JP5527442B2 - Vibrator and oscillator - Google Patents

Description

  The present invention effectively eliminates the problem that the resonance frequency of a piezoelectric vibration element hermetically sealed in a state where it is fixed in an insulating container with a silicone-based conductive adhesive decreases with time without causing a decrease in productivity. The present invention relates to a piezoelectric vibration element, a piezoelectric vibrator, a piezoelectric oscillator, a frequency stabilization method, and a piezoelectric vibrator manufacturing method that can be solved.

A surface mount type piezoelectric device having a structure in which a piezoelectric vibration element is hermetically sealed in an insulating container, such as a crystal resonator, is a reference frequency generation source in communication equipment such as a mobile phone and a pager, and electronic equipment such as a computer. Although these are used as filters, etc., miniaturization is also required for piezoelectric devices in response to miniaturization of these various devices.
In addition, a piezoelectric oscillator as a piezoelectric device for surface mounting is a concave in a state where a piezoelectric vibration element and a circuit component constituting an oscillation circuit are housed in a recess formed on the upper surface of an insulating container body made of, for example, ceramic. The opening is sealed with a metal lid.
The piezoelectric vibration element has a structure in which a metal film constituting an excitation electrode and a lead electrode is formed on the surface of a piezoelectric substrate, and the piezoelectric vibration element is formed on the internal electrode in an insulating container for surface mounting with a silicone-based conductive adhesive. The container is hermetically sealed in a state of being held using (hereinafter referred to as a silicone adhesive).
FIG. 4 shows a phenomenon in which the resonance frequency of the quartz resonator element hermetically sealed in the insulating container decreases. As is clear from FIG. 4, the frequency decrease does not occur suddenly, but gradually with time. It can be seen that the frequency decreases.
In other words, the tendency hardly appears when the piezoelectric device manufacturer manufactures the crystal unit, but the piezoelectric device is mounted on the printed circuit board by the assembly manufacturer, and when the product is put on the market, the frequency drop appears on the surface. The troublesome situation of doing appears.
Furthermore, it has been found that the tendency of frequency reduction appears strongly after a reflow process for mounting a piezoelectric device on a printed circuit board by an assembly manufacturer. In addition, there is also a fact that the frequency of occurrence of the frequency decrease is increasing with the recent miniaturization of the quartz crystal vessel due to the demand for miniaturization.
However, although various inferences have been made about the causes of these phenomena, no clear factor has been grasped and no fundamental solution has been made.
For example, Japanese Patent Application Laid-Open No. 7-154187 discloses a technique aimed at solving an aged frequency decrease phenomenon of a crystal resonator.
This publication considers that the cause of the frequency reduction phenomenon of the crystal unit over time is the oxidation phenomenon that occurs on the surface layer of the metal film that constitutes the electrode. A solution is disclosed in which a protective film is formed by attaching a film (SiO ₂ film) and covering the entire surface thereof, or by previously oxidizing, nitriding or carbonizing the surface layer of the metal film.
It should be noted that this oxidation phenomenon occurs only in the nickel portion deposited up to the surface layer of the gold film when a nickel underlayer is provided under the gold film. Gold parts other than the nickel part are stable and do not oxidize.

However, this conventional technique has many problems as follows. That is, when the SiO ₂ film is formed and covered on the surface of the metal film by vapor deposition or the like, strict thickness control is required. While the SiO ₂ film is poor in adhesion with gold and easily peeled off, if the film thickness is increased so that the SiO ₂ film does not peel from the gold surface, residual stress is generated in the vibrator due to the film stress. That is, distortion occurs due to temperature change, leading to deterioration of temperature characteristics. Furthermore, when a protective film such as an oxide film, a nitride film, or a carbonized film is formed on the gold film surface, the film is formed only on the portion where nickel is deposited. Since there is a variation in the area of the individual, there is a variation in mass addition by the protective film, and a frequency adjustment is required. Since a protective film is not formed on the gold film portion on which nickel is not deposited, the phenomenon of aging frequency reduction after sealing is not eliminated for the reason described later in the description of the embodiment (silicon molecules are gradually added to the gold film portion. To chemisorb).
In other words, it was found that the oxidation of the nickel portion partially or irregularly deposited on the gold film surface is one cause of the frequency decrease but not the fundamental cause. Therefore, the solution proposed by the above publication is not sufficient.
In addition, in order to delay the speed at which the resonance frequency after hermetic sealing decreases, it is possible to extract silicone vapor from the inside of the insulating container before sealing (so-called annealing), but even if degassing is performed once, As long as the silicone adhesive is present in the container, silicone vapor is generated and gradually adheres to the excitation electrode film, resulting in frequency fluctuations. Although it is conceivable to change the type of adhesive, a silicone adhesive is extremely useful in order to satisfy the specifications of impact resistance, and at present there is no adhesive superior to a silicone adhesive.

JP 7-154187 A

The present invention has been made in view of the above, and grasps the cause of an aged frequency decrease phenomenon of a piezoelectric vibrator and seeks a fundamental solution to prevent the frequency decrease, and the frequency is increased over time. Is to provide a stable crystal resonator.
Specifically, the present invention relates to a piezoelectric device having a structure in which the piezoelectric vibration element is hermetically sealed in a state where the piezoelectric vibration element is held in the insulating container by the conductive bonding member. To provide a piezoelectric vibration element, a piezoelectric vibrator, a piezoelectric oscillator, and a frequency stabilization method capable of solving the problem that the resonance frequency lowers over time from the final target frequency by being deposited on the metal film It is an object.

In order to achieve the above object, a first embodiment of the present invention includes a substrate provided with an excitation electrode on a main surface thereof, and a container in which the substrate is accommodated, wherein the excitation electrode is dangling. Gold having a bond is exposed on the surface, and the gold is characterized by a vibrator covered with a monomolecular film by chemical adsorption between the dangling bond and a dimethylpolysiloxane molecule having a non-bonded electron pair. To do.
In addition, the second embodiment of the present invention is characterized by the vibrator according to the first embodiment in which the gold base film is nickel or chromium.
In addition, the third embodiment of the present invention is characterized by the vibrator of the first or second embodiment in which the dimethylpolysiloxane molecule is a cyclic molecule.
In the fourth embodiment of the present invention, the vibrator according to any one of the first to third embodiments is characterized in that a substance having a non-bonded electron pair is disposed inside the container. It is characterized by.
Further, the fifth embodiment of the present invention is characterized in that the dimethylpolysiloxane molecule is the vibrator according to the fourth embodiment, which is a component evaporated from the substance.
In addition, the sixth embodiment of the present invention is characterized by the vibrator of the fourth or fifth embodiment in which the substance is included in a conductive bonding member.
In addition, the seventh embodiment of the present invention is characterized by the vibrator according to any one of the fourth to sixth embodiments, wherein the substance is a silicone-based adhesive.
The eighth embodiment of the present invention is characterized in that the container is the vibrator according to any one of the first to seventh embodiments in which the container is hermetically sealed.
The ninth embodiment of the present invention is characterized by an oscillator including the vibrator of any one of the first to eighth embodiments and an oscillation circuit.
[Application Example 1] A piezoelectric vibration element according to this application example includes a piezoelectric substrate made of a thickness-slip type piezoelectric material and a metal film formed on the surface of the piezoelectric substrate. The film is covered with a film formed by chemisorption with a substance having a non-bonded electron pair.
Application Example 2 A piezoelectric vibration element according to this application example is a piezoelectric vibration element including a piezoelectric substrate and a metal film formed on the surface of the piezoelectric substrate, wherein the metal film surface has a non-bonded electron pair. The film is covered with a film formed by chemical adsorption, and even if a film is further formed on the surface of the metal film that is not covered with the film, the resonance frequency is reduced substantially less than 1 ppm so that the amount of decrease in resonance frequency is less than 1 ppm. Is covered with the film.
Application Example 3 A piezoelectric vibrator according to this application example includes the piezoelectric vibration element according to Application Example 1 or 2, and a container in which the piezoelectric vibration element is hermetically sealed.
Application Example 4 A piezoelectric vibrator according to this application example is accommodated in a state where the piezoelectric vibration element according to Application Example 1 or 2 and the piezoelectric vibration element are held using a silicone-based conductive adhesive. And a container hermetically sealed in an inert gas.
Application Example 5 A piezoelectric oscillator according to this application example is characterized in that an oscillation circuit component is disposed inside or outside the container described in Application Example 3 or 4.
[Application Example 6] The frequency stabilization method for a piezoelectric vibration element according to this application example is such that a piezoelectric vibration element having a metal film on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material is placed in an atmosphere of cyclic dimethylpolysiloxane vapor. The cyclic dimethylpolysiloxane molecules are chemically adsorbed on the surface of the metal film to form a film of the cyclic dimethylpolysiloxane molecules.

Application Example 7 A piezoelectric vibrator according to this application example includes a piezoelectric vibration element including a piezoelectric substrate made of a thickness-slip type piezoelectric material and a metal film formed on the surface of the piezoelectric substrate. In the piezoelectric vibrator held therein, the surface of the metal film exposed in the atmosphere is covered with a film formed by chemical adsorption with a substance having a non-bonded electron pair.
Application Example 8 A piezoelectric vibrator according to this application example is a piezoelectric vibrator held in a container by a piezoelectric vibration element conductive bonding member including a piezoelectric substrate and a metal film formed on the surface of the piezoelectric substrate. The surface of the metal film exposed in the atmosphere is covered by a monomolecular film formed by chemical adsorption with a substance having a non-bonded electron pair, and the surface of the metal film not covered by the film is further monomolecular. Even when the film is formed, almost the entire surface of the metal film is covered with the monomolecular film so that the decrease amount of the resonance frequency is less than 1 ppm.
[Application Example 9] In the piezoelectric vibrator according to this application example, the resonance frequency in the application example 8 in which the area occupied by the monomolecular film on the entire surface of the metal film corresponds to 100% of the entire surface of the metal film. Matches the target frequency in the atmosphere.
Application Example 10 A piezoelectric vibrator according to this application example is characterized in that the piezoelectric vibration element according to Application Example 1 or 2 is hermetically sealed in a container.
[Application Example 11] A piezoelectric vibrator according to this application example is accommodated in a state where the piezoelectric vibration element according to Application Example 1 or 2 is held using a silicone-based conductive adhesive and in an inert gas atmosphere. It is hermetically sealed.
Application Example 12 A piezoelectric oscillator according to this application example is characterized in that an oscillation circuit component is disposed inside or outside the container described in Application Example 7, 8, 9, 10 or 11.

[Application Example 13] A frequency stabilization method for a piezoelectric vibration element according to this application example is an annular structure in which a piezoelectric vibration element having a metal film on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material is held in a container. A monomolecular film of the cyclic dimethylpolysiloxane molecules is formed by chemical adsorption of the cyclic dimethylpolysiloxane molecules on the surface of the metal film exposed in the atmosphere by being placed in an atmosphere of dimethylpolysiloxane vapor. To do.
[Application Example 14] In the frequency stabilization method for a piezoelectric resonator element according to this application example , in the application example 13, the monomolecular film further includes a film formed on the surface of the metal film not covered with the monomolecular film. Is characterized by covering almost the entire surface of the metal film so that the amount of decrease in the resonance frequency is less than 1 ppm.
Application Example 15 A method for stabilizing the frequency of a piezoelectric vibration element according to this application example is a container in which a piezoelectric vibration element in which a metal film is formed on a piezoelectric substrate surface made of a thickness sliding piezoelectric material is held by a silicone adhesive. A cyclic dimethylpolysiloxane liquid is dropped into the surface to seal the surface mounting container, thereby chemically adsorbing the cyclic dimethylpolysiloxane molecules on the exposed metal film surface to form a film of the cyclic dimethylpolysiloxane molecules. It is characterized by that.

[Application Example 16] In the frequency stabilization method according to this application example , in the application example 15, the monomolecular film has a resonance frequency even when a film is further formed on the surface of the metal film not covered with the monomolecular film. It is characterized by covering almost the entire surface of the metal film so that the amount of decrease is less than 1 ppm.
Application Example 17 In the method of manufacturing a piezoelectric vibrator according to this application example, a piezoelectric vibration element in which a metal film is formed on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material is held in a container by a conductive bonding member. A holding step; a frequency adjusting step for adding or reducing the thickness of the metal film to adjust the resonance frequency of the piezoelectric vibration element to a predetermined value; and the container holding the piezoelectric vibration element has a non-bonded electron pair. An adsorption process in which a substance having a non-bonded electron pair is chemisorbed on a metal film exposed by leaving it in an atmosphere filled with vapor of the substance, and the container is hermetically sealed in a state where the inert gas atmosphere is substituted. And a sealing step.
[Application Example 18] In the method of manufacturing a piezoelectric vibrator according to this application example, a piezoelectric vibration element in which a metal film is formed on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material is placed in a container with a silicone-based conductive adhesive. A holding step for holding, a frequency adjusting step for adding or reducing the thickness of the metal film in order to adjust the resonance frequency of the piezoelectric vibration element to a predetermined value, and the container hermetically sealed in a state replaced with an inert gas atmosphere And an adsorption step of chemically adsorbing a substance having a non-bonded electron pair evaporating from the silicone adhesive to the metal film by heat-treating the hermetically sealed container for a predetermined time. Features.
[Application Example 19] A method of manufacturing a piezoelectric vibrator according to this application example includes a piezoelectric vibration element in which a metal film is formed on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material, and a silicone-based conductive adhesive in a container. A holding step for holding, a frequency adjusting step for adding or reducing the thickness of the metal film in order to adjust the resonance frequency of the piezoelectric vibration element to a predetermined value, and the container hermetically sealed in a state replaced with an inert gas atmosphere And an adsorption step of chemically adsorbing a substance having a non-bonded electron pair evaporating from the silicone-based adhesive by leaving the hermetically sealed container in a temperature K atmosphere for a time T or longer. The relationship between the temperature K and the time T satisfies T = 24294e ^−0.0251K .
[Application Example 20] A method for manufacturing a piezoelectric vibrator according to this application example includes a piezoelectric vibration element in which a metal film is formed on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material, and a silicone-based conductive adhesive in a container. A holding step for holding, a frequency adjusting step for adding or reducing the thickness of the metal film to adjust the resonance frequency of the piezoelectric vibration element to a predetermined value, and a substance having a non-bonded electron pair in the container are placed. And a sealing step for hermetically sealing the container in a state replaced with an inert gas atmosphere, and heating to a temperature necessary for evaporation of a substance having a non-bonded electron pair for a predetermined time to perform non-bonding An adsorption step of chemically adsorbing a substance having an electron pair to a metal film.

  Silicone conductive adhesive with excellent impact resistance as a means for fixing the piezoelectric vibration element in the insulating container is extremely useful, while the silicone vapor component released from the silicone adhesive when the insulating container is hermetically sealed. If it adheres and accumulates on the metal film of the piezoelectric vibration element, the resonance frequency decreases with time over the final target frequency, which may cause malfunction of the device equipped with the piezoelectric device. According to the present invention, a film composed of silicone molecules is formed on a metal film within a very short time of several seconds to several minutes by a low-cost apparatus and method using simple equipment and procedures to saturate the adsorption amount of silicone molecules. Therefore, the piezoelectric vibration element, the piezoelectric vibrator, the piezoelectric oscillator, the frequency stabilization method, and the conventional problem can be solved without stopping the decrease in the resonance frequency and stabilizing, and causing the decrease in productivity. A method for manufacturing a piezoelectric vibrator can be provided.

(A) is sectional drawing which shows the structure of the crystal oscillator as an example of the surface mount-type piezoelectric oscillator which concerns on one Embodiment of this invention, (b) is the principal part expansion explanatory drawing. (A) thru | or (d) is explanatory drawing which shows the manufacturing process including the process of forming a silicone monomolecular film | membrane on the excitation electrode film | membrane of a quartz-crystal vibrating element in this invention. (A) thru | or (c) is a figure which shows the relationship between ambient temperature and the period until the frequency of a piezoelectric vibration element reaches a stable area | region. Explanatory drawing which shows the phenomenon in which the resonant frequency of the crystal vibration element airtightly sealed in the insulating container falls.

Prior to the description of the embodiment, the background of the present invention will be described.
That is, as described above, conventionally, there has been known a phenomenon in which the frequency of the quartz vibration element hermetically sealed in the container continues to decrease over time, but the cause has not been investigated. Therefore, as a method for solving such a problem, a measure for how to delay the speed of decreasing the frequency has been studied so far.
In response to this situation, the present inventors have continued to investigate the cause of the decrease in frequency, but in a test for accelerating aging (accelerated aging test) performed in the course of the research, the frequency reaches a predetermined value. We found for the first time that there was a stable region after the drop, and found that once the frequency stable region was reached, no further frequency fluctuations occurred. Based on this discovery, the present inventors have come up with a processing method in which the frequency of the crystal resonator element before shipment is quickly reduced to reach the stable region before shipment.
That is, as shown in FIG. 3, the period until reaching the stable region becomes shorter as the ambient temperature is increased. From this, it was found that the conventional piezoelectric device has a remarkable frequency reduction phenomenon after heating for reflow.
However, when the heating temperature exceeds 230 ° C., the silicone adhesive may be deteriorated. Therefore, it is desirable to heat at 230 ° C. or lower. When the temperature actually exceeds 230 ° C., FIG. It has been confirmed that even after reaching the frequency stable region as shown in (a), a phenomenon in which the frequency continues to decrease below that frequency occurs.
From this, it was found that a crystal resonator with little frequency fluctuation over time can be obtained by performing heat treatment at a temperature of 230 ° C. or lower until reaching the frequency stable region.

In the method using heat treatment, it was confirmed that the resonance frequency of the crystal resonator reached the frequency stable region by leaving it at 230 ° C. for 70 hours. On the other hand, such a heat treatment method has low production efficiency.
As a result of further investigation based on the above research results, the present inventors have constituted a silicone resin conductive adhesive for adhering the crystal resonator element on the electrode in the container as the cause of the frequency decrease phenomenon over time. Found that the increase in mass due to the chemical adsorption of silicone molecules (cyclic dimethylpolysiloxane molecules: dimethylpolysiloxane 4 to 7 polymerized) evaporated from the silicone resin on the crystal film is found. It was. Then, since the concentration of silicone molecules is easily set higher in a narrow sealed space, the cause of occurrence of a phenomenon in which the frequency lowering phenomenon becomes conspicuous with the miniaturization of the crystal resonator container has been found.
In addition, the phenomenon found by the present inventor that the period for reaching the frequency stable region by heat treatment is shortened is clearly caused by the accelerated evaporation of silicone molecules from the silicone resin by heating. became.
However, the heat treatment method requires 70 hours at 230 ° C. at the shortest, so that the production efficiency is poor.
Accordingly, the present inventors have devised a technique for attaching silicone molecules to a metal film at a stretch by exposing a quartz crystal vibrating element housed in an open container to an atmosphere filled with silicone vapor. It was.
According to this method, it has been found that the frequency of the crystal resonator element reaches the frequency stable region within a few seconds, which can be said to be a mass production method.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
FIG. 1A is a cross-sectional view showing a configuration of a crystal oscillator as an example of a surface-mount piezoelectric oscillator according to an embodiment of the present invention, and FIG. 1B shows a state of the surface of an excitation electrode film at a molecular level. FIG.
This crystal oscillator (piezoelectric oscillator) is provided with an insulative container 1 (for example, a ceramic) having a substantially H-shaped longitudinal cross-section with recesses 2 and 3 at the top and bottom and four mounting terminals 5 on an annular bottom surface 4. Container) and two excitation electrode films 21 on a quartz vibrating element (piezoelectric vibrating element) 12 made of, for example, an AT-cut quartz plate as a thickness-slip type piezoelectric material on two internal pads 11 provided in the upper recess 2. A metal lid 15 that hermetically seals the upper recess 2 in an electrically and mechanically connected state using a silicone-based conductive adhesive (hereinafter referred to as a silicone adhesive) 13 and a ceiling of the lower recess 3. A lower pad 6 arranged on the surface 3 a and connected to each internal pad 11 and each mounting terminal 5, and an IC component 25 constituting an oscillation circuit mounted on the lower pad 6 are provided.
Of the mounting terminals 5, the crystal oscillator side mounting terminal is electrically connected to one of the internal pads 11.
The upper part of the insulating container 1 having the upper recess 2, the internal pad 11, the crystal resonator element 12, and the metal lid 15 constitute a crystal resonator (piezoelectric resonator). That is, the quartz resonator is electrically and mechanically connected to the internal electrode 11 in the upper recess 2 of the insulating container 1 made of an insulating material such as ceramic by using a silicone adhesive 13 to insulate. The inside of the recess 2 is hermetically sealed by electrically and mechanically connecting a metal lid 15 to the conductor ring on the upper surface of the outer wall of the container 1 by welding or the like. The quartz resonator element 12 includes an excitation electrode film (metal film) 21 made of a metal material such as gold on both the front and back surfaces of a quartz substrate (piezoelectric substrate) 20 that is a thickness-slip piezoelectric material, and the excitation electrode film 21 from the substrate edge to the substrate edge. It has a configuration in which an extended lead electrode 22 is formed.

As described above, the cause of the phenomenon in which the frequency decreases over time after the quartz resonator element is hermetically sealed in the container has not been clarified so far. However, as a result of research by the present inventor, it is generated from the silicone adhesive 13. It is considered that the cause is that the silicone molecules in the cyclic dimethylpolysiloxane vapor (hereinafter referred to as silicone vapor) filled in the container gradually chemisorbs on the surface of the excitation electrode film.
In other words, the silicone adhesive 13 is a conductive adhesive in which a silver filler is mixed in a silicone resin. At room temperature, the silicon oscillator 13 is heated when the crystal oscillator is mounted on the motherboard by reflow, and the IC component 25 is flipped. Silicone vapor is also released from the silicone resin by heating during chip mounting. The released silicone vapor diffuses into the insulating container 1 sealed with the lid 15 as described above. The silicone molecule 30 having a non-bonded electron pair has a property of easily adsorbing to the metal surface constituting the excitation electrode film (metal film) 21, and when the silicone molecule film is adsorbed on the excitation electrode film surface more than a predetermined amount, This causes a problem that the oscillation frequency of the crystal oscillator as a finished product decreases with time. Such a problem occurs more remarkably in the present situation where the insulating container is miniaturized and the internal volume is minimized.

As a first embodiment of the present invention for solving such problems, an early frequency stabilization method by heating before shipment is provided. That is, in this early stabilization method, the piezoelectric device is in a sealed state at a temperature higher than room temperature, preferably a temperature exceeding the boiling point of the silicone molecule (for example, 188 ° C. for D3) and lower than the thermal decomposition temperature of silicone. For example, by performing heat treatment at 230 ° C. for 70 hours or more, silicone vapor can be actively ejected from the silicone adhesive in an airtightly sealed insulating container, so compared with the case of natural aging It is possible to increase the amount of silicone molecules adsorbed on the surface of the excitation electrode film per unit time by increasing the concentration of silicone vapor in a short time. As a result, the time required to reach the frequency stable region (state) can be greatly shortened, the time to shipment can be shortened, and the total productivity can be increased.
That is, in the first embodiment, an excitation electrode film as a metal film (a structure in which nickel or chromium is used as a base film and gold is formed on a surface layer) on a piezoelectric substrate surface made of a thickness-slip type piezoelectric material such as the quartz substrate 20. A holding step of holding the crystal resonator element (piezoelectric resonator element) 12 formed with 21 in the container 1 with a silicone adhesive (conductive bonding member) 13, and a resonance frequency of the crystal resonator element 12 at a predetermined value (when completed) A frequency adjusting step for adding or reducing the thickness of the excitation electrode film 21 to adjust to a value higher than the resonance frequency of the crystal resonator element, and a sealing step for hermetically sealing the container 1 in a state where the thickness is replaced with an inert gas atmosphere. An adsorption step of chemically adsorbing a substance (silicone molecule) having non-bonded electron pairs evaporating from the silicone adhesive to the excitation electrode film by subjecting the hermetically sealed container 1 to heat treatment for a predetermined time; Performed sequentially.

FIG. 3A shows the relationship between the difference in heating temperature and the fluctuation characteristics of the resonance frequency in a crystal resonator element having a resonance frequency of 26 MHz. FIG. 3B shows the result of measuring the time until the resonance frequency of the crystal resonator element reaches a substantially constant value (resonance frequency at which the frequency is reduced by about −4 ppm from the start of heating) during heating. FIG.3 (c) plots the measurement result shown in FIG.3 (b), and drawn the approximate line which shows the relationship between heating temperature and heating time.
As shown in FIG. 3A, when the heating temperature is 230 ° C. or lower, the resonance frequency tends to decrease immediately after the start of heating, but when the specific time has elapsed, the amount of decrease in the resonance frequency decreases, There was a tendency for the resonance frequency to stabilize over time.
Further, when the heating temperature is 230 ° C. or less, the amount of decrease in frequency until stabilization is the same regardless of the heating temperature. For example, in the case of a resonance frequency of 26 MHz, the amount of decrease in frequency until stabilization is about − It was 4 ppm.
On the other hand, when the heating temperature is higher than 230 ° C., for example, when the heating temperature is 250 ° C., 270 ° C., or 300 ° C., a sudden frequency decrease occurs after the start of heating, and the frequency is stabilized after the same frequency decrease amount. There was no such tendency.
Therefore, it can be seen from this result that if the crystal resonator element is heated at least at 230 ° C. or less, there is a heating time necessary for the frequency to stabilize after the frequency is lowered by a specific frequency.
Therefore, as a result of measuring the time required until the resonance frequency was stabilized (in a state where the resonance frequency was lowered by −4 ppm) under each heating temperature condition, values as shown in FIG. 3B were obtained.
Further, based on the numerical data shown in FIG. 3 (b), the relationship between the heating temperature and the time required for frequency stabilization is shown by an approximate line as shown in FIG. 3 (c).
And the relationship between the heating temperature K and the time required for frequency stabilization from the approximate line is
T = 24294e ^{-0 ・ 0251K}
It was confirmed that
That is, as a heat treatment method in this adsorption step, specifically, for example, a silicone-based conductive adhesive (conductive bonding member) is formed by leaving the hermetically sealed container 1 in a temperature K atmosphere for a time T or longer. A substance having a non-bonded electron pair evaporating from 13 is chemisorbed on the excitation electrode film 20 (metal film), and the relationship between the temperature K and the time T is
T = 24294e ^-0.0251K (25 ℃ <K ≦ 230 ℃)
Is preferably satisfied.

Next, in the second embodiment of the present invention, there is provided a silicon molecule adsorption acceleration technique that allows the frequency of the crystal resonator element to reach the frequency stable region in a short time without being heated.
That is, in the present embodiment, a monomolecular film of silicone molecules is formed so as to cover the entire surface of the excitation electrode film 21 by exposing the excitation electrode film 21 to an atmosphere of silicone vapor prepared in advance before sealing the insulating container 1. 30 is formed in advance. According to this, since there is no long-term heat treatment step for making the inside of the recess 2 of the insulating container 1 necessary for the first embodiment into an atmosphere of silicone vapor, the resonance frequency of the crystal resonator element is adjusted in frequency. A set value at the time of the process can be lowered to a predetermined target value (target frequency) at once, and a stable state can be obtained. The predetermined target frequency is the resonance frequency of the crystal resonator element 12 immediately before completion with the metal lid 15 (in a state where the frequency adjustment by mass addition has been completed), and the resonance frequency in the atmosphere. When measured, the resonance frequency in the state of being hermetically sealed in the inert gas atmosphere in the insulating container is almost the same as this. However, when sealing in a vacuum, as is well known, from the target frequency in the atmosphere. Is a value several ppm higher.
Further, the target frequency is a state in which no substance that gives a mass addition effect other than the silicone monomolecular film 30 is attached to the surface of the excitation electrode film 21, in other words, other substances are deposited on the silicone monomolecular film 30. It is the resonance frequency in the state which is not.

That is, the atoms of metal materials such as gold have dangling bonds and are easily adsorbed chemically with substances having non-bonded electron pairs. The dangling bonds of all the metal atoms 21 located on the surface of the excitation electrode are adsorbed to the non-bonded electron pairs of the silicone molecule 30 in a very short time (several seconds) only by exposing the surface of the excitation electrode film for a short time. As a result, the monomolecular film 30 is formed on the entire surface of the excitation electrode film in a short time. The number of dangling bonds on the surface of the excitation electrode and the surface of the lead electrode is finite, and the silicone molecules forming the monomolecular film 30 of the silicone once formed on the entire surface of the excitation electrode film by chemical adsorption are adsorbed by hand (electron Therefore, the number of silicone molecules that can be attached (the number of monomolecular films) cannot be increased. The film thickness and mass) are determined, and the resonance frequency does not decrease due to chemical adsorption after the silicone molecules cover the entire surface of the excitation electrode. In addition, as shown in FIG. 1B, the monomolecular film 30 has a thickness equivalent to one silicone molecule, so that film thickness control is unnecessary. Since the thickness of the single layer film 30 can be determined in this way, it is possible to accurately predict or calculate the amount of decrease in the resonance frequency of the crystal resonator element due to the influence of the single layer film 30, and the monomolecular film 30 is formed. In the frequency adjustment process, the frequency can be set higher in advance than the target frequency so that the resonance frequency at the time point is set to the target frequency. Accordingly, it is possible to manufacture a crystal resonator and a crystal oscillator having a stable frequency with a high yield. On the other hand, since the quartz material constituting the quartz substrate is a SiO ₂ crystal structure having no dangling bonds, silicone molecules cannot be chemically adsorbed on the quartz substrate surface.

FIG. 2 is a schematic diagram showing a manufacturing process including a process of forming a silicone monomolecular film on the excitation electrode film of the quartz crystal resonator element in the present invention.
In the processing step (a) for the quartz substrate wafer, electrodes are formed on each piece region 36 on the quartz wafer 35 having a large area by etching or vapor deposition of a quartz material by a photolithography technique. And a frequency adjustment step (a step of adding or reducing the thickness of the excitation electrode film) is performed so that the resonance frequency of each piece is set higher than the target frequency by a predetermined frequency. The predetermined frequency higher than the target frequency is the final target frequency. As described later, a silicone monomolecular film is formed on the entire surface of the excitation electrode film in the chamber and then opened in the atmosphere to open the silicone monomolecular film on the silicone monomolecular film. This is a frequency in a state where an insulating container filled with an inert gas is hermetically sealed with a lid after removing an excessive silicone component that has adhered (not chemically adsorbed).
The piezoelectric material used as the substrate material is not limited to quartz as long as it is a thickness-slip type piezoelectric material whose frequency is determined by the difference in thickness. The electrode material used for the excitation electrode is, for example, gold, aluminum, or the like, but any metal that causes chemical adsorption with silicone vapor may be used.
In the dividing step (b), the crystal wafer is divided along the boundaries of the individual regions by dicing, etching, or the like.

In the next step (c), the divided crystal resonator element 12 is connected to the internal electrode 11 in the upper recess 2 of the insulating container 1 using a silicone adhesive (conductive bonding member) 13 (holding step). .
In the next silicone monomolecular film formation step (adsorption step) (d), for example, as shown in (d), the quartz crystal vibration is contained in the chamber 40 filled with silicone vapor (vapor of a substance having a non-bonded electron pair). The insulating container 1 holding the element 12 inside is disposed, and silicone molecules are chemically adsorbed to the surface of the excitation electrode film 21 to form a monomolecular film having a uniform thickness. Thereby, the silicone monomolecular film 30 is formed with a uniform thickness on the entire surface of the excitation electrode film.
It is preferable to use a silicone having a component having a low molecular weight ([(CH ₃ ) ₂ SiO] _n : Dn polymerization degree n value of 4 to 7) having high volatility. Silicone tends to volatilize even at room temperature. For example, when the degree of polymerization is D5, the boiling point is 211 ° C., so the silicone stock solution 41 is heated to an arbitrary temperature below or below the boiling point in the chamber 40. Thus, it becomes possible to fill the chamber with silicone vapor [(CH ₃ ) ₂ SiO] ₅ at a desired concentration in a short time, and when the concentration (ppm) is increased, the time for forming a monomolecular film (saturation) Time). The temperature in the chamber may be room temperature, or may be heated to a predetermined level or more in order to stably maintain the silicone vapor state.

Individual metal atoms constituting the surface layer of the excitation electrode film 21 and the surface layer of the lead electrode 22 have dangling bonds. A non-bonded electron pair on the silicone molecule side is attached to this dangling bond and chemically adsorbed, whereby a stable monomolecular film 30 that is difficult to separate from the excitation electrode film 21 and the lead electrode 22 can be obtained. At the stage where all the dangling bonds are adsorbed to the silicone molecules, no further silicone molecules are chemisorbed, but when the silicone molecule concentration in the chamber is high, the silicone molecules floating in the chamber adhere to the silicone monomolecular film 30. In order to deposit (physically adhere), the frequency when other silicone components are deposited on the silicone monomolecular film than the frequency when only the silicone monomolecular film 30 is chemisorbed on the excitation electrode. The frequency is lower due to the effect of mass addition due to physical deposits. Therefore, if a silicone monomolecular film is formed and then released to the atmosphere (or in a dry gas) outside the chamber, only the silicone component deposited by physical adhesion is scattered (evaporated) and removed, so that a single layer film is obtained. It is possible to easily configure the single-layer film 30 having a desired thickness and easily obtain a predetermined target frequency without the need for precise film thickness management when forming the film 30. However, since this target frequency is the resonance frequency in the atmosphere, it becomes the final target frequency as it is when enclosed in an insulating container together with an inert gas, but when sealed in a vacuum, the resonance frequency in the atmosphere is By setting the target frequency offset by the decrease due to vacuum sealing to the target frequency, it is possible to match the frequency at the time of vacuum sealing with the final target frequency.
When the film is formed by physical adsorption methods such as vapor deposition or sputtering to simply increase the mass of the excitation electrode, it is difficult to form a monomolecular film (single layer film), and it is easy to form a multi-layer film. However, since the silicone monomolecular film is almost equal to the monomolecular thickness and has a constant thickness, there is no need for film thickness management such as film thickness monitoring or strict measurement of the film formation time. By setting the film thickness of the vibrating part of the quartz substrate in advance, in other words, depending on the area (mass) of the excitation electrode formed on the vibrating part and the mass of the silicone monomolecular film adsorbed on the entire surface thereof If the film thickness of the crystal substrate vibrating portion is set so that the target resonance frequency can be obtained after taking into account the frequency drop, the frequency accuracy can be easily ensured.
That is, the thickness (monomolecular size) of the silicone monomolecular film 30 is about 1.3 nm when the polymerization degree of the silicone is D4. Thus, in the case of a monomolecular film, the thickness and the amount of decrease in frequency can be accurately predicted. By setting the resonance frequency before forming the silicone monomolecular film to a certain extent, The frequency after film formation can be easily set to the target frequency. For example, the resonance frequency (for example, 26 megahertz) when the silicone monomolecular film 30 is formed on the entire surface of the excitation electrode film is 5 ppm lower than the resonance frequency before the silicone monomolecular film is formed. In the case of quartz resonator elements having the same resonant frequency and the same dimensional structure, the same frequency drop occurs between individuals, so that fine adjustment of the frequency becomes very easy.

It has been confirmed by a long-term accelerated aging test that, after the silicone monomolecular film is formed and the frequency is stabilized, for example, it varies by 1 ppm in 50 years and takes about 500 years to move to the next 1 ppm. Thus, since the state after saturation is stable, no problem occurs in reliability evaluation and temperature cycle.
When the silicone monomolecular film is formed on the excitation electrode of the quartz crystal vibrating element in the silicone monomolecular film forming step, the silicone monomolecular film is formed on the entire surface of the excitation electrode after a few seconds by setting the silicone vapor concentration to a predetermined value or more. The area of the formed monomolecular film occupying the entire excitation electrode surface is the maximum area corresponding to 100% of the entire excitation electrode surface.
However, the resonance frequency obtained by forming a silicone monomolecular film having an occupation ratio that does not reach the maximum area (100%) (excitation electrode is partially covered with the silicone monomolecular film). When the resonance frequency of the crystal resonator element in a non-existing state is within a range of +1 ppm to 0 ppm higher than the resonance frequency of the piezoelectric resonator element in the maximum area (when the excitation electrode is completely covered with a silicone monomolecular film) Even if the area of the silicone monomolecular film occupies less than 100% of the entire surface of the excitation electrode, the resonance frequency remains at the target frequency ± 1 ppm for 50 years (according to the accelerated aging test) even if the resonance frequency decreases. Because it is within the range of (the range of variation that can be compensated for general operation), there will be no operational problems during the lifetime of the device incorporating the crystal unit. That is, almost the entire surface of the excitation electrode film is covered with the monomolecular film so that the reduction amount of the resonance frequency is less than 1 ppm even if an additional film is formed on the surface of the excitation electrode film not covered with the silicone monomolecular film 30. It only has to be.
In the silicone monomolecular film forming step (d), after the silicone monomolecular film is formed in the chamber 40, it is opened to the atmosphere and dried, and the silicone component adhering to the monomolecular film is scattered and removed. .
In the final sealing step, the opening is sealed with a lid in a state where an inert gas such as nitrogen is sealed in the insulating container to obtain the state shown in FIG.
By configuring each process shown in FIG. 2 so as to be performed along a series of manufacturing lines, a highly productive manufacturing apparatus and manufacturing method can be realized.

In the manufacturing apparatus or manufacturing method shown in FIG. 2 (d), the piezoelectric vibration element 12 having the excitation electrode film (metal film) 21 on the surface of the quartz substrate 20 as a thickness-slip type piezoelectric material is placed in the chamber 40. Although an example in which a silicone molecule is chemically adsorbed on the surface of the excitation electrode film by placing it in a high concentration atmosphere of the silicone vapor (cyclic dimethylpolysiloxane vapor) is shown, This is only an example, and it is possible to form a monomolecular film by other apparatus configurations and methods. For example, a small amount of a silicone stock solution is dropped in an insulating container 1 in which a piezoelectric vibration element 12 having an excitation electrode film 21 formed on a surface of a piezoelectric substrate 20 made of a thickness-slip type piezoelectric material is held by a silicone-based adhesive. The container is sealed and, if necessary, heated at a temperature suitable for the silicone stock solution to evaporate, thereby chemically adsorbing silicone molecules on the surface of the excitation electrode film to form a monomolecular film of the silicone molecules. You may do it.
That is, in the manufacturing method according to this embodiment, a crystal resonator element (piezoelectric resonator element) 12 in which an excitation electrode film 21 as a metal film is formed on the surface of a crystal substrate 20 as a piezoelectric substrate made of a thickness-slip piezoelectric material is used as a container. 1 is a frequency of adding or reducing the thickness of the excitation electrode film 21 in order to adjust the resonance frequency of the piezoelectric vibration element 12 to a predetermined value. An adjustment step, a placement step of placing a substance having a non-bonded electron pair in the container 1, a sealing step of hermetically sealing the container 1 in a state of being replaced with an inert gas atmosphere, and a non-bonded electron pair And an adsorption process in which the substance having a non-bonded electron pair is chemically adsorbed on the excitation electrode film 21 by heating to a temperature necessary for the substance having a vaporization to evaporate for a predetermined time.
At this time, the area that the monomolecular film occupies on the entire surface of the metal film does not need to be the maximum area (100%), and is allowed to decrease by 1 ppm (allowable range in the specification) from the resonance frequency of the piezoelectric vibration element in the maximum area. If it is within the range, even if the area of the silicone monomolecular film occupies the entire surface of the excitation electrode is less than 100%, there is no problem in the specification as long as it is within the allowable range. That is, almost the entire surface of the excitation electrode film is covered with the monomolecular film so that the reduction amount of the resonance frequency is less than 1 ppm even if an additional film is formed on the surface of the excitation electrode film not covered with the silicone monomolecular film 30. It only has to be.
The substance for forming a monomolecular film by chemisorbing with the excitation electrode is not limited to silicone, and any substance having a non-bonded electron pair may be used. Accordingly, in each of the embodiments described above, the conductive bonding member that holds the piezoelectric vibration element in the container is not limited to the silicone adhesive, and any adhesive that generates a substance having a non-bonded electron pair may be used.

  DESCRIPTION OF SYMBOLS 1 Insulation container, 2, 3 recesses, 4 bottom surface, 5 mounting terminal, 11 internal pad, 12 crystal vibration element (piezoelectric vibration element), 3 silicone type conductive adhesive (conductive joining member), 15 metal lid, 20 Quartz substrate (Piezoelectric substrate), 21 Excitation electrode (Metal film), 22 Lead electrode, 25 IC component, 30 Silicone monomolecular film, 40 Chamber, 41 Silicone stock solution

Claims (9)

A substrate provided with excitation electrodes on the main surface;
A container containing the substrate;
Including
The excitation electrode has gold dangling bonds exposed on the surface,
The vibrator is characterized in that the gold is covered with a monomolecular film formed by chemisorption of the dangling bond and a dimethylpolysiloxane molecule having a non-bonded electron pair.   In claim 1,
  The vibrator according to claim 1, wherein the gold base film is nickel or chromium.   In claim 1 or 2,
  The vibrator, wherein the dimethylpolysiloxane molecule is a cyclic molecule.   In any one of Claims 1 thru | or 3,
  A vibrator having a non-bonded electron pair disposed inside the container.   In claim 4,
  The vibrator, wherein the dimethylpolysiloxane molecule is a component evaporated from the substance.   In claim 4 or 5,
  The vibrator is characterized in that the substance is contained in a conductive bonding member.   In any one of Claims 4 thru | or 6,
  The vibrator is characterized in that the substance is a silicone-based adhesive.   In any one of Claims 1 thru | or 7,
  The vibrator is hermetically sealed.   The vibrator according to any one of claims 1 to 8,
  An oscillation circuit;
An oscillator comprising:

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