JP2003087089A - Piezoelectric device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric device, capable of preventing manufacturing yield from being reduced by decreasing the dispersion of an equivalent circuit constant, such as serial inductance which is generated in response to the deviation of substrate parallelism, in the device to be manufactured. SOLUTION: The piezoelectric device comprises an overall surface electrode formed over substantially the entire surface of a recess side of a piezoelectric substrate having a thin oscillation section, a thick annular surrounding section integrally constituted with the oscillation section to hold a periphery of the oscillation section by forming the recess at a predetermined position of one main surface, and a main electrode of a predetermined size formed in a region, corresponding to the oscillation section on other main surface of the substrate. The device further comprises at least one substrate thickness measuring electrode disposed at a predetermined distance from the main electrode, to evaluate a thickness of the substrate in the region corresponding to the oscillation section of the other main surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric device such as a piezoelectric vibrator and a manufacturing method thereof, and more particularly to a piezoelectric device formed as an ultrathin plate vibrator and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, an AT-cut crystal resonator utilizing thickness shear vibration has high frequency stability and is widely used in the field of communication equipment. Generally, the resonance frequency of a piezoelectric vibrator that utilizes thickness shear vibration is expressed by the following equation. f = k / t (1) where f is the resonance frequency, k is the elastic constant of the piezoelectric body, and t is the thickness of the piezoelectric body.

Therefore, in order to increase the resonance frequency by using this vibrator, the thickness t of the piezoelectric body may be made thin, but from the viewpoint of manufacturing technology (manufacturing accuracy) and mechanical strength,
The limit was the thickness at which a resonance frequency (fundamental vibration) of about MHz was obtained.

In recent years, an ultra-thin plate crystal oscillator that can generate a resonance frequency of about several hundred MHz by using the fundamental wave vibration of an AT-cut crystal oscillator has been put into practical use. FIG. 3 is a diagram showing a configuration example of an ultra-thin plate crystal resonator as a conventional piezoelectric device. FIG. 3 (a) is a plan view and FIG. 3 (b) is a sectional view taken along line AA ′.

The ultra-thin plate crystal oscillator shown in this example has a thin vibrating portion 32 and a thickness for holding the vibrating portion 32 around the thin vibrating portion 32 by recessing a predetermined portion of one main surface of the AT-cut quartz crystal substrate 31. A flesh annular surrounding portion 33 is integrally formed, and a full-surface electrode 34 is formed on almost the entire surface of the concave side. On the other main surface of the crystal substrate 31, a main electrode 35 having a predetermined size is arranged in a region corresponding to the vibrating portion 32, and the main electrode 35 is connected to a pad electrode 37 via a lead electrode 36. ing.

FIG. 4 is a sectional view of an essential part showing an example of a manufacturing process of the above-mentioned ultra-thin plate crystal resonator. In the manufacturing process of the ultra-thin plate crystal resonator shown in this example, first, as shown in FIG. 3A, a protective film 41 is formed on a predetermined portion on both main surfaces of the piezoelectric substrate 31 by photolithography, and then etching is performed. The same figure (b)
As shown in FIG. 3, the exposed portion of the piezoelectric substrate 31 is recessed to integrally form a thin plate-shaped vibrating portion 32 and a thick annular surrounding portion 33 that supports the periphery thereof.

Next, after the protective film 41 is peeled off, a conductor film is attached to the entire concave side by vapor deposition or the like to form a full-scale electrode 34, as shown in FIG. The main electrode 35, the lead electrode 36, and the pad electrode 37 are formed at predetermined positions by various methods.

[0008]

However, the conventional ultra-thin plate crystal resonator as described above has the following problems. In other words, in the ultra-thin plate crystal resonator, the substrate thickness of the vibrating part becomes thinner (tens of μm to several μm) as the resonance frequency becomes higher (more than 100 MHz). Get tougher. This substrate parallelism is
Depends on the polishing process before etching, and at the current state of the art, when processing a substrate of 20 mm square or more by batch processing, the parallelism of the substrate is limited to about 0.5 μm, and the substrate thickness of the thin vibrating part is limited. It is a large value on the order of several percent. This is about an order of magnitude larger than that of a piezoelectric vibrator with a relatively thick substrate in the 10MHz to 20MHz band. If the substrate parallelism is large (the substrate inclination is large), the distance between the entire surface electrode and the main electrode, that is, the thickness of the quartz substrate is not uniform, so the substrate thickness corresponding to the desired resonance frequency is limited to a very small area. Will be. Therefore, the total vibration energy cannot be extracted due to the reason that the vibration mode corresponding to the desired resonance frequency is biased to a part of the main electrode and excited, and the loss increases accordingly. As is well known, the equivalent series inductance of the equivalent circuit constants of a piezoelectric vibrator is equivalent to the value obtained by dividing the displacement energy of the entire vibrator (in this case, the entire thin vibration part) by the displacement energy of the electrode part. When the peak of the vibration energy deviates from the center of the electrode due to the non-uniform thickness of the portion, the displacement energy of the electrode portion decreases and the series inductance increases. The increase of the series inductance means that the series capacitance of the equivalent circuit is relatively decreased, and as a result, the capacitance ratio γ of the vibrator is increased. For example, when a voltage controlled piezoelectric oscillator (VCXO) is configured using a piezoelectric vibrator, the frequency variable width for the control voltage depends on the capacitance ratio γ, so the piezoelectric vibrator used for this has a uniform capacitance ratio γ. It is hoped that However, since the substrate parallelism of the piezoelectric vibrator varies during manufacturing, the capacitance ratio γ
Is not constant and a desired value cannot be stably obtained, so that there is a problem that the manufacturing yield is reduced. FIG. 5 is a diagram showing a configuration example of an ultra-thin crystal resonator for investigating the correlation between the substrate parallelism in the vibrating section and the equivalent circuit constant.
(a) is a plan view and (b) is a cross-sectional view of a main part. The ultra-thin plate crystal unit shown in this example is an AT with the structure shown in Fig. 3.
Main electrodes on the flat main surface of the cut crystal unit
Two conductor films 50a and 50b composed of 55a and 55b, lead electrodes 56a and 56b, and pad electrodes 57a and 57b are arranged to face each other. In order to obtain the resonance frequency of 100 MHz, the substrate thickness of the vibrating section 32 is 16.7 μm, the film thickness of each electrode is 50 nm, the area of the main electrodes 55a and 55b is 0.18 mm ² , and the main electrode interval is 0.1 mm. Figure 6
6 is experimental data showing series inductance with respect to substrate parallelism in the configuration of FIG. First, each main electrode 55a, 55b
The resonance frequency is measured, and from this, the board thickness of each main electrode portion is calculated back based on the above equation (1) to calculate the board parallelism and the series inductance at that time. As a result of performing the above measurement by manufacturing 50 crystal units as measurement samples, the series inductance tends to increase as the substrate parallelism increases (deteriorates) as shown in FIG. 6, with an average value of 0.68 mH, The standard deviation was 0.11 mH, and the variation in constant values (standard deviation / average value) was as large as about 16.4%. The present invention has been made to solve the problems relating to the piezoelectric device such as the conventional ultra-thin plate piezoelectric vibrator described above, and an equivalent circuit such as a series inductance generated according to the deviation of the parallelism of the substrates in the manufactured piezoelectric device. It is an object of the present invention to provide a piezoelectric device that can reduce the variation of the constant from a predetermined value and thus prevent the production yield from decreasing.

[0009]

In order to achieve the above object, the invention according to claim 1 of the piezoelectric device according to the present invention is such that a thin vibrating portion is formed by forming a recess at a predetermined location on one main surface. A full-scale electrode is formed on almost the entire concave side of the piezoelectric substrate integrally formed with a thick annular surrounding portion that holds the periphery thereof, and the vibrating portion is formed on the other main surface of the piezoelectric substrate. A piezoelectric device in which a main electrode having a predetermined size is formed in a region corresponding to, at least 1 in order to evaluate the thickness of the piezoelectric substrate in a region corresponding to the vibrating portion of the other main surface. One substrate thickness measuring electrode is arranged at a predetermined distance from the main electrode. The invention according to claim 2 of the piezoelectric device according to the present invention,
In the piezoelectric device described, the substrate thickness measuring electrode 2
The main electrodes were arranged as one set so as to be sandwiched between them. The invention according to claim 3 of the method for manufacturing a piezoelectric device according to the present invention is a thick-walled structure in which one principal surface of a piezoelectric substrate is depressed by a predetermined range to integrally hold a thin vibrating portion and its periphery. While forming the annular surrounding portion, the procedure of forming a full-scale electrode on the entire surface of the concave side, the procedure of forming a main electrode of a predetermined size in a region corresponding to the vibrating portion of the other main surface, and the other of the other. A procedure of forming at least one substrate thickness measuring electrode for evaluating the thickness of the piezoelectric substrate in a region corresponding to the vibrating portion of the main surface, and measuring the resonance frequency of each substrate thickness measuring electrode. The procedure includes a procedure and a procedure for adjusting the measured resonance frequencies to be substantially equal to each other.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on the illustrated embodiments. 1A and 1B are diagrams showing a first embodiment of an ultrathin plate AT-cut quartz crystal resonator according to the present invention. FIG. 1A is a plan view and FIG. 1B is a sectional view taken along line AA '. The crystal resonator shown in this example integrally includes a thin-walled vibrating portion 12 and a thick-walled annular surrounding portion 13 that holds the periphery of the vibrating portion 12 by recessing a predetermined portion of one main surface of the AT-cut quartz crystal substrate 11. The structure is such that a full surface electrode 14 is formed on almost the entire concave side of the crystal substrate 11. On the other main surface of the crystal substrate 11, a main electrode 15 having a predetermined size is arranged in a region corresponding to the vibrating portion 12, and the main electrode 15 is connected to a pad electrode 17 via a main lead electrode 16. Has been done.

Further, in order to evaluate the thickness of the vibrating portion 12 of the crystal substrate 11 within the area corresponding to the vibrating portion 12 on the other main surface, the first and second substrate thickness measuring electrodes 18a and 18b are mainly provided. The electrodes 15 are arranged with the electrodes 15 sandwiched therebetween, and the electrodes 15 are arranged respectively on the first and second lead electrodes 19
First and second probing electrodes 20a, 20b via a, 19b
Connect to. At this time, it is desirable that the substrate thickness measuring electrodes 18a and 18b are arranged at a predetermined distance so as not to affect the vibration excited by the main electrode 15.

Since the basic manufacturing process of the piezoelectric device according to the present invention is the same as the conventional one, the description thereof will be omitted. However, in the present invention, the first and second substrate thickness measuring electrodes 18a and 18b are used. The feature is that the substrate thickness of the vibrating section 12 is evaluated, the substrate parallelism is calculated based on the evaluation, and the parallelism is adjusted. Hereinafter, this will be described in detail.

First, the first (second) substrate thickness measuring electrode 18a (18
The resonance frequency f1 (f2) related to b) is set to the first (second) lead electrode 19
First (second) probing electrode 20a (20b) via a (19b)
To measure. If the vibrating part 12 is tilted, f1 ≠
It becomes f2.

Therefore, the plate thickness of the vibrating portion 12 on the substrate thickness measuring electrode (here, 18a) side exhibiting a high resonance frequency (thin substrate thickness) may be increased. In practice, it is difficult to make the crystal substrate thick, so a conductor film corresponding to the plate thickness of the recess side electrode is added by vapor deposition or the like. As is well known, the resonance frequency of the crystal unit is determined by the thickness of the substrate including the electrode film.Therefore, by attaching the conductor film 14a so that f1 = f2 as shown in FIG. The vibrating section is equivalent to the achievement of a predetermined parallelism, and as a result, it is possible to reduce the variation in the equivalent circuit constant related to the deviation in the parallelism of the substrate. In fact, by oblique vapor deposition that tilts the quartz substrate at the time of film formation and devising a mask pattern,
Weighting of film thickness can be realized.

Next, in order to adjust the resonance frequency to the design value f0, a conductor film is uniformly vapor-deposited on the entire surface of the recess side electrode so that f1 = f2 = f0. Since such frequency adjustment is performed, it is general that the thickness of the vibrating portion is previously etched to be thinner than the designed value.

With the above-described structure of the substrate thickness measuring electrode and the manufacturing process, it is possible to reduce the variation in the equivalent circuit constant related to the parallelism of the substrate, and thus to prevent the manufacturing yield from decreasing. Actually, when 50 piezoelectric devices according to the present invention were manufactured and the series inductance was measured, an average value of 0.51 mH and a standard deviation of 0.
It becomes 005 mH and the constant value variation (standard deviation / average value) is about 1.1%
Therefore, it was confirmed that it could be improved by an order of magnitude compared to the past.

In the above-described embodiment, the two substrate thickness measuring electrodes 18a and 18b are used, but if the main electrode 15 is also used for this substrate thickness measurement, the substrate thickness measuring electrode is 1 One good thing is that it doesn't require any explanation.

In the above-described embodiment, an example in which the parallelism in the x direction of the AT-cut quartz crystal substrate is evaluated and adjusted is explained. However, in actuality, the substrate inclination may occur also in the z direction. . 2A and 2B are diagrams showing a second embodiment of the piezoelectric device according to the present invention. FIG. 2A is a plan view and FIG. 2B is a sectional view taken along the line AA '. Since the AT-cut crystal unit shown in this example evaluates the substrate parallelism two-dimensionally, in the configuration of the first embodiment example shown in FIG. 1, the third substrate thickness measuring electrode 18c is further used as a main component. The electrode 15 is arranged on the right side of the electrode 15 at a predetermined interval, and this is placed via the third lead electrode 19c.
It is connected to a third probing electrode 20c arranged below the second probing electrode 20b.

The manufacturing process of the crystal unit and the method for evaluating the substrate parallelism shown in this example are performed in the same manner as in the above-described first embodiment, but the first and second substrate thickness measuring electrodes 18a and 18b are used. In addition to the evaluation of the substrate parallelism in the x direction by using, the substrate parallelism in the z direction is also evaluated using the third substrate thickness measuring electrode 18c and the main electrode 15, so that these substrate thicknesses can be adjusted. did.

In short, in order to evaluate the substrate parallelism of the vibrating portion, at least two electrodes including the main electrode are arranged at predetermined positions in the crystal unit according to the present invention, and the resonance frequency of each is measured. The substrate thickness is back-calculated from the equation (1) to evaluate the substrate parallelism, and the required portions are adjusted in thickness by conductor film deposition or the like to achieve the required substrate parallelism.

As the piezoelectric device according to the present invention, not only a vibrator using an AT-cut quartz substrate but also Langasite (La3Ga5SiO1) as a piezoelectric substrate that can be etched is used.
A piezoelectric substrate such as 4) or lithium tetraborate (Li2B4O7) may be used, and it can be applied to any piezoelectric device such as a monolithic filter. Instead of attaching the conductive film to the thin side of the substrate, dry etching using an ion beam or an electron beam may be performed in order to reduce the thickness of the electrode on the thick side, or a combination thereof may be used.

[0022]

As described above, according to the present invention, a predetermined number of electrodes for measuring substrate thickness are provided on the flat main surface, the resonance frequency is measured, the substrate thickness is calculated backward, and the substrate parallelism is evaluated based on this. At the same time, by adjusting the thickness of the required film by vapor deposition of a conductor film, etc., it was possible to achieve a predetermined substrate parallelism.
The variation of the equivalent circuit constants due to the deviation of the parallelism of the substrate can be reduced, and thus it is remarkably effective in realizing the piezoelectric device in which the reduction of the manufacturing yield is prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment example of a piezoelectric device according to the present invention.

FIG. 2 is a diagram showing a second embodiment of a piezoelectric device according to the present invention.

FIG. 3 is a diagram showing a configuration example of a conventional ultrathin plate crystal resonator as a piezoelectric device.

FIG. 4 is a sectional view of an essential part showing an example of a manufacturing process of an ultra-thin plate crystal resonator as a conventional piezoelectric device.

FIG. 5 is a diagram showing a configuration example of an ultrathin plate piezoelectric vibrator for investigating a correlation between substrate parallelism and an equivalent circuit constant in a vibrating section.

[Fig. 6] Experimental data showing the relationship between the parallelism of the vibrating part and the equivalent circuit constant (series inductance)

[Explanation of symbols]

11 ... Crystal substrate 12 ... Vibrating section 13 ··· Circular enclosure 14 ... Full surface electrode 15 ... Main electrode 16 ... Main lead electrode ..Pad electrodes 18a, 18b, 18c ... First, second and third substrate thickness measuring electrodes 19a, 19b, 19c ... First, second and third lead electrodes 20a, 20b, 20c ... First, second and third probing electrodes

Claims (3)

[Claims] 1. A piezoelectric substrate which is integrally formed with a thin vibrating portion and a thick annular surrounding portion for holding the vibrating portion by forming a concave portion at a predetermined position on one main surface. In the piezoelectric device, a full-scale electrode is formed on the main surface of the piezoelectric substrate, and a main electrode having a predetermined size is formed in a region corresponding to the vibrating portion on the other main surface of the piezoelectric substrate. In order to evaluate the thickness of the piezoelectric substrate, at least one substrate thickness measuring electrode is arranged at a predetermined distance from the main electrode in a region corresponding to the vibrating part of the piezoelectric device. 2. The piezoelectric device according to claim 1, wherein two electrodes for measuring the substrate thickness are set as one set and the main electrode is arranged so as to be sandwiched therebetween. 3. A piezoelectric body substrate is formed by recessing one main surface in a predetermined range to form a thin vibrating portion and a thick annular surrounding portion integrally holding the vibrating portion, and the entire surface on the concave side. A step of forming a full surface electrode on the other main surface, a step of forming a main electrode of a predetermined size in a region corresponding to the vibrating portion of the other main surface, and a step of forming the piezoelectric electrode in a region corresponding to the vibrating portion of the other main surface. A procedure for forming at least one substrate thickness measurement electrode for evaluating the thickness of the body substrate, a procedure for measuring the resonance frequency of each of the substrate thickness measurement electrodes, and the measured resonance frequencies are substantially equal to each other. A method for manufacturing a piezoelectric device, which comprises the steps of: