Oven-controlled crystal oscillator

Abstract

In an OCXO (1) in which a core part (4) is sealed in a vacuum state inside an external package (2) for heat insulation, a base substrate (72) is interposed between a heater IC (6) and a crystal vibrating plate (71), the base substrate (72) and the heater IC (6) are surface-bonded to each other by a non-conductive adhesive (42), and the core part (4) is mechanically bonded to the external package (2) via a holding member (8), is electrically connected to the external package (2) via a wire (9), satisfies a relationship in which the thermal conductivity of the crystal vibrating plate (71) is less than the thermal conductivity of the base substrate (72) and a relationship in which the thermal conductivity of the holding member (8) is less than the thermal conductivity of the base substrate (72), and also satisfies a relationship in which the volume of the crystal vibrating plate (71) is less than or equal to the volume of the heater IC (6), and the volume of the heater IC (6) is less than the volume of the base substrate (72).

Description

Oven-type piezoelectric oscillator

[0001] The present invention relates to an oven-controlled piezoelectric oscillator.

[0002] Piezoelectric oscillators, such as quartz crystal oscillators, have vibration frequencies that change depending on temperature based on their inherent frequency-temperature characteristics. To maintain a constant temperature around the piezoelectric oscillator, oven-controlled piezoelectric oscillators (hereinafter also referred to as "OCXOs") are known, in which the piezoelectric oscillator is enclosed in a thermostatic oven (see, for example, Patent Document 1). In the OCXO described in Patent Document 1, the vibration device section enclosed in the thermostatic oven is a three-layered piezoelectric oscillator, thereby achieving miniaturization while improving the thermal insulation of the core section.

[0003] International Publication No. 2022 / 149541

[0004] In the OCXO described above, as the vibration device section is miniaturized, the volume of the piezoelectric diaphragm is reduced, and the heat capacity of the piezoelectric diaphragm is also reduced. This makes the piezoelectric diaphragm more susceptible to changes in the external thermal environment, making it difficult to stabilize the frequency-temperature characteristics. In particular, even a slight change in the heat of the heating section in response to a change in the external environment can have an overly sensitive effect on the piezoelectric diaphragm, causing the frequency-temperature characteristics to become unstable and deteriorate.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide an oven-controlled piezoelectric oscillator that can stabilize the temperature of a piezoelectric diaphragm and stabilize frequency-temperature characteristics.

[0006] The present invention provides a means for solving the above-described problems as follows: That is, the present invention provides an oven-controlled piezoelectric oscillator having a core unit sealed in a vacuum state inside a thermally insulating external package, the core unit including at least an oscillation circuit unit, a vibration device unit, and a heating unit, the vibration device unit including a base substrate, a piezoelectric diaphragm mounted on one main surface of the base substrate, and a sealing member that hermetically seals the piezoelectric diaphragm mounted on the base substrate in a vacuum state, the base substrate is interposed between the heating unit and the piezoelectric diaphragm, and the base substrate and the heating unit are surface-bonded to each other with a bonding material, the core unit is mechanically bonded to the external package via a holding member and electrically connected to the external package via a wire, and the relationships of thermal conductivity of the piezoelectric diaphragm<thermal conductivity of the base substrate and thermal conductivity of the holding member<thermal conductivity of the base substrate are satisfied, and the relationship of volume of the piezoelectric diaphragm≦volume of the heating unit<volume of the base substrate is satisfied.

[0007] This configuration stabilizes the temperature of the piezoelectric diaphragm and stabilizes the frequency-temperature characteristics while meeting the demand for miniaturization. Specifically, the volume of the base substrate, which has a higher thermal conductivity than the piezoelectric diaphragm, is larger than that of the heating section, while the volume of the piezoelectric diaphragm, which has a lower thermal conductivity than the base substrate, is smaller than or equal to that of the heating section. This allows heat transferred from the heating section to be stored in the base substrate. This increases the thermal capacity of the entire vibration device, including the piezoelectric diaphragm. By interposing the base substrate, which acts as a thermal buffer, between the piezoelectric diaphragm and the heating section, the thermal changes of the piezoelectric diaphragm can be reduced in sensitivity to thermal changes in the heating section. Furthermore, the piezoelectric diaphragm is less susceptible to changes in the external thermal environment, thereby suppressing thermal changes in the piezoelectric diaphragm and stabilizing its temperature. Furthermore, because the core section is mounted inside the external package via a support member with a lower thermal conductivity than the base substrate, it is less susceptible to changes in the external environment, suppressing thermal changes in the core section and stabilizing its temperature. In particular, the piezoelectric diaphragm is enclosed in a double vacuum state in a space surrounded by a base substrate and a sealing member inside the external package, and is bonded to a holding member via the base substrate and connected to the external package via the holding member, thereby improving insulation against changes in the external thermal environment. As a result, the temperature environment of the piezoelectric diaphragm can be stabilized. Furthermore, because wires with small cross-sectional areas are used for electrical connections, heat loss can be more effectively suppressed in response to changes in the external thermal environment. As a result, the temperature of the piezoelectric diaphragm can be stabilized, and the frequency-temperature characteristics can be stabilized.

[0008] In the above configuration, it is preferable that the base substrate of the vibration device section serves as a foundation for the oscillation circuit section and the heating section, and the core section is supported by the external package. In this way, by interposing the base substrate between the piezoelectric diaphragm and the heating section, heat from the heating section is stored in the base substrate, mitigating heat transfer to the piezoelectric diaphragm and making the piezoelectric diaphragm less susceptible to changes in the external thermal environment, thereby suppressing thermal changes in the piezoelectric diaphragm and stabilizing its temperature.

[0009] In the above configuration, it is preferable that the base substrate has a heat transfer section with a higher thermal conductivity than the base substrate, and the heat transfer section overlaps the mounting area of ​​the heating section on the vibration device section in a planar view. By overlapping the heat transfer section with a higher thermal conductivity than the base substrate on the mounting area of ​​the heating section on the vibration device section, a strong thermal connection between the heating section and the piezoelectric diaphragm can be achieved, allowing heat from the heating section to be quickly transferred to the piezoelectric diaphragm, thereby reducing delays in heat transfer. As a result, the temperature difference between the heating section and the piezoelectric diaphragm can be kept small.

[0010] In the above configuration, it is preferable that a temperature sensor for detecting the temperature of the core portion is provided separately from the heating portion, and that the temperature sensor is disposed on the outer surface of the vibration device portion or inside the vibration device portion, thereby enabling precise temperature control of the core portion in response to changes in the external environment and reducing phase noise compared to when a temperature sensor built into the heating portion is used.

[0011] According to the oven-controlled piezoelectric oscillator of the present invention, the temperature of the piezoelectric diaphragm can be stabilized, and the frequency-temperature characteristics can be stabilized.

[0012] 1 is a cross-sectional view showing a schematic configuration of an OCXO according to an embodiment of the present invention. It is a cross-sectional view of the OCXO of FIG. 1 taken along line X1-X1. It is a cross-sectional view of the OCXO of FIG. 1 taken along line X2-X2. It is a diagram showing a first modified OCXO equivalent to FIG. 1. It is a diagram showing a second modified OCXO equivalent to FIG. 1. It is a diagram showing a third modified OCXO equivalent to FIG. 1. It is a cross-sectional view of the OCXO of FIG. 6 taken along line X3-X3. It is a cross-sectional view of the OCXO of FIG. 6 taken along line X4-X4. It is a diagram showing a fourth modified OCXO equivalent to FIG. 1. It is a diagram showing a fifth modified OCXO equivalent to FIG. 1. It is a diagram showing a sixth modified OCXO equivalent to FIG. 1. It is a diagram showing a seventh modified OCXO equivalent to FIG. 1. It is a diagram showing an eighth modified OCXO equivalent to FIG. 1.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] As shown in FIGS. 1 to 3 , the OCXO 1 according to this embodiment has a core 4 disposed inside a heat-insulating external package (housing) 2, which is hermetically sealed by a lid 3. Specifically, the OCXO 1 has an external package 2 with a recess 2a that opens upward. The external package 2 is made of, for example, ceramic. The core 4 is hermetically sealed inside the recess 2a of the external package 2. The lid 3 is fixed to the upper surface of a peripheral wall 2b surrounding the recess 2a by seam welding via a sealing material 3a, thereby sealing (airtightly sealing) the interior of the recess 2a. The lid 3 is made of a metal base plate, such as Kovar, with a required plating of nickel or the like formed on its surface. The sealing material 3a is attached to the top of the peripheral wall 2b of the external package 2 and is made of, for example, a metal ring, such as Kovar, with a required plating of nickel or the like formed on its surface. The lid 3 and the sealing material 3a are then joined together by seam welding after heating. The internal space of the recess 2a is preferably in a high vacuum state (for example, a vacuum level of 10 Pa or less), a low vacuum state, or an atmosphere with low thermal conductivity such as low-pressure nitrogen or argon. The hermetic sealing (seam sealing) by seam welding is not limited to the above, and direct seam sealing without using a metal ring may also be employed. Furthermore, instead of seam sealing, other techniques such as beam sealing or brazing sealing using a metal-based sealing material such as an Au—Sn alloy or solder may also be used. Furthermore, without being limited to these, when a ceramic plate or the like is used for the lid 3, a sealing material such as low-melting-point glass may also be used.

[0015] A pair of steps 2c, 2c are formed facing each other on the inner wall surface of the peripheral wall 2b of the recess 2a of the outer package 2. The step 2c is provided at each of both longitudinal ends of the recess 2a of the outer package 2, and extends along the short side of the recess 2a. The core 4 is disposed on the bottom surface (inner bottom surface) of the recess 2a between the pair of step 2c, 2c. The step 2c may be formed continuously along the four sides of the peripheral wall 2b of the recess 2a.

[0016] A plurality of (e.g., eight) external connection terminals 2e are formed on the lower surface (bottom surface) of the external package 2 for electrically connecting the OCXO 1 to an external circuit board (not shown) provided externally via solder or the like. The external package 2 may have an H-shaped cross section, and a recess that opens downward may be formed in the external package 2, and a circuit component such as a capacitor may be housed in the space of this recess.

[0017] The core unit 4 includes at least an oscillation IC (oscillating circuit unit) 5, a heater IC (heating unit) 6, and a crystal unit (oscillating device unit) 7. The core unit 4 is a package of various electronic components used in the OCXO 1, and in this embodiment, it has a three-layer structure (laminated structure) in which the oscillation IC 5, heater IC 6, and crystal unit 7 are stacked in this order from the top. The areas of the oscillation IC 5, heater IC 6, and crystal unit 7 in a plan view gradually decrease upward.

[0018] The quartz crystal unit 7 is a surface-mount type quartz crystal unit and includes a quartz crystal plate (piezoelectric diaphragm) 71 having a vibrating portion (not shown), a base substrate 72 having the quartz crystal plate 71 mounted on one of its main surfaces, and a sealing member 73 that hermetically seals the quartz crystal plate 71 mounted on the base substrate 72 in a vacuum. The base substrate 72 is made of, for example, ceramic or the like, and has a recess for accommodating the quartz crystal plate 71. The sealing member 73 is made of, for example, metal, ceramic, or the like. The quartz crystal plate 71 is mounted on the bottom surface of the recess in the base substrate 72 via a conductive adhesive 74, and the space in the recess in the base substrate 72 is sealed with the sealing member 73. Note that the configuration of the quartz crystal unit 7 is merely an example, and quartz crystal units with configurations other than those described above may also be used. For example, a quartz crystal unit may be used in which the quartz crystal plate 71 is enclosed in a space surrounded by the plate-shaped base substrate 72 and the cap-shaped sealing member 73. Alternatively, a quartz crystal oscillator with a three-layer structure may be used. In this case, the quartz crystal oscillator as the vibration device part comprises a quartz crystal vibration plate (piezoelectric vibration plate) having a vibration part on which an excitation electrode is formed, a sealing member bonded to one main surface side of the quartz crystal vibration plate, and a base substrate bonded to the other main surface side of the quartz crystal vibration plate, and the vibration part of the quartz crystal vibration plate is hermetically sealed in a vacuum state.

[0019] The crystal oscillator is composed of the crystal resonator 7 in the core unit 4 and the oscillation IC 5. The oscillation IC 5 can be, for example, a VCXO IC, in which case the crystal oscillator is configured as a VCXO. The oscillation frequency of the OCXO 1 is controlled by controlling the piezoelectric vibration of the crystal resonator 7 using the oscillation IC 5.

[0020] The heater IC 6 is configured to integrate, for example, a heating element (heating region), a control circuit (temperature control region) for controlling the temperature of the heating element, and a temperature sensor for detecting the temperature of the heating element, thereby enabling miniaturization and power saving. In the heater IC 6, the amount of heat generated by the heating element is controlled by controlling the current supplied to the heating element. This controls the temperature of the core unit 4, maintaining the temperature of the core unit 4 at a substantially constant temperature and stabilizing the oscillation frequency of the OCXO 1. Note that, for example, as shown in Variation 3 of FIGS. 6 to 8 , the heating element (heating region) and the control circuit (temperature control region) of the heater IC may be separated. Alternatively, for example, as shown in Variations 4 and 5 of FIGS. 9 and 10 , the temperature sensor may be provided as a separate component from the heater IC 6.

[0021] 1 to 3, the crystal unit 7 is disposed with the base substrate 72 of the crystal unit 7 located on the upper side and the sealing member 73 located on the lower side. The base substrate 72 of the crystal unit 7 serves as a base for mounting the oscillation IC 5 and the heater IC 6, and the core unit 4 is supported by the external package 2.

[0022] A non-conductive adhesive 41 is interposed between the opposing surfaces of the heater IC 6 and the oscillation IC 5, and the opposing surfaces of the heater IC 6 and the oscillation IC 5 are fixed together by the non-conductive adhesive 41. In this case, the upper surface of the heater IC 6 and the lower surface of the oscillation IC 5 are bonded via the non-conductive adhesive 41. The oscillation IC 5 has a smaller area in a planar view than the heater IC 6, and the entire oscillation IC 5 is located within the arrangement area of ​​the heater IC 6 in a planar view. The entire lower surface of the oscillation IC 5 is bonded to the upper surface of the heater IC 6. For example, a resin adhesive such as a polyimide adhesive or an epoxy adhesive is used as the non-conductive adhesive 41. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 41, which further improves heat transfer between the heater IC 6 and the oscillation IC 5.

[0023] A non-conductive adhesive 42 is interposed between the opposing surfaces of the crystal unit 7 and the heater IC 6, and the opposing surfaces of the crystal unit 7 and the heater IC 6 are fixed together by the non-conductive adhesive 42. In this case, the top surface of the crystal unit 7 (the bottom surface of the base substrate 72) and the bottom surface of the heater IC 52 are bonded via the non-conductive adhesive 42. The crystal unit 7 has a larger area in a plan view than the heater IC 6, and the entire heater IC 6 is located within the arrangement area of ​​the crystal unit 7 in a plan view. The entire heater IC 6 is bonded to the top surface of the crystal unit 7 (the bottom surface of the base substrate 72). The non-conductive adhesive 42 may be a resin adhesive such as a polyimide adhesive or an epoxy adhesive. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 42. In this case, it is possible to further improve heat transfer between the crystal unit 7 and the heater IC 6.

[0024] The core unit 4 is mechanically bonded to the inner bottom surface of the recess 2a of the external package 2 via holding members 8. In this embodiment, the core unit 4 is supported by two holding members 8, and a space (gap) 2d is formed in the lower portion of the core unit 4. The holding members 8 are respectively disposed at both longitudinal ends of the core unit 4, and each holding member 8 extends along the short direction of the core unit 4. More specifically, the holding members 8 are bonded to the sealing member 73 of the crystal unit 7 of the core unit 4 via a non-conductive adhesive 43. The holding members 8 are also bonded to spacer members 2f formed on the inner bottom surface of the recess 2a of the external package 2 via a non-conductive adhesive 44. The spacer members 2f are disposed on the inner bottom surface of the recess 2a of the external package 2 at a predetermined interval, and the holding members 8 are bonded onto each spacer member 2f via the non-conductive adhesive 44.

[0025] The holding member 8 is formed of a heat-resistant and flexible resin material such as polyimide. The spacer member 2f is formed of a paste material (metallized material) such as molybdenum or tungsten. Resin adhesives such as polyimide adhesives and epoxy adhesives are used as the non-conductive adhesives 43 and 44. The holding member 8 may also be formed of quartz crystal. Furthermore, as shown in Modifications 1 to 5 of FIGS. 4 to 10, the holding member 8 may be formed of a single plate-shaped substrate. Alternatively, four holding members 8 (not shown) may be provided to support the four corner regions of the core portion 4.

[0026] The core unit 4 is electrically connected to the external package 2 via wires 9. Specifically, wire pads (not shown) are formed on the step surfaces of the step portions 2c of the external package 2, and are connected via the wires 9 to wire pads formed on the bottom surface of the base substrate 72 of the quartz crystal resonator 7 of the core unit 4 by wire bonding. Furthermore, the wire pads formed on the bottom surface of the base substrate 72 of the quartz crystal resonator 7 of the core unit 4 are connected via wires 9 to wire pads formed on the oscillation IC 5 and wire pads formed on the heater IC 6, respectively. The excitation electrodes of the vibrating portion of the quartz crystal vibrating plate 71 of the quartz crystal resonator 7 are electrically connected to the wires 9 via wiring, through holes, etc. in the base substrate 72, making it possible to apply an AC voltage of a predetermined frequency to the excitation electrodes of the vibrating portion of the quartz crystal vibrating plate 71.

[0027] In this embodiment, the OCXO 1 has a base substrate 72 interposed between the heater IC 6 and the quartz crystal plate 71. The base substrate 72 and the heater IC 6 are surface-bonded to each other with a non-conductive adhesive 42. The core 4 is mechanically bonded to the external package 2 via a holding member 8 and electrically connected to the external package 2 via wires 9. The relationships of thermal conductivity of the quartz crystal plate 71 < thermal conductivity of the base substrate 72, and thermal conductivity of the holding member 8 < thermal conductivity of the base substrate 72 are satisfied, and the relationship of volume of the quartz crystal plate 71 ≦ volume of the heater IC 6 < volume of the base substrate 72 is also satisfied. This feature is explained below. The thermal conductivity of the quartz crystal plate 71 refers to the thermal conductivity of the quartz crystal plate 71, excluding conductive parts (metal parts) such as excitation electrodes, lead wiring, and via electrodes formed on or inside the quartz crystal plate 71. Similarly, the thermal conductivity of the base substrate 72 and the thermal conductivity of the holding member 8 refer to the thermal conductivity of the base substrate 72 and the thermal conductivity of the holding member 8 excluding the conductor portions formed on the surface of and inside the base substrate 72 and the holding member 8. Furthermore, the volume of the quartz crystal vibrating plate 71 refers to the volume of the quartz crystal plate excluding the conductor portions (metal portions) such as the excitation electrodes, lead wiring, and via electrodes formed on the surface of and inside the quartz crystal vibrating plate 71. Similarly, the volume of the base substrate 72 refers to the volume of the base substrate 72 excluding the conductor portions formed on the surface of and inside the base substrate 72. The volume of the heater IC 6 refers to the volume of the heater IC 6 including the conductor portions formed on the surface of the heater IC 6, etc.

[0028] As described above, the base substrate 72 is made of ceramic such as alumina, and the thermal conductivity of the base substrate 72 (approximately 21 W / m·K at room temperature when made of alumina) is higher than the thermal conductivity of the quartz crystal vibration plate 71 (5.4 W / m·K (orthogonal to the Z axis) to 9.3 W / m·K (parallel to the Z axis) at 70°C). The holding member 8 is made of polyimide, for example, and the thermal conductivity of the base substrate 72 is higher than the thermal conductivity of the holding member 8 (0.16 to 0.18 W / m·K at room temperature when made of polyimide). The thermal conductivity of the quartz crystal vibration plate 71 is higher than the thermal conductivity of the holding member 8. In this embodiment, the volume of the heater IC 6 is equal to or larger than the volume of the quartz crystal vibration plate 71, and the volume of the base substrate 72 is larger than the volume of the heater IC 6. If the heater IC 6 is a substantially rectangular parallelepiped, the volume of the heater IC 6 is calculated as the product of the length, width, and top-bottom dimensions of the heater IC 6. If the quartz crystal plate 71 is rectangular in plan view, the volume of the quartz crystal plate 71 is calculated as the product of the length, width, and thickness of the quartz crystal plate 71. The volume of the base substrate 72 is calculated as the product of the length, width, and top-bottom dimensions of the base substrate 72 minus the volume of the recess in the base substrate 72.

[0029] Heat transfer in the OCXO 1 occurs in the following order: First, heat from the heater IC 6, which serves as the heating unit, is transferred to the quartz crystal plate 71 via the base substrate 72. Meanwhile, heat from the quartz crystal plate 71 is transferred to the external package 2 via the base substrate 72 and the holding member 8. Furthermore, heat from the quartz crystal plate 71 is transferred to the external package 2 via the base substrate 72 and the wires 9.

[0030] In this embodiment, the thermal capacity of the entire crystal unit 7, including the crystal oscillating plate 71, is increased. By interposing a base substrate 72 between the crystal oscillating plate 71 and the heater IC 6 as a thermal buffer, the crystal oscillating plate 71 is made less sensitive to (gradually changes in) thermal changes in response to thermal changes in the heater IC 6. Furthermore, the crystal oscillating plate 71 is less susceptible to changes in the external thermal environment, suppressing thermal changes in the crystal oscillating plate 71 and stabilizing its temperature. Furthermore, the core unit 4 is mounted inside the external package 2 via a holding member 8 with a lower thermal conductivity than the base substrate 72, making it less susceptible to changes in the external environment. This suppresses thermal changes in the core unit 4 and stabilizes its temperature. In particular, the crystal oscillating plate 71 is doubly vacuum-sealed in the space enclosed by the base substrate 72 and the sealing member 73 inside the external package 2. The crystal oscillating plate 71 is also bonded to the holding member 8 via the base substrate 72 and connected to the external package 2 via the holding member 8, enhancing its thermal insulation against changes in the external thermal environment. As a result, the temperature environment of the crystal oscillating plate 71 can be stabilized. Furthermore, since the wires 9 have a small cross-sectional area, heat loss due to changes in the external thermal environment can be more effectively suppressed, thereby stabilizing the temperature of the quartz crystal plate 71 and the frequency-temperature characteristics of the OCXO 1.

[0031] In this embodiment, the base substrate 72 of the crystal unit 7 serves as a foundation for the oscillator IC 5 and heater IC 6, supporting the core unit 4 in the external package 2. By interposing the base substrate 72 between the crystal unit 71 and the heater IC 6, heat from the heater IC 6 is stored in the base substrate 72, mitigating heat transfer to the crystal unit 71. This also makes the crystal unit 71 less susceptible to changes in the external thermal environment, suppressing thermal changes in the crystal unit 71 and stabilizing its temperature. This stabilizes the temperature of the crystal unit 71 and the frequency-temperature characteristics of the OCXO 1. Furthermore, since the size of the crystal unit 7 can be increased compared to a triple-layer crystal unit, the Q value of the crystal unit 7 is increased, thereby reducing the phase noise of the OCXO 1.

[0032] Furthermore, in this embodiment, an existing quartz crystal unit 7 can be used as the vibration device unit, and the quartz crystal unit 7 is arranged with the base substrate 72 of the quartz crystal unit 7 positioned on the upper side and the sealing member (lid) 73 positioned on the lower side. In this way, by mounting the upper surface of the sealing member 73 facing downward and the bottom surface of the base substrate 72 having a recess facing upward on the holding member 8, the external terminals formed on the bottom surface of the base substrate 72 can be used as wire bonding portions for connecting wires 9. This eliminates the need to manufacture a new dedicated package with a separate wire bonding portion, reduces the complexity of wiring, and contributes to space savings.

[0033] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined by the scope of the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included.

[0034] For example, Modification 1 shown in FIG. 4 differs from the above embodiment in that the holding member 8 is formed from a single plate-shaped substrate. The holding member 8 is formed from a resin film such as polyimide. As shown in FIG. 4 , the holding member 8 and the sealing member 73 of the crystal unit 7 of the core portion 4 are bonded via a non-conductive adhesive 43. The non-conductive adhesive 43 is interposed between the opposing surfaces of the sealing member 73 and the holding member 8, and the opposing surfaces of the sealing member 73 and the holding member 8 are fixed together by the non-conductive adhesive 43. In this case, the surface of the sealing member 73 and the upper surface of the holding member 8 are bonded via the non-conductive adhesive 43. The holding member 8 has a larger area in a plan view than the sealing member 73, and the entire sealing member 73 is located within the arrangement area of ​​the holding member 8 in a plan view. The entire sealing member 73 is bonded to the upper surface of the holding member 8.

[0035] In this way, by interposing the holding member 8 (resin film) between the crystal unit 7 and the external package 2, the crystal unit 71 is less susceptible to changes in the external thermal environment, suppressing thermal changes in the crystal unit 71 and stabilizing its temperature. This allows the heater IC 6 to efficiently heat the crystal unit 7, reducing current consumption for heating and stabilizing the temperature of the core unit 4.

[0036] Furthermore, Modification 2 shown in FIG. 5 differs from the above embodiment in that a heat transfer portion 75 having a higher thermal conductivity than the base substrate 72 is formed on the base substrate 72. The heat transfer portion 75 can be configured, for example, by filling a through hole formed in the base substrate 72 with a conductor. As shown in FIG. 5, three heat transfer portions 75 are provided at predetermined intervals on the base substrate 72, and the heat transfer portions 75 are located in the region directly below the heater IC 6. The heat transfer portions 75 are formed from a paste material such as molybdenum or tungsten. The thermal conductivity of the heat transfer portion 75 is approximately 147 W / m·K at room temperature when made of molybdenum, and 53 to 66 W / m·K when made of tungsten.

[0037] Here, the base substrate 72 is interposed between the quartz crystal plate 71 and the heater IC 6, which is thought to make it difficult for heat from the heater IC 6 to be transferred to the quartz crystal plate 71. However, by providing a heat transfer portion 75 on the base substrate 72 as in Variation 2, the heater IC 6 and the quartz crystal plate 71 can be thermally strongly connected, allowing heat from the heater IC 6 to be transferred quickly to the quartz crystal plate 71, reducing the delay in heat transfer. As a result, the temperature difference between the heater IC 6 and the quartz crystal plate 71 can be kept small.

[0038] 6 to 8, a third modification shown in FIG. 6 differs from the above embodiment in that the heating element 6A (heating portion) of the heater IC is separated from the control IC 5A. The control IC 5A has the function of controlling the heater IC 6 in addition to the function of the oscillation IC 5 of the above embodiment. For example, a chip resistor or a film resistor can be used as the heating element 6A, and the amount of heat generated by the heating element 6A can be controlled by controlling the current supplied to the heating element 6A by the control IC 5A.

[0039] As shown in Figures 6 to 8, the control IC 5A and the heating element 6A are arranged side by side at a predetermined distance above the upper surface of the crystal unit 7 (the bottom surface of the base substrate 72). A non-conductive adhesive 45 is interposed between the opposing surfaces of the crystal unit 7 and the control IC 5A, and the opposing surfaces of the crystal unit 7 and the control IC 5A are fixed together by the non-conductive adhesive 45. In this case, the upper surface of the crystal unit 7 (the bottom surface of the base substrate 72) and the lower surface of the control IC 5A are bonded together via the non-conductive adhesive 45. The crystal unit 7 has a larger area in a plan view than the control IC 5A, and the entire control IC 5A is located within the arrangement area of ​​the crystal unit 7 in a plan view. The entire control IC 5A is bonded to the upper surface of the crystal unit 7 (the bottom surface of the base substrate 72). The non-conductive adhesive 45 may be a resin adhesive such as a polyimide adhesive or an epoxy adhesive. In addition, instead of the non-conductive adhesive 45, a conductive adhesive containing, for example, a metallic conductive filler may be used, in which case it is possible to further improve the heat transfer between the quartz oscillator 7 and the control IC 5A.

[0040] A non-conductive adhesive 46 is interposed between the opposing surfaces of the quartz crystal unit 7 and the heating element 6A, fixing the opposing surfaces of the quartz crystal unit 7 and the heating element 6A together. The top surface of the quartz crystal unit 7 (the bottom surface of the base substrate 72) and the bottom surface of the heating element 6A are bonded via the non-conductive adhesive 46. The quartz crystal unit 7 has a larger area in a plan view than the heating element 6A, and the entire heating element 6A is located within the arrangement area of ​​the quartz crystal unit 7 in a plan view. The entire heating element 6A is bonded to the top surface of the quartz crystal unit 7 (the bottom surface of the base substrate 72). The non-conductive adhesive 46 may be a resin adhesive such as a polyimide adhesive or an epoxy adhesive. Instead of the non-conductive adhesive 46, a conductive adhesive containing, for example, a metallic conductive filler may be used, which further improves heat transfer between the quartz crystal unit 7 and the heating element 6A.

[0041] The base substrate 72 is made of ceramic such as alumina, and its thermal conductivity (approximately 21 W / m·K at room temperature when made of alumina) is higher than that of the quartz crystal vibration plate 71 (5.4 W / m·K (orthogonal to the Z axis) to 9.3 W / m·K (parallel to the Z axis) at 70°C). The holding member 8 is made of polyimide, for example, and its thermal conductivity is higher than that of the holding member 8 (0.16 to 0.18 W / m·K at room temperature when made of polyimide). The thermal conductivity of the quartz crystal vibration plate 71 is higher than that of the holding member 8. The volume of the heating element 6A is equal to or greater than that of the quartz crystal vibration plate 71, and the volume of the base substrate 72 is greater than that of the heating element 6A. The volume of the heating element 6A is calculated as the product of the length, width, and top-bottom dimensions of the heating element 6A when the heating element 6A is a substantially rectangular parallelepiped. The volume of the quartz crystal plate 71 is calculated as the product of the length, width, and thickness of the quartz crystal plate 71 when the quartz crystal plate 71 is rectangular in plan view. The volume of the base substrate 72 is calculated as the product of the length, width, and top-bottom dimensions of the base substrate 72 minus the volume of the recess in the base substrate 72.

[0042] 9 and 10 differ from the above embodiment in that the temperature sensor 13 is provided as a separate component from the heater IC. The temperature sensor 13 is, for example, a thermistor. In the fourth modification shown in FIG. 9 , the temperature sensor 13 is disposed on the top surface of the crystal unit 7 (the bottom surface of the base substrate 72). In the fifth modification shown in FIG. 10 , the temperature sensor 13 is disposed in the internal space of the crystal unit 7, i.e., the space enclosed by the base substrate 72 and the sealing member 73. By disposing the temperature sensor 13 relatively close to the crystal plate 71 of the crystal unit 7 in this manner, the temperature of the core unit 4 can be precisely controlled in response to changes in the external environment, and the phase noise of the OCXO 1 can be reduced compared to when a temperature sensor built into the heater IC 6 is used.

[0043] In the above embodiment, the heater IC 6 is disposed above the crystal unit 7, but this is not limiting. For example, as in Modifications 6 and 7 shown in Figures 11 and 12, the heater IC 6 may be disposed in the space inside the crystal unit 7, i.e., the space surrounded by the base substrate 72 and the sealing member 73. In the above embodiment, the oscillation IC 5 is disposed above the crystal unit 7, but this is not limiting. For example, as in Modifications 6 and 8 shown in Figures 11 and 13, the oscillation IC 5 may be disposed in the space inside the crystal unit 7, i.e., the space surrounded by the base substrate 72 and the sealing member 73. Note that although wires are not shown in Figures 11 to 13, the core unit 4 is electrically connected to the external package 2 via wires, as in the above embodiment (see Figures 1 to 3).

[0044] 11 , the oscillation IC 5 and the heater IC 6 are disposed in the space inside the crystal resonator 7. The oscillation IC 5 is bonded to the bottom (inner bottom surface) of the recess in the base substrate 72 via a conductive adhesive 76. The heater IC 6 is bonded to the inner bottom surface of the recess in the base substrate 72 via a conductive adhesive 77. The crystal vibration plate 71 is mounted via a conductive adhesive 74 on a step 78 formed on the inner bottom surface of the recess in the base substrate 72. By providing the step 78 on the inner bottom surface of the recess in the base substrate 72, a space is secured between the inner bottom surface of the recess in the base substrate 72 and the crystal vibration plate 71 in which the oscillation IC 5 and the heater IC 6 can be disposed.

[0045] 12, the heater IC 6 is disposed in the space inside the crystal unit 7, and the oscillation IC 5 is disposed outside the crystal unit 7. The variation 7 in FIG. 12 differs from the variation 6 in FIG. 11 in that the oscillation IC 5 is bonded to the top surface of the crystal unit 7 (the bottom surface of the base substrate 72) via a conductive adhesive 79, but the other configurations are substantially the same.

[0046] 13, the oscillation IC 5 is disposed in the space inside the crystal unit 7, and the heater IC 6 is disposed outside the crystal unit 7. The variation 8 of Fig. 13 differs from the variation 6 of Fig. 11 in that the heater IC 6 is bonded to the top surface of the crystal unit 7 (the bottom surface of the base substrate 72) via a conductive adhesive 80, and that the crystal vibration plate 71 is mounted on the inner bottom surface of the recess in the base substrate 72 via a conductive adhesive 74, and no step portion 78 is provided on the inner bottom surface of the recess in the base substrate 72; however, the other configurations are the same.

[0047] In the OCXO 1 of the sixth to eighth modifications, as in the above-described embodiment, the core unit 4 includes an oscillation IC (oscillator circuit unit) 5, a crystal unit (oscillator device unit) 7, and a heater IC (heating unit) 6. A base substrate 72 is interposed between the heater IC 6 and a crystal diaphragm 71. The base substrate 72 and the heater IC 6 are surface-bonded to each other with conductive adhesives (bonding materials) 77 and 80. The core unit 4 is mechanically bonded to the external package 2 via a holding member 8 and electrically connected to the external package 2 via wires. The relationships of thermal conductivity of the crystal diaphragm 71<thermal conductivity of the base substrate 72 and thermal conductivity of the holding member 8<thermal conductivity of the base substrate 72 are satisfied, and the relationship of volume of the crystal diaphragm 71≦volume of the heater IC 6<volume of the base substrate 72 is satisfied. As a result, the OCXO 1 of the sixth to eighth modifications can achieve the same effects as the above-described embodiment.

[0048] This application claims priority from Japanese Patent Application No. 2024-012675, filed in Japan on January 31, 2024, the entire contents of which are incorporated herein by reference.

[0049] REFERENCE SIGNS LIST 1 OCXO (oven-controlled piezoelectric oscillator) 2 External package 3 Lid 4 Core section 5 Oscillator IC (oscillator circuit section) 6 Heater IC (heating section) 7 Quartz crystal unit (oscillating device section) 8 Holding member 9 Wire 13 Temperature sensor 42 Non-conductive adhesive (bonding material) 71 Quartz crystal diaphragm (piezoelectric diaphragm) 72 Base substrate 73 Sealing member 75 Heat transfer section

Claims

1. An oven-controlled piezoelectric oscillator having a core section sealed in a vacuum state inside a thermally insulating external package, wherein the core section includes at least an oscillation circuit section, a vibration device section, and a heating section, wherein the vibration device section comprises a base substrate, a piezoelectric diaphragm mounted on one main surface of the base substrate, and a sealing member that hermetically seals the piezoelectric diaphragm mounted on the base substrate in a vacuum state, wherein the base substrate is interposed between the heating section and the piezoelectric diaphragm, and the base substrate and the heating section are surface-bonded to each other with a bonding material, wherein the core section is mechanically bonded to the external package via a holding member and electrically connected to the external package via a wire, wherein the relationships of thermal conductivity of the piezoelectric diaphragm < thermal conductivity of the base substrate and thermal conductivity of the holding member < thermal conductivity of the base substrate are satisfied, and the relationship of volume of the piezoelectric diaphragm < volume of the heating section < volume of the base substrate is satisfied.

2. The oven-controlled piezoelectric oscillator according to claim 1, wherein the base substrate of the vibration device section serves as a foundation for the oscillation circuit section and the heating section, and the core section is supported by the external package.

3. An oven-controlled piezoelectric oscillator according to claim 1 or 2, wherein a heat transfer section having a higher thermal conductivity than the base substrate is formed on the base substrate, and the heat transfer section overlaps the mounting area of the piezoelectric diaphragm in a plan view.

4. An oven-controlled piezoelectric oscillator according to claim 1 or 2, characterized in that a temperature sensor for detecting the temperature of the core section is provided separately from the heating section, and the temperature sensor is located on the external surface of the vibration device section or inside the vibration device section.

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