JPH04240911A - Kt-cut crystal vibrator - Google Patents

Abstract

PURPOSE:To realize an excellent frequency temperature characteristic even at a low temperature and a high temperature by applying KT-cut to a broadwise longitudinal crystal vibrator. CONSTITUTION:A coordinate system consists of an origin O, an electric axis (x), a mechanical axis (y), and an optical axis (z) to form O-xyz system. Moreover, the broadwise longitudinal crystal vibrator 1 whose width is x0, whose thickness is z0 and whose length is y0 and vibrated in the elongation and contraction direction in the direction of the width x0 is placed so as to coincident with the z-plate crystal perpendicular to the z-axis. Then the crystal is cut (KT-cut) off a cutting azimuth by making the x-axis as a rotary axis by an angle of phi=20-35 deg. counterclockwise. Thus, the broadwise longitudinal crystal vibrator 2 after coordinate rotation is formed. Since the temperature coefficient and the expansion coefficient of the elastic stiffness constant are changed by the angle phi, an optional frequency temperature characteristic is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cut angle of a wide vertical quartz crystal resonator. In particular, the present invention relates to a newly cut wide vertical crystal oscillator that is ideal as a reference signal source for pagers, IC cards, mobile radios, etc., which have strong demands for miniaturization, high precision, shock resistance, and low cost.

0002

[Prior Art] A crystal resonator with a frequency of 4 MHz or more is
Thickness-shear crystal oscillators, whose frequency is roughly determined by the plate thickness, have been used. In particular, AT cut, which has excellent frequency-temperature characteristics, has been widely used. Furthermore, these vibrators have been formed by machining.

0003

[Problems to be Solved by the Invention] However, when the AT-cut crystal resonator, which has been widely used in the past, is miniaturized because it is formed by machining, it is difficult to support the resonator, and the equivalent series resistance due to vibration leakage is reduced. There was an increase in R1 and an increase in the occurrence of spurious vibrations, and there was a limit to miniaturization. Furthermore, extremely important issues remain for ultra-compact crystal resonators for mobile devices, such as being weak against shock and having to mechanically process each resonator, which limits the cost reduction. Ta. From this, when the frequency is 4MHz or higher,
Furthermore, there was a desire for a new cut crystal resonator that was ultra-small, had a zero temperature coefficient, and was easy to etch.

0004

[Means for Solving the Problems] The present invention solves the conventional problems by the following method. That is, in a crystal resonator that vibrates in a width-longitudinal vibration mode, the Z-plate crystal, which is perpendicular to the Z-axis (optical axis), is rotated by 20° to 35° with the x-axis (electrical axis) as the rotation axis. The problem is solved by forming a vibrator.

[0005]

[Operation] As described above, the present invention is a wide vertical crystal resonator, and the cut angle φ is such that the z plate is rotated by φ=20° to 35° around the x axis, and the resonator is formed from this plate by an etching method. By doing so, a wide vertical crystal resonator with a zero temperature coefficient can be obtained.

[0006]

[Examples] Next, the present invention will be specifically described based on examples. FIG. 1 shows a perspective view of a widthwise-vertical crystal resonator 1 of the present invention and its coordinate system. The coordinate system is origin 0, electrical axis x, mechanical axis y,
It consists of an optical axis z and constitutes 0-xyz. First, it consists of width x0, thickness z0, and length y0.
A width-longitudinal crystal oscillator 1 that vibrates by expanding and contracting in the direction is placed so as to coincide with a z-plate crystal that is perpendicular to the z-axis. Next, the sheet is cut out from a cutting direction rotated counterclockwise by an angle φ=20° to 35° with the x-axis as the rotation axis. From now on, use this cut as K.
It's called a T-cut. This state is shown by the broken line in FIG. 1, and is shown by the width-vertical crystal resonator 2 after the coordinate rotation. Since the temperature coefficient and expansion coefficient of the elastic stiffness constant change according to this angle φ, an arbitrary frequency temperature characteristic can be obtained. Next, the behavior of temperature characteristics due to changes in cut angle will be described.

FIG. 2 shows the thickness z0 of the width-longitudinal crystal resonator of the present invention.
is much smaller than the width x0, and the length y0 is the width x0
FIG. 3 is a characteristic diagram of the relationship between the cut angle φ and the primary and secondary temperature coefficients α and β when the cut angle is much larger. As the cut angle φ increases from zero degrees, the first-order temperature coefficient α increases, and becomes α=0 when the cut angle φ=24.6°, so that a wide longitudinal quartz crystal resonator having a zero temperature coefficient near room temperature is obtained. If the angle is further increased, α becomes even larger. In this way, since the first-order temperature coefficient α changes significantly depending on φ, the peak temperature can be set to an arbitrary temperature. On the other hand, the secondary temperature coefficient β is β=-1.21×10− when φ=20°
8/℃2, the absolute value of β decreases as φ increases, and at φ=35°, β=-0.925×10−
10/℃2.

FIG. 3 shows an example of the frequency-temperature characteristics when the cut angle φ of the wide vertical crystal resonator of the present invention shown in FIG. 2 is used as a parameter. When φ=20°, since α and β have negative values, the peak temperature TP is largely on the negative side. However, since α=0 approximately at φ=25°, TP
comes to room temperature. When φ=35° is further increased, α has a larger positive value, and therefore the peak temperature TP becomes higher. In this way, the apex temperature TP can be set to any temperature by selecting the cut angle φ, so if a vibrator with excellent frequency-temperature characteristics on the low temperature side is required depending on the usage conditions, φ can be set to φ.
On the other hand, if high temperature is required, it may be set as large as φ = around 35°. Of course, it goes without saying that it is sufficient to set φ=25° at around room temperature. Also, as mentioned in Figure 2, the secondary temperature coefficient β is φ=
At 20°, β=-1.21×10-8/℃2,
As φ becomes larger, the absolute value of β becomes smaller, so that when used on the high temperature side, a widthwise vertical crystal resonator with better frequency-temperature characteristics can be obtained than when used on the low temperature side.

FIG. 4 shows the side ratio γ (=z0 /x0 :thickness z
0 and the width x0) and the first-order temperature coefficient α. Up until now, we have shown the frequency temperature characteristics when the side ratio γ=z0 /x0 is very small, but in Fig. 4, the side ratio γ=
It shows how the primary temperature coefficient α changes when z0 /x0 is increased little by little. As is clear from FIG. 4, when the side ratio γ=z0/x0 is increased, the influence of the thickness z0 appears, and the value of α changes accordingly. Furthermore, to explain the reason in detail, three vibrations that depend on the thickness z0: (1) thickness shear vibration, (2) thickness longitudinal vibration, and (3) cross-sectional deformation vibration in the thickness direction that depends on Poisson's ratio are mainly caused by the width-longitudinal quartz crystal. This is because it affects the vibrator. Of these three vibrations, (3) always affects α, regardless of the size of the thickness z0 and the magnitude of its influence. From Figure 4, the side ratio γ=z0/x0
As becomes larger (if x0 is held constant, the thickness z0 becomes larger), the main vibration of the thickness-shear vibration, which depends on the thickness, is coupled to the width-longitudinal crystal oscillator, so that α takes on a more positive value. At this time, the thickness longitudinal vibration is hardly coupled with the main vibration. However, if the side ratio γ=z0/x0 is further increased, the coupling with the thickness shear vibration becomes weaker (2
) becomes stronger, so α changes to a negative value. This situation can be well understood from the experimental values shown in FIG.

FIG. 5 shows another example of the frequency-temperature characteristics of the wide-vertical crystal resonator of the present invention. The condition of the vibrator is cut angle φ = 2
4°, side ratio γ=z0/x0 =0.5, frequency f=1
This is the case of 3.5MHz. At this time, the first temperature coefficient α
=-1.36×10-8/℃, second-order temperature coefficient β=-1.
28×10-8/℃2, α is approximately zero, and β is the well-known DT cut (β=-1.8×10
-8/°C2), and excellent frequency-temperature characteristics could be obtained.

Next, the relationship between the width dimension and the frequency f of the wide-vertical crystal resonator of the present invention will be shown.

FIG. 6 shows the width x0 of the width vertical crystal resonator of the present invention.
The relationship between and frequency f is shown below. The frequency constant (f x0 ) of the KT cut crystal resonator of the present invention varies slightly depending on the cut angle φ, but is approximately 270 KHz cm for the fundamental wave.
Therefore, in order to realize a vibrator with a frequency f=4.0 MHz or higher, the width x0 should be approximately smaller than x0 = 675 μm. Of course, if harmonics are used, a frequency equal to 3.57 times the fundamental wave, which is an odd number, can be obtained. Also, in order to avoid coupling with the long-side vibration that depends on the length y0,
The length y0 is much larger than the width x0, and in order to further reduce the equivalent series resistance R1, it is usually x0 /
It is designed so that y0 <0.1. However, the frequency is 7MHz
As the width x0 becomes lower, the width x0 becomes larger. Therefore, in order to obtain a smaller vibrator, x0 /y0 <0.2 is designed, but even in this case, there is no influence due to long side vibration.

Up to now, the frequency temperature characteristics and frequency have been described. Next, the arrangement of the electrodes for exciting the wide-vertical crystal resonator of the present invention will be described.

FIGS. 7(a), (b), and (c) show K of the present invention.
A cross-sectional view of an example of the arrangement of excitation electrodes of a T-cut width vertical quartz crystal resonator is shown. In FIG. 7(a), excitation electrodes 3, 4, 5, and 6 are provided on the plane perpendicular to the z' axis of the width-longitudinal crystal oscillator 2, and the counter electrodes 3, 4 and the counter electrodes 5, 6 have the same polarity. The electrode terminals A and B are formed as shown in FIG. Further, FIG. 7(b) is an example in which excitation electrodes 7 and 8 are provided on the etched surfaces perpendicular to the x-axis of the width-longitudinal crystal oscillator 2, and the electrode terminals A, 8 are provided as in FIG. 7(a), respectively. It forms B. Furthermore, FIG. 7(c) is an example in which excitation electrodes 9 and 10 are provided on the etched surface perpendicular to the z' and x axes of the width-longitudinal crystal oscillator 2. is formed. Therefore, by applying an alternating voltage between the electrode terminals A and B, an electric field is generated in the x-axis direction, thereby easily exciting the width-longitudinal crystal resonator that vibrates largely in the width x0 direction. As a result, a wide vertical crystal resonator with a small equivalent series resistance R1 can be obtained. Also, FIGS. 7(a), (b), (c)
The size of the excitation electrode 3-10 provided in is determined in consideration of spurious vibrations, electric field efficiency, and the like. In particular, when the length of the electrode in the y'-axis direction is arranged over the entire surface at length y0, R1 can be reduced most.

[0015]

As described above, the KT cut width vertical crystal resonator of the present invention has the following remarkable effects. (1) Since the apex temperature TP of a vertical crystal resonator with a width of cut angle φ = 20° to 35° can be set to any temperature, it is possible to obtain excellent frequency-temperature characteristics on either the low temperature side or the high temperature side depending on the requirements. can.

(2) KT with cut angle φ=20° to 35°
Since the cuts can be easily formed by etching, the device can be made smaller and thinner. (3) Since the frequency is roughly determined by the width x0, 4M
For frequencies above Hz, ultra-miniaturization is particularly possible. (4) Since a large number of vibrators can be batch-processed on one wafer at the same time, costs can be reduced.

(5) By arranging excitation electrodes on the upper and lower surfaces or side surfaces of the resonator, or on the upper and lower surfaces and the side surfaces, a vertical crystal resonator with a small width and equivalent series resistance R1 can be obtained. (6) Since this vibrator can be formed into any shape by etching, a vibrator with excellent impact resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a widthwise-vertical crystal resonator of the present invention and its coordinate system.

[Fig. 2] Cut angle φ and primary order of the width-longitudinal crystal oscillator of the present invention,
It is a characteristic diagram which shows the relationship with secondary temperature coefficient (alpha) and (beta).

FIG. 3 is a characteristic diagram showing an example of frequency-temperature characteristics when the cut angle φ of the width-vertical crystal resonator of the present invention is used as a parameter.

[Fig. 4] Side ratio γ=z0/x of the width-vertical crystal resonator of the present invention
0 is a characteristic diagram of the relationship between 0 and the first-order temperature coefficient α.

FIG. 5 is a characteristic diagram showing another example of the frequency-temperature characteristics of the width-vertical crystal resonator of the present invention.

[Figure 6] Width x0 and frequency f of the wide vertical crystal oscillator of the present invention
FIG.

FIGS. 7(a), (b), and (c) are cross-sectional views of three types of excitation electrode arrangement of the KT cut width vertical quartz crystal resonator of the present invention.

[Explanation of symbols]

1 Width vertical crystal oscillator 2 Width-vertical crystal oscillator after coordinate rotation 3-10 Excitation electrode A, B Electrode terminal x0 Transducer width y0　　　Length of the vibrator z0 Transducer thickness x Electric axis y Machine axis z Optical axis φ Cut angle

Claims (1)

[Claims] Claim 1: A crystal resonator that vibrates in a width-longitudinal vibration mode, in which a Z-plate crystal perpendicular to the Z-axis (optical axis) is rotated by 20° to 35° with the x-axis (electrical axis) as the rotation axis. A KT cut crystal resonator, characterized in that the resonator is formed from a plate.