JP2010230387A - Membrane-type gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein the detection element of a gas sensor is damaged by the mechanical stresses applied to a holding member or the heat stress due to the combustion of gas. <P>SOLUTION: A gas sensor region R is formed into a circular shape or a shape having no corner parts, and a membrane heat sensing member and a gas sensing member are provided to the upper part and center region of the holding member which holds the membrane heat-sensing member and the gas sensing member. Furthermore, a plurality of through-holes are provided to the holding member in a dispersed state so as to avoid loading part of the membrane heat sensing member. According to such a constitution, an effect for suppressing the occurrence of the damage of the detection element of the gas sensor by cracks, or the like, can be obtained even if heat stress is applied to a support substrate or mechanical stress is applied to the holding member. As a result, the lifetime of the gas sensor is prolonged. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a catalytic combustion type gas sensor that detects various gas leaks, and more particularly to a thin film type gas sensor.

  Conventionally, a gas sensor has been used as a sensor for detecting a combustible gas such as hydrogen gas or methane gas. The gas sensor captures a change in the electrical signal of the detection element by an interaction caused by the arrival of gas on the detection surface of the detection element. In the following description, combustible gas is simply expressed as gas.

  Many proposals have been made regarding the configuration of the gas sensor. Among them, the catalytic combustion type gas sensor is widely known. This contact combustion type gas sensor detects the arrival of gas by causing an exothermic reaction by contacting the gas with the catalyst on the detection surface.

  Such a contact combustion type gas sensor is widely used as a gas leak detection device in various devices using a combustible gas or in a room where the combustible gas is installed, for home use, industrial use and the like.

  In recent years, a type called a bulk type has been widely used among catalytic combustion type gas sensors, but on the other hand, a microsensor element manufacturing that forms a thin-film heat transfer film, catalyst film, electrode, wiring, and heater on a silicon wafer. A thin-film gas sensor using a sensor chip based on MEMS (Micro Electro Mechanical Systems) using technology has also been used (for example, see Patent Document 1).

The prior art disclosed in Patent Document 1 will be described with reference to FIG. FIG. 5 is a plan view rewritten so as not to depart from the gist thereof for easy explanation.
In FIG. 5, 19 is an electrode pad, 18 is an electrical wiring, 3 is a cavity, 2 is a semiconductor substrate, 17 is a heat sensing part, and 16 is a beam part. Reference numeral 2a denotes a corner portion of the inner wall of the semiconductor substrate, and reference numeral 16a denotes a connection corner portion between the beam portion 16 and the semiconductor substrate 2.

Since the semiconductor substrate 2 is processed into a frame shape, there are four corners on its inner wall, but since the beam portion 16 is formed so as to bridge the frame-shaped semiconductor substrate 2, it is shown in FIG. In such a plan view, there are two corners (corner part 2a). The connection portion between the beam portion 16 and the semiconductor substrate 2 has four connection corner portions 16a in plan view.
A portion without the beam portion 16 is a cavity 3. The cavity 3 is also called an air hole and is a portion through which gas passes.
The heat sensing part 17 provided on the upper part of the beam part 16 undergoes an exothermic reaction and changes its resistance value when the gas arrives.

  A thin film gas sensor is configured by the sensor chip having such a configuration and a circuit for controlling the sensor chip. In order to detect the arrival of gas, a voltage is applied between the electrode pads 19 in advance, and a change in resistance caused by heat generation of the heat sensing unit 17 due to the arrival of gas is detected.

The sensor chip of the thin-film gas sensor is characterized in that it has a higher degree of integration and higher mass productivity than the bulk-type catalytic combustion gas sensor because the components can be formed by semiconductor manufacturing technology. In addition, since the heater and the like can be formed of a metal thin film heat sensing element, the thermal response is good.

JP-A-8-247981 (page 6, FIG. 1)

  In the prior art disclosed in Patent Document 1, as shown in FIG. 5, in the connection corner portion 16a, the angle formed between the beam portion 16 and the semiconductor substrate 2 in a plan view is 45 degrees. The corner 2a of the semiconductor substrate 2 is 90 degrees. According to a study by the inventor, it was found that the smaller the angle of the corner 2a and the connection corner 16a (the more acute the angle), the more easily cracks occur in this portion.

In the contact combustion type gas sensor, the heat sensing part 17 is used by generating heat to a high temperature. For this reason, the generated heat is transmitted from the beam portion 16 to the semiconductor substrate 2, and thermal stress tends to concentrate on the corner portion 2a. For this reason, in the prior art shown in Patent Document 1, cracks and the like are likely to enter the corner 2a.
In some cases, the gas detection sensitivity may be improved by increasing the resistance value of the heat sensing unit 17 to generate heat at a higher temperature. However, the higher the temperature is, the higher the thermal stress is applied. Furthermore, cracks are likely to occur.

In addition, the beam portion 16 may bend due to the flow pressure of the incoming gas, but the beam portion 16 may be bent even when an impact or vibration is applied to the sensor chip. In such a case, so-called mechanical stress tends to concentrate on the connection corner portion 16 a of the connection portion between the beam portion 16 and the semiconductor substrate 2. For this reason, in the prior art shown in Patent Document 1, a crack or the like is likely to enter the connection corner portion 16a.
In the example shown in FIG. 5, one heat sensing part 17 is provided on the upper part of the beam part 16. However, if this number is increased to increase the detection sensitivity, the weight of the beam part 16 also increases. It becomes easier to crack 16a.

  As described above, when the conventional technique disclosed in Patent Document 1 is operated as a gas sensor, the beam portion and the semiconductor substrate may be damaged due to mechanical stress due to thermal stress or bending of the beam portion. Furthermore, if the sensitivity of the sensor is to be improved, the sensor is more easily damaged. In other words, there is no technology known in the art that achieves both the sensitivity and durability of the sensor.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain a gas sensor having good durability performance in which cracks and the like are not generated in a support member such as a beam.

  As a means for achieving the above object, the thin film gas sensor of the present invention uses the inside of a support substrate having a frame shape as a sensor region, and holds an insulating film provided on the support substrate extending from the support substrate in the sensor region. In the thin-film gas sensor provided with a member and provided with a thin-film heat sensing element on the holding member, the sensor region has a circular shape or a polygonal shape in which all internal angles are obtuse in a plan view. Is.

  As a result, in the connection portion between the holding member and the support substrate, the entire region over the circumference of the inner edge of the support substrate becomes a fixed region. For this reason, the strength of the holding member is increased, and the load applied to the holding member is dispersed in the fixed region over the entire circumference, so that the mechanical stress generated in the holding member is very small, and the occurrence of cracks and the like is further suppressed. .

  The holding member has a beam structure, and in the sensor region, an area that is divided in a plane by the holding member and the support substrate is a through hole. The through hole has a circular shape or a plurality of internal angles that are obtuse in plan view. You may make it comprise the square shape.

  With such a configuration, a region defined by the holding member and the support substrate can be a through hole. And since there is no acute angle part in a through-hole, stress does not concentrate on a beam structure.

  The holding member is a membrane structure provided so as to cover the sensor region in plan view, and the holding member has a plurality of through holes avoiding the mounting portion of the thin film heat sensing element, and the through holes are circular in plan view. Or you may make it comprise the polygonal shape whose all internal angles are obtuse angles.

  With such a configuration, the membrane structure can be provided with a through hole having no acute angle portion. And since there is no acute angle part in a through-hole, stress does not concentrate on a membrane structure.

  The through holes may be distributed in the sensor region at a predetermined interval.

  Thereby, since the through holes can be dispersed, the load of the gas flow pressure can also be dispersed. For this reason, the bending of the holding member due to the gas flow pressure can be kept small.

  Adjacent through holes may have the same center-to-center distance.

  Accordingly, the gas flow is uniformly dispersed and the load due to the gas flow pressure applied to the holding member is also dispersed and uniform.

  The membrane structure may be composed of a first thin film and a beam-shaped second thin film passing through the center point of the sensor region.

  Thus, if the holding member is composed of a plurality of thin films, the strength of the holding member can be further increased.

  The thin film gas sensor of the present invention can obtain the effect of suppressing the occurrence of damage due to cracks or the like even when thermal stress or mechanical stress is applied to the support substrate. This also improves the life of the gas sensor.

It is the top view and end view which showed typically the structure of the detection element which concerns on 1st Embodiment of the thin film type gas sensor of this invention. It is the top view and end view which showed typically the structure of the detection element which concerns on 2nd Embodiment of the thin film type gas sensor of this invention. It is a top view explaining 3rd Embodiment of the thin film type gas sensor of this invention. It is the top view and end view which showed typically the structure of the detection element which concerns on 4th Embodiment of the thin film type gas sensor of this invention. 2 is a plan view of a gas sensor described in Patent Document 1. FIG.

In the thin film gas sensor of the present invention, the inside of a support substrate connected to a holding member on which a thin film thermal sensor for detecting gas is formed into a circular shape or a polygonal shape with all internal angles being obtuse. In addition, the circle mentioned here includes an ellipse. Moreover, the strength of the holding member is further increased by making the holding member a membrane structure.

In the description of the embodiment of the thin film gas sensor of the present invention, the case where a gas detector is provided on the upper part of the thin film heat detector will be described as an example. In the gas detection procedure, a current is passed through the thin-film heat sensing element, and the process waits until the gas arrives in a state where a predetermined temperature is reached due to heat generated by energization. When the gas arrives and the gas comes into contact with the gas detector above the thin film heat detector, the gas detector burns, and the thin film heat detector further generates heat. As a result, the value of the current flowing through the thin film thermal sensor changes, and this is detected.
Since such a detection procedure is already known, a detailed description thereof will be omitted.
Details of the embodiment will be described below with reference to the drawings.

[Description of First Embodiment: FIG. 1]
A first embodiment of the thin film gas sensor of the present invention will be described with reference to FIG. FIG. 1 is a diagram schematically showing the structure of a first embodiment of a thin film gas sensor of the present invention. FIG. 1A is a plan view thereof, and FIG. 1B is an end view schematically showing an end surface taken along a cutting line XX ′ of FIG.

  In FIG. 1, 21 is a frame-shaped support substrate, 21c is an inner wall of the support substrate 21, 22 is an insulating film, and 22h is a through hole. Reference numeral 23 denotes a beam portion. Reference numeral 23 a denotes a connection corner portion between the beam portion 23 and the support substrate 21. Reference numerals 24a and 24b denote electrode pads. Reference numerals 25a and 25 denote metal thin film resistors. Reference numeral 26 denotes a thin film thermal sensor. 28 is a gas sensor. And these comprise the gas detection element 20.

  A symbol R indicates a sensor region. The symbol C indicates the center point of the sensor region R and is indicated by “+”.

As shown in FIG. 1, the gas detection element 20 is configured such that a beam portion 23 bridges the support substrate 21 in a plan view as shown in FIG. 1A from a frame-shaped support substrate 21. Has been. The beam portion 23 is provided with a thin film heat detector 26, metal thin film resistors 25 a and 25 b, and a gas detector 28.
Thus, the sensor region R is a region where a configuration for detecting gas is provided, and is a portion surrounded by the inner wall 21c of the support substrate 21. In FIG. 1 (a), it is indicated by a broken line.

[Description of external shape: Fig. 1]
First, the outer shape will be described.
As shown in FIG. 1, the support substrate 21 has a frame shape in plan. For the support substrate 21, a material having insulating properties, low thermal conductivity, and excellent heat resistance is suitable. Furthermore, considering the ease of processing, for example, silicon (Si) is suitable because a known semiconductor element manufacturing method can be applied. Of course, other materials may be used.

  The sensor region R is a portion surrounded by the inner wall 21c of the support substrate 21, and a portion overlapping the edge of the through hole 22h on the upper surface of the support substrate 21 in a plan view as shown in FIG. There is a circle. Thus, the inner wall 21c does not have an acute angle portion and has a smooth round shape, so that the concentration of thermal stress does not occur.

As shown in FIG. 1B, an insulating film 22 is formed on the surface of the support substrate 21. The insulating film 22 is made of, for example, silicon oxide (SiO ₂ ). Needless to say, silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), tantalum oxide (Ta ₂ O ₅ ), or the like can also be used. Moreover, it is good also as a laminated film which laminated | stacked these.

As shown in FIG. 1A, the shape of the insulating film 22 is formed so as to bridge the frame-shaped support substrate 21 with a predetermined width, and constitutes a beam portion 23. The connection portion between the beam portion 23 and the support substrate 21 has four connection corner portions 23a in plan view. As shown to Fig.1 (a), in the connection corner | angular part 23a, the angle which the beam part 23 and the support substrate 21 make by planar view is an obtuse angle.
For this reason, even if the beam portion 23 is bent due to the flow pressure of the incoming gas, the mechanical stress is not concentrated.

  In the example illustrated in FIG. 1, the beam portion 23 is configured by only the insulating film 22 without the support substrate 21 on the back side. The beam portion 23 is a holding member on which the thin film heat sensing element 26 and the metal thin film resistors 25a and 25b are mounted.

By the way, such a structure in which the beam portion is provided so as to bridge the support substrate is called a double-supported beam structure. A configuration in which the beam portion extends from the support substrate and its end portion is an open end is called a cantilever structure.
In either beam structure, it is necessary to provide strength so that the beam does not break even if a gas arrives and a force generated by the pressure of the gas is applied to the beam 23 and mechanical stress is generated. is there.

When the insulating film 22 is a laminated film, the stress characteristics of the laminated film may be changed. For example, when two films are stacked, the lower film is a film having tensile stress, and the upper film is a film having compressive stress.
In this way, the stress of both films can be canceled out. Then, even if a force generated by the arrival of gas is applied to the beam portion 23, the stress characteristic of the insulating film 22 itself is not involved in the bending generated in the beam portion, so that the beam portion can be easily designed.

  As shown in FIG. 1A, a region in which the support substrate 21 is planarly divided by the beam portion 23 in a plan view is a through hole 22h serving as a gas circulation portion. In the example shown in FIG. 1, since there is one beam portion 23, there are two through holes 22h. This through hole 22h is called a so-called air hole and is a portion through which gas passes. The through hole 22h has a circular shape or a polygonal shape in which all internal angles are obtuse angles in a plan view. In the example shown in FIG. 1, the through hole 22h has an elliptical shape.

Although not shown, the two through holes 22h may have different sizes, but the through holes 22h are formed by bridging the frame-shaped support substrate 21 by the beam portions 23. It is preferable that both the through holes have the same shape because the balance of the beam portion 23 is improved.
Further, it is preferable that both through holes have the same distance from the center point C of the sensor region R. Here, the distance from the center point C is either the distance from the center point C to the center of the through hole 22h or the distance from the center point C to the edge of the through hole 22h. Good. What is important is that in the sensor region R, the through holes 22h are arranged in a well-balanced manner.

By having the through hole 22h, the gas flows through the through hole to the upper surface side and the back surface side of the beam portion 23 that is the holding member. Then, since the gas that has arrived at the sensor region R does not stay, the gas inflow is not hindered.

[Explanation of thin film thermal detector, metal thin film resistor, electrode pad: FIG. 1]
Next, the thin film heat sensing body 26 and the metal thin film resistors 25a and 25b provided on the beam portion 23 and the electrode pads 24a and 24b connected to these will be described.
A thin film heat sensing element 26 and metal thin film resistors 25a and 25b are provided on the upper portion of the beam portion 23, which is a holding member constituted by the insulating film 22. Electrode pads 24 a and 24 b are provided on the insulating film 22 on the support substrate 21.
The electrode pad may be provided anywhere on the upper side of the support substrate 21. However, in the example shown in FIG. 1, the electrode pad 24a is located at 9 o'clock in the plan view of FIG. Similarly, the electrode pads 24b are provided in the 3 o'clock direction.

The thin film heat sensing element 26 is connected to the electrode pad 24a on the support substrate 21 via the metal thin film resistor 25a, and is connected to the electrode pad 24b via the metal thin film resistor 25b.
As shown in FIG. 1 (a), the thin film heat sensing element 26 is overlapped on the center point C, and is also overlapped with the center of the beam portion 23 in the width direction. 25a, the thin film heat sensing element 26, the metal thin film resistor 25b, and the metal pad 24b are provided linearly in this order. By adopting such a configuration, a weight-balanced arrangement structure is formed.

  A gas sensor 28 is provided on the thin film heat sensor 26. With such a configuration, the gas detector 28 generates heat due to the arrival of gas, and the accuracy such as sensitivity characteristics and reaction rate characteristics for detecting the gas can be improved.

By the way, the reaction rate characteristic when detecting gas is the rate at which the thin film heat sensing element reaches a predetermined temperature at which it senses that the gas has arrived when the gas arrives and the thin film heat sensing element generates heat. It is shown.
Sensitivity characteristics refer to the amount of change in which the resistance value of the thin film thermal detector changes due to the arrival of gas and heat generation.
That is, as a sensor, when gas arrives, it changes quickly to a predetermined temperature, and the greater the amount of change in the resistance value, the better the sensitivity.

[Description of the shape of the thin film thermal detector: FIG. 1]
Next, the shape of the thin film heat detector will be described.
The thin film heat sensing element 26a has a 99-fold pattern having a plurality of folded portions. In the example shown in FIG. 1, ten folding portions of one thin film heat sensing element are provided.

  By the way, there is a suitable value for the resistance value of the thin film thermal sensor 26. Of course, a higher resistance is preferable because the sensitivity characteristics and reaction rate characteristics of gas detection are improved. In order to increase the resistance value, although it becomes difficult to process, the thin film heat sensing element may be formed thin and thin.

However, if the pattern width or the like of the thin film heat sensing element is reduced, the power density is increased and the film is easily affected by electromigration.
Electromigration is a phenomenon in which metal atoms move gradually because electrons moving in an electric conductor collide with metal atoms and exchange of momentum is performed between them. For this reason, a defect occurs in a portion where the metal atom is deficient.
When electromigration occurs, the thin film heat sensing element is disconnected and the life of the gas sensor is shortened.

Under such circumstances, the resistance value of the thin-film heat sensing element has a value that achieves both sufficient sensitivity as a gas sensor and resistance to electromigration.
In view of such circumstances, the shape of the thin film heat sensing element 26 is determined. Generally, when the pattern width of the thin film heat sensing element 26 is reduced, a large number of folded portions can be provided, and the pattern is substantially reduced. The overall length can be increased and high resistance can be obtained. Therefore, in addition to the pattern width and film thickness of the thin film heat sensing element, the resistance value is determined in consideration of the number of folded portions.
Such values vary depending on the type of gas to be detected, the temperature of the thin film thermal sensor, the applied voltage (that is, the power supply voltage of the system system), etc. For example, the material of the thin film thermal sensor is platinum ( Pt) and the film thickness is 0.3 μm, the wiring width is 10 μm and the resistance value is 500Ω.

When the thin film heat sensing element 26 has a ninety-nine fold pattern having a plurality of folded portions, in order to make the resistance value of the thin film heat sensing element 26 higher, the width of the pattern should be reduced (thinned). Good.
If the width of the pattern is reduced, a large number of folded portions can be provided, and the overall length of the pattern can be substantially increased, resulting in high resistance.
Moreover, by having a ninety-nine fold shape, the distribution density as a resistor is increased, the heat generation efficiency is increased, and a higher heat generation amount is obtained.

In the example shown in FIG. 1, the ninety-nine fold pattern shape of the thin film heat sensing element 26 has a folded portion in the short direction (width direction) of the beam portion 23, but it is not limited to this. . Although not shown, it may have a folded portion in the longitudinal direction (length direction).
In any case, the 99-fold pattern shape can reduce the arrangement space of the thin film heat sensing element, so that the sensor region R can be reduced in size, and as a result, the thin film gas sensor itself can also be reduced in size. This also has the effect.

[Description of insulating film constituting beam portion: FIG. 1]
Next, the characteristics of the structure of the beam portion will be described.
The beam portion 23 which is a holding member is provided with a thin film heat sensing body 26 on the upper surface side, metal thin film resistors 25a and 25b connected to the thin film heat sensing body 26, and a gas sensing body 28 on the thin film heat sensing body 26. It needs to be strong enough to hold the member. Therefore, the film thickness of the insulating film 22 constituting the beam portion 23 needs a predetermined thickness.
However, in order to improve the detection performance of the incoming gas, it is desirable to reduce the heat capacity of the portion (beam portion 23) on which the thin film thermal detector 26 is mounted. This is because if the heat capacity is large, the heat generated by the arrival of gas is absorbed by the beam portion. In this state, the heat of the thin-film heat sensing element cannot be raised (that is, the resistance value cannot be changed), and even if gas arrives, it cannot be sensed.

  Thus, since the strength of the beam portion 23 and the performance for detecting the gas are in a trade-off relationship, the film thickness of the insulating film 22 constituting the beam portion 23 is appropriately set in view of this. . Since the heat generation temperature varies depending on the type of incoming gas, the thin film heat detector, and the material of the gas detector, for example, the thickness of the insulating film 22 may be set by repeating experiments and collecting data.

The same applies to the width of the portion of the beam portion 23 where the thin film heat sensing element 26 is mounted. If this width is wide, the strength of the beam portion is improved.
As a result of examination by the inventors, it has been found that the width of the portion of the beam portion 23 on which the thin film heat sensing element 26 is mounted and the film thickness thereof are preferably “film thickness <width”. The reason is that the thermal conductivity is the highest directly under the portion where the thin film thermal detector 26 is mounted. Therefore, it is preferable to reduce the thickness of the insulating film 22 constituting the beam portion 23 to reduce the heat capacity and increase the width to maintain the strength.

In the example shown in FIG. 1, for example, when the electrode pad 24 a and the electrode pad 24 b are electrically connected on an external substrate or the like, and a power source and an ammeter are connected to them, a current flows through the thin film heat sensing element 26. Can be measured and the amount of current can be measured. Specifically, a voltage is applied from a power source (not shown) between the electrode pad 24a and the electrode pad 24b, and the thin film heat sensing element 26 is energized. Thereafter, when the gas arrives, the gas detector 28 generates heat in response to the gas, the temperature of the thin film heat detector 26 also rises, and the current amount changes. By capturing this change in the amount of current, it is possible to know the arrival of gas.
Note that a gas detector 28 is provided above the thin film heat detector 26 for the purpose of improving the detection sensitivity by quickly generating heat due to the arrival of gas. Details of the material and the like will be described later.

  By the way, since the thin film heat sensing element 26 generates heat due to the arrival of the gas, it is possible to know the arrival of the gas. Therefore, the arrangement of the electrode pad connected to the thin film heat sensing element and the drawing of the metal thin film resistor, etc. It is obvious that how the current flows through the heat sensing element and how the current is measured is arbitrary, and the arrangement of each element is not limited to the example shown in FIG.

  These thin film heat sensing elements, metal thin film resistors, and electrode pads can be made of the same metal. These are often refractory noble metals, such as platinum (Pt).

The reason for using such a refractory noble metal is temperature. That is, a gas sensor 28 is provided above the thin film heat sensor 26. The gas sensor 28 functions as a catalyst and generates heat when gas arrives to improve detection sensitivity. effective. The gas detector 28 is sintered on the thin film heat detector 26. However, the sintering temperature of the gas detector 28 is high, and is about 600 to 700 degrees, for example, depending on the material of the catalyst used. The temperature generated when the gas arrives is called a so-called combustion temperature, and the temperature exceeds, for example, 400 degrees.
Thus, since the thin film heat sensing element 26 and the metal thin film resistors 25a and 25b are exposed to a high temperature, a high melting point noble metal is used.

The thin film heat detector 26, the metal thin film resistors 25a and 25b, and the electrode pads 24a and 24b are made of chromium (Cr), titanium (Ti), or A metal film made of these alloys may be provided as a base layer, and platinum (Pt) may be formed thereon. For example, platinum (Pt) can be formed by a known forming method such as a sputtering method.
The thin film heat sensing element, metal thin film resistor, and electrode pad are made of a material other than platinum (Pt), such as rhodium (Rd), palladium (Pd), gold (Au), or other high melting point noble metals, or these An alloy metal or the like can be used.

[Description of gas detector]
The gas sensor 28 provided on the upper surface of the thin film heat sensor 26 is a catalyst provided for the purpose of improving the detection sensitivity by quickly generating heat due to the arrival of gas. Although not particularly limited, for example, it has a heat conductive layer made of aluminum oxide (Al 2 _{O 3),} an arrangement of repeated combustion catalyst layer on the surface of the thermally conductive layer.
The combustion catalyst layer is made of, for example, tin oxide (SnO ₂ ) as a main component, and a fine powder of platinum (Pt) and palladium (Pd) combustion catalyst is mixed with a solvent to form a slurry, which is made into a heat conductive layer. It is applied to the surface and sintered at a temperature of 600 ° C.

In the example shown in FIG. 1, the gas detector 28 is provided in the sensor region R so as to cover the thin film heat detector 26 on the upper side of the beam portion 23 so as to be horizontally long in the drawing.
Of course, the gas detector 28 may not be provided depending on the resistance value of the thin film heat detector 26a, the type of incoming gas, and the like.

Further, as shown in FIG. 1B, the gas sensor 28 is provided only on the upper surface side of the thin film heat sensor 26d. However, the present invention is not limited to this. Since the incoming gas flows through the through hole 22h, although not shown, it may be provided on the back side of the beam portion 23 as a holding member. That is, the beam part 23 may be wrapped from above and below by the gas sensing body 28.
With such a structure, the surface area of the combustion catalyst layer is increased, the contact area with the gas is increased, and combustion can be performed faster. And the effect which further speeds up the reaction speed of gas detection is acquired.

[Explanation of the effect of the invention]
Here, the effects of the first embodiment are summarized as follows.
The first effect is that the sensor region R has a circular shape in a plan view, and thus has high durability against thermal stress.
That is, since there are no acute corners on the inner wall 21c of the support substrate 21, even when heat is generated due to the arrival of gas, the distortion due to the thermal stress is small, and the thermal stress is not concentrated in a specific place. No cracks or the like occur in the support substrate 21.

The second effect is that even in the connection corner portion 23a between the beam portion 23 that is a holding member and the support substrate 21, there is no corner portion having an acute angle in a plan view, so that durability against mechanical stress is achieved. It is expensive.
That is, even if the beam portion 23 is bent due to the flow pressure of the incoming gas or due to unexpected shock or vibration, mechanical stress is not concentrated on the connection portion between the beam portion 23 and the support substrate 21. A crack or the like does not occur in the beam portion 23.

The third effect is that the weight balance of the sensor region R is good.
That is, the metal thin film resistors 25a and 25b, the thin film thermal detector 26, and the gas sensor 28 are provided on a line passing through the center point C of the sensor region R, and the thin film thermal detector 26 and the gas sensor 28 are provided in the central region. As a result, a balanced weight balance without uneven weight can be obtained and stabilized.

The fourth effect is that the gas combustion efficiency can be increased.
That is, the through-holes 22h are arranged so as to be dispersed at a predetermined interval, and even when the gas arrives, there is no bias in the flow rate. For this reason, the gas comes into contact with the gas detector 28 in a uniform state, and as a result, the combustion efficiency of the gas increases.

  In other words, the thin film gas sensor of the present invention has high durability against thermal stress and mechanical stress, and the durability of the thin film gas sensor decreases even if the number of thin film heat sensing elements is increased in order to improve gas detection sensitivity. There is nothing to do. As a result, the lifetime as a sensor is extended.

[Description of Second Embodiment: FIG. 2]
Next, a gas detection element according to a second embodiment will be described with reference to FIG. FIG. 2 is a diagram schematically showing the structure of the second embodiment. 2A is a plan view thereof, and FIG. 2B is an end view schematically showing an end surface taken along a cutting line YY ′ of FIG.

In FIG. 2, reference numeral 22 a denotes a membrane structure composed of an insulating film 22. 22i, 22j, 22k, 22l, 22m, and 22n are through holes. The through holes 22i to 22n are provided in the membrane structure 22a. 22kc is the center point of the through hole 22k. Similarly, 22lc is the center point of the through hole 22l, 22mc is the center point of the through hole 22m, and is indicated by "+". And these comprise the gas detection element 30. L1, L2, L3, and L4 indicate distances between the through holes. In addition, the same code | symbol is provided about the same structure already demonstrated, and detailed description is abbreviate | omitted.

  The feature of the gas detection element 30 of the second embodiment shown in FIG. 2 is that the holding member has a membrane structure. In the first embodiment already described, an insulating film 22 is provided on the upper side of the support substrate 21, and the beam portion is configured to bridge the frame-shaped support substrate 21 with a predetermined width by the insulating film 22. It was. In the second embodiment shown in FIG. 2, the holding member is not composed of a beam portion, but is a membrane structure 22a.

  The membrane structure 22a is configured by forming the insulating film 22 provided on the support substrate 21 with a thin film that is uniform in the direction of the sensor region R. The membrane means a “film”, and the membrane structure means the structure itself. However, in the embodiment of the present invention, the sensor region of the insulating film 22 is easy to explain. The portion R is a membrane structure 22a.

On the upper part of the membrane structure 22a, a thin film heat sensing body 26 is provided in the central region including the central point C of the sensor region R. Then, both ends of the thin film heat sensing element 26 are connected to a pair of electrode pads 24a and 24b on the upper side of the support substrate 21 via two metal thin film resistors 25a and 25b.
As shown in FIG. 2A, the center of the thin film thermal sensor 26 is set on the center point C, and from the electrode pad 24a, the metal thin film resistor 25a, the thin film thermal sensor 26, the metal thin film resistor 25b, and the metal pad. They are provided linearly in the order of 24b. By adopting such a configuration, a weight-balanced arrangement structure is formed.

[Description of shape of insulating film: FIG. 2]
As shown in FIG. 2, the insulating film 22 is provided on the upper portion of the support substrate 21 and the sensor region R. Although the insulating film 22 provided in the sensor region R is represented as a membrane structure 22a, the membrane structure 22a is uniformly formed by extending the insulating film 22 provided on the support substrate 21 in the direction of the sensor region R. It is composed of a thin film.

  Since the membrane structure 22a functions as a holding member, the membrane structure 22a needs to be strong enough to be held. Further, it is necessary to provide strength that does not damage the membrane structure 22a even when the gas arrives and the membrane structure 22a is bent by the pressure of the gas. The film thickness of the insulating film 22 is a thin film of about 1 μm, for example. However, it is not particularly limited, and may be appropriately set in consideration of the above. The insulating film 22 can also be a laminated film as in the first embodiment. At this time, as already described, the stress characteristics of the laminated films may be changed.

The membrane structure 22a is provided with a plurality of through holes in a portion where the thin film thermal sensor 26, the metal thin film resistors 25a and 25b, and the gas sensor 28 are not provided. In the example shown in FIG. 2, six through holes 22i to 22n are provided.
The through holes 22i to 22n have the same size, and are circular in the example shown in FIG. The sensor regions R are distributed at a predetermined interval.
In this way, adjacent through holes are spaced apart from each other by a predetermined distance. When the sensor region R is viewed as a whole, they are generally dispersed.

In the example shown in FIG. 2, the adjacent through holes are, for example, the through hole 22i and the through hole 22j, the through hole 22i and the through hole 22n, the through hole 22l and the through hole 22k, and the through hole 22l and the through hole 22m. is there. Adjacent through holes are separated by the same distance.
In FIG. 2, the distance L1 and the distance L2 are the same, and the distance L3 and the distance L4 are the same. The distance L3 is the distance between the center point 22kc and the center point 22lc of the through hole, and the distance L4 is the distance between the center point 22lc and the center point 22mc of the through hole.

  That is, even if the distance L1 that is the distance between the edges of the through holes opened in the membrane structure 22a is the same as the distance L2, the distance L3 that is the distance between the centers of the through holes is the same as the distance L4. It is good. What is important is that the through holes are arranged in a balanced manner in the sensor region R.

In the example shown in FIG. 2, the through holes 22i to 22n have a circular shape. However, the shape is only an example, and may be a polygon. For example, a regular hexagon and a regular octagon. Further, a polygon and a circle may be combined and can be freely changed.
Note that the circle used in the description of the shape of the through hole includes an ellipse, and a shape obtained by chamfering and smoothing the corners of the polygon is also defined as a circle in a broad sense.

[Explanation of the effect of the invention]
Here, the effects of the second embodiment will be summarized. If the same points as the effects of the first embodiment already described are omitted, the following is obtained.
Since the membrane structure 22a as the holding member is uniformly formed extending from the support substrate 21, even if mechanical stress is generated, there is no portion where the stress is concentrated throughout the film. For this reason, no cracks or the like occur in the membrane structure 22a.

  Further, the through holes 22i to 22n are arranged to be dispersed at a predetermined interval, and even when the gas arrives, the flowing flow rate is not biased. For this reason, the gas comes into contact with the gas sensing element 28 in a uniform state, and as a result, the combustion efficiency of the gas can be further improved.

[Description of other shapes of sensor region R: FIG. 3]
Next, another shape of the sensor region R will be described with reference to the plan view of FIG. FIG. 3 is a plan view for explaining the support substrate when viewed from the same direction as that shown in FIGS. 1 (a) and 2 (a). In FIG. 3, parts not necessary for the description are omitted.

  In FIG. 3, reference numerals 31, 32, and 33 denote support substrates. Reference numerals 31c, 32c, and 33c denote inner walls of the support substrate. α1, α2, α3, α4, α5, and α6 are angles of the inner wall 33c. Since the support substrates 31 to 33 correspond to the support substrate 21 of the first and second embodiments already described, in the description, refer to FIGS. 1 and 2 as appropriate.

  In the first embodiment and the second embodiment already described, the example in which the sensor region R is formed in a circular shape has been described. However, the sensor region R is not necessarily limited to a circular shape. For example, the shape shown in FIG. FIG. 3 shows other shapes of the sensor region.

In FIG. 3A, the sensor region R has an elliptical shape, that is, the inner wall 31c of the support substrate 31 has an elliptical shape. In the example shown in FIG. 3A, a long elliptical shape is shown in the left-right direction of the drawing, but it may have a long elliptical shape in the vertical direction of the screen or in an oblique direction. Since the elliptical shape has no corners, there is no portion where stress is excessively concentrated. Therefore, the same effect as in the case of the circular shape is obtained.
In the present invention, an elliptical shape is also expressed as a circular shape.

FIG. 3B is an example in which the shape of the sensor region R has a shape in which square corners close to an ellipse are eliminated. That is, the inner wall 32c of the support substrate 32 has a smooth rectangular shape with no corners. Since such a shape does not have a corner portion, there is no portion where stress is excessively concentrated. Therefore, the same effect as in the case of the circular shape is obtained.

  In FIG. 3C, the sensor region R has a regular hexagonal shape, that is, a regular hexagonal shape in which the inner wall 33c of the support substrate 33 is surrounded by six sides. The regular hexagon forms an obtuse angle of 120 degrees in any of the inner angles α1 to α6. When the inner angle is 120 degrees, stress is not excessively concentrated as compared with the case of an acute angle or a right angle, and the same effect as in the case of a circular shape is achieved. The illustrated example is a regular hexagon, but of course, other polygons may be used.

[Description of Fourth Embodiment: FIG. 4]
Next, a fourth embodiment will be described with reference to FIG.
FIG. 4 is a plan view schematically showing the structure of the fourth embodiment. 4A is a plan view thereof, and FIG. 4B is an end view schematically showing an end surface taken along a cutting line ZZ ′ of FIG. 4A.
In FIG. 4, 99 is an insulating film. Reference numeral 99 a denotes a membrane structure constituted by the insulating film 99. 22o and 22p are through holes provided in the membrane structure 99. Reference numeral 40 denotes a gas detection element. The same reference numerals are given to the same components that have already been described, and detailed description thereof is omitted.

  A feature of the gas detection element 40 of the fourth embodiment shown in FIG. 4 is that the holding member is a beam portion and a membrane structure. 1 is a configuration combining the first embodiment described with reference to FIG. 1 and the second embodiment described with reference to FIG. 2, and a membrane structure 99 as a first thin film is provided on the lower side, It is the structure which has piled up the beam part 23 as a 2nd thin film on the upper side.

  The through holes 22o and 22p have a hexagonal shape in the example shown in FIG. As shown in FIG. 4A, these two through holes are arranged opposite to each other with the beam portion 23 interposed therebetween.

  Since the gas detection element 40 of the fourth embodiment constitutes a holding member with the membrane structure 99a and the beam portion 23, the strength thereof is increased, and the resistance against bending and mechanical stress of the holding member is further improved. The durability performance of the gas sensor is further improved.

  In the example illustrated in FIG. 4, the configuration in which the beam portion 23 is provided on the upper portion of the membrane structure 99 a has been described. However, although not illustrated, the membrane structure 99 a may be provided on the upper portion of the beam portion 23. . Of course, the shapes of the through holes 22o and 22p may be different from the hexagonal shape, and can be changed as appropriate.

  As described above, in the embodiment described above, the configuration in which the gas sensor is provided on the upper part of the thin film heat sensor is exemplified, but the present invention is not limited to this. If the thin film thermal sensor is made of a semiconductor, the gas sensor is unnecessary.

  The thin film type gas sensor of the present invention has improved durability against mechanical stress and thermal stress. Therefore, the thin film type gas sensor is suitable as a gas sensor for an environment where the gas flow rate is high and the temperature is higher.

20, 30, 40 Gas detection element 21, 31, 32, 33 Support substrate 21c, 31c, 32c, 33c Inner wall 22, 99 Insulating film 22a, 99a Membrane structure 22h-22p Through-hole 23 Beam portion 23a Connection corner portion 24a, 24b Electrode pad 25a, 25b Metal thin film resistor 26 Thin film thermal sensor 28 Gas sensor R Sensor region C Center point

Claims (6)

The inside of the support substrate having a frame shape is used as a sensor region, and an insulating film provided on the support substrate is provided with a holding member extending from the support substrate in the sensor region, and the thin film heat sensing element is provided on the holding member. In a thin film gas sensor equipped with
The thin film gas sensor according to claim 1, wherein the sensor region has a circular shape or a polygonal shape in which all inner angles are obtuse angles in a plan view. The holding member has a beam structure;
In the sensor region, a region divided planarly by the holding member and the support substrate is a through hole,
2. The thin film gas sensor according to claim 1, wherein the through hole has a circular shape or a polygonal shape in which all inner angles are obtuse angles in a plan view. The holding member is a membrane structure provided so as to cover the sensor region in plan view,
The holding member has a plurality of through holes avoiding the mounting portion of the thin film heat sensing element,
2. The thin film gas sensor according to claim 1, wherein the through hole has a circular shape or a polygonal shape in which all inner angles are obtuse angles in a plan view.   The thin-film gas sensor according to claim 3, wherein the through holes are distributed in the sensor region at a predetermined interval.   The thin film type gas sensor according to claim 3 or 4, wherein the adjacent through holes have the same center-to-center distance. 5. The thin film gas sensor according to claim 3, wherein the membrane structure includes a first thin film and a beam-shaped second thin film that passes through a center point of the sensor region. .

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