JP2010276459A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor avoiding such problems that a crack is formed in a protection film covering a gas sensing layer, and that the protection film is peeled from the gas sensing layer. <P>SOLUTION: The gas sensor 1 is configured such that contour projection lines of the gas sensing layer, the protection film and a heating element are disposed on a bottom contour projection line P or in an area surrounded by the bottom contour projection line P, wherein the contour projection lines and the bottom contour projection line P are represented by projecting members of the gas sensor 1 onto one surface of a substrate 15 along its thickness direction, and following equation (M-L)/T&le;500 is assured, wherein L is the minimum distance between the bottom contour projection line and the contour projection line of the protection film, and M is the minimum distance between the contour projection line and the center of a graphic surrounded by the bottom contour projection line, and T is the minimum thickness of the substrate on the bottom contour projection line. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a gas sensor including a gas detection layer including a metal oxide semiconductor.

  2. Description of the Related Art Conventionally, a gas sensor is known that includes a metal oxide semiconductor such as tin oxide as a gas detection layer on a base such as a semiconductor substrate (see, for example, Patent Document 1). In this type of gas sensor, the metal oxide semiconductor detects the specific gas by utilizing the change in electrical characteristics (for example, resistance value) according to the change in concentration of the specific gas contained in the gas to be detected. When the gas to be detected contains a poisoning gas component such as silicon, the gas detection layer may be poisoned by the poisoning gas. In this case, since the detection performance of the gas sensor may be lowered, the gas sensor described in Patent Document 1 covers the gas detection layer with a protective film that allows the gas to be detected to pass through.

  The gas detection layer does not react with the gas to be detected at normal temperature, but is activated by being heated to, for example, 200 to 400 ° C., and reacts with the gas to be detected. For this reason, in order to heat the gas detection layer, a heating resistor is generally provided on the base at a position corresponding to the gas detection layer. And in order to improve the heating efficiency by the heating resistor, a recess is provided on the surface of the substrate opposite to the surface on which the gas detection layer is formed, and the portion where the heating resistor is provided and its surroundings. The thickness of the substrate is reduced.

European Patent Application Publication No. 1950558

  However, when the gas detection layer is heated by the heating resistor, the substrate is also heated and thermally expanded, and the portion of the substrate provided with the recess may be deformed. At this time, the thermal expansion coefficient differs between the protective film covering the gas detection layer and the substrate, and thermal stress is applied to the protective film. For this reason, if the deformation | transformation of a base | substrate is repeated by using a gas sensor for a long period of time, there existed a possibility that a crack might arise in a protective film or a protective film might peel from a gas detection layer. When a crack occurs in the protective film or the protective film peels off from the gas detection layer, the gas detection layer may be poisoned by the poison gas, and the detection performance of the gas sensor may deteriorate.

  The present invention has been made to solve the above-described problems, and provides a gas sensor that avoids the generation of cracks in the protective film covering the gas detection layer or the separation of the protective film from the gas detection layer. For the purpose.

  A gas sensor according to an embodiment of the present invention is mainly composed of a plate-shaped substrate and a metal oxide semiconductor whose electrical characteristics change according to the concentration change of the specific gas in the gas to be detected, and one surface of the substrate. A gas detection layer provided on the gas detection layer; a protective film provided to cover at least a part of the gas detection layer; and protecting the gas detection layer; and on the other surface opposite to the one surface of the substrate. A gas sensor comprising a recess recessed in the thickness direction of the base and a heating element embedded in the base and generating heat upon energization; and a bottom surface of the recess on the one surface of the base. When the gas detection layer, the protective film, and the heating element are respectively projected along the thickness direction, respective contour projection lines of the gas detection layer, the protective film, and the heating element are formed on the bottom surface. On the contour projection line, The shortest distance between the contour projection line of the bottom surface and the contour projection line of the protective film on the one surface of the base body is set to L on the inside of the region surrounded by the contour projection line of the bottom surface, When the shortest distance between the center of the figure surrounded by the contour projection line of the bottom surface and the contour projection line of the bottom surface is M, and the minimum thickness when the thickness of the base on the contour projection line of the bottom surface is seen is T And (M−L) / T ≦ 500 is satisfied.

  In the case where the base of the portion provided with the recess is deformed by heat, the amount of deformation differs between the outer peripheral portion of the bottom surface of the recess and the inner portion of the outer periphery of the bottom surface of the recess. The larger the distance on the plane from the outer peripheral portion of the bottom surface of the recess, the greater the difference in deformation amount compared to the case where the distance on the plane is small. On the other hand, paying attention to the relationship between the thickness of the base in the portion provided with the recess and the amount of deformation, the greater the thickness of the base in the portion provided with the recess, the smaller the amount of deformation compared to when the thickness is small. In other words, the greater the thickness of the substrate at the portion where the recess is provided, the more difficult it is to deform than when the thickness is small. Therefore, in the gas sensor according to the present embodiment, the shortest distances L and M are considered as a value in consideration of the planar positional relationship between the concave portion and the protective film, and the minimum thickness T as a representative value of the thickness of the substrate in the portion where the concave portion is provided Is defined as (ML) / T ≦ 500. If L, M, and T are determined as in the gas sensor of this embodiment, it is possible to avoid cracks in the protective film and peeling of the protective film from the gas detection layer. The center of the figure surrounded by the bottom contour projection line is, for example, the center of the circle if the figure surrounded by the bottom contour projection line is a circle, and the longest diagonal line in the case of a regular polygon. It is an intersection. When the figure surrounded by the contour projection line on the bottom surface has another shape, for example, the center of gravity of the figure is set as the center of the figure surrounded by the contour projection line on the bottom surface.

  As the thickness of the protective film is larger, the protective film is less likely to follow the variation of the substrate in the portion where the recess is provided, as compared with the case where the thickness of the protective film is small. Therefore, as the thickness of the protective film increases, stress is more likely to occur in the protective film than when the protective film is small, and the protective film is easily cracked or peeled off from the gas detection layer. On the other hand, in the gas sensor according to the embodiment of the present invention, the protective film may be a gas sensor having a film thickness of 10 μm or less. When the thickness of the protective film is 10 μm or less, it is possible to avoid cracks in the protective film or peeling of the protective film from the gas detection layer, compared to when the thickness is larger than 10 μm.

2 is a plan view of the gas sensor 1. FIG. It is a schematic diagram of the cross section of the gas sensor 1 seen from the arrow direction in the dashed-dotted line AA of FIG. 3 is a plan view of a heating resistor 5. FIG. It is a schematic diagram of the cross section of the gas sensor 1 seen from the arrow direction in the dashed-dotted line BB of FIG. FIG. 3 is an explanatory diagram in which the bottom surface 23 of the recess 21, the gas detection layer 7, the protective film 8, and the heating resistor 5 are projected on the one surface 51 of the base body 15 along the thickness direction of the base body 15. It is a graph showing the result of evaluation 1. It is a photograph showing the result of Evaluation 1 under the conditions of L = 0 μm, M = 500 μm, and T = 0.7 μm. It is a photograph showing the result of Evaluation 1 under the conditions of L = 150 μm, M = 500 μm, and T = 0.7 μm. It is a photograph showing the result of Evaluation 1 under the conditions of L = 200 μm, M = 500 μm, and T = 0.7 μm. It is a graph showing the power consumption at the time of 250 degreeC control (M = 500micrometer, T = 0.7micrometer). FIG. 3 is a view corresponding to FIG. 2 of the gas sensor 101.

  Embodiments of the present invention will be described below with reference to the drawings. These drawings are used to explain technical features that can be adopted by the present invention, and the configuration, shape, and the like of the described gas sensor are not intended to be limited to only that, but are merely an explanation. It is an example.

  First, the structure of the gas sensor 1 as an example will be described with reference to FIGS. As shown in FIG. 1, the gas sensor 1 is referred to as one surface 51 (hereinafter, referred to as “upper surface 51”) of a plate-like base body 15 having a planar shape formed in a substantially rectangular shape having a length of 2.3 mm and a width of 2 mm. ) Side has a structure in which a gas detector 16 for detecting a specific gas in the gas to be detected is formed. The thickness direction of the substrate 15 (the front and back direction in FIG. 1 and the direction indicated by the arrow C in FIG. 2) is the vertical direction of the gas sensor 1, and the upper surface 51 side of the substrate 15 on which the gas detector 16 is formed is the gas sensor. 1 is described as the upper side. Moreover, in FIG. 2 and FIG. 4, each member which comprises the gas sensor 1 is shown typically, and it has not illustrated in consideration of the actual dimension of each member.

  As shown in FIG. 2, the base 15 of the gas sensor 1 includes a silicon substrate 2 having a predetermined thickness, an insulating coating layer 3 formed on the upper surface of the silicon substrate 2, and an insulating coating formed on the lower surface of the silicon substrate 2. Layer 4. A recess 21 is provided in the thickness direction of the substrate 15 on the other surface 52 (hereinafter referred to as “lower surface 52”) of the surface of the substrate 15 opposite to the upper surface 51. The concave portion 21 has a shape roughly cut off at the apex side of the quadrangular pyramid in parallel with the upper surface 51. The bottom surface 23 of the recess 21 corresponds to a surface in which the apex side of the quadrangular pyramid is cut off in parallel with the top surface 51. The planar shape of the bottom surface 23 of the recess 21 is a substantially square with a side of 1 mm. Bigger than The thickness of the base 15 in the portion where the recess 21 is provided is set as follows. A contour projection line P obtained by projecting the bottom surface 23 onto the top surface 51 along the thickness direction of the base body 15 is assumed. When the minimum value of the thickness of the substrate 15 on the contour projection line P is T, the value of T is determined in consideration of the shape and size of the protective film 8 described later and the formation position on the plane. In this embodiment, T is 0.7 μm.

The insulating coating layer 3 includes insulating layers 31 to 34 and a protective layer 35. The insulating layer 31 is formed on the upper surface of the silicon substrate 2 and is made of a SiO ₂ film having a predetermined thickness. On the upper surface of the insulating layer 31, an insulating layer 32 made of a Si ₃ N ₄ film having a predetermined thickness is formed. Furthermore, an insulating layer 33 and an insulating layer 34 made of a SiO ₂ film having a predetermined thickness are formed on the upper surface of the insulating layer 32. Between the insulating layer 33 and the insulating layer 34, there are provided a heat generating resistor 5, which will be described later, and a lead portion 12 for energizing the heat generating resistor 5. A protective layer 35 made of an Si ₃ N ₄ film having a predetermined thickness is formed on the upper surface of the insulating layer 34. The protective layer 35 prevents the heating resistor 5 and the lead portion 12 from being damaged by corrosion or trauma.

The insulating coating layer 4 includes an insulating layer 41 and an insulating layer 42. The insulating layer 41 is formed on the lower surface of the silicon substrate 2 and is made of a SiO ₂ film having a predetermined thickness, like the insulating layer 31. On the lower surface of the insulating layer 41, an insulating layer 42 made of a Si ₃ N ₄ film having a predetermined thickness is formed. Insulating layers 41 and 42 have portions removed corresponding to the recesses 21 of the silicon substrate 2, respectively.

  Next, the heating resistor 5 and the lead portion 12 are provided between the insulating layer 33 and the insulating layer 34 as described above. The heating resistor 5 and the lead portion 12 have a two-layer structure including a Pt layer made of Pt and a Ta layer made of Ta. A method for forming the heating resistor 5 and the lead portion 12 between the insulating layer 33 and the insulating layer 34 will be described later. As shown in FIG. 3, the heating resistor 5 has a spiral planar shape. The heating resistor 5 generates heat when energized, and heats and activates a gas detection unit 16 (particularly the gas detection layer 7) described later. The heating resistor 5 is provided at a position corresponding to the gas detection unit 16, specifically, below the gas detection unit 16. The position on the plane of the heating resistor 5 and the position on the plane with the bottom surface 23 of the recess 21 have the following relationship. On the upper surface 51 of the substrate 15, the bottom surface 23 of the recess 21 and the heating resistor 5 are respectively projected along the thickness direction of the substrate 15 (the direction indicated by the arrow C in FIG. 2). As shown in FIG. 5, the contour projection line R of the heating resistor 5 is in a region surrounded by the contour projection line P of the bottom surface 23 of the recess 21. In FIG. 5, a boundary between the heating resistor 5 and the lead portion 12 is defined by a contour projection line Q obtained by projecting the gas detection unit 16 on the upper surface 51. By determining the positions of the recess 21 and the heating resistor 5 as described above, the heating efficiency of the gas detection unit 16 by the heating resistor 5 can be increased.

  As shown in FIG. 4, a through hole 14 that penetrates the insulating layer 34 and the protective layer 35 is formed at each terminal position of the lead portion 12. The through hole 14 is provided with an extraction electrode 13 that is in electrical contact with the lead portion 12 exposed inside and leads out to the upper surface side of the protective layer 35. The extraction electrode 13 is composed of a Pt layer and a Ti layer. On the surface of the extraction electrode 13, a pair of connection terminals 9 made of Au and responsible for connection with an external circuit (not shown) for energizing the heating resistor 5 is formed. As shown in FIG. 1, the connection terminal 9 is disposed with a connection terminal 10 described later at a position near one edge in the longitudinal direction of the gas sensor 1.

  Next, as shown in FIG. 2, the gas detector 16 is formed on the upper surface 51 of the substrate 15 (the upper surface of the protective layer 35 of the insulating coating layer 3). The gas detection unit 16 includes a detection electrode 6, a gas detection layer 7, and a protective film 8. As shown in FIG. 1, the gas detector 16 projects a contour projection line in which the bottom surface 23 of the recess 21 is projected on the upper surface 51 of the base body 15 along the thickness direction of the base body 15 (the direction indicated by the arrow C in FIG. 2). Arranged in a region surrounded by P.

  The detection electrode 6 is composed of a pair of electrodes formed in a comb-like pattern on the upper surface 51 of the base body 15, and the other electrode is disposed between the parts of the comb-like shape of one electrode so as not to contact each other. The part which makes the comb-tooth shape of an electrode is arrange | positioned. A pair of electrodes constituting the detection electrode 6 are electrically connected to each other via the gas detection layer 7, and detects a change in electrical characteristics in the gas detection layer 7. The detection electrode 6 is disposed at a position overlapping the heating resistor 5 in the thickness direction of the base body 15.

The gas detection layer 7 covers the detection electrode 6. The gas detection layer 7 has SnO ₂ that is a metal oxide semiconductor as a main component, and has a property that its own electric characteristics (specifically, an electric resistance value) change depending on a specific gas in the gas to be detected. Examples of the specific gas include CO, H ₃ , NO ₂ , NH ₃ , H ₂ S, (CH ₃ ) ₂ S ₂ , CH ₃ SH, and (CH ₃ ) ₃ N. The position on the plane of the gas detection layer 7 and the position on the plane of the bottom surface 23 of the recess 21 have the following relationship. On the upper surface 51 of the substrate 15, the bottom surface 23 of the recess 21 and the gas detection layer 7 are projected along the thickness direction of the substrate 15. As shown in FIG. 5, the contour projection line S of the gas detection layer 7 is in a region surrounded by the contour projection line P of the bottom surface 23 of the recess 21. By determining the positions of the recess 21 and the gas detection layer 7 as described above, the heating efficiency of the gas detection unit 16 by the heating resistor 5 is increased.

  The protective film 8 is a film that has a substantially square planar shape with a side of 600 μm and covers the gas detection layer 7. The protective film 8 protects the gas detection layer 7 from poisoning while permeating the gas to be detected. The thickness of the protective film 8 is preferably 10 μm or less. As the thickness of the protective film 8 increases, the amount of heat generated in the heating resistor 5 is transferred to the protective film 8 more than in the case where the thickness of the protective film 8 is small. This is because the heating efficiency decreases.

  The size, shape, and formation position on the plane of the protective film 8 are determined in consideration of the minimum value T of the thickness of the substrate 15 on the contour projection line P described above. Specifically, the bottom surface 23 of the recess 21 and the protective film 8 are projected on the upper surface 51 of the base body 15 along the thickness direction of the base body 15. As shown in FIG. 5, the shortest distance between the contour projection line P of the bottom surface 23 and the contour projection line Q of the protective film 8 is L, and the center X of the figure Z surrounded by the contour projection line P of the bottom surface 23 and the contour projection line P And M and L are values satisfying (ML) / T ≦ 500. In this embodiment, T is 0.7 μm, M is 500 μm, and L is 200 μm. In the present embodiment, the figure Z and the figure W surrounded by the contour projection line Q of the protective film 8 are all square. The figure W is arranged at the center of the figure Z. Therefore, the shortest distance M is equal to the distance between one side of the figure Z and a line Y passing through the center X and parallel to the one side. (ML) is equal to a distance N between one side of the figure W and a line Y passing through the center X and parallel to the one side. Thus, by determining the position on the plane of the gas detection unit 16 with respect to the bottom surface 23, the gas detection layer 7 can be efficiently heated by the heating resistor 5.

  As shown in FIG. 1, the upper surface of the base 15 (protective layer 35) has a pair of lead portions 11 connected to the detection electrode 6 in order to energize the pair of electrodes constituting the detection electrode 6. A pattern is formed. As shown in FIG. 4, a pair of connection terminals 10 made of Au and responsible for connection with an external circuit (not shown) are formed on the surface of the end of each lead portion 11. Similarly to the extraction electrode 13, the detection electrode 6 and the lead portion 11 also have a two-layer structure composed of a Pt layer and a Ti layer.

  Hereinafter, the manufacturing process of the gas sensor 1 will be described. In addition, the intermediate body of the gas sensor 1 in the middle of manufacture is called a board | substrate. Moreover, the number in the parenthesis attached to the process name used for description of each process has shown the execution order of each process.

(1) Cleaning of silicon substrate 2 A silicon substrate 2 having a thickness of 400 μm was immersed in a cleaning solution and subjected to a cleaning process.

(2) Formation of insulating layers 31 and 41 The silicon substrate 2 is put into a heat treatment furnace, and the insulating layers 31 and 41 made of a SiO ₂ film having a thickness of 100 nm are formed on both surfaces (upper and lower surfaces) of the silicon substrate 2 by thermal oxidation. Formed.

(3) Formation of insulating layers 32 and 42 SiH ₂ Cl ₂ and NH ₃ are used as a source gas by LP-CVD, and 200 nm thick Si ₃ N ₄ films are formed on the surfaces of the insulating layers 31 and 41, respectively. Insulating layers 32 and 42 were formed.

(4) Formation of Insulating Layer 33 An insulating layer 33 made of a SiO ₂ film having a thickness of 100 nm was formed on the surface of the insulating layer 32 by plasma CVD using TEOS and O ₂ as source gases.

(5) Formation of heating resistor 5 and lead portion 12 Using a DC sputtering apparatus, a Ta layer having a thickness of 20 nm was formed on the surface of the insulating layer 33, and a Pt layer having a thickness of 220 nm was formed on the Ta layer. After sputtering, the resist was patterned by photolithography, and the pattern of the heating resistor 5 and the lead portion 12 was formed by wet etching.

(6) Formation of insulating layer 34 As in (4), TEOS, O ₂ is used as a source gas by plasma CVD, and a thickness of 100 nm is formed on the surfaces of the insulating layer 33, the heating resistor 5 and the lead portion 12. An insulating layer 34 made of a SiO ₂ film was formed. In this way, the heating resistor 5 and the lead portion 12 were embedded in the insulating layers 33 and 34 made of the SiO ₂ film.

(7) Formation of protective layer 35 Similar to (3), SiH ₂ Cl ₂ and NH ₃ are used as source gases by LP-CVD, and an Si ₃ N ₄ film having a thickness of 200 nm is formed on the upper surface of the insulating layer 34. A protective layer 35 was formed.

(8) Formation of the opening of the connection terminal 9 The resist is patterned by photolithography, the protective layer 35 and the insulating layer 34 are etched by the dry etching method, and the through hole 14 is opened in the portion where the connection terminal 9 is to be formed. A part of the end of the lead portion 12 was exposed.

(9) Formation of detection electrode 6, lead portion 11 and extraction electrode 13 Using a DC sputtering apparatus, a Ti layer having a thickness of 20 nm is formed on the surface of protective layer 35, and a Pt layer having a thickness of 40 nm is further formed on the surface. Formed. After sputtering, the resist was patterned by photolithography, and the patterns of the detection electrode 6 and the lead portion 11 having a comb-like planar shape were formed by wet etching. Further, a Ti layer and a Pt layer were also formed in and around the through hole 14 formed in (8), and a pattern of the extraction electrode 13 was formed so that the end of the lead portion 12 was drawn to the upper surface side of the protective layer 35.

(10) Formation of connection terminals 9 and 10 Using a DC sputtering apparatus, an Au layer having a thickness of 400 nm was formed on the electrode-side surface of the substrate on which the electrode part was fabricated. After sputtering, the resist was patterned by photolithography, and the connection terminals 9 and 10 were formed by wet etching. Thereby, the connection terminal 9 was electrically connected to the end of the lead portion 12, and the connection terminal 10 was electrically connected to the end of the lead portion 11 via the extraction electrode 13.

(11) Formation of recesses 21 Resist was patterned by photolithography, and an insulating film (not shown) serving as a mask was formed by dry etching. Then, the substrate was immersed in the TMAH solution, and the silicon substrate 2 was anisotropically etched to form the recess 21.

(12) Formation of the gas detection layer 7 Using an RF sputtering apparatus, while heating the silicon substrate 2 so that the temperature of the silicon substrate 2 becomes 240 ° C., on the comb-shaped detection electrode 6 and the protective layer 35 in the peripheral portion thereof A SnO ₂ film having a thickness of 200 nm was formed. Thereafter, Au was deposited on the SnO ₂ film by a DC sputtering apparatus without heating to form catalyst particles.

(13) Heat treatment Using an RF sputtering apparatus or a vacuum heat treatment furnace, heat treatment was performed at 360 ° C. for 3 hours in an atmosphere having an O ₂ concentration of 10 ppm or less (preferably 0.2 ppm or 5 ppm).

(14) Formation of protective film 8 A binder and an organic solvent were mixed with TiO ₂ powder, and then kneaded using a tri-roll mill to prepare a TiO ₂ paste. A TiO ₂ paste was printed on a predetermined location of the silicon substrate 2 using a metal mask, and then baked at 350 ° C.

(15) Cutting the substrate The substrate was cut using a dicing saw, and the size was 2.3 mm × 2 mm in a rectangular shape in plan view. The gas sensor 1 shown in FIG. 1 was completed by the above manufacturing process.

  Next, the gas sensor 1 was produced according to the above manufacturing process, and the following evaluation test was performed.

[Evaluation 1]
In Evaluation 1, the probability of occurrence of cracks / peeling of the protective film 8 of the gas sensor 1 was evaluated. First, according to the manufacturing process described above, 100 gas sensors 1 having different values of L were prepared on a condition that T was 0.7 μm and M was 500 μm. A total of five values of 0, 50, 100, 150, and 200 were used as the value of L. The thickness of the protective film 8 was 7 ± 3 μm. For each gas sensor 1, energization control at 400 ° C. in a 25 ° C. atmosphere for 1 second and non-energization for 1 second were repeated 20,000 times alternately to check whether cracks or peeling occurred in the protective film. Then, the probability of occurrence of cracks / peeling of the protective film was determined. Further, under the conditions where T is 0.35 and M is 500 μm, the same evaluation was performed for L where (ML) / T is 1000, 500, and 429. Further, the same evaluation was performed for L where (ML) / T was 476 and 429 under the conditions of T = 1.05 μm and M = 500 μm. In the gas sensor having the minimum thickness T of 0.35 or 1.05 μm, the thicknesses of the insulating layers 31 to 34, the protective layer 35, the heating resistor 5 and the lead portion 12 included in the insulating coating layer 3 are relatively set. Created by changing.

  The results of Evaluation 1 when T is 0.7 μm and M is 500 μm are shown in FIGS. As shown in FIG. 6, when (ML) / T is 714, the probability of occurrence of cracking / peeling of the protective film 8 was 100%. As shown in FIG. 7, when (ML) / T is 714, the protective film 8 is cracked in the peripheral portion of the contour projection line P. Although not shown, when the same evaluation was performed on a gas sensor in which the contour projection line Q of the protective film 8 was outside the contour projection line P of the bottom surface 23 under the conditions of T of 0.7 μm and M of 500 μm, the protective film 8 cracked. On the other hand, as shown in FIG. 6, when (ML) / T is smaller than 714, as (ML) / T decreases, the probability of occurrence of cracks and delamination decreases, and (ML) / T is In the case of 500 or less, the probability of occurrence of cracks / peeling was 0%. When (ML) / T shown in FIG. 8 is 500 and (ML) / T shown in FIG. 9 is 429, no cracks or peeling occurred in the protective film. Although not shown in the figure, even when T is 0.35 and M is 500 μm, and T is 1.05 μm and M is 500 μm, if (ML) / T is 500 or less, The occurrence probability of peeling was 0%. From the result of evaluation 1, L, M so that the contour projection line of the gas detection unit 16 is on or inside the contour projection line P of the bottom surface 23 and (ML) / T ≦ 500. When T and T are set, it has been confirmed that cracks and peeling can be avoided in the protective film 8. In addition, by setting L, M, and T so that (ML) / T ≦ 429, it is possible to more reliably avoid the occurrence of cracks or peeling in the protective film 8.

[Evaluation 2]
Next, the power consumption of the heating resistor 5 was measured when the temperature of the heating resistor 5 was controlled to be 250 ° C. under conditions where T was 0.7 μm and M was 500 μm. The result of evaluation 2 is shown in FIG. In addition, the case where (ML) / T = 0 is a case where the protective film 8 is not provided. As shown in FIG. 7, the power consumption at 250 ° C. control is 40.1 mW when (ML) / T is 500, and (M−L) / T is less than 500 under the condition that (ML) / T is less than 500. The power consumption decreased as L) / T decreased. From the result of evaluation 2, if L, M, and T are set so that (ML) / T ≦ 500, the power consumption when energization control is performed so that the temperature of the heating resistor 5 becomes a predetermined temperature. It was confirmed that it is possible to avoid the occurrence of cracks and peeling in the protective film 8 without damaging the film.

  The present invention is not limited to the above embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the following modifications (A) to (C) may be added.

  (A) The silicon substrate 2 of the base 15 is made of silicon, but may be made of other semiconductor materials. Further, the planar shape of the gas sensor 1 is not limited to a rectangle, and may be an arbitrary shape, and the size, thickness, and arrangement of each member are not limited.

(B) Although the insulating coating layers 3 and 4 have a multi-layer structure composed of a SiO ₂ film and a Si ₃ N ₄ film, they may have a single layer structure composed of a SiO ₂ film or a Si ₃ N ₄ film. Further, although the heating resistor 5 is embedded between the insulating layer 33 and the insulating layer 34, it is only necessary to be disposed at a position where the gas detection unit 16 can be efficiently heated.

(C) The protective film should just cover at least one part of a gas detection layer. Further, the configuration of the base body 15 at the portion where the recess 21 is provided can be variously changed according to the thickness T. For example, the modification shown in FIG. 11 may be used. In FIG. 11, the same reference numerals are given to the same components as those in the above embodiment shown in FIG. As shown in FIG. 11, in the modified gas sensor 101, the protective film 108 covers a part of the upper surface of the gas detection layer 107. The thicknesses of the insulating layers 131 to 134 of the insulating coating layer 103, the protective layer 135, the insulating layers 141 and 142 included in the insulating coating layer 104, the heating resistor 105, and the lead portion 112 are the same as those of the embodiment shown in FIG. It is relatively thinner than a gas sensor. In the modification, the insulating layer 131 is the bottom surface 123 of the recess 121.

DESCRIPTION OF SYMBOLS 1,101 Gas sensor 5,105 Heating resistor 7,107 Gas detection layer 8,108 Protective film 15,115 Base | substrate 21,121 Recess 23,123 Bottom 51 Upper surface 52 Lower surface

Claims (2)

A plate-like substrate;
A gas detection layer provided on one surface of the substrate, the main component of which is a metal oxide semiconductor whose electrical characteristics change according to the concentration change of the specific gas in the gas to be detected;
A protective film provided to cover at least a part of the gas detection layer and protecting the gas detection layer;
A recess formed in the other surface opposite to the one surface of the base and recessed in the thickness direction of the base;
A gas sensor comprising a heating element embedded in the substrate and generating heat when energized,
When the bottom surface of the recess, the gas detection layer, the protective film, and the heating element are respectively projected along the thickness direction on the one surface of the base, the gas detection layer and the protective film And the contour projection lines of the heating element and the heating element are arranged on the contour projection line of the bottom surface or inside the region surrounded by the contour projection line of the bottom surface,
On the one surface of the substrate, L is the shortest distance between the contour projection line of the bottom surface and the contour projection line of the protective film,
The shortest distance between the center of the figure surrounded by the contour projection line of the bottom surface and the contour projection line of the bottom surface is M,
(M−L) / T ≦ 500, where T is the minimum thickness when the thickness of the substrate on the contour projection line of the bottom surface is seen.
Gas sensor characterized by satisfying.   The gas sensor according to claim 1, wherein the protective film has a thickness of 10 μm or less.