JP2010230386A - Membrane-type gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of cracks in a holding member, consisting of an insulating film loaded with a membrane heat-sensing member by dispersing the heat stress produced in the membrane heat-sensing member. <P>SOLUTION: The membrane heat-sensing member 46 mounted on the holding member constituted of the insulating film is formed into a zigzag pattern shape, having curved folding-back parts D, and the cross section of the pattern width (w) of the pattern shape is formed into a trapezoidal shape having inclined surfaces 46d formed to both ends. Right angle or acute angle corner parts are eliminated from the zigzag folding-back parts or both end parts of the width of a pattern, heat stress is dispersed and becomes small, and the effect of heat on the holding member is suppressed and suppresses the occurrence of cracks in the holding member. <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 gas, indoors where the gas sensor is installed, and the like in 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. 6 is a diagram rewritten so as not to depart from the gist for easy explanation.
In FIG. 6, 10 is a substrate, 11 is a recess provided in the substrate 10, 12 is a thin film insulator, 12a is a bridging portion, 12b is a central portion, 13 is a heating resistor, 13a is a pad portion, and 13b is a lead portion. .

  As shown in FIG. 6, the atmosphere sensor disclosed in Patent Document 1 is provided with a recess 11 in the substrate 10. A thin film insulator 12 is provided on the upper part of the substrate 10, and this is extended to the upper part of the recess 11 to have a bridge structure in which a bridge part 12 a and a center part 12 b are provided. The heating resistor 13 made of platinum (Pt) or the like is provided on the center portion 12b.

  The heating resistor 13 is a continuous line having a narrower width than the lead portion 13b, has a ninety-nine fold shape having a folded portion D, and the center of the thin film insulator 12 located above the recess 11 The portion 12b has a structure formed over almost the entire area.

JP-A-6-102227 (page 3, FIG. 1)

  According to Patent Document 1, since the heating resistor 13 is formed in a continuous thin line shape in almost the entire area of the central portion 12b located at the upper portion of the recess 11, high resistance is obtained.

  However, the shape of the heating resistor 13 shown in Patent Document 1 is a ninety-nine fold shape having a folded portion D, and the folded portion D has a shape folded at a right angle. That is, both the outer shape and the inner shape of the folded portion D are bent at a right angle.

A metal such as platinum (Pt) is used for the heating resistor 13, but a metal such as platinum (Pt) has a film stress, that is, a flat film has a strong characteristic against stress, but is square. The resulting edge portion has a characteristic that thermal stress is particularly concentrated.
For this reason, in the ninety-nine fold shape having the folded portion D at a right angle of the conventional heating resistor 13 shown in Patent Document 1, thermal stress is concentrated on that portion.

The thermal stress concentrated on the folded portion D of the heating resistor 13 also affects the thin film insulator 12, and a large distortion of the thermal stress appears in the thin film resistor 12. That is, the distortion propagates from the central portion 12b to the bridging portion 12a.
Since the heating resistor 13 is formed in almost the entire area of the central portion 12b on which the heating resistor 13 is mounted, the thermal stress generated in the folded portion D is dispersed and there are few places to escape, and the thermal stress is accumulated. It is.
For this reason, a large strain of thermal stress appears in the thin film insulator 12, and there arises a problem that thermal stress destruction such as cracks occurs in the thin film insulator 12.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a thin-film gas sensor having a long life while providing a structure in which an insulating film is not damaged such as a crack. .

  As means for solving the above problems, the thin film type gas sensor of the present invention employs the following configuration.

In the thin film type gas sensor including the inside of the support substrate having a frame shape as a sensor region, a holding member extending from the support substrate in the sensor region, and a thin film thermal sensor on the holding member,
The thin film heat sensing element has a ninety-nine fold shape including a folded portion having a curved shape in plan view, and has a trapezoidal cross section.

  As a result, there are no sharp edges perpendicular to the 99-fold shape, and the generated thermal stress is dispersed and reduced. For this reason, the influence of the thermal stress on the holding member on which the thin film thermal sensor is mounted is mitigated, and the occurrence of thermal stress destruction such as cracks in the holding member is suppressed.

  The cross section of the thin film heat sensing element may be formed in a trapezoidal shape by forming both end surfaces of the thin film in the shape of inclined surfaces.

  With such a configuration, the trapezoidal shape is uniform in cross section, and there is no portion where thermal stress is concentrated.

  Further, it is preferable that the holding member has a membrane structure.

  As a result, the thermal stress received from the thin film heat sensing element is dispersed in the four directions of the membrane (film), and the influence of the distortion is reduced as a whole. Moreover, since the strength of the holding member is increased, the generation of cracks in the holding member can be further suppressed.

The membrane structure has a plurality of through holes, and these through holes are preferably dispersed in the sensor region at a predetermined interval.

  As a result, gas passes through the through-holes to the upper surface side and the lower surface side of the holding member, and the sensitivity characteristics and reaction rate characteristics of gas detection can be improved. Further, since the through holes are dispersed at a predetermined interval, the load of the gas flow pressure is dispersed. For this reason, the bending of the holding member due to the gas flow pressure can be kept small.

  Further, adjacent through holes preferably 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 through hole is preferably circular or polygonal.

  In this way, it is possible and convenient according to the environment and gas used.

  The holding member may have a laminated structure in which a plurality of films having different stress characteristics are laminated.

  If it does in this way, the stress concerning a holding member can be relieved.

  The thin film type gas sensor of the present invention eliminates the concentration of thermal stress on the thin film heat sensing element having a ninety-nine fold shape, suppresses the distortion of the thermal stress of the holding member on which the thin film heat sensing element is mounted, and generates cracks. To prevent. A thin film gas sensor having a long life can be obtained.

It is the top view and sectional view which showed typically the structure of the gas detection element which concerns on 1st Embodiment of the thin film type gas sensor of this invention. It is the principal part enlarged plan view and sectional drawing of the thin film heat sensing element in FIG. It is sectional drawing which showed the cross section of the thin film sensor in FIG. 1, and other shapes of trapezoid shape. It is the top view which showed typically the structure of the gas detection element which concerns on the 2nd Embodiment of this invention. It is the top view and sectional view which showed typically the structure of the gas detection element which concerns on the 3rd Embodiment of this invention. FIG. 6A is a plan view and FIG. 6B is a sectional view bb ′ in FIG. 6A, illustrating a plan view and a cross-sectional view illustrating the structure of the atmosphere sensor disclosed in Patent Document 1. It is sectional drawing showing the cross section of.

  The thin film type gas sensor of the present invention is such that the shape of a thin film heat sensing element for detecting gas is a ninety-nine fold shape having a curved fold in plan view, and the cross section is formed in a trapezoidal shape. .

In the gas detection procedure of the thin film type gas sensor of the present invention, a current is passed through the thin film heat sensing element, and the process waits until the gas arrives in a state where the temperature has reached a predetermined temperature 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: FIGS. 1 and 2]
A first embodiment of a thin film gas sensor of the present invention will be described with reference to FIGS. FIG. 1 is a diagram schematically showing the structure of the first embodiment. FIG. 1A is a plan view thereof, and FIG. 1B is a cross-sectional view schematically showing a cross section taken along a cutting line XX ′ of FIG. 2 is an enlarged view of the main part of the thin film thermal sensor shown in FIG. 1 (a), FIG. 2 (a) is a plan view thereof, and FIG. 2 (b) is a cutting line Y in FIG. 2 (a). It is sectional drawing which showed the cross section in -Y 'typically.

  In FIG. 1, 41 is a frame-shaped support substrate, 41c is an inner wall of the support substrate 41, 42 is an insulating film, and 42h is a through hole. 43 is a beam part. 44a and 44b are electrode pads, 45a and 45b are metal thin film resistors, and 46a is a thin film heat sensor. Reference numeral 48 denotes a gas sensor. And these comprise the gas detection element 40.

Similarly, the symbol R represents the sensor area. Thus, the sensor region R is a region where a configuration for detecting gas is provided, and the inner side of the four inner walls 41c of the support substrate 41 is the sensor region R.
The symbol C represents the center point of the sensor region R. In FIG. 1, it is indicated by “+”.

  In FIG. 2, a symbol D is a folded portion of the thin film heat sensor 46. As indicated by the arrows, the 99-fold folded portion is shown. Further, 46a is an outer shape portion at the folded portion D, 46b is an inner shape portion, and 46c is a straight portion. Further, w represents the width of the thin film thermal sensor 46.

[Description of external shape: Fig. 1]
First, the outer shape will be described.
As shown in FIG. 1, the support substrate 41 has a frame shape in plan. The support substrate 41 is preferably made of a material having insulating properties, low thermal conductivity, and excellent heat resistance. 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.

  As shown in FIG. 1B, an insulating film 42 is formed on the surface of the support substrate 41. The insulating film 42 is made of, for example, silicon oxide (SiO 2). Of course, silicon nitride (Si3N4), aluminum oxide (Al2O3), magnesium oxide (MgO), tantalum oxide (Ta2O5), 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 42 bridges the insulating film provided on the upper portion of the frame shape of the support substrate 41 with a predetermined width from two opposite sides of the frame shape. It is comprised from the insulating film which makes the provided beam part 43. FIG. In the example shown in FIG. 1, the beam portion 43 is configured by only the insulating film 42 without the support substrate 41 on the back side. The beam portion 43 is a holding member on which a thin film heat sensing element or a metal thin film resistor is mounted.

  The beam portion 43 is provided in a straight line through the center point C of the sensor region R. Since the thin film thermal sensor 46, the metal thin film resistors 45a and 45b, and the gas sensor 48 are mounted on the beam 43, it is necessary to consider the overall weight balance. Considering the balance of weight balance, it is preferable that the beam portion 43 passes through the center point C of the sensor region R.

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 have strength that does not cause damage to the beam even if a gas arrives and a force generated by the pressure of the gas is applied to the beam 43 and mechanical stress is generated. is there.

When the insulating film 42 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 43, the stress characteristics of the insulating film 42 itself are 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 where the support substrate 41 is divided into two by a central beam portion 43 is a through hole 42h serving as a gas circulation portion. In the example shown in FIG. 1, since there is one beam portion 43, there are two through holes 42h. This through hole 42h is called a so-called air hole and is a portion through which gas flows.

  By having the through hole 42h, gas flows through the through hole to the upper surface side and the back surface side of the beam portion 43 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 46 and the metal thin film resistors 45a and 45b provided on the beam portion 23 and the electrode pads 44a and 44b connected to these will be described.
A thin film heat sensing element 46 and metal thin film resistors 45a and 45b are provided on the upper portion of the beam portion 43, which is a holding member constituted by the insulating film 42. Electrode pads 44 a and 44 b are provided on the insulating film 42 on the support substrate 41.
The electrode pad may be provided anywhere on the upper side of the support substrate 41. However, in the example shown in FIG. 1, the electrode pad 44a is located at 9 o'clock in the plan view of FIG. Similarly, the electrode pads 44b are provided in the 3 o'clock direction.

The thin film heat sensing element 46 is connected to the electrode pad 44a on the support substrate 41 via the metal thin film resistor 45a, and is connected to the electrode pad 44b via the metal thin film resistor 45b.
As shown in FIG. 1 (a), the thin film heat sensing element 46 is almost overlapped with the center point C, and is also overlapped with the center of the beam portion 43 in the width direction. 45a, the thin film heat sensing element 46, the metal thin film resistor 45b, and the metal pad 44b are provided linearly in this order. By adopting such a configuration, a weight-balanced arrangement structure is formed.

  A gas sensor 48 is provided on the thin film heat sensor 46. With such a configuration, the gas detector 48 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: FIGS. 1 and 2]
Next, the shape of the thin film heat detector will be described.
The thin film heat sensing element 46 has a ninety-nine fold pattern shape having a plurality of folded portions. In the example shown in FIG. 1, ten folding portions of the thin film heat sensing element are provided.

  By the way, a suitable value exists for the resistance value of the thin film heat sensing element 46. 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 46 is determined. Generally, when the pattern width of the thin film heat sensing element 46 is reduced, a large number of folded portions can be provided. 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.

  In the example shown in FIG. 1, the ninety-nine fold pattern shape of the thin film heat sensing element 46 has a folded portion in the short direction (width direction) of the beam portion 43, but it is of course not limited thereto. . 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.

[Detailed description of thin film thermal detector: FIG. 2]
The ninety-nine fold pattern shape of the thin film heat sensing element 46 will be described in more detail with reference to FIG.
More specifically, the ninety-nine fold pattern shape is formed such that the folded portion D is curved as shown in FIG. That is, in the folded portion D, the outer shape portion 46a and the inner shape portion 46b are curved in an arc shape. And the width of the pattern of the part of the folding | returning part D is formed in the width | variety substantially the same as the width | variety of the part of the linear part 46c.

Further, the cross section of the 99-fold pattern shape is formed in a trapezoidal shape as shown in FIG. That is, both end surfaces of the width w portion are formed to have the inclined surfaces 46d. The angle θ between the inclined surface 46d and the flat surface on the upper surface is, for example, 140 degrees to 150 degrees. Thus, the angle θ is formed to be a considerably obtuse angle.
This trapezoidal shape has a trapezoidal shape in all of the straight portion 46c and the folded portion D, and has a trapezoidal shape over the entire length of the ninety-nine fold pattern.

By adopting such a shape, the 99-fold pattern has no corners that are perpendicular to the folded portion D, and there are no corners that are perpendicular or acute in the cross section in terms of thickness.
Since thermal stress tends to concentrate on sharp corners, concentration of thermal stress can be prevented by eliminating such right-angled corners.

  The thermal stress generated in the thin film heat sensing element 46 affects the insulating film 42 constituting the beam portion 43 on which the thin film heat sensing element 46 is mounted. Thus, by reducing the thermal stress generated in the thin film thermal sensor 46, the distortion of the thermal stress generated in the insulating film 42 is also reduced, and damage such as the generation of cracks in the insulating film 42 can be prevented.

[Description of different cross-sectional shapes of thin-film heat sensing element: FIG. 3]
The cross-sectional shape of the thin film heat sensing element 46 is not limited to the shape shown in FIG. The shape shown in FIG. 3 is also possible. FIG. 3 is a cross-sectional view seen from the same direction as FIG.
As shown in FIG. 3, the inclined surface 46d forms a gentle curve and has a shape bulging outward. The angled portion of θ between the inclined surface 46d shown in FIG. 2B and the flat surface of the upper surface is almost attached, and forms an inclined surface having a gentle curve.
By having such a cross-sectional shape, the thin-film heat sensing element 46 has no more corners, so that the concentration of thermal stress is further eliminated.

[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 43 which is a holding member is provided with a thin film heat sensor 46 on the upper surface side, metal thin film resistors 45a and 45b connected to the thin film heat sensor 46, and a gas sensor 48 on the thin film heat sensor 46. It needs to be strong enough to hold the member. Therefore, the film thickness of the insulating film 42 constituting the beam portion 43 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 43) on which the thin film thermal detector 46 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 43 and the performance for detecting the gas are in a trade-off relationship, the film thickness of the insulating film 42 constituting the beam portion 43 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, the film thickness of the insulating film 42 may be set by, for example, repeating data to obtain data.

The same applies to the width of the portion of the beam 43 where the thin film heat sensing element 46 is mounted. If this width is wide, the strength of the beam portion is improved.
As a result of examination by the inventor, it has been found that the width of the portion of the beam portion 43 on which the thin film heat sensing element 46 is mounted and the 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 sensor 46 is mounted. Therefore, it is preferable to reduce the thickness of the insulating film 42 constituting the beam portion 43 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 44 a and the electrode pad 44 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 thermal sensor 46. 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 44a and the electrode pad 44b, and the thin film heat sensing element 46 is energized. Thereafter, when the gas arrives, the gas detector 48 reacts with the gas to generate heat, the temperature of the thin film heat detector 46 also rises, and the amount of current changes. By capturing this change in the amount of current, it is possible to know the arrival of gas.
Note that a gas detector 48 is provided above the thin film heat detector 46 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 46 generates heat due to the arrival of the gas, it is possible to know the arrival of the gas, so how to pass a current to each thin film heat sensing element and measure the current Obviously, the present invention 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 48 is provided above the thin film heat sensor 46. The gas sensor 48 functions as a catalyst, and generates heat when gas arrives to improve detection sensitivity. effective. The gas detector 48 is sintered on the thin film heat detector 46. However, the sintering temperature of the gas detector 48 is high, and is, for example, about 600 to 700 degrees 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 46 and the metal thin film resistors 45a and 45b are exposed to a high temperature, a high melting point noble metal is used.

The thin film heat detector 46, the metal thin film resistors 45a and 45b, and the electrode pads 44a and 44b 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 48 provided on the upper surface of the thin film heat sensor 46 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 48 is provided in the sensor region R so as to cover the thin film heat detector 46 on the upper side of the beam portion 43 so as to be horizontally long in the drawing.
Of course, the gas detector 48 may not be provided depending on the resistance value of the thin film heat detector 46a, the type of incoming gas, and the like.

In addition, as shown in FIG. 1B, the example in which the gas sensor 48 is provided only on the upper surface side of the thin film heat sensor 46 is shown, but the present invention is not limited to this. Since the incoming gas flows through the through-hole 42h, although not shown, it may be provided on the back side of the beam portion 43 as a holding member. That is, the beam part 43 may be wrapped from above and below by the gas sensor 48.
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 Second Embodiment: FIG. 4]
Next, the gas detection element of 2nd Embodiment is demonstrated using FIG. FIG. 4 is a plan view schematically showing the sensing element of the second embodiment. Also, parts having the same configuration described in the first embodiment are given the same reference numerals, and detailed description thereof is omitted.

Compared with the configuration of the gas detection element of the first embodiment described above, the gas detection element of the second embodiment is a beam portion in which the thin film thermal sensor and the metal thin film resistor of the first embodiment are insulating films. The second embodiment is different from the configuration provided in the upper part of the membrane structure in that it is provided in the upper part of the membrane structure which is an insulating film.
Hereinafter, the gas detection element of 2nd Embodiment is demonstrated in detail.

  In FIG. 4, 52 is an insulating film. Reference numeral 52 a denotes a membrane structure composed of the insulating film 52. 52i, 52j, 52k, 52l, 52m, and 52n are through holes. The through holes 52i to 52n are provided in the membrane structure 52a. 52kc is the center point of the through hole 52k. Similarly, 52lc is the center point of the through hole 52l, and 52mc is the center point of the through hole 52m, which is indicated by “+”. And these comprise the gas detection element 50. L1, L2, L3, and L4 indicate distances between the through holes.

  A feature of the gas detection element 50 of the second embodiment shown in FIG. 4 is that the holding member has a membrane structure. In the first embodiment described above, an insulating film is provided on the support substrate, and the beam portion is configured to bridge the frame-shaped support substrate with a predetermined width by this insulating film. In the second embodiment shown in FIG. 4, the holding member is not composed of a beam portion, but is a membrane structure 52a.

  The membrane structure 52a is configured by forming the insulating film 52 provided on the support substrate 41 with a thin film that is uniform in the direction of the sensor region R. The membrane means “film”, and the membrane structure means the structure itself. However, in the embodiment of the present invention, the sensor region of the insulating film 52 is easy to explain. The portion R is a membrane structure 52a.

A thin film heat sensing element 46 is provided in the central area including the central point C of the sensor area R on the upper part of the membrane structure 52a. Then, both ends of the thin film heat sensing element 46 are connected to a pair of electrode pads 44a, 44b on the support substrate 41 via two metal thin film resistors 45a, 45b.
As shown in FIG. 4, the center of the thin film heat sensing element 46 is placed on the center point C, and from the electrode pad 44a, the metal thin film resistor 45a, the thin film heat sensing element 46, the metal thin film resistor 45b, and the metal pad 44b in this order. It is provided linearly. By adopting such a configuration, a weight-balanced arrangement structure is formed.

[Description of shape of insulating film: FIG. 4]
Since the membrane structure 52a functions as a holding member, the membrane structure 52a needs to be strong enough to hold it. Further, it is necessary to provide strength that does not damage the membrane structure 52a even when the gas comes and the membrane structure 52a is bent by the pressure of the gas. The film thickness of the insulating film 52 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 52 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 52a is provided with a plurality of through holes in a portion where the thin film heat sensor 46, the metal thin film resistors 45a and 45b, and the gas sensor 48 are not provided. In the example shown in FIG. 4, six through holes 52i to 52n are provided.
The through holes 52i to 52n 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. 4, the adjacent through holes are, for example, the through hole 52i and the through hole 52j, the through hole 52i and the through hole 52n, the through hole 52l and the through hole 52k, and the through hole 52l and the through hole 52m. is there. Adjacent through holes are separated by the same distance.
In FIG. 4, 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 52kc and the center point 52lc of the through hole, and the distance L4 is the distance between the center point 52lc and the center point 52mc 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 52a 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. 4, the through holes 52 i to 52 n 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.
The through holes 52i to 52n shown in FIG. 4 have a circular shape. The circular shape includes an ellipse, and the corners of the polygon are chamfered smoothly. This shape 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.
The membrane structure 52a, which is a holding member, extends from the support substrate 41 and is uniformly formed. Therefore, even if mechanical stress is generated, the membrane structure 52a is dispersed throughout the film and there is no portion where stress is concentrated. For this reason, no cracks or the like occur in the membrane structure 52a.
Further, the heat generated by the thin film heat sensing element 46 is transmitted to the membrane structure 52a, but the heat transmitted to the membrane structure 52a is dispersed in four directions of the membrane (film) having a large area. For this reason, the distortion of the thermal stress generated in the membrane structure 52a is small, and the generation of cracks is further suppressed.

  In addition, since the through holes 52i to 52n are arranged at predetermined intervals and at the same distance between the centers, even if gas arrives, there is no bias in the flow rate. Therefore, the gas comes into contact with the gas sensing element 48 in a uniform state, and as a result, the combustion efficiency of the gas can be further improved.

[Explanation of Third Embodiment: FIG. 5]
Next, a gas detection element according to a third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram schematically showing the structure of the third embodiment of the thin film gas sensor of the present invention. FIG. 5A is a plan view thereof, and FIG. 5B is a cross-sectional view schematically showing a cross section taken along a cutting line ZZ ′ of FIG. Moreover, the same code | symbol is provided about the same structure already demonstrated, and detailed description is abbreviate | omitted.

  In FIG. 5, 52o, 52p, 52q, 52r, 52s, 52t indicate through holes, which are through holes provided in the membrane structure 52a. Reference numeral 60 denotes a gas detection element.

  The feature of the gas detection element 60 of the third embodiment shown in FIG. 5 is that the holding member is a beam portion and a membrane structure. The first embodiment described with reference to FIG. 1 and the second embodiment described with reference to FIG. 4 are combined, and a membrane structure 52a as a first thin film is provided on the lower side, It is the structure which has piled up the beam part 43 as a 2nd thin film on the upper side.

The through holes 52o to 52t have a regular hexagonal shape in the example shown in FIG. As shown in FIG. 5A, these six through-holes are arranged opposite to each other with the beam portion 43 interposed therebetween. It is to be noted that the adjacent through holes are spaced apart from each other by a predetermined distance, and when the sensor region R is viewed as a whole, they are generally dispersed in the same manner as in the embodiment described above.
In the third embodiment, the through hole has a regular hexagonal shape, but is not limited to a regular hexagonal shape, and an appropriate shape may be selected according to the type of gas, the usage environment, and the like.

  Since the gas detection element 60 of the third embodiment constitutes a holding member with the membrane structure 52a and the beam portion 43, the strength thereof is increased, and the resistance against bending, mechanical stress, and thermal stress of the holding member is further increased. The durability performance of the gas sensor is further improved.

  In the example illustrated in FIG. 5, the configuration in which the beam portion 43 is provided on the upper portion of the membrane structure 52 a has been described. However, although not illustrated, the membrane structure 52 a may be provided on the upper portion of the beam portion 43. . Of course, the shape of the through holes 52o to 52t 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.

40, 50, 60 Gas sensing element 41 Support substrate 41c Inner wall 42, 52 Insulating film 42h Through hole 43 Beam part 44a, 44b Electrode pad 45a, 45b Metal thin film resistor 46 Thin film heat sensing element 46a Outer part 46b Inner part 46c Linear Portion 46d Inclined surface 48 Gas sensing element 52i-52t Through hole 52a Membrane structure D Folding portion R Sensor region C Center point

Claims (7)

In the thin film type gas sensor including the inside of the support substrate having a frame shape as a sensor region, the sensor region extending from the support substrate to provide a holding member, and a thin film thermal sensor on the holding member,
The thin-film heat sensor has a ninety-nine fold shape including a folded portion having a curved shape in a plan view, and a thin-film gas sensor having a trapezoidal cross section.   2. The thin film gas sensor according to claim 1, wherein the cross section of the thin film heat sensing element forms the trapezoidal shape by forming both end faces of a sloped surface.   The thin film gas sensor according to claim 1, wherein the holding member has a membrane structure. The membrane structure has a plurality of through holes,
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 4, wherein the adjacent through holes have the same center-to-center distance.   5. The thin film gas sensor according to claim 4, wherein the through hole is circular or polygonal. 7. The thin film gas sensor according to claim 1, wherein the holding member has a laminated structure in which a plurality of films having different stress characteristics are laminated.

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