JP2007158465A - Piezoelectric device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric device, the jitter characteristics of which are improved by shielding electromagnetic noises or the like that have infiltrated from the outside of the device. <P>SOLUTION: In the piezoelectric device, wherein at least a piezoelectric resonator element is mounted in a recessed space formed to the inside of a rectangular package, a metal-made lid of a rectangular flat plate shape is arranged to the top face of sidewall parts for surrounding the space of the package, in a form of covering the opening of the space, and the lid and a conductor layer, provided to the top face of the side wall parts are joined and fixed to each other so as to hermetically seal the piezoelectric resonator element in the space, the thickness of the lid is 150μm or larger and the thickness of the piezoelectric device is 2mm or smaller. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric device such as a piezoelectric vibrator or a piezoelectric oscillator used as an electronic component in an electronic device such as a portable communication device.

  A piezoelectric vibrator in which a piezoelectric vibration element in which electrode films are formed on both main surfaces of the piezoelectric element plate is mounted inside the container body, a piezoelectric oscillator in which the piezoelectric vibrator and the oscillation circuit are mounted in the same container body, or Piezoelectric devices such as piezoelectric filters that separate specific frequency bands are often used as electronic components in electronic devices such as portable communication devices and electronic computers. In recent years, piezoelectric devices in a form corresponding to surface mounting have been developed. Further, along with the downsizing of electronic devices to be mounted, these piezoelectric devices are also being reduced in size and thickness.

  As a conventional piezoelectric device, for example, a piezoelectric oscillator which is one of piezoelectric devices is shown in FIG. That is, the piezoelectric vibration element 22 in which excitation electrodes are formed on both main surfaces of a rectangular plate-like element plate made of a piezoelectric material, which is a piezoelectric material, and an oscillation circuit electrically connected to the excitation electrode of the piezoelectric vibration element 22 In a piezoelectric oscillator comprising an electronic component 23 that constitutes an electronic circuit network such as a piezoelectric vibration element 22 and a container body 21 that houses the electronic component 23, the container body 21 has a concave shape that houses only the piezoelectric vibration element 22 therein. The first space portion 24 and the concave second space portion 25 in which the electronic component 23 is accommodated are independently known.

  External connection electrode terminals 26 functioning as a power supply voltage terminal, a ground terminal, an oscillation output terminal, and an oscillation control terminal are formed on the outer bottom surface of the container body 21. A lid 27 in a form that integrally covers the openings of all the space portions is disposed on the top surface of the side wall portion surrounding each space portion of the container body 21, and a conductor formed on the top surface of the lid body 27 and the side wall portion. The layers are bonded and fixed, and at least the first space 24 in which the piezoelectric vibration element 22 is mounted is hermetically sealed. If the lid body 27 is connected to the ground terminal of the external connection electrode terminals 26 via the wiring pattern of the container body 21 or the like, the lid body 27 is grounded during use, thereby providing an electromagnetic shielding function. As a result, the EMC effect can be obtained in which the piezoelectric vibration element 22 and the like mounted therein are well protected from unnecessary external electrical effects (noise, etc.).

A piezoelectric oscillator which is one of the piezoelectric devices as described above is disclosed in the following prior art documents.
Japanese Patent Laid-Open No. 1998-75120

  In addition, the applicant did not come to discover prior art documents related to the present invention by the time of the filing of the application other than the prior art documents specified by the prior art document information described above.

  However, as the piezoelectric device becomes smaller and thinner, the lid may become thinner and the distance between the lid and the piezoelectric vibration element mounted inside may become extremely close. In such a form, the EMC effect by the lid is not sufficient, and the stray capacitance becomes unstable due to the influence of external noise in the piezoelectric vibration element or electronic element mounted in the container.

  For example, a voltage controlled piezoelectric oscillator (VCXO), which is one of the piezoelectric oscillators, has a drawback of deteriorating the jitter characteristics of a PLL circuit connected to a subsequent stage of the control circuit. When jitter characteristics deteriorate, the piezoelectric device is connected to an external PLL circuit, or incorporated in the piezoelectric device and used as a reference signal source or an output signal source for data transfer. If the data is disturbed, there is a possibility that data transfer is not successful and a bit error occurs.

  The present invention has been devised in view of the above disadvantages, and an object thereof is to provide a piezoelectric device having improved jitter characteristics by reducing and shielding the influence of external noise.

  As one form of the piezoelectric device of the present invention, at least a piezoelectric vibration element is mounted in a concave space formed inside a rectangular container body, and the top of the side wall portion surrounding the space part of the container body is mounted. A rectangular flat plate-shaped metal lid is arranged on the surface so as to cover the opening of the space, and the lid and the conductor layer provided on the top surface of the side wall are bonded and fixed. In the piezoelectric device in which the piezoelectric vibration element is hermetically sealed, the lid body has a thickness of 150 μm or more, and the device has a thickness of 2 mm or less.

  As another embodiment of the piezoelectric device of the present invention, at least a piezoelectric vibration element is mounted in a concave space formed inside a rectangular container body, and a side wall portion surrounding the space portion of the container body A rectangular flat plate-shaped metal lid is arranged on the top surface of the space portion so as to cover the opening of the space portion, and the lid body and the conductor layer provided on the top surface of the side wall portion are bonded and fixed. In the piezoelectric device that hermetically seals the piezoelectric vibration element in the unit, the distance between the main surface on the space portion side of the lid and the excitation electrode formed on the main surface on the lid of the piezoelectric vibration element is 400 μm or more. And the thickness of the device is 2 mm or less.

  Furthermore, in the above-described piezoelectric device, two or more spaces are formed in the container body, and the piezoelectric vibration element is mounted in at least one of the spaces.

  According to the piezoelectric device of the present invention, the thickness of the lid that hermetically seals the piezoelectric vibration element in the container body by being fixed to the conductor layer in the opening of the space formed in the container body on which the piezoelectric vibration element is mounted. Is 150 μm or more and the thickness of the device is 2 mm or less, so that the electromagnetic noise blocking function of the lid connected to the ground terminal functions stably stably while maintaining the thinness of the device. As a result, the stray capacitance generated at the gap between the lid and the excitation electrode of the piezoelectric vibration element can be stabilized without fluctuation, so that the jitter characteristics are not deteriorated and the data transfer is performed reliably. Is possible.

  In addition, according to the piezoelectric device of the present invention, the distance between the lid body and the excitation electrode of the piezoelectric vibration element is 400 μm or more, and the thickness of the device is 2 mm or less, thereby maintaining the thinness of the device. In addition, it is possible to minimize the piezoelectric vibration element from being electrically affected by the lid body that has received electromagnetic noise, thereby preventing jitter characteristics from deteriorating and reliably transferring data. It becomes possible.

  Due to such an action, the present invention has an effect of being able to respond to a reduction in size and thickness and providing a piezoelectric device having a high EMC effect.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an upper perspective view showing an embodiment of a piezoelectric device according to the present invention, taking as an example a crystal oscillator which is one of the piezoelectric devices. FIG. 2 is a cross-sectional view of the crystal oscillator disclosed in FIG. Note that the crystal oscillator shown in these drawings is roughly composed of a container body 1, a crystal resonator element 5 as a piezoelectric resonator element, an integrated circuit element 6 including or constituting an oscillation circuit, a frequency adjusting circuit, and the like. It is formed by the component element 7 and its thickness dimension is 2 mm.

  The external shape of the crystal oscillator is made of, for example, a ceramic material such as glass-ceramic or alumina ceramic, and has a container body 1 in which two space portions having openings on one main surface of the container body 1 are formed. 42, and a lid 4 made of metal such as alloy, Kovar, phosphor bronze, etc., and a metallized layer (not shown) such as tungsten (W) or molybdenum (Mo) on the upper surface of the outer peripheral wall of the container body 1. The conductor layer 3 plated with nickel (Ni) and gold (Au) is provided on the upper surface of the metallized layer, and the lid 4 is provided on the upper surface of the conductor layer 3 with openings in the respective spaces. The external shape of the crystal oscillator is configured by placing the conductor layer 3 and the lid 4 in a covering form. Of the two spaces formed in the container body 1, the crystal resonator element 5 and the integrated circuit element 6 are mounted in the first space 8, and the electronic component element 7 is mounted in the second space 9. Has been.

  The crystal resonator element 5 accommodated in the container body 1 is formed by attaching and forming a pair of excitation electrodes 11 on both main surfaces of a crystal piece that has been cut out from the artificial crystal at a so-called AT cut angle. Thus, when a variable voltage from the outside is applied to the crystal piece via the pair of excitation electrodes 11, a thickness shear vibration occurs at a predetermined frequency. This quartz crystal resonator element 5 includes a pair of excitation electrodes 11 formed on both main surfaces thereof, and a resonator element connection electrode pad 12 formed on a support base provided in the first space through a conductive adhesive. The crystal resonator element 5 is mounted on the container body 1 by being electrically and mechanically connected to the container body 1. Note that the crystal resonator element 5 in this embodiment is compatible with higher frequencies while maintaining the strength of the crystal resonator element 5 itself by thinning only the excitation vibration region of the crystal piece from the surroundings by etching or the like. A so-called inverted mesa type crystal vibrating element 5 is used.

  The lid 4 is mainly composed of a flat rectangular metal plate such as 42 alloy, Kovar, phosphor bronze, etc., and a brazing filler metal layer 2 of Au and Sn is applied to the main surface of this metal plate. In addition, you may use the clad material of Au-Sn for the production | generation of the brazing filler metal layer 2. FIG. The brazing filler metal layer 2 such as Au—Sn and the conductor layer 3 on the container body 1 side thus formed are melt-bonded in a heating means such as an oven to hermetically seal each space. In this method, it is possible to join the partition wall portions between the first space portion 8 and the second space portion 9 in the form as in the present embodiment, which cannot be achieved by conventional seam welding.

  If the lid 4 is connected to the ground electrode terminal of the external connection electrode terminals 10 formed on the outer bottom surface of the container body 1 via the wiring conductor formed in the container body 1, the crystal When the oscillator is used, the lid 4 is grounded to give an EMC effect by an electromagnetic shield function. Therefore, it is preferable that the lid 4 is electrically connected to the ground electrode terminal of the external connection electrode terminal 10.

  The integrated circuit element 6 mounted in the same space as the crystal resonator element 5 includes an IC connection electrode pad formed on the bottom surface in the first space and a container body connection formed on the surface of the integrated circuit element 6. The electrode pad is electrically connected by a wire bonding method or a flip chip method in which a gold bump or the like is connected, and a circuit forming surface of the integrated circuit element 6 is used as a crystal oscillator based on an output signal from the crystal vibrating element 5. An oscillation circuit for generating the output signal is formed, and the oscillation output signal generated by the oscillation circuit is used as a reference signal such as a clock signal, for example.

  The electronic component element 7 mounted in the second space 9 is a variable capacitance diode, a chip component or the like, and is used for further adjusting the frequency of the output signal from the integrated circuit element 6. The variable capacitance diode plays a role of adjusting the oscillation frequency by applying an external control voltage, and the inductor element has a role of expanding the frequency adjustment range when connected in series with the crystal vibrating element 5. It is conceivable to add a resistance element or the like.

  Here, since the stray capacitance generated due to the distance between the lid 4 and the excitation electrode 11 formed on the crystal resonator element 5 exists in parallel with the variable capacitance diode for adjusting the oscillation frequency, the stray capacitance is floated due to external noise. When the capacitance is disturbed, the oscillation frequency is also affected and the jitter characteristics are deteriorated. Since the piezoelectric device is used as a reference signal source at the time of data transfer, if the oscillation frequency is disturbed, the data transfer is not successful and a bit error occurs.

  Next, the effect of this invention is demonstrated based on FIG. First, according to the structure of the crystal oscillator shown in FIGS. 1 and 2, the crystal resonator element 5 and the integrated circuit element 6 are mounted in the first space portion 8 of the container body 1, and the second space portion 9 has a varistor. Electronic component elements 7 such as cap diodes and chip inductors are mounted, and power supply voltage terminal electrodes, output terminal electrodes, and external connection electrode terminals 10 that are ground electrodes are formed at the four corners of the outer bottom surface of the container body 1. Further, the thickness b of the cover 4 that covers each space of the container body 1 and is connected to the ground terminal of the external connection terminal electrode 10 and is grounded is changed to 80 μm, 150 μm, 200 μm, and 350 μm. The crystal oscillators were each manufactured by mounting the crystal oscillator on an external PLL circuit, and the jitter value of the PLL output was measured. An oscilloscope was used to measure the jitter value.

  The result is shown in the graph of FIG. When the stray capacitance generated between the excitation electrode 11 and the lid 4 of the crystal resonator element 5 is about 68 fF and the lid thickness b is 80 μm, the external electromagnetic noise is considered to be one of the factors causing the numerical increase. Is confirmed to be about 2000 ps, and when the thickness b of the lid is 150 μm or more, the jitter characteristic can fall below the allowable value of about 1000 ps.

  As described above, when the thickness b of the lid 4 is 150 μm or more, the jitter characteristic is improved by about 1000 ps as compared with the case where the thickness b is less than 150 μm. However, this difference becomes smaller as the stray capacitance becomes smaller (the distance between the excitation electrode 11 of the crystal resonator element 5 and the lid 4 increases).

Next, another effect of the present invention will be described. By varying the distance a between the surface of the excitation electrode 11 facing the first space portion opening side of the crystal resonator element 5 and the surface of the main surface facing the first space portion side of the lid 4, the crystal vibration The experiment was performed by varying the stray capacitance generated between the surface of the excitation electrode 11 facing the first space portion opening side of the element 5 and the main surface of the lid 4 facing the first space portion side. went. The shape of the crystal resonator element 5 to be used is an inverted mesa type, and the stray capacitance between the surface of the excitation electrode 11 and the cover body surface facing the first space opening side of the crystal resonator element 5 is C1, The stray capacitance between the electrode formed on the excitation vibration portion of the electrode facing the bottom surface in the first space portion of the crystal resonator element 5 and the lid is C2, and the electrode facing the bottom surface in the first space portion of the crystal resonator element 5 Let C3 be the stray capacitance between the electrode other than the electrode formed in the excitation vibration portion and the lid. If the combined capacity of C1, C2, and C3 is Cs,
C = εS / d (A)
From the above equation, the stray capacitances C1, C2 and C3 are calculated,
Cs = C1 (C2 + C3) / C1 + C2 + C3 (B)
The total stray capacitance Cs is calculated from the following equation.

  The thickness of the lid at this time is made constant, and the distance a between the surface of the excitation electrode 11 on the first space portion opening side of the crystal resonator element 5 and the surface of the first space portion side main surface of the lid 4 is 200 μm, Crystal oscillators are manufactured using 300 μm, 400 μm, 500 μm, and 600 μm with variable stray capacitance Cs, and the jitter characteristics of each sample are measured with an oscilloscope.

  The result is shown in FIG. When the distance a between the surface of the excitation electrode 11 on the opening side of the first space portion of the crystal resonator element 5 and the surface of the first space portion side main surface of the lid 4 is 200 μm (total stray capacitance Cs = 68 fF) When the distance a is 300 μm (total stray capacitance Cs = 45 fF), the jitter value in which the external electromagnetic noise can be considered as one of the factors of increasing the numerical value is confirmed. The jitter value is about 1300 ps. When the distance a is 400 μm (total stray capacitance Cs = 27 fF), the jitter value is about 900 ps, and when the distance a is 500 μm (total stray capacitance Cs = 20 fF), the jitter value is about 750 ps. It is. Further, when the distance a is 600 μm (total stray capacitance Cs = 15 fF), the jitter value is 600 ps.

  From the above results, the distance a between the surface of the excitation electrode 11 on the first space portion opening side of the crystal resonator element 5 and the surface of the first space portion side main surface of the lid 4 is 400 μm or more (total stray capacitance When Cs is about 30 fF or less), the jitter value in which external electromagnetic noise is considered as one of the factors of increasing the numerical value can fall below the allowable value of 1000 ps. Therefore, by widening the distance a between the excitation electrode 11 of the crystal resonator element 5 and the lid 4 and maximizing the EMC effect, the total stray capacitance can be reduced and the jitter value can be improved. Become.

  In addition, this invention is not limited to the above-mentioned embodiment, A various change, improvement, etc. are possible in the range which does not deviate from the summary of this invention. For example, in the above-described embodiment, the quartz resonator element using quartz as the piezoelectric material of the piezoelectric resonator element is shown as an example. However, when other piezoelectric materials such as lithium tantalate, lithium niobate, and piezoelectric ceramics are used. In addition, the present invention is applicable. In the above-described embodiment, the piezoelectric oscillator (crystal oscillator) is illustrated and described. However, the present invention can be applied to other piezoelectric devices such as a piezoelectric vibrator and a piezoelectric filter.

  Furthermore, in the above-described embodiment, the first space portion and the second space portion have been described as an example of a structure in which openings are formed in parallel on the same main surface of the container body. And a structure in which each opening portion of the second space portion is formed on a different main surface of the container body, or all components including a piezoelectric vibration element and an integrated circuit element are formed in the space portion. The present invention can also be implemented in a structure in which it is housed and mounted. In addition, the present invention can be appropriately implemented also in a piezoelectric device configured by joining two or more container bodies.

FIG. 1 is an exploded perspective view showing a crystal oscillator as an example of a piezoelectric device in the piezoelectric device according to the present invention. FIG. 2 is a cross-sectional view of the crystal oscillator shown in FIG. FIG. 3 is a graph showing the relationship between the jitter value and the distance between the excitation electrode surface and the lid surface of the crystal resonator element mounted in the crystal oscillator when the thickness of the lid is changed. FIG. 4 is a graph illustrating the relationship between the jitter value and the stray capacitance value between the excitation electrode and the lid of the crystal resonator element mounted in the crystal oscillator. FIG. 5 is a cross-sectional view of a conventional piezoelectric oscillator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Container body 2 ... Brazing material layer 3 ... Conductor layer 4 ... Lid body 5 ... Quartz crystal vibration element (piezoelectric vibration element)
DESCRIPTION OF SYMBOLS 6 ... Integrated circuit element 7 ... Electronic component element 8 ... 1st space part 9 ... 2nd space part 10 ... External connection electrode terminal

Claims (3)

At least a piezoelectric vibration element is mounted in a concave space formed inside the rectangular container, and an opening of the space is formed on the top surface of the side wall that surrounds the space of the container. A rectangular flat plate-shaped metal lid is arranged so as to cover, and the lid and a conductor layer provided on the top surface of the side wall are bonded and fixed, and the piezoelectric vibration element in the space is hermetically sealed. In the piezoelectric device that has stopped,
A piezoelectric device having a thickness of 150 μm or more and a thickness of 2 mm or less as a device. At least a piezoelectric vibration element is mounted in a concave space formed inside the rectangular container, and an opening of the space is formed on the top surface of the side wall that surrounds the space of the container. A rectangular flat plate-shaped metal lid is arranged so as to cover, and the lid and the conductor layer provided on the top surface of the side wall are bonded and fixed, and the piezoelectric vibration element in the space is hermetically sealed. Piezoelectric devices
The distance between the main surface of the lid on the space side and the excitation electrode formed on the main surface of the lid of the piezoelectric vibration element is 400 μm or more, and the thickness of the device is 2 mm or less. A piezoelectric device characterized by the above.   3. The piezoelectric device according to claim 1, wherein the container body has two or more spaces, and the piezoelectric vibration element is mounted in at least one of the spaces. .

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