JPH027705A - Piezoelectric vibrator element and its frequency adjusting method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding a piezoelectric vibrating element using a single crystal of lithium niobate, a new configuration that miniaturizes the piezoelectric body and facilitates mounting, and a new method for adjusting the resonant frequency suitable for the configuration. For the purpose of providing a piezoelectric vibrating element using a lithium niobate single crystal as a piezoelectric body, the electrode formation surface of the piezoelectric body, which has a rod shape with a square cross section, is cut out from a Y plate rotated by 60 degrees to 95 degrees from the single crystal. and a pair of opposing electrodes are formed on the same electrode formation surface, and when the surface on which the pair of opposing electrodes are formed is the surface of the piezoelectric body, the resonance frequency is adjusted by the piezoelectric body. It is characterized by the fact that the back surface is carved by mechanical means.

[Industrial application field]

The present invention relates to a piezoelectric vibrating element using a single crystal of lithium niobate, and in particular to structural improvements that make the piezoelectric material smaller and easier to implement, and a method for adjusting the resonant frequency suitable for a piezoelectric vibrating element with a new structure. .

[Conventional technology]

On May 30, 1980, the applicant formed suitable electrodes on the opposing main surfaces of a piezoelectric material cut out from a rotating Y temporary of a lithium niobate single crystal, and utilized the thickness shear vibration of the piezoelectric material. A piezoelectric vibrating element (Japanese Patent Application No. 58-95265) was proposed.

The piezoelectric vibrating element of the above-mentioned Japanese Patent Application No. 58-95265 has a piezoelectric body made of a lithium niobate single crystal whose opposing main surfaces are cut out from a Y-plate rotated by 165 degrees in the single crystal, and
Furthermore, the longitudinal direction of the piezoelectric body is oriented at 90 degrees with respect to the X axis of the rotating Y plate, and IMIlz~30
It has become widely used for the MHz band.

FIG. 6 is a perspective view showing a conventional piezoelectric vibrating element, in which the piezoelectric vibrating element 1 is formed by forming opposing electrodes 3 on opposing main surfaces (upper and lower surfaces) of a piezoelectric body 2.

The piezoelectric body 2 has a width of H1, a length of L2, and a thickness of T when viewed from the opposite main surface. A lead portion 3a extends from one end of the electrode 3, and the lead portion 3a is connected to an external connection terminal 4 formed at the end of the opposing main surface. The thickness shear vibration of the piezoelectric body 2 generated by applying an appropriate electric field to the electrode 3 is displaced in the length direction, as shown by the broken line 5 in the figure, and the amount of displacement increases near the opposing principal surface. .

FIG. 7 is a side view of the piezoelectric vibrating element mounted on its mounting substrate. At least a pair of conductor layers 7 are formed on the upper surface of the insulating substrate 6, and the mounted piezoelectric vibrating element 1 is connected via a spacer 8. Terminal 4 is electrically connected to opposing conductor layer 7 by solder or conductive adhesive 9 . Such automatic adjustment of the resonant frequency of the piezoelectric vibrating element 1 is carried out by increasing or decreasing the mass of the electrode 3 using a laser trimming device, a vapor deposition device, or the like.

In such a vibrator, the size of the strip-type piezoelectric body, which is a bar with a rectangular cross section, becomes larger as the frequency becomes lower. That is, for example, if the dimensions of the piezoelectric body for the 6Ml1z band are 0.
3mm Xo, about 5mm x 5mm, whereas for 2MHz band, the piezoelectric body size is 0.9mm Xo,
The size is approximately 9 mm x 7 mm, and the piezoelectric material for 2 MHz is approximately 7.6 times larger in volume ratio than the piezoelectric material for 6 MHz.

[Problem to be solved by the invention]

As explained above, the conventional piezoelectric vibrating element in which a piezoelectric material is cut out from a single crystal of lithium niobate has a problem in that the piezoelectric material is large for use in a low frequency band.

In addition, since drive electrodes are formed on both opposing main surfaces of the piezoelectric body, it is possible to mount them on a substrate etc. in the thickness direction of the piezoelectric body.
At the time, there was a structural disadvantage in that the electrode formed on the upper main surface had to be connected to the conductor layer of the mounting board through the side end surface of the piezoelectric body.

An object of the present invention is to reduce the size of a piezoelectric body for low frequency bands, to facilitate its mounting, and to provide a new frequency adjustment method that is easier than the conventional method.

[Means to solve the problem]

According to FIG. 1, the piezoelectric vibrating element of the present invention is a piezoelectric vibrating element 11.
21, the electrode forming surface of the piezoelectric body 12, which is rod-shaped with a rectangular cross section, is the cut surface of the single crystal Y plate rotated by 60 degrees to 95 degrees, and a pair of opposing electrodes 13 or 22 are formed on the same electrode forming surface. Further, when the length of the piezoelectric body 12 is l, the direction of the length l is set at 90 degrees ± 5 degrees with respect to the X axis of the rotating Y plate, The width of the piezoelectric body 12 seen from the electrode forming surface is calculated, and the thickness is t.
Then, the thickness t is less than or equal to the width A, the relationship between the length 2 of the piezoelectric body 12 and the width is 17h>8, and the external connection terminal 23 connected to the counter electrode 22. is formed at the end of the piezoelectric body 12 in the length l direction and at the center in the width direction, and when adjusting the frequency, the surface on which the pair of opposing electrodes 13 or 22 are formed is formed on the piezoelectric body 12, the back surface of the piezoelectric body 12 is cut by mechanical means.

[Effect]

According to the above means, 60% of lithium niobate single crystal
By cutting out a piezoelectric body from a Y plate rotated by 95 degrees and forming a pair of opposing electrodes on the same surface of the piezoelectric body, the piezoelectric body is thinner and smaller than conventional ones, and it is easy to mount. At the same time, the frequency adjustment is achieved by cutting the back surface of the exposed piezoelectric body using machining means, thereby making it possible to significantly reduce the equipment cost required for this purpose.

〔Example〕

Below, a piezoelectric vibrating element according to the present invention will be explained using the drawings.

FIG. 1 is a perspective view of a piezoelectric vibrating element according to an embodiment of the present invention.

In FIG. 1(a), the piezoelectric vibrating element 11 is a piezoelectric body 12
A pair of opposing electrodes 13 are formed on the upper surface (or lower surface) of. When viewed from the surface on which the counter electrode 13 is formed, the width and length are 1. In the piezoelectric body 12 having a thickness of t, the cut surface of a 60-95 degree rotated Y plate (wafer) of lithium niobate single crystal is the surface on which the counter electrode 13 is formed, and the piezoelectric body is formed from one end of each electrode 13. The lead portion 13a extending linearly along the edge of the piezoelectric body 12 is connected to an external connection terminal 14 formed at the longitudinal end of the piezoelectric body 12 and on the same surface as the electrode 13.

The width shear vibration of the piezoelectric body 12 generated by applying an appropriate electric field to the electrode 13, that is, the width shear vibration corresponding to the thickness shear vibration of the conventional piezoelectric vibrating element 1, is as shown by the broken line 15 and the arrow in the figure. It is displaced in the length l direction, and the amount of displacement becomes larger closer to the longitudinal side surface (the main surface facing the vibration).

This piezoelectric body 12 corresponds to a conventional piezoelectric body 2 cut in the direction of arrow A to have a thickness t, as shown by the dashed line in FIG. Corresponds to the front of 2. The dimensional relationship between the conventional piezoelectric body 2 and the piezoelectric body 12 according to the present invention having the same resonance frequency is A#
L, h#T, and the thickness t of the piezoelectric body 12 is equal to or less than 2 of the width H of the piezoelectric body 2.

That is, in the conventional piezoelectric vibration element 1 for 2MHz, the piezoelectric body 2 has a width H = 0.9 mm, a thickness T = 0.9 mm, and a length L = 7 mm, whereas the piezoelectric vibration element 1 for 2MHz according to the present invention has a width H = 0.9 mm, a thickness T = 0.9 mm, and a length L = 7 mm. The piezoelectric body 12 of the element 11 has a length of 1-7 mm, a width h = 0.9 mm and a thickness t = 0 in the exemplary embodiment.
3 mm, the length f' of the electrode 13 = 4 nun, and the opposing gap g of the electrode 13 = 0.5 mm, the resonance resistance was 80 Ω.

In FIG. 1(0), the piezoelectric vibrating element 21 is
A pair of opposing electrodes 22 and the like are formed on the upper surface (or lower surface) of. A piezoelectric vibrating element 21 that uses the same piezoelectric body 12 as the piezoelectric vibrating element 11 described above and has a counter electrode 22 and the like formed on the same surface as the counter electrode 13 has an external connection terminal 23 that is the same as the electrode 22 of the piezoelectric body 12. It is formed at the end in the length direction and the center in the width direction of the surface, and is led out from the end of the counter electrode 22 and has a diameter of approximately 7.
A letter-shaped lead portion 22a is connected to an external connection terminal 23.

In such a piezoelectric vibrating element 21, the width shear vibration and admittance characteristics that occur when an appropriate electric field is applied to the electrodes 22 are equivalent to those of the piezoelectric vibrating element 11, but as will be described later, the piezoelectric vibrating element 21 is attached to its mounting substrate. By providing the external connection terminal 23 at the center of the piezoelectric body 12 in the width direction, stability can be obtained in the admittance characteristic related to the connection with the substrate.

In the piezoelectric vibrating element of Japanese Patent Application No. 58-95265, in which driving electrodes are formed on the opposing main surfaces of a piezoelectric body made of a lithium niobate single crystal, the opposing main surfaces are the 16565 degree rotated Y plate protruding surfaces of the single crystal, It was proposed that the longitudinal direction of the piezoelectric body be oriented at 90 degrees with respect to the X axis of the rotating Y plate;
The piezoelectric vibrator of the present invention uses thickness shear vibration as width shear vibration, and is made of lithium niobate single crystal at 75 degrees (16 degrees).
5 degrees - 90 degrees) A drive electrode is formed on the cut-out surface of the rotated Y plate, and the length direction of the piezoelectric body is 75 degrees with respect to the X axis of the rotated Y plate.
It is easily assumed that the vibration characteristics will be excellent by setting the direction to 0 degrees.

Figure 2 is a diagram showing the measurement of the rotation angle dependence of the rotary Y plate for cutting out the piezoelectric material of the present invention, and the resonance resistance is 300Ω.
The rotation angle of the rotating Y plate that falls within the practical range is 60 degrees to 95 degrees.
degree. Therefore, the wafer of lithium niobate single crystal from which the piezoelectric body 12 according to the present invention is cut is heated at an angle of 60° to
A 95 degree rotated Y plate is suitable, and in particular, the piezoelectric body 12 using a 70 degree to 85 degree rotated Y plate has an excellent resonance resistance of 100Ω or less.

FIG. 3 shows the admittance characteristics of a piezoelectric vibrator in which the length direction of a piezoelectric body cut from a 75-degree rotated Y plate of lithium niobate single crystal is 90 degrees with respect to the X-axis of the single crystal.

In FIG. 3, the vertical axis represents resonance level (dB) and the horizontal axis represents frequency (MHz), as shown in the figure, a high frequency AC power source 51.
In the admittance characteristic obtained by connecting the piezoelectric vibrator 11 or 21 to the measurement circuit consisting of the resistor Rin, the resistor Rout, and the detector 52, one strong resonance peak was found around 2.19 MtIz. It has high characteristics with no spurious waves caused by unnecessary waves.

Similarly, the piezoelectric vibrators 11 and 21 are made by swinging the length direction of the piezoelectric body cut from a 75 degree rotated Y plate of lithium niobate single crystal within a range of 90 degrees ± 5 degrees with respect to the X axis of the single crystal. When we measured the admittance characteristics, no harmful spurious signals appeared near the resonance peak.

Note that in the piezoelectric vibrators 11 and 21 shown in FIG. 1, the direction of the electric field within the piezoelectric body 12 is from one electrode 13 or 22 to the other electrode 13 or 22.

In order to suppress the spurious caused by such an electric field,
It is sufficient to reduce the thickness t of the piezoelectric body 12 so that the direction of the propagating electric field to be used is uniform.
In the present invention, by setting the thickness t<H-h, unnecessary spurious waves due to propagating electric fields within the piezoelectric body can be suppressed successfully.

In the piezoelectric vibrators 11 and 21, the ratio of the length l and the width of the piezoelectric body 12 is related to its equal series resistance, and the spurious that is harmful to the piezoelectric vibrators 11 and 21 increases as the equal series resistance increases. It is known to do.

FIG. 4 is a diagram showing the relationship between E/h and equal series resistance. Equal series resistance increases rapidly when 1/h becomes 8 or less, and spurious noise also occurs and increases in that range.
In the present invention, piezoelectric vibrators 11 and 21 with excellent admittance characteristics were obtained by setting l/h to 8 or more.

FIG. 5 is a side view for explaining a mounting example of a piezoelectric vibrator and its frequency adjustment method according to the present invention. A conductor layer 7 corresponding to 23) is formed, and a spacer 8 is mounted on the conductor layer 7. Then, the piezoelectric vibrator 11 is connected to the terminal 14 with the electrode 13 facing downward.
and spacer 8 are connected by solder, conductive adhesive 9, or the like.

In such a piezoelectric vibrator 11 (or 21), when the surface on which the electrodes 13 (or 22) are formed is the surface of the piezoelectric body 12, the back surface of the piezoelectric body 12 that is exposed after mounting is ground by a machining method such as sandblasting to reduce the thickness. Thinner t by Δt, e.g. 1=6h~toh, t=5/8・h~27
The resonant frequency of the vibrator 11 using the piezoelectric material 12 of 8.h can be adjusted higher by about 1.5% by reducing the thickness L by 1/100 of the length l. Become.

In addition, conventional frequency adjustment that increases or decreases the mass of the electrode involves
Methods using etching or plating, laser trimming methods, and vapor deposition methods are used, but the equipment costs for dry type laser trimming equipment or vapor deposition equipment that can be automatically adjusted are usually tens of millions of yen. . However,
Frequency automatic adjustment equipment using sandblasting equipment is
The cost is about several million yen, making it possible to set up equipment at a lower cost than those using laser trimming and vapor deposition.

〔Effect of the invention〕

As explained above, according to the present invention, a piezoelectric material is cut out from a 60-95 degree rotated Y plate of lithium niobate single crystal, and a pair of opposing electrodes are formed on the same surface of the piezoelectric material. is thinner and more compact than conventional ones, making it easier to mount, and also imposes regulations on the relative relationship between the thickness and width and length and width of the piezoelectric body to improve vibration characteristics, and has the same performance as conventional ones. By providing a piezoelectric vibrating element that is small in size and small in size, and by cutting the back surface of the piezoelectric body that is exposed using machining means, the frequency adjustment has the effect of significantly reducing the equipment cost required for frequency adjustment. be.

[Brief explanation of the drawing]

Fig. 1 is a piezoelectric vibrating element according to an embodiment of the present invention, Fig. 2 is a diagram showing rotation angle dependence in a rotating Y plate of the present invention, Fig. 3 is an admittance characteristic diagram in an embodiment of the present invention, Fig. 4 is a diagram showing the relationship between l/h and equal series resistance, FIG. 5 is an explanatory diagram of an example of mounting a piezoelectric vibrator according to the present invention and its frequency adjustment method, FIG. 6 is a conventional piezoelectric vibrator, and FIG. The figure shows an example of mounting a conventional piezoelectric vibrating element. In the figure, 11.21 is a piezoelectric vibration element, 12 is a piezoelectric body, 13.22 is an electrode, 14.23 is an external connection terminal, h is the width of the piezoelectric body, l is the length of the piezoelectric body, and t is the piezoelectric body. Indicates the body thickness. Figure 1 (A) Go 70 80 '10 (degrees) rotation angle Honnaaki's rotation Wasaka 1-J: Romandensaka moving rope Chi Figure 1 (A) Go 70 80 '10 (degrees) rotation angle Figure 2 (, fl) Diagram showing the relationship between f2/E and the 11 resistance of the 11 resistors.
Figure Cd B) 2.15 2J8 2,2j 2,2422
7 2.3 laps (more (M)
2) This complete date of the month is 1is, 31 Admi.../
Figure 3 (Conventional piezoelectric plate cable) Figure 6

Claims (1)

[Scope of Claims] (1) A piezoelectric vibrating element using a lithium niobate single crystal as a piezoelectric body (12), and the electrode forming surface of the piezoelectric body (12) having a rod shape with a square cross section The cutout surface of a Y plate rotated by 95 degrees and a pair of opposing electrodes (13, 2
2) is formed on the same electrode forming surface. (2) When the length of the piezoelectric body (12) is l, the direction of the length l is a direction of 90 degrees ± 5 degrees with respect to the X axis of the rotating Y plate. The piezoelectric vibrating element described in 1. (3) The piezoelectric body (
12) The piezoelectric vibrating element according to claim 1 or 2, wherein the thickness t is 1/2 or less of the width h, where h is the width and t is the thickness of the piezoelectric vibrating element. (4) The relationship between the length l and the width h of the piezoelectric body (12) is
The piezoelectric vibrating element according to any one of claims 1 to 3, characterized in that l/h>8. (5) The external connection terminal (23) formed on the same surface as the counter electrode (22) is formed at the end of the piezoelectric body (12) in the length l direction and at the center in the width h direction. The piezoelectric vibrating element according to any one of claims 1 to 4, characterized in that: (6) When the surface on which the pair of opposing electrodes (13, 22) are formed is the surface of the piezoelectric body (12), the resonance frequency can be adjusted by scraping the back surface of the piezoelectric body (12) by mechanical means. A method for adjusting the frequency of a piezoelectric vibrating element, characterized by: