Thermostatic chamber type piezoelectric oscillator

Abstract

To provide a thermostatic chamber type piezoelectric oscillator capable of stabilizing a temperature of a piezoelectric vibrating plate and stabilizing a frequency-temperature characteristic.SOLUTION: In an OCXO 1 in which a core part 4 is sealed inside a heat insulating external package 2 in a vacuum state, the core part 4 is mechanically bonded to the external package 2 via a holding member 8, and is electrically connected to the external package 2 via a wire 9. A crystal oscillator 7 and a heater IC 6 are mounted on the holding member 8 in a side-by-side state, and are thermally connected to each other by a heat transfer part 7A provided on an upper side of the holding member 8, satisfies the relationship of a thermal conductivity of a quartz vibrating plate 71<the thermal conductivity of a base substrate 72, and the relationship of the thermal conductivity of the holding member 8<the thermal conductivity of the base substrate 72<the thermal conductivity of the heat transfer portion 7A, and the relationship of the volume of the quartz vibrating plate 71≤the volume of the heater IC 6<the volume of the base substrate 72.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Piezoelectric oscillators such as quartz crystal oscillators change their oscillation frequency depending on the temperature based on their inherent frequency-temperature characteristics. Therefore, oven-controlled piezoelectric oscillators (hereinafter also referred to as "OCXOs") are known in which the piezoelectric oscillator is enclosed in a thermostatic oven to maintain a constant temperature around the piezoelectric oscillator (see, for example, Patent Document 1). In the OCXO described in Patent Document 1, the oscillation 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 149541 Summary of the Invention [Problem to be solved by the invention]

[0004] In the OCXO described above, as the vibration device becomes smaller, the volume of the piezoelectric diaphragm also becomes smaller, and the heat capacity of the piezoelectric diaphragm also becomes smaller. 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 temperature 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 even to 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 the piezoelectric diaphragm and stabilize the frequency-temperature characteristics. [Means for solving the problem]

[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 outer package, the core unit including at least an oscillation circuit unit, a vibration device unit, a heating unit, and a heat transfer 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 vibration device unit and the heating unit being mounted side by side on a holding member and thermally connected to each other by the heat transfer unit provided on an upper side of the holding member, satisfying the relationships: 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<thermal conductivity of the heat transfer unit, and satisfying the relationship: volume of the piezoelectric diaphragm≦volume of the heating unit<volume of the base substrate.

[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 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 the heating section. Furthermore, the vibration device section and the heating section are thermally connected by a heat transfer section with high thermal conductivity. This allows heat transferred from the heating section to be stored in the base substrate. This increases the heat capacity of the entire vibration device section, including the piezoelectric diaphragm, making the piezoelectric diaphragm less sensitive to thermal changes in the heating section. Furthermore, the piezoelectric diaphragm is less susceptible to changes in the external thermal environment, suppressing thermal changes in the piezoelectric diaphragm and stabilizing its temperature. Furthermore, since the heating section and vibration device section are arranged side-by-side on the support member, heat transfer from the heating section to the vibration device section is reduced, making it less sensitive to thermal changes in the external thermal environment. Furthermore, because the heating unit and the vibration device unit are arranged side by side on the support member, the height of the oven-controlled piezoelectric oscillator can be reduced. As a result, the temperature of the piezoelectric diaphragm is stabilized, stabilizing the frequency-temperature characteristics and enabling the product to be made low-profile.

[0008] In the above configuration, the oscillator circuit unit is preferably mounted on the upper side of the holding member or on the upper side of a member mounted on the holding member. This allows the oscillator circuit unit to be located close to other core members such as a vibration device unit and a heating unit, reducing the temperature difference between the oscillator circuit unit and these other core members, leading to stable frequency-temperature characteristics. Furthermore, the oscillator circuit unit can be easily connected to other core members such as a vibration device unit and a heating unit from above, improving mounting stability and productivity.

[0009] In the above configuration, the core unit is preferably mechanically joined to the external package via a holding member and electrically connected to the external package via a wire. This allows the core unit to be mounted inside the external package via a holding member with a lower thermal conductivity than the base substrate, making it less susceptible to changes in the external environment. This suppresses thermal changes in the core unit and stabilizes its temperature. In particular, the piezoelectric diaphragm is enclosed in a double vacuum state in a space surrounded by the base substrate and the sealing member inside the external package and is connected to the external package via the holding member, improving insulation against changes in the external thermal environment. As a result, the temperature environment of the piezoelectric diaphragm can be stabilized. Furthermore, since a wire with a small cross-sectional area is used for electrical connection, heat loss due to changes in the external thermal environment can be more effectively suppressed. This improves heat transfer between the base substrate of the vibration device unit of the core unit and the heating unit, resulting in a configuration in which temperature differences between the two are less likely to occur.

[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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an OCXO according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the OCXO of FIG. 1 taken along line X1-X1. [Figure 3]2 is a cross-sectional view of the OCXO of FIG. 1 taken along line X2-X2. [Figure 4] FIG. 2 is a diagram equivalent to FIG. 1 showing a first modified example of an OCXO. [Figure 5] 5 is a cross-sectional view of the OCXO of FIG. 4 taken along line X3-X3. [Figure 6] 5 is a cross-sectional view of the OCXO of FIG. 4 taken along line X4-X4. [Figure 7] FIG. 10 is a diagram equivalent to FIG. 1 showing a second modified example of an OCXO. [Figure 8] FIG. 10 is a diagram equivalent to FIG. 1 showing a third modified example of an OCXO. DETAILED DESCRIPTION OF THE INVENTION

[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 and 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, 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, etc. 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 (oscillation circuit unit) 5, a heater IC (heating unit) 6, a crystal unit (oscillating device unit) 7, and a heat transfer unit 7A. The core unit 4 is a package of various electronic components used in the OCXO 1, and in this embodiment, the oscillation IC 5, heater IC 6, and crystal unit 7 are mounted on the heat transfer unit 7A. More specifically, the crystal unit 7 and heater IC 6 are mounted side-by-side on the heat transfer unit 7A, and the oscillation IC 5 is mounted on the heater IC 6.

[0018] The quartz crystal unit 7 is a surface-mount type quartz crystal unit and includes a quartz crystal vibrating plate (piezoelectric vibrating plate) 71 on which a vibrating portion (not shown) is formed, a base substrate 72 on one main surface of which the quartz crystal vibrating plate 71 is mounted, and a sealing member 73 that hermetically seals the quartz crystal vibrating plate 71 mounted on the base substrate 72 under vacuum conditions. The base substrate 72 is made of, for example, ceramic or the like, and has a recess for accommodating the quartz crystal vibrating plate 71. The sealing member 73 is made of, for example, metal, ceramic, or the like. The quartz crystal vibrating plate 71 is mounted on the bottom surface of the recess of the base substrate 72 via a conductive adhesive 74, and the space in the recess of 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, the quartz crystal vibrating plate 71 may be sealed in a space surrounded by the plate-shaped base substrate 72 and the cap-shaped sealing member 73.

[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 1 in FIGS. 4 to 6, the heating element (heating region) and the control circuit (temperature control region) of the heater IC may be configured separately. Furthermore, for example, as shown in Variations 2 and 3 in FIGS. 7 and 8, the temperature sensor may be provided as a separate component from the heater IC 6.

[0021] In this embodiment, as shown in FIGS. 1 to 3, the crystal unit 7 is arranged 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 crystal unit 7 is mounted on a heat transfer portion 7A formed on the surface of the holding member 8. The heat transfer portion 7A is a film-like member formed on the surface of the holding member 8, and is configured, for example, by forming a copper foil pattern on the surface of the holding member 8 and then plating the surface of this copper foil pattern with gold. Note that the heat transfer portion 7A may be, for example, either a copper foil pattern or gold plating, or may be a flat metal plate or the like instead of a film-like member.

[0022] A non-conductive adhesive 43 is interposed between the opposing surfaces of the crystal unit 7 and the heat transfer unit 7A, and the opposing surfaces of the crystal unit 7 and the heat transfer unit 7A are fixed together by the non-conductive adhesive 43. In this case, the upper surface of the heat transfer unit 7A and the lower surface of the crystal unit 7 (the outer surface of the sealing member 73) are joined via the non-conductive adhesive 43. For example, a resin adhesive such as a polyimide adhesive or an epoxy adhesive is used as the non-conductive adhesive 43. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 43, in which case it is possible to further improve the heat transfer between the crystal unit 7 and the heat transfer unit 7A.

[0023] The heater IC 6 is mounted on the heat transfer unit 7A at a predetermined distance from the crystal unit 7 in the left-right direction. A non-conductive adhesive 42 is interposed between the opposing surfaces of the heater IC 6 and the heat transfer unit 7A, and the opposing surfaces of the heater IC 6 and the heat transfer unit 7A are fixed together by the non-conductive adhesive 42. In this case, the upper surface of the heat transfer unit 7A and the lower surface of the heater IC 6 are joined via the non-conductive adhesive 42. For example, a resin adhesive such as a polyimide adhesive or an epoxy adhesive is used as the non-conductive adhesive 42. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 42, which further improves heat transfer between the heater IC 6 and the heat transfer unit 7A.

[0024] 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 top surface of the heater IC 6 and the bottom 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 bottom surface of the oscillation IC 5 is bonded to the top 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.

[0025] The area of the heat transfer portion 7A is larger than the combined area of the heater IC 6 and the crystal unit 7 in a plan view, and the entire heater IC 6 and the entire crystal unit 7 are located within the arrangement area of the heat transfer portion 7A in a plan view. The area of the heat transfer portion 7A is smaller than the area of the holding member 8 in a plan view, and the heat transfer portion 7A is provided in an area inside the holding member 8, but this is not limiting, and the heat transfer portion 7A may be formed on the entire surface of the holding member 8.

[0026] The core 4 is mechanically joined to the inner bottom surface of the recess 2a of the outer package 2 via a holding member 8. In this embodiment, the core 4 is supported by one holding member 8 formed in a flat plate shape, and a space (gap) 2d is formed in the lower part of the core 4. Two spacer members 2f are arranged at a predetermined interval on the inner bottom surface of the recess 2a of the outer package 2, and the holding member 8 is joined onto each spacer member 2f via a non-conductive adhesive 44.

[0027] The holding member 8 is made of a heat-resistant and flexible resin material such as polyimide. The spacer members 2f are made of a paste material (metallized material) such as molybdenum or tungsten. The non-conductive adhesive 44 may be a resin adhesive such as a polyimide adhesive or an epoxy adhesive. The holding member 8 may also be made of quartz. Four spacer members 2f may be provided below the holding member 8 to support the four corners of the holding member 8.

[0028] 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 surface of the step portion 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 crystal unit 7 of the core unit 4 by wire bonding. Furthermore, the wire pads formed on the step surface of the step portion 2c of the external package 2 are connected via wires 9 to wire pads formed on the top surface of the heater IC 6 of the core unit 4 by wire bonding. Furthermore, the wire pads formed on the bottom surface of the base substrate 72 of the crystal unit 7 of the core unit 4 are connected via wires 9 to wire pads formed on the oscillation IC 5 and the heater IC 6, respectively. Furthermore, the wire pads formed on the heater IC 6 are connected via wires 9 to wire pads formed on the oscillation IC 5 by wire bonding. The excitation electrode of the vibrating portion of the quartz crystal vibrating plate 71 of the quartz crystal vibrator 7 is electrically connected to the wire 9 via wiring or through holes in the base substrate 72, making it possible to apply an AC voltage of a predetermined frequency to the excitation electrode of the vibrating portion of the quartz crystal vibrating plate 71.

[0029] In this embodiment, in the OCXO 1 configured as described above, the core unit 4 is mechanically joined to the external package 2 via the holding member 8 and electrically connected to the external package 2 via wires 9. The crystal unit 7 and the heater IC 6 are mounted side-by-side (flat) on the holding member 8 and are thermally connected to each other via a heat transfer unit 7A provided on the upper side of the holding member 8. This satisfies the relationships: thermal conductivity of the crystal vibration plate 71<thermal conductivity of the base substrate 72, and thermal conductivity of the holding member 8<thermal conductivity of the base substrate 72<thermal conductivity of the heat transfer unit 7A. In addition, the relationship: volume of the crystal vibration plate 71≦volume of the heater IC 6<volume of the base substrate 72 is satisfied. This feature will be described below.

[0030] As described above, the base substrate 72 is made of a 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 that of the holding member 8. The heat transfer unit 7A is made of gold or copper, for example. Specifically, a copper foil is formed on the top of the holding member 8, or a gold plating is further formed on top of the copper foil. The thermal conductivity of the heat transfer portion 7A (if made of gold, it is approximately 295 W / m·K at room temperature, or if made of copper, it is approximately 372 W / m·K at room temperature) is higher than that of the holding member 8. The thermal conductivity of the heat transfer portion 7A is higher than that of the base substrate 72.

[0031] In this embodiment, the volume of the heater IC 6 is equal to or larger than the volume of the quartz crystal plate 71, and the volume of the base substrate 72 is larger than the volume of the heater IC 6. Here, if the heater IC 6 is a substantially rectangular parallelepiped, the volume of the heater IC 6 is calculated by multiplying the length, width, and top-bottom dimensions of the heater IC 6. If the quartz crystal plate 71 is a substantially rectangular shape in plan view, the volume of the quartz crystal plate 71 is calculated by multiplying the length, width, and thickness of the quartz crystal plate 71. If the base substrate 72 has a recess, the volume of the base substrate 72 is calculated by subtracting the volume of the recess from the product of the length, width, and top-bottom dimensions of the base substrate 72. If the base substrate 72 is plate-shaped, the volume of the base substrate 72 is calculated by multiplying the length, width, and top-bottom dimensions of the base substrate 72.

[0032] 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 base substrate 72 via the heat transfer unit 7A, and then from the base substrate 72 to the quartz crystal plate 71. Meanwhile, heat from the quartz crystal plate 71 is transferred to the external package 2 via the base substrate 72, the heat transfer unit 7A, 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.

[0033] In this embodiment, the thermal capacity of the entire crystal unit 7, including the crystal plate 71, is increased, making the crystal plate 71 less sensitive (gradual) to thermal changes in response to thermal changes in the heater IC 6. Furthermore, the crystal plate 71 is less susceptible to changes in the external thermal environment, suppressing thermal changes in the crystal plate 71 and stabilizing its temperature. Furthermore, the heater IC 6 and the crystal unit 7 are not stacked but are arranged side-by-side (flat) at a predetermined distance, thereby mitigating heat transfer from the heater IC 6 to the crystal unit 7 and reducing sensitivity to thermal changes in the external thermal environment, thereby suppressing phase noise. In this case, noise from the heater IC 6 is not directly transmitted to the crystal unit 7, effectively suppressing phase noise in the vicinity of 1 Hz to 3 Hz. Furthermore, while phase noise in the vicinity of 1 Hz to 3 Hz is thought to increase when the heater IC 6 is activated, this embodiment also reduces such phase noise when the heater IC 6 is activated. Furthermore, since the heater IC 6 and the crystal unit 7 are arranged side by side on the holding member 8, it is possible to reduce the product height of the OCXO 1. This makes it possible to stabilize the temperature of the crystal unit 71, which in turn stabilizes the frequency-temperature characteristics of the OCXO 1, allowing for a low-profile product and suppressing phase noise.

[0034] Furthermore, the core unit 4 is mounted inside the external package 2 via a holding member 8 with 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 quartz crystal plate 71 is enclosed in a double vacuum state within the external package 2, surrounded by the base substrate 72 and the sealing member 73, and is connected to the external package 2 via the holding member 8. This enhances insulation against changes in the external thermal environment. As a result, the temperature environment of the quartz crystal plate 71 is stabilized. Furthermore, the use of wires 9 with small cross-sectional areas for electrical connection effectively suppresses heat loss in response to changes in the external thermal environment. This improves heat transfer between the base substrate 72 of the quartz crystal unit 7 of the core unit 4 and the heater IC 6, reducing temperature differences between them. This reduces the amount of heat generated by the heater IC 6 and the current consumption of the heater IC 6.

[0035] In this embodiment, the oscillation IC 5 is mounted above the heater IC 6 mounted on the holding member 8. This allows the oscillation IC 5 to be located close to other components of the core unit 4, such as the heater IC 6, reducing the temperature difference between the oscillation IC 5 and these other components of the core unit 4, leading to stable frequency-temperature characteristics. Furthermore, the oscillation IC 5 can be easily connected to other components of the core unit 4, such as the heater IC 6, from above using techniques such as wire bonding, improving mounting stability and productivity. Furthermore, the size of the crystal unit 7 can be increased compared to when a triple-layer crystal unit is used, thereby increasing the Q value of the crystal unit 7 and reducing the phase noise of the OCXO 1.

[0036] 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 claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included.

[0037] For example, Modification 1 shown in Figures 4 to 6 differs from the above embodiment in that the heating element 6A (heating unit) of the heater IC and the control IC 5A are separate. The control IC 5A has the function of controlling the heater IC 6 in addition to the function of the oscillation IC 5 in 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 using the control IC 5A.

[0038] 4 to 6, the control IC 5A and the heating element 6A are arranged side by side at a predetermined distance above the holding member 8. More specifically, the crystal unit 7 and the heating element 6A are mounted side by side at a predetermined distance in the left-right direction on a heat transfer section 7A formed on the upper side of the holding member 8, and further, the control IC 5A is mounted on a portion of the upper side of the holding member 8 where the heat transfer section 7A is not formed, at a predetermined distance in the left-right direction from the heating element 6A. In this first modification, the core unit 4 is configured to include the control IC 5A, the heating element 6A, the crystal unit 7, and the heat transfer section 7A.

[0039] A non-conductive adhesive 43 is interposed between the opposing surfaces of the crystal unit 7 and the heat transfer unit 7A, and the opposing surfaces of the crystal unit 7 and the heat transfer unit 7A are fixed to each other by the non-conductive adhesive 43. A non-conductive adhesive 46 is interposed between the opposing surfaces of the heating element 6A and the heat transfer unit 7A, and the opposing surfaces of the heating element 6A and the heat transfer unit 7A are fixed to each other by the non-conductive adhesive 46. The non-conductive adhesives 43 and 46 may be resin adhesives such as polyimide adhesives or epoxy adhesives. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 43, which further improves heat transfer between the crystal unit 7 and the heat transfer unit 7A. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 46, which further improves heat transfer between the heating element 6A and the heat transfer unit 7A.

[0040] A non-conductive adhesive 45 is interposed between the opposing surfaces of the control IC 5A and the holding member 8, and the opposing surfaces of the control IC 5A and the holding member 8 are fixed together by the non-conductive adhesive 45. In this case, the upper surface of the holding member 8 and the control IC 5A are joined via the non-conductive adhesive 45. For example, a resin adhesive such as a polyimide adhesive or an epoxy adhesive is used as the non-conductive adhesive 45. Note that a conductive adhesive containing, for example, a metallic conductive filler may be used instead of the non-conductive adhesive 45, in which case the heat transfer between the control IC 5A and the holding member 8 can be further improved.

[0041] The area of the heat transfer section 7A is larger than the combined area of the heating element 6A and the crystal unit 7 in a plan view, and the entire heating element 6A and the entire crystal unit 7 are located within the arrangement area of the heat transfer section 7A in a plan view. The area of the heat transfer section 7A is smaller than the area of the holding member 8 in a plan view, and the heat transfer section 7A is provided in an area inside the holding member 8. Note that in this modification 1, the control IC 5A is not mounted above the heat transfer section 7A, and the control IC 5A is not located within the arrangement area of the heat transfer section 7A in a plan view. However, in addition to the heating element 6A and the crystal unit 7, the control IC 5A may also be mounted above the heat transfer section 7A, and the control IC 5A may also be located within the arrangement area of the heat transfer section 7A in a plan view.

[0042] The base substrate 72 is made of ceramic such as alumina, and has a higher thermal conductivity (approximately 21 W / m·K at room temperature when made of alumina) 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 has a higher thermal conductivity than 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 heat transfer section 7A is made of gold or copper, for example. Specifically, a copper foil is formed on the top of the holding member 8, or a gold plating is further formed on top of the copper foil. The heat transfer portion 7A has a thermal conductivity (approximately 295 W / m·K at room temperature if made of gold, or approximately 372 W / m·K at room temperature if made of copper), which is higher than the thermal conductivity of the holding member 8. The heat transfer portion 7A also has a thermal conductivity higher than that of the base substrate 72. The volume of the heating element 6A is equal to or greater than the volume of the quartz crystal oscillating plate 71, and the volume of the base substrate 72 is larger than the volume of the heating element 6A. If the heating element 6A is a substantially rectangular parallelepiped, the volume of the heating element 6A is calculated by multiplying the length, width, and top-to-bottom dimensions of the heating element 6A. If the quartz crystal oscillating plate 71 is rectangular in plan view, the volume of the quartz crystal oscillating plate 71 is calculated by multiplying the length, width, and thickness of the quartz crystal oscillating plate 71. The volume of the base substrate 72 is calculated by subtracting the volume of the recess of the base substrate 72 from the product of the length, width, and top-bottom dimensions of the base substrate 72 .

[0043] Furthermore, in Modifications 2 and 3 shown in FIGS. 7 and 8 , the temperature sensor 13 is provided as a separate component from the heater IC, which differs from the above embodiment. The temperature sensor 13 is, for example, a thermistor. In Modification 2 shown in FIG. 7 , the temperature sensor 13 is disposed on the top surface of the crystal unit 7 (the bottom surface of the base substrate 72). In Modification 3 shown in FIG. 8 , 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, precise temperature control of the core unit 4 in response to external environmental changes can be performed, 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. For example, when a temperature sensor 13 such as a thermistor is used, the temperature sensor's sensitivity can be improved compared to when a temperature sensor built into the heater IC 6 is used, making it possible to reduce the heater gain of the heater IC 6 and also reduce phase noise.

[0044] Furthermore, in the above embodiment, the oscillation IC 5 is disposed above the heater IC 6, but this is not limiting, and the oscillation IC 5 may be disposed in the space inside the crystal unit 7, that is, in the space surrounded by the base substrate 72 and the sealing member 73. Alternatively, the oscillation IC 5 may be disposed on the top surface of the crystal unit 7 (the bottom surface of the base substrate 72), or on the top surface of the holding member 8, spaced a predetermined distance from the heater IC 6 in the left-right direction. [Explanation of symbols]

[0045] 1 OCXO (oven-controlled piezoelectric oscillator) 2 External Package 3 Lid 4 Core section 5 Oscillation IC (oscillation circuit section) 6 Heater IC (heating part) 7. Crystal unit (vibration device part) 7A Heat transfer section 8 Retaining member 9 wire 13 Temperature Sensor 71 Quartz crystal diaphragm (piezoelectric diaphragm) 72 Base board 73 Sealing member

Claims

1. An oven-controlled piezoelectric oscillator in which a core is sealed in a vacuum state inside a heat-insulating outer package, the core unit includes at least an oscillation circuit unit, a vibration device unit, a heating unit, and a heat transfer unit, the vibration device unit includes a base substrate, a piezoelectric vibration plate mounted on one main surface of the base substrate, and a sealing member that hermetically seals the piezoelectric vibration plate mounted on the base substrate in a vacuum state; the vibration device unit and the heating unit are mounted side by side on a holding member and are thermally connected to each other by the heat transfer unit provided on an upper side of the holding member, a relationship of thermal conductivity of the piezoelectric diaphragm < a relationship of thermal conductivity of the base substrate, and a relationship of thermal conductivity of the holding member < a relationship of thermal conductivity of the base substrate < a relationship of thermal conductivity of the heat transfer portion are satisfied; An oven-controlled piezoelectric oscillator, wherein the volume of the piezoelectric diaphragm is less than or equal to the volume of the heating portion and less than the volume of the base substrate.

2. 2. The oven-controlled piezoelectric oscillator according to claim 1, The oven-controlled piezoelectric oscillator is characterized in that the oscillation circuit section is mounted on the upper side of the holding member or on the upper side of a member mounted on the holding member.

3. 3. The oven-controlled piezoelectric oscillator according to claim 1, the core is mechanically joined to the external package via the holding member and electrically connected to the external package via a wire.

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

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