Gas sensor

Abstract

To provide a compact and inexpensive gas sensor.SOLUTION: A gas sensor 100 includes a quartz crystal resonator element 30, a package 10 having an internal space C capable of accommodating the quartz crystal resonator element 30, and a lid portion 20 that partitions the internal space C and an external space E of the package 10, where the internal space C is a vacuum or has negative pressure with respect to the external space E, and the lid portion 20 includes a gas-permeable material and is permeable to gas from the external space E to the internal space C.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] BACKGROUND ART Conventionally, there are gas sensors that can detect flammable gases and the like and are used in gas leak alarms and gas concentration meters.

[0003] A gas sensor capable of detecting flammable gases and the like is a hydrogen gas sensor described in Patent Document 1. The hydrogen gas sensor described in Patent Document 1 includes a ceramic package, a hydrogen gas sensor chip bonded within the ceramic package, and a hydrogen gas permeable cover that seals the opening of the ceramic package.

[0004] The hydrogen gas sensor chip is made of an SOI substrate consisting of a Si substrate, an SiO2 film formed on the surface of the Si substrate, and a Si film formed on the surface of the SiO2 film. An oscillator is formed on the Si film using MEMS processing technology. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-230071 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when an SOI substrate is used as a hydrogen gas sensor chip, the gas sensor may become large due to its complicated shape, and the gas sensor may become expensive due to the high cost of the SOI substrate.

[0007] In view of the above circumstances, an object of the present invention is to provide a small-sized, inexpensive gas sensor. [Means for solving the problem]

[0008] A gas sensor according to a first aspect of the present invention comprises a quartz crystal vibrating piece, a package having an internal space capable of accommodating the quartz crystal vibrating piece, and a lid portion separating the internal space from an external space of the package, wherein the internal space is a vacuum or a negative pressure relative to the external space, and the lid portion contains a gas-permeable material and allows gas to pass from the external space to the internal space.

[0009] According to the gas sensor of the first aspect, a predetermined gas (permeating gas) flows from the external space into the internal space by permeating the lid. The permeating gas reduces the degree of vacuum in the internal space, and the change in the resistance of the quartz crystal resonator element due to the reduced vacuum is detected, thereby enabling gas detection. Therefore, an SOI substrate is not required for the gas sensor, and compared to conventional gas sensors using SOI substrates, the complexity of the shape and the increase in the cost of components can be suppressed. Furthermore, the gas sensor of the first aspect can be realized by, for example, replacing the lid of a conventional quartz crystal resonator with a gas-permeable lid. Therefore, the gas sensor can have a size comparable to that of a conventional quartz crystal resonator and can be manufactured using at least some of the manufacturing equipment for conventional quartz crystal resonators. As a result, a compact and inexpensive gas sensor can be provided.

[0010] A gas sensor according to a second aspect of the present invention is the gas sensor according to the first aspect, wherein the quartz crystal vibrating piece may be a tuning fork type.

[0011] According to the gas sensor of the second aspect, by using a tuning-fork type quartz crystal vibrating piece, the sensitivity to a decrease in the vacuum level in the internal space is higher than when using an AT-cut type vibrating piece, and the detection accuracy of the permeable gas that has flowed into the internal space can be improved.

[0012] A gas sensor according to a third aspect of the present invention may be the gas sensor according to the first aspect, wherein the lid portion has a flat plate shape extending perpendicular to the direction in which the lid portion and the quartz crystal vibrating piece face each other.

[0013] In the gas sensor according to the third aspect, the use of a flat lid allows the size of the gas sensor to be reduced in the direction in which the lid and the quartz crystal resonator element face each other (thickness direction), thereby enabling the gas sensor to be miniaturized. Furthermore, since the flat lid and the quartz crystal resonator element face each other in the thickness direction, the gas sensor can more quickly detect permeating gas that has passed through the lid and flowed into the internal space.

[0014] A gas sensor according to a fourth aspect of the present invention is the gas sensor according to the first aspect, and may further include a getter material provided in the internal space and capable of adsorbing the gas in the internal space.

[0015] According to the gas sensor of the fourth aspect, the getter material adsorbs the permeable gas that has flowed into the internal space, thereby returning the degree of vacuum in the internal space to the state before the permeable gas flowed in. Therefore, the permeable gas can be detected multiple times or continuously while maintaining the detection accuracy of the permeable gas.

[0016] A gas sensor according to a fifth aspect of the present invention is the gas sensor according to the fourth aspect, wherein the quartz crystal vibrating piece is disposed between the lid portion and the getter material in a direction in which the lid portion and the quartz crystal vibrating piece face each other.

[0017] The gas sensor according to the fifth aspect can prevent the permeable gas that has passed through the lid and flowed into the internal space from being adsorbed by the getter material before being detected by the gas sensor. Therefore, the permeable gas can be adsorbed by the getter material after the degree of vacuum in the internal space is reduced by the permeable gas and the resistance value of the quartz crystal resonator element changes to a level that allows the gas sensor to adequately detect the permeable gas.

[0018] A gas sensor according to a sixth aspect of the present invention is the gas sensor according to the fourth aspect, wherein the package has a mounting portion that supports the quartz crystal vibrating piece, the quartz crystal vibrating piece has a base supported by the mounting portion and vibrating arms extending from the base, and the getter material may be provided on the vibrating arms.

[0019] In the gas sensor according to the sixth aspect, the mass of the getter material changes as a result of adsorption of the permeable gas that has flowed into the internal space, thereby changing the frequency of the quartz crystal resonator element. Therefore, based on the change in frequency of the quartz crystal resonator element, it is possible to estimate the amount of permeable gas adsorbed by the getter material, and therefore the time to replace the getter material or the gas sensor can be estimated.

[0020] A gas sensor according to a seventh aspect of the present invention is the gas sensor according to the first aspect, and may further include a temperature detection portion capable of detecting temperature.

[0021] According to the gas sensor of the seventh aspect, even if the frequency of the quartz crystal resonator element changes due to the frequency-temperature characteristics, temperature compensation is possible by detecting the temperature in the internal space using the temperature detection unit, and the permeating gas can be detected with high accuracy.

[0022] A gas sensor according to an eighth aspect of the present invention is the gas sensor according to the seventh aspect, wherein the temperature detection portion is provided in the internal space.

[0023] According to the gas sensor of the eighth aspect, the temperature detection portion is provided at a location closer to the quartz crystal resonator element, and therefore, more accurate temperature compensation is possible.

[0024] A gas sensor according to a ninth aspect of the present invention is the gas sensor according to the seventh aspect, wherein the package is provided on the opposite side of the lid, sandwiching the quartz crystal vibrating piece in a direction in which the lid and the quartz crystal vibrating piece face each other, and has a bottom that separates the internal space from the external space, and the temperature detection unit is provided on the external space side of the bottom.

[0025] In the gas sensor according to the ninth aspect, the temperature detection unit is located in the external space near the quartz crystal resonator element across the bottom, so that even if the temperature detection unit is located in the external space, it can adequately detect the temperature around the quartz crystal resonator element and perform temperature compensation.

[0026] A gas sensor according to a tenth aspect of the present invention is the gas sensor according to any one of the first to ninth aspects, and may further include an integrated circuit chip electrically connected to the quartz crystal vibrating piece and having an oscillation circuit.

[0027] The gas sensor according to the tenth aspect can be realized by replacing the cover of the quartz crystal unit included in a conventional oscillator with a cover that is gas permeable, so that the gas sensor can have a size comparable to that of a conventional oscillator and can be manufactured using at least part of the manufacturing equipment for conventional oscillators. As a result, a compact and inexpensive gas sensor can be provided. [Effects of the Invention]

[0028] According to the gas sensor of the present invention, it is possible to provide a small-sized gas sensor at a low cost. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is an external perspective view showing a gas sensor according to a first embodiment. [Figure 2] 1 is a plan view showing a gas sensor according to a first embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 10 is an external perspective view showing a gas sensor according to a second embodiment. [Figure 5] FIG. 10 is an exploded perspective view showing a gas sensor according to a second embodiment. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0030] (First embodiment) A first embodiment of the present invention will be described with reference to the drawings.

[0031] Fig. 1 is an external perspective view showing a gas sensor 100 according to a first embodiment. Fig. 2 is a plan view showing the gas sensor 100 according to the first embodiment. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2.

[0032] The gas sensor 100 includes a package 10, a lid 20, a quartz crystal vibrating piece 30, a getter material 40, and a temperature detection unit 50.

[0033] In this embodiment, as shown in FIGS. 1, 2, and 3, the direction in which the lid 20 and the quartz-crystal vibrating piece 30 face each other is defined as the "thickness direction (vertical direction) T," the direction in which the lid 20 is provided is defined as the "upper side T1" in the thickness direction T, and the opposite direction is defined as the "lower side T2" ​​in the thickness direction T. The longitudinal direction of the quartz-crystal vibrating piece 30 is defined as the "longitudinal direction L," one side in the longitudinal direction L is defined as the "base end side L1," and the other side is defined as the "tip side L2" in the longitudinal direction L. The shorter side of the quartz-crystal vibrating piece 30 is defined as the "width direction (horizontal direction) W," one side in the width direction W is defined as the "right side W1," and the other side is defined as the "left side W2" in the width direction W.

[0034] The package 10 includes a first base substrate (bottom) 11, a second base substrate 12, and a seal ring 13. The package 10 has an internal space (cavity) C capable of accommodating the quartz crystal vibrating piece 30 therein.

[0035] The first base substrate (bottom) 11 is a substrate having a rectangular shape in a plan view seen from the thickness direction T. An upper surface 11a of the first base substrate 11 forms the bottom surface of the internal space C. The upper surface 11a of the first base substrate 11 is the surface of the first base substrate 11 facing upward T1. The first base substrate 11 may be made of a material such as ceramics.

[0036] A pair of external electrodes 14, 15 are formed on the lower surface of the first base substrate 11 with a gap in the longitudinal direction L. Of the pair of external electrodes 14, 15, the external electrode provided on the base end side L1 is also referred to as the base end side external electrode 14, and the external electrode provided on the tip end side L2 is also referred to as the tip end side external electrode 15.

[0037] The base end external electrode 14 and the tip end external electrode 15 are each made of a single layer film of a single metal formed by vapor deposition, sputtering, or the like, or a laminated film in which different metals are laminated.

[0038] The second base substrate 12 is a substrate provided above T1 the first base substrate 11. In a plan view seen from the thickness direction T, the outer shape of the first base substrate 11 and the outer shape of the second base substrate 12 are the same. As the material of the second base substrate 12, for example, ceramics can be used.

[0039] The second base substrate 12 is stacked on the upper side T1 of the first base substrate 11 and integrally bonded thereto by sintering or the like. Note that examples of ceramic materials that can be used for the first base substrate 11 and the second base substrate 12 include alumina-made HTCC (High Temperature Co-Fired Ceramic) and glass-ceramic-made LTCC (Low Temperature Co-Fired Ceramic).

[0040] 2 and 3, the second base substrate 12 has a through portion 12h formed therein that penetrates the second base substrate 12 in the thickness direction T. The through portion 12h has a rounded rectangular shape in a plan view seen from the thickness direction T.

[0041] On the inner surface of the through portion 12h, a pair of mounting portions 16 are formed at the corners on the right side W1 and left side W2 located on the base end side L1, protruding into the internal space C. Of the pair of mounting portions 16, the mounting portion 16 provided on the right side W1 is also referred to as a first mounting portion 16a, and the mounting portion 16 provided on the left side W2 is also referred to as a second mounting portion 16b.

[0042] A pair of electrode pads 17 are formed on the upper T1 surfaces of the first mounting portion 16a and the second mounting portion 16b, as connection electrodes with the quartz crystal vibrating piece 30. Of the pair of electrode pads 17, the electrode pad 17 formed on the first mounting portion 16a is also referred to as the first electrode pad 17a, and the electrode pad 17 formed on the second mounting portion 16b is also referred to as the second electrode pad 17b.

[0043] The first electrode pad 17a and the second electrode pad 17b, like the base-side external electrode 14 and the tip-side external electrode 15, are composed of, for example, a single-layer film made of a single metal formed by vapor deposition, sputtering, etc., or a laminated film in which different metals are stacked.

[0044] The first electrode pad 17a and the second electrode pad 17b are electrically connected to the base end external electrode 14 and the tip end external electrode 15 via through-wiring (not shown) that penetrates the first base substrate 11 and the second base substrate 12 in the thickness direction T.

[0045] At the four corners of the first base substrate 11 and the second base substrate 12, quadrant-arc cutouts are formed across the entire thickness direction T of the first base substrate 11 and the second base substrate 12 when viewed in a plane from the thickness direction T.

[0046] First base substrate 11 and second base substrate 12 are fabricated by, for example, stacking and bonding two wafer-like ceramic substrates, forming a matrix of through-holes that penetrate the two bonded ceramic substrates, and cutting the two ceramic substrates into a grid pattern based on each through-hole. At this time, the through-holes are divided into four, thereby forming the notches described above.

[0047] The seal ring 13 is a frame-shaped member that is slightly smaller than the outer shapes of the first base substrate 11 and the second base substrate 12, and is joined to the upper surface T1 of the second base substrate 12. The seal ring 13 is formed, for example, from a conductive material.

[0048] The seal ring 13 is bonded to the second base substrate 12 by baking a brazing material such as silver brazing or a solder material, or by welding to a metal bonding layer formed on the second base substrate 12.

[0049] The seal ring 13, together with the inner surface of the through portion 12h in the second base substrate 12, constitutes the side wall of the internal space C. In this embodiment, the inner surface of the seal ring 13 is disposed flush with the inner surface of the second base substrate 12, as shown in FIG.

[0050] The material of seal ring 13 may be, for example, a nickel-based alloy, and more specifically, may be Kovar, Elinvar, Invar, 42-alloy, etc. When ceramics are used as the material of first base substrate 11 and second base substrate 12, it is preferable to use, as the material of seal ring 13, a material having a thermal expansion coefficient close to that of first base substrate 11 and second base substrate 12 made of ceramics.

[0051] For example, the first base substrate 11 and the second base substrate 12 have a thermal expansion coefficient of 6.8×10 -6 / °C, the seal ring 13 has a thermal expansion coefficient of 5.2 × 10 -6 / ℃ Kovar and thermal expansion coefficient 4.5~6.5×10 -6 It is preferable to use 42-alloy with a temperature of 1000 K / °C.

[0052] The lid portion 20 is a lid member that is joined to the upper surface T1 of the seal ring 13 and covers the internal space C from above T1. As shown in Fig. 3, the lid portion 20 separates the internal space C from the external space E of the package 10.

[0053] The lid portion 20 has a flat plate shape extending perpendicular to the thickness direction T. By using the flat plate-shaped lid portion 20, the dimensions of the gas sensor 100 in the thickness direction T can be reduced, and the gas sensor 100 can be made smaller.

[0054] The internal space C is a space formed inside the package 10, and is separated from the external space E by the package 10 and the lid portion 20. The internal space C is a vacuum or has a negative pressure relative to the external space E.

[0055] The lid 20 includes a gas-permeable material and is capable of transmitting gas from the external space E to the internal space C. An appropriate material can be used for the lid 20 depending on the gas that is to be transmitted from the external space E to the internal space C. For example, when the gas to be transmitted is hydrogen gas, palladium can be used as the material for the lid 20.

[0056] The quartz crystal vibrating piece 30 is a vibrating piece including a piezoelectric plate made of quartz crystal. The quartz crystal vibrating piece 30 is housed in the internal space C of the package 10. The quartz crystal vibrating piece 30 is, for example, a tuning fork-type vibrating piece.

[0057] The quartz crystal vibrating piece 30 includes a base 31 and a pair of vibrating arms 32 extending from the base 31 in the longitudinal direction L. Of the pair of vibrating arms 32, the vibrating arm 32 provided on the right side W1 is also referred to as the first vibrating arm 32a, and the vibrating arm 32 provided on the left side W2 is also referred to as the second vibrating arm 32b.

[0058] The base 31 is supported from below T2 by the first mounting portion 16a and the second mounting portion 16b via the first electrode pads 17a and the second electrode pads 17b.

[0059] The first vibrating arm 32a and the second vibrating arm 32b extend from the base 31 to the tip side L2. The first vibrating arm 32a and the second vibrating arm 32b are disposed apart from the first base substrate 11 in the thickness direction T.

[0060] An electrode film (not shown) is disposed on the outer surface, including the front and back surfaces, of the quartz-crystal vibrating piece 30. The electrode film includes excitation electrodes (described later), mount electrodes that serve as mounts when the base 31 is mounted on the package 10, and connection wiring that connects the excitation electrodes and mount electrodes.

[0061] The excitation electrodes included in the electrode film are disposed on the outer surfaces of the first vibrating arm 32 a and the second vibrating arm 32 b. Two systems of excitation electrodes (not shown) are disposed on the outer surfaces of the first vibrating arm 32 a and the second vibrating arm 32 b, which vibrate the first vibrating arm 32 a and the second vibrating arm 32 b when a predetermined voltage is applied.

[0062] When a predetermined voltage is applied to the external electrodes 14 and 15, a current flows through the excitation electrodes of the vibrating arm 32, generating an electric field. The first vibrating arm 32a and the second vibrating arm 32b vibrate at a predetermined resonance frequency in directions in which they approach and move away from each other (width direction W) due to, for example, an inverse piezoelectric effect caused by the generated electric field.

[0063] The first vibrating arm 32a and the second vibrating arm 32b are arranged in parallel in the width direction W, and are each connected to the base 31. The first vibrating arm 32a and the second vibrating arm 32b have their ends on the base end side L1 connected to the base 31 as fixed ends and their ends on the tip end side L2 as free ends, and vibrate in directions in which they approach and move away from each other (the width direction W).

[0064] The electrode film is, for example, a laminated film of chromium (Cr) and gold (Au), which is formed by depositing a chromium film that has good adhesion to quartz crystal as a base, and then laminating a thin gold film on the chromium film. The film configuration of the electrode film is not limited to this, and for example, a thin gold film may be further laminated on a laminated film of chromium and nichrome (NiCr), or it may be a single layer film of chromium, nickel, aluminum (Al), titanium (Ti), etc.

[0065] The getter material 40 is provided in the internal space C. In this embodiment, the getter material 40 is provided on the upper surface 11a of the first base substrate 11. The getter material 40 is also arranged below T2 the first vibrating arm portion 32a and the second vibrating arm portion 32b.

[0066] That is, the quartz-crystal vibrating piece 30 is provided between the lid 20 and the getter material 40 in the thickness direction T, in which the lid 20 and the quartz-crystal vibrating piece 30 face each other. The getter material 40 is formed with a thickness dimension (dimension in the thickness direction T) that does not interfere with the vibrating first vibrating arm portion 32a and second vibrating arm portion 32b.

[0067] The getter material 40 is made of a material capable of adsorbing a predetermined gas. The gas that the getter material 40 can adsorb is the same as the gas that can permeate the lid portion 20. For example, if the lid portion 20 is permeable to hydrogen gas, the getter material 40 can adsorb hydrogen gas.

[0068] As the material of the getter material 40 capable of adsorbing hydrogen gas, for example, magnesium (Mg), a mixture of magnesium and titanium (Ti), or an alloy containing lanthanum (La), zirconium (Zr), or the like can be used.

[0069] The gas sensor 100 may include a heater (not shown) for heating the getter material 40. The getter material 40 is activated by heating with a heater, for example, and the gas adsorption efficiency is improved. The heater for heating the getter material 40 is provided near the getter material 40, for example, on the lower surface T2 of the first base substrate 11.

[0070] The temperature detection unit 50 is a temperature sensor capable of detecting temperature, such as a thermistor. In this embodiment, the temperature detection unit 50 is provided in the internal space C. The temperature detection unit 50 is also provided on the upper surface 11a of the first base substrate 11, and is disposed below the quartz-crystal vibrating piece 30 at a position T2.

[0071] Next, the gas detection operation of the gas sensor 100 will be described.

[0072] As described above, when a predetermined voltage is applied to the external electrodes 14 and 15, the first vibrating arm 32a and the second vibrating arm 32b vibrate at a predetermined resonant frequency in a direction in which they approach and move away from each other (width direction W) due to the inverse piezoelectric effect.

[0073] For example, weight films formed by vapor deposition are provided on the ends of the tip side L2 of the first vibrating arm 32 a and the second vibrating arm 32 b. By adjusting the mass of these weight films, the first vibrating arm 32 a and the second vibrating arm 32 b can be configured to vibrate at a predetermined frequency when a predetermined voltage is applied.

[0074] As described above, a predetermined gas is permeable through the lid portion 20. In the following description, the gas that can permeate the lid portion 20 is also referred to as a permeating gas.

[0075] Furthermore, the internal space C is a vacuum or has a negative pressure relative to the external space E. Therefore, when a permeable gas (e.g., hydrogen gas) is present in the external space E, the permeable gas permeates the lid portion 20 and flows from the external space E into the internal space C. At this time, the vibrating arm portion 32 is vibrating due to the application of a voltage.

[0076] The degree of vacuum in the internal space C changes as the permeable gas flows into the internal space C from the external space E. Specifically, the degree of vacuum in the internal space C decreases.

[0077] When the degree of vacuum in the internal space C decreases, the vibrating arms 32 vibrating in the internal space C become less likely to vibrate. That is, the permeable gas that has flowed from the external space E into the internal space C inhibits the vibration of the vibrating arms 32.

[0078] When the vibration of the vibrating arms 32 is inhibited by the permeating gas, the equivalent series resistance (R1) of the quartz crystal vibrating piece 30 changes. By detecting this changed resistance (R1) of the quartz crystal vibrating piece 30, the gas sensor 100 can detect that the permeating gas has flowed into the internal space C, and can detect the presence of the permeating gas around the gas sensor 100.

[0079] Here, the shape of the quartz crystal vibrating piece 30 is preferably tuning fork-shaped. Tuning fork-shaped vibrating pieces, which have a flexural vibration mode, have a larger change in resistance when the degree of vacuum decreases than AT-cut vibrating pieces, which have a thickness-shear vibration mode, and are therefore more sensitive to decreases in the degree of vacuum. Therefore, by using a tuning fork-shaped vibrating piece as the quartz crystal vibrating piece 30, the detection accuracy of permeating gas can be improved.

[0080] In this embodiment, the lid 20 has a flat plate shape extending in a direction perpendicular to the thickness direction T, and faces the quartz-crystal vibrating piece 30 in the thickness direction T. Therefore, the gas sensor 100 can detect the permeating gas that has flowed into the internal space C more quickly than when the lid 20 and the quartz-crystal vibrating piece 30 are not opposed to each other in the thickness direction T.

[0081] In addition, the getter material 40 adsorbs the permeable gas that has flowed into the internal space C. By the getter material 40 adsorbing the permeable gas, the degree of vacuum in the internal space C can be returned to the state (initial state) before the permeable gas flowed into the internal space C.

[0082] For example, if the internal space C is filled with permeable gas, there is a possibility that new permeable gas cannot flow into the internal space C. In this case, even if permeable gas is present around the gas sensor 100, there is a possibility that the gas sensor 100 cannot accurately detect the permeable gas.

[0083] By returning the degree of vacuum in the internal space C to the initial state by the getter material 40, the gas sensor 100 can detect the permeable gas multiple times or continuously while maintaining the detection accuracy of the permeable gas.

[0084] The getter material 40 does not have to adsorb all of the permeable gas that has flowed into the internal space C. Even if the getter material 40 does not adsorb all of the permeable gas in the internal space C, the degree of vacuum in the internal space C can be made close to the initial state, and a decrease in the detection accuracy of the permeable gas in the gas sensor 100 can be suppressed.

[0085] In this embodiment, the getter material 40 is disposed at a position T2 below the quartz-crystal vibrating piece 30. The lid 20 is disposed at a position T1 above the quartz-crystal vibrating piece 30.

[0086] Therefore, the getter material 40 can adsorb the permeable gas after the degree of vacuum in the internal space C decreases due to the permeable gas that has permeated through the lid portion 20 and flowed into the internal space C, and the resistance value of the quartz vibrating piece 30 changes to a level that allows the gas sensor 100 to adequately detect the permeable gas.

[0087] When the resistance value of the quartz crystal vibrating piece 30 changes due to the inflow of permeable gas, the temperature detection unit 50 detects the temperature within the internal space C, thereby enabling temperature compensation.

[0088] For example, the quartz crystal vibrating piece 30 has a frequency-temperature characteristic in which the frequency changes with temperature. Even if the frequency of the quartz crystal vibrating piece 30 changes due to the frequency-temperature characteristic, the gas sensor 100 can accurately detect the permeating gas by detecting the temperature in the internal space C using the temperature detection unit 50.

[0089] In this embodiment, the temperature detection unit 50 is provided in the internal space C and is located closer to the quartz crystal vibrating piece 30, which allows for more accurate temperature compensation.

[0090] The gas sensor 100 according to the first embodiment includes a quartz crystal vibrating piece 30, a package 10 having an internal space C capable of accommodating the quartz crystal vibrating piece 30, and a lid 20 separating the internal space C from an external space E of the package 10.

[0091] The internal space C is at a vacuum or a negative pressure relative to the external space E, and the cover portion 20 includes a gas-permeable material, allowing gas to pass from the external space E to the internal space C.

[0092] The gas sensor 100 detects gas by detecting the resistance value of the quartz crystal vibrating piece 30 that changes as the degree of vacuum in the internal space C decreases due to the permeating gas that has flowed into the internal space C.

[0093] The gas sensor 100 does not require an SOI substrate as a gas sensor, and compared to conventional gas sensors that include an SOI substrate, the gas sensor 100 can suppress the complexity of the shape and the increase in the cost of the components, thereby making it possible to provide a compact, inexpensive gas sensor 100.

[0094] Furthermore, the gas sensor 100 can be realized by utilizing at least some of the components and manufacturing equipment of a conventional quartz crystal unit.

[0095] A conventional crystal unit is, for example, a ceramic package type surface-mounted crystal unit that is used as a time source, a timing source for control signals, a reference signal source, etc., by applying a voltage to the crystal unit to vibrate it.

[0096] Conventional quartz crystal units are used by hermetically sealing a package containing a quartz crystal piece in an internal space with a lid. Therefore, conventional quartz crystal units do not have a lid 20 that allows gas to pass through, and permeating gas does not flow from the external space of the package into the internal space.

[0097] The gas sensor 100 according to this embodiment can be realized by replacing the lid of a conventional quartz crystal resonator with the lid 20 that is gas permeable.

[0098] Therefore, the gas sensor 100 can have a small size comparable to that of a conventional quartz crystal unit. Furthermore, the gas sensor 100 can be manufactured using at least part of the manufacturing equipment for conventional quartz crystal units, thereby reducing the costs of manufacturing equipment and the like.

[0099] As a result, it is possible to provide a small-sized, inexpensive gas sensor 100.

[0100] Second Embodiment A gas sensor 100A according to a second embodiment of the present invention will be described below. In the following description, components common to those already described will be assigned the same reference numerals and redundant description will be omitted.

[0101] Fig. 4 is an external perspective view showing the gas sensor 100A according to the second embodiment, Fig. 5 is an exploded perspective view showing the gas sensor 100A according to the second embodiment, and Fig. 6 is a cross-sectional view taken along line VI-VI in Fig. 4.

[0102] The gas sensor 100A includes a package 10A, a lid 20, a quartz crystal vibrating piece 30A, and a temperature detection unit (integrated circuit chip) 50A.

[0103] The package 10A includes a first base substrate 11, a second base substrate 12, a third base substrate 18, and a seal ring 13. The package 10 has an internal space C capable of accommodating the quartz crystal vibrating piece 30A.

[0104] In this embodiment, a pair of mounting portions 16A protruding into the internal space C are formed on the inner surfaces of the right side W1 and the left side W2 of the through portion 12h of the second base substrate 12. Of the pair of mounting portions 16A, the mounting portion 16A provided on the right side W1 is also referred to as the first mounting portion 16Aa, and the mounting portion 16A provided on the left side W2 is also referred to as the second mounting portion 16Ab. The first mounting portion 16Aa and the second mounting portion 16Ab are arranged near the center in the longitudinal direction L.

[0105] A pair of electrode pads 17A, which are connection electrodes with the quartz-crystal vibrating piece 30A, are formed on the upper T1 surfaces of the first mounting portion 16Aa and the second mounting portion 16Ab. Of the pair of electrode pads 17A, the electrode pad 17A formed on the first mounting portion 16Aa is also referred to as the first electrode pad 17Aa, and the electrode pad 17A formed on the second mounting portion 16Ab is also referred to as the second electrode pad 17Ab.

[0106] The third base substrate 18 is a substrate provided on the lower surface T2 of the second base substrate 12. The third base substrate 18 is integrally bonded to the lower surface T2 of the second base substrate 12 by sintering or the like.

[0107] In a plan view seen from the thickness direction T, the outer shape of the first base substrate 11 and the outer shape of the second base substrate 12 are the same as the outer shape of the third base substrate 18. For example, the same material as that of the first base substrate 11 and the second base substrate 12 can be used for the third base substrate 18. For example, ceramics can be used as the material of the third base substrate 18.

[0108] 5 and 6, the third base substrate 18 has a through portion 18h formed therein that penetrates the third base substrate 18 in the thickness direction T. The through portion 18h has a rounded rectangular shape in a plan view seen from the thickness direction T.

[0109] External electrodes (base end external electrode 14A and tip end external electrode 15A) are provided on the lower surface T2 of the third base substrate 18, spaced apart in the longitudinal direction L. In the following description, the base end external electrode 14A and the tip end external electrode 15A will also be simply referred to as external electrodes 14A, 15A.

[0110] The base end external electrode 14A has a first external electrode 14Aa and a second external electrode 14Ab formed at an interval in the width direction W. The tip end external electrode 15A has a third external electrode 15Aa and a fourth external electrode 15Ab formed at an interval in the width direction W.

[0111] The base end external electrode 14A and the tip end external electrode 15A are configured, for example, as a single layer film made of a single metal formed by vapor deposition, sputtering, or the like, or as a laminated film made of laminated layers of different metals.

[0112] The first electrode pad 17Aa and the second electrode pad 17Ab, like the base-side external electrode 14A and the tip-side external electrode 15A, are composed of, for example, a single-layer film made of a single metal formed by vapor deposition, sputtering, etc., or a laminated film in which different metals are stacked.

[0113] The first electrode pad 17Aa and the second electrode pad 17Ab are electrically connected to the base end external electrode 14A and the tip end external electrode 15A via through-wiring (not shown) that penetrates the first base substrate 11, the second base substrate 12, and the third base substrate 18 in the thickness direction T.

[0114] At the four corners of the first base substrate 11, the second base substrate 12 and the third base substrate 18, quadrant-arc cutouts are formed across the entire thickness direction T of the first base substrate 11, the second base substrate 12 and the third base substrate 18 when viewed in a plane from the thickness direction T.

[0115] First base substrate 11, second base substrate 12, and third base substrate 18 are fabricated by, for example, stacking and bonding three wafer-like ceramic substrates, forming a matrix of through-holes that penetrate the three bonded ceramic substrates, and cutting the three ceramic substrates into a grid pattern based on each through-hole. At this time, the through-holes are divided into four, thereby forming the notches described above.

[0116] The quartz crystal vibrating piece 30A is a vibrating piece including a piezoelectric plate made of quartz crystal. The quartz crystal vibrating piece 30A is housed in the internal space C of the package 10A. The quartz crystal vibrating piece 30A is, for example, a tuning fork-shaped vibrating piece.

[0117] The quartz crystal vibrating piece 30A includes a base 31A and a pair of vibrating arms 32A. Of the pair of vibrating arms 32A, the vibrating arm 32A provided on the right side W1 is also referred to as the first vibrating arm 32Aa, and the vibrating arm 32A provided on the left side W2 is also referred to as the second vibrating arm 32Ab.

[0118] The base 31A includes a base main body 31Aa and a pair of support arms (a first support arm 31Ab and a second support arm 31Ac).

[0119] The first support arm 31Ab and the second support arm 31Ac are connected to the right side W1 and left side W2 of the base body 31Aa and extend in the longitudinal direction L. As shown in Fig. 5, most of the first support arm 31Ab and the second support arm 31Ac are located on the distal end side L2 of the base body 31Aa.

[0120] In the base portion 31A, the first support arm portion 31Ab and the second support arm portion 31Ac are supported from below T2 by the first mounting portion 16Aa and the second mounting portion 16Ab via the first electrode pad 17Aa and the second electrode pad 17Ab.

[0121] The first vibrating arm 32Aa and the second vibrating arm 32Ab extend from the base body 31Aa to the tip side L2. The first vibrating arm 32Aa and the second vibrating arm 32Ab are disposed apart from the first base substrate 11 in the thickness direction T.

[0122] An electrode film (not shown) is disposed on the outer surface, including the front and back surfaces, of the quartz-crystal vibrating piece 30A. The electrode film includes excitation electrodes, mount electrodes that serve as mounts when the base 31A is mounted on the package 10A, and connection wiring that connects the excitation electrodes and the mount electrodes.

[0123] The excitation electrodes of the electrode film are arranged on the outer surfaces of the first vibrating arm 32Aa and the second vibrating arm 32Ab. Two systems of excitation electrodes (not shown) are arranged on the outer surfaces of the first vibrating arm 32Aa and the second vibrating arm 32Ab, and vibrate the first vibrating arm 32Aa and the second vibrating arm 32Ab when a predetermined voltage is applied.

[0124] When a predetermined voltage is applied to the external electrodes 14A and 15A, a current flows through the excitation electrodes of the vibrating arm 32A, generating an electric field. The first vibrating arm 32Aa and the second vibrating arm 32Ab vibrate at a predetermined resonance frequency in directions in which they approach and move away from each other (width direction W) due to, for example, an inverse piezoelectric effect caused by the generated electric field.

[0125] The first vibrating arm 32Aa and the second vibrating arm 32Ab are arranged parallel to each other in the width direction W, and are each connected to the base body 31Aa. The first vibrating arm 32Aa and the second vibrating arm 32Ab vibrate in directions approaching and separating from each other (the width direction W) with their ends on the base end side L1 connected to the base body 31Aa as fixed ends and their ends on the tip side L2 as free ends.

[0126] The temperature detection unit 50A is housed in the through-hole 18h of the third base substrate 18 and is provided on the lower surface 11b of the first base substrate (bottom) 11. In other words, the temperature detection unit 50A is provided on the external space E side of the first base substrate 11.

[0127] The temperature detection unit 50A is, for example, an integrated circuit chip having an oscillation circuit, and functions as a temperature sensor capable of detecting temperature.

[0128] The temperature detection unit 50A, the base end external electrode 14A, and the tip end external electrode 15A are electrically connected to each other via through-wiring (not shown) that penetrates the first base substrate 11 and the third base substrate 18 in the thickness direction T.

[0129] The temperature detection unit 50A is electrically connected to the first electrode pad 17Aa and the second electrode pad 17Ab via through-wiring (not shown) that penetrates the first base substrate 11 and the second base substrate 12 in the thickness direction T.

[0130] Like the gas sensor 100 according to the first embodiment, the gas sensor 100A includes a lid 20 that allows a predetermined gas (permeation gas) to permeate from the external space E to the internal space C. When the permeation gas flows into the internal space C, the degree of vacuum in the internal space C decreases.

[0131] The gas sensor 100A, like the gas sensor 100 according to the first embodiment, is capable of detecting permeating gas based on the resistance value of the quartz crystal vibrating piece 30A, which changes as the degree of vacuum in the internal space C decreases.

[0132] The gas sensor 100A includes a temperature detection unit 50A capable of detecting temperature, and therefore, like the gas sensor 100 according to the first embodiment, temperature compensation is possible in the detection of permeable gas.

[0133] The temperature detection unit 50A also functions as an integrated circuit chip that can oscillate the quartz crystal vibrating piece 30A.

[0134] 6, the temperature detection unit 50A is located in the external space E, near the quartz-crystal vibrating piece 30A across the first base substrate 11. Even when the temperature detection unit 50A is located in the external space E, it can detect the ambient temperature of the quartz-crystal vibrating piece 30A. Therefore, the gas sensor 100A is capable of temperature compensation.

[0135] There is a conventional oscillator that includes the above-mentioned conventional crystal unit and an integrated circuit chip that can oscillate the crystal unit.

[0136] The gas sensor 100A according to this embodiment can be realized by replacing the cover of a quartz crystal resonator included in a conventional oscillator with a gas-permeable cover 20, for example.

[0137] Therefore, the gas sensor 100A can have a small size comparable to that of conventional oscillators. Furthermore, the gas sensor 100A can be manufactured using at least part of the manufacturing equipment for conventional oscillators, thereby reducing costs, such as equipment costs, required for manufacturing.

[0138] As a result, it is possible to provide a small-sized, inexpensive gas sensor 100A.

[0139] Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments and includes design modifications within the scope of the present invention. Furthermore, the components shown in the above-described embodiments and the modified examples shown below can be appropriately combined to form a configuration.

[0140] (Variation 1) In the first embodiment, the getter material 40 is provided on the upper surface 11a of the first base substrate 11, but the form of the getter material is not limited to this. The getter material may also be provided on the vibrating arms of the quartz crystal vibrating piece.

[0141] For example, the getter material may be provided on the top surface of the vibrating arm at the tip of the vibrating arm. The getter material increases in mass by adsorbing the permeation gas that has flowed into the internal space.

[0142] When the mass of the getter material changes, the frequency of the vibrating arms with the getter material at their tips also changes, so the amount of permeable gas adsorbed by the getter material can be estimated based on the change in frequency of the quartz crystal resonator.

[0143] By estimating the amount of gas adsorbed by the getter material, it is possible to estimate when to replace the gas sensor. For example, when the user estimates that the amount of gas adsorbed by the getter material has reached saturation and it is difficult for the getter material to adsorb new permeating gas, the user replaces the gas sensor with a new one.

[0144] The location of the getter material in the vibrating arm is not limited to the upper surface of the vibrating arm. For example, at the tip of the vibrating arm, a weight for adjusting the frequency may be provided on the upper surface, and the getter material may be provided on the lower surface. When performing a frequency adjustment process using ion milling on a quartz crystal vibrating piece, providing a weight on the upper surface of the vibrating arm and a getter material on the lower surface can reduce the impact on the opposite surface compared to a laser.

[0145] When a getter material is provided at the tip of the vibrating arm, the getter material adsorbs the permeating gas, causing a change in mass, which makes it easier to change the frequency of the quartz crystal vibrating piece.

[0146] (Variation 2) In the second embodiment, the gas sensor 100A does not include the getter material 40, but the gas sensor 100A according to the second embodiment is not limited to this. The gas sensor 100A according to the second embodiment may include the getter material 40, similar to the gas sensor 100 according to the first embodiment. [Explanation of symbols]

[0147] 100, 100A...gas sensor, 10, 10A...package, 11...first base substrate (bottom), 16, 16A...mounting portion, 20...lid portion, 30, 30A...quartz crystal vibrating piece, 31, 31A...base portion, 32, 32A...vibrating arm portion, 40...getter material, 50, 50A...temperature detection portion (integrated circuit chip), C...internal space, E...external space

Claims

1. A quartz crystal resonator element; a package having an internal space capable of accommodating the crystal vibrating piece; a lid portion that separates the internal space from the external space of the package; Equipped with the internal space is a vacuum or has a negative pressure relative to the external space; The lid portion includes a gas-permeable material and is capable of transmitting gas from the external space to the internal space. Gas sensor.

2. The quartz crystal vibrating piece is a tuning fork type.

2. The gas sensor according to claim 1.

3. The lid portion has a flat plate shape extending perpendicular to the direction in which the lid portion and the quartz crystal vibrating piece face each other.

2. The gas sensor according to claim 1.

4. a getter material provided in the internal space and capable of adsorbing the gas in the internal space; 2. The gas sensor according to claim 1.

5. The quartz crystal vibrating piece is provided between the lid and the getter material in a direction in which the lid and the quartz crystal vibrating piece face each other.

5. The gas sensor according to claim 4.

6. the package has a mounting portion that supports the crystal resonator element, the quartz crystal vibrating piece has a base portion supported by the mounting portion and vibrating arms extending from the base portion, The getter material is provided on the vibrating arm portion.

5. The gas sensor according to claim 4.

7. A temperature detection unit capable of detecting a temperature is provided.

2. The gas sensor according to claim 1.

8. The temperature detection unit is provided in the internal space.

8. The gas sensor according to claim 7.

9. the package has a bottom portion that is disposed on the opposite side of the lid portion across the quartz crystal resonator element in a direction in which the lid portion and the quartz crystal resonator element face each other, and that separates the internal space from the external space; The temperature detection unit is provided on the outside space side of the bottom portion.

8. The gas sensor according to claim 7.

10. an integrated circuit chip electrically connected to the crystal resonator element and having an oscillation circuit; The gas sensor according to any one of claims 1 to 9.

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