JP2006108949A - Crystal-controlled oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystal-controlled oscillator for enlarging a capacitance ratio γ in a basic wave vibration and maintaining productivity. <P>SOLUTION: The crystal-controlled oscillator is formed of a crsytal piece including a thick center part as a vibrating region, an external circumferential part thinner than the center part, and a lead-out electrode extended to the external circumference by providing exciting electrodes provided opposed with each other to both main surfaces of the vibrating region. The opposing unit is provided by superimposing the lead-out electrode between both main surfaces of the external circumferential part, and the crystal piece is processed externally from a sheet of crystal wafer with the etching process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a crystal resonator in the technical field, and more particularly to a crystal resonator in which a capacitance ratio γ is increased to prevent a frequency change due to load fluctuation.

BACKGROUND OF THE INVENTION A crystal resonator is built in an electronic device as a frequency and time reference source. For example, in a wireless device (oscillator) employed in a wireless LAN relay base station, there is a demand for a crystal resonator that suppresses frequency fluctuations by increasing the capacity ratio γ.

(Example of Prior Art) FIG. 4 is a diagram of a crystal resonator (crystal piece) for explaining one conventional example.

  The crystal resonator is composed of a rectangular crystal piece 1 having an AT cut. A pair of opposing excitation electrodes 2 (ab) are formed on both main surfaces of the crystal piece 1, and for example, extraction electrodes 3 (ab) extend on both sides of one end. Then, both ends of the extended end portion of the extraction electrode 3 (ab) are held and sealed in a container (not shown).

  Such a thing has a resonance characteristic (reactance frequency characteristic) as shown in FIG. That is, it has resonance characteristics that obtain the series resonance point fs and the antiresonance point (parallel resonance point) fa as the frequency increases. In this case, between the series resonance point fs and the antiresonance point fa is inductive (ωL), and the others are capacitive (1 / ωC).

  These are generally shown by an equivalent circuit shown in FIG. 5 (b), and are composed of a serial arm and a parallel arm. The series arm includes an equivalent series resistance R1, a series capacitance C1, and a series inductor L1, and is caused by an inherent resonance phenomenon due to the piezoelectric action of the crystal piece 1. The parallel arm is composed of an equivalent parallel capacitance C0, and particularly depends on the capacitance between the electrodes due to the opposing area of the excitation electrode 2 (ab). The resonance frequency by the series arm becomes the series resonance point fs, and the resonance frequency by the series arm and the parallel arm becomes the antiresonance point fa.

  When configuring an oscillation circuit, generally, an inductive region (between fs-fa) of reactance frequency characteristics is used, that is, a crystal resonator is used as an inductor. Then, a resonance frequency with a capacitance component (load capacitance CL) of an oscillation circuit (not shown) connected to the crystal resonator is set as an oscillation frequency.

The oscillation frequency f0 is generally represented by a frequency deviation Δf / fs from the series resonance point fs as shown in the following equation (1). However, Δf = f0−fs and γ = C0 / C1, and γ is called a capacity ratio.
Δf / fs = 1 / 2γ (1 + CL / C0) (1)

  As is apparent from this equation, the frequency deviation Δf / fs is inversely proportional to the capacity ratio γ. That is, the frequency deviation Δf is smaller as the capacity ratio γ is larger, and is larger as the capacity ratio γ is smaller. Since the frequency variable width increases as the frequency deviation Δf increases, the capacitance ratio γ of the crystal resonator is normally designed to be small.

  The capacity ratio γ is inversely proportional to the equivalent series capacity C1, and is proportional to the parallel capacity C0. The equivalent series capacitance C1 (fF) and the parallel capacitance C0 (pF) increase depending on the facing area of the excitation electrode 2 (ab). However, the equivalent series capacitance C1 has a larger change amount and is saturated with respect to the facing area. Therefore, the facing area is usually set near the saturation point of the equivalent series capacitance C1. Then, the capacity ratio γ is reduced.

(Problems of the prior art) However, the quartz resonator having the above-described configuration has the following problems by increasing the equivalent series capacitance C1 and reducing the capacitance ratio γ. That is, since the reactance (1 / ωC1) is smaller as the equivalent series capacitance C1 is larger, the oscillation frequency f0 is easily affected by the load capacitance CL (oscillation circuit) connected in series. Therefore, there is a problem of so-called load fluctuation in which the oscillation frequency f0 changes depending on the load capacitance CL.

  In particular, an oscillator used in a repeater for a wireless LAN or the like is a non-adjustable type that does not have a variable frequency adjusting element such as a trimming capacitor after assembling to a set substrate, that is, does not have a load capacitance (oscillation frequency) adjusting element. . Accordingly, the load capacitance CL becomes non-uniform due to variations in circuit element values constituting the oscillation circuit, and load fluctuations are likely to occur.

  Even if a load capacitance CL adjustment element is provided, a load change occurs due to a change in the load capacitance CL caused by the stray capacitance of the set substrate on which the oscillation circuit is mounted. Note that the stray capacitance CL varies depending on environmental conditions such as humidity. From these facts, there has been a demand for a crystal resonator that has a large capacitance ratio γ and suppresses load fluctuations at the oscillation frequency f0.

  From this, it was considered to use overtone vibration. The overtone vibration is an odd-order harmonic of the fundamental wave vibration. For example, when obtaining a third-order overtone vibration with a vibration frequency of 40 MHz (thickness of about 41 μm) and an order n of 3, the vibration frequency of the fundamental wave is It becomes about 13.3MHz.

  When the overtone order is n, the capacity ratio γ ′ is n2γ with respect to the capacity ratio γ in the fundamental wave. By the way, in the case of AT cut, γ at the fundamental wave is about 250, which is 2000 or more when the third-order overtone vibration is used. From this, the capacity ratio γ ′ can be increased.

  However, in this case, the vibration frequency of the fundamental wave is 13.3 MHz, and the thickness of the crystal piece 1 is increased (about 125 μm). Further, as the thickness is increased, the planar outer shape is also increased, and end face processing such as bevel processing is required. Generally, when the vibration frequency is about 30 MHz or less, end face processing is required. Further, since the quartz piece 1 is thick, the amount of the artificial quartz is reduced, resulting in a lack of productivity.

(Object of the Invention) An object of the present invention is to provide a crystal resonator in which the capacity ratio γ in the fundamental wave vibration is increased and productivity is maintained.

  The present invention has a central portion having a large thickness as an oscillating region and an outer peripheral portion having a smaller thickness than the central portion, and both main surfaces of the oscillating region, as indicated in the claims (Claim 1). A quartz crystal unit comprising a quartz crystal piece provided with an excitation electrode facing the outer periphery and extending an extraction electrode on the outer peripheral portion, and a configuration in which the opposing portion is provided by superimposing the extraction electrode between both main surfaces of the outer peripheral portion; To do.

  With such a configuration, the interelectrode capacitance C0 can be increased by the opposing portion of the extraction electrode. On the other hand, since the opposing area of the excitation electrode is constant, the equivalent series capacitance C1 is not changed and is maintained constant. Therefore, the capacity ratio γ in the fundamental wave vibration can be increased without using overtone vibration. Further, since the thickness is small, end face processing such as a bevel is not required, and the amount taken from the artificial quartz is increased, so that productivity can be improved.

  According to a second aspect of the present invention, the excitation electrode according to the first aspect is provided on the entire surface of the central portion, and the opposing portion is the entire outer periphery of the excitation electrode. In the third aspect of the invention, the crystal piece according to the first aspect is processed by etching from a single crystal wafer.

  FIGS. 1A and 1B are diagrams of a crystal resonator for explaining an embodiment of the present invention. FIG. 1A is a plan view and FIG. In addition, the same number is attached | subjected to the same part as a prior art example, and the description is simplified or abbreviate | omitted.

  As described above, the crystal resonator is composed of the rectangular crystal piece 1 which is AT-cut. Here, the crystal piece 1 is externally processed by etching using a photoengraving technique, and is composed of a thick central portion and a thick outer peripheral portion surrounding the outer periphery thereof. The central portion having a large thickness is used as a vibration region, and excitation electrodes 2 (ab) are formed on both main surfaces.

  The extraction electrode 3 (ab) is provided on the outer peripheral portion having a small thickness, and has an annular facing portion 4 that is connected to the entire outer periphery of each excitation electrode 2 (ab) at both main surfaces and is opposed between both main surfaces. Then, it extends from the annular facing portion 4 to both sides of one end of the crystal piece 1. The excitation electrode 2 (ab) and the extraction electrode 3 (ab) are formed by etching using a photoengraving technique when processing the outer shape of the crystal piece 1. Then, both ends of the extended end portion of the extraction electrode 3 (ab) are held in the same manner as described above, and the crystal piece 1 is hermetically sealed in the container.

  With such a configuration, the interelectrode capacitance C01 between the two main surfaces that determines the equivalent parallel capacitance C0 depends on the annular facing portion 4 of the excitation electrode 2 (ab) and the extraction electrode 3 (ab). That is, the sum of the interelectrode capacitance C0a by the excitation electrode 2 (ab) and the interelectrode capacitance C0b by the annular facing portion 4 is obtained.

Incidentally, the vibration frequency is 40 MHz, that is, the thickness d1 of the vibration region is 41 μm, the thickness d2 of the annular facing portion 4 (outer peripheral portion) is 10 μm, and the area S1 of the excitation electrode 2 (ab) is 0.72 mm ² (one side is 0.85 mm, square ) If the area S2 of the annular facing portion 4 is 0.41 mm ² and the dielectric constant ε is 4.5, the interelectrode capacitance C01 is as follows.
C01 = C0a + C0b = εS1 / d1 + εS2 / d2 = 1 + 2.3 = 3.3pF

  Therefore, in this case, the interelectrode capacitance C01 (3.3 pF) is 3.3 times that in the case of only the excitation electrode 2 (ab) (C0a = 1 pF). On the other hand, the equivalent series capacitance C1 is 3.5 fF depending on the size of the excitation electrode 2 (ab). From this, the capacity ratio γ = C0 / C1 is about 1000. Note that stray capacitance is added to the interelectrode capacitance C01 to the equivalent parallel capacitance C0.

  As a result, the capacity ratio γ can be increased to, for example, 1000 or more, so that the frequency variable width can be reduced to prevent load fluctuation of the oscillation frequency. And since it is a fundamental wave vibration with a vibration frequency of 40 MHz, compared with the case where overtone vibration is used, the thickness is small and the planar outer shape is not enlarged. Therefore, end face processing such as a bevel is not required, and the productivity is increased by increasing the portion of the artificial quartz because the thickness is small.

  The energy is confined by the annular facing portion 4 of the extraction electrode 3 (ab), and sub-vibration occurs. However, since it occurs in a higher frequency than the vibration frequency of the vibration region, no particular problem occurs. Further, as the vibration frequency is higher, the thickness is reduced, the area of the excitation electrode 2 (ab) can be reduced, and the area of the annular facing portion 4 can be increased.

(Other matters) In the above embodiment, the excitation electrode 2 (ab) is provided on the entire surface of the vibration region having a large thickness. However, for example, it may be as shown in FIG. That is, the excitation electrode 2 (ab) may be formed in the center separated from the contour of the vibration region, and the annular facing portion 4 may be provided on the outer peripheral portion having a small thickness.

  Further, the opposing portion of the extraction electrode 3 (ab) has an annular shape surrounding the excitation electrode 2 (ab). However, the present invention is not limited to this, and there is an opposing portion 4 between both main surfaces. For example, as shown in FIG. Also good. That is, the opposing portion 4 of the extraction electrode 3 (ab) may be provided on the outer peripheral portion that is on both sides of the excitation electrode 2 (ab) in the length direction of the crystal piece 1. Further, the capacitance ratio can be controlled by trimming the extraction electrode 3 (ab) provided in the annular facing portion.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure of the crystal oscillator (crystal piece) explaining one Example of this invention, The figure (a) is a top view, The figure (b) is AA sectional drawing. 4A and 4B are diagrams of a crystal resonator illustrating another embodiment of the present invention, in which FIG. 4A is a plan view and FIG. It is a top view of the crystal oscillator explaining the further another Example of this invention. It is a top view of the crystal oscillator explaining a prior art example. It is a figure explaining a prior art example, the figure (a) is a resonance characteristic figure of a crystal oscillator, and the figure (b) is an equivalent circuit diagram.

Explanation of symbols

  1 crystal piece, 2 excitation electrode, 3 extraction electrode, 4 facing part.

Claims (3)

  The vibration region has a central portion with a large thickness and an outer peripheral portion with a smaller thickness than the central portion, and excitation electrodes are provided opposite to both main surfaces of the vibration region to extend the extraction electrode to the outer peripheral portion. A quartz resonator comprising a quartz piece, wherein the lead electrode is overlapped between both main surfaces of the outer peripheral portion to provide a facing portion.   2. The crystal resonator according to claim 1, wherein the excitation electrode is provided on the entire surface of the central portion, and the opposing portion is the entire outer periphery of the excitation electrode.   The crystal piece is a crystal resonator that is externally processed by etching from a single crystal wafer.

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