JP2024086564A - Gas Sensors - Google Patents

Abstract

A gas sensor that can be manufactured by a simple process and has good detection stability and detection responsiveness is provided.
[Solution] A gas sensor comprising: a substrate in which a cavity is formed; a first insulating film having a plurality of beam portions connected to a cavity periphery, which is the periphery of the cavity in the substrate, and a first insulating film membrane portion held on the cavity via the beam portions; a second insulating film stacked on the upper side of the first insulating film; a heater portion provided on the upper side of the first insulating film membrane portion; a flat portion provided between the first insulating film membrane portion and the second insulating film, positioned toward the center of the first insulating film membrane portion relative to the heater portion when viewed from above, and forming a flat surface facing upward; and a gas detection portion positioned above the flat portion via at least the second insulating film, and having an area narrower than the flat surface.
[Selected Figure] Figure 6

Description

The present invention relates to a gas sensor.

A gas sensor is a device that detects gases present in the atmosphere and converts information such as the type and concentration of the gas into an electrical signal and outputs it. Such gas sensors are installed in home appliances, industrial equipment, environmental monitoring equipment, etc., and are used to detect the concentration of specific gases that have an impact on humans, the environment, etc.

There are a variety of gas sensor detection methods known, differing in the type of gas to be detected, concentration range, accuracy, operating principle, and constituent materials. Among these, a sensor that combines a detection unit with a heater to control the temperature around the detection unit is being developed as a sensor that can reduce errors caused by temperature effects.

For example, one of the conventional gas sensors has a heater wire arranged on the outer periphery of the membrane and a detection electrode arranged on the inner part of the membrane (see, for example, Patent Document 1, etc.). In such a gas sensor, since heat from the heater wire is not easily transmitted near the center of the membrane, the temperature distribution around the detection electrode becomes uneven, which may adversely affect the detection stability. On the other hand, a technique for overlapping the heater wire and the detection electrode in layers in the membrane has also been proposed (see, for example, Patent Document 2, etc.). In such a technique, it is difficult to form the detection electrode in the upper layer on a flat surface due to the unevenness caused by the pattern shape of the heater wire in the lower layer, so there is a problem that the shape of the detection electrode is easily locally distorted, making the detection signal unstable and reducing the detection response. In addition, in the technique for overlapping the heater wire and the detection electrode in layers, it is possible to planarize the intermediate layer by CMP, etc., but such an approach leads to problems of increased process lead time and increased costs.

Patent No. 6960645 Patent No. 6877397

The present invention has been made in consideration of these circumstances, and provides a gas sensor that can be manufactured using a simple process and has good detection stability and detection responsiveness.

The gas sensor according to the present invention comprises:
a substrate in which a cavity is formed;
a first insulating film having a plurality of beam portions connected to a cavity periphery that is a periphery of the cavity in the base material, and a first insulating film membrane portion held on the cavity via the beam portions;
a second insulating film laminated on an upper side of the first insulating film;
a heater section provided on an upper side of the first insulating film membrane section;
a flat portion provided between the first insulating film membrane portion and the second insulating film, disposed closer to the center of the first insulating film membrane portion than the heater portion when viewed from above, and forming a flat surface facing upward;
The gas detector has a gas detection portion disposed above the flat portion with at least the second insulating film interposed therebetween, the gas detection portion having an area smaller than that of the flat surface.

In this type of gas sensor, a flat portion having a flat surface is formed inside the heater portion, and a gas detection portion having an area smaller than that of the flat portion is formed on the flat portion via a second insulating film. Therefore, the gas detection portion can be formed with high precision without being affected by unevenness due to the shape of the lower layer, and good responsiveness can be achieved. Furthermore, since the flat portion only needs to be formed with a substantially uniform thickness in the planar direction, this type of gas sensor can be manufactured by a simple process, and the process efficiency is also good. Furthermore, since the heat of the heater portion is transferred to the gas detection portion via the second insulating film, the flat portion, etc., local temperature variations in the gas detection portion are reduced, and the detection stability of the gas sensor is also good.

Also, for example, the flat portion may have a higher thermal conductivity than the second insulating film.

By increasing the thermal conductivity of the flat portion, heat from the heater section is transferred more efficiently to the gas detection section, and local temperature variations in the gas detection section are reduced, effectively improving the detection stability of the gas sensor.

Also, for example, the flat portion may be made of the same material as the heater portion.

By using the same material for the flat portion and the heater portion, both of which are between the first insulating film and the second insulating film, the flat portion and the heater portion can be formed using the same film formation process, making this type of gas sensor highly efficient to produce.

Also, for example, the heater portion may have a bending portion that repeatedly bends with an amplitude of less than 1/2 the length of a side of the first insulating film membrane portion, which is substantially rectangular.

A heater section having such a bent portion can prevent the thermal contraction of the first insulating film and the second insulating film with which the heater section comes into contact from being biased in a specific direction along the plane. Therefore, a gas sensor having such a heater section can effectively prevent problems such as detection errors and noise caused by thermal stress in the first insulating film and the second insulating film that constitute the membrane.

Also, for example, the heater portion may have a symmetrical shape with respect to a reference line that passes through the center of the first insulating film membrane portion and extends horizontally.

Such a heater section can uniformly distribute the temperature of the gas detection section, which is located closer to the center of the first insulating film membrane section than the heater section when viewed from above, and can therefore effectively improve the detection stability of the gas sensor.

The heater portion may be connected to the flat portion.

In such a gas sensor, heat is transferred more efficiently from the heater portion to the flat portion, improving the thermal response of the gas sensor and making it possible to uniformize the temperature distribution of the gas detection portion formed above the flat portion, thereby improving the detection stability of the gas sensor.

Also, for example, the gas detection unit may have at least one pair of electrodes in contact with a semiconductor material,
The gas sensor may detect the gas based on a change in resistance between the electrodes.

Such a gas sensor can provide high sensitivity and reliability, especially in the low concentration range.

Also, for example, the gas detection portion may have a Pt wire in contact with a catalytic material,
The gas sensor may detect gas based on a change in resistance of the Pt wire.

A gas sensor having such a configuration can realize a gas sensor with good responsiveness and reliability with a simple structure.

Also, for example, the gas detection unit may have at least one pair of electrodes in contact with a thermistor film,
The gas sensor may detect the gas based on a change in resistance between the electrodes.

A gas sensor having such a configuration can realize a gas sensor with good stability with a simple structure.

The thermistor film may also be in contact with a catalyst material.

A gas sensor having such a configuration can realize a gas sensor with a simple structure, high thermal response, and high output value.

The gas sensor may further include a heater wiring portion that connects a heater terminal provided on the periphery of the cavity and the heater portion, passing through an upper side of any one of the beam portions.
The gas sensor may further include a detection wiring portion that connects a detection terminal provided on the periphery of the cavity and the gas detection portion, passing through an upper side of any one of the beam portions.

FIG. 1 is a schematic plan view of a gas sensor according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 taken along line II-II. FIG. 3 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 taken along line III-III. FIG. 4 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 taken along line IV-IV. FIG. 5 is a partial enlarged view showing the shapes of the heater portion, the gas sensor portion, etc. in the gas sensor shown in FIG. FIG. 6 is a partial enlarged view showing the shapes of the heater portion, flat portion, etc. in the gas sensor shown in FIG. FIG. 7 is an enlarged cross-sectional view of a portion of the gas sensor shown in FIG. 2 that is disposed above the cavity. FIG. 8 is a schematic plan view of a gas sensor according to a second embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of the gas sensor shown in FIG. 8 taken along line IX-IX. FIG. 10 is a schematic cross-sectional view of the gas sensor shown in FIG. 8 taken along line XX. FIG. 11 is a partial enlarged view showing the shapes of the heater portion, the gas sensor portion, etc. in the gas sensor shown in FIG. FIG. 12 is an enlarged cross-sectional view of a portion of the gas sensor shown in FIG. 9 that is disposed above the cavity. FIG. 13 is a schematic plan view of a gas sensor according to a third embodiment of the present invention. FIG. 14 is a schematic cross-sectional view of the gas sensor shown in FIG. 13 taken along line XIV-XIV. FIG. 15 is a schematic view of the gas sensor shown in FIG. 13 taken along line XV-XV. FIG. 16 is a partial enlarged view showing the shapes of the heater portion, the gas sensor portion, etc. in the gas sensor shown in FIG. FIG. 17 is an enlarged cross-sectional view of a portion of the gas sensor shown in FIG. 14 that is disposed above the cavity. FIG. 18 is a partial enlarged view showing a flat portion, a heater portion, and the like according to the first modified example. FIG. 19 is a partial enlarged view showing the flat portion, the heater portion, and the like according to the second to fourth modified examples. FIG. 20 is a schematic plan view of a gas sensor according to a comparative example. FIG. 21 is an enlarged cross-sectional view of a portion of the gas sensor shown in FIG. 20 that is disposed above the cavity. FIG. 22 is a graph showing the calculation results of the temperature distribution of the gas sensors according to the example and the comparative example. FIG. 23 is a graph showing the element response of the gas sensor according to the comparative example. FIG. 24 is a graph showing the element response of the gas sensor according to the example.

Hereinafter, the present invention will be described in detail based on specific embodiments in the following order.
1. First embodiment 1.1. Overall configuration 1.2. Substrate 1.3. First and second insulating films 1.4. Heater section and heater wiring section 1.5. Flat section 1.6. Gas detection section and detection wiring section 1.7. Semiconductor material 1.8. Manufacturing method 1.9. Function 2. Second embodiment 3. Third embodiment 4. Modification 5. Examples and comparative examples

1. First embodiment
Fig. 1 is a schematic plan view showing a gas sensor 10 according to a first embodiment, as viewed from above. In Fig. 1, the second insulating film 40 is seen through, and only the location of the semiconductor material 92 is shown by imaginary lines. The gas sensor 10 has a heater section 50 and a gas detection section 60 supported by a thin membrane 18. The gas to be detected is a combustible gas and _a reducing gas, and specific examples thereof include carbon monoxide (CO), methane ( _CH4 ), propane ( _C3H8 ), and _{ethanol (C2H5OH )} .

The gas sensor 10 has a semiconductor material 92 whose resistance value changes upon contact with a reducing gas. The gas detection section 60 of the gas sensor 10 has at least one pair of electrodes 62a, 62b in contact with the semiconductor material 92. The gas sensor 10 detects the gas concentration by the change in resistance of the semiconductor material 92 connecting the electrodes 62a, 62b. The gas sensor 10 using the semiconductor material 92 realizes a gas sensor 10 that is highly sensitive and reliable, especially in the low concentration range.

The gas sensor according to the present invention is not limited to those having a semiconductor material 92 and a pair of electrodes 62a, 62b, but includes those having a catalyst material, a Pt wire, a thermistor film, etc. (see the second and third embodiments, etc.). The gas sensor according to the present invention also includes those having a reference gas sensor that does not have direct gas detection capability, and those having multiple mutually different gas detection units.

(1.1. Overall configuration)
FIG. 2 is a schematic cross-sectional view of the gas sensor 10 cut along a plane along line II-II in FIG. 1. FIG. 3 is a schematic cross-sectional view of the gas sensor 10 cut along a plane along line III-III in FIG. 1, and FIG. 4 is a schematic cross-sectional view of the gas sensor 10 cut along a plane along line IV-IV in FIG. 1. In the description of the gas sensor 10, the vertical direction of the gas sensor 10 is the Z axis, the direction perpendicular to the Z axis and parallel to the reference line A1 (see FIG. 6) which is the symmetrical axis of the heater section 50 is the Y axis, and the direction perpendicular to the Z axis and the Y axis is the X axis. The Z axis direction of the gas sensor 10 coincides with the lamination direction of the first insulating film 30 and the second insulating film 40, which will be described later. In the description of the gas sensor 10, the side of the first insulating film 30 and the second insulating film 40 from the substrate 20 is the upper side and the Z axis positive direction, and the opposite direction to the upper side and the Z axis positive direction is the lower side and the Z axis negative direction.

As shown in Figs. 1 and 2, the gas sensor 10 has a substrate 20 in which a cavity 22 is formed. As shown in Fig. 2, other components of the gas sensor 10 are disposed on the cavity 22 of the substrate 20 and on the cavity periphery 24 which is the periphery of the cavity 22. Other components of the gas sensor 10 besides the substrate 20 include a first insulating film 30, a second insulating film 40, a heater section 50, a gas detection section 60, heater terminals 58a, 58b, heater wiring sections 59a, 59b, detection terminals 68a, 68b, detection wiring sections 69a, 69b, a flat section 70, and a semiconductor material 92.

(1.2. Substrate)
1, the cavity 22 is formed near the center of the substrate 20. The membrane 18 is disposed above the cavity 22, and in FIG. 1, the cavity 22 visible below the membrane 18 is shown in dark gray.

As shown in Figures 1 to 3, the cavity 22 in the substrate 20 is configured as a substantially rectangular through-hole in the substrate 20, but the shape of the cavity 22 is not limited to a rectangle. In addition, the cavity 22 is not limited to a through-hole as shown in Figures 2 and 3, and the cavity 22 may be configured as a recess that is recessed downward from the cavity periphery 24 on the substrate surface side.

The material of the substrate 20 is not particularly limited as long as it has sufficient mechanical strength to support the members formed on the cavity 22 and on the cavity periphery 24, and is made of a material suitable for microfabrication such as etching. In this embodiment, examples of the substrate 20 include a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, a quartz substrate, a glass substrate, and a ferrite substrate.

(1.3. First and second insulating films)
1 to 3, a first insulating film 30 and a second insulating film 40 are formed on the upper side of a cavity 22 formed in the center of the substrate 20 and on the upper side of a cavity peripheral portion 24 constituting the upper surface of the substrate 20. As shown in FIG. 1, the first insulating film 30 is formed on the entire upper side of the substrate 20 except for a portion corresponding to a membrane peripheral hole 18a formed around the outer edge of the cavity 22, and the second insulating film 40 is formed on the entire upper side of the substrate 20 except for a portion corresponding to a membrane peripheral hole 18a and a portion where heater terminals 58a, 58b are formed in the cavity peripheral portion 24. Of the first insulating film 30 and the second insulating film 40, the first insulating film membrane portion 32 and the second insulating film membrane portion 44 (see FIG. 7) arranged on the cavity 22 constitute the membrane 18 in the gas sensor 10.

As shown in FIG. 1, the first insulating film 30 has multiple (four in the embodiment) beam portions 31a, 31b, 31c, and 31d that connect to the cavity peripheral portion 24, which is the peripheral portion of the cavity 22 in the substrate 20, and a first insulating film membrane portion 32 (see FIG. 2 and FIG. 3) that is held on the cavity 22 via the beam portions 31a to 31d. Also, as shown in FIG. 1, the first insulating film 30 has a first insulating film peripheral portion 36 that is formed on the cavity peripheral portion 24. The beam portions 31a to 31d of the first insulating film 30 and the first insulating film peripheral portion 36 are connected on the cavity peripheral portion 24.

As shown in FIG. 2 to FIG. 4, the second insulating film 40 is laminated on the upper side of the first insulating film 30. The planar shape of the second insulating film 40 shown in FIG. 1 is similar to that of the first insulating film 30, except that the second insulating film 40 is not formed in the portion where the heater terminals 58a, 58b are formed. That is, the second insulating film 40 also has a portion laminated on the beam portions 31a to 31d of the first insulating film 30, a second insulating film membrane portion 44 laminated on the first insulating film membrane portion 32 of the first insulating film 30, and a second insulating film peripheral portion 46 laminated on the first insulating film peripheral portion 36. However, the second insulating film 40 is not limited to the shape shown in the embodiment, and the planar shape of the second insulating film 40 does not necessarily have to be the same as the planar shape of the first insulating film 30.

Figure 7 is an enlarged cross-sectional view of the portion of the gas sensor 10 shown in Figure 2 that is disposed above the cavity 22. As shown in Figure 7, the second insulating film membrane portion 44 that is laminated on the first insulating film membrane portion 32 of the first insulating film 30 has a first portion 41, a second portion 42, and a third portion 43. The portion of the gas sensor 10 that is disposed above the cavity 22 will be described in detail later.

As shown in Figures 1 to 3, a membrane peripheral hole 18a is formed around the membrane 18, which is composed of the first insulating film membrane portion 32 and the second insulating film membrane portion 44, so as to surround the membrane 18. Also, as shown in Figures 2 and 3, a cavity 22 is formed below the first insulating film membrane portion 32, and the first insulating film membrane portion 32 does not contact the substrate 20, but is supported by the substrate 20 via beam portions 31a to 31d and the like, which have narrow cross-sectional areas.

Such a gas sensor 10 can reduce the heat capacity of other materials near the gas detection section 60, except for the gas detection section 60 and the semiconductor material 92 with which the gas detection section 60 comes into contact. In addition, due to the structure of the membrane 18 having the beam sections 31a to 31d, the gas detection section 60 and other parts located in the central portion of the membrane 18 are suitably insulated from the substrate 20 that supports the membrane 18. Such a gas sensor 10 can greatly reduce the power consumption of the heater section 50 required to heat the gas detection section 60 and the semiconductor material 92 to a predetermined temperature.

As shown in Figures 2 to 4, the first insulating film 30 is generally flat except for the membrane peripheral hole 18a, and has no steps or slopes inside the first insulating film 30. This is because the first insulating film 30 is formed on a flat surface like a flat substrate surface, as described below. In contrast, the second insulating film 40 has a portion that directly contacts the first insulating film 30 and a portion that sandwiches other layers, such as the heater section 50, between the first insulating film 30. Therefore, the second insulating film 40 has steps and slopes, especially in the second insulating film membrane section 44 shown in Figure 7, etc.

As will be described later with reference to FIG. 7, the gas sensor 10 controls the arrangement of steps and slopes formed in the second insulating film membrane portion 44 by providing a flat portion 70, thereby preventing the problem of the gas detection portion 60 formed on the second insulating film membrane portion 44 being affected by unevenness in the lower layer.

The thicknesses of the first insulating film 30 and the second insulating film 40 are not particularly limited, but it is preferable that the thickness of the first insulating film 30 is thicker than the thickness of the second insulating film 40 from the viewpoint of efficiently transferring heat from the heater section 50 to the gas detection section 60 and the semiconductor material 92 while ensuring the strength of the membrane 18. The thickness of the first insulating film 30 is preferably, for example, 0.1 to 10 μm, and more preferably, for example, 0.5 to 5 μm. The thickness of the second insulating film 40 is preferably, for example, 0.1 to 5 μm, and more preferably, for example, 0.2 to 2 μm.

The material of the first insulating film 30 and the second insulating film 40 is selected taking into consideration durability against thermal stress, mechanical strength, film stress, adhesion, electrical insulation, etc., and examples of such materials include aluminum oxide and ditantalum pentoxide. The materials of the first insulating film 30 and the second insulating film 40 may be the same or different. In addition, the first insulating film 30 and the second insulating film 40 may be a laminated film of films made of the above-mentioned materials.

(1.4. Heater section and heater wiring section)
1 and 2, the heater section 50 is provided above the first insulating film membrane section 32, and in the embodiment, is provided between the first insulating film 30 and the second insulating film 40 of the membrane 18 in the up-down direction. As shown in FIG. 7, which is an enlarged view of a portion of the gas sensor 10 in the cross-sectional view of FIG. 2 that is located above the cavity 22, the heater section 50 is disposed between the first insulating film membrane section 32 of the first insulating film 30 and the second insulating film membrane section 44 of the second insulating film 40. The heater section 50 generates Joule heat when energized, and adjusts the temperature of the gas detection section 60.

Figure 6 is a partial explanatory diagram showing the membrane 18 of the gas sensor 10, the first insulating film 30 at its peripheral portion, the heater section 50, the heater wiring sections 59a and 59b, and the flat section 70. In Figure 6, the second insulating film 40 of the gas sensor 10 and the gas detection section 60 arranged above the second insulating film 40 are not shown.

As shown in FIG. 6, the heater section 50 is formed on the first insulating film membrane section 32, outside the central region R1 of the first insulating film membrane section 32 so as to surround the central region R1 of the first insulating film membrane section 32. The heater section 50 has a bent section 52 that repeatedly bends with an amplitude L2 that is less than 1/2 the length L1 of the side 32a of the first insulating film membrane section 32, which is substantially rectangular. In particular, most of the bent sections 52 in the heater section 50 are composed of a rectangular wave shape (meander pattern) with a predetermined amplitude L2.

Such a heater section 50 can prevent the thermal contraction of the first insulating film membrane section 32 in the first insulating film 30 and the second insulating film membrane section 44 in the second insulating film 40, which the heater section 50 contacts, from being biased in a particular direction. Therefore, the gas sensor 10 can effectively suppress detection errors and noise caused by thermal stress in the first insulating film 30 and the second insulating film 40 that constitute the membrane 18.

The heater section 50 has a symmetrical shape with respect to a reference line A1 that passes through the center 34 of the first insulating film membrane section 32 and extends horizontally. Such a heater section 50 can homogenize the temperature distribution of the gas detection section 60 that is disposed in the central region R1 of the membrane 18, which is closer to the center than the heater section 50, and can improve the detection stability of the gas sensor 10.

The heater section 50 is connected to a heater wiring section 59a that passes through the beam section 31a, and a heater wiring section 59b that passes through the beam section 31b. As shown in FIG. 1, the heater wiring sections 59a and 59b connect the heater terminals 58a and 58b provided on the cavity periphery 24 to the heater section 50 by passing through the upper side of one of the multiple beam sections 31a to 31b (in this embodiment, two beam sections 31a and 31b).

The heater wiring parts 59a, 59b are formed between the first insulating film 30 and the second insulating film 40 in the vertical direction, similar to the heater part 50. However, as shown in FIG. 4, the second insulating film 40 is not formed on the upper side of the heater wiring parts 59a, 59b in the parts formed below the heater terminals 58a, 58b.

As shown in FIG. 6, the heater section 50 in the gas sensor 10 has a substantially symmetrical portion connected to the heater wiring section 59a and a portion connected to the heater wiring section 59b, and these two portions are electrically connected via the conductive flat section 70. However, the heater section 50 is not limited to having two portions electrically connected via the flat section 70, and the portion connected to the heater wiring section 59a and the portion connected to the heater wiring section 59b may be directly connected.

The material of the heater section 50 and the heater wiring section 59a is not particularly limited as long as it is conductive, but from the viewpoint of enabling high-temperature processes in the formation process of the gas detection section 60 and the semiconductor material 92, it is preferable that the material has a relatively high melting point. Examples of such materials include molybdenum (Mo), platinum (Pt), nickel-chromium alloy (NiCr), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing two or more of these. In this embodiment, platinum is particularly preferable because it allows high-precision patterning such as lift-off and has high durability. It is preferable that the heater section 50 and the heater wiring sections 59a and 59b are made of the same material from the viewpoint of being able to be formed in the same film formation process, but the heater section 50 and the heater wiring sections 59a and 59b may be made of different materials.

As shown in Figs. 1 and 2, the heater terminals 58a, 58b are provided on the heater wiring parts 59a, 59b at the cavity peripheral part 24 of the substrate 20 so as to be in contact with the heater wiring parts 59a, 59b. As shown in Fig. 4, the upper surfaces of the heater terminals 58a, 58b are exposed to the upper side of the gas sensor 10, and external wiring that supplies power to the heater part 50 is connected to the heater terminals 58a, 58b.

The material of the heater terminals 58a, 58b is not particularly limited as long as it is a good conductor, but examples include gold (Au), silver (Ag), platinum (Pt), and aluminum (Al), with gold (Au) being preferred from the standpoint of adhesion to external wiring.

(1.5. Flat part)
6, the flat portion 70 is provided between the first insulating film 30 and the second insulating film 40 of the membrane 18 in the vertical direction, similar to the heater portion 50. That is, as shown in FIG. 7, the flat portion 70 is disposed between the first insulating film membrane portion 32 of the first insulating film 30 and the second insulating film membrane portion 44 of the second insulating film 40.

As shown in FIG. 6, the flat portion 70 is disposed in a central region R1, which is a region closer to the center of the first insulating film membrane portion 32 than the heater portion 50 when viewed from above. As shown in FIGS. 6 and 7, the flat portion 70 has a flat surface 72 that faces upward and is flat.

The flat portion 70 is substantially rectangular when viewed from above, but the planar shape of the flat portion 70 is not limited to this and may be circular, elliptical, or a polygon other than a rectangle. It is preferable that the flat portion 70 overlaps the center 34 of the first insulating film membrane portion 32 when viewed from above, from the viewpoint of arranging the gas detection portion 60 formed on the flat portion 70 in the central portion of the membrane 18 and uniformizing the temperature distribution of the gas detection portion 60.

The area of the flat portion 70 as viewed from above is preferably 5 to 25% of the area of the first insulating film membrane portion 32, and more preferably 10 to 20% of the area of the first insulating film membrane portion 32. By making the area ratio of the flat portion 70 to the first insulating film membrane portion 32 larger than a predetermined value, the formation area of the gas detection portion 60 can be secured widely, and the detection sensitivity of the gas sensor 10 can be secured favorably. On the other hand, by making the area ratio of the flat portion 70 to the first insulating film membrane portion 32 smaller than a predetermined value, the formation area of the heater portion 50 can be secured widely, and the temperature responsiveness of the gas detection portion 60 can be secured favorably.

As shown in FIG. 7, the flat portion 70 preferably has a higher thermal conductivity than the second insulating film 40 in order to effectively transfer heat from the heater portion 50 to the gas detection portion 60 disposed on the flat portion 70 via the second insulating film membrane portion 44 of the second insulating film 40. Also, as shown in FIG. 6, the flat portion 70 may be connected to the heater portion 50. By connecting the flat portion 70 and the heater portion 50, the heat from the heater portion 50 is effectively transferred to the flat portion 70 disposed closer to the gas detection portion 60, and the thermal responsiveness of the gas sensor 10 can be improved. Also, if the flat portion 70 has high thermal conductivity, the temperature uniformity of the gas detection portion 60 is improved.

As shown in FIG. 6, when the two parts of the heater section 50 are connected (connected in series) through the flat section 70, current also flows through the flat section 70, generating Joule heat, and the heat generated in the flat section 70 may contribute to the temperature adjustment of the gas detection section 60. However, since the cross-sectional area of the flat section 70 perpendicular to the current direction is larger than that of the heater section 50, if the flat section 70 and the heater section 50 are made of the same material, the amount of heat generated in the flat section 70 is smaller than that of the heater section 50. The Joule heat generated in the flat section 70 can be adjusted by the material of the flat section 70, the thickness of the flat section 70, and the connection form (series/parallel) between the two parts of the heater section 50 and the flat section 70. The thickness of the flat section 70 may be the same as or different from that of the heater section 50.

The material of the flat portion 70 is, for example, a metal. More specifically, as with the heater portion 50, examples include molybdenum (Mo), platinum (Pt), nickel-chromium alloy (NiCr), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing two or more of these. The flat portion 70 may also be made of the same material as the heater portion 50. In this case, the flat portion 70 can be formed by the same film formation process as the heater portion 50, simplifying the manufacturing process. However, the flat portion 70 may also be made of a different material from the heater portion 50. Examples of materials of the flat portion 70 that are different from the heater portion 50 include silver (Ag), copper (Cu), and aluminum (Al), in addition to those mentioned above.

(1.6. Gas Detection Section and Detection Wiring Section)
1 and 2, the gas detection section 60 is provided on the second insulating film 40 of the membrane 18. Fig. 5 is a partial view showing the membrane 18 and the first insulating film 30 at its peripheral portion, the heater section 50, the heater wiring sections 59a and 59b, the flat section 70, the gas detection section 60, and the detection wiring sections 69a and 69b in the gas sensor 10. In Fig. 5, the second insulating film 40 of the gas sensor 10 is seen through, and only the location of the semiconductor material 92 is shown by virtual lines.

As shown in FIG. 5, the gas detection unit 60 is disposed in a central region R1, which is a region closer to the center 34 of the first insulating film membrane unit 32 than the heater unit 50 when viewed from above. As shown in FIG. 5, the gas detection unit 60 has a pair of electrodes 62a, 62b, and as shown in FIG. 7, the pair of electrodes 62a is in contact with the semiconductor material 92.

As shown in FIG. 5, the pair of electrodes 62a, 62b face each other horizontally with a predetermined distance between them, and detects the resistance change of the semiconductor material 92 that is arranged to connect the pair of electrodes 62a, 62b. The pair of electrodes 62a, 62b have a comb-tooth shape and are arranged so that the gaps between the comb teeth interdigitate with each other. The gas detection unit 60 having such comb-tooth electrodes 62a, 62b can increase the length over which the electrodes 62a, 62b face each other in a small area, thereby improving the detection sensitivity.

The gas detection section 60 in the gas sensor 10 is the portion where the pair of electrodes 62a, 62b face each other, i.e., the portion surrounded by the dashed line (thick line) in Fig. 5 and Fig. 7. The portion outside the portion surrounded by the dashed line in Fig. 5 is the portion that does not face each other, and is not included in the gas detection section 60 and the electrodes 62a, 62b, but is included in the detection wiring sections 69a, 69b described below.

As shown in FIG. 5, the gas sensor 10 has a pair of detection wiring portions 69a and 69b. As shown in FIG. 7, the pair of detection wiring portions 69a and 69b are also provided on the second insulating film 40, similar to the gas detection portion 60. As shown in FIG. 5, the detection wiring portion 69a is connected to the electrode 62a within the membrane 18, and the detection wiring portion 69b is connected to the electrode 62b within the membrane 18.

As shown in FIG. 1, the detection wiring sections 69a, 69b connect the detection terminals 68a, 68b provided on the cavity periphery 24 to the gas detection section 60 through one of the multiple beam sections 31a-31b (two beam sections 31c, 31d in this embodiment) and the upper side of the beam section of the second insulating film 40 that overlaps it.

The gas detection unit 60 is disposed above the flat portion 70 with at least the second insulating film 40 interposed therebetween. As shown in FIG. 5, the gas detection unit 60 having a pair of electrodes 62a, 62b is disposed so as to overlap the flat surface 72 (see FIG. 6) when viewed from above, and has an area smaller than that of the flat surface 72. As shown in FIG. 7, the entire gas detection unit 60 is formed on the flat surface 72 of the flat portion 70 with the second insulating film 40 interposed therebetween, and is preferably formed within the range of the flat surface 72 when viewed from above.

As shown in FIG. 7, the second insulating film membrane portion 44 of the second insulating film 40 formed on the first insulating film membrane portion 32 has a first portion 41 that is in direct contact with the first insulating film membrane portion 32, a second portion 42 that sandwiches the heater portion 50 between the first insulating film membrane portion 32, and a third portion 43 that sandwiches the flat portion 70 between the first insulating film membrane portion 32. The first portion 41 is lower in height than the second portion 42 and the third portion 43 that sandwich the heater portion 50 and the flat portion 70 between the first insulating film membrane portion 32, so that undulations and steps are formed in the second insulating film membrane portion 44.

As shown in FIG. 7, the detection wiring portion 69a is formed across the first portion 41, the second portion 42, and the third portion 43, so the shape of the detection wiring portion 69a itself is affected by the undulations of the lower layers, making it more likely for shape variation to occur. In contrast, the gas detection portion 60 is formed on the third portion 43, which is formed on the flat surface 72, so the shape of the gas detection portion 60 is not affected by the undulations and steps of the second insulating film membrane portion 44, and there is less variation. For example, the gap between the pair of electrodes 62a, 62b can also be precisely controlled.

The gas detection unit 60 having a pair of electrodes 62a, 62b and the detection wiring units 69a, 69b may be made of a conductor such as metal, for example, gold (Au), silver (Ag), platinum (Pt), aluminum (Al), etc. It is preferable that the gas detection unit 60 and the detection wiring units 69a, 69b are made of the same material from the viewpoint of being able to form them in the same film formation process, but the gas detection unit 60 and the detection wiring units 69a, 69b may be made of different materials.

As shown in Figures 1 and 2, the detection terminals 68a, 68b are provided on the cavity peripheral portion 24 of the substrate 20 so as to contact the detection wiring portions 69a, 69b. As shown in Figure 4, the upper surfaces of the detection terminals 68a, 68b are exposed to the upper side of the gas sensor 10, and external wiring that transmits the output of the gas detection portion 60 is connected to the detection terminals 68a, 68b.

The material of the detection terminals 68a, 68b is not particularly limited as long as it is a good conductor, but examples include gold (Au), silver (Ag), platinum (Pt), and aluminum (Al), with gold (Au) being preferred from the standpoint of adhesion to external wiring.

(1.7. Semiconductor Materials)
7 and 5, the semiconductor material 92 is provided between the electrodes 62a, 62b of the gas detection unit 60 arranged in the central region R1 of the membrane 18 and on the gas detection unit 60. The semiconductor material 92 is preferably formed to have an area larger than that of the gas detection unit 60 so as to overlap the entire gas detection unit 60 when viewed from above. The semiconductor material 92 contacts both of the pair of electrodes 62a, 62b that constitute the gas detection unit 60. In addition, a part of the semiconductor material 92 may contact the detection wiring parts 69a, 69b that are connected to the gas detection unit 60.

As shown in FIG. 7, the semiconductor material 92 has a generally dome-shaped outer shape. From the viewpoint of uniformity of temperature distribution in the semiconductor material 92, the semiconductor material 92 is preferably generally circular or generally elliptical when viewed from above, and more preferably generally circular.

The semiconductor material 92 is not particularly limited as long as the material changes its resistance value upon contact with a reducing gas, but is preferably a metal oxide from the viewpoint of thermal stability and chemical stability. Examples of metal oxides used for the semiconductor material 92 include tin oxide (SnO ₂ ), zirconium oxide (ZrO ₂ ), iron oxide (Fe ₂ O ₃ ), tungsten oxide (WO ₃ ), indium oxide (In ₂ O ₃ ), and cobalt oxide (Co ₃ O ₄ ). In order to further increase the sensitivity to the gas to be detected, the metal oxide constituting the semiconductor material 92 may support a precious metal such as platinum (Pt) or palladium (Pd). These materials may also be composited or alloyed.

(1.8. Manufacturing method)
An example of a method for manufacturing the gas sensor 10 will be described below. However, the method for manufacturing the gas sensor 10 is not limited to the manufacturing method described below. First, in manufacturing the gas sensor 10, a substrate material that is a raw material for the substrate 20 is prepared. The substrate material is a flat plate in which the cavity 22 is not formed. Next, a first insulating film 30 is formed on one main surface (the surface that will become the cavity periphery 24 after the cavity 22 is formed) of the prepared substrate material. The first insulating film 30 may be formed by a known film formation method such as a thermal oxidation method or a CVD (Chemical Vapor Deposition) method.

The heater section 50, the flat section 70, and the heater wiring sections 59a and 59b are formed on the first insulating film 30. The heater section 50, the flat section 70, and the heater wiring sections 59a and 59b can be formed in the same film formation process. The shapes of the heater section 50, the flat section 70, and the heater wiring sections 59a and 59b are formed, for example, by a lift-off method. In the lift-off process, first, a resist is applied to the entire surface on which a predetermined pattern is to be formed, and the resist is exposed and developed to form a predetermined pattern shape. The resist corresponding to the predetermined pattern shape is dissolved by development, and the predetermined pattern shape is patterned. After the resist is dissolved, a film of the material that constitutes the pattern is formed by a film formation method such as sputtering or vapor deposition. After the film formation, the remaining resist is removed with a stripping solution, and the material formed on the resist is also removed, and the material formed in the film remains only in the patterned area, forming the predetermined pattern.

After forming the heater section 50, flat section 70, and heater wiring sections 59a, 59b, the second insulating film 40 is formed by a known film formation method in the same manner as the first insulating film 30 so that it at least covers these sections.

Next, the gas detection unit 60 and the detection wiring units 69a, 69b are formed on the second insulating film 40. The gas detection unit 60 and the detection wiring units 69a, 69b can be formed in the same film formation process. The shapes of the gas detection unit 60 and the detection wiring units 69a, 69b are formed by a lift-off method or the like, similar to the heater unit 50, the flat unit 70, and the heater wiring units 59a, 59b. Furthermore, after forming a predetermined opening in the second insulating film 40, the detection terminals 68a, 68b and the heater terminals 58a, 58b are formed.

Next, an etching mask is applied to a predetermined area of the main surface of the base material on which the first insulating film 30 is not formed, and the base material is etched until the first insulating film 30 formed on the opposite main surface is exposed, forming a cavity 22. The first insulating film 30 corresponding to the area in which the cavity 22 is formed becomes the first insulating film membrane portion 32.

Furthermore, a semiconductor material 92 is formed on top of the pair of electrodes 62a, 62b of the gas detection unit 60 so as to contact the pair of electrodes 62a, 62b, thereby obtaining the gas sensor 10. In the process of forming the semiconductor material 92, a coating body is formed using a semiconductor material paste containing the raw material of the semiconductor material 92, and the coating body is heat-treated at a predetermined temperature to form the semiconductor material 92.

The semiconductor material paste is obtained by mixing the raw materials of the semiconductor materials described above with a solvent, a binder, and additives. As the raw material of the semiconductor material, for example, a metal oxide powder is used. The average particle size of the metal oxide powder is not particularly limited, but is preferably 0.1 to 20 μm.

1.9. Operation
In the gas sensor 10, the heater section 50 is connected to an external circuit (not shown) via heater wiring sections 59a, 59b, the flat section 70, and heater terminals 58a, 58b. The electrodes 62a, 62b of the gas detection section 60 are connected to an external circuit (not shown) via detection wiring sections 69a, 69b and detection terminals 68a, 68b. When the gas sensor 10 is operated, current is applied and a predetermined voltage is applied to the heater section 50, so that the gas detection section 60 and its surroundings are heated to a predetermined temperature.

When the gas sensor 10 is placed in a space containing a gas to be detected, the resistance of the semiconductor material 92 that is in contact with the gas detection unit 60 changes depending on the amount of electron movement resulting from an oxidation-reduction reaction that occurs between the oxygen adsorbed on the surface of the semiconductor material 92 and the gas to be detected. The amount of electron movement corresponds to the concentration of the gas to be detected, so the electrodes 62a and 62b of the gas detection unit 60 detect this change in resistance, and the concentration of the gas to be detected can be measured. The change in resistance of the semiconductor material 92 is highly sensitive even when the concentration of the gas to be detected is very low, so the gas sensor 10 is suitable for detecting low concentrations of the gas to be detected. However, when the gas to be detected is highly concentrated, the change in resistance saturates, making it difficult to measure the concentration, although detection is possible.

As shown in Figures 5 to 7, the gas sensor 10 has a flat portion 70 having a flat surface 72 formed inside the heater portion 50, and a gas detection portion 60 having a smaller area than the flat surface 72 is formed on the flat portion 70 via the second insulating film 40. Therefore, the gas detection portion 60 can be formed with high precision without being affected by unevenness due to the shape of the lower layer, and noise caused by shape variations can be reduced and good responsiveness can be achieved. In addition, since the flat portion 70 only needs to be formed with a substantially uniform thickness in the planar direction, such a gas sensor 10 has good process efficiency. In addition, the heat of the heater portion 50 is transferred to the gas detection portion 60 not only via the second insulating film 40 but also via the flat portion 70, so local temperature variations in the gas detection portion 60 are reduced, and the detection stability of the gas sensor 10 is also good.

In the gas sensor 10, the flat surface 72 is made of the same material as the heater section 50, is connected to the heater section 50, and has higher thermal conductivity than the second insulating film 40. In such a gas sensor 10, the heat of the heater section 50 is effectively transferred to the gas detection section 60 via the flat section 70, so that local temperature variations in the gas detection section 60 are reduced, and the detection stability of the gas sensor 10 is improved.

In addition, in the gas sensor 10, the heater section 50 has a shape that is symmetrical with respect to the reference line A1 that passes through the center 34 of the first insulating film membrane section 32 and extends horizontally, so that the temperature distribution in the gas detection section 60 can be made uniform. In addition, the heater section 50 of the gas sensor 10 has a bent section 52 that repeatedly bends with a predetermined amplitude, so that detection errors and noise caused by thermal stress generated in the first insulating film 30 and the second insulating film 40 can be effectively suppressed.

(2. Second embodiment)
FIG. 8 is a schematic plan view showing the gas sensor 110 according to the second embodiment, and is a view of the gas sensor 110 seen from above. In FIG. 8, the second insulating film 40 is seen through, and only the arrangement of the catalyst material 192 is shown by virtual lines. The gas sensor 110 according to the second embodiment is different from the gas sensor 10 according to the first embodiment in that the gas detection section 160 has a Pt wire 165 (see FIG. 11) that contacts the catalyst material 192, and gas is detected by a change in resistance of the Pt wire 165. However, the gas sensor 110 is similar to the gas sensor 10 according to the first embodiment in parts other than the gas detection section 160 and the catalyst material 192. The gas sensor 110 will be described mainly with respect to differences from the gas sensor 10, and common reference numerals will be used to denote common parts with the gas sensor 10, and description thereof will be omitted.

Figure 9 is a schematic cross-sectional view of the gas sensor 110 cut along a plane along line IX-IX in Figure 8, and Figure 10 is a schematic cross-sectional view of the gas sensor 110 cut along a plane along line X-X in Figure 8. The gas sensor 110 has a substrate 20, a first insulating film 30, a second insulating film 40, a heater section 50, a gas detection section 160, heater terminals 58a, 58b, heater wiring sections 59a, 59b, detection terminals 68a, 68b, detection wiring sections 69a, 69b, a flat section 70, a catalyst material 192, and the like. The gas sensor 110 has the same structure as the gas sensor 10 according to the first embodiment below the second insulating film 40, including the substrate 20, first insulating film 30, second insulating film 40, heater section 50, heater terminals 58a, 58b, heater wiring sections 59a, 59b, detection terminals 68a, 68b, and flat section 70.

As shown in Figures 8 and 9, the gas detection section 160 is provided on the second insulating film 40 of the membrane 18. Figure 11 is a partial view showing the membrane 18 of the gas sensor 110 and the first insulating film 30 at its peripheral portion, the heater section 50, the heater wiring sections 59a, 59b, the flat section 70, the gas detection section 160, and the detection wiring sections 69a, 69b. In Figure 11, the second insulating film 40 of the gas sensor 110 is seen through, and only the location of the catalyst material 192 is shown by virtual lines.

As shown in FIG. 11, the gas detection unit 160 is disposed in the central region R1, which is the region closer to the center of the first insulating film membrane unit 32 than the heater unit 50 when viewed from above, similar to the gas detection unit 60 shown in FIG. 5. The gas detection unit 160 of the gas sensor 110 has a Pt wire 165 instead of the comb-shaped electrodes 62a, 62b shown in FIG. 5. The Pt wire 165 is a platinum (Pt) thin film patterned in a meandering shape. The gas detection unit 160 having such a meandering Pt wire 165 can increase the length of the Pt wire 165 that contacts the catalyst material 192 in a small area, thereby improving the detection sensitivity.

One end of the Pt wire 165 is connected to the detection wiring portion 69a, and the other end of the Pt wire 165 is connected to the detection wiring portion 69b. Note that the detection wiring portions 69a and 69b connect the gas detection portion 160 arranged on the membrane 18 to the detection terminals 68a and 68b arranged on the cavity periphery 24, as in the gas sensor 10 according to the first embodiment. The material of the detection wiring portions 69a and 69b may be platinum (Pt) like the gas detection portion 160, or may be other conductive materials such as gold (Au).

12 is an enlarged cross-sectional view of the portion of the gas sensor 110 shown in FIG. 9 that is disposed above the cavity 22. As shown in FIG. 12, the gas detection section 160 having the Pt wire 165 is disposed so as to overlap the flat surface 72 (see FIG. 11) when viewed from above, and has a smaller area than the flat surface 72. As shown in FIG. 12, the entire gas detection section 160 is formed on the flat surface 72 of the flat section 70 via the second insulating film 40, and is preferably formed within the range of the flat surface 72 when viewed from above. The gas detection section 160 in the gas sensor 110 extends from one end to the other end of the Pt wire 165, that is, the portion surrounded by the dashed line (thick line) in FIG. 11.

The gas detection section 160 shown in FIG. 12 is formed on the third portion 43 which is formed on the flat surface 72, so the shape of the gas detection section 60 is not affected by the undulations and steps of the second insulating film membrane section 44 and has less variation. For example, the line width, total length and cross-sectional area of the Pt wire 165 can also be precisely controlled.

As shown in FIG. 12, the catalyst material 192 is provided between the Pt wires 165 of the gas detection unit 160 arranged in the central region R1 of the membrane 18 and on the gas detection unit 160. The catalyst material 192 is preferably formed over an area larger than the gas detection unit 160 so as to overlap the entire gas detection unit 160 when viewed from above and to contact the entire Pt wires 165. The catalyst material 192 has an approximately dome-shaped outer shape, but the shape of the catalyst material 192 is not particularly limited.

The material constituting the catalyst material 192 is not particularly limited as long as it is a material known as a catalyst for gas sensors. Typically, a carrier carrying precious metal particles is used. Examples of the carrier include oxide materials such as aluminum oxide (such as gamma alumina) and silicon oxide. Examples of the precious metal particles carried by the carrier include precious metal particles such as platinum (Pt), palladium (Pd), ruthenium (Ru), and rhodium (Rh).

The gas detection section 160 of the gas sensor 110 is formed by known film formation methods and lift-off processes, etc., in the same manner as the gas detection section 60 of the gas sensor 10. The catalyst material 192 is formed by paste application and heat treatment processes, etc., in the same manner as the semiconductor material 92 of the gas sensor 10.

When the gas sensor 110 contains a target gas in a space in which the gas sensor is placed, the combustible gas and oxygen combine and burn on the catalytic material 192 depending on the proportion of the gas present. The Pt wire 165 of the gas detection unit 160 of the gas sensor 110 detects the temperature change caused by the combustion of the combustible gas generated in the catalytic material by the change in resistance.

In the gas sensor 110, like the gas sensor 10, a gas detection section 160 having a smaller area than the flat surface 72 is formed on the flat section 70. Therefore, the gas detection section 160 can be formed with high precision without being affected by unevenness due to the shape of the underlying layer, reducing noise caused by shape variations and providing good responsiveness. In addition, in the gas sensor 110, heat from the heater section 50 is transferred to the gas detection section 160 via the flat section 70, so that local temperature variations in the gas detection section 160 are reduced and detection stability is improved.

In addition, the gas sensor 110 has the same effects as the gas sensor 10 according to the first embodiment in terms of the commonalities between them.

3. Third embodiment
FIG. 13 is a schematic plan view showing a gas sensor 210 according to the third embodiment, and is a view of the gas sensor 210 seen from above. In FIG. 13, the second insulating film 40 is seen through, and only the arrangement of the catalyst material 192 is shown by virtual lines. The gas sensor 210 according to the third embodiment is different from the gas sensor 10 according to the first embodiment in that the gas detection unit 260 has a pair of electrodes 262a, 262b (see FIG. 16) that contact the thermistor film 294 (which contacts the catalyst material 192), and detects gas by the resistance change caused by the catalytic reaction heat of the thermistor film 294 detected by the electrodes 262a, 262b. However, the gas sensor 210 is similar to the gas sensor 10 according to the first embodiment in parts other than the gas detection unit 260, the thermistor film 294, and the catalyst material 192. The gas sensor 210 will be described mainly with respect to the differences from the gas sensor 10, and the common parts to the gas sensor 10 will be denoted by the common reference numerals and will not be described.

Figure 14 is a schematic cross-sectional view of the gas sensor 210 cut along a plane along line XIV-XIV in Figure 13, and Figure 14 is a schematic cross-sectional view of the gas sensor 210 cut along a plane along line XV-XV in Figure 13. The gas sensor 210 has a substrate 20, a first insulating film 30, a second insulating film 40, a heater section 50, a gas detection section 260, heater terminals 58a, 58b, heater wiring sections 59a, 59b, detection terminals 68a, 68b, detection wiring sections 69a, 69b, a flat section 70, a thermistor film 294, a catalyst material 192, and the like. The gas sensor 210 has the same structure as the gas sensor 10 according to the first embodiment below the second insulating film 40, including the substrate 20, first insulating film 30, second insulating film 40, heater section 50, heater terminals 58a, 58b, heater wiring sections 59a, 59b, detection terminals 68a, 68b, and flat section 70.

As shown in Figures 14 and 15, the gas detection section 260 is provided on the second insulating film 40 of the membrane 18. Figure 16 is a partial view showing the membrane 18 of the gas sensor 210 and the first insulating film 30 at its peripheral portion, the heater section 50, the heater wiring sections 59a, 59b, the flat section 70, the gas detection section 260, the thermistor film 194, and the detection wiring sections 69a, 69b. In Figure 16, the second insulating film 40 of the gas sensor 110 is seen through, and only the location of the catalyst material 192 is shown by virtual lines.

As shown in FIG. 16, the gas detection section 260 is disposed in the central region R1, which is the region closer to the center of the first insulating film membrane section 32 than the heater section 50 when viewed from above, similar to the gas detection section 60 shown in FIG. 5. The gas detection section 260 of the gas sensor 210 has a pair of electrodes 262a, 262b in contact with the thermistor film 294, instead of the comb-shaped electrodes 62a, 62b shown in FIG. 5.

As shown in FIG. 16, the pair of electrodes 262a, 262b are substantially linear and face each other horizontally with a predetermined gap between them. The thermistor film 294 is formed to straddle the pair of electrodes 262a, 262b and contact both of the pair of electrodes 262a, 262b. The electrode 262a of the gas detection unit 260 is connected to the detection wiring portion 69a, and the electrode 262b of the gas detection unit 260 is connected to the detection wiring portion 69b. Note that the detection wiring portions 69a, 69b connect the gas detection unit 260 arranged on the membrane 18 to the detection terminals 68a, 68b arranged on the cavity peripheral portion 24, which is the same as in the gas sensor 10 according to the first embodiment. The material of the electrodes 262a, 262b in the gas detection unit 260 is the same as the electrodes 26a, 26b of the gas sensor 10.

17 is an enlarged cross-sectional view of the portion of the gas sensor 210 shown in FIG. 14 that is disposed above the cavity 22. As shown in FIG. 17, the gas detector 260 having a pair of electrodes 262a, 262b is disposed so as to overlap the flat surface 72 (see FIG. 16) when viewed from above, and has a smaller area than the flat surface 72. As shown in FIG. 17, the entire gas detector 260 is formed on the flat surface 72 of the flat portion 70 via the second insulating film 40, and is preferably formed within the range of the flat surface 72 when viewed from above. The gas detector 260 in the gas sensor 210 is the electrodes 262a, 262b that face each other across the thermistor film 294, and is the portion surrounded by the dashed line (thick line) in FIG. 16 and FIG. 17.

As shown in FIG. 17, the thermistor film 294 is disposed between the electrodes 262a, 262b constituting the gas detection unit 260 and on top of the gas detection unit 260. That is, a part of the thermistor film 294 contacts the second insulating film 40 (the third part 43 of the second insulating film membrane part 44) between the electrodes 262a, 262b. In addition, another part of the thermistor film 294 also contacts the detection wiring parts 69a, 69b that connect to the outside of the electrodes 262a, 262b.

The thermistor film 294 contacts the catalyst material 192 provided on the thermistor film 294. The thermistor film 294 has a negative temperature coefficient of resistance. The thermistor film 294 is thermally connected to the catalyst material 192, and a change in the thermal conductivity of the thermistor film 294 occurs due to a temperature change caused by the combustion of a combustible gas in the catalyst material 192, and the resistance value of the thermistor film 294 changes accordingly. There are no particular limitations on the material constituting the thermistor film 294 as long as it is a material that can be used as a thermistor, and examples of the material include composite metal oxides containing metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe). The thermistor film 294 is formed by a known film formation method such as sputtering.

When the gas sensor 210 is placed in a space where the gas sensor 210 is placed, the combustible gas and oxygen combine on the catalyst material 192 and combust depending on the proportion of the gas present. The electrodes 262a, 262b of the gas detection unit 260 of the gas sensor 210 detect the resistance change of the thermistor film 294 caused by the combustion heat generated in the catalyst material 192 by the combustion of the combustible gas. Such a gas sensor 210 is particularly suitable for detecting high concentrations of the gas to be detected, since it is easier to detect the resistance change of the thermistor film 294 when the gas to be detected is in high concentration.

In the gas sensor 210, similar to the gas sensor 10, a gas detection section 260 having a smaller area than the flat surface 72 is formed on the flat section 70. Therefore, the gas detection section 260 can be formed with high precision without being affected by unevenness due to the shape of the underlying layer, reducing noise caused by shape variations and providing good responsiveness. In addition, in the gas sensor 210, heat from the heater section 50 is transferred to the gas detection section 60 via the flat section 70, so that local temperature variations in the gas detection section 60 are reduced and detection stability is improved.

The electrodes 262a, 262b of the gas sensor 210 may be comb-shaped like the electrodes 62a, 62b of the gas sensor 10. The gas sensor 210 may not have the catalyst material 192 and may detect gas by a change in resistance of a thermistor film in contact with the electrodes 262a, 262b. In addition, the gas sensor 210 has the same effects as the gas sensor 10 in terms of the points in common with the gas sensor 10 according to the first embodiment.

(4.1. First Modified Example)
In the above-described gas sensors 10, 110, and 210, the heater section 50 and the flat section 70 having the shape shown in Fig. 6 are used, but various shapes are conceivable for the heater section 50 and the flat section 70 used in the gas sensors 10, 110, and 210 other than those shown in Fig. 5. Fig. 18 is a partial explanatory diagram showing the heater section 450 and the flat section 470 according to the first modified example together with the membrane 18, the first insulating film 30 on its peripheral portion, the heater wiring sections 59a, 59b, etc.

As shown in FIG. 18, the heater section 450 according to the first modified example is not connected to the flat section 470. The heater section 450 has a portion that connects to the heater wiring section 59a and a portion that connects to the heater wiring section 59a that are substantially symmetrical, and these two portions are directly connected. The material of the heater section 450 is the same as the material of the heater section 50 shown in FIG. 5.

The flat portion 470 has an upwardly facing flat surface 472 similar to the flat portion 70 shown in FIG. 6, and has the same shape and arrangement as the flat portion 70. However, the flat portion 470 is separated from the heater portion 450 arranged to surround the flat portion 470, and the current flowing through the heater portion 450 does not pass through the flat portion 470.

The material of the flat portion 470 may be the same as the material of the heater portion 450, but since the flat portion 470 is separated from the heater portion 450, it is easy to use a material different from that of the heater portion 450. For example, the material of the flat portion 470 may be a material having a higher thermal conductivity than the heater portion 450.

The flat portion 470 is not connected to the heater portion 450, but it functions effectively as a heat conduction path to the gas detection portion 60, 160, 260. Similarly to the flat surface 72 shown in FIG. 5, the flat surface 472 of the flat portion 470 suppresses the shape variation of the upper gas detection portion 60, 160, 260, and contributes to improving the responsiveness of the gas sensor. Therefore, a gas sensor using the heater portion 450 and flat portion 470 according to the first modified example instead of the heater portion 50 and flat portion 70 shown in FIG. 5 also achieves the same effect as the gas sensors 10, 110, 210.

(4.2. Second Modified Example)
19(a) is a partial explanatory diagram showing a heater section 550 and a flat section 570 according to the second modified example together with the membrane 18, the first insulating film 30 at its peripheral portion, heater wiring sections 59a, 59b, etc. As shown in Fig. 19(a), the heater section 550 according to the second modified example is connected to the flat section 570, similar to the heater section 50 shown in Fig. 5.

The heater section 550 has a portion connected to the heater wiring section 59a and a portion connected to the heater wiring section 59b that are approximately symmetrical, and these two portions are electrically connected via the conductive flat section 570. The heater section 550 is connected to the flat section 570 at two central positions in the Y direction of the flat section 570. The bent portion of the heater section 550 is made up of a combination of portions having multiple different amplitudes, and such a heater section 550 also has the same effect as the heater section 50.

The flat portion 570 has an upwardly facing flat surface 572 similar to the flat portion 70 shown in FIG. 6, and has the same shape and arrangement as the flat portion 70. The materials of the heater portion 550 and the flat portion 570 are the same as those of the heater portion 50 and the flat portion 70 shown in FIG. 5.

A gas sensor that uses the heater section 550 and flat section 570 of the second modified example instead of the heater section 50 and flat section 70 shown in FIG. 5 also achieves the same effects as the gas sensors 10, 110, and 210.

(4.3. Third Modification)
19(b) is a partial explanatory diagram showing a heater section 650 and a flat section 670 according to the third modified example together with the membrane 18, the first insulating film 30 at its peripheral portion, heater wiring sections 59a, 59b, etc. As shown in Fig. 19(b) , the heater section 650 according to the third modified example is connected to the flat section 670, similar to the heater section 50 shown in Fig. 5 .

The heater section 650 has a portion connected to the heater wiring section 659a that passes over the beam section 31c and a portion connected to the heater wiring section 59b that are 180 degrees rotationally symmetrical with respect to the center position of the flat section 670. These two portions of the heater section 650 are electrically connected via the conductive flat section 670. The heater section 650 is connected to the flat section 670 at two corners that are arranged on a predetermined diagonal line in the approximately rectangular flat section 670. The heater wiring sections 659a, 59b also pass over the beam sections 31c, 31b that connect to two corners that are arranged on a predetermined diagonal line in the approximately rectangular first insulating film membrane section 32.

The flat portion 670 has an upwardly facing flat surface 672 similar to the flat portion 70 shown in FIG. 6, and has the same shape and arrangement as the flat portion 70. The materials of the heater portion 650 and the flat portion 670 are the same as those of the heater portion 50 and the flat portion 70 shown in FIG. 5.

A gas sensor that uses the heater section 650 and flat section 670 of the third modified example instead of the heater section 50 and flat section 70 shown in FIG. 5 also achieves the same effects as the gas sensors 10, 110, and 210.

(4.5. Fourth Modification)
19(c) is a partial explanatory diagram showing the heater section 750 and flat section 770 according to the fourth modification together with the membrane 18, the first insulating film 30 at its peripheral portion, the heater wiring sections 59a, 59b, etc. As shown in Fig. 19(c), the heater section 750 according to the third modification is connected to the flat section 770, similar to the heater section 50 shown in Fig. 5.

The heater section 750 has a portion connected to the heater wiring section 759a that passes over the beam section 31c and a portion connected to the heater wiring section 59b that are 180 degrees rotationally symmetrical with respect to the center position of the flat section 770. These two portions of the heater section 750 are electrically connected via the conductive flat section 770. The heater section 750 is connected to the flat section 770 at two central positions in the X direction on the outer edge of the flat section 770. The heater wiring sections 759a and 59b also pass over the beam sections 31c and 31b that connect to two corners arranged on a predetermined diagonal line in the substantially rectangular first insulating film membrane section 32.

The flat portion 770 has a flat surface 772 facing upward like the flat portion 70 shown in FIG. 6, and has the same shape and arrangement as the flat surface 70. The material of the heater portion 750 and the flat portion 770 is the same as that of the heater portion 50 and the flat portion 70 shown in FIG. 5.

A gas sensor that uses the heater section 750 and flat section 770 of the fourth modified example instead of the heater section 50 and flat section 70 shown in FIG. 5 also achieves the same effects as the gas sensors 10, 110, and 210.

5. Examples and Comparative Examples
The present invention will be described in more detail below using examples and comparative examples, although the present invention is not limited to the following examples.

As a sample according to the example, the gas sensor 10 according to the first embodiment shown in Figures 1 to 7 was prepared. The main materials used in the gas sensor 10 are as follows.
Substrate 20: Si
First insulating film 30: SiN/SiO ₂
Second insulating film 40: SiN
Heater section 50: Pt
Gas detection unit 60: Pt
Flat portion 70: Pt

As a sample for the comparative example, a gas sensor was prepared that did not have a flat portion and only changed the shape of the heater portion 850, and was fabricated in the same manner as gas sensor 10. Figure 20 is a partial view showing the membrane 18 and the first insulating film 30 at its peripheral portion, heater portion 850, heater wiring portions 59a and 59b, gas detection portion 60, and detection wiring portions 69a and 69b in the gas sensor for the comparative example.

As shown in FIG. 20, the heater section 850 of the gas sensor according to the comparative example is formed over almost the entire area of the first insulating film membrane section 32, including the central region of the first insulating film membrane section 32. FIG. 21 is an enlarged cross-sectional view of a portion of the gas sensor according to the comparative example that is disposed above the cavity 22.

20 and 21, the gas sensor according to the comparative example does not have a flat portion, and a part of the heater section 850 is also disposed under the gas detection section 60. Therefore, in the gas sensor according to the comparative example, the gas detection section 60 is formed on the second insulating film 40, which has undulations and irregularities. Therefore, although the shape of the gas detection section 60 in the gas sensor according to the comparative example is similar to that of the gas sensor 10 shown in FIG. 5 in the plan view shown in FIG. 20, due to the influence of the undulations and irregularities of the lower layer, the three-dimensional shape has undulations and slopes different from those of the gas detection section 60 of the gas sensor 10, and the shape variation is also thought to be large.

First, the temperature of the area near the center of the membrane 18 in each sample was calculated using the prepared samples according to the embodiment and comparative example. The results are shown in Figure 22. In the sample according to the comparative example, as shown by the dotted line in Figure 22, the temperature peak (highest value) appears in the center of the membrane 18, and the temperature drops parabolically as it moves away from the center. In the sample according to the comparative example, a temperature difference of approximately 2.3 degrees was formed between the position with the highest temperature (the center of the membrane 18) and the position with the lowest temperature (a position 75 μm away from the center of the membrane 18).

In contrast, in the sample according to the embodiment, as shown by the solid line in Figure 22, temperature peaks (maximum values) appeared at two locations approximately 50 μm away from the center of the membrane 18, and in the central part of the membrane 18 between the two peaks, the temperature gradually decreased from the location where the peak appeared. In the sample according to the embodiment, a temperature difference of approximately 1.3 degrees was formed between the location with the highest temperature (location 50 μm away from the center of the membrane 18) and the location with the lowest temperature (location 75 μm away from the center of the membrane 18).

As shown in FIG. 22, in the sample according to the embodiment in which the flat portion 70 is formed closer to the center than the heater portion 50, the difference between the maximum and minimum temperatures is smaller than in the sample according to the comparative example in which no flat portion is formed and the heater portion 850 is also formed in the center of the membrane 18, and it has been confirmed that the temperature distribution in the membrane 18 is uniform.

Next, the response waveforms in the detection of CO gas were obtained using the prepared samples according to the embodiment and the comparative example. Figures 23 and 24 are graphs showing the response waveforms (left vertical axis, unit Ω, represented by black circles representing detection values and approximate curves of the detection values) obtained by the gas sensors according to the comparative example and the embodiment. Note that the rectangular waveforms shown together with the response waveforms in Figures 23 and 24 indicate the change in concentration of CO gas supplied to the element (right vertical axis, ppm). In obtaining the response waveforms, the CO gas concentration was changed from 0 ppm to 100 ppm at the point when the elapsed time (horizontal axis) was 6200 sec, and the CO gas concentration was changed from 100 ppm to 0 ppm at the point when the elapsed time (horizontal axis) was 6800 sec.

As shown in Figure 23, in the sample according to the comparative example, an overshoot was observed in the response waveform when CO gas was detected, and it took a long time for the overshoot to disappear, with the effect remaining until after 6,600 seconds. In addition, the response waveform when CO gas was removed took a long time to converge to the baseline, and had not yet completely converged even at 7,200 seconds.

As shown in Figure 24, in the sample according to the embodiment, no overshoot was observed in the response waveform when CO gas was detected, and the time elapsed until the detection value stabilized was short, with the detection value stabilizing by the time point before 6600 seconds. In addition, the response waveform when CO gas was removed quickly converged to the baseline, and convergence was achieved even before 7200 seconds.

In the comparative sample, as shown in FIG. 22, the temperature gradient of the membrane 18 is large, and the temperature in the center tends to be too high, which is thought to be one of the causes of the overshoot in the response waveform as shown in FIG. 23. In addition, in the comparative sample, the gas detection part has undulations and inclinations, and is not uniform in shape, which is thought to be one of the causes of the delay in convergence to the baseline in the response waveform.

In the sample according to the embodiment, it is believed that the temperature distribution of the membrane 18 is uniform as shown in Figure 22, which is why overshooting of the response waveform was prevented. In addition, in the sample according to the embodiment, the gas detection section 60 is formed on the flat section 70, so that it has a uniform shape, and the flat section 70 improves the thermal conductivity while making the temperature distribution uniform, which is why it is believed that the time until the response waveform stabilizes and converges is shortened.

The gas sensors 10, 110, and 210 have been described above with reference to embodiments, modifications, and examples. However, the present invention is not limited to these embodiments, and it goes without saying that many other embodiments and modifications are included in the technical scope of the present invention. For example, the shapes of the flat portion 70, heater portion 50, and gas detection portion 60 are not limited to shapes that connect straight lines such as polygons or rectangular waves, but may be shapes that connect curved lines such as circles, ellipses, or arcs, or shapes that connect curved lines and straight lines. In addition, the gas detection portions 60 and 260 may have two or more pairs of electrodes 62a, 62b, 262a, and 262b.

10, 110, 210...gas sensor 18...membrane 18a...membrane peripheral hole R1...central region 20...substrate 22...cavity 24...cavity peripheral portion 30...first insulating film 31a, 31b, 31c, 31d...beam portion 32...first insulating film membrane portion 32a...side 34...center A1...reference line 36...first insulating film peripheral portion 40...second insulating film 41...first portion 42...second portion 43...third portion 44...second insulating film membrane portion 46...second insulating film peripheral portion 50, 450, 550, 65 0, 750... heater portion 52... bending portion L1... length L2... amplitude 60, 160, 260... gas detection portion 62a, 62b, 262a, 262b... electrodes 58a, 58b... heater terminals 59a, 59b, 659a, 759a... heater wiring portion 68a, 68b... detection terminals 69a, 69b... detection wiring portion 70, 470, 570, 670, 770... flat portion 72, 472, 572, 672, 772... flat surface 92... semiconductor material 165... Pt wire 192... catalyst material 294... thermistor film

Claims (12)

a substrate in which a cavity is formed;
a first insulating film having a plurality of beam portions connected to a cavity periphery that is a periphery of the cavity in the base material, and a first insulating film membrane portion held on the cavity via the beam portions;
a second insulating film laminated on an upper side of the first insulating film;
a heater section provided on an upper side of the first insulating film membrane section;
a flat portion provided between the first insulating film membrane portion and the second insulating film, disposed closer to the center of the first insulating film membrane portion than the heater portion when viewed from above, and forming a flat surface facing upward;
a gas detection portion disposed above the flat portion via at least the second insulating film and having an area smaller than that of the flat surface;
A gas sensor having The gas sensor according to claim 1, characterized in that the flat portion has a higher thermal conductivity than the second insulating film. The gas sensor according to claim 1, characterized in that the flat portion is made of the same material as the heater portion. The gas sensor according to claim 1, wherein the heater portion has a bent portion that repeatedly bends with an amplitude of less than 1/2 the length of a side of the first insulating film membrane portion, which is substantially rectangular. The gas sensor according to claim 1, wherein the heater portion has a symmetrical shape with respect to a reference line that passes through the center of the first insulating film membrane portion and extends in the horizontal direction. The gas sensor according to claim 1, wherein the heater portion is connected to the flat portion. The gas detection portion has at least one pair of electrodes in contact with a semiconductor material;
2. The gas sensor according to claim 1, wherein the gas is detected based on a change in resistance between the electrodes. the gas detection portion has a Pt wire in contact with a catalytic material;
2. The gas sensor according to claim 1, wherein the gas is detected by a change in resistance of the Pt wire. The gas detection unit has at least one pair of electrodes in contact with a thermistor film,
2. The gas sensor according to claim 1, wherein the gas is detected based on a change in resistance between the electrodes. The gas sensor according to claim 9, wherein the thermistor film is in contact with a catalytic material. The gas sensor according to claim 1, which has a heater wiring section that connects a heater terminal provided on the periphery of the cavity and the heater section through the upper side of one of the beam sections. The gas sensor according to claim 1, which has a detection wiring section that connects a detection terminal provided on the periphery of the cavity and the gas detection section through the upper side of one of the multiple beam sections.

Images