JPH0674834A - Quartz oscillator for detecting temperature - Google Patents

Abstract

PURPOSE:To make the equivalent series resonance resistance of a quartz oscillator small and the temperature characteristic thereof uniform, by extracting a specified directional part of alpha-quartz single crystal and forming a tuning fork-shaped quartz piece. CONSTITUTION:A plane formed by a quartz water 200 agrees with a plate surface obtained by rotating a Z-cut water plate composed of the electrical axis +X 201 and mechanical axis +Y 202 of an alpha-quartz single crystal clockwise by theta degree about the axis 201. A Y' axis 204 is in the position after the rotation of the axis 202 and forms a side of the wafer 200. The longitudinal direction of the arms 101 of a tuning fork-shaped quartz piece 205 is made about parallel to the axis 204. The plate thickness of the wafer 200 is in the range of 80 to 150mum. In the case producing the piece 205 as an oscillator, the ratio of width to length of each arm 101 is set as W/L=0.1-0.2 in the range of an angle theta=15-25 deg. so that the top temperature of temperature characteristic of an equivalent series resonance resistance value is in the range of 25+ or -15 deg.C. Thus, after the external shape working of the quartz piece 205 in made by reducing a fin with photoetching, a driving electrode is formed, and is supported and received within a heat resistant housing 100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting crystal unit for detecting temperature by changing resonance or oscillation frequency.

[0002]

2. Description of the Related Art As a conventional crystal oscillator for temperature detection,
For example, Japanese Patent Publication No. 61-29652 or Japanese Patent Publication 1-2.
No. 9089 can be cited.

[0003]

However, in all of the above-mentioned prior arts, the fact that the designated range of the crystal wafer orientation is wide and the first-order coefficient of the frequency-temperature characteristic of the crystal unit is large is taken into consideration in practical application. There is no mention of whether the characteristics to be done are appropriate. The characteristics to be considered include the value of equivalent series resonance resistance (CI value) of the vibrator and its change characteristics with respect to temperature, and so-called fins generated when the tuning fork-shaped crystal piece is externally processed by photoetching. There are vibration instability of the oscillator due to the remaining part, and spurious phenomenon in which the characteristic is abnormal due to the frequency matching with the unnecessary vibration mode at a certain temperature within the operating temperature range. First, the CI value and the CI
Regarding the temperature characteristics of the value, for a specific angular orientation,
The CI value was large and the temperature change of the CI value was large, so that the oscillation was stopped at a high temperature when the oscillation circuit was constructed. Further, the fins also remained largely, and problems such as a great loss of vibration stability occurred. Further, even if the same bending vibration mode is used, if the higher order vibration mode is used, the one having the spurious phenomenon sometimes occurs, and there is a problem that a strict frequency temperature characteristic inspection is required over the operating temperature range.

Therefore, the present invention solves the above-mentioned problems, and its object is to have a small equivalent series resonance resistance, a flat temperature characteristic and a small change, and excellent vibration stability. , It is to provide an excellent temperature detecting crystal unit that does not cause a spurious phenomenon to the market at a low cost, and to help realize a highly accurate and compact temperature measuring system device.

[0005]

The temperature detecting crystal unit according to the present invention comprises (1) an electric axis + X and a mechanical axis + of an α crystal single crystal.
A plate formed by rotating a Z-cut wafer whose main plane is a plane formed by Y in the range of 15 to 25 degrees, which is an angle in the range in which the electromechanical coupling coefficient is substantially maximum, in the clockwise direction around the electric axis + X. From a crystal wafer with a thickness of 80 to 150 μm,
It is a tuning-fork type having the longitudinal direction of the arm parallel to the Y ′ axis which is the + Y axis after rotation of the quartz wafer, and the side ratio of the arm shape dimensions is (arm width / arm length) ratio is 0. ．The crystal characteristics of 1 to 0.2 crystal pieces were processed by photo-etching to reduce the fins, and then the external electrodes were formed so that they could vibrate in the fundamental vibration mode. Assuming that the temperature difference between the top and bottom of the
The fins are supported and housed in a heat-resistant container, and the cross-sectional area of the fins generated when the crystal forks having the tuning fork shape according to the item (1) are photo-etched to form the outer shape, When converted into an equivalent increment of the arm width, the ratio of the equivalent arm width to the arm width is 5% or less. (3) One of the crystal pieces having the tuning fork shape according to the item (1). By increasing or decreasing the arm width from the other to improve the vibration stability, at least a part of the case and the stem constituting the heat-resistant container according to (4) (1), the pbsn solder and the pb component are A heat-resistant solder plating treatment of 90 wt% or more is applied, and a similar heat-resistant solder plating is applied to at least a part of the inner lead penetrating the stem, so that the crystal fork having a tuning fork shape and the inner lead are Solder plating Is secured to, and wherein the said casing stem is press-fitted bonded via the solder.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing an embodiment of a temperature detecting crystal unit according to the present invention. First, the names of the respective parts in FIG. 1 are listed, 100 is a case, 101 is a tuning-fork-shaped quartz piece arm portion 102 is a tuning-fork-shaped quartz piece base portion, 103 is a stem, and 104 is the aforementioned. The inner lead of the stem, 105 is the outer lead of the stem, 10
6 is heat resistant solder plating of the stem, 107 is solder for fixing the crystal piece and the inner lead, and 108 and 109 are heat resistant solder plating on the surface of the case. Next, a detailed description will be given in order for each of the parts.

First, the quartz piece having the tuning fork shape shown by 101 and 102 will be described. The crystal piece is processed in a specific orientation from the α crystal single crystal. FIG. 2 shows its azimuth diagram. In the figure, 200 is a crystal wafer made from the α-crystal single crystal, and the plane formed by the crystal wafer is one of the basic crystal axes of the α-crystal single crystal: electrical axis + X (201) and mechanical axis + Y. (20
The Z-cut plate wafer formed by 2) coincides with the plate surface obtained by rotating the Z-cut plate wafer clockwise about the electric axis + X by θ degrees. Two
The Y ′ axis of 04 is obtained by rotating the Y axis of 202, and forms one side of the rotated quartz wafer. The + Z axis of 203 indicates the optical axis which is one of the basic crystal axes of the α quartz single crystal. Further, 205 is a crystal piece,
The main plane forming the tuning fork type shape of the crystal is in the plane of the crystal wafer of 200, and is 101 in FIG.
The longitudinal direction of the arm portion of the crystal piece shown in (1) is substantially parallel to the Y ′ axis. The meaning of being substantially parallel is that the angle with the Y ′ axis is within a few degrees. The 200 crystal wafer has a plate thickness of 80 to 150 μm. The angle θ is in the range of 15 to 25 degrees for the reason described later. The 200 crystal wafer is cut out from the α crystal single crystal with the above-mentioned orientation and plate thickness, and is then subjected to sufficient surface polishing finish. The crystal piece 205 is a crystal wafer 2.
After forming a thin film of Au as a Cr underlayer on the front and back sides of the surface of No. 00 by means such as vapor deposition or sputtering, a series of photo processes such as resist coating and exposure are performed to form a tuning fork type outer shape pattern made of a Cr + Au thin film with a crystal. It is formed on the wafer plane. Thereafter, outer shape etching is performed with hydrofluoric acid (AF) or a mixed solution of hydrofluoric acid and ammonium fluoride (NH ₄ F) using the metal film of Cr + Au as an outer shape mask to complete a tuning fork-shaped crystal piece.

Next, the reason for setting the rotation angle θ of the quartz wafer will be described with reference to FIG. The horizontal axis in the figure is the rotation angle θ, the vertical axis is the left side K ² is the electromechanical coupling coefficient,
Further, a (ppm / ° C.) on the right side shows the value of the primary temperature coefficient of the frequency temperature characteristic of the temperature detecting crystal resonator of the present invention. A curve 300 in the figure shows the change of K ² and a of 301 shows the change of the primary temperature coefficient. In the temperature detecting crystal unit, the larger the absolute value of the primary temperature coefficient α, the higher the temperature decomposition accuracy, which is preferable. Therefore, FIG.
The larger θ becomes, the better. On the other hand, considering the equivalent series resonance resistance CI, which is an important characteristic as a temperature detecting crystal unit, the CI is preferably as small as possible and stable as it does not change with temperature. Further, the CI value is related to the electromechanical coupling coefficient K ² described above, and the larger K ² is, the smaller the CI value is.

The curve of 300 K ^{2 in} FIG. 3 is the largest in the vicinity of θ = 15 ° in the range of θ = −90 to + 90 °. Therefore, when θ is close to 15 °, and a concrete numerical value is within the range of θ = 15 ± 10 °, a good CI value close to the minimum can be obtained. As the temperature detecting crystal unit, the θ can be set in the range of 15 to 25 ° in consideration of the CI value and the value of a. At this time a
Of about −15 to −33 ppm / ° C. By the way, the above-mentioned K ² is in accordance with the following equation and is a factor that determines the CI value of the bending vibration mode having a tuning fork shape.

[0010]

[Equation 1]

Here, d ₁₂ , S ₂₂ ^E , ε ₁₁ ^T, etc. are each material constants of α quartz single crystal, d ₁₂ is a component of piezoelectric coefficient tensor, S ₂₂ ^E is a component of elastic coefficient tensor, Furthermore, ε ₁₁ ^T is a component of the dielectric constant tensor. These values at θ = 0 ° are d ₁₂ = 6.88 × 10 ^-8 esu, S ₂₂ ^E
= 12.7759 × 10 ⁻¹³ cm ² / dyne, ε ₁₁ ^T
= 4.5.

Next, the outer shape etching of the crystal using the above-mentioned photo process, that is, the photo etching will be described with reference to FIGS. First, FIG. 4 will be described.
FIG. 4 is a view showing a pair of left and right cross-sections of the arm portion 101 of the crystal fork having the tuning fork shape shown in FIG. 1 mentioned above. The arm portions having a right-angled quadrilateral cross section of the crystal piece having the reference numerals 402 and 403 are fin portions having a triangular cross-section formed during the above-described photoetching. Furthermore, 406, 407, 408, 409
And the like are excitation electrodes made of a metal film of a Cr underlayer Au formed around the one arm portion of the quartz crystal, and are formed in the same arrangement along the longitudinal direction of the arm portion. The electrodes are connected by a metal film of Cr + Au formed on the crystal piece as shown in FIG. 4 and can be excited by a signal source 404.

With the electrode arrangement shown in FIG. 4, the crystal element resonates in the fundamental bending vibration mode (see FIG. 10). The crystal piece thus obtained is used as the temperature detecting crystal resonator of the completed body of FIG. 1, and the equivalent series resonance resistance CI value is measured. The CI value fluctuated depending on the method of fixing the child to the circuit board. This fluctuation of the CI value is considered to be a so-called vibration leakage phenomenon. This is because the displacement of the stem at the base of the crystal fork having the tuning fork shape shown in FIG. In order to leak and swing the stem and the case (100 in FIG. 1) through 104 of No. 1), the degree of energy loss of the temperature detecting crystal unit changes depending on how the case is fixed to the circuit board. Has occurred.

Regarding this phenomenon, the relationship between the etching processing time of the quartz piece and the fluctuation characteristics of the CI value in various photo-etching was experimentally examined, and the result as shown in FIG. 5 was obtained. The horizontal axis in the figure is the arm width dimension W which should be as large as the amount ΔW μm equivalently converted from the fin to the arm width.
Is expressed as a percentage, and the vertical axis indicates the above-mentioned CI.
The amount of change in value is expressed in%. The ΔW is calculated as follows. Since the fin portions 402 and 403 in FIG. 4 have substantially the same cross-sectional area S, this S is determined as ΔT≈2S / t as the plate thickness t of the crystal wafer.

As far as the characteristic 500 of FIG. 5 is concerned, ΔW
It is understood that it is necessary to reduce the remaining amount of fins within 5% / W, and more preferably within 4%. Furthermore, we were able to find the following facts by conducting an analysis by experiments and calculations by the finite element method. The results are shown in FIG. The horizontal axis in FIG. 6 is the amount indicated by ε in FIG. 4, and represents the dimensional difference between the pair of arm widths of the crystal piece. The vertical axis in FIG. 6 is a characteristic diagram showing the degree Ux in the width direction (+ X axis direction in FIG. 4) of the base (102 in FIG. 1) having the tuning fork shape. The straight line 600 is calculated for the case where the equivalent conversion width ΔW / W of the fin is 4.3%, and Ux = 0 at ε = + 2 μm, which theoretically eliminates the fluctuation of the CI value due to vibration leakage. It will be. Therefore, when a crystal piece was made as a prototype with such dimensions, good results were obtained.

The crystal wafer cutting direction described above is as follows:
The tuning fork shape dimension of the crystal piece was set next under the photo-etching processing condition of the crystal piece. The characteristic diagrams of interest in this case are shown in FIGS. 7 and 8. First, FIG. 7 is a part of what is called a so-called mode chart, which is based on the natural resonance frequency f ₀ of the fundamental bending vibration mode of the tuning fork-shaped crystal piece under specific dimensional conditions. The frequency ratio f / f ₀ of other vibration modes is shown on the vertical axis. Circles in the figure indicate relative frequency positions indicated by various vibration modes, and 700 is a second-order in-phase bending vibration having a displacement Uz perpendicular to the principal plane of the quartz piece,
Reference numeral 1 is a fundamental wave bending vibration (vibration as shown in FIG. 10 having a displacement Ux) which is a target of the above design, 702 is a vibration mode in which a pair of left and right arms vibrates in synchronization in the same direction, and 703 is 70
A vibration mode in which the left and right arms are displaced in the opposite direction in the Z direction, such as 0, and 704 is a Z mode in which the left and right arms are the same as 703
It is a vibration mode that vibrates in synchronization with the direction. Z- in the figure
The symbols FS-1 to Z-FS-2 correspond to the right and are entered to identify the above vibration modes.

The important point in FIG. 7 is that even if the maximum first-order temperature coefficient a = −33 ppm / ° C. is taken in the temperature range of −50 to 100 ° C. where the temperature detecting crystal unit is normally used, it is never the case. That is, the vibration mode and frequency do not match. This is because the fundamental bending vibration mode was selected instead of the higher order mode. The frequency difference between 701 and 702 in FIG. 7 is as far as 10% apart, and is sufficiently far apart even if the temperature change of the above-mentioned frequency is calculated. The mode chart of FIG. 7 shows that the thickness of the tuning fork-shaped crystal element is 80 to 150 μm, and the ratio t / w of the thickness t to w of the pair of arms is 0.24 to 0.6. Ratio c / w of distance c to w is 0.3 to 0.6
If it is between, it is a sufficient relationship. If you have this relationship,
It can be confirmed that the frequencies of the nearest vibration modes are separated by 8% or more. Therefore, it does not occur that a strange phenomenon occurs due to collision with a so-called spurious mode during temperature measurement. Next, the temperature characteristics of the CI value were examined under the above dimensional conditions.

FIG. 8 shows the temperature characteristic of the IC value and the temperature characteristic of the resonance frequency of the specifically manufactured temperature detecting crystal unit. In the figure, the horizontal axis is the ambient temperature T (° C.), the left side of the vertical axis is the frequency-temperature characteristic represented by the frequency change rate Δf / f _O , and the right side is the CI value (KΩ). In the figure, the curve 800 indicates the frequency temperature characteristic, and the curve 801 indicates the temperature characteristic of the CI value. Furthermore, the curve 801 is a parabola having an upward convex shape, and is substantially symmetrical with respect to the apex temperature 802 showing the minimum value. This peak temperature was examined with respect to various crystal wafer orientations and the arm shape of the crystal piece, in particular, the ratio W / L of the width dimension W and the arm length L (L in FIG. 1).
As the condition range in which the apex temperature is 25 ± 15 ° C., the cutting orientation θ of the quartz wafer described above can be substantially achieved within the range of θ = 15 to 25 ° and W / L = 0.1 to 0.2. I understood. By the way, the secondary temperature coefficient of CI ground was calculated to be 40.8ppm / ℃ ² (2
The increase in CI value between 5 ° C and 95 ° C is as small as 20%). Further, the size of the crystal piece used in FIG. 1 is L = 25.
20 μm, W = 324 μm, t = 130 μm, c = 17
Add 6 μm.

Since the detailed description of the crystal piece of FIG. 1 has been completed, the remaining components of the temperature detecting crystal resonator of the present invention will be described below.

The container for storing the crystal piece comprises a case 100 and a stem 103. First, the stem has a substantially cylindrical side surface made of metal such as Kovar. Inside the cylinder, two lead wire members made of the same Kovar material are arranged in parallel, and the inside of the stem is made of an airtight glass member. Once melted and fixed, it is made airtight. The case 100 is made by deep-pressing a nickel-white plate made of Cu and Ni alloy with a press. Further, in the present invention, the case is plated with Ni or heat-resistant solder is further plated thereon, and the stem is made of Cu or Ni including inner leads and outer leads.
The above heat resistant solder plating treatment is applied on the base plating.

The characteristics of the heat resistant solder plating will be described with reference to FIG. FIG. 9 is a state diagram of an alloy in which the abscissa represents the component ratio (wt%) of pbsn, which is the composition of solder, and the ordinate represents the temperature (° C.). The heat-resistant solder used in the temperature detecting crystal unit of the present invention has a pb component of 90 wt% or more,
Therefore, Sn uses a region of 10 wt% or less.
Therefore, its melting temperature is as high as 260 ° C., and it has a performance capable of sufficiently covering the operating temperature range of the temperature detecting crystal resonator. The procedure for assembling the temperature detecting crystal unit is as follows. First, in a state where the Cr + Au electrode film of the crystal piece and the inner lead (104 in FIG. 1) of the stem are in contact with each other, the temperature is raised to about 327 ° C. or higher. Fix it.

Next, the stem to which the crystal piece is fixed and the case are left in a high vacuum and high temperature state of 10 ⁻⁵ to 10 ⁻⁶ Torv (the temperature of the hatched portion shown by 900 in FIG. 9) and the heat resistant solder plating is performed. In the semi-molten state, the gas existing inside the solder plating is released, and then the temperature is lowered to press the case and the stem under pressure to insert the crystal piece in an airtight container. The crystal unit for temperature detection completed in this way is
There is little residual gas inside the container, and extremely stable frequency accuracy can be maintained. Finally, when I touched on the size of the heat-resistant container consisting of the case and the stem, the size was 2 mm in diameter x 6 mm in length, or even 1.5 mm in diameter.
A small size with a length of about 4 mm is possible.

[0023]

As described above, according to the present invention, after the cutting direction of the crystal wafer and the shape and size of the crystal piece having the tuning fork shape are appropriately set, the electrode for exciting in the fundamental bending vibration mode is set. Due to the formation, the equivalent series resonance resistance value CI of the temperature detecting crystal resonator is small and its change with respect to temperature is suppressed, and the frequency and the CI depp phenomenon due to spurious do not occur. Furthermore, the degree of fins generated when the crystal piece having a tuning fork shape is externally processed by photo-etching is sufficiently reduced, or one arm width is increased or decreased to reduce the vibration displacement of the crystal piece base. As a result, it is possible to provide a crystal oscillator for temperature detection with a high degree of stability while suppressing the fluctuation of the CI value due to the mounting state.

Further, by providing high vacuum sealing in a high temperature process using heat resistant solder plating in a high temperature treatment, a highly accurate temperature detecting crystal unit having a wide operating temperature range and high frequency accuracy is provided to the market. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cross-sectional structure of an embodiment of a temperature detecting crystal resonator of the present invention.

FIG. 2 is a view showing a cutting direction of a crystal wafer forming a crystal piece of the temperature detecting crystal resonator of the present invention.

FIG. 3 is a characteristic diagram of K ² and a shown by the temperature detecting crystal unit of the present invention.

FIG. 4 is a cross-sectional view showing a structure of an arm section of a crystal piece which is a constituent member of the present invention.

FIG. 5 is a characteristic diagram showing fins.

FIG. 6 is another characteristic diagram showing fins.

FIG. 7 is a mode chart showing the temperature detecting crystal unit of the present invention.

FIG. 8 is a characteristic diagram showing the temperature characteristics of the equivalent series resonance resistance and the frequency, which the crystal unit for temperature detection of the present invention shows.

FIG. 9 is a state diagram of an alloy contained in heat resistant solder plating which is a constituent member of the present invention.

FIG. 10 is a diagram showing a vibration mode shown by a crystal piece which is a constituent member of the present invention.

[Explanation of symbols]

 100 ... Case 101 ... Arm part of crystal piece having tuning fork shape 103 ... Stem

Claims (4)

[Claims] 1. An electric axis + X and a mechanical axis + Y of an α quartz single crystal.
A plate thickness formed by rotating a Z-cut wafer whose main plane is the plane created by the above in the range of 15 to 25 °, which is an angle in the range in which the electromechanical coupling coefficient is substantially maximum, in the clockwise direction around the electric axis + X. From a quartz wafer having a diameter of 80 to 150 μm, a tuning fork type shape having a longitudinal direction of the arm parallel to the Y ′ axis which is the + Y axis after the rotation of the quartz wafer, and the side ratio of the dimension of the arm shape is (arm The width / arm length ratio is 0.1 to 0.
After the fin of crystal No. 2 was processed by photo-etching to reduce the fin shape, the excitation electrode was formed so that it could vibrate in the fundamental vibration mode, and the peak temperature of the temperature characteristic of the equivalent series resonance resistance of the vibrator was almost the same. A temperature detecting crystal unit, which is supported and stored in a heat-resistant container at room temperature (25 ± 15 ° C.). 2. A cross-sectional area of a fin generated when a quartz piece having a tuning fork shape is photo-etched for outer shape processing,
When the plate thickness of the quartz wafer is converted into an increment of the arm width equivalent to one side, the ratio of the arm width equivalent to the arm width is 5%.
The crystal resonator for temperature detection according to claim 1, wherein: 3. The crystal resonator for temperature detection according to claim 1, wherein one arm width of the crystal piece having a tuning fork shape is increased or decreased as compared with the other arm to improve vibration stability. 4. A pbsn solder containing 9 parts of pb in at least a part of a case and a stem constituting a heat-resistant container.
At least one of inner leads penetrating the stem while being subjected to heat-resistant solder plating treatment of 0 wt% or more
The same heat-resistant solder plating is also applied to the portion, the crystal fork having a tuning fork shape and the inner lead are fixed via the solder, and the case and the stem are press-fitted and coupled via the solder. The crystal resonator for temperature detection according to claim 1.