JP6781431B2 - Gas sensor - Google Patents

Description

The present invention relates to a gas sensor that detects a gas to be detected such as hydrogen gas, and more particularly to a gas sensor that detects gas by adsorbing the gas to be detected in the pores of a porous body.

In the sensor that detects gas, a method of increasing the specific surface area of the gas detection unit by using a porous body is adopted in order to improve the performance of the sensor such as improving the detection sensitivity. As a prior art of the above method, Non-Patent Document 1 below proposes a hydrogen gas sensor using titanium dioxide nanotubes (pores) in the gas detection unit.

Further, Patent Document 1 below proposes a gas sensor in which the adsorption area (surface area) is increased by using a porous material of semiconductor or metal for the gas detection unit, and the sensitivity and response characteristics are improved. Further, a means for increasing the sensitivity by carrying a catalyst such as platinum or palladium in the porous gas detection unit to promote the adsorption / desorption of the detection gas has been proposed.

Further, Patent Document 2 below proposes a gas sensor having a structure in which a porous titanium oxide layer, which is a gas detection unit, is formed on titanium metal.

Further, Patent Document 3 below discloses a hydrogen gas sensor in which a sensor element having a fine tubular structure containing titanium oxide as a main component is formed on the surface of an insulator substrate.

The gas sensor described in these prior arts is characterized by a structure in which a porous body, which is a gas detection unit, is formed on a substrate for supporting the porous body.

Oomman K. Varghese et al., “Hydrogen sensing using titania nanotubes”, Sensor and Actuators B 93 (2003) 338-344

Japanese Unexamined Patent Publication No. 6-213851 Japanese Unexamined Patent Publication No. 8-145925 Japanese Unexamined Patent Publication No. 2013-40961

In the gas sensors described in Non-Patent Documents 1 and Patent Documents 1 to 3, gas detection is performed by adsorbing the gas to be detected on the inner wall of the pores of the porous body. The gas to be detected enters the inside of the hole by diffusing in the air inside the hole. Since it takes time to diffuse to the inside, there is a problem that the response time of the sensor (following speed when increasing the concentration) is slow. In order to accelerate the decomposition and diffusion of gas, a method of heating the sensor with a heater or the like is adopted, but there is a problem that the power consumption of the sensor becomes high.

Further, Non-Patent Document 1 shows a change in the resistance of the sensor when only nitrogen gas is flowed after flowing hydrogen of a certain concentration, but it takes time to return to the resistance value in the state without hydrogen gas. , It is very long, about 2000 seconds, and there is a problem that the recovery speed of the sensor (following speed when decreasing the concentration) is slow. It is presumed that the gas sensors shown in Patent Documents 1 and 2 having the same sensor structure have the same problem.

Further, Patent Documents 1 and 3 propose a method of carrying a catalyst such as platinum or palladium in the gas detection unit of the porous body as a means for increasing the sensitivity. In Patent Document 1, the pores of the porous body on one side penetrate, but the pores of the porous body on the opposite side do not penetrate because there is a substrate that supports the porous body. Therefore, when the metal catalyst is carried by a wet method such as the liquid phase method, it is difficult for the solution to penetrate into the inside of the porous body, so that the catalyst metal is not carried inside the porous body, and the effect of the catalyst is obtained. There is a problem that is not sufficiently obtained.

Therefore, an object of the present invention is to provide a gas sensor capable of detecting gas with higher sensitivity and faster response speed.

The gas sensor of the present invention for solving the above problems includes a porous body in which a large number of pores are formed, and a pair of electrodes electrically connected to both sides of the porous body. A gas sensor that measures the concentration of gas by measuring the electrical characteristics between a pair of electrodes, and the pores have a tubular structure that penetrates substantially vertically from the front surface side to the back surface side of the porous body. , Each pore is formed so as to be oriented in substantially the same direction, and the gas can permeate from the front surface side to the back surface side of the porous body without closing the pores on the front surface side and the back surface side of the porous body. It is characterized by being.

The porous body used for the gas detection unit is preferably a metal or semiconductor oxide having the ability to change its electrical properties by adsorbing gas molecules, and titanium dioxide is typical, but zinc oxide and dioxide are also used. Zirconium, strontium titanate, ditantal pentoxide, niobium pentoxide, etc. Furthermore, although it is not an oxide, silicon carbide, cadmium sulfide, etc. can also be mentioned.

According to the gas sensor of the present invention, since the pores in the porous body penetrate from the front surface side to the back surface side of the porous body and are not blocked on both sides, the gas to be detected is the porous body which is the gas detection unit. Can permeate from the front surface side to the back surface side, easily enter the pores of the porous body, and can detect gas with high sensitivity and fast response speed.

It is a figure which shows the 1st structural example of the gas sensor in embodiment of this invention. It is a partially enlarged sectional view of a porous body 14. It is a partial cross-sectional perspective view which shows typically the pore 15 of a porous body 14. It is a figure which shows the 2nd structural example of the gas sensor in embodiment of this invention. It is a figure which shows the 3rd structural example of the gas sensor in embodiment of this invention. It is a figure which shows the 4th structural example of the gas sensor in embodiment of this invention. It is a schematic diagram which shows the arrangement example of the gas sensor in embodiment of this invention. It is a figure which shows an example of the manufacturing process of the gas sensor 10A in the 1st configuration example. It is a figure which shows an example of the manufacturing process of the gas sensor 10B in the 2nd configuration example. It is a figure which shows an example of the manufacturing process of the gas sensor 10C in the 3rd configuration example. It is a figure which shows an example of the manufacturing process of the gas sensor 10C in the 3rd configuration example. It is a figure which shows an example of the manufacturing process of the gas sensor 10D in the 4th configuration example.

Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings. The examples of the embodiments are for understanding the present invention, and the technical scope of the present invention is not limited thereto.

The present invention has a structure in which a large number of pores formed in a porous body, which is a part for detecting a gas, are penetrated from the front surface (one side) to the back surface (opposite surface), so that the sensitivity is high and the gas to be detected is detected. It provides a gas sensor having a fast response speed and recovery speed to a gas sensor. A porous body is a gas sensor that is formed by being sandwiched between a pair of electrodes and measures the concentration of gas by measuring the electrical characteristics (for example, current value) between the electrodes. Specifically, each configuration example of the gas sensor according to the embodiment of the present invention described below is arranged with a porous body in which a large number of pores are formed and electrically connected to both sides of the porous body. It is a gas sensor that measures the concentration of gas by measuring the electrical characteristics between the pair of electrodes, and the pores penetrate from the front side to the back side of the porous body. It is formed, and the pores are not closed on the front surface side and the back surface side of the porous body, and the gas can permeate from the front surface side to the back surface side of the porous body. Here, in the gas sensor of the present embodiment, the metal or semiconductor is made into a porous body by a method such as anodizing. The formed porous body is an oxide of a metal or a semiconductor. Further, if the pores constituting the porous body are regularly arranged, there is an advantage that the gas sensor to which the porous body is applied exhibits stable gas detection characteristics. Therefore, it is preferable that the formed porous body has a tubular structure (nanotube porous body) having a diameter of nano-order.

[First configuration example of gas sensor]
1 and 2 are views showing a first configuration example of the gas sensor according to the embodiment of the present invention, FIG. 1 (a) is a perspective view, FIG. 1 (b) is a top view, and FIG. 1 (c). Is a sectional view taken along the line AA of FIG. 1 (b). Further, FIG. 2 is a partially enlarged cross-sectional view of the porous body 14, and FIG. 3 is a partial cross-sectional perspective view schematically showing the pores 15 of the porous body 14. FIG. 3A schematically shows the pores 15 of the porous body 14 in the first configuration example, and FIG. 3B schematically shows the pores 15 of the porous body 14 in the third configuration example described later. Shown.

The gas sensor 10A in the first configuration example is a gas sensor in which a part of a thin plate 12 of a metal or a semiconductor is formed in a porous body 14, and the thin plate portions on both sides of the porous body 14 form a pair of electrodes 18a and 18b. .. The porous body 14 serves as a gas detection unit for detecting gas. Specifically, the gas sensor 10A is a piece of metal or semiconductor thin plate 12, and a part of the surface of the thin plate 12 is oriented in a direction substantially perpendicular to the thin plate surface by, for example, anodic oxidation. Moreover, a porous body 14 having a large number of tubular pores 15 penetrating from one side to the other side is formed. The pores 15 of the porous body 14 in the first configuration example are schematically shown in FIGS. 2 and 3 (a).

The porous body 14 is formed across the thin plate by anodizing the region from one end of the substantially central portion of the thin plate member 12 to the opposite end. The pores 15 penetrating from one side to the other side of the thin plate 12 are anodized until just before the bottom of the pores 15 reaches the other side, and then the other side is penetrated by a technique such as polishing. By polishing until it is finished, pores 15 with both ends open are formed. As illustrated in FIG. 2, since one end side of the pore 15 is not blocked by a substrate or the like, it can pass through the opening on the other end side of the gas flowing in from the opening on one end side of the pore 15. Since the gas can permeate from one side to the other side of the porous body 14, the gas can easily enter the inside of the pores 15, and the sensitivity and responsiveness of gas detection can be improved.

The thin plate portions on both sides of the porous body 14 having the pores 15 form a pair of electrodes 18a and 18b. The electrodes 18a and 18b are separated by a porous body 14. Therefore, since the portion other than the porous portion of the thin plate can be used as the electrode, there is an advantage that the step of forming the electrode is unnecessary. The detailed manufacturing method of the gas sensor 10A will be described later.

[Second configuration example of gas sensor]
4A and 4B are views showing a second configuration example of the gas sensor according to the embodiment of the present invention, FIG. 4A is a perspective view, FIG. 4B is a top view, and FIG. 4C is FIG. It is sectional drawing of AA of (b).

In the gas sensor 10B in the second configuration example, the porous body 14 serving as the gas detection means is formed on a part of the thin plate 12 of the metal or semiconductor, and further, the porous body 14 of the thin plate 12 is not formed on the portion. This is a gas sensor in which a pair of electrodes 18a and 18b are formed via the insulating films 16a and 16b provided.

Specifically, in the gas sensor 10B in the second configuration example, a part of the metal or semiconductor thin plate 12 is formed in the porous body 14, and the porous body 14 is a gas, similarly to the gas sensor 10A in the first configuration example. It becomes a part to detect. Specifically, the gas sensor 10B uses a metal or semiconductor thin plate 12 as a base material, and a part of the surface of the thin plate 12 is oriented substantially perpendicular to the thin plate surface and one side by, for example, anodizing. A porous body 14 having a large number of pores 15 penetrating from the surface to the opposite surface is formed. The pores 15 of the porous body 14 are the same as the pores 15 shown in FIG.

The porous body 14 is formed by anodizing the substantially central region of the thin plate 12 as in the first configuration example, and the pores 15 penetrating from one side to the other side of the thin plate 12 are the bottom of the pores 15. Anodizing is performed until just before reaching the opposite surface, and then the opposite surface is polished by a technique such as polishing until the pores 15 penetrate to form pores 15 having both ends open. Similar to the first configuration example, since one end side of the pore 15 is not blocked by a substrate or the like, it can pass through the opening on the other end side of the gas flowing in from the opening on one end side of the pore 15. Since the gas can permeate from one side to the other side of the porous body 24, the gas easily enters the inside of the pores 15, and the sensitivity and responsiveness of gas detection can be improved.

The porous body 14 having the pores 15 is formed so as to be surrounded by a thin plate portion other than the portion of the porous body 14 in a substantially central region of the thin plate, and unlike the first configuration example, the substantially central portion of the thin plate 12 is formed. Since it is not formed so as to cross the region from one end of the porous body to the opposite end, both side portions of the porous body 14 are electrically short-circuited. Therefore, in the gas sensor 10B, unlike the gas sensor 10A, both side portions on which the porous body 14 of the thin plate is not formed cannot be used as a pair of electrodes, and therefore, a pair of insulating films for insulating the both side portions and the electrodes. 16a and 16b are formed on a part of both side portions, and a pair of electrodes 18a and 18b are formed on the 16a and 16b. The detailed manufacturing method of the gas sensor 10B will be described later.

[Third configuration example of gas sensor]
5A and 5B are views showing a third configuration example of the gas sensor according to the embodiment of the present invention, FIG. 5A is a perspective view, FIG. 5B is a top view, and FIG. 5C is FIG. It is sectional drawing of AA of (b).

The gas sensor 10C in the third configuration example has a substrate 11 and a metal or semiconductor thin film 13 formed on the substrate 11, and a part of the thin film 13 becomes a porous body 14 which is a portion for detecting gas, and is porous. This is a gas sensor in which both side portions other than the portion of the body 14 form a pair of electrodes 18a and 18b.

Specifically, in the gas sensor 10C in the third configuration example, the metal or semiconductor thin film 13 formed on the substrate 11 is patterned in a substantially rectangular shape, and the vicinity of the center of the substantially rectangular shape is, for example, anodized. A porous body 14 having a large number of pores 15 oriented substantially perpendicular to the thin film surface is formed. The porous body 14 is formed across the thin film 13 by anodizing the region from one end of the substantially central portion of the thin film 13 to the opposite end. The pores 15 penetrating from one side to the other side of the thin film 13 are generally formed by the following procedure. First, the thin film 13 is anodized to form pores 15 from the surface to the vicinity of the interface with the substrate 11. At this time, since the pores 15 do not penetrate near the interface with the substrate 11, the pores 15 are penetrated by using a chemical or a reactive gas. After that, the substrate portion under the porous body 14 is removed to form a through hole 19 in the substrate 11. Not only the entire substrate portion under the porous body 14 may be removed, but also a part of the substrate portion or a part of the substrate portion may be removed at a plurality of locations. By removing the substrate portion directly under the porous body 14 to form the through hole 19, since one end side of the pore 15 is not blocked by the substrate 11, it flows in from the opening on one end side of the pore 15. Since the gas can pass through the opening on the other end side of the gas and the gas can permeate from one side to the other side of the porous body 14, the gas easily enters the inside of the pores 15, and the sensitivity and responsiveness of gas detection are improved. Can be improved. The pores 15 of the porous body 14 in the third configuration example are schematically shown in FIG. 3 (b).

The thin film portions on both sides of the porous body 14 having the pores 15 form a pair of electrodes 18a and 18b. The electrodes 18a and 18b are separated by a porous body 14. Therefore, since the portion other than the porous portion of the thin plate can be used as the electrode, there is an advantage that the step of forming the electrode is unnecessary. The detailed manufacturing method of the gas sensor 10C will be described later.

[Fourth configuration example of gas sensor]
6A and 6B are views showing a fourth configuration example of the gas sensor according to the embodiment of the present invention, FIG. 6A is a perspective view, FIG. 6B is a top view, and FIG. 6C is FIG. It is sectional drawing of AA of (b).

The gas sensor 10D in the fourth configuration example has a substrate 11 and a metal or semiconductor thin film 13 formed on the substrate 11, and a part of the thin film 13 becomes a porous body 14 which is a portion for detecting gas. This is a gas sensor in which a pair of electrodes 18a and 18b are formed via insulating films 16a and 16b provided on a portion of 13 in which the porous body 14 is not formed.

Specifically, the gas sensor 10D in the fourth configuration example has an anode on a part of the surface of the metal or semiconductor thin film 13 formed on the substrate 11, for example, a region near the center, as in the third configuration example. By oxidation, a porous body 14 having a large number of pores 15 oriented substantially perpendicular to the thin film surface is formed. The pores 15 penetrating from one side to the other side of the thin film 13 are formed by the same method as the gas sensor 10C in the third configuration example. Since the substrate portion under the porous 14 having the formed pores 15 is removed, one end side of the pores 15 is not blocked by the substrate 11 and is opened through the opening on the one end side of the pores 15. Since the gas can pass through the opening on the other end side of the inflowing gas and the gas can permeate from one side to the other side of the porous body 14, the gas easily enters the inside of the pores 15, and the sensitivity and responsiveness of gas detection. Can be improved.

The porous body 14 having the pores 15 is formed so as to be surrounded by a thin film portion other than the portion of the porous body 14 in a substantially central region of the thin film 13, and unlike the third configuration example, the porous body 14 is formed substantially in the center of the thin film 12. Since it is not formed so as to cross the region from one end of the portion to the opposite end, both side portions of the porous body 44 are not separated and are electrically short-circuited. Therefore, in the gas sensor 10D, unlike the gas sensor 10C, both side portions where the porous body 14 of the thin film 13 is not formed cannot be used as a pair of electrodes, and therefore, a pair of insulations for insulating the both side portions and the electrodes. The films 16a and 16b are formed on a part of both side portions, and a pair of electrodes 18a and 18b are formed on the films 16a and 16b. The detailed manufacturing method of the gas sensor 10D will be described later.

The gas sensors 10C and 10D in the third configuration example and the fourth configuration example described above include a substrate 11 on which a back surface side of the porous body 14 and a pair of electrodes 18a and 18b are placed and supported, and the porous body 11 is porous. A through hole 19 is provided in a portion of the material 14 facing the back surface side, and the gas permeating from the front surface side to the back surface side of the porous body 14 can further permeate the through hole 19 of the substrate 11.

In the gas sensors 10A, 10B, 10C and 10D described above (hereinafter, may be collectively referred to as a gas sensor 10), a large number of pores 15 are formed so as to be oriented in a substantially fixed direction as a portion for detecting gas. Since a metal or semiconductor porous body 14 is used, it has electrical conductivity and a large surface area. Further, since the porous body 14 penetrates from the front surface (one side) to the back surface (opposite surface) and is not blocked, the gas to be detected easily enters the pores 15, and the sensitivity and response speed are increased. It is dramatically improved compared to the conventional gas sensor.

In addition, when an inert gas such as nitrogen is flowed through the pores for the purpose of cleaning the inside of the pores after measuring the gas to be detected, the adsorbed gas to be detected is efficiently discharged. ， Recovery speed is also dramatically improved.

FIG. 7 is a schematic view showing an arrangement example of the gas sensor according to the embodiment of the present invention. FIG. 7 shows an example in which the gas sensor 10A of the first configuration example is arranged in the cross section of the pipe as a representative, and of course, the gas sensors 10B, 10C or 10D may be arranged. If the gas sensor 10 is attached in the middle of the pipe 50 through which the gas to be detected is flowing, the gas to be detected can easily enter the pores 15 of the porous body 14 that detects the gas. That is, the gas to be detected is sucked from the leeward side of the gas flow (arrow 52) using a vacuum pump (not shown) or the like, or the gas to be detected is sucked from the leeward side by a pressure pump (not shown) or the like. By pushing out the gas, the gas to be detected can be forcibly entered into the porous body 14 of the gas sensor 10. As a result, the sensitivity, response speed, and recovery speed are all dramatically improved compared to conventional gas sensors.

In addition, when a catalyst such as platinum or palladium is carried in the porous body by a wet method such as the liquid phase method in order to improve the sensitivity and the selectivity of the gas to be detected, the solution penetrates into the porous body. Since it is easy, the catalyst metal is carried inside the porous body, and a gas sensor with improved sensitivity and selectivity of the gas to be detected can be realized.

Further, if a plurality of gas sensors having different supported catalyst metals are integrated, the concentration of each gas component in the mixed gas can be measured by calculating the signal from each gas sensor.

Further, when a substance having a photocatalytic function, for example, a porous body of titanium dioxide is used as the material of the porous body, the porous body is irradiated with ultraviolet rays by using an ultraviolet lamp or an ultraviolet LED to make the porous body porous. Since the detection target gas adsorbed on the body can be decomposed and removed, the recovery speed of the sensor can be increased.

Next, the manufacturing process of the gas sensors 10A, 10B, 10C and 10D described above will be described. In the following, titanium dioxide will be described as an example of the porous body used in the gas detection unit.

[Manufacturing process of gas sensor 10A]
FIG. 8 shows an example of the manufacturing process of the gas sensor 10A in the first configuration example. In the manufacturing process of FIG. 8, as shown below, the porous body of the gas sensor 10A is formed by anodizing a part of a thin plate of a metal or semiconductor, and the thin plate portions on both sides of the portion where the porous body is formed. A pair of electrodes is formed in.

(A) A thin titanium plate rolled to a thickness of 50 μm is cut out to an arbitrary size. The cut-out thin plate corresponds to the thin plate 12 in FIG. If the surface is rough, perform mechanical polishing or electrolytic polishing to make it a mirror surface. The surface of the thin plate 12 is ultrasonically cleaned with an organic solvent such as ethanol, acetone, or 2-propanol. Since the resistance value increases when the thin titanium plate 12 becomes a porous body of titanium dioxide by anodizing, the region to be made a porous body of titanium dioxide by anodizing should be as narrow as possible. Therefore, film resists 24a and 24b (or Kapton tape or the like) are used to limit the region of the thin plate 12 to be anodized.

(B) Anodizing the transverse region from one end of the substantially central portion of the thin plate 12 to the opposite end. Anodization was performed with a solution (anodized solution) 26 in which ammonium fluoride was dissolved so as to be 0.05 M in an ethylene glycol solution containing 5 vol% pure water with the platinum wire 27 as the cathode and the titanium thin plate 12 as the anode. .. The voltage to be applied is 20 to 60 V, and the larger the voltage, the larger the hole diameter. When the applied voltage is 40 V, a porous body made of nanotubes having a pore diameter of about 40 nm and a pore-to-pore spacing of about 100 nm is formed.

(C) Porousization is performed by forming titanium dioxide nanotubes 30 (amorphous phase) by anodizing.

(D) The film resists 24a and 24b are peeled off, and the surface opposite to the surface made porous by anodizing is penetrated through the pores by mechanical polishing or the like.

(E) In order to improve the performance, the titanium dioxide nanotube 30 is transferred from the amorphous phase to the anatase phase by heat treatment in the air at 400 ° C. for 1 hour and 450 ° C. for 30 minutes. The nanotube 31 transferred to the anatase phase corresponds to the pore 15 of the porous 14.

(F) The pair of thin plate portions separated by the porous body 31 (14) are used as electrodes 18a and 18b, and the external lead wires 33a and 33b are connected by a method such as wire bonding. The gas sensor 10A can be manufactured by the process shown in FIG.

[Manufacturing process of gas sensor 10B]
FIG. 9 shows an example of the manufacturing process of the gas sensor 10B in the second configuration example. In the manufacturing process of FIG. 9, as shown below, the porous body of the gas sensor 10B is formed by anodizing a part of the thin plate of the metal or semiconductor, and the thin plate portions on both sides of the portion where the porous body is formed. A pair of electrodes is formed and provided on the film.

(A) A thin titanium plate rolled to a thickness of 50 μm is cut out to an arbitrary size. The cut-out thin plate corresponds to the thin plate 12 in FIG. If the surface is rough, perform mechanical polishing or electrolytic polishing to make it a mirror surface. The surface of the thin plate 12 is ultrasonically cleaned with an organic solvent such as ethanol, acetone, or 2-propanol.

(B) The periphery of the central portion of the titanium thin plate 12 is anodized. The anodization is carried out in the same manner as in the manufacturing process of the gas sensor 10A of the first configuration example shown in FIG. 8 above.

(C) Porousization is performed by forming titanium dioxide nanotubes (amorphous phase) 30 by anodizing.

(D) The hole is penetrated through the surface opposite to the surface made porous by anodizing by mechanical polishing or the like.

(E) In order to improve the performance, the titanium dioxide nanotube 30 is transferred from the amorphous phase to the anatase phase by heat treatment in the air at 400 ° C. for 1 hour and 450 ° C. for 30 minutes. The nanotube 31 transferred to the anatase phase corresponds to the pore 15 of the porous 14.

(F) Insulating films 16a and 16b are formed on the thin plate 12 near the boundary between the non-porous portion and the porous portion by sputtering or the like. Alternatively, a method of covering with an insulating paste, non-conductive heat or an ultraviolet curable resin or the like may be used.

(G) A metal film such as gold, silver, copper, or aluminum is formed on the film by sputtering or the like so as to be electrically connected to the porous body 14 which is a gas detection unit, and electrodes 18a and 18b are formed. To do. Alternatively, the electrode can be formed with a conductive paste or the like.

(H) The external lead wires 33a and 33b are connected to the electrodes 18a and 18b by a method such as wire bonding. The gas sensor 10B can be manufactured by the process shown in FIG.

[Manufacturing process of gas sensor 10C]
10A and 10B show an example of the manufacturing process of the gas sensor 10C in the third configuration example. In the manufacturing process of FIGS. 10A and 10B, as shown below, the porous body of the gas sensor 10C is formed by anodizing a part of a thin film of a metal or semiconductor formed on a substrate, and is a porous body. A pair of electrodes are formed on the thin film portions on both sides of the formed portion. In FIGS. 10A and 10B, a silicon substrate is used as a substrate for supporting a porous body made of titanium dioxide and a titanium thin film serving as an electrode. A wafer having a surface orientation of (100) and a thin thickness is suitable because the holes are penetrated from one side to the other side of the silicon substrate by wet etching.

(A) The silicon substrate 11 having a thickness of 200 μm is washed with sulfuric acid hydrogen peroxide, dilute hydrofluoric acid, or the like. The silicon substrate 11 corresponds to the substrate 11 of FIG.

(B) A silicon oxide film 36 is formed on one side of the silicon substrate 11 by 500 nm by a chemical vapor deposition method or the like. When a film is formed by thermal oxidation, an oxide film is formed on both sides, so the oxide film on one side is removed by a method such as etching or polishing. Next, a silicon nitride film 37 is formed at 300 nm on the silicon side of the substrate 11 by a chemical vapor deposition method or the like. In the next step, a titanium thin film, which is the base of the gas detection unit, is formed on the silicon nitride film 37. Therefore, it is desirable that the silicon nitride film 37 has a low stress.

(C) The silicon oxide film 36 is patterned by photolithography and etching in order to be used as a mask for wet etching of silicon. Here, for example, the silicon oxide film 36 is removed with a mixed solution of hydrofluoric acid and ammonium fluoride in a rectangular shape having a side number of about 100 μm.

(D) A titanium thin film 38 having a thickness of 500 nm is formed on a surface opposite to the surface on which the silicon oxide film 36 is patterned by a method such as sputtering. The titanium thin film 38 corresponds to the thin film 13 in FIG.

(E) The titanium thin film 38 is patterned using photolithography and etching. For example, the portion of the titanium thin film 38 other than the portion that becomes the gas detection part and the portion that becomes the electrode, which are formed as a porous body by the subsequent anodizing step, is a commercially available titanium etching solution, TIW-I and TIW manufactured by Wako Pure Chemical Industries, Ltd. Remove with a mixture of −II. As shown in FIG. 10A (e) (top view), a strip-shaped titanium thin film 38 portion is left on the substrate 11, the upper and lower titanium thin film 38 portions are removed, and the removed portion is silicon. The nitride film 37 is exposed. At this time, the titanium thin film 38 is patterned so that the central portion of the gas detection unit is aligned directly above the rectangular hole patterned in (c).

(F) Since the resistance value increases when the gas detection part of the titanium thin film 38 patterned in (e) becomes a porous body of titanium dioxide by anodizing, a region where the porous body of titanium dioxide is formed by anodizing is possible. The narrower it is, the better. Therefore, in order to form a silicon dioxide thin film for limiting the region of the titanium thin film 38 to be anodized by the lift-off method, the lift-off resists 39a, 39b, and 39c are patterned.

(G) Silicon dioxide thin films 40a and 40b are formed into a 300 nm film by using a technique such as vacuum deposition. Then, the resists 39a, 39b, 39c and the silicon dioxide thin films 40a, 40b on the resist are removed using a resist stripping solution.

(H) Since the titanium thin film 38 is etched with tetramethylammonium hydroxide (TMAH) or the like, which is an etching solution for silicon, an alkali-resistant protective film 41 is formed on the titanium thin film 38.

(I) Using TMAH or the like, the silicon substrate 11 is etched from the side of the patterned silicon oxide film 36 until the silicon nitride film 37 on the opposite side is exposed. Silicon etching is performed in TMAH heated to 90 ° C. For example, when TMAH-25 manufactured by Toyo Gosei Co., Ltd., which is a product of TMAH, is used, it takes about 6 hours to penetrate a silicon wafer having a thickness of 200 μm.

(J) The silicon nitride film 37 exposed by silicon etching is dry-etched to remove it. As a result, the through hole 19 is formed. Then, the alkali-resistant protective film 41 is removed on the titanium thin film 38.

(K) Anodizing the periphery of the central portion of the patterned titanium thin film 38. The anodization is carried out in the same manner as in the manufacturing process of the gas sensor 10A of the first configuration example shown in FIG. 8 above.

(L) Porousization is performed by forming titanium dioxide nanotubes 30 (amorphous phase) by anodizing.

(M) Since the pores do not penetrate only by anodizing, the titanium dioxide at the bottom of the pores is etched with a mixed solution of hydrofluoric acid and ammonium fluoride until the pores penetrate. At this time, the inner wall portion of the hole is also etched, but the inner wall does not disappear in the time required to etch the bottom of the hole.

(N) In order to improve the performance, the titanium dioxide nanotubes are transferred from the amorphous phase to the anatase phase by heat treatment in the air at 400 ° C. for 1 hour and 450 ° C. for 30 minutes. The nanotube 31 transferred to the anatase phase corresponds to the pore 15 of the porous 14.

(O) The pair of titanium thin films at both ends of the porous body are used as electrodes, and the external lead wires 33a and 33b are connected by a method such as wire bonding. The gas sensor 10C can be manufactured by the steps of FIGS. 10A and 10B.

[Manufacturing process of gas sensor 10D]
FIG. 11 shows an example of the manufacturing process of the gas sensor 10D in the fourth configuration example. In the manufacturing process of FIG. 11, as shown below, the porous body of the gas sensor 10D is formed by anodizing a part of the thin film of the metal or semiconductor formed on the substrate, and the porous body is formed. A pair of electrodes is further formed and provided on the thin film portions on both sides of the portion. In FIG. 11, a silicon substrate is used as a substrate that supports a porous body made of titanium dioxide and a titanium thin film that serves as an electrode. A wafer having a surface orientation of (100) and a thin thickness is suitable because the holes are penetrated from one side to the other side of the silicon substrate by wet etching.

(A) A silicon substrate having a thickness of 200 μm is washed with sulfuric acid hydrogen peroxide, dilute hydrofluoric acid, or the like. The silicon substrate 11 corresponds to the substrate 11 of FIG.

(B) A silicon oxide film 36 is formed on one side of the silicon substrate 11 by 500 nm by a chemical vapor deposition method or the like. When a film is formed by thermal oxidation, an oxide film is formed on both sides, so the oxide film on one side is removed by a method such as etching or polishing. Next, a silicon nitride film 37 is formed at 300 nm on the silicon side of the substrate 11 by a chemical vapor deposition method or the like. In the next step, a titanium thin film, which is the base of the gas detection unit, is formed on the silicon nitride film 37. Therefore, it is desirable that the silicon nitride film 37 has a low stress.

(C) The silicon oxide film 36 is patterned by photolithography and etching in order to be used as a mask for wet etching of silicon. Here, for example, the silicon oxide film 36 is removed with a mixed solution of hydrofluoric acid and ammonium fluoride in a rectangular shape having about 100 sides.

(D) A titanium thin film 38 having a thickness of 500 nm is formed on a surface opposite to the surface on which the silicon oxide film 36 is patterned by a method such as sputtering. The titanium thin film 38 corresponds to the thin film 13 in FIG.

(E) Since the titanium thin film 38 is etched with tetramethylammonium hydroxide (TMAH) or the like, which is an etching solution for silicon, an alkali-resistant protective film 41 is formed on the titanium thin film 38.

(F) Using TMAH or the like, the silicon substrate 11 is etched from the side of the patterned silicon oxide film 36 until the silicon nitride film 37 on the opposite side is exposed. Silicon etching is performed in TMAH heated to 90 ° C. For example, when TMAH-25 manufactured by Toyo Gosei Co., Ltd., which is a product of TMAH, is used, it takes about 6 hours to penetrate a silicon wafer having a thickness of 200 μm.

(G) The silicon nitride film 37 exposed by silicon etching is dry-etched and removed. As a result, the through hole 19 is formed. Then, the alkali-resistant protective film 41 is removed on the titanium.

(H) The periphery of the central portion of the titanium thin film 38 is anodized. The anodization is carried out in the same manner as in the manufacturing process of the gas sensor 10A of the first configuration example shown in FIG. 8 above.

(I) Porousization is performed by forming titanium dioxide nanotubes 30 (amorphous phase) by anodizing.

(J) Since the pores do not penetrate only by anodizing, the titanium dioxide at the bottom of the pores is etched with a mixed solution of hydrofluoric acid and ammonium fluoride until the pores penetrate. At this time, the inner wall portion of the hole is also etched, but the inner wall does not disappear in the time required to etch the bottom of the hole.

(K) In order to improve the performance, the titanium dioxide nanotubes are transferred from the amorphous phase to the anatase phase by heat treatment in the air at 400 ° C. for 1 hour and 450 ° C. for 30 minutes. The nanotube 31 transferred to the anatase phase corresponds to the pore 15 of the porous 14.

(L) Insulating films 16a and 16b are formed on the vicinity of the boundary between the non-porous portion and the porous portion of the titanium thin film 38 by sputtering or the like to obtain insulation from the titanium thin film 38. Alternatively, it can be covered with an insulating paste or non-conductive heat or UV curable resin.

(M) A metal film such as gold, silver, copper, or aluminum is formed on the film by sputtering or the like so as to be electrically connected to the porous body which is a gas detection unit to form electrodes 18a and 18b. .. Alternatively, the electrode can be formed of a conductive paste or the like.

(N) The external lead wires 33a and 33b are connected to the electrodes by a method such as wire bonding. The gas sensor 10D can be manufactured by the process shown in FIG.

If the titanium thin film is patterned into a substantially rectangular shape or a substantially circular shape after the step (d) and the entire region is made porous by anodization, the formation of the insulating film shown in the step (l) is omitted. can do.

The gas sensor according to the embodiment of the present invention described above includes a porous body in which a large number of pores are formed and a pair of electrodes electrically connected to both sides of the porous body. A gas sensor that measures the concentration of gas by measuring the electrical characteristics between the electrodes of the porous body. The pores are formed so as to penetrate from the front surface side to the back surface side of the porous body, and the porous body has. The pores are not blocked on the front surface side and the back surface side, and the gas can permeate from the front surface side to the back surface side of the porous material.

The present invention is not limited to the above-described embodiment, and there are design changes within a range that does not deviate from the gist including various modifications and modifications that can be conceived by a person having ordinary knowledge in the field of the present invention. Of course, it is also included in the present invention.

10 (10A, 10B, 10C, 10D): Gas sensor 11: Substrate 12: Thin plate 13: Thin film 14: Porous body 15: Pore 16a, 16b: Insulating film 18a, 18b: Electrode 19: Through hole 24a, 24b Resist 26 Anodized solution 27 Platinum electrode 30 Titanium dioxide (amorphous phase) nanotube 31 Titanium dioxide (anathase phase) nanotubes 33a, 33b External extraction lead wire 36 Silicon oxide film 37 Silicon nitride film 38 Titanium thin film 39a, 39b, 39c Resist 40a, 40b Silicon thin film 41 Alkali-resistant protective film 50: Gas pipe 52: Direction of gas flow

Claims (6)

By providing a porous body in which a large number of pores are formed and a pair of electrodes electrically connected and arranged on both sides of the porous body, and measuring the electrical characteristics between the pair of electrodes. A gas sensor that measures the concentration of gas.
The pores have a tubular structure that penetrates substantially vertically from the front surface side to the back surface side of the porous body , and each pore is formed so as to be oriented in a substantially constant direction, and the front surface side and the back surface side of the porous body are formed. A gas sensor characterized in that the pores are not closed on the side and gas can permeate from the front surface side to the back surface side of the porous body. By providing a porous body in which a large number of pores are formed and a pair of electrodes electrically connected and arranged on both sides of the porous body, and measuring the electrical characteristics between the pair of electrodes. A gas sensor that measures the concentration of gas.
The pores are formed so as to penetrate from the front surface side to the back surface side of the porous body, and the pores are not closed on the front surface side and the back surface side of the porous body, and gas is emitted from the surface of the porous body. It is transparent from the side to the back side,
A substrate on which the back surface side of the porous body and the pair of electrodes are placed and supported is provided, and through holes are provided in a portion of the substrate facing the back surface side of the porous body. features and to Ruga Susensa that gas that has passed through on the back side from the front surface side can be further transmitted through the through hole of the substrate. By providing a porous body in which a large number of pores are formed and a pair of electrodes electrically connected and arranged on both sides of the porous body, and measuring the electrical characteristics between the pair of electrodes. A gas sensor that measures the concentration of gas.
The pores are formed so as to penetrate from the front surface side to the back surface side of the porous body, and the pores are not closed on the front surface side and the back surface side of the porous body, and gas is emitted from the surface of the porous body. It is transparent from the side to the back side,
The porous body, a substantially central portion of the metal or semiconductor thin plate is formed by anodic oxidation treatment, you wherein a portion other than the portion where the porous body is formed and said pair of electrodes moth Susensa. By providing a porous body in which a large number of pores are formed and a pair of electrodes electrically connected and arranged on both sides of the porous body, and measuring the electrical characteristics between the pair of electrodes. A gas sensor that measures the concentration of gas.
The pores are formed so as to penetrate from the front surface side to the back surface side of the porous body, and the pores are not closed on the front surface side and the back surface side of the porous body, and gas is emitted from the surface of the porous body. It is transparent from the side to the back side,
The porous body is formed by anodizing a substantially central portion of a thin plate of a metal or semiconductor, and the pair of electrodes are placed on a portion other than the portion where the porous body is formed via an insulator. characterized in that it is provided with to Ruga Susensa. The porous body is formed by anodizing a substantially central portion of a thin film of a metal or semiconductor formed on the substrate, and a portion other than the portion on which the porous body is formed is formed by the pair of electrodes. The gas sensor according to claim 2, wherein the gas sensor is characterized. The porous body is formed by anodizing a substantially central portion of a thin film of a metal or semiconductor formed on the substrate, and is further insulated on a portion other than the portion where the porous body is formed. The gas sensor according to claim 2, wherein the pair of electrodes is provided via a body.