JP2008294852A - Piezoelectric vibrator, and oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric vibrator having a rectangle thickness-shear mode vibration chip which is a rotation Y plate of a crystal system 32 and capable of suppressing spurious caused by face shear mode vibration. <P>SOLUTION: An electrode is formed on the surface of a vibration chip symmetrically to a center line in the Z' axis direction and formed in the shape for canceling induction charge based on n-th vibration of odd-order that is third order or higher of the face shear mode vibration generated in the vibration chip. The electrode may be constituted by providing a rectangle area whose length along the Z' axis direction is 2m (m is an integer) of length of the vibration chip in the Z' axis direction/n [provided, 2m/n<1], however, it is desirable that the outer edge shape in the X direction is the cos shape since electrode distribution in the Z' axis is represented by cos. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode shape for suppressing spurious due to contour slip vibration in a piezoelectric vibrator having a rectangular thickness slip vibration piece made of a crystal system 32 rotating Y plate, for example, a crystal piece such as an AT cut.

As materials belonging to the crystal system 32 (belonging to the point group 32) in the piezoelectric vibrating piece, quartz, GaPO ₄ (gallium phosphate), langasite (LGS, LGN, LGT), quartz, and the like are known. The rotating Y plate of this type of piezoelectric vibrating piece, for example, the rotating Y plate of quartz, is vibrated by both thickness shearing vibration and contour sliding vibration. Piezoelectric vibrating pieces using thickness-shear vibration are AT-cut and BT-cutting, and piezoelectric vibrating pieces using contour-slip vibration are CT-cut and DT-cutting, and both have temperature characteristics. Is excellent. The thickness-shear vibration and the contour-slip vibration are coupled to each other to disturb the temperature characteristics and the like, but the coupling of both vibrations can be eliminated by inclining the end face of the vibration piece at a predetermined angle.

  However, since the sliding vibration is still excited piezoelectrically, when an electrode is formed on the vibrating piece, the electric charge induced by the vibration is supplemented to pick up noise corresponding to the vibration. For example, if the main vibration is 10 MHz, the sub-vibration is as small as about 500 kHz. However, since the contour slip vibration includes n-order mode vibration, the electrode picks up the charge distribution induced by the vibration, and eventually slip vibration Will generate spurious near the main vibration, causing a frequency jump. At present, in order to avoid the influence of contour sliding vibration, there is a large limitation on the shape and size of the crystal piece, and there is a problem that the degree of freedom in design is small.

  The present invention has been made under such circumstances, and it is an object of the present invention to provide a piezoelectric vibrator that can suppress spurious due to contour slip vibration with respect to a piezoelectric vibrator having a rectangular thickness-slip vibration piece. To do. Another object of the present invention is to provide an oscillation circuit including such a piezoelectric vibrator.

  The present invention provides a rectangular thickness-shear vibrating piece comprising a rotating Y plate of a crystal system 32 in which the Z′-axis and the X-axis are one side and the other side and the Y′-axis is the thickness direction, and the one side on the surface of the vibrating piece. And a piezoelectric vibrator having an electrode formed symmetrically with respect to the center line, and has the following characteristics. The electrode has a length along the one side of 2 m of one side of the vibrating piece in order to cancel an induced charge based on an n-th order vibration that is an odd order of the third or higher order of the contour sliding vibration generated in the vibrating piece. (M is a natural number) / n [where 2 m / n <1]. In this case, for example, the nth-order vibration is a fifth-order vibration or more, and the electrode has a length along the one side that satisfies 2 m / n of one side of the vibrating piece and has a length along the one side. A plurality of different rectangular regions may be provided, and the lengths of the rectangular regions along the other side may be set so as to cancel induced charges based on odd-order vibrations other than the fifth order.

  In addition, the electrode is arranged on the one side so as to cancel all or most of the induced charge based on the vibration of a specific odd order selected from the odd order of the fifth or higher order of the contour slip vibration generated in the resonator element. A rectangular area having a first value along the length and a rectangular area having a second value that is greater than the first value along the one side, and the other of the rectangular areas. The length along the side may be set so as to cancel all or most of the induced charges based on the vibration of the odd order other than the specific odd order.

The electrode may be formed in a shape in which the dimension in the Z′-axis direction gradually decreases from the central part in the X-axis direction toward both end parts in the X-axis direction, or one end in the X-axis direction. It is good also as a structure formed in the shape where the dimension of a Z'-axis direction becomes small gradually toward the other end part of a X-axis direction from a part. In this case, the outer edge shape of the electrode along the Z′-axis direction is preferably a cos shape.
In addition, an oscillation circuit according to the present invention includes the piezoelectric vibrator described above.

  According to the present invention, the shape of the electrode is set so that the positive charge and the negative charge induced in the resonator element are canceled based on the vibration of the nth-order mode of the contour slip vibration. The spurious based can be suppressed.

[First embodiment]
FIG. 1 is a diagram showing a crystal piece 1 of a rotating Y plate, which is a thickness-shear vibrating piece used in an embodiment of the present invention. This crystal piece 1, for example, an AT-cut crystal piece, has a long side on the X axis. (Corresponding to the other side of the claims), the Y′-axis is in the thickness direction, and the Z′-axis is a short side (corresponding to one side of the claims). The X axis is the X axis of the crystal axis of the crystal, and the Y ′ axis and the Z ′ axis correspond to the cutting direction of the plate when cutting the crystal piece. For example, in the case of an AT-cut crystal piece, the Y ′ axis and the Z ′ axis correspond to axes that are inclined 35 degrees from the Y axis and the Z axis of the crystal axis, respectively.

  In the description of this embodiment, the length in the long side direction is called depth, and the length in the short side direction is called horizontal width. In the crystal piece 1, the induced charge is substantially uniform on both the upper and lower surfaces with respect to the thickness-shear vibration, but the induced charge with respect to the contour-slip vibration has a sine wave distribution symmetrically with a peak at the center of the width. Has spread as. FIG. 2 is a diagram showing this state, and FIG. 2A shows the distribution of induced charges corresponding to the 1st harmonic wave of the contour slip vibration. FIGS. 2B and 2C show the distributions of induced charges corresponding to the third and fifth harmonics of the contour slip vibration, respectively.

3 (a) to 3 (c) are two-dimensionally describing the charge distributions of FIGS. 2 (a) to 2 (c) and indicate the charge codes in association with the position of the lateral width of the crystal piece 1. FIG. is there. If the charge amount induced by the nth harmonic wave of the contour sliding vibration (hereinafter referred to as n-order charge amount) and the charge amount in the lateral width direction of the crystal piece 1 is f (z), f (z) Is represented by equation (1).
f (z) = cos {n · (π / 2) · z} (1)
However, the width dimension is normalized by setting the coordinate position of the middle point of the crystal piece 1 to 0 and the coordinate positions of the left end and the right end to -1 and 1, respectively. Therefore, z is the z coordinate position in the lateral width direction, that is, the z-axis direction. Note that z is a coordinate position in the xyz coordinate system when the axes extending in the depth direction, the thickness direction, and the lateral width direction of the crystal piece 1 are the x axis, the y axis, and the z axis, respectively.

Here, assuming that the coordinate positions of both ends of the crystal piece 1 in the Z′-axis direction, that is, the z direction are −c and c, when z / c is z _n , the charge when the z coordinate position corresponds to z _n The quantity f (z _n ) will be expressed as f (z _n ) = cos {n · (π / 2) · z _n }. In the present invention, the ratio of the crystal piece 1 to the dimension becomes a problem when defining the dimensions of the electrodes. Therefore, even if the left and right coordinate positions of the short side of the crystal piece 1 are treated as -1 and 1, respectively, it can be obtained. The results will not be affected at all, so we will deal with them in this way. In this case, the coordinate positions of the left end and the right end of the electrode are represented by −z _n and z _n , respectively.

  When the electrodes are formed on both surfaces of the crystal piece 1, the charges induced by the electrodes are captured and ride on the output waveform. Therefore, in the present invention, the positive charges and the negative charges captured by the electrodes are canceled out. The shape of the electrode is determined. Since the amount of charge at the z position in the crystal piece 1 is expressed by the formula (1), the amount of charge captured by the electrode is expressed by the formula (2).

Therefore, the value of z _n at which the amount of charge captured by the electrode becomes zero is 2 m / n because the right side of the equation (2) is zero. However, m is a natural number, and 2 m / n is a value of 1 or less. The reason that 2 m / n is larger than 1 is that the lateral width of the electrode is larger than the lateral width of the crystal piece 1. Since the charge amount cannot be erased when n is 1, by setting z _n to 2 m / n when n is an odd number of 3 or more, the charge amount captured by the electrode becomes zero.

FIG. 4 shows a configuration of the electrode 2 in which the amount of charge is zero when n is 3, that is, the third order. In this case, m is 2 and z _n is 2/3. 5A and 5B show the configuration of the electrode 2 in which the amount of charge is zero when n is 5, that is, the fifth order. In this case, m is 2 or 4, and z _n is 2/5 or 4/5. Although not shown in the figure, the same applies to the charge amount of the seventh or higher order.
According to such an embodiment, even if contour sliding vibration occurs in the crystal piece 1, harmonics of the n-th harmonic corresponding to the dimension of the electrode 2 can be eliminated or suppressed, and based on this harmonic. Spurious can be suppressed.

[Second Embodiment]
In this embodiment, an induced charge based on vibrations of two orders different from each other is to be erased. FIG. 6 shows an example of erasing induced charges based on the vibrations of the third and fifth orders. Yes. In order to eliminate the induced charge based on the fifth-order vibration, there are two values of z _n that are the coordinate position of the electrode 2 in the Z′-axis direction, as described above, 2/5 and 4/5. However, the electrodes 2 having these two dimensions are formed here. A rectangular area whose value of z _n is 2/5 is S1, and a rectangular area whose value of z _n is 4/5 is S2. In this case, the rectangular area S1 exists on both sides of the rectangular area S2 in the X-axis direction, and the horizontal widths of the rectangular areas S1 and S2 correspond to the first value and the second value, respectively, in the claims.

Only one of these rectangular regions S1 and S2 cannot erase induced charges based on vibrations other than the fifth order, but by forming both rectangular regions S1 and S2 and adjusting their X-axis lengths, That is, by adjusting the ratio of the depth a which is the length of the rectangular region S1 in the X-axis direction and the depth b which is the length of the rectangular region S2 in the X-axis direction, an induced charge based on vibrations of orders other than the fifth order. Can be erased.
First, if two types of rectangular regions of electrodes are formed in order to erase the (n + 2) next induced charge, the values of z _n of these rectangular regions are 2m / (n + 2) and 2 (m + 1) / ( n + 2), and if n is 3, then 2/5 and 4/5 as described above.

In FIG. 6, numerical values in the fifth order are described, but in these rectangular regions S1 and S2, the values of z _n are 2m / (n + 2) and 2 (m + 1) / (n + 2) as general values, respectively. Then, the charge amounts in the rectangular regions S1 and S2 are expressed by the equations (3) and (4), respectively, and the sum of these charge amounts is expressed by the equation (5).

  However, 2m / (n + 2) is replaced with A, and 2 (m + 1) / (n + 2) is replaced with B. In order to erase the n-th order induced charge, since the total amount of charges in the rectangular regions S1 and S2 becomes zero, the ratio of a and b in which the right side of the equation (5) becomes zero is obtained. The shape of the electrode 2 may be set so that the ratio is obtained. When erasing the induced charges based on the vibrations of the third and fifth orders, since n = 3 and only when m = 1, a: b = 0.588: 1.90. .

Further, by using the equation (5), the induced charges based on the fifth and seventh order vibrations can be erased, and the induced charges based on the seventh and ninth order vibrations can be erased.
According to such an embodiment, even when contour sliding vibration occurs in the crystal blank 1, harmonics of the nth harmonic and the (n + 2) harmonic corresponding to the dimension of the electrode 2 can be eliminated or suppressed. .

[Third embodiment]
As described in the first embodiment, the charge amount f _{(z n)} when the z coordinate position corresponds to _{z n is, f (z n) = cos} {n · (π / 2) · z _n }, because of the orthogonality of the trigonometric function, when f (z _n ) is multiplied by cos {(π / 2) · z _n } except for n = 1, it becomes zero. It holds.

  This is because, as shown in FIG. 7A, all the orders are obtained by forming the electrode 2 so as to form cos-shaped outer edges on both sides of the central axis L passing through the midpoint of the long side of the electrode 2. This means that the charge can be erased. The cos shape has a peak value at the zero position when the midpoint on the short side is set to zero, and is zero at the positions normalized by -1 and 1 as both end coordinate positions of the short side. It is formed.

  Further, the outer edge shape of the electrode 2 in the z-axis direction is the lower half or the upper half of the cos shape as shown in FIG. 7B, that is, the shape shown in FIG. The same effect can be obtained even when the shape is divided in half vertically and vertically. Furthermore, even if the outer edge shape of the electrode 2 in the z-axis direction is not a cos shape, it swells at the middle point in the z-axis direction, and the depth dimension (dimension in the x-axis direction) toward the end side in the z-axis direction. Even if the shape is small, such as a leaf shape, it can be adopted as long as most of the charges of each order can be erased.

In the present invention, if the spurious reduction effect based on the contour slip vibration can be obtained, the contour slip is not necessary even if the electrode dimensions are the same as the calculated values as in the first and second embodiments. Any value can be used as long as the induced charge based on vibration can be almost eliminated.
Furthermore, the present invention extends to the scope of rights of an oscillation circuit using the above-described piezoelectric vibrator, for example, a crystal vibrator. As the oscillation circuit, for example, the crystal vibrator is sealed in a package and the crystal vibrator component is used. And those configured by mounting this component on a substrate.

It is a perspective view which shows the general view of the thickness shear vibration piece used by embodiment of this invention. It is explanatory drawing which shows the fundamental wave based on the outline slip vibration which generate | occur | produces in a thickness sliding vibration piece in three dimensions corresponding to a vibration piece. It is explanatory drawing which shows the fundamental wave based on the said contour slip vibration, a 3rd harmonic, and a 5th harmonic. It is explanatory drawing which matches and shows the 3rd harmonic based on the said contour sliding vibration, and the electrode shape for erasing the electric charge by this harmonic. It is explanatory drawing which shows the 5th harmonic based on the said contour sliding vibration, and the two types of electrode shapes for erasing the electric charge by this harmonic corresponding to each other. It is explanatory drawing which shows the electrode shape for erasing the electric charge by the 3rd harmonic based on the said contour sliding vibration, and a 5th harmonic. It is a top view which shows the electrode shape for erasing the electric charge by all the harmonics based on the said contour sliding vibration.

Explanation of symbols

1 Crystal piece 2 Electrode

Claims (7)

A rectangular thickness sliding vibration piece made of a rotating Y plate of a crystal system 32 with one side and the other side being the Z ′ axis and the X axis, and the Y ′ axis being the thickness direction, and the center line of the one side on the surface of the vibration piece An electrode formed symmetrically with respect to,
The electrode has a length along the one side of 2 m of one side of the vibrating piece in order to cancel an induced charge based on an n-th order vibration that is an odd order of the third or higher order of the contour sliding vibration generated in the vibrating piece. (M is a natural number) / n [where 2 m / n <1] is provided with a rectangular region. The nth-order vibration is a fifth-order vibration or more,
The electrode includes a plurality of rectangular regions whose length along the one side satisfies 2 m / n of one side of the vibrating piece and whose lengths along the one side are different from each other,
2. The piezoelectric vibrator according to claim 1, wherein lengths of the rectangular regions along the other side are set so as to cancel induced charges based on vibrations of odd orders other than the fifth order. A rectangular thickness sliding vibration piece made of a rotating Y plate of a crystal system 32 with one side and the other side being the Z ′ axis and the X axis, and the Y ′ axis being the thickness direction, and the center line of the one side on the surface of the vibration piece An electrode formed symmetrically with respect to,
The electrode is arranged along the one side so as to cancel all or most of the induced charge based on the vibration of a specific odd order selected from the odd order of the fifth or higher order of the slip profile vibration generated in the resonator element. A rectangular area having a first value and a rectangular area having a second value whose length along the one side is greater than the first value;
A length of the rectangular region along the other side is set so as to cancel all or most of the induced charge based on the vibration of the odd order other than the specific odd order. . A rectangular thickness sliding vibration piece made of a rotating Y plate of a crystal system 32 with one side and the other side being the Z ′ axis and the X axis, and the Y ′ axis being the thickness direction, and the center line of the one side on the surface of the vibration piece An electrode formed symmetrically with respect to,
The piezoelectric vibrator is characterized in that the electrode is formed in a shape in which the dimension in the Z′-axis direction gradually decreases from the central part in the X-axis direction toward both end parts in the X-axis direction. A rectangular thickness sliding vibration piece made of a rotating Y plate of a crystal system 32 with one side and the other side being the Z ′ axis and the X axis, and the Y ′ axis being the thickness direction, and the center line of the one side on the surface of the vibration piece An electrode formed symmetrically with respect to,
The piezoelectric vibrator is characterized in that the electrode is formed in a shape in which the dimension in the Z′-axis direction gradually decreases from one end part in the X-axis direction toward the other end part in the X-axis direction.   6. The piezoelectric vibrator according to claim 4, wherein an outer edge shape of the electrode along the Z′-axis direction is a cos shape.   An oscillation circuit comprising the piezoelectric vibrator according to any one of claims 1 to 6.

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