JPS5833309A - Slip wave resonator - Google Patents

Abstract

PURPOSE:To obtain an inexpensive resonator which has the excellent temperature characteristics and is insensitive to the contaimination on the surface, by setting the thickness of film at a prescribed value for a multipair interdigital transducer electrode provided on a quartz substrate that transmits the slip wave. CONSTITUTION:The rotary Y-cut angle is set counterclockwise in a range of -43 deg.--52 deg. in terms of the axis X for a quartz substrate which transmits the slip wave. The bus bar electrodes 2 and 3 are formed with Al on the substrate 1 in the direction of the axis Z'. These electrodes are so extended as to cross interdigital electrode fingers 4 and 5 alternately. The ratio h/lambda betwen the film thickness (h) of the extended electrode and the propagating slip wavelength lambda is regulated to >=2%, and the number of pairs of electrodes 4 and 5 is regulated to 800+ or -200. At the same time, the w/lambda ratio is regulated to 8-15 between the cross length (w) of the electrode finger and the wavelength lambda. As a result, the right-under-electrode enclosing effect is improved for the oscillating energy of the slip wave along with excellent temperature characteristics. Thus an inexpensive resonator, which is insensitive to the surface contamination and the aging and oscillates the high frequency up to about 1GHz with the basic wave and with virtually no spuriousness and high Q.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a wave propagating just below the surface of a piezoelectric base #L (such type of wave O
I! In the specification of the present invention, the name is referred to as Betanha)
A type of resonator is used which is excited by an interdigital transformer and confines the vibrational energy immediately below the electrode.

Conventionally, to obtain a stable high frequency, in most cases nine vibrations across the thickness of a crystal thin plate were used, but the maximum frequency depended on the thickness of the crystal substrate, so the fundamental wave was limited to about 40MHz. K to obtain even higher frequencies usually utilized an overtone vibrating tube of the fundamental frequency. However, the usable limit is up to the 9th overtone order, and as the order increases, the target capacitance ratio r deteriorates in proportion to the O square of the order, and the impedance also increases, making it difficult to match the circuit and O. That would cause problems such as difficulty.)

Recently, as a means of solving the above-mentioned interdigital transition, an interdigital transistor has been developed that uses elasticity by electrodes. l
I! It generates a plane wave and can be excited at a frequency used for 1 m.

However, in surface acoustic wave resonators, the excited waves propagate on the surface of the piezoelectric substrate, so the radical I
Not only is there a defect, but also a frequency-warm JI! Even if the characteristics of the product are not enough to satisfy the customers, even better characteristics are required.

This was developed to eliminate the defects and problems in the piezoelectric resonator, which can excite the fundamental wave at a high frequency equivalent to that of a surface acoustic wave resonator. This will be explained in detail based on the resonance test results, which have excellent characteristics and temperature characteristics, and have extremely few spurious components.

It has been known for some time that there are smooth waves that propagate just below the surface of the piezoelectric substrate, and that these waves can be excited by multiple pairs of interdigital transducer electrodes.
Very little research has been done on attempts to apply it to resonators, and it has been difficult to satisfy the oscillation condition for PET wave resonators, although it is difficult to install a transducer electrode in the receiver. This is because even if it oscillated, its Q was extremely low and could hardly be put to practical use.

On the other hand, the inventors of the present invention have already filed a series of patent applications related to surface acoustic wave resonators, and Japanese Patent Application No. 56-56710.
In such cases, a sufficiently large Q can be achieved with a small number of pairs of electrode fingers by providing an interdigital transistor electrode assembly with an extremely large film thickness (more than 1.5 times the surface wave length) on the surface of a crystal substrate. And small im with little sub-resonance! o
It is inferred that this is due to the enhancement of the surface wave vibration energy confinement effect due to the resonance addition effect and the decrease in the equivalent resistance due to the increase in the cross-sectional area of the electrode fingers.

Based on this reasoning, an ink digital transformer assembly that uses all nine waves KfIk to excite all multi-waves can be considered, but the effect of adding mass and reducing the equivalent resistance can be expected.

The present invention was made based on the above estimation.]
It was confirmed that a sufficiently high Qt for practical use can be obtained when the electrode film thickness is increased beyond a certain level.

Below, we will explain in detail the results of the Yui experiment, which form the basis of this project.

1Ia is a diagram showing the configuration of the smooth wave resonator used in this experiment.

First, line temperature as a piezoelectric substrate! [Taking into consideration the characteristics, the rotation of the crystal is Y-cut, and the cutting angle is 143 p counterclockwise with respect to the lx axis.
I don't use anything in the range of °Sv2°. If a crystal fundamental wave having this cutting angle is used, the wave propagation speed is only a few times faster than that of the same rotating Y-cut crystal substrate with a straight propagation table, but the temperature-frequency characteristics are It becomes a cubic curve and is extremely hot (if it has good characteristics).

Incidentally, when the cut angle tube is in the range of 35@~42°, the temperature f
However, the propagation velocity J becomes approximately 1.6 of the surface acoustic wave propagation velocity.

Now, buspar electrodes 2 and 3 are provided in the Z-axis direction on the crystal substrate 1 as described above, and a large number of ink digital electrode fingers 4, 4, .
, The arc is long so that it intersects the light.

As is well known, this process is performed by photo-etching the evaporated AjK through the i-splash. Further, the total width of each of the interdigital transformer electrode fingers 4 or 5 and the adjacent non-electrode portion is set to be half of the sliding length λ, and the width ratio of the two is set to be easy to manufacture. From side 1: It is common to have an IK configuration.

Furthermore, the interdigital electrode fingers 4, 4.・・・・・・
and the overlap width of 5, 5... is the intersection length W
By changing this value, the characteristics of the resonator can be controlled.

The interdigital transducer electrode having the shape described above has a simpler structure than a resonator equipped with interdigital metal interdigitators or grooves or holes for reflecting surface waves, at least in constructing a surface acoustic wave resonator, It is thought that the same effect as in 4 is produced in the resonator.

To explain the results of experiments conducted using a resonator provided with interdigital transducer electrodes as described above, first, the number of electrode pairs N f is 800, and the crossover length W is all normalized by the wavelength λ. As a result of an investigation using an admittance chart assuming an equivalent circuit of , Figures 2(b) to (cl) were obtained.

As is clear from this chart, when the electrode film thickness h/λ is less than 2 waves, the characteristics of this nine-wave resonator are as follows: there is no inductive region on the chart, and the characteristic is that of a Hartley or Colpitts crystal.
i! It was found that it could not oscillate even if inserted into the @ path.

Now, the results of investigating the Q and sub-resonance levels of shear wave resonators owned by various electrode agricultural welfare associations are shown in the third EK.

In this figure, as the electrode film thickness h/λ increases, the Q and sub-resonance levels also increase, and when h/λ is near the curtain tip, Qit
It appears to be saturated and the sub-resonance level to increase rapidly.

On the other hand, when the electrode film thickness h/λ is fixed and the number of electrode pairs N1 is varied, the results of investigating how Q, m1ll resonance level, and r change are shown in FIG. 4.

As is clear from this figure, the larger the number of electrode pairs N, the higher the Q.Therefore, as a desirable configuration for a resonator, it depends on the required specifications, but in general, as long as a crystal substrate is used, the number of electrode pairs N is 8oo±200.

It can be seen that the electrode film thickness h/λ is between 0.025 and 0.03 degrees.

Mainly, the sub-resonance level is determined by the electrode film thickness h/for the number of electrode pairs N.
decreases slightly in translation as λ decreases, while r1
A slight tendency to increase in translation was observed as the thickness h/λ of one electrode decreased, but this is omitted to avoid clutter in the drawing.

In addition, FIG. 5 shows the results of an investigation regarding the crossover length W/λ. As is clear from this figure, there appears to be an optimum value for the cross length W/λ, and the range is generally between 8# and 150, and the Q or r obtained by varying the cross length W/λ. The change in electrode film thickness h/
This is small compared to the change in the resonator characteristics caused by changing λ or the number of electrode pairs N, and the IHI can be said to be secondary.

The results of the experiment explained above were obtained by making the resonator resonate in air, but surface acoustic wave resonators resonate in vacuum, and the Q of the resonator is 15 compared to that in air. It is known that it improves by 30 inches. As a result of applying this knowledge to a shear wave resonator, an improvement in Q of approximately 51i was observed, although the effect was not as great as in the case of a surface acoustic wave resonator.

From the above experimental results, the most important component that influences the characteristics of the Bek wave resonator is the electrode film thickness h/
λ, and other elements, such as the number of electrode pairs N, are the electrode film thickness h/
Since λ is almost an atonal coefficient, Kr must be set at a constant value from the sub-resonance level, and the crossover length W/λ also affects the resonator characteristics. However, it became clear that the effect was secondary.

The above describes the results of experiments conducted in accordance with the present invention. Other than O analogy d Au
-A g * Cr 5Z, ij N i, etc. were not mentioned, so I will briefly explain them.

If the above-mentioned negative effect of the electrode emphasizes the vibration energy trapping effect, the electrode should be made of a metal material with a much larger tm than AJ, and the O film thickness should be the same as the density of AI. It seemed that a similar effect would be obtained even if the thickness was made thinner in proportion to the ratio of The result was that there were more.

The reason for this is currently unknown, but given that similar results are more pronounced in the case of surface acoustic wave resonators, the shear waves that propagate directly beneath the crystal substrate also appear between the crystal substrate and the electrodes. In the vicinity of the boundary between the two, the influence of perturbation due to the difference in the impedance between the two is affected, and at the same time, the difference between the two impedances O is too large, which works in the direction of worsening the propagation of shear waves and the confinement effect of vibration energy. I have no choice but to think of it as something to do.

Therefore, at present, it is preferable to use quartz crystal, which has an acoustic impedance similar to that of the substrate crystal, as the electrode material.

Since the present invention is constructed as described above, it has extremely good temperature characteristics, has almost no spurious waves, is insensitive to surface contamination and aging, and can inexpensively generate resonance S that oscillates as a fundamental wave at a high frequency up to IGHz@II. This makes it possible to easily meet the demands of electronic devices whose frequency bands have been increasing in recent years, and it is also extremely effective in making these devices more compact and highly stable. It is something.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the electrode configuration of the super 9-wave resonator of the present invention,
Figure 2 (a) is the cape value circuit of the speciwave resonator in Figure 1, and (b) i to (e) are the same as those shown in Figure 1.
Diagram of at5 tans e chart for 0.91, 1.41G, 2.111 and -1t4, @arm is the Q for change in electrode film thickness when the number of electrode finger pairs of the nine-wave resonator is fixed. and - A diagram showing the experimental results of variation O11 in the J resonance level, a diagram showing the experimental results of the variation in Q, r and sub-resonance level when the electrode finger vs. tube changes well for each electrode film thickness in the fourth round,
Figure 5 is a diagram of experimental results showing changes in Q and r with respect to changes in electrode finger cross-over. 1...Crystal substrate, 4.5...Interdigital transformer, -Selector patent applicant Toyo Tsushinki Co., Ltd. Procedural Amendments Showa 1/2019, 2F, Japan Patent Office Director-General 1, Display of the incident Showa evening/year Sha Jf Application No. 1 J/73 No. 2,
Name of I & B 1-1...S5L length rh, each 3, person making the amendment Relationship with the case ゛Revision applicant 5, number of inventions increased by the amendment ri'L6,
Target of correction I-Destruction

Claims (3)

[Claims] (1) Multiple pairs of interdigital transducer electrodes are placed on the main IN surface of the crystal substrate to completely eliminate wave transmission.
1! In the smooth wave resonance S that is applied to the wrinkled electrode and converts large electrical energy into a shear wave, the crystal substrate ta
Rotation Y cut, cut anno 1 roux 43"4km-5'2°, all) wave propagation direction z
The vibration of the shear wave can be suppressed by setting the direction of the shear wave in the direction of the ' axis, and by making the multi-pair interdigital transistor electrode tAJK provided on the crystal substrate, and making the thickness of the O film greater than LoI 11 of the propagating shear wave length. A total of 9 resonators with improved O confinement efficiency directly below the electrode. (2) The claim of 4111k is that by setting the number of electrode pairs of the interdigital transformer a to 800±209, a high Qt can be obtained while keeping the capacitance ratio of the resonator and the sub-resonance level at a low level. 1. The speciwave resonator described in 1. (3) In the interdigital transformer, when - is set to 8: to -15 times the length of the shear wave excited by the electrodes at -1 kt, the capacitance ratio of the resonator is kept at a low level. A nine-wave resonator according to claim 1 or 2, wherein a high Q is obtained.