阅读说明：本技术 热式传感器装置 (Thermal sensor device ) 是由 中野洋 松本昌大 小野瀬保夫 太田和宏 于 2020-06-09 设计创作，主要内容包括：本发明提供能够通过抑制发热电阻体的热膨胀引起的塑性变形而减小发热电阻体的电阻变化,维持长期测定精度的热式传感器装置。在包括形成有开口部(2a)的基片(2)和具有以桥接开口部(2a)的方式层叠下层层叠膜(3a)、发热电阻体(5)和上层层叠膜(3b)的结构的膜片(4)的热式传感器装置(1)中,下层层叠膜(3a)的膜厚大于上层层叠膜(3b)的膜厚,下层层叠膜(3a)的平均热膨胀系数大于上层层叠膜(3b)的平均热膨胀系数,下层层叠膜(3a)由热膨胀系数不同的多个膜构成,所述多个膜中的热膨胀系数最大的膜形成在与下层层叠膜(3a)的厚度中心相比的下侧。(The invention provides a thermal sensor device capable of reducing resistance change of a heating resistor by suppressing plastic deformation caused by thermal expansion of the heating resistor, and maintaining long-term measurement accuracy. In a thermal sensor device (1) including a substrate (2) having an opening (2a) formed therein and a diaphragm (4) having a structure in which a lower-layer laminated film (3a), a heating resistor (5), and an upper-layer laminated film (3b) are laminated so as to bridge the opening (2a), the thickness of the lower-layer laminated film (3a) is larger than the thickness of the upper-layer laminated film (3b), the average thermal expansion coefficient of the lower-layer laminated film (3a) is larger than the average thermal expansion coefficient of the upper-layer laminated film (3b), the lower-layer laminated film (3a) is composed of a plurality of films having different thermal expansion coefficients, and the film having the largest thermal expansion coefficient among the plurality of films is formed on the lower side than the thickness center of the lower-layer laminated film (3 a).)

1. A thermal sensor device comprising a substrate having an opening formed therein and a diaphragm having a structure in which a lower-layer laminated film, a heating resistor, and an upper-layer laminated film are laminated so as to bridge the opening, characterized in that:

the film thickness of the lower layer laminated film is larger than that of the upper layer laminated film,

the average thermal expansion coefficient of the lower layer laminated film is larger than that of the upper layer laminated film,

the lower laminated film is composed of a plurality of films having different thermal expansion coefficients,

the film having the largest thermal expansion coefficient among the plurality of films is formed on the lower side than the thickness center of the underlying laminated film.

2. Thermal sensor apparatus according to claim 1, characterized in that:

silicon oxide films and silicon nitride films are alternately formed on the lower layer laminated film,

the film thickness of the silicon oxide film of the lowermost layer of the lower-layer laminated film is smaller than the film thickness of the silicon oxide film of the uppermost layer of the lower-layer laminated film.

3. Thermal sensor apparatus according to claim 2, characterized in that:

at least 2 silicon nitride films are formed on the lower layer laminated film,

the film thickness of the silicon oxide film sandwiched between the 2 silicon nitride films of the lower laminated film is smaller than the film thickness of the silicon oxide film of the uppermost layer of the lower laminated film.

4. Thermal sensor device according to any of claims 1 to 3, characterized in that:

the upper layer laminated film is composed of a silicon oxide film and a silicon nitride film,

the film thickness of the silicon nitride film included in the upper layer laminated film is smaller than the film thickness of the silicon nitride film included in the lower layer laminated film.

5. Thermal sensor apparatus according to claim 3, characterized in that:

the film thickness of the silicon nitride film at the lowermost layer among the plurality of silicon nitride films included in the lower-layer laminated film is the largest.

Technical Field

The present invention relates to a thermal sensor device in which a heating resistor is formed on a diaphragm.

Background

As a background art in this field, there is patent document 1. Patent document 1 describes an airflow sensor capable of increasing the mechanical strength by increasing the thickness of a lower thin film and an upper thin film that hold a heating resistor, and reducing the overall warpage. The airflow sensor includes a film heat generating portion (hereinafter referred to as a "diaphragm") having a structure in which a lower film, a heating layer, and an upper film are stacked so as to bridge a cavity portion formed in a silicon substrate. The lower film and the upper film are laminated so that the lower film and the upper film sandwich the heating layer and have a symmetrical structure, respectively, in a structure in which the compressive stress film and the tensile stress film are combined. The compressive stress film is composed of a silicon oxide film having good adhesion, and the tensile stress film is composed of a silicon nitride film having good moisture resistance. By making the lower film and the upper film have a symmetrical structure, the warping moment can be eliminated and the warping of the entire diaphragm can be suppressed. Thus, the airflow sensor of patent document 1 can increase the thicknesses of the lower thin film and the upper thin film, thereby improving the mechanical strength of the diaphragm.

Further, patent document 2 is a background art in the present technical field. In patent document 2, a film having a compressive stress and a film having a tensile stress are alternately arranged for the insulating film at the lower layer of the heating resistor, and 2 or more films having a tensile stress are arranged. Thereby reducing the deflection of the diaphragm.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 11-271123

Patent document 2: japanese laid-open patent publication No. 2010-133897

Disclosure of Invention

Problems to be solved by the invention

In order to detect a slight change in the flow, concentration, or the like of the gas, it is necessary to increase the temperature of the heating resistor and to improve the detection sensitivity. For example, in the airflow sensor, the heating resistor is heated to a high temperature of about 200 ℃. The heating resistor is heated to about 500 ℃ for measuring the gas concentration such as humidity.

When the heating resistor is heated, the temperature of the diaphragm rises and thermal expansion occurs. If the heating resistor is deformed by thermal expansion and this state is maintained for a long period of time, the heating resistor is plastically deformed, and the resistance value changes. The heating temperature changes due to the change in the resistance value, and an error occurs in the measurement value.

In patent documents 1 and 2, although warpage of the diaphragm at room temperature can be reduced, expansion of the diaphragm due to heating of the heating resistor occurs. The influence of this expansion on the heating resistor is not considered and is not considered sufficiently.

In order to reduce the resistance change of the heating resistor caused by the long-term high-temperature state, it is effective to suppress the expansion-reducing deformation of the heating resistor. In order to reduce the strain due to the temperature change, it is preferable to cover the heating resistor with a silicon oxide film having a small thermal expansion coefficient, and to use a silicon nitride film having a large thermal expansion coefficient as little as possible. However, with such a configuration, the difference in thermal expansion coefficient between the diaphragm and the silicon substrate holding the diaphragm becomes large, and the diaphragm is deformed due to wrinkles. When the diaphragm is deformed, cracks are easily generated in the diaphragm to deteriorate the mechanical reliability.

The present invention has been made in view of the above problems, and an object thereof is to provide a thermal sensor device capable of reducing a resistance change of a heating resistor by suppressing plastic deformation caused by thermal expansion of the heating resistor, and maintaining measurement accuracy for a long period of time.

Means for solving the problems

In order to achieve the above object, the present invention is a thermal sensor device including a substrate having an opening formed therein and a diaphragm having a structure in which a lower layer laminated film, a heating resistor, and an upper layer laminated film are laminated so as to bridge the opening, wherein a film thickness of the lower layer laminated film is larger than a film thickness of the upper layer laminated film, an average thermal expansion coefficient of the lower layer laminated film is larger than an average thermal expansion coefficient of the upper layer laminated film, the lower layer laminated film is composed of a plurality of films having different thermal expansion coefficients, and a film having a largest thermal expansion coefficient among the plurality of films is formed on a lower side than a thickness center of the lower layer laminated film.

According to the present invention configured as described above, since the film thickness of the lower-layer laminated film is larger than the film thickness of the upper-layer laminated film, the heating resistor is disposed on the upper layer side with respect to the thickness center of the diaphragm. Further, since the average thermal expansion coefficient of the lower laminated film is larger than that of the upper laminated film, the film is bent and deformed when the heating resistor is heated. Therefore, not only the extension deformation due to the thermal expansion of the diaphragm but also the compression deformation due to the bending deformation of the diaphragm occurs on the upper layer side than the thickness center of the diaphragm. As a result, the extension strain of the heating resistor disposed on the upper layer side with respect to the thickness center of the diaphragm is reduced by the compression strain caused by the bending deformation of the diaphragm. With the above-described operation, plastic deformation due to thermal expansion of the heating resistor is suppressed, and the resistance change of the heating resistor is reduced, so that the measurement accuracy of the thermal sensor device can be maintained for a long period of time.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the thermal sensor device of the present invention, it is possible to reduce the resistance change of the heating resistor by suppressing the plastic deformation due to the thermal expansion of the heating resistor, and maintain the long-term measurement accuracy.

Drawings

Fig. 1 is a top view of one embodiment of a sensor element used in the thermal sensor device of the present invention.

Fig. 2 is a sectional view showing the X-X' section of fig. 1.

Fig. 3 is a circuit diagram showing an embodiment of a drive circuit (circuit configuration) of the thermal sensor device of the present invention.

Fig. 4 is a diagram showing the warp shape in the case where the film sheet is stretchable and the case where the film sheet is compressible.

Fig. 5 is an enlarged cross-sectional view of a heat generating portion in one embodiment of the sensor element of the present invention.

Fig. 6 is a diagram showing deformation in a cross-sectional direction of a heat generating portion in one embodiment of the sensor element of the present invention.

Fig. 7 is a cross-sectional view of one embodiment of a sensor element for use in the thermal sensor device of the present invention.

Fig. 8 is a cross-sectional view of one embodiment of a sensor element for use in the thermal sensor device of the present invention.

Fig. 9 is a cross-sectional view of one embodiment of a sensor element for use in the thermal sensor device of the present invention.

Detailed Description

The following describes embodiments of the present invention. Each embodiment is described as an example of the content of flow measurement of intake air flowing through an intake passage attached to an intake passage of an engine, and can also be applied to a gas sensor that measures humidity and hydrogen concentration of gas from changes in heat radiation amount and temperature of a heat generating resistor.

Example 1

The following describes example 1 of the present invention. The structure of the sensor element 1 of the thermal flowmeter according to the present embodiment will be described with reference to fig. 1. The substrate 2 of the sensor element 1 is made of a material having good thermal conductivity such as silicon. Then, a lower layer laminated film 3a and an upper layer laminated film 3b are formed on the substrate 2. The heating resistor 5 is formed so as to be sandwiched between the lower-layer laminated film 3a and the upper-layer laminated film 3b, a heating temperature sensor 7 for detecting the heating temperature of the heating resistor 5 is formed around the heating resistor 5, and upstream-side temperature sensors 8a and 8b and downstream-side temperature sensors 9a and 9b are formed on both sides of the heating temperature sensor 7. The upstream temperature sensors 8a and 8b are disposed on the upstream side of the heating resistor 5 with respect to the airflow of the airflow 6, and the downstream temperature sensors 9a and 9b are disposed on the downstream side of the heating resistor 5 with respect to the flow of the airflow 6. Further, temperature sensitive resistors 10, 11, and 12 whose resistance value changes in accordance with the temperature of the air flow 6 are disposed on the lower layer laminated film 3 a. The outermost surface of the sensor element 1 is covered with the upper layer laminate film 3 b. The upper layer laminated film 3b functions as a protective film in addition to electrical insulation. Further, a part of the substrate 2 is removed from the back surface by etching or the like, thereby forming a membrane 4 as a thin film heat generating portion.

In the above configuration, the temperature of the heating resistor 5 is detected by the heating temperature sensor 7, the heating control is performed so as to raise the temperature of the air flow 6 to a constant temperature, and the air flow rate is detected from the temperature difference between the upstream side temperature sensors 8a and 8b and the downstream side temperature sensors 9a and 9b caused by the air flow 6.

The heating resistor body 5, the heating temperature sensor 7, the upstream side temperature sensors 8a and 8b, the downstream side temperature sensors 9a and 9b, and the temperature sensitive resistor bodies 10, 11, and 12 are formed of a material whose resistance value changes with temperature. For example, it may be made of a metal material having a high temperature coefficient of resistance, such as platinum, molybdenum, tungsten, or nickel alloy. The lower-layer laminated film 3a and the upper-layer laminated film 3b are made of silicon oxide (SiO)₂) Or silicon nitride (Si)₃N₄) The film is formed in a thickness of about 2 μm to obtain a thermal insulation effect.

At the end of the sensor element 1, an electrode pad 13 is provided, on which a plurality of electrodes for connecting the respective resistors constituting the heating resistor 5, the heating temperature sensor 7, the upstream side temperature sensors 8a and 8b, the downstream side temperature sensors 9a and 9b, and the temperature sensitive resistors 10, 11, and 12 to a drive/detection circuit are formed. In addition, the electrode pad 13 is formed of aluminum or the like. Further, wires for connecting the heating resistor 5, the temperature sensors, and the electrode pads 13 are formed.

Fig. 2 shows a cross-sectional structure of the sensor element 1. A lower layer laminated film 3a is formed on the substrate 2. The lower layer laminated film 3a has a structure in which a silicon oxide film and a silicon nitride film are alternately laminated. A silicon oxide film 14a, a silicon nitride film 15a, and a silicon oxide film 14c, which are obtained by thermally oxidizing a Si substrate, are formed in this order from the lower layer. These silicon oxide films 14a and 14c and the silicon nitride film 15a can be formed by a CVD method. A heating resistor 5, a heating temperature sensor 7, upstream side temperature sensors 8a and 8b, and downstream side temperature sensors 9a and 9b are formed on the lower layer laminated film 3 a. An upper layer laminated film 3b is formed on these upper layers. The upper layer laminated film is formed with a silicon oxide film 14d, a silicon nitride film 15c, and a silicon oxide film 14e in this order from below. The silicon oxide films 14d to 14e and the silicon nitride film 15c can be formed by a plasma CVD method.

In the present embodiment, a silicon oxide film and a silicon nitride film having different thermal expansion coefficients are used as the materials of the lower layer laminated film 3a, but the present invention is not limited to these materials. For example, the thermal expansion coefficient of the silicon oxide film is 0.5X 10^-6(/ deg.C), the thermal expansion coefficient of the silicon nitride film was 3.6X 10^-6(v. degree. C.) or so. In addition to these films, materials having different thermal expansion coefficients can be used, and for example, a silicon nitride film such as aluminum nitride can be used instead. The coefficient of thermal expansion of aluminum nitride is 5.7X 10^-6(v. degree. C.) or so.

In the present embodiment, a silicon oxide film and a silicon nitride film are used as the material of the upper layer laminated film 3b, but the present invention is not limited to these films. In the practice of the present invention, the upper laminated film 3b may have a smaller average thermal expansion coefficient than the lower laminated film 3 a. Therefore, it is not necessary to use 2 kinds of seed films such as a silicon oxide film and a silicon nitride film, and only the silicon oxide film may be used. The average thermal expansion coefficient is defined as a weighted average of the film thicknesses of the thermal expansion coefficients of the respective films.

The specific thicknesses of the silicon oxide film and the silicon nitride film described above will be described later together with the operation and effect of the present invention.

Next, a driving/detecting circuit of the sensor element 1 will be described.

As shown in fig. 3, a bridge circuit is configured in which a series circuit including a heating temperature sensor 7 and a temperature sensing resistor 10 whose resistance value varies with the temperature of the heating resistor 5 and a series circuit including a temperature sensing resistor 11 and a temperature sensing resistor 12 are connected in parallel, and a reference voltage Vref is applied to each series circuit. The intermediate voltage of these series circuits is extracted and connected to an amplifier 16. The output of amplifier 16 is connected to the base of transistor 17. The transistor 17 has a collector connected to the power supply VB and an emitter connected to the heating resistor 5, thereby constituting a feedback circuit. Thus, the temperature Th of the heating resistor 5 is controlled to have a high temperature Δ Th (Th — Ta) with respect to the temperature Ta of the air flow 6.

A bridge circuit is formed by connecting a series circuit of the upstream side temperature sensor 8a and the downstream side temperature sensor 9a in parallel with a series circuit of the downstream side temperature sensor 9b and the upstream side temperature sensor 8b, and the reference voltage Vref is applied to the bridge circuit. When a temperature difference occurs between the upstream side temperature sensors 8a, 8b and the downstream side temperature sensors 9a, 9b due to the air flow, the resistance balance of the bridge circuit changes to generate a differential voltage. The output Vout corresponding to the air flow rate is obtained by detecting the difference voltage by the amplifier 18.

Hereinafter, a change in the resistance of the heating resistor 5 in the thermal sensor device as described above will be described. The resistance change occurs not only in the heating resistor 5 but also in resistors formed on the diaphragm 4, such as the heating temperature sensor 7, the upstream side temperature sensors 8a and 8b, and the downstream side temperature sensors 9a and 9 b.

In particular, the heating resistor 5 and the heating temperature sensor 7, which have a high temperature, have a large resistance change, and the effect obtained by the present invention is excellent.

The experiments of the inventor clearly show that: in order to reduce the resistance change of the heating resistor 5, it is preferable to use films having a small thermal expansion coefficient for the lower layer laminated film 3a and the upper layer laminated film 3b forming the heating resistor 5. That is, the film thickness of the silicon oxide film needs to be increased and the film thickness of the silicon nitride film needs to be decreased.

However, when the diaphragm 4 is formed of silicon oxide, the diaphragm 4 becomes irregular. Fig. 4 shows the warp shape in the case where the film 4 is stretchable and the case where it is compressible.

Fig. 4 (a) is a cross-sectional view conceptually showing a deformation of a sensor element used in the thermal sensor device, and is a view of a cross-sectional shape of the diaphragm 4 in a case where a film thickness is not set so that a resultant stress of a laminated film forming the diaphragm 4 becomes stretchability. In fig. 4 (a), a silicon oxide film and a silicon nitride film are stacked to form the membrane 4. The film thicknesses are set so that the resultant stress of the silicon oxide film and the silicon nitride film becomes tensile. In this case, as shown in fig. 4 (a), the diaphragm 4 can be formed in a flat shape and can be manufactured satisfactorily.

Fig. 4 (B) is a diagram showing the cross-sectional shape of the membrane sheet 4 in the case where the membrane thickness is set so that the resultant stress of the laminated film forming the membrane sheet 4 becomes compressive. In fig. 4 (B), the thicknesses of the silicon oxide film and the silicon nitride film are set so that the resultant stress becomes compressive. When the compressibility of the membrane 4 is achieved by increasing the ratio of the silicon oxide film, wrinkles are generated in the membrane 4 as shown in the figure, and the membrane 4 is deformed.

As described above, since the film structure of the diaphragm 4 needs to be formed to have stretchability, the silicon nitride film needs to have a predetermined thickness so as to obtain tensile stress.

As described above, since the silicon nitride film needs to be set to a predetermined thickness, a limitation is imposed on the reduction of the thermal expansion coefficient of the diaphragm 4. The present invention is intended to satisfy this restriction and suppress the deformation of the heating resistor 5 due to the expansion of the diaphragm 4. According to the present invention, expansion of the heating resistor 5 can be suppressed without changing the film thickness ratio of the silicon nitride film and the silicon oxide film of the entire diaphragm 4. Specific examples are described below.

Fig. 5 is a cross-sectional view showing deformation when the heating resistor 5 of the sensor element 1 in fig. 2 is heated. The lower layer laminated film 3a is formed with a silicon oxide film 14a, a silicon nitride film 15a, and a silicon oxide film 14c in this order from the lower layer. Here, in the lower-layer laminated film 3a, the film thickness T1 of the silicon oxide film 14a on the lower layer side and the film thickness T3 of the silicon oxide film on the upper layer side are formed so as to be T1 < T3. Thereby, the silicon nitride film 15a having a large thermal expansion coefficient is disposed further below. That is, the lower laminated film 3a is composed of silicon oxide films 14a and 14c and a silicon nitride film 15a having different thermal expansion coefficients, and the silicon nitride film 15a having the largest thermal expansion coefficient among these films is formed on the lower layer side from the thickness center of the lower laminated film 3 a. With this configuration, when the heating resistor 5 is heated, the lower layer side of the lower laminated film 3a expands greatly, and the bending moment acting on the diaphragm 4 increases, so that the bending shape generated in the diaphragm 4 can be greatly changed.

The effect of increasing the bending strain will be described below. Fig. 6 shows the deformation of the inside of the film 4 which occurs when the heating resistor 5 is heated in the structure of the present invention. When the heating resistor 5 is heated, the deformation epsilon s occurs according to the average thermal expansion coefficient of the entire film constituting the membrane 4. In addition, the difference in thermal expansion coefficient between the upper layer side and the lower layer side due to the asymmetry of the film structure causes the bending strain ε b. The inner periphery side of the bending deformation is compressed and the outer periphery side is extended. Since the heating resistor 5 is disposed on the inner peripheral side of the bending deformation, i.e., on the upper layer side of the thickness center of the diaphragm 4, the deformation due to the bending deformation ∈ b acts as the compression deformation ∈ bm. The strain ε sm of the heating element is a value obtained by canceling the extension strain ε s by the compression strain ε bm. This reduces the extension strain of the heating element, suppresses the expansion and contraction of the heating element due to a change in temperature, and reduces the change in resistance of the heating element due to the expansion and contraction.

In the present embodiment, in the thermal sensor device 1 including the substrate 2 having the opening 2a formed therein and the diaphragm 4 having a structure in which the lower laminated film 3a, the heating resistor 5, and the upper laminated film 3b are laminated so as to bridge the opening 2a, the lower laminated film 3a has a film thickness larger than that of the upper laminated film 3b, the lower laminated film 3a has an average thermal expansion coefficient larger than that of the upper laminated film 3b, the lower laminated film 3a is formed of a plurality of films 14a, 15a, and 14c having different thermal expansion coefficients, and the film 15a having the largest thermal expansion coefficient among the plurality of films 14a, 15a, and 14c is formed below the thickness center of the lower laminated film 3 a.

According to the present embodiment configured as described above, since the thickness of the lower laminated film 3a is larger than that of the upper laminated film 3b, the heating resistor 5 is disposed on the upper layer side with respect to the thickness center of the diaphragm 4. Since the average thermal expansion coefficient of the lower-layer laminated film 3a is larger than that of the upper-layer laminated film 3b, the diaphragm 4 is deformed by bending when the heating resistor 5 is heated. Therefore, not only the extension deformation ∈ s due to the thermal expansion of the diaphragm 4 but also the compression deformation ∈ bm due to the bending deformation of the diaphragm 4 occurs on the upper layer side of the thickness center of the diaphragm 4. As a result, the extension strain of the heating resistor 5 disposed on the upper layer side with respect to the thickness center of the diaphragm 4 is reduced by the compression strain ∈ bm caused by the bending deformation of the diaphragm 4. With the above-described operation, plastic deformation due to thermal expansion of the heating resistor 5 is suppressed, and the resistance change of the heating resistor 5 is reduced, so that the measurement accuracy of the thermal sensor device 1 can be maintained for a long period of time.

In addition, silicon oxide films and silicon nitride films are alternately formed in the lower stacked film 3a, and the film thickness T1 of the silicon oxide film 14a in the lowermost layer of the lower stacked film 3a is smaller than the film thickness T3 of the silicon oxide film 14c in the uppermost layer of the lower stacked film 3 a. Thus, the silicon nitride film 15a having a large thermal expansion coefficient is formed closer to the lower layer side than the thickness center of the lower layer laminated film 3 a. With this configuration, when the heating resistor 5 is heated, the lower layer side of the lower laminated film 3a expands greatly, and the bending moment acting on the diaphragm 4 increases, so that the bending shape generated in the diaphragm 4 can be greatly changed.

The upper laminated film 3b is composed of a silicon oxide film and a silicon nitride film, and the film thickness of the silicon nitride film 15c included in the upper laminated film 3b is smaller than the film thickness of the silicon nitride film 15a included in the lower laminated film 3 a. This makes it possible to reduce the thermal expansion coefficient of the upper layer laminated film 3b and increase the thermal expansion coefficient of the lower layer side of the diaphragm 4. With this configuration, when the heating resistor 5 is heated, the expansion of the lower layer side of the lower layer laminated film 3a increases, and the bending moment increases, whereby the diaphragm 4 can be subjected to excessive bending deformation.

Further, since the heating resistor 5 is disposed between the 2 silicon nitride films 15c and 15a, oxidation of the heating resistor 5 can be prevented.

Example 2

The following describes embodiment 2 of the present invention. The same components as those in embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, a structure in which a plurality of silicon nitride films are provided on the lower-layer laminated film 3a will be described. Fig. 7 shows a cross-sectional structure of the sensor element 1. A lower layer laminated film 3a is formed on the substrate 2. The lower layer laminated film 3a has a structure in which a silicon oxide film and a silicon nitride film are alternately laminated. A silicon oxide film 14a, a silicon nitride film 15a, a silicon oxide film 14b, a silicon nitride film 15b, and a silicon oxide film 14c, which are thermally oxidized from a Si substrate, are formed in this order from the lower layer. These silicon oxide films 14a to 14c and silicon nitride films 15a and 15b can be formed by a CVD method. A heating resistor 5, a heating temperature sensor 7, upstream side temperature sensors 8a and 8b, and downstream side temperature sensors 9a and 9b are formed on the lower layer laminated film 3 a. An upper layer laminated film 3b is formed on these upper layers. The upper layer laminated film 3b is formed with a silicon oxide film 14d, a silicon nitride film 15c, and a silicon oxide film 14e in this order from below. These silicon oxide films 14d and 14e and the silicon nitride film 15c can be formed by a plasma CVD method.

In the present embodiment, a silicon oxide film and a silicon nitride film are used as the material of the upper layer laminated film 3b, but the present invention is not limited to these films. In the present embodiment, the average thermal expansion coefficient of the upper laminated film 3b does not exceed the average thermal expansion coefficient of the lower laminated film 3 a. Therefore, it is not necessary to use 2 kinds of seed films such as a silicon oxide film and a silicon nitride film, and only the silicon oxide film may be used.

In this embodiment, a silicon oxide film and a silicon nitride film are used for the lower layer film 3a, and materials having different thermal expansion coefficients can be used in addition to these films. For example, a silicon nitride film can be replaced with aluminum nitride.

Fig. 7 is a cross-sectional view showing deformation when the heating resistor 5 of the sensor element 1 in fig. 5 is heated. Here, in the lower-layer laminated film 3a, the film thickness T1 of the silicon oxide film 14a in the lowermost layer and the film thickness T3 of the silicon oxide film in the uppermost layer are formed so as to be T1 < T3. This allows the silicon nitride films 15a and 15b having a large thermal expansion coefficient to be formed closer to the lower layer side than the thickness center of the lower layer laminated film 3 a. With this configuration, when the heating resistor 5 is heated, the lower layer side of the lower laminated film 3a expands greatly, and the bending moment acting on the diaphragm 4 increases, so that the bending shape generated in the diaphragm 4 can be greatly changed.

The following describes a more effective configuration in the present embodiment.

In the lower-layer laminated film 3a shown in fig. 8, the silicon oxide film 14b sandwiched by the silicon nitride films is formed so as to have a film thickness of T2, which is T3 > T2. Accordingly, the silicon nitride film 15b is formed on the lower layer side, and when the heating resistor 5 is heated, the lower layer side of the lower laminated film 3a is greatly expanded, and the bending moment acting on the diaphragm 4 is increased, so that the bending shape generated in the diaphragm 4 can be greatly changed.

Next, fig. 9 shows a structure in which the effects of the present invention are further obtained with respect to a plurality of silicon nitride films included in the lower-layer laminated film 3a in this embodiment. In fig. 9, the silicon nitride film 15a in the lowermost layer among the plurality of silicon nitride films 15a and 15b included in the lower-layer laminated film is formed thickest. That is, the silicon nitride film 15b is made thinner by the amount of the silicon nitride film 15a that is made thicker. This makes it possible to increase the expansion of the lower layer side when heating the heating resistor 5 without changing the thickness of the silicon nitride film as a whole. With this configuration, when the heating resistor 5 is heated, the lower layer side of the lower laminated film 3a expands greatly, and the bending moment acting on the diaphragm 4 increases, so that the bending shape generated in the diaphragm 4 can be greatly changed.

Next, a structure in which the silicon nitride film included in the upper layer laminated film 3b further achieves the effects of the present invention will be described. In fig. 9, the upper laminated film 3b is composed of silicon oxide films 14d and 14e and a silicon nitride film 15c, and the silicon nitride film 15c included in the upper laminated film 3b is formed thinner than the silicon nitride films 15a and 15b included in the lower laminated film 3 a. This makes it possible to reduce the thermal expansion coefficient of the upper layer laminated film 3b and increase the thermal expansion coefficient of the lower layer side of the diaphragm 4. With this configuration, when the heating resistor 5 is heated, the expansion on the lower layer side of the lower layer laminated film 3a increases, and the bending moment increases, so that the diaphragm 4 can be subjected to a larger bending strain.

In this embodiment, a structure in which 2 layers are formed of a silicon nitride film included in the lower-layer laminated film 3a is described, but the effects of the present invention can be obtained also with a structure in which 3 layers are formed. When any one of the plurality of silicon nitride films included in the lower-layer laminated film 3a is formed to be extremely thin, the thin silicon nitride film has little influence on the expansion of the entire diaphragm. Therefore, such a significantly thin film (for example, about 20nm, or 1/10 or less of the total film thickness of the entire silicon nitride) is ignored.

In this embodiment, at least 2 silicon nitride films may be formed on the lower laminated film 3a, and the film thickness T2 of the silicon oxide film 14b sandwiched by the 2 silicon nitride films 15a and 15b of the lower laminated film may be smaller than the film thickness T3 of the silicon oxide film 14c at the uppermost layer of the lower laminated film 3 a.

According to the present embodiment configured as described above, the silicon nitride film 15b is formed on the lower layer side, and when the heating resistor 5 is heated, the lower layer side of the lower layer laminated film 3a is greatly expanded, and the bending moment acting on the diaphragm 4 is increased, so that the bending shape generated in the diaphragm 4 can be greatly changed.

In the modification of the present embodiment (shown in fig. 9), the film thickness Tn1 of the silicon nitride film 15a in the lowermost layer among the plurality of silicon nitride films 15a and 15b included in the lower-layer laminated film 3a is the largest. This makes it possible to increase the expansion of the lower layer side when heating the heat generating resistor 5 without changing the combined thickness Tn1+ Tn2 of the silicon nitride films 15a and 15b of the entire film. With this configuration, when the heating resistor 5 is heated, the lower layer side of the lower laminated film 3a expands greatly, and the bending moment acting on the diaphragm 4 increases, so that the bending shape generated in the diaphragm 4 can be greatly changed.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible. For example, the above-described embodiments are described in detail to explain the present invention easily and clearly, but the present invention is not necessarily limited to include all the structures described. In addition, the structure of another embodiment can be added to the structure of one embodiment, and a part of the structure of one embodiment can be deleted or substituted for a part of the structure of another embodiment.

Description of reference numerals

1 … sensor element (thermal sensor device); 2 … a substrate; 2a … opening; 3a … lower layer laminated film; 3b … upper laminated film; 4 … a membrane sheet; 5 … heating resistor body; 6 … air flow; 7 … heating the temperature sensor; 8a, 8b … upstream side temperature sensors; 9a, 9b … downstream side temperature sensors; 10. 11, 12 … temperature sensing resistor body; 13 … electrode pads; 14a, 14b, 14c, 14d, 14e … silicon oxide film; 15a, 15b, 15c … silicon nitride film; a 16 … amplifier; a 17 … transistor; 18 … amplifier.