JP3885281B2 - Manufacturing method of crystal unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method of manufacturing a crystal resonator that is suitably used for a clock generator of a computer, a local oscillator of a wireless communication device, a filter, and the like, and that can obtain a stable resonance frequency and filter frequency even when the ambient temperature varies. Is.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a resonator used in an oscillator resonance circuit that generates an electric signal having a constant frequency, there is a crystal resonator that can obtain a stable resonance frequency with respect to a temperature change. FIG. 16 is a perspective view showing a conventional crystal unit. In the figure, reference numeral 1 denotes an AT-cut crystal substrate having an electric axis (X) and a frequency temperature coefficient of 0, and 2, 3 are crystal substrates. An excitation electrode made of aluminum, gold, or the like formed on both surfaces of 1 is an excitation portion that is a box-shaped region sandwiched between electrodes 2 and 3.
This crystal resonator can generate an electric vibration having a specific frequency within a range of about 1 kHz to 100 MHz by applying a high-frequency voltage near the resonance frequency between the electrodes 2 and 3.
[0003]
By the way, the resonance frequency of the above-described crystal resonator has a characteristic represented by a cubic curve when the ambient temperature is used as a parameter. Therefore, when the temperature fluctuation is small, the fluctuation of the resonance frequency is small enough not to cause a problem. When used in an environment where the temperature fluctuates greatly, the resonance frequency fluctuates greatly and cannot be ignored.
Therefore, by combining with a temperature-sensitive element that can obtain a temperature compensation voltage that cancels this characteristic, for example, a temperature compensation circuit that uses a thermistor whose temperature characteristic is represented by an exponential function, the resonance frequency is set to the ambient temperature. There is provided a temperature compensated crystal oscillator (TCXO) that is changed substantially linearly.
[0004]
In general, if twins exist in a crystal for an electronic device, the characteristics of the device are adversely affected. Therefore, it is essential that no twins are formed in the crystal. Also in crystal oscillators, it is natural that there are no twins in the quartz substrate used as the vibrator.
[0005]
[Problems to be solved by the invention]
However, in the above-described crystal oscillator (TCXO), several electronic components are required in addition to the thermistor in order to form a temperature compensation circuit, and the number of electronic components to be used increases, resulting in a high price. There are various drawbacks such as complicated adjustment of the crystal oscillator circuit.
On the other hand, the resonance frequency-temperature characteristic of the quartz substrate represented by the cubic curve is considered to be a characteristic unique to the quartz substrate, and it was considered that there is no room for improvement in the quartz substrate itself.
[0006]
  The present invention has been made in view of the above circumstances, and even when the ambient temperature fluctuates, a stable resonance frequency and filter frequency can be obtained with a relatively simple temperature compensation circuit, and the handling is simple. It is an object of the present invention to provide a method for manufacturing a crystal resonator that does not require complicated adjustment work and that can achieve low cost.
[0007]
[Means for Solving the Problems]
  It is known that quartz undergoes an α / β phase transition at 573 ° C. (Tc), but the transition temperature is lowered due to stress or the like, and the electric axis (X axis) is inverted at a temperature lower than Tc.
  The present inventors apply a heat treatment by attaching a metal electrode to the surface of the quartz substrate, so that the electric axis of the quartz substrate is reversed at a temperature much lower than Tc depending on the cutting orientation of the substrate and the type of metal. In view of this, a method for manufacturing a crystal resonator in which an axis reversal part having an electric axis opposite to the electric axis of the excitation part is formed in a quartz substrate is provided.
[0008]
  That is,According to the present inventionThe quartz resonator is a quartz resonator in which excitation electrodes are formed on both sides of a quartz substrate and a region sandwiched between the electrodes is used as an excitation unit. The quartz resonator is located at a position different from the excitation unit in the quartz substrate. A shaft reversal unit having an electric axis opposite to the electric axis of the excitation unit is formed.
[0009]
In this crystal resonator, by forming an axis reversal unit having an electric axis in a direction opposite to the electric axis of the excitation unit, part of vibration energy generated in the excitation unit is leaked to the axis reversal unit. Performs temperature compensation of the vibrator. For example, an AT-cut quartz substrate has a negative temperature characteristic at the room temperature, whereas the resonance frequency of the axis inversion unit has a positive temperature characteristic at room temperature. Thus, the temperature characteristic is compensated. As a result, even when the ambient temperature fluctuates, a stable resonance frequency can be obtained with a relatively simple temperature compensation circuit.
[0010]
  thisIn quartz crystalIsThe shaft reversing part is formed close to one side or both sides of the excitation part.You can,The axis reversal part is formed around the excitation part.May be.
  In these crystal resonators, by forming the axis reversal portion at or near the excitation portion, a part of the vibration energy from the excitation portion is leaked to the axis reversal portion, thereby causing the temperature of the excitation portion. Make compensation more reliably.
[0011]
  Also thisIn quartz crystalIsIn addition, an excitation electrode part is formed on the axis reversing part to form a temperature sensor partMay be.
  In this crystal resonator, the axis reversal unit is a temperature sensor having a substantially linear temperature coefficient. As a result, if this vibrator is applied to a conventional crystal oscillator (TCXO), it becomes possible to directly obtain temperature information of the crystal substrate, and highly accurate temperature compensation becomes possible.
[0012]
  Where like thisManufacturing method of crystal unitAsIs a method for manufacturing a crystal resonator in which excitation electrodes are formed on both sides of a quartz substrate and the region sandwiched between the electrodes is used as an excitation unit, in one side of the electrode part on the surface of the quartz substrate or Metal films are formed on both sides, and then the quartz substrate is heat-treated at a temperature lower than the α / β transition temperature of the quartz, and the quartz substrate has an electrical axis opposite to the electrical axis of the excitation unit. Form axis reversal partCan be mentioned.
[0013]
In this manufacturing method, the quartz substrate on which the metal film is formed is heat-treated at a temperature not higher than the α / β transition temperature of the quartz, so that the inversion portion in the quartz substrate is formed by the stress caused by the metal film. The electric axis reverses at a temperature lower than the α / β transition temperature. As a result, an axis reversal unit having an electric axis in a direction opposite to the electric axis of the excitation unit is formed in a region different from the excitation unit in the quartz substrate. Therefore, the axis reversal unit and the excitation are formed in the quartz substrate. A twin structure consisting of parts is formed.
[0014]
As a result, an axis reversal unit having an electric axis opposite to the electric axis of the excitation unit is formed at a position different from the excitation unit in the quartz substrate. It becomes possible to manufacture a crystal resonator that can obtain a filter frequency.
[0015]
  In this case,The metal film is any one of a Cr film, a Ni film, and a NiCr film.May be.
  In this manufacturing method, reversal of the electric axis occurs at a temperature of about 540 to 550 ° C. by using a Cr film, a Ni film, or a NiCr film. This makes it possible to cause the α · β transition in the quartz substrate at a temperature much lower than the α · β transition temperature.
[0016]
  Also,The heat treatment is performed in either an inert atmosphere or a vacuum atmosphere.May be.  In this manufacturing method, by preventing the oxidation of the metal film, there is no possibility that the stress of the metal film is reduced, and the formation of the axis reversal portion inside the quartz substrate is more reliable.
[0017]
  And the present inventionThe manufacturing method of quartz crystalPrimarily,A thin film made of a conductive material on the surface of a crystal substrate in a method for manufacturing a crystal resonator in which excitation electrodes are formed on both sides of a crystal substrate, and a region sandwiched between the electrode portions is used as an excitation unit. Next, a quartz substrate on which the thin film is formed is formed.Up to 500-520 ° CAfter heatingthisBy applying an electric current to the thin film in a heated state, stress necessary for axial reversal is applied to a portion below the thin film of the quartz substrate, and an axial reversal unit having an electric axis opposite to the electric axis of the excitation unit is formed. To do.
  Also,Of the present inventionThe manufacturing method of quartz crystalSecond, the first manufacturing methodAs with the quartz substrate with a thin filmUp to 500-520 ° CAfter heatingthisBy irradiating the thin film with an electron beam in a heated state, stress necessary for axis reversal is applied to form an axis reversal part.
  Also,Of the present inventionThe manufacturing method of quartz crystalThird, the first and second manufacturing methodsAs with the quartz substrate with a thin filmUp to 500-520 ° CAfter heatingthisBy applying a high electric field to the quartz crystal substrate through the thin film in a heated state, stress necessary for axis reversal is applied to form an axis reversal part.
[0018]
  theseFirst to third inventionsThis method for manufacturing a quartz resonator provides a means for reliably and efficiently performing the formation of the axis reversal portion on the quartz substrate. The feature is that the cause of the axis reversal is the stress caused by the film formed on the quartz substrate, and the stress is efficiently applied to the film forming part of the quartz substrate by using external electrical means. Is to give. Specifically, the electrical means here means:1.Current flows through the conductive thin film,2.Irradiate the conductive thin film with an electron beam,3.A high electric field is applied to the quartz substrate through the conductive thin film.
[0019]
  Here, these first to third inventionsIn the manufacturing method of any quartz crystalIsThe thin film is either a Cr film, a Ni film or a NiCr film.May be.
  In this manufacturing method, reversal of the electric axis occurs at a lower temperature by using a Cr film, a Ni film, or a NiCr film. This makes it possible to cause the α · β transition in the quartz substrate at a temperature much lower than the α · β transition temperature.
[0020]
  Furthermore, the present inventionManufacturing method of crystal unitsoThe heating is performed in either an inert atmosphere or a vacuum atmosphere.May be.
  In this manufacturing method, by preventing the oxidation of the metal film, there is no possibility that the stress of the metal film is reduced, and the formation of the axis reversal portion inside the quartz substrate is more reliable.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Each embodiment of the present invention will be described.
(First embodiment)
1A and 1B are diagrams showing a crystal resonator according to a first embodiment of the present invention, in which FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view taken along the line I-I in FIG. It is. In the figure, reference numerals 11 and 12 denote axis reversal portions having an electric axis (−X) opposite to the electric axis (X) of the excitation unit 4 formed in the quartz substrate 1 and in the vicinity of both sides of the excitation unit 4. is there.
In FIG. 1, W is the width of the electrodes 2 and 3, L is the length of the electrodes 2 and 3, d is the distance between the excitation unit 4 and the axis reversing units 11 and 12, and s is the axis reversing unit 11 and 12. The length, t is the thickness of the quartz substrate 1, and f is the amplitude distribution of vibration displacement in the length direction.
[0022]
In this crystal resonator, when a high-frequency voltage near the resonance frequency is applied between the electrodes 2 and 3, an amplitude distribution f of vibration displacement as shown in FIG. That is, most of the vibrational energy is concentrated on the excitation unit 4 due to the energy confinement effect based on the mass addition effect of the electrodes 2 and 3, but part of it leaks and reaches the axis inversion units 11 and 12, resulting in temperature characteristics. Is improved.
[0023]
Here, the effect of improving the temperature characteristics of the crystal resonator of the present embodiment will be described with reference to FIG.
In FIG. 2, A is an optimum characteristic of the crystal resonator of the present embodiment, B is a characteristic of an AT cut crystal resonator without an axis inversion portion, and C is a crystal resonator in which the X axis of the AT cut crystal substrate is inverted. Characteristic D is the result of an experiment conducted to confirm the temperature compensation principle of the crystal resonator of the present embodiment.
The sample used in the experiment (D) was t of 205 μm, W of 5.0 mm, L of 2.5 mm, s of 2.5 mm and d of 2.0 mm, and the heat treatment conditions were 550 ° C. 1 hour 30 minutes. The frequency fr used for the measurement was 8.0 MHz.
[0024]
As is clear from this, the resonance frequency of the AT-cut quartz crystal resonator (B) is represented by a cubic curve, and has a negative temperature coefficient near room temperature. On the other hand, the inverted crystal unit (C) has a very large positive temperature coefficient. Therefore, as shown in FIG. 1B, by leaking a part of the vibration energy (the bottom part of the amplitude distribution f) to the axis inversion parts 11 and 12, the positive temperature coefficient and the negative temperature coefficient are obtained. It cancels out and the optimum characteristic (A) is obtained. That is, the temperature coefficient becomes substantially 0 in the temperature range of about 0 to 70 ° C., and increases slightly with the temperature rise when it exceeds 70 ° C.
[0025]
As described above, the temperature characteristics can be compensated by causing a part of the vibration energy to leak to the axis inversion units 11 and 12 and canceling out the positive temperature coefficient and the negative temperature coefficient. As a result, even when the ambient temperature fluctuates, a stable resonance frequency can be obtained without using a temperature compensation circuit or the like.
[0026]
Next, a method for manufacturing a crystal resonator will be described with reference to FIG.
First, a transition metal such as Cr or Ni, or NiCr that is an alloy of these is formed by electron beam (EB) vapor deposition or the like at a position where the axis reversal portions 11 and 12 on the surface of the AT-cut quartz crystal substrate 1 are to be formed. Metal thin films 21 and 22 made of any of the above materials are formed (FIG. 3A).
[0027]
In this case, in order to effectively form the axis reversal portions 11 and 12 in the quartz substrate 1, the thickness (t 2) of the metal thin films 21 and 22 is a certain ratio to the thickness (t 1) of the quartz substrate 1 ( R = t2 / t1) or more.
[0028]
For example, as shown in FIG. 4, in the case of a Cr film, there is a critical value that enables axis reversal in the vicinity of R = 1.3 × 10 −3, and axis reversal becomes impossible below this critical value. In the case of a NiCr film, there is a critical value that enables axis reversal in the vicinity of R = 0.4 × 10 −3, and axis reversal becomes impossible below this critical value. Therefore, for example, in the case of a NiCr film, when the thickness t1 of the quartz substrate 1 is 200 μm, stable axis inversion
In order to obtain the above, the thickness of the NiCr film needs to be 200 nm or more (R ≧ 1 × 10 −3). In this case, the film formation temperature is 200 ° C.
[0029]
Next, the quartz substrate 1 on which the metal thin films 21 and 22 are formed is heated to a temperature lower than the α-β transition temperature (573 ° C.) of the quartz crystal in an inert atmosphere such as N 2 gas or a vacuum atmosphere, for example, metal. When the thin films 21 and 22 are NiCr films, heat treatment is performed at 550 to 560 ° C. for 30 minutes.
[0030]
Due to the stress caused by the metal thin films 21 and 22 during the heat treatment, the electrical axis at the position where the reversal portions 11 and 12 are to be formed in the quartz substrate 1 is reversed at a temperature lower than the α / β transition temperature. Thereby, the axis inversion parts 11 and 12 which have the electric axis (-X) of the direction opposite to the electric axis (X) of the excitation part 4 are formed in the quartz substrate 1 (FIG.3 (b)).
[0031]
Next, if necessary, the metal thin films 21 and 22 are removed, and electrodes 2 and 3 are formed on both surfaces of the quartz substrate 1 by an electron beam (EB) vapor deposition method or the like (FIG. 3C).
As described above, a crystal resonator having the amplitude distribution f of the vibration displacement shown in FIG. 1B can be obtained.
[0032]
Here, the resonance characteristics of the crystal resonator of this embodiment before and after the heat treatment will be described.
5A and 5B are diagrams showing resonance characteristics before and after the heat treatment, in which FIG. 5A is a resonance characteristic before the heat treatment of the quartz substrate 1 on which Cr films are formed, and FIG. 5B is a resonance characteristic after the heat treatment. (C) shows the resonance characteristics after heat treatment of the Al film formed on both sides of the quartz substrate 1.
Here, as shown in FIG. 6, a structure in which Cr films (metal films) 25 and 25 and Al films (metal films) 26 and 26 are respectively formed on opposite sides of the AT-cut quartz crystal substrate 1. A sample was used.
[0033]
According to (a) and (b), the resonance frequency before and after the heat treatment is greatly changed in the Cr films 25 and 25. The frequency ratio before and after the heat treatment is the same as that of the quartz substrate 1 (+ 35 ° 15′RY-cut) and the axis inversion portion. 11 and 12 (-35 ° 15 'RY-cut), which is almost the same as the frequency constant ratio, and it is clear that axis reversal has occurred. On the other hand, in the Al films 26 and 26, no clear change in the resonance frequency is observed before and after the heat treatment, and it is difficult to recognize that axis reversal has occurred.
[0034]
As described above, according to the crystal resonator of the present embodiment, the electric axis (−X) in the direction opposite to the electric axis (X) of the excitation unit 4 is provided in the quartz substrate 1 and in the vicinity of both sides of the excitation unit 4. ) Is formed, the temperature characteristics of the excitation unit 4 can be compensated by the axis inversion units 11 and 12, and therefore, even when the ambient temperature fluctuates, it is relatively simple. A stable resonance frequency can be obtained by the temperature compensation circuit.
[0035]
Further, according to the method for manufacturing a crystal resonator of the present embodiment, the metal thin films 21 and 22 are formed on the surface of a region different from the excitation unit 4 of the crystal substrate 1, and then the crystal substrate with the metal thin films 21 and 22 is provided. 1 is heat-treated at a temperature lower than the α · β transition temperature of the crystal, so that the axis inversion portions 11 and 12 having the electric axis opposite to the electric axis of the excitation portion 4 are formed in the quartz substrate 1, and the ambient temperature It is possible to manufacture a crystal resonator that can obtain a stable resonance frequency and filter frequency against fluctuations.
[0036]
The shapes of the excitation unit 4 and the axis inversion units 11 and 12 are parallel to each other as described above. For example, the horizontal cross sections of the mutually facing surfaces of the excitation unit 4 and the axis inversion units 11 and 12 are comb-shaped. Various shapes such as a shape in which the horizontal cross sections of the upper end portions of the excitation unit 4 and the axis reversing portions 11 and 12 facing each other are comb-shaped and the horizontal cross sections of the lower end portions thereof are parallel are possible.
[0037]
(Second Embodiment)
7A and 7B are diagrams showing a crystal resonator according to a second embodiment of the present invention, in which FIG. 7A is a perspective view, and FIG. 7B is a cross-sectional view taken along line II-II in FIG. It is.
The crystal resonator of this embodiment is different from the crystal resonator of the first embodiment described above in the direction opposite to the electric axis (X) of the excitation unit 4 in the crystal substrate 1 and in the vicinity of one side of the excitation unit 4. This is the point where the axis reversal unit 12 having the electrical axis (−X) is formed.
[0038]
In this crystal resonator, when a high-frequency voltage near the resonance frequency is applied between the electrodes 2 and 3, an amplitude distribution f of vibration displacement as shown in FIG. 7B is obtained. Due to the energy confinement effect based on the mass addition effect of the electrodes 2 and 3, most of the vibration energy is concentrated in the excitation unit 4, but part of it leaks and reaches the axis inversion unit 12, and as a result, the temperature characteristics are improved. .
[0039]
This crystal unit can be manufactured by the same manufacturing method as the crystal unit of the first embodiment described above.
For example, a metal thin film 22 made of a NiCr film or the like having a thickness of 200 nm or more is formed at a position where the axis reversal portion 12 on the surface of the AT-cut quartz crystal substrate 1 having a thickness of 200 μm is to be formed. If heat treatment is performed at a temperature not higher than the α-β transition temperature (573 ° C.) of the crystal, for example, 550 to 560 ° C. for 30 minutes in either an active atmosphere or a vacuum atmosphere, the electric shaft of the excitation unit 4 is provided inside the crystal substrate 1. An axis reversing unit 12 having an electric axis (−X) in the direction opposite to (X) is formed, and a crystal resonator having an amplitude distribution f of vibration displacement shown in FIG. 7B can be obtained.
[0040]
Also in the crystal resonator of the present embodiment, the temperature characteristics of the excitation unit 4 can be compensated by the axis inverting unit 12 in exactly the same manner as the crystal resonator of the first embodiment described above. Even when it fluctuates, a stable resonance frequency can be obtained with a relatively simple temperature compensation circuit.
[0041]
(Third embodiment)
8A and 8B are views showing a crystal resonator according to a third embodiment of the present invention. FIG. 8A is a perspective view, and FIG. 8B is a cross-sectional view taken along line III-III in FIG. It is.
The crystal resonator of this embodiment differs from the crystal resonators of the first and second embodiments described above in that excitation electrodes 31 and 32 having a radius r are formed on both surfaces of the crystal substrate 1 and these electrodes 31 are formed. , 32 is an exciter 33, and an electric axis (−X) opposite to the electric axis (X) of the exciter 33 is positioned outside the radius R around the exciter 33. This is the point where the axis reversal part 34 having a) is formed.
[0042]
Also in the crystal resonator of the present embodiment, the temperature characteristics of the excitation unit 33 can be compensated by the axis inversion unit 34 in exactly the same manner as the crystal resonators of the first and second embodiments described above. Even when the ambient temperature fluctuates, a stable resonance frequency can be obtained with a relatively simple temperature compensation circuit.
[0043]
(Fourth embodiment)
FIG. 9 is a perspective view showing a crystal resonator with a temperature sensor according to a fourth embodiment of the present invention. In FIG. 9, reference numeral 41 denotes the excitation unit formed in the crystal substrate 1 and in the vicinity of one side of the excitation unit 4. Reference numerals 42, 43 denote excitation electrodes formed on the axis reversal part 41, which have an electric axis (−X) opposite to the electric axis (X) 4.
[0044]
In this quartz crystal resonator with a temperature sensor, the AT-cut quartz crystal substrate 1 is partially subjected to axis inversion processing, and a transducer is formed in each of the non-inversion portion and the inversion portion. The non-inverting part 44 is a normal AT-cut quartz crystal vibrator, and the inverting part 45 is a −35 ° 15 ′ RY-cut vibrator and a temperature sensor having a temperature coefficient of +29 ppm / deg.
[0045]
FIG. 10 is a diagram showing the resonance frequency-temperature characteristics of the crystal resonator with a temperature sensor according to the present embodiment. In the figure, E is a characteristic of the non-inversion part, and F is a characteristic of the inversion part.
As is clear from this, the resonance frequency of the non-inversion part (E) is represented by a cubic curve and has a negative temperature coefficient near room temperature. On the other hand, the inversion part (F) has a temperature coefficient of +29 ppm / deg. Therefore, if the inversion part (F) is used as a temperature sensor, the temperature information of the quartz crystal substrate 1 can be obtained directly.
This crystal oscillator with a temperature sensor can be applied to a conventional crystal oscillator (TCXO) or the like.
In particular, when applied to a crystal oscillator (TCXO), temperature information of the crystal substrate 1 can be directly obtained, and highly accurate temperature compensation can be performed.
[0046]
(Fifth embodiment)
In the first embodiment, the method for manufacturing a crystal resonator has been described with reference to FIG. 3, but in the following embodiments, another manufacturing method, particularly, three methods related to the method for forming the axis reversal part will be described.
That is, in order to form the axis reversal part, in the first embodiment, after forming a metal thin film on the quartz substrate, the entire quartz substrate is heat-treated. In this method, after a metal thin film is formed on the substrate, a current is passed through the metal thin film to apply stress to the quartz substrate therebelow.
[0047]
FIG. 11 is a diagram showing a method of forming an axis reversal part in this embodiment. In the figure, reference numeral 1 is a quartz substrate, 51 is a metal thin film (conductive thin film), 52 is a substrate holder, 53a and 53b are lead wires, 54 Is a heater, 55 is a vacuum vessel, 56 is a power source, and 57 is a switch. Hereinafter, the process of forming the axis reversal part will be described with reference to this drawing.
[0048]
First, as shown in FIG. 11, the surface of the quartz substrate 1 is made of a transition metal such as Cr or Ni, or any material such as NiCr, which is an alloy thereof, using a known method such as an electron beam evaporation method. A metal thin film 51 is formed.
[0049]
Next, the quartz crystal substrate 1 on which the metal thin film 51 is formed is fixed on the substrate holder 52, and a power source 56 is connected to both ends of the metal thin film 51 via lead wires 53 a and 53 b and a switch 57. And after exhausting the inside of the vacuum container 55 which accommodates the quartz substrate 1 to make a vacuum atmosphere, the quartz substrate 1 is heated to about 500-520 degreeC using the heater 54 for a heating. In this state, since the temperature of the quartz substrate 1 does not reach the α / β transition temperature (573 ° C.), the inversion of the electric axis (X) does not occur. Note that the inside of the vacuum vessel 55 may be an inert atmosphere instead of a vacuum atmosphere.
[0050]
Next, the switch 57 is closed with the quartz substrate 1 kept at the above temperature. Then, since the thin film 51 is a metal, a current flows, and the thin film 51 is heated and expands simultaneously with current conduction due to the film resistance, and stress necessary for axis reversal is applied to the quartz substrate 1 and at the same time below the thin film 51. As the temperature of the crystal rises locally, the electrical axis is reversed. On the other hand, since the stress due to the film is not applied to the portion other than under the thin film 51 and the temperature rise is small, the condition for causing the axis reversal is not reached, and the direction of the electric axis remains in the original state.
[0051]
Here, an experimental example based on the method of the present embodiment is shown.
The sample of this experiment used an AT cut plate having a width of 8.5 mm, a length of 9.2 mm, and a thickness of 0.16 mm as a quartz substrate. Then, a chromium film having a width of 1.0 mm, a length of 8.0 mm, and a thickness of 250 nm was formed on the quartz substrate as a metal thin film. As an experimental condition, the atmosphere in the vacuum vessel is 5 × 10.^-FiveTorr (0.005 Pa), substrate temperature during current conduction is 520 ° C., applied power is 2 V × 0.05 A = 100 mW (12.5 mW / mm²), And the application time was about 1 second.
[0052]
At the same time as the X-axis reversal occurs, the Y-axis is also reversed, and the relationship between the cutting orientation of the crystal plate and the crystal axis is as shown in FIG. That is, the AT cut plate is a so-called 35 ° 15 ′ rotating Y-cut in which the plane line is inclined 35 ° 15 ′ from the Y-axis toward the Z-axis, whereas the X-axis inverted portion is −35 ° 15 ′. Rotation Y cut. As is well known, the frequency constant for the piezoelectric resonance of the AT cut plate is about 1650 Hz · m, while the frequency constant of the −35 ° 15 ′ rotated Y cut plate is calculated to be about 2520 Hz · m. That is, when the X-axis direction is reversed in the AT cut plate, the resonance frequency rises about 1.47 times.
[0053]
In the experiment, the sample was heated to 520 ° C. in a vacuum, and a current was passed through the thin film on the quartz substrate in the heated state. Then, in order to see the state of X axis inversion, the resonance characteristics were observed with a network analyzer. FIG. 13 shows changes in the resonance frequency at each time point in the experiment. (A) is an initial state at room temperature, (b) is a state heated to 520 ° C., and (c) is 520. The state immediately after the current is applied and cut off at 0 ° C., (d) shows the state when the temperature is returned to room temperature again.
[0054]
As shown in FIG. 13 (a), resonance is observed in the vicinity of 10 MHz in the initial state at room temperature. However, as shown in FIG. 13 (b), even if the sample is heated to 520 ° C., the resonance frequency is 11 MHz alone. Almost the same as the initial state. That is, the resonance frequency difference between FIG. 13A and FIG. 13B is due to temperature characteristics, and both of these resonances correspond to AT cuts. On the other hand, as shown in FIG. 13 (c), when a current is passed through the thin film in a heated state, the resonance frequency rises to about 14.3 MHz, and then the temperature is changed to room temperature as shown in FIG. 13 (d). It returned to about 14.7MHz. Thus, it was confirmed by this experiment that the resonance frequency after current application was about 1.47 times that in the initial state, and it was proved that this method by current application was effective for the inversion processing of the X axis.
[0055]
(Sixth embodiment)
Next, another method for forming the axis reversal part will be described.
The method of the present embodiment is a method of applying stress to the underlying quartz substrate by irradiating a metal thin film on the quartz substrate with an electron beam.
[0056]
FIG. 14 is a diagram showing a method of forming an axis reversal part in the present embodiment, in which reference numeral 1 is a quartz substrate, 51 is a metal thin film (conductive thin film), 52 is a substrate holder, 53a and 53b are lead wires, 54 Is a heater, 55 is a vacuum vessel, 61 is a cathode, 62 is a heater for cathode heating, 63 is a DC voltage source, and 64 is a switch. As shown in this figure, the metal thin film 51 formed on the quartz substrate 1 is connected to a DC voltage source 63 through a switch 64 so that a negative voltage is applied to the cathode 61. The formation process of the axis reversal part in this embodiment is as follows.
[0057]
After the metal thin film 51 is formed on the quartz substrate 1 as in the fifth embodiment, the inside of the vacuum vessel 55 is set to a vacuum or an inert atmosphere, and the quartz substrate 1 is heated to 500 to 520 ° C. using the heater 54 for heating. Heat to the extent. Next, in a state where the substrate 1 is kept at the above temperature, the cathode heating heater 62 is energized to heat the cathode 61 to be in the state of thermionic emission. When the switch 64 is closed, the metal thin film 51 on the quartz substrate 1 has a positive potential with respect to the cathode 61, so that a current flows, and the thin film 51 portion is rapidly heated and expanded, as described in the fifth embodiment. X-axis inversion occurs by the same mechanism as described above. On the other hand, since stress due to the thin film is not applied to the portion other than under the thin film 51, the condition for causing the axis reversal is not reached, and the electric axis direction remains the original state.
[0058]
Here, as an example of specific conditions in the method of the present embodiment, an AT-cut plate having a width of 8.5 mm, a length of 9.2 mm and a thickness of 0.16 mm as a quartz substrate, and a width of 1.0 mm as a metal thin film. A chromium film having a length of 8.0 mm and a thickness of 250 nm is used (same as in the fifth embodiment), and the atmosphere in the vacuum vessel is 5 × 10^-FiveTorr (0.005 Pa), substrate temperature during electron beam irradiation is 520 ° C., power is 195 V (acceleration voltage) × 0.1 mA = 19.5 mW (2.4 mW / mm²) Electron beam irradiation time is about 5 seconds.
[0059]
(Seventh embodiment)
Next, another method for forming the axis reversal part will be described.
The method of this embodiment is a method of applying stress to a quartz substrate underneath by applying a high voltage to a metal thin film on the quartz substrate.
[0060]
FIG. 15 is a diagram showing a method of forming an axis reversal part in the present embodiment, in which reference numeral 1 is a quartz substrate, 51 is a metal thin film (conductive thin film), 52 is a substrate holder, 53a and 53b are lead wires, 54 Is a heater, 55 is a vacuum vessel, 71 is an electrode for voltage application, 72 is a high voltage power source, and 73 is a switch. The electrode 71 may be provided on the front surface of the substrate holder 52 or may be provided on the back surface of the crystal substrate 1.
[0061]
As shown in this figure, in this embodiment, when the switch 73 is closed, a high voltage is applied to the crystal substrate 1. The same substrate 1 as in the fifth and sixth embodiments is prepared and heated to about 500 to 520 ° C. Next, when the switch 73 is closed while the substrate 1 is maintained at the above temperature, a high voltage is applied to the quartz substrate 1 interposed between the metal thin film 51 and the electrode 71 and a strong electric field is applied. Stress is applied depending on the nature. When the magnitude of the stress exceeds the stress value necessary for the axis reversal, the electric axis is reversed. On the other hand, since stress due to a high electric field is not applied to the portion of the quartz substrate 1 other than under the thin film 51, the condition for causing the axis inversion is not reached, and the electric axis direction remains the original state. Note that the stress required for axis reversal is 10^Five-10⁶N / m²In order to obtain this, an electric field of about 5000 to 10000 V / cm is required for the AT cut plate, and therefore, a power supply of several hundred volts may be used with a 200 μm thick substrate.
[0062]
In the case of this embodiment, since a high electric field is applied only to the portion directly below the metal thin film 51, it can be applied to any film shape, and an axis reversal part corresponding to the film shape can be formed.
[0063]
When the axis reversal part forming method according to the fifth to seventh embodiments is used, unlike the method of the first embodiment in which the entire substrate on which the thin film is formed is simply heated, the crystal substrate has a very local area directly under the thin film. The axial reversal can be caused at a lower temperature by both the action of applying heat from the thin film to the target region and the action of applying stress due to the expansion of the thin film. For example, while the α / β transition temperature of quartz is 573 ° C., the substrate temperature is 550 to 560 ° C. in the first embodiment, but in the method of these embodiments, the heating temperature is 500 to 520 ° C. Can be reduced. In addition, when these methods are used, there is an effect that heat and stress are locally applied directly under the thin film. Therefore, as long as the thin film is formed at the position where the axis inversion portion is to be formed, the axis inversion portion is formed. The position and shape can be controlled more reliably.
[0064]
【The invention's effect】
  As explained above,According to the present inventionAccording to the crystal resonator, in the crystal resonator in which the excitation electrode portions are formed on both surfaces of the crystal substrate and the region sandwiched between the electrode portions is the excitation portion, the crystal resonator is different from the excitation portion in the crystal substrate. Since the shaft reversal part having the electric axis in the direction opposite to the electric axis of the excitation part is formed at the position, a part of vibration energy from the excitation part is leaked to the axis reversal part to compensate the temperature of the excitation part. Even when the ambient temperature fluctuates, a stable resonance frequency and filter frequency can be obtained with a relatively simple temperature compensation circuit.
[0065]
Therefore, it is not necessary to adjust the electronic components constituting the temperature compensation circuit and the circuit of the crystal oscillator, which are required in the conventional crystal oscillator (TCXO) and the like, and a crystal oscillator and a filter that are easy to handle and inexpensive can be obtained. .
In addition, if this crystal unit is used in a portable wireless communication device, it has excellent effects such as a small mounting volume due to the small number of parts used and a long-time use due to a reduction in battery consumption. Can be played.
[0066]
  Also,The axis reversal part is formed close to one side or both sides of the excitation part.By doingA part of the vibration energy from the excitation unit can be leaked to the shaft inversion unit, so that temperature compensation of the excitation unit can be performed more reliably.
[0067]
  further,The axis reversal part is formed around the excitation part.By doingA part of the vibration energy from the excitation unit can be leaked to the shaft inversion unit, so that temperature compensation of the excitation unit can be performed more reliably.
[0068]
  Furthermore,An electrode part for excitation is formed in the axis reversing part, and a temperature sensor partBy doingThe axis reversal unit becomes a temperature sensor having a substantially linear temperature coefficient. Therefore, if this vibrator is applied to a conventional crystal oscillator (TCXO), the temperature information of the crystal substrate can be directly obtained, and a high-precision Temperature compensation can be performed.
[0069]
  here,In a method for manufacturing a crystal resonator in which excitation electrodes are formed on both sides of a quartz substrate and the region sandwiched between the electrodes is used as an excitation unit, the quartz substrate is provided on one or both sides of the electrode on the surface of the quartz substrate. Then, a metal film is formed, and then the quartz substrate is heat-treated at a temperature lower than the α-β transition temperature of the quartz, and the quartz substrate has an axis reversal having an electrical axis opposite to the electrical axis of the excitation unit. Forming partIf you doIt is possible to manufacture a crystal resonator that can obtain a stable resonance frequency and filter frequency against fluctuations in ambient temperature.
[0070]
  Also,The metal film is either a Cr film, a Ni film or a NiCr film.By doingThe electric axis can be reversed inside the quartz substrate at a temperature (540 to 550 ° C.) much lower than the α / β transition temperature.
[0071]
  further,The heat treatment is performed in either an inert atmosphere or a vacuum atmosphere.ByOxidation of the metal film can be prevented, and therefore there is no possibility that the stress of the metal film is reduced, and the axis reversal part can be more reliably formed inside the quartz substrate.
[0072]
  And the present inventionAccording to the crystal resonator manufacturing method of the present invention, stress can be applied to the film forming portion of the quartz substrate using an external electrical means, so that the axis reversal portion can be efficiently formed. Thus, the position and shape for forming the axis reversal part can be controlled more reliably.
[0073]
  In addition, the present inventionAccording to the method for manufacturing a quartz crystal resonator, the thin film may be a Cr film, a Ni film, or a NiCr film.By doingThe electric axis can be reversed inside the quartz substrate at a temperature (500 to 520 ° C.) much lower than the α / β transition temperature.
[0074]
  Furthermore, the present inventionAccording to the method for manufacturing a quartz crystal resonator, the heating is performed in either an inert atmosphere or a vacuum atmosphere.ByOxidation of the metal film can be prevented, and therefore there is no possibility that the stress of the metal film is reduced, and the axis reversal part can be more reliably formed inside the quartz substrate.
[0075]
  As a result, even when the ambient temperature fluctuates, a stable resonance frequency and filter frequency can be obtained with a relatively simple temperature compensation circuit, and handling is simple and no complicated adjustment work is required. It is possible to provide a method for manufacturing a crystal resonator that can be realized.
[Brief description of the drawings]
1A and 1B are diagrams showing a crystal resonator according to a first embodiment of the present invention, in which FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view taken along line II in FIG.
FIG. 2 is a diagram showing resonance frequency-temperature characteristics of the crystal resonator according to the first embodiment of the present invention.
FIG. 3 is a process diagram illustrating the method for manufacturing the crystal resonator according to the first embodiment of the invention.
FIG. 4 is a diagram showing the film thickness dependence of axis inversion.
FIG. 5 is a diagram showing resonance characteristics before and after heat treatment of a quartz substrate with a metal thin film.
FIG. 6 is a cross-sectional view showing the shape of a quartz substrate with a metal thin film.
7A and 7B are diagrams illustrating a crystal resonator according to a second embodiment of the present invention, in which FIG. 7A is a perspective view, and FIG. 7B is a cross-sectional view taken along line II-II in FIG.
8A and 8B are diagrams showing a crystal resonator according to a third embodiment of the present invention, in which FIG. 8A is a perspective view and FIG. 8B is a cross-sectional view taken along line III-III in FIG.
FIG. 9 is a perspective view illustrating a crystal resonator with a temperature sensor according to a fourth embodiment of the present invention.
FIG. 10 is a diagram illustrating a resonance frequency-temperature characteristic of a crystal resonator with a temperature sensor according to a fourth embodiment of the present invention.
FIG. 11 is a diagram for explaining a method for forming an axis reversal part according to a fifth embodiment of the present invention.
FIG. 12 is a diagram showing the relationship between the cutting orientation of the crystal plate and the crystal axis, showing (a) a normal AT cut plate and (b) an X-axis inversion portion.
13 shows how the resonance frequency changes at each time point during the experiment based on the embodiment. (A) is at room temperature, (b) is heated at 520 ° C., and (c) is current. (D) is a figure which shows the time of returning to room temperature immediately after interruption | blocking.
FIG. 14 is a diagram for explaining a method for forming an axis reversal part according to a sixth embodiment of the present invention.
FIG. 15 is a view for explaining a method of forming an axis reversal part according to a seventh embodiment of the present invention.
FIG. 16 is a perspective view showing a conventional crystal resonator.
[Explanation of symbols]
1 AT-cut quartz substrate
2,3 Excitation electrodes
4 excitation section
11, 12 axis reversing part
21, 22 Metal thin film
25 Cr film (metal film)
26 Al film (metal film)
31, 32 Excitation electrodes
33 Excitation part
34 axis reversing part
41 Axis reversing part
42, 43 Excitation electrodes
44 Non-inverted vibrator
45 Inverter vibrator
51 Metal thin film (conductive thin film)
52 Substrate holder
53a, 53b Lead wire
54 Heating heater
55 Vacuum container
56 power supply
57, 64, 73 switches
61 cathode
62 Heater for cathode heating
63 DC voltage source
71 Electrode for voltage application
72 High voltage power supply
W electrode width
L Electrode length
d Distance between excitation part and axis reversal part
s Length of axis reversal part
f Amplitude distribution of vibration displacement in the length direction
A Optimum characteristics of crystal unit
Characteristics of B AT-cut crystal unit
C Characteristics of inverted quartz crystal
D Result of temperature confirmation principle confirmation experiment
E Characteristics of non-inverted part
F Characteristics of reversing part
X Electric shaft
-X Electrical axis in opposite direction

Claims (5)

A thin film made of a conductive material on the surface of a crystal substrate in a method for manufacturing a crystal resonator in which excitation electrodes are formed on both sides of a crystal substrate, and a region sandwiched between the electrode portions is used as an excitation unit. Then, the quartz substrate on which the thin film is formed is heated to 500 to 520 ° C., and then a current is passed through the thin film in this heated state, so that a portion of the quartz substrate that is below the thin film is necessary for axis reversal. A method for manufacturing a crystal resonator, comprising applying an stress to form an axis reversal part having an electric axis opposite to the electric axis of the excitation part. A thin film made of a conductive material on the surface of a crystal substrate in a method for manufacturing a crystal resonator in which excitation electrodes are formed on both sides of a crystal substrate, and a region sandwiched between the electrode portions is used as an excitation unit. Then, the quartz substrate on which the thin film is formed is heated to 500 to 520 ° C. , and then the thin film is irradiated with an electron beam in this heated state, thereby reversing the axis to the portion below the thin film of the quartz substrate. A method for manufacturing a crystal resonator, comprising applying an necessary stress and forming an axis reversal portion having an electric axis opposite to the electric axis of the excitation portion. A thin film made of a conductive material on the surface of a crystal substrate in a method for manufacturing a crystal resonator in which excitation electrodes are formed on both sides of a crystal substrate, and a region sandwiched between the electrode portions is used as an excitation unit. Then, the quartz substrate on which the thin film is formed is heated to 500 to 520 ° C., and then a high electric field is applied to the quartz substrate through the thin film in this heating state, so that the quartz substrate is below the quartz substrate. A method for manufacturing a crystal resonator, comprising applying stress necessary for axis reversal to a portion to form an axis reversal unit having an electric axis opposite to the electric axis of the excitation unit. 4. The method for manufacturing a crystal resonator according to claim 1 , wherein the thin film is any one of a Cr film, a Ni film, and a NiCr film. 5. The method for manufacturing a crystal resonator according to claim 1 , wherein the heating is performed in an inert atmosphere or a vacuum atmosphere.

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