piezoelectric elements

Abstract

This invention provides a piezoelectric element (10) in which a piezoelectric vibrating plate (11) and a temperature sensor (13) are longitudinally arranged and mounted in a container (15). The piezoelectric element (10) has a novel structure that easily prevents short circuits between the excitation electrode (11a) of the piezoelectric vibrating plate and the electrode terminal (13a) of the temperature sensor. The piezoelectric vibrating plate is rectangular in shape when viewed from above, has an excitation electrode on its surface, and is cantilevered to the container on its first short side. The temperature sensor is cuboid in shape, has electrode terminals at both ends in the length direction, is smaller in planar shape than the excitation electrode, and is mounted in the container in a position where the length direction of the temperature sensor is parallel to the length direction of the piezoelectric vibrating plate, and is contained in the region below the excitation electrode. Part or all of the front side electrode terminal of the temperature sensor facing the excitation electrode is provided with an insulating member (10a) to prevent short circuits between the excitation electrode and the front side electrode terminal.

Description

Piezoelectric elements The present invention relates to a piezoelectric element having a structure in which a temperature sensor and a piezoelectric vibrating piece are installed in a container. A typical example of a piezoelectric element with a temperature sensor and a piezoelectric resonator mounted within a single container is a crystal element with a built-in temperature sensor. These crystal elements, when used with a specific chipset, perform temperature compensation on the chipset based on information from the temperature sensor, thereby achieving a stable reference frequency. For example, an example of the crystal element is described in Patent Document 1. The crystal element described in Patent Document 1 is formed by installing a crystal vibrating piece as a piezoelectric vibrating piece and a thin-film thermistor as a temperature sensor in a container composed of a substrate and a cap bonded to the substrate. Specifically, in the container, the thermistor and the crystal vibrating piece are installed in this order longitudinally from the substrate side (for example, FIG. 2 of Patent Document 2). The thermistor is covered by a sealing portion (for example, paragraph 55 and FIG. 2 of Patent Document 1). The sealing portion protects the thermistor from the external environment (for example, paragraph 57 of Patent Document 1). The sealing portion is made of an insulating resin, such as an epoxy resin or a silicone resin. [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-92934 [Problem to be Solved by the Invention] With the demand for miniaturization and thinning of electronic devices in which crystal elements are installed, the demand for miniaturization and thinning of crystal elements with built-in temperature sensors is also increasing. Therefore, in crystal elements with a structure in which a thermistor and a crystal resonator are installed vertically in the same container, the structure described below is often adopted, and this also causes problems associated with it. Figures 5(A), 5(B), and 6(A) to 6(C) are figures used to illustrate this. In particular, Figure 5(A) is a plan view of the crystal element 50, Figure 5(B) is a cross-sectional view of the crystal element 50 along the PP line in Figure 5(A), Figure 6(A) is a top view of the crystal element 50, Figure 6(B) is a bottom view and internal perspective view of the crystal element 50, and Figure 6(C) is a figure illustrating the problem. The crystal element 50 comprises a container 55 with a recess 55a for longitudinally accommodating a crystal resonator plate 51 and a thermistor 53; the crystal resonator plate 51; the thermistor 53; and a lid member 57 for sealing the container 55. The crystal resonator plate 51 is rectangular in plan view, with excitation electrodes 51a on both sides. Two adhesive terminals 55b on one side are connected and fixed to the container 55 using conductive adhesive 59. The thermistor 53 is a rectangular wafer-type thermistor with electrode terminals 53a at each end in the longitudinal direction. The thermistor 53 is smaller in plan view than the excitation electrodes 51a of the crystal resonator plate 51. The thermistor 53 and the crystal resonator plate 51 are mounted longitudinally in this order from the bottom surface of the container 55. The thermistor 53 is mounted so as to be included in a region below the excitation electrode 51 a of the crystal vibrating piece 51 and a region obtained by projecting the excitation electrode 51 a (region between dot-dashed lines X in FIG. 5B ). In the case of the crystal element 50, the adhesive terminals 55b of the container 55 are connected to external connection terminals 55c provided on the outer bottom surface of the container 55 using via wiring (not shown). Therefore, as shown in the perspective view of FIG6(B), the crystal resonator plate 51 and thermistor 53 are connected to the external connection terminals 55c in a predetermined relationship. Therefore, when the crystal element 50 is mounted in an electronic device (not shown), the crystal resonator plate 51 and thermistor 53 are connected to the chipset (not shown) within the electronic device in a predetermined electrical relationship. In the case of the crystal element 50, with the demand for miniaturization and thinness, the long side dimension La, short side dimension Lb, and thickness t (see FIG5(A) and FIG5(B)) have been reduced to, for example, approximately 1.2 mm, 1.0 mm, and 0.55 mm or less. In other words, the commonly used dimensions of crystal elements are 1210 mm or less. If it is small and thin like this, the gap g1 between the upper surface of the crystal vibrating plate 51 and the cover member 57 is about 0.04 mm, and the gap g2 between the lower surface of the crystal vibrating plate 51 and the electrode terminal 53a of the thermistor 53 is about 0.04 mm. The gap g2 between the excitation electrode 51a of the crystal vibrating plate 51 and the electrode terminal 53a of the thermistor 53 becomes extremely small. In the case of a small, thin crystal element 50, if a user accidentally drops an electronic device, such as a mobile phone, the impact of the drop causes the crystal resonator plate 51 of the crystal element 50 inside the mobile phone to bend, as shown in the cross-sectional view of FIG6C , with the conductive adhesive 59 serving as a fulcrum. This causes the portion 51ax of the excitation electrode 51a opposite the conductive adhesive 59 to contact the electrode terminal 53a of the thermistor 53. Since the crystal resonator plate 51 and the thermistor 53 are each electrically connected to a chip assembly (not shown), contact between the excitation electrode 51a and the electrode terminal 53a of the thermistor 53 creates a short circuit, leading to cessation of oscillation of the crystal resonator plate 51. This problem becomes more severe as the piezoelectric element becomes smaller and thinner. This application was developed in light of the above-mentioned circumstances, and therefore, an object of the present invention is to provide a piezoelectric element having a structure in which a temperature sensor and a piezoelectric vibrating reed are mounted vertically side by side within a single container. This piezoelectric element has a novel structure that can easily prevent short circuits between the excitation electrodes of the piezoelectric vibrating reed and the electrode terminals of the temperature sensor. [Solution] In order to achieve the above-mentioned object, the inventors of the present application focused on the protective film described in Patent Document 1 and conducted research on simplifying the protective film. Therefore, a piezoelectric element according to the present invention is a piezoelectric element comprising a piezoelectric vibrating reed, a temperature sensor, and a container accommodating the piezoelectric vibrating reed and the temperature sensor in a longitudinally aligned manner. The piezoelectric vibrating reed has a rectangular shape in a plan view, has excitation electrodes on both sides, and is cantilevered on a first short side of the container. The temperature sensor has a rectangular parallelepiped shape, has electrode terminals at both ends in the longitudinal direction, is smaller in plan view than the excitation electrodes, and is mounted in the container such that the longitudinal direction of the temperature sensor is parallel to the longitudinal direction of the piezoelectric vibrating reed and the temperature sensor is contained within a region below the excitation electrodes. The piezoelectric element is characterized in that an insulating member is provided on a portion or all of a surface of the electrode terminal on the opposite side of the cantilevered piezoelectric vibrating reed (hereinafter also referred to as the front-end electrode terminal) of the electrode terminals at both ends of the temperature sensor, the surface facing the excitation electrode. The insulating member prevents short circuiting between the excitation electrode and the front-end electrode terminal when the piezoelectric vibrating reed is bent by an impact. When implementing the present invention, it is preferred that the insulating member is provided at a portion of the electrode terminal on the front end side that abuts against a ridge portion along the short side of the temperature sensor. With this preferred embodiment, the object of the present invention can be achieved with the minimum amount of insulating member required. When implementing the present invention, it is preferred that the insulating member be formed of a material that does not contain silicone. When the insulating member is formed of an adhesive containing silicone, silicone gas is generated from the insulating member over time and adheres to the excitation electrode, causing the frequency of the piezoelectric vibrating piece to fluctuate. If the insulating member is formed of a material that does not contain silicone, adverse effects caused by silicone gas can be prevented. When implementing the present invention, it is preferred that the outer shape of the container have a long side of approximately 1.2 mm or less, a short side of approximately 1.0 mm or less, and a thickness of 0.6 mm or less, that is, in terms of the commonly known dimensions of crystal elements, it is 1210 size or less, and the thickness is 0.6 mm or less. Here, the range of approximately 1.2 mm and 1.0 mm can be ±0.1 mm, which is recognized as a standard for containers. In such a small and thin piezoelectric element, as described above, the distance between the electrode terminal of the temperature sensor and the excitation electrode of the piezoelectric vibrating piece becomes extremely small, increasing the risk of short circuit between the two. Therefore, the application of the present invention can significantly demonstrate the effects of the present invention. [Effects of the Invention] According to the piezoelectric element of the present invention, simply by providing an insulating member on a portion of the terminal electrode on the front end side of the temperature sensor, a short circuit between the excitation electrode and the electrode terminal on the center side can be prevented when the piezoelectric vibrating reed bends due to an impact. Consequently, a piezoelectric element can be provided in which a temperature sensor and a piezoelectric vibrating reed are mounted vertically side by side within a single container. This piezoelectric element has a novel structure that easily prevents short circuits between the excitation electrode of the piezoelectric vibrating reed and the electrode terminal of the temperature sensor. Hereinafter, embodiments of the piezoelectric element of the present invention will be described with reference to the accompanying drawings. The accompanying drawings are only schematically shown to facilitate understanding of the present invention. In the accompanying drawings, identical components are denoted by the same reference numerals, and their descriptions are sometimes omitted. The shapes, sizes, and materials described in the following description are merely examples within the scope of the present invention. Therefore, the present invention is not limited to the following embodiments. 1. Piezoelectric Element According to the First Embodiment Figures 1(A) and 1(B) illustrate a piezoelectric element 10 according to the first embodiment. In particular, Figure 1(A) is a plan view of the piezoelectric element 10 showing a state where a crystal resonator plate 11 serving as a piezoelectric resonator plate 11 has been removed from a container 15. Figure 1(B) is a cross-sectional view of the piezoelectric element 10 taken along line PP in Figure 1(A). The piezoelectric element 10 includes a piezoelectric vibrating reed 11, a temperature sensor 13, a container 15 that houses the piezoelectric vibrating reed 11 and the temperature sensor 13 in a longitudinally aligned manner, a predetermined insulating member 10a (described later) provided at a predetermined position (described later) of the temperature sensor 13, and a cover member 17. Each component is described in detail below. In this case, the piezoelectric vibrating piece 11 is an AT-cut crystal vibrating piece with a rectangular shape when viewed from above. The long and short side dimensions of the crystal vibrating piece are determined based on the size of the container 15 and the side ratio that satisfies the characteristics of the crystal vibrating piece. However, when viewed from above, it is larger than the temperature sensor 13. Furthermore, the thickness of the crystal vibrator is determined based on the target frequency. The piezoelectric vibrating piece 11 has excitation electrodes 11a on both sides, and the portion on the first short side is fixed to the adhesive terminal 15b of the container 15 using a conductive adhesive 19. The piezoelectric vibrating piece 11 is fixed to the container 15 using a so-called cantilever support structure. Furthermore, the excitation electrode 11a also has a quadrilateral shape when viewed from above. The temperature sensor 13 is a rectangular wafer-type temperature sensor with electrode terminals 13a at both ends in the longitudinal direction. However, the temperature sensor 13 is smaller in plan view than the excitation electrode 11a of the piezoelectric vibrating piece 11. The temperature sensor 13 is mounted on a predetermined pad provided on the container 15 such that the longitudinal direction of the temperature sensor 13 is parallel to the longitudinal direction of the piezoelectric vibrating piece 11 and the temperature sensor 13 is contained in the region below the excitation electrode (contained between the single-dotted dashed lines X in FIG. 1B ). In this example, container 15 has a recess 15a that accommodates piezoelectric vibrating reed 11 and temperature sensor 13. Recess 15a is structured as follows: a portion for accommodating temperature sensor 13 and a stepped portion located above the portion and connected to the first side of piezoelectric vibrating reed 11. Adhesion terminals 15b are included in the stepped portion. The periphery of recess 15a in container 15 forms a dam surrounding recess 15a. A lid member 17 is connected to the top surface of the dam, thereby airtightly sealing recess 15a. Container 15 includes external connection terminals 15c on its outer bottom surface. Container 15 can be formed, for example, of a ceramic package. Lid member 17 can be formed of any material and structure appropriate for the sealing method. Conductive adhesive 19 is preferably any conductive adhesive suitable for the design; for example, a silicone-based conductive adhesive can be used. Next, a specific example of the insulating member 10a, a characteristic feature of the present invention, will be described. The insulating member 10a is provided on a portion or all of the surface of the electrode terminals 13a at both ends of the temperature sensor 13, namely, the electrode terminal 13aa on the side opposite to the side where the piezoelectric vibrating reed 11 is cantilevered, that faces the excitation electrode 11a. This insulating member 10a prevents short circuits between the excitation electrode 11a and the tip electrode terminal 13aa when the piezoelectric vibrating reed 11 bends due to an impact. In the examples shown in Figures 1(A) and 1(B), the insulating member 10a is provided on a portion of the surface of the tip electrode terminal 13aa facing the excitation electrode 11a, which abuts the ridgeline along the short side of the temperature sensor 13, and extends along the entire area along the short side. In this case, a portion of the insulating member 10a also reaches the side surface of the temperature sensor 13 along the short side. In addition, the width of the insulating member 10a (the length in the horizontal direction of (A) in FIG1 ) can be any width corresponding to the design, as long as it is greater than the width of the covered ridge portion, for example, as long as it is 10% to 50% or 10% to 30% of the width of the electrode terminal 13aa on the front end side (the length in the horizontal direction of (A) in FIG1 ). In the case of the piezoelectric element 10 shown in Figures 1(A) and 1(B), if the tip of the piezoelectric vibrating reed 11 bends due to a drop shock or other cause, there is a risk that the excitation electrode 11a may contact the portion of the electrode terminal 13aa at the tip of the temperature sensor 13 along the short side of the temperature sensor 13, causing a short circuit. However, the insulating member 10a shown in Figures 1(A) and 1(B) covers the electrode terminal 13aa at the tip of the temperature sensor 13, thus preventing a short circuit. The thickness of the insulating member 10a is preferably sufficient to ensure insulation, and can be, for example, several microns. The material of the insulating member 10a can be any insulating material, and can be composed of, for example, silicone resin, epoxy resin, imide resin, or the like. However, since the insulating member 10a is in close contact with the excitation electrode 11a of the piezoelectric vibrating reed 11, if the insulating member 10a is made of a material containing siloxane, it is likely to cause adverse effects on the piezoelectric vibrating reed 11 due to siloxane gas. To mitigate such adverse effects, the insulating member 10a is preferably made of a material that does not contain siloxane. In the case of the piezoelectric element 10 of the first embodiment, for example, a so-called 1210-size piezoelectric element, as shown in FIG2(A), the gap g1 between the upper surface of the piezoelectric vibrating piece 11 and the cover member 17 is approximately 0.04 mm, and the gap g2 between the lower surface of the piezoelectric vibrating piece 11 and the electrode terminal 13aa at the front end of the temperature sensor 13 is approximately 0.04 mm (see FIG1(B)). Therefore, if the piezoelectric element 10 is subjected to a drop shock, the front end of the piezoelectric vibrating piece 11 bends, and the excitation electrode 11a tends to contact the electrode terminal 13aa at the front end of the temperature sensor 13, causing a short circuit. However, the provision of the insulating member 10a prevents this short circuit, as shown in FIG2(B). 2. Other Embodiments 2-1. Second Embodiment In the piezoelectric element 10 of the first embodiment, as shown in FIG1A , the insulating member 10a is provided in a portion of the surface of the distal electrode terminal 13aa facing the excitation electrode 11a that abuts the ridgeline along the short side of the temperature sensor 13, extending along the entire short side. However, as shown in FIG3 , in the piezoelectric element 30 of the second embodiment, the insulating member 31 is provided in a portion of the surface of the distal electrode terminal 13aa facing the excitation electrode 11a that abuts the ridgeline along the short side of the temperature sensor 13, extending along a portion of the short side, specifically, only near the center. The dimension of the insulating member 31 along the short side of the temperature sensor 13 can be, for example, 30% to 70% or 20% to 50% of the length of the short side of the temperature sensor 13. 2-2. Third Embodiment In the piezoelectric element 10 of the first embodiment, as shown in FIG1B , the container 15 has a recess 15a, and the cover member 17 is flat. However, as shown in FIG4 , in the piezoelectric element 40 of the third embodiment, the container 41 is formed by a flat base 43 and a cap-shaped cover member 45 having a recess for accommodating the piezoelectric vibrating reed 11 and the temperature sensor 13. The effects of the present invention can also be achieved with this container 41. While the above embodiments describe examples using a crystal vibrating reed as the piezoelectric vibrating reed, the piezoelectric vibrating reed may also be made of other piezoelectric materials, such as piezoelectric ceramics or lithium niobate. 10: Piezoelectric element (piezoelectric element) of the first embodiment 10a, 31: Insulating member 11: Piezoelectric vibrating piece (quartz crystal vibrating piece) 11a, 51a: Excitation electrode 13: Temperature sensor 13a, 53a: Electrode terminal 13aa: Electrode terminal on the front end 15, 41, 55: Container 15a, 55a: Recess 15b, 55b: Adhesion terminal 15c, 55c: External connection terminal 17, 57: Cover member 19, 59: Conductive adhesive 30: Piezoelectric element (piezoelectric element) of the second embodiment 40: Piezoelectric element (piezoelectric element) of the third embodiment 43: Base 45: Cap-shaped cover member (cover member) 50: Quartz crystal element 51: Quartz crystal vibrating piece 51ax: Portion 53: Thermistor g1, g2: Gap La: Long side dimension Lb: Short side dimension PP: Line t: Thickness X: Single-point dashed line FIG1(A) and FIG1(B) are diagrams for explaining a piezoelectric element 10 according to a first embodiment. FIG2(A) and FIG2(B) are diagrams for explaining the effects of the piezoelectric element 10 according to the first embodiment. FIG3 is a diagram for explaining a piezoelectric element 30 according to a second embodiment. FIG4 is a diagram for explaining a piezoelectric element 40 according to a third embodiment. FIG5(A) and FIG5(B) are diagrams for explaining the structure and problems of a crystal element 50 having a structure in which a temperature sensor and a piezoelectric vibrator are arranged vertically. FIG6(A) to FIG6(C) are diagrams subsequent to FIG5(A) and FIG5(B) for explaining the structure and problems of a crystal element 50 having a structure in which a temperature sensor and a piezoelectric vibrator are arranged vertically. 10: Piezoelectric Element of First Embodiment (Piezoelectric Element) 10a: Insulating member 11: Piezoelectric vibrating piece (crystal vibrating piece) 11a: Excitation electrode 13: Temperature sensor 13a: Electrode terminal 13aa: Electrode terminal on the front end 15:Container 15a: concave part 15b: Adhesive terminal 15c: External connection terminal 17: Cover member 19: Conductive adhesive PP:Thread X: single dotted line

Claims

1. A piezoelectric element comprising a piezoelectric vibrating plate, a temperature sensor, and a container longitudinally arranged housing the piezoelectric vibrating plate and the temperature sensor, wherein the piezoelectric vibrating plate is rectangular in shape when viewed from above, has an excitation electrode on its surface and is cantilevered on a first short side of the container, and the temperature sensor is cuboid in shape, having electrode terminals at both ends in the length direction, smaller in planar shape than the excitation electrode, and is mounted in the container such that the length direction of the temperature sensor is parallel to the length direction of the piezoelectric vibrating plate, and in a position where the temperature sensor is contained in the region below the excitation electrode, characterized in that, when defining the electrode terminal opposite to the side where the piezoelectric vibrating plate is cantilevered on one end of the electrode terminal at both ends of the temperature sensor as the front-end electrode terminal, a portion or all of the surface of the front-end electrode terminal facing the excitation electrode is provided with an insulating member, the insulating member preventing a short circuit between the excitation electrode and the front-end electrode terminal when the piezoelectric vibrating plate bends due to impact. The insulating member is disposed on the portion that is part of the electrode terminal on the front end side and mates with the ridge portion along the short side of the temperature sensor.

2. The piezoelectric element as claimed in claim 1, wherein the insulating member is made of a siloxane-free material.

3. The piezoelectric element as claimed in claim 1, wherein the container has a long side of 1.2 mm or less, a short side of 1.0 mm or less, and a thickness of 0.6 mm or less.

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