JPS6258173B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a crystal resonator.

The present invention accurately and efficiently adjusts both the frequency and temperature characteristics of a complex vibration type crystal resonator in which the resonant frequency temperature characteristics of a crystal resonator having a relatively low resonant frequency are to be improved. It is something to do.

As electronic clocks become more precise, attention is being focused on increasing the precision of the crystal oscillators that serve as their time standard sources.

Currently, for example, the crystal vibration used in wristwatches is a tuning fork crystal resonator with a bending vibration that has an oscillation frequency of about 32KHz, but due to its low current consumption characteristics,
It has become mainstream. However, this bending vibration mode tuning fork crystal resonator has a frequency temperature characteristic of 0.
It varies by 15 to 20 PPm between ℃ and 20℃, and cannot be called a time standard source for high-precision crystal resonators, which is currently required. On the other hand, as an existing high-precision crystal oscillator, there is an AT-cut crystal oscillator that vibrates through the thickness, and it has a fairly good cubic curve frequency-temperature characteristic, but this has a high oscillation frequency of several MHz and consumes Not only does it have a high current, but it is also large in size.

In this way, conventional crystal oscillators had trade-offs, but in order to improve the precision of electronic watches, it was necessary to improve the frequency-temperature characteristics, which were trade-offs, and to reduce current consumption by lowering the oscillation frequency. It is necessary to realize both. The tuning fork type crystal resonator that utilizes the combination of the bending vibration mode and the torsional vibration mode described in the present invention achieves both the improvement of frequency temperature characteristics for the above-mentioned high precision and the reduction of current consumption. The characteristics show a cubic curve as shown in Figure 1, and the example shown in Figure 1 has almost flat temperature characteristics in the temperature range of 0℃ to 40℃, with bending vibration mode and torsional vibration mode. There are various types of vibrations, including those that utilize higher-order vibrations ranging from main vibration to secondary vibration.

Hereinafter, a tuning fork type crystal resonator that improves frequency-temperature characteristics by utilizing the combination of two vibration modes, a bending vibration mode and a torsional vibration mode, will be referred to as a compound vibration type crystal resonator, and an overview thereof will be described below. explain.

Generally, the frequency-temperature characteristics of a crystal resonator are approximated by Taylor expansion up to third order centered at 20°C, as shown in the following equation.

= ₂₀ + α (T-20) + β (T-20) ² + γ (T-20) ³ However, T...Temperature α...Primary coefficient β...Second order coefficient γ...Third order coefficient ₂₀ ...Oscillation at 20℃ Frequency The tuning fork type crystal resonator of the present invention, which is cut out from the crystal at the cutting angle shown in Fig. 2 with respect to the electrical axis, mechanical axis, and optical axis, performs bending vibration approximately in the Z' plane, and bends. The oscillation frequency _F of the vibration is mainly determined by the length l and width w of the tuning fork arm, and the oscillation frequency _T of the torsional vibration centered on the Y′ axis of the tuning fork arm is determined by the front, l, and w. It is also determined by the thickness t.

When the oscillation frequency _F of the bending vibration and the oscillation frequency of the torsional vibration are far apart from each other, the two vibration modes do not affect each other, but when _F and _T become close values, each crystal axis of the crystal of the crystal resonator Appropriately select the cutting angles, θ and ψ from ₁ , θ ₁ ,
If ψ is ₁ , the dimensions l, w, and t of each part of the crystal oscillator are appropriately selected, and l ₁ , w ₁ , and t ₁ , then in the frequency-temperature characteristic equation, both the first-order coefficient α and the second-order coefficient β are almost 0. The frequency-temperature characteristics of the crystal resonator are
The result is an extremely good cubic curve.

However, the compound vibration type crystal resonator described in the present invention is manufactured from the initial processing so that both the first order coefficient α and the second order coefficient β in the frequency temperature characteristic equation are almost 0. This is extremely difficult because there are too many processing parameters that affect the frequency-temperature characteristics of a crystal resonator. On the other hand, the first-order coefficient α and second-order coefficient β of the frequency-temperature characteristics of the complex vibration type crystal resonator are:
It is closely related to the difference ( _F - _T ) between the frequency _F of the bending vibration mode and the frequency _T of the torsional vibration mode, and for example, α has a relationship with ( _F - _T ) as shown in Figure 3. Therefore, in a compound vibration type crystal resonator, the cutting angle from each crystal axis of the crystal, θ,
ψ, arm length l, arm width w, and thickness t are manufactured with a certain processing accuracy, and then the frequency _F of the bending vibration mode and the frequency _T of the torsional vibration mode are adjusted by vapor deposition, etc. Accordingly, ( _F - _T ) can be driven to a predetermined value, α and β in the frequency-temperature characteristic equation can be driven to almost 0, and the frequency-temperature characteristic can be made to have a good cubic curve.

On the other hand, when a composite type crystal oscillator is used as a time standard source for an electronic watch, the oscillation frequency of the reference vibration mode must almost match a predetermined standard frequency. Therefore, in order to use a compound vibration type crystal oscillator as a time standard source for electronic watches and to achieve good frequency-temperature characteristics, it is necessary to aim the oscillation frequency of the reference vibration mode to a predetermined standard frequency. ( _F − _T )
It was necessary to adjust the frequency and temperature characteristics at the same time, which was extremely complicated and required the simultaneous adjustment of frequency and temperature characteristics.

An object of the present invention is to simplify and streamline the complicated interaction between frequency adjustment and temperature characteristic adjustment of such a complex vibration type crystal resonator.

An example is shown below.

For example, when the bending vibration mode is the secondary vibration and the torsional vibration mode is the main vibration, as shown in FIG. Adjust ( _F − _T ) using the amount of change in frequency _F of vibration mode △ _F and the amount of change in frequency _T of torsional vibration mode △ _T ratio △ _T / △ _F to adjust frequency temperature characteristics. Can be done.

However, even if the deposition position and amount at the tip of the tuning fork are the same, the above △ _T / _△ The value is different for the case of evaporation from the ′ plane. Figure 5 shows the fourth part of a thin plate tuning fork type crystal resonator manufactured by photolithography.
As shown in Figure A, the difference between the oscillation frequency _F of the bending vibration mode and the oscillation frequency _T of the torsional vibration mode when the entire tip of the tuning fork is deposited from the +Z' plane and from the -Z' plane ( _F - _T ) This shows the relationship between the amount of change in and the amount of change in _F. In Figure 5,
△ _T / △ _F in evaporation from +Z′ plane is 2.9, while △ in evaporation from −Z′ plane
_T /△ _F is 0.85, exhibiting completely opposite changes.

△ _T / △ _F when deposited from this +Z′ plane
and △ _T / △ _F when deposited from the −Z′ plane.
The value of is determined by the cutting angle from the crystal axis of the crystal of the tuning fork compound vibration type crystal resonator, the deposition position and deposition area, and the size of the etching residue in the -X' direction due to the etching time in the photolithography manufacturing method. It varies depending on the size.

In a complex vibration type crystal resonator manufactured under certain processing conditions, △ _T / △ _F when vapor deposited from the +Z' plane is determined by adjusting the vapor deposition position to the tip of the tuning fork and the vapor deposition area appropriately, as shown in Figure 6. By choosing , it can be almost 1, it can be less than 1, or it can be more than 1. On the other hand, when deposited from the -Z' plane, _ΔT / _ΔF almost always shows a value larger than 1. In a compound vibration type crystal resonator, as mentioned above, △ T _/ △ F when deposited from the -Z' plane to the tuning fork tip and △ _T / △ _F when deposited from the +Z' plane to the tuning _fork tip. By making good use of this characteristic, it has become possible to easily drive both the oscillation frequency and temperature characteristics of a complex vibration type crystal resonator to predetermined values.

Seventh, △ _T / △ _F is achieved by vapor deposition on the +Z' plane and -Z' plane of the tuning fork tip of the complex vibration type crystal resonator.
This describes an example of a method for adjusting the oscillation frequency and temperature characteristics using the above-mentioned characteristics of. 7th
In the figure, 1 indicates a predetermined oscillation frequency that serves as a time standard source, and 2 indicates a predetermined (△ _T / △ _F) that exhibits good temperature characteristics. In Fig. 7, -
The vapor deposition position and area are selected so that △ _T /△ _F due to vapor deposition from the Z' plane becomes 1. In Fig. 7, _F and _T before vapor deposition are as shown in 3 and 4 in the figure. Ignoring the oscillation frequency 1 of , first drive _F and _T to values of 6 and 7 so that (△ _F - △ _T ) becomes a predetermined value. Next, it is deposited at an appropriate position and area on the +Z' plane so that ( _F - _T ) does not change, that is, △ _T / △ _F becomes 1, and the reference oscillator _F of this complex vibration type crystal oscillator is deposited. The frequency is driven to frequency 1 in FIG. 7 as a predetermined standard oscillation source. Therefore, both the frequency and temperature characteristics of the present compound vibration type crystal resonator can be brought to predetermined values.

After adjusting the oscillation frequency and temperature characteristics of the crystal oscillator by vapor deposition from the +Z' plane and -Z' plane of the above-mentioned tuning fork type crystal oscillator, a part of the crystal oscillator is removed by laser. Accordingly, the oscillation frequency and temperature characteristics of the crystal resonator can be driven to predetermined target values with higher accuracy.

Furthermore, even if the above-mentioned crystal resonator has a thickness of 500 μm or less and is manufactured by photolithography, the vibration theory of the crystal resonator,
Regarding the effect on the amount of change in the flexural vibration mode oscillation frequency _F and the torsional vibration mode oscillation frequency _T due to vapor deposition from each of the +Z' and -Z' planes, the same thing can be said as described above, and the present invention The method for adjusting the frequency and temperature characteristics of a crystal resonator can be applied as is.

As described above, the present invention is based on depositing simultaneously or separately on both the +Z' plane and -Z' plane on a part of the complex vibration mode crystal resonator, and in some cases, crystal vibration using a laser. To simplify and clarify the adjustment of the oscillation frequency and temperature characteristics of the reference vibration of a complex vibration mode crystal resonator, including using it in combination with the method of partially removing the child mass, and to reduce the man-hours for the above adjustment and improve the yield. It is something.

[Brief explanation of the drawing]

Figure 1: Frequency-temperature characteristics of a tuning fork crystal resonator that utilizes the combination of bending vibration mode and torsional vibration mode described in the present invention. Fig. 2: An example of the external shape and cutting angle of the tuning fork type crystal resonator described in the present invention. Figure 3: Linear function α of the frequency temperature characteristic of a complex vibration type crystal resonator, and the difference _F between the frequency _F of the bending vibration mode and the frequency _T of the torsional vibration mode.
− Relationship with _T. Figure 4: An example of vapor deposition on the tip of a tuning fork crystal resonator in order to adjust the vibration frequency in the present invention. Figure 5: A case where the entire tip of the tuning fork is vapor-deposited from the +Z' plane in a thin plate tuning fork type crystal resonator manufactured by photolithography, and
An example of the difference in behavior of the difference _F − _T between the frequencies _F and _T of the bending vibration mode and torsional vibration mode when deposited from the −Z′ plane. Figure 6: An example of the relationship between the vapor deposition area at the tip of the tuning fork and the ratio of change in each frequency of bending mode and torsion mode vibration △ _T / △ _F in the complex vibration type tuning fork type crystal resonator described in the present invention. . FIG. 7: A graph showing a frequency adjustment method for the frequency and temperature characteristics of the complex vibration type crystal resonator according to the present invention. 1... Frequency of a predetermined target reference vibration (in this case, bending vibration). 2...Difference _F between the frequencies of the target bending vibration mode and torsional vibration mode
_−T . 3, 8...Oscillation frequency of bending vibration mode before adjusting frequency and temperature characteristics. 4, 9...Oscillation frequency of torsional vibration mode before frequency and temperature characteristic adjustment.
5, 10...Oscillation frequency of a predetermined target torsional vibration mode. 6, 11...Oscillation frequency of bending vibration mode in the middle stage of frequency and temperature characteristic adjustment. 7,
12...Oscillation frequency of torsional vibration mode in the middle stage of frequency and temperature characteristic adjustment. 13... Vapor deposition section.

Claims (1)

[Claims] 1. In a method for adjusting the frequency and temperature characteristics of a tuning fork type crystal resonator having a thickness of 500 μm or less and exciting bending vibration and torsional vibration simultaneously, a first adjustment step of depositing a metal film serving as a weight at one location to adjust the frequency difference between the vibration frequency _F of the bending vibration and the vibration frequency _T of the torsional vibration; and a +Z surface side of the tuning fork type crystal resonator. a second adjustment step of reducing the vibration frequencies of the bending vibration and torsional vibration by approximately the same amount by depositing a metal film as a weight at one location near the tip of the tuning fork, and setting the value of the frequency; A method for adjusting the frequency and temperature characteristics of a tuning fork crystal resonator.