JPH0476527B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a piezoelectric resonator, particularly a piezoelectric resonator for overtone oscillation that enables oscillation at a desired overtone frequency without the need for a special oscillation circuit. Regarding the electrode structure of a resonator.

(Prior art) In recent years, demands for higher frequencies and ultra-miniaturization have become increasingly strict in various electronic devices such as communication devices. In addition to the use of overtone vibrations of piezoelectric resonators such as vibrators, surface acoustic waves (SAW)
Resonators have become widely used.

However, the former method generally involves extracting the desired output through an LC tuning circuit that tunes to the desired overtone frequency, or inserting an LC tuning circuit into a part of the oscillation circuit so that the negative resistance of the circuit can match the desired overtone frequency. They were designed to be sufficiently large only in the frequency domain, and both required coils, which was extremely inconvenient for the development of integrated circuits for oscillation circuits.

On the other hand, as is well known, the oscillation frequency of a SAW resonator is uniquely determined by the material of the piezoelectric substrate and the pitch of the interdigital transducer (IDT) electrodes formed on its surface, so it is important to miniaturize the resonator itself. Although it is possible and does not have the above-mentioned circuit problems, it has the drawback of being far inferior to AT-cut crystal resonators in terms of frequency-temperature characteristics.

In order to eliminate the defects of conventional piezoelectric resonators as mentioned above, the inventor of this application has filed a patent application (Japanese Patent Application No.
77065), the electrode at the center of the piezoelectric substrate confines the vibration energy of a desired overtone order or higher, while allowing the vibration energy of lower overtone vibrations, including the fundamental wave vibration, to leak. We propose a piezoelectric resonator for overtone oscillation, which oscillates at the desired overtone vibration without using a special oscillation circuit by converting it into heat through acoustic loss and consuming it at a suitable location on the outer circumference of a piezoelectric substrate. ing.

However, when using the above-mentioned resonator, in order to adapt it to any oscillation circuit, considering that the absolute value of the load resistance on the oscillation circuit side is larger on the lower frequency side, the vibration energy of the low-order overtone vibration is Since it is necessary to sufficiently absorb vibration energy, there has been a problem in that simply providing a vibration energy absorbing section on the outer periphery of the resonator piezoelectric substrate may not provide satisfactory results.

(Invention and Object) The present invention aims to solve the above-mentioned problems in the piezoelectric resonator for overtone oscillation and to provide a piezoelectric resonator for overtone oscillation that is essentially independent of the characteristics of the oscillation circuit. purpose.

(Summary of the Invention) In order to achieve the above-mentioned object, the resonator according to the present invention basically requires a resistance of an appropriate value, especially (2πfnCo), between the double-sided electrodes of the energy absorbing portion provided near the outer periphery of the piezoelectric substrate. ^-1 [However, Co is the interelectrode capacitance of the part, fn
connects a resistor corresponding to the overtone frequency to be absorbed.

(Embodiments of the Invention) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

In order to facilitate understanding of the present invention, before describing embodiments, a resonator for overtone oscillation to which the present invention is applied will be briefly explained using FIG. 2.

In FIG. 2a, electrodes 2 and 2' having a diameter of 2a are attached to both sides of the central part of the piezoelectric substrate 1 having a thickness of H, and the cutoff frequency of this part is lowered by _f1, and the cutoff frequency of the surrounding area is reduced by _f2.
A cut-off frequency difference of f ₂ - _{f 1} is provided between the electrodes 2 and 2' attachment part as a vibration energy trapping part,
The non-electrode parts 3 and 3' are used as vibration energy propagation parts of unnecessary vibrations, and the cutoff frequency f ₃ (however, f ₁ ≒ f ₃ <
f ₂ ) vibration energy absorbing portions 4, 4' are provided.

Now, if we consider the case where this resonator is used as a resonator for fifth-order overtone oscillation, for example, the fundamental wave (1
If the vibration energy confinement rate of the 3rd overtone vibration is made small and that of the 7th overtone is made large, the equivalent resistance for the 5th or higher overtone vibration in which the vibration energy is trapped is the overtone. The higher the order, the larger the resonator, and the smaller the Q of the resonator. On the other hand, the energy of the fundamental wave and third-order overtone vibration leaks toward the outer periphery of the piezoelectric substrate 1 and is converted via the energy absorbing section 4, so the impedance of these vibrations becomes extremely high and eventually becomes the fifth-order overtone. This is to obtain a resonator for oscillation.

In order to obtain the above characteristics, first, the vibration energy confinement rate _T5 of the fifth-order overtone vibration is set to, for example, about 80%, as shown in FIG.
From this figure, the confinement coefficient na√ at T ₅ = 80%
△/H is approximately 0.53, but the confinement coefficient na
√Δ/H=na√( ₂ − ₁ ) ₂ Since n, H, f ₂ and a in /H are given conditions, it is easy to calculate what value f ₁ should be selected. Once f ₁ is determined, the cutoff frequency difference f ₂ −f ₁ is a quantity directly related to the so-called plate back, and since the amount of electrode attachment that satisfies this is already well known, the resonator as shown in FIG. It can be easily manufactured.

Note that when a highly bonded material such as lithium niobate, lithium tantalate, or piezoelectric ceramics is used as a piezoelectric substrate, an extremely large frequency drop occurs due to a small amount of electrode adhesion. It would be more convenient to manipulate the electrode size a as a matter of fact.

Further, the cutoff frequency f ₃ of the vibration energy absorbing portions 4, 4' may generally be the same as f ₁ , but it may be increased or decreased as necessary so that the consumption of vibration energy through the portion is as large as possible. desirable.

Figure c qualitatively shows the distribution of vibration energy of various waves in a resonator having the above-described configuration.

By the way, if the consumption of overtone vibration energy lower than the desired overtone vibration by conversion into heat through the vibration energy absorbing section 4 is insufficient and the impedance at the frequency does not rise sufficiently, then as shown in FIG. As shown in FIG. 2, desired overtone oscillation may become impossible due to the negative resistance characteristic of the oscillation circuit.

In order to solve such problems, the overtone oscillation resonator according to the present invention has the following configuration.

That is, as shown in FIG. 1, a required resistance R is connected between the double-sided electrodes 4 and 4' attached to the vibration energy absorbing section.

By doing so, the vibration energy of an order lower than the desired overtone order propagated to the vibration energy absorbing section excites the piezoelectric substrate 1 in that section, and as a result, it is generated in the electrodes 4 and 4' of that section. The generated charges are electrically converted into thermal energy and consumed by the resistor R, thereby sufficiently increasing the impedance for these low-order overtone vibrations including fundamental wave vibrations.

The value of the resistance R is approximately equal to (2πfnCo) ^-1 , where Co is the capacitance between the electrodes 4 and 4', and fn is the frequency of overtone vibration that should convert the vibrational energy into heat and consume it. It will be understood that this is the most efficient way to absorb unnecessary vibration energy since it corresponds to a state in which the impedances are matched in an AC circuit.

Furthermore, when it is necessary to consume a plurality of vibration energies of the fundamental wave (first order) and third-order overtone vibration, such as a resonator for fifth-order overtone oscillation, the fundamental wave frequency fn ₁ and the third-order overtone are used. Either use a frequency fm intermediate between the frequency fn ₃ and set the value of the resistance to R=(2πfmCo) ^-1 , or divide the vibration energy absorption part electrodes 4 and 4 and set a resistance for each as shown in FIG. Value R ₁ = (2πfn ₁ Co) ^-1 , R ₂
= (2πfn ₃ Co) ^-1 may be connected.

Now, although the principle of the overtone oscillation resonator according to the present invention is as described above, it is convenient from the viewpoint of productivity and use to configure the actual resonator as shown in FIG.

FIG. 5a is a plan view showing an embodiment of the electrode structure of the piezoelectric resonator for overtone oscillation according to the present invention, in which vibration energy confinement electrodes 2 and 2' are provided on both sides of the central part of the crystal substrate 1. At the same time, the electrodes 2, 2' are connected to vibration energy absorbing portion electrodes 4, 4' provided at appropriate locations on the outer circumference of the substrate 1 via lead patterns 5, 5'.

In the electrodes 4, 4', resonator holding members 6, 6 and conductive adhesives 7, 7, which are not shown, are installed upright from a base that supports the resonator.
Electrical conduction and mechanical fixation are achieved by fixing with.

At this time, care must be taken not to short-circuit the front and back surfaces 4 and 4' of the electrodes due to the conductive adhesives 7, 7.

At this time, adhesives 8, 8, which are part of the electrodes 4, 4' and have a required resistance value, are attached to the end surface of the substrate 1.
By applying , the energy absorption of unnecessary vibrations is increased.

The adhesive 8 may be, for example, an epoxy resin in which the amount of carbon particles dispersed is controlled.

Incidentally, FIG. 5b shows a cross section taken along line AA in FIG. 5a.

Furthermore, as described above, when there are multiple waves to absorb vibration energy, the vibration energy absorbing portion electrodes 4, 4 on the outer periphery of the substrate 1 are divided as shown in FIG. The front and back sides may be connected using the aforementioned resistance adhesives 8, 8, . . . at the respective ends of the substrate 1. In this case, it goes without saying that the resistance value of each adhesive should correspond to the frequency of the waves to absorb vibrational energy.

Furthermore, the present invention may be applied to a two-port resonator in which the main vibration confinement electrode 2 is divided, thereby making it easier to oscillate at a desired overtone frequency.

Although the present invention has been described above only as a vibrator for overtone oscillation, the present invention is not limited thereto and can be used as an element for a monolithic piezoelectric filter.

That is, as is well known, by providing split electrodes on a single piezoelectric substrate with a predetermined gap between them, vibrations of the same frequency are acoustically coupled, and the resulting resonance and anti-resonance are used to widen the passband. This filter is widely used, and it is obvious that if the electrode attached to the main vibration confinement region is a divided electrode having a desired gap, the filter will have a pass band corresponding to the gap.

Although only the most common resonator in which electrodes are attached to a piezoelectric substrate has been described as an example, the present invention is not limited to this, and the Q of the resonator is
Needless to say, the present invention can also be applied to a type of resonator in which electrodes are arranged on the surface of a piezoelectric substrate through an air gap in order to improve the quality.

(Effects of the Invention) Since the present invention is constructed as described above, it is possible to obtain the desired overtone order by adding extremely few steps to the piezoelectric resonator for overtone oscillation that the inventor has already proposed. Since it is possible to secure a sufficient difference between the impedance for the frequency and that for the overtone frequency below the above-mentioned order, it has a remarkable effect in further reducing the dependence of the resonator on the characteristics of the oscillation circuit. demonstrate.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic principle of the electrode structure of a piezoelectric resonator for overtone oscillation according to the present invention, and FIGS. A cross-sectional view showing the relationship between the vibration energy confinement rate of the overtone order for which oscillation is desired and other overtone orders, and a diagram showing the vibration energy distribution of each overtone vibration of the resonator for 5th overtone oscillation. 3 is a diagram showing the relationship between the resonator impedance and the characteristics of the oscillation circuit for each overtone frequency, and FIG. 4 is a diagram showing the relationship between the resonator impedance and the characteristics of the oscillation circuit for each overtone frequency. A plan view showing the basic principle in a certain case, FIGS. 5a and 5b are a plan view and an A-A sectional view showing an embodiment of the present invention, and FIG. 6 is a plan view showing another embodiment of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1...Piezoelectric substrate, 2...Vibration energy confinement part (electrode), 3...Vibration energy propagation part, 4...Vibration energy absorption part (electrode), R, _R1 and _R2 ...Resistance.

Claims (1)

[Claims] 1. A vibration energy confinement portion having a cutoff frequency f ₁ is provided on the piezoelectric substrate, and a cutoff frequency f ₂ (however, f ₁
A vibration energy propagation section with a cut-off frequency f ₃ (where f 1 ≒ f 3 < f _{2 )} is further arranged at a suitable location on the outer circumference of the vibration energy propagation section, and a vibration energy absorption section with a cutoff frequency f 3 (where f ₁ ≒ f ₃ < f 2 ) is disposed at a desired location in the vicinity of the vibration energy confinement section and its periphery. traps the energy of overtone vibrations of an order higher than the order of the overtone vibration of the desired overtone vibration, and causes a large amount of vibration energy of overtone vibrations of a lower order than the desired overtone vibration, including fundamental wave vibration, to leak to the vibration energy propagation section. , the difference between the cutoff frequencies f ₁ and f ₂ and the gap between the vibration energy confinement part and the vibration energy absorption part so that the leaked vibration energy is consumed through the vibration energy absorption part.
In the piezoelectric resonator for overtone oscillation, in which the oscillation by the desired overtone vibration is made easier than that by the overtone vibration of a lower order than the desired overtone vibration by setting the above-mentioned Between the electrodes attached to both sides of the vibration energy absorption part of the piezoelectric substrate (2πfCo) ^-1
[However, f is the fundamental wave vibration frequency at which vibration energy should be absorbed, C ₀ is the capacitance between the electrodes] or (2πf _n C ₀ ) ^-1
By connecting a resistor approximately equivalent to [where f _n is a frequency with an appropriate value between the frequencies of the fundamental wave vibration and the higher-order overtone vibration that should absorb vibration energy], the leaked vibration energy can be absorbed. An electrode structure of a piezoelectric resonator for overtone oscillation characterized by increased consumption. 2. Divide the electrodes attached to both sides of the vibration energy absorption part into a plurality of parts, and set the values of the resistances connected between the electrodes on both sides as (2πf _o1 C ₀ ) ^-1 , (2πf _o3 C ₀ ) ^-1 ,...
...[However, f _o1 , f _o3 , ... are respectively the fundamental wave frequency, 3
The electrode structure of a piezoelectric resonator for overtone oscillation according to claim 1, characterized in that the electrode structure of the piezoelectric resonator for overtone oscillation is made to substantially match the next overtone frequency, ...]. 3. The electrode structure of a piezoelectric resonator for overtone oscillation according to claim 1 or 2, characterized in that the electrode attached to the vibration energy trapping portion is divided to form a two-port resonator.