JP3102872B2 - Ultra-thin piezoelectric vibrator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultra-thin piezoelectric vibrator capable of obtaining a high resonance frequency ranging from several tens to several hundreds MHz by fundamental wave vibration.

(Prior Art) In recent years, demands for higher frequency and higher frequency stability have become strict in various electronic devices and communication devices, but general ATs which have been frequently used as piezoelectric devices (vibrators and filters) have been used in the past. Although the cut-quartz resonator has excellent temperature-frequency characteristics, its resonance frequency is inversely proportional to the plate thickness. Therefore, the limit is about 40 MHz from the viewpoint of manufacturing technology and mechanical strength.

A so-called overtone oscillator that extracts the harmonic component of the AT-cut crystal oscillator and obtains a frequency that is an odd multiple of the fundamental wave resonance frequency is also widely used. Therefore, there are disadvantages in that the oscillation circuit is disadvantageous in forming a semiconductor integrated circuit, and oscillation is sometimes difficult due to a large capacitance ratio and a high impedance level.

On the other hand, surface acoustic wave resonators whose resonance frequency is determined by the electrode finger pitch of the interdigital transducer
Although it has been possible to achieve an output of about the same degree, there has been a problem that the temperature-frequency characteristics of a piezoelectric substrate that can be used for this are significantly inferior to AT-cut quartz.

In order to solve the above-mentioned problems, piezoelectric resonators as shown in FIGS. 4A and 4B have been studied.

That is, this piezoelectric resonator is formed by machining or etching a concave portion 2 in the center of one side of the AT-cut quartz block 1.
Is formed, and the thickness of the vibrating portion 3 located on the bottom surface of the concave portion 2 is set to about 17 μm in order to obtain a fundamental wave resonance frequency of, for example, 100 MHz.

As a result of the formation of the concave portion 2, a thick annular surrounding portion (rib) 4 is formed integrally with the vibrating portion 3 on the peripheral surface of the ultra-thin plate-shaped vibrating portion 3 on the block surface on the concave portion 2 side. This mechanically supports the ultra-thin vibrating part.

The conductor film 5 is adhered to the entire surface including the concave inner side wall of the piezoelectric element having the above-described structure, and the partial electrode 6 and the electrode lead 7 extending therefrom are formed on the surface of the vibrating portion 3 on the opposite surface side by vacuum evaporation or the like. If the piezoelectric resonator is attached using a technique, a piezoelectric resonator having an extremely high resonance frequency can be obtained.

The main reason for attaching the conductive film 5 to the entire surface including the inner wall of the concave portion of the piezoelectric element is that forming the conductive film partially by a special deposition technique using a precise mask is complicated and reduces the production efficiency. However, on the other hand, since the entire recess 2 is covered with the conductive film 5, a capacitor is formed between the electrode lead 7 extending from the partial electrode 6 and the capacitance ratio of the entire piezoelectric resonator increases. However, there arises a problem that the width in which the frequency can vary becomes small.

That is, if the area of the electrode lead portion is increased in order to give sufficient conductivity to the electrode lead 7 extending from the partial electrode 6,
The large capacity C is formed due to the ultra-thin thickness of the vibrating part. When the large capacitance C is formed, the parallel capacitance C _O in the equivalent circuit of the piezoelectric resonator shown in FIG. 5 increases, and the capacitance ratio γ = C ₀ / C _{1 of} the piezoelectric resonator increases. Resonators of this type will have limited application to oscillator circuits that need to vary the oscillation frequency within a certain range, such as voltage controlled crystal oscillators (VCXOs), and even if they are not applied to multimode filter elements. If a relatively wide passband is required, a defect is expected that it is difficult to respond.

In order to solve such a problem, a method of preventing the conductive film from being attached to a portion corresponding to the lead of the entire surface electrode can be considered. However, for that purpose, vapor deposition using a mask is required, and a mask is not required for vapor deposition. This results in completely deteriorating the merits of the full-surface electrode configuration.

(Objects of the Invention) The present invention has been made in view of the above-mentioned problems expected in an ultra-thin piezoelectric resonator, and has a concave bottom formed on the surface of a piezoelectric block made of quartz or the like. In the ultra-thin piezoelectric vibrator used as the piezoelectric vibrating portion, the electrode and the electrode lead pattern face each other through the ultra-thin vibrating portion, thereby forming a capacitor and increasing the parallel capacitance of the resonator. It is an object of the present invention to provide an ultra-thin piezoelectric vibrator that can eliminate various inconveniences caused by the vibration.

(Summary of the Invention) In order to achieve the above object, an ultra-thin piezoelectric vibrator according to the present invention includes a thick annular surrounding portion of an electrode lead pattern extending from an electrode formed on one surface of an ultra-thin vibrating portion. It is characterized in that the corresponding part is sufficiently wider than the other parts.

Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

Prior to the description of the embodiments, in order to assist the understanding of the present invention, an electrode configuration such that the ultra-thin piezoelectric vibrator serving as the basis of the present invention is provided with a full-surface electrode in its concave portion and a partial electrode on its opposing surface side I will explain a little about whether to adopt.

First, from the viewpoint of the vacuum deposition technique, extending a partial electrode to the piezoelectric substrate recess side vibrating portion as described above, and extending a narrow electrode lead from the electrode over the inner wall and the step of the piezoelectric substrate, It is extremely difficult to use a troublesome method such as performing evaporation by inclining the electrode with respect to the horizontal plane, and it is extremely difficult to secure conduction of the electrode leads. It is something that can be secured.

Secondly, this type of resonator originally aims at miniaturization of the device, and the size of the piezoelectric substrate is desired to be, for example, 3 mm × 3 mm or less. In other words, a method is adopted in which a large number of chips are formed all at once in a batch process on one piezoelectric wafer, and the chips are finally cut into individual chips. In this case, if an electrode configuration of the type described above is employed, it is sufficient to simply deposit a conductor film over the entire surface of the wafer, and fine alignment of a photomask or photolithographic mask is not required. Thus, the yield can be improved and the cost can be reduced.

For the above reasons, it should be noted that the ultra-thin piezoelectric vibrator which has been studied in the past is basically based on attaching the entire surface electrode to the concave side surface.

However, when the electrode configuration as described above is used, a large-capacity capacitor is formed between the entire surface electrodes on the front and back sides of the vibrating portion and the electrode lead portion because the thickness of the vibrating portion is extremely small. As described above, the capacity ratio of the container becomes large, causing various inconveniences.

To solve this problem, the ultra-thin piezoelectric vibrator according to the present invention has the following electrode structure.

FIG. 1 is a plan view showing a basic configuration of the present invention,
The width of a portion 7a corresponding to the annular surrounding portion 4 of the electrode lead 7 extending from the counter electrode 6 on the surface facing the entire surface electrode formed on the concave 2 side of the ultra-thin piezoelectric block 1 is made wider.

The reason why the width of the electrode lead portion 7a located on the back surface of the annular surrounding portion 4 is widened while the width of the electrode lead portion 7b located on the vibration portion 3 is minimized as described above is because vibration The portion 3 has a very small thickness, and a large-capacity capacitor is formed if a large-area conductive film is present on both the front and back surfaces of the portion, whereas the annular surrounding portion 4 has a small thickness. This is because even if the conductor film is present on the front and back surfaces, the capacitance is not so large, and the capacitance ratio of the resonator is not considered to be significantly affected.
Also, by limiting the length of the thin electrode lead portion 7b, ohmic loss can be reduced.

In addition, as shown in FIG. 2, the ultra-thin piezoelectric vibrator as described above is provided with its recess 2 side on the inner bottom surface of a dish-shaped package 8 in which ceramics is sintered, for example, and is housed so as to face the conductive film 10. The entire surface electrode 5 on the side of the recess 2 is adhered and fixed to the conductor film 10 with a conductive adhesive 11 on one edge surface of the annular surrounding portion 4 and connected to the external lead terminal 12 of the package via the conductor film 10. On the other hand, the wide part 7a of the electrode lead 7 extending from the partial electrode 6 is connected to the conductor pad 14 provided on the step part on the inner wall of the package 8 which is connected to the lead terminal 13 on the outer wall of the package by the bonding wire 15. It is convenient to use.

As described above, the case where the present invention is applied to the piezoelectric vibrator has been described. However, the present invention can be similarly applied to an ultra-thin multi-mode filter. As is well known, the most frequently used dual mode piezoelectric filter among the multimode filters is that the whole surface electrode 5 on one main surface (in this case, the recess 2 side) of the piezoelectric substrate is used as a ground electrode and the divided proximity electrode 16 is provided on the opposite surface. And an alternating electric field is applied to both electrodes to generate acoustic coupling between the two electrodes. As a result, a band-pass filter is constructed using two vibration modes having different resonance frequencies to be excited. .

It is well known that the filter bandwidth of such a filter element also decreases as the equivalent parallel capacitance C _O increases, that is, as the capacitance ratio γ increases. Therefore, as shown in FIG.
The portions 17, 17 attached to the surface may be thin, and the portions 17a, 17a on the surface of the annular surrounding portion 4 may be wide.

In this way, a vibrator that obtains a resonance frequency of several tens to 100 MHz by the fundamental vibration or a filter element having this frequency as a center frequency is formed in a very small size, and these characteristics, particularly, the variable width of the resonance frequency are formed. , The bandwidth of the filter can be secured to a sufficiently large value.

(Effect of the Invention) Since the present invention is configured as described above,
The capacitance ratio of the ultra-thin piezoelectric vibrator or the filter element is kept at a low value, the variable width of the resonance frequency is sufficiently secured for the vibrator, and a wide pass band is provided for the filter element. Has a remarkable effect. Further, since the lead area on the surface of the resonator vibrating part is smaller than that of the electrode, the effect of generating unnecessary waves is also reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of an ultra-thin piezoelectric vibrator according to the present invention, FIG. 2 is a cross-sectional view showing an example of a packaging method of the ultra-thin piezoelectric vibrator according to the present invention, and FIG. Plan view showing an embodiment of an ultra-thin plate multi-mode filter element to which
4 (a) and 4 (b) are a perspective view and a sectional view taken along the line XX, respectively, showing the structure of an ultra-thin plate piezoelectric resonator which has been studied conventionally, and FIG. 5 is an equivalent circuit diagram of the resonator. . 1 ... ultra-thin plate piezoelectric block, 2 ... recess, 3 ... vibrating part, 4 ... annular surrounding part, 5 ... full-surface electrode, 6 ... partial electrode, 7 ... electrode lead, 7a ... wide part , 7b …… narrow part

Continuation of front page (56) References JP-A-62-185403 (JP, A) JP-A-61-3514 (JP, A) JP-A-61-3513 (JP, A) JP-A-58-219810 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H03H 9/00-9/215 H03H 9/54-9/60

Claims (2)

(57) [Claims] 1. A concave portion is provided on one surface of a piezoelectric block, so that an ultra-thin vibrating portion and a thick annular surrounding portion supporting the peripheral portion of the vibrating portion are integrally formed on the bottom surface of the concave portion, A whole surface electrode is formed on the concave side of the piezoelectric block, and a partial electrode and an electrode lead extending from the piezoelectric block to the edge of the piezoelectric block are provided on the opposing surface of the piezoelectric block facing the concave. An ultra-thin piezoelectric vibrator characterized in that a portion attached to the surface of the surrounding portion is a wide portion wider than other portions. 2. An ultra-thin vibrating portion and a thick annular surrounding portion for supporting the peripheral portion of the vibrating portion are integrally formed on the bottom surface of the concave portion by providing a concave portion on one surface of the piezoelectric block. A whole surface electrode is formed on the concave side of the piezoelectric block, and a partial electrode and an electrode lead extending from the piezoelectric block to the edge of the piezoelectric block are provided on the opposing surface of the piezoelectric block facing the concave. The portion attached to the surrounding portion surface is a wide portion wider than other portions, and the piezoelectric block is housed in the package such that the recess of the piezoelectric block faces the conductive film provided on the inner bottom surface of the package,
The whole surface electrode of the piezoelectric block is adhered and fixed to the conductive film with a conductive adhesive on one edge surface of the annular surrounding portion, and the wide portion of the electrode lead and the conductive pad provided in the package are bonded to a bonding wire. An ultra-thin piezoelectric vibrator characterized in that the piezoelectric vibrator is connected by connecting.