth 11gb for the other electrode are arranged so that the teeth of the first comb tooth 11ga and the second comb tooth 11gb are alternating, thus forming a normal comb-shaped electrode. The line and space dimensions of the comb-shaped electrode 11g are defined as line dimension L and space dimension S. Therefore, the period is λ = 2(L + S).

[0014] In addition, in order to make the effect as the capacitive electrode portion effective, the space dimension S of the comb-shaped electrode 11g should satisfy S < T with respect to the thickness T of the crystal resonator 11, and more preferably, satisfy S << T. Also, since the line dimension L and the space dimension S can change the frequency of the surface wave generated by these values, it is advisable to set them to preferable dimensions within the range that satisfies the target capacitance addition amount. In other words, on the premise of satisfying the target capacitance addition amount, the line dimension L and the space dimension S may be changed to control the generation frequency of unnecessary vibration, and an auxiliary structure may be adopted to reduce the influence on the main vibration. In the example of FIG. 1, the comb-shaped electrode 11g is provided only on the crystal resonator 11. However, if it is desired to further increase the capacitive electrode portion, it may be provided on one or both of the base plate 13 and the lid plate 15. Also, in the case of the laminated crystal resonator 30, instead of providing the comb-shaped electrode 11g on the crystal resonator 11, there may be a case where the comb-shaped electrode 11g is provided on one or both of the base plate 13 and the lid plate 15.

[0015] The crystal resonator 11 having the above configuration can be manufactured, for example, using a crystal wafer as a material and manufacturing techniques such as photolithography technology and film formation technology. In particular, compared with SC-cut crystal wafers and the like, AT-cut crystal wafers with a large diameter, for example, those with a diameter of 4 inches, are also mass-produced. Therefore, it is advantageous when manufacturing various AT-cut crystal resonators 11 that want to increase the capacitance ratio and are manufactured by photolithography technology including the laminated AT-cut crystal resonator 30.

[0016] 2. Test Results Regarding Unnecessary Vibration Next, to deepen the understanding of the present invention, the test results regarding unnecessary vibrations will be described. The inventors of this application prepared an AT-cut crystal resonator having excitation electrodes and the comb-shaped electrodes referred to in the present invention, and prepared (a) a crystal resonator of an example formed such that the repeating direction of the comb teeth is along the Z'-axis of the crystal, and (b) a crystal resonator of a comparative example formed such that the repeating direction of the comb teeth is along the X-axis of the crystal. However, crystal resonators of the example and the comparative example were prepared with different line and space dimensions L, S of the comb teeth of the comb-shaped electrodes (see the following table). Then, the generation state of surface waves and the frequencies of the generated unnecessary vibrations were investigated for each of the crystal resonators of the example and the comparative example. The results are shown in Table 1.

[0017]

Table 1

[0018] From the results shown in Table 1, it can be seen that even when unnecessary vibrations occur, the frequency of the unnecessary vibrations can be changed by changing the line and space dimensions. Also, in the case of the crystal resonator of the example, it can be seen that the generation of longitudinal waves and SV waves can be prevented regardless of the line and space dimensions. Therefore, according to the present invention, it can be seen that even when a capacitive electrode portion by a comb-shaped electrode is provided for an AT-cut crystal resonator in which it is difficult to increase the capacitance ratio, unnecessary vibrations caused by surface waves can be suppressed.

[0019] 3. Other Embodiments In the above-described embodiment, an example in which the present invention is applied to a laminated crystal resonator has been shown, but the present invention is not limited to this, and for example, it can also be applied to a crystal resonator having the following structure. This will be described with reference to FIGS. 4 to 6. FIGS. 4 to 6 are plan views of the crystal resonators of the application examples. However, in FIGS. 5(A) and 6, side views are also used. The example shown in Figure 4(A) is an example of applying the present invention to a single-plate AT-cut quartz crystal vibrator 40. Specifically, an excitation electrode 11e and a wiring electrode 11f are provided on both sides of a predetermined region of an AT-cut quartz crystal 41 having a thickness corresponding to a desired frequency, and a comb-shaped electrode 11g as a capacitive electrode portion is provided in a portion of at least one of the main surfaces on the front and back of a part of the quartz crystal 41. The quartz crystal oscillator 50 shown in Figure 4(B) differs from the one shown in Figure 4(A) in that a notch 51a is provided on one end of the AT-cut quartz crystal 51, extending from the side of the crystal 51 towards the center, and a comb-shaped electrode 11g, which serves as the capacitive electrode portion of the present invention, is provided on the portion of the quartz crystal opposite to the crystal 51 of the notch 51a.

[0020] The quartz crystal vibrator 60 shown in Figure 5(A) differs from the one shown in Figure 4(A) in that a portion of the AT-cut quartz crystal 61 other than the vibrating portion is a support portion 61a which is thicker than the vibrating portion, and a comb-shaped electrode 11g as the capacitive electrode portion of the present invention is provided on this support portion 61a. The quartz crystal vibrator 70 shown in Figure 5(B) differs from the one shown in Figure 4(A) in that a through-hole 75 is provided around the vibrating portion 73 of the AT-cut quartz crystal vibrator 71, a frame portion 77 is provided around the through-hole 75, a connecting portion is provided between the vibrating portion 73 and the frame portion 77 to connect parts of each other, and a comb-shaped electrode 11g, which serves as the capacitive electrode portion of the present invention, is provided on a part of the frame portion 77. This quartz crystal vibrator 70 corresponds to the quartz crystal vibrator 11 provided in a part of the bonded quartz crystal oscillator 30 shown in Figure 1, but it is an example of using it as a single unit rather than in a laminated structure. The quartz crystal vibrator 80 shown in Figure 6 differs from the one shown in Figure 4(A) in that it has convex regions 83 defining the vibrating portion on both main surfaces of an AT-cut quartz crystal 81, an excitation electrode 11e is provided only on this convex region 83 or in a wider area including the convex region (not shown), and a comb-shaped electrode 11g as the capacitive electrode portion of the present invention is provided in a part of the quartz crystal outside the convex region 83. The effects of the present invention can be obtained even with various AT-cut quartz crystal oscillators as described using Figures 4 to 6. [Explanation of symbols]

[0021] 11: Crystal vibrator of the embodiment 11e: Excitation electrode 11g: Comb-shaped electrode 30: Crystal device of the embodiment 40, 50, 60, 70, 80: Crystal oscillators of other embodiments

Claims

1. In an AT-cut quartz crystal vibrator comprising an excitation electrode and a comb-shaped electrode as a capacitive electrode, The AT-cut quartz crystal vibrator is characterized in that the comb-shaped electrodes are provided on at least one of the main surfaces of the front and back main surfaces of the quartz crystal vibrator such that the repeating direction of the comb teeth is aligned with the Z' axis of the quartz crystal vibrator. However, the Z' axis of the quartz crystal refers to the axis that is offset from the Z axis of the crystal axis of the quartz crystal due to the cutting angle of the AT-cut quartz crystal vibrator.

2. The AT-cut quartz crystal vibrator according to claim 1, characterized in that the space dimension S in the line and space of the comb-shaped electrode is set to S < T with respect to the thickness T of the quartz crystal vibrator.

3. An AT-cut quartz crystal vibrator comprising an excitation electrode and a comb-shaped electrode as a capacitive electrode portion, wherein the comb-shaped electrode is provided on at least one main surface of the front and back main surfaces of the quartz crystal vibrator such that the repeating direction of the comb teeth is aligned with the Z' axis of the quartz crystal vibrator, A crystal device characterized by comprising a container for housing the crystal vibrator. However, the Z' axis of the quartz crystal refers to the axis that is offset from the Z axis of the crystal axis of the quartz crystal due to the cutting angle of the AT-cut quartz crystal vibrator.

4. An AT-cut quartz crystal vibrator comprising an excitation electrode and a comb-shaped electrode as a capacitive electrode portion, wherein the comb-shaped electrode is provided on at least one main surface of the front and back main surfaces of the quartz crystal vibrator such that the repeating direction of the comb teeth is aligned with the Z' axis of the quartz crystal vibrator, A base plate is joined to the quartz crystal vibrator on one of the main surfaces of the front and back surfaces of the quartz crystal vibrator, A quartz device characterized by comprising a lid plate joined to the quartz crystal vibrator on the other side of the main surface of the quartz crystal vibrator. However, the Z' axis of the quartz crystal refers to the axis that is offset from the Z axis of the crystal axis of the quartz crystal due to the cutting angle of the AT-cut quartz crystal vibrator.

5. The quartz device according to claim 3 or 4, characterized in that the space dimension S in the line and space of the comb-shaped electrode is set to S < T with respect to the thickness T of the quartz vibrating element.

6. The crystal device according to claim 4, characterized in that the base plate and the lid plate are each made of crystal.

7. The quartz device according to claim 6, further comprising the comb-shaped electrodes on one or both of the base plate and the lid plate.

8. An AT-cut quartz crystal oscillator equipped with an excitation electrode, A base plate made of an AT-cut quartz crystal is bonded to one of the main surfaces of the aforementioned quartz crystal vibrator, A lid plate made of an AT-cut quartz crystal is bonded to the other main surface side of the aforementioned quartz crystal vibrator, and 5 A crystal device characterized by comprising a comb-shaped electrode as a capacitive electrode portion provided on both or one of the base plate and the lid plate, wherein the comb-shaped electrode provided on both or one of the base plate and the lid plate is such that the repeating direction of the comb teeth is aligned with the Z' axis of the crystal of the crystal piece.

9. The quartz device according to claim 8, characterized in that the space dimension S in the line and space of the comb-shaped electrode is set such that S < T with respect to the thickness T of the quartz piece on which the comb-shaped electrode is provided.

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