Heat sensor device

Abstract

Heat sensor device, which includes: a substrate with an opening; and a membrane with a structure in which a lower stacked film, a heat-generating resistor and an upper stacked film are stacked in such a way as to bridge the opening, where the film thickness of the lower stacked film is greater than the film thickness of the upper stacked film, and the average coefficient of thermal expansion of the lower stacked film is greater than the average coefficient of thermal expansion of the upper stacked film. The lower stacked film contains several films with different coefficients of thermal expansion, and a film with the largest coefficient of thermal expansion among the multiple films below a thickness center of the lower stacked film is formed.

Description

Technical field

[0001] The present invention relates to a heat sensor device in which a heat-generating resistance is formed on a membrane. Technical background

[0002] As a technical background to this field, there is PTL 1. PTL 1 discloses an air flow sensor that can increase the film thicknesses of a lower thin film and an upper thin film, which provide heat-generating resistance, to increase mechanical strength and reduce overall warping. This air flow sensor has a heat-generating thin film section (hereinafter referred to as a membrane) with a structure in which a lower thin film, a heating layer, and an upper thin film are stacked to bridge a cavity section formed in a silicon substrate. Both the lower thin film and the upper thin film have a configuration in which a compressive stress film and a tensile stress film are combined, with the lower thin film and the upper thin film being stacked to form a symmetrical structure with the heating layer inserted between them.The compressive stress film consists of a silicon oxide film with good adhesion, while the tensile stress film consists of a silicon nitride film with good moisture resistance. By forming the lower and upper thin films in a symmetrical structure, it is possible to eliminate the warping moment and suppress warping of the entire membrane. As a result, in the PTL 1 air flow sensor, the film thicknesses of the lower and upper thin films can be increased, thereby enhancing the mechanical strength of the membrane.

[0003] As a technical background to this field, there is the PTL 2. In the PTL 2, a film with compressive stress and a film with tensile stress are arranged alternately on an insulating film under a heat-generating resistor, with two or more films being arranged with a tensile stress film. This reduces the deflection of the membrane. List of oppositions patent literature PTL 1: JP H11-271123 A PTL 2: JP 2010-133897 A Summary of the invention: Technical problem

[0004] To detect minute changes in the flow and concentration of a gas, it is necessary to increase the temperature of the heat-generating resistor to improve detection sensitivity. In an air flow sensor, for example, the heat-generating resistor is heated to a high temperature of approximately 200 °C. To measure a gas concentration, such as humidity, the heat-generating resistor is heated to approximately 500 °C.

[0005] When the heat-generating resistor is heated, the temperature of the diaphragm rises, causing thermal expansion. This thermal expansion creates stress, and if this condition persists for a long time, the heat-generating resistor undergoes plastic deformation, changing its resistance value. This change in resistance value alters the heating temperature, introducing an error into the measured value.

[0006] In PTLs 1 and 2, it is possible to reduce the membrane distortion at room temperature, but the membrane expands due to the heating of the heat-generating resistor. The influence of this expansion on the heat-generating resistor was not considered, and the consideration given was insufficient.

[0007] To reduce the resistance change of the heat-generating resistor caused by prolonged exposure to high temperatures, it is effective to suppress the expansion of the resistor and thus reduce stress. To minimize stress due to temperature changes, it is desirable for the heat-generating resistor to be covered with a silicon oxide film, which has a low coefficient of thermal expansion, and to avoid using a silicon nitride film, which has a high coefficient of thermal expansion, as much as possible. However, with such a configuration, the difference in the coefficient of thermal expansion between the silicon substrate supporting the membrane increases, leading to wrinkles and deformation of the membrane.If the membrane is deformed, it is likely that cracks will occur in the membrane, impairing its mechanical reliability.

[0008] The present invention has been made in consideration of the above problems, the object of which is to provide a heat sensor device which can maintain measurement accuracy over a long period of time by suppressing plastic deformation due to thermal expansion of a heat-generating resistor and reducing resistance change of the heat-generating resistor. Solution to the problem

[0009] To solve the above problem, the present invention provides a heat sensor device comprising: a substrate with an opening; and a membrane with a structure in which a lower stacked film, a heat-generating resistor, and an upper stacked film are stacked such that they bridge the opening, wherein the thickness of the lower stacked film is greater than the thickness of the upper stacked film, the average coefficient of thermal expansion of the lower stacked film is greater than the average coefficient of thermal expansion of the upper stacked film, the lower stacked film contains several films with different coefficients of thermal expansion, and a film with the highest coefficient of thermal expansion among the several films is formed below the midpoint of the thickness of the lower stacked film.

[0010] According to the present invention, configured as described above, the heat-generating resistor is located on the side of the upper layer at the midpoint of the membrane's thickness, because the film thickness of the lower stacked film is greater than that of the upper stacked film. Furthermore, because the average coefficient of thermal expansion of the lower stacked film is greater than that of the upper stacked film, bending deformation occurs in the membrane when the heat-generating resistor is heated. Therefore, in addition to the tensile stress due to thermal expansion, a compressive stress due to bending deformation of the membrane also occurs on the side of the upper layer at the midpoint of the membrane's thickness.As a result, the tensile stress on the heat-generating resistor, located on the side of the upper layer at the midpoint of the membrane's thickness, is reduced by the compressive stress due to the membrane's bending deformation. This effect suppresses the plastic deformation caused by thermal expansion of the heat-generating resistor and reduces its resistance change, thus maintaining the measurement accuracy of the heat sensor device over a long period. Advantageous effects of the invention

[0011] According to the heat sensor device of the present invention, it is possible to maintain the measurement accuracy over a long period of time by suppressing the plastic deformation due to the thermal expansion of the heat-generating resistor and by reducing a change in the resistance of the heat-generating resistor. Brief description of the drawings Fig. Figure 1 is a top view according to an embodiment of a sensor element used in a heat sensor device of the present invention. Fig. 2 is a cross-sectional view showing along line XX' in Fig. 1. The determined cross-section is illustrated. Fig. Figure 3 is a circuit diagram illustrating an embodiment of a control circuit (circuit configuration) of the heat sensor device of the present invention. Fig. Figure 4 is a view illustrating a fault shape in a case where a membrane is extensible and a fault shape in the case where the membrane is compressible. Fig. Figure 5 is an enlarged cross-sectional view of a heat generator in an embodiment of a sensor element according to the present invention. Fig. Figure 6 is a graphic representation illustrating the distortion in a cross-sectional direction of a heat generator in an embodiment of a sensor element according to the present invention. Fig. Figure 7 is a cross-sectional view according to an embodiment of a sensor element used in the heat sensor device of the present invention. Fig. Figure 8 is a cross-sectional view according to an embodiment of a sensor element used in the heat sensor device of the present invention. Fig. Figure 9 is a cross-sectional view of an embodiment of a sensor element used in the heat sensor device of the present invention. Description of the embodiments

[0012] Examples according to the present invention are described below. In each embodiment, an example is a device attached to an inlet port of a power engine that measures the flow rate of the inlet air flowing through the inlet port. However, the present invention can also be applied to a gas sensor that measures the humidity and hydrogen concentration of the gas from changes in the amount of thermal radiation and the temperature of the heat-generating resistor. First embodiment

[0013] A first embodiment according to the present invention is described below. A configuration of a sensor element 1 of a thermal flow meter according to the present invention is described with respect to Fig. As described in Figure 1, a substrate 2 of the sensor element 1 is made from a material with high thermal conductivity, such as silicon. A lower stacked film 3a and an upper stacked film 3b are then formed on the substrate 2. A heat-generating resistor 5 is inserted between the lower stacked film 3a and the upper stacked film 3b. A heating temperature sensor 7, which detects the heating temperature of the heat-generating resistor 5 around the heat-generating resistor 5, and temperature sensors 8a and 8b are formed on the upstream side and temperature sensors 9a and 9b on the downstream side on both sides of the heating temperature sensor 7.The temperature sensors 8a and 8b on the upstream side are arranged on the upstream side of the airflow 6 with respect to the heat-generating resistor 5, while the temperature sensors 9a and 9b on the downstream side are arranged on the downstream side of the airflow 6 with respect to the heat-generating resistor 5. The temperature-sensitive resistors 10, 11, and 12 are arranged on the lower stacked film 3a, and their resistance values ​​change according to the temperature of the airflow 6. The outermost surface of the sensor element 1 is then covered with the upper stacked film 3b. The upper stacked film 3b provides electrical insulation and also serves as a protective film. Furthermore, a portion of the substrate 2 is removed from the back side by etching or the like to form a membrane 4, which serves as a heat-generating section of a thin film.

[0014] In the above configuration, the temperature of the heat-generating resistor 5 is detected by the heating temperature sensor 7, the heating is controlled so that it is a constant temperature that is higher than the temperature of the airflow 6, and the airflow rate is detected from the temperature difference between the temperature sensors 8a and 8b on the upstream side and the temperature sensors 9a and 9b on the downstream side, which is generated by the airflow 6.

[0015] The heat-generating resistor 5, the heating temperature sensor 7, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the temperature-sensitive resistors 10, 11, and 12 are made of a material whose resistance changes with temperature. For example, a metallic material with a high temperature coefficient of resistance, such as platinum, molybdenum, tungsten, or a nickel alloy, can be used. Additionally, the lower stacked film 3a and the upper stacked film 3b are formed as thin films approximately 2 micrometers thick of silicon dioxide (SiO2) or silicon nitride (Si3N4), exhibiting a structure that provides thermal insulation.

[0016] An electrode contact surface 13 is provided at one end section of the sensor element 1. This surface incorporates several electrodes for connecting the resistors—the heat-generating resistor 5, the heating temperature sensor 7, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the temperature-sensitive resistors 10, 11, and 12—to the control / detection circuit. The electrode contact surface 13 is made of aluminum or a similar material. Additionally, wiring is provided to connect the heat-generating resistor 5 and each temperature sensor to the electrode contact surface 13.

[0017] Fig. Figure 2 illustrates a cross-sectional structure of the sensor element 1. The lower stacked film 3a is formed on the substrate 2. The lower stacked film 3a has a configuration in which silicon oxide films and silicon nitride films are stacked alternately. A silicon oxide film 14a, a silicon nitride film 15a, and a silicon oxide film 14c, obtained by thermal oxidation of a Si substrate, are formed in the order of the lower layer. The silicon oxide films 14a and 14c and the silicon nitride film 15a can be formed by a CVD process. The heat-generating resistor 5, the heating temperature sensor 7, the upstream temperature sensors 8a and 8b, and the downstream temperature sensors 9a and 9b are formed on the lower stacked film 3a. The upper stacked film 3b is formed on these layers.On the upper stacked film, a silicon oxide film 14d, a silicon nitride film 15c, and a silicon oxide film 14e are formed in order from bottom to top. The silicon oxide films 14d to 14e and the silicon nitride film 15c can be formed by a plasma-CVD process.

[0018] In the present embodiment, silicon oxide films and silicon nitride films with different coefficients of thermal expansion are used as the materials of the lower stacked film 3a, although the materials are not limited to these films. The coefficient of thermal expansion of the silicon oxide film is, for example, 0.5 × 10 -6 ( / °C), while the coefficient of thermal expansion of the silicon nitride film is approximately 3.6 × 10 -6( / °C). In addition to these films, materials with other coefficients of thermal expansion can be used, for example, aluminum nitride or the like can be used instead of a silicon nitride film. The coefficient of thermal expansion of aluminum nitride is approximately 5.7 × 10 -6 ( / °C).

[0019] In the present embodiment, the silicon oxide film and the silicon nitride film are used as the materials of the upper stacked film 3b, although the materials are not limited to these films. In the implementation of the present invention, the average coefficient of thermal expansion of the upper stacked film 3b can be smaller than the average coefficient of thermal expansion of the lower stacked film 3a. Therefore, it is not necessary to use two types of films, such as a silicon oxide film and a silicon nitride film, as the silicon oxide film alone can be used. The average coefficient of thermal expansion is defined by a weighted average of the film thicknesses and the coefficients of thermal expansion of the respective films.

[0020] The specific film thicknesses of the silicon oxide film and the silicon nitride film described above will be described later together with the operations and effects according to the present invention.

[0021] Next, a control / detection circuit for sensor element 1 will be described.

[0022] As in Fig. As illustrated in Figure 3, a bridge circuit is formed in which a series circuit containing the heating temperature sensor 7 and the temperature-sensitive resistor 10, whose resistance changes according to the temperature of the heat-generating resistor 5, and a series circuit containing the temperature-sensitive resistor 11 and the temperature-sensitive resistor 12 are connected in parallel, with a reference voltage Vref applied to each series circuit. An intermediate voltage of these series circuits is extracted and connected to an amplifier 16. The output of the amplifier 16 is connected to the base of the transistor 17. The collector of the transistor 17 is connected to a power supply VB, while one emitter is connected to the heat-generating resistor 5 to form a feedback circuit.As a result, the temperature Th of the heat-generating resistance 5 is controlled so that it is higher than the temperature Ta of the airflow 6 by the temperature ΔTh (= Th - Ta).

[0023] A bridge circuit is then configured in which a series circuit containing temperature sensor 8a on the upstream side and temperature sensor 9a on the downstream side, and a series circuit containing temperature sensor 9b on the downstream side and temperature sensor 8b on the upstream side, are connected in parallel, with the reference voltage Vref applied to the bridge circuit. When a temperature difference occurs between temperature sensors 8a and 8b on the upstream side and temperature sensors 9a and 9b on the downstream side due to airflow, the resistance equilibrium of the bridge circuit changes, resulting in a differential voltage. Detecting this differential voltage via an amplifier 18 yields an output Vout corresponding to the airflow rate.

[0024] The following describes the change in resistance of the heat-generating resistor 5 in the heat sensor device described above. This change in resistance occurs not only in the heat-generating resistor 5, but also in the resistors formed on the diaphragm 4, such as the heating temperature sensor 7, the temperature sensors 8a and 8b on the upstream side, and the temperature sensors 9a and 9b on the downstream side.

[0025] In particular, the heat-generating resistor 5 and the heating temperature sensor 7, which have a high temperature, exhibit a large change in resistance, whereby the effect obtained by the present invention is high.

[0026] To reduce the resistance change of the heat-generating resistor 5, the inventors have determined through experiments that it is preferable for the lower stacked film 3a and the upper stacked film 3b, on which the heat-generating resistor 5 is formed, to be films with a low coefficient of thermal expansion. That is, it is necessary to increase the film thickness of the silicon oxide and decrease the film thickness of the silicon nitride film.

[0027] However, if membrane 4 is made of silicon dioxide, membrane 4 will be deformed. Fig. Figure 4 is a view illustrating a fault shape in a case where the membrane 4 is extensible, and a fault shape in a case where the membrane is compressible.

[0028] Fig. Figure 4(A) is a cross-sectional view that conceptually illustrates the deformation of a sensor element used in the heat sensor device, and is a view illustrating a cross-sectional shape of the membrane 4 in a case where a film thickness is specified such that a combined stress of a stacked film forming the membrane 4 is a tensile stress. Fig. 4(A) A silicon oxide film and a silicon nitride film are stacked to form membrane 4. Each film thickness is specified such that the combined stress of the silicon oxide film and the silicon nitride film is a tensile stress. In this case, membrane 4, as shown in Fig. Figure 4(A) illustrates a flat shape which can be advantageously produced.

[0029] Fig. Figure 4(B) is a view illustrating a cross-sectional shape of the membrane 4 in a case where the film thickness is specified such that the combined stress of the stacked film forming the membrane 4 is a compressive stress. Fig. 4(B) The respective film thicknesses are set such that the combined stresses of the silicon oxide film and the silicon nitride film are compressive stresses. If the ratio of the silicon oxide film of membrane 4 is increased to make the membrane 4 compressible, folds are created in the membrane 4, causing the membrane 4 to deform, as illustrated in the drawing.

[0030] From the above, it is necessary to provide a silicon nitride film of a predetermined thickness in order to obtain a tensile stress, because the film configuration of the membrane 4 must be designed to have tensile properties.

[0031] Because it is necessary to provide the silicon nitride film with a predetermined thickness, as described above, the reduction in the coefficient of thermal expansion of the membrane 4 is limited. It is an object of the present invention to meet this limitation and suppress the distortion of the heat-generating resistor 5 due to the expansion of the membrane 4. According to the present invention, the expansion of the heat-generating resistor 5 can be suppressed without changing the film thickness ratio between the silicon nitride film and the silicon oxide film of the entire membrane 4. Specific examples are described below.

[0032] Fig. Figure 5 is a cross-sectional view illustrating deformation when the heat-generating resistor 5 of the sensor element 1 is in Fig. 2 is heated. On the lower stacked film 3a, the silicon oxide film 14a, the silicon nitride film 15a, and the silicon oxide film 14c are formed in this order from the lower layer. Here, in the stacked film 3a, a film thickness T1 of the silicon oxide film 14a on the side of the lower layer and a film thickness T3 of the silicon oxide film on the side of the upper layer are formed such that they satisfy T1 < T3.

[0033] As a result, the silicon nitride film 15a, which has a large coefficient of thermal expansion, is located on the side of the lower layer. That is, the lower stacked film 3a contains the silicon oxide films 14a and 14c and the silicon nitride film 15a, each with different coefficients of thermal expansion. The silicon nitride film 15a, with the highest coefficient of thermal expansion among these films, is located on the side of the lower layer with respect to the center of the thickness of the lower stacked film 3a. When the heat-generating resistor 5 is heated in this configuration, the side of the lower layer of the lower stacked film 3a expands significantly, increasing the bending moment acting on the membrane 4 and thus further increasing the bending stress generated in the membrane 4.

[0034] The following describes the effect of increasing the bending stress. Fig. Figure 6 illustrates the stress within the film of the membrane 4 that is generated when the heat-generating resistor 5 is heated in the configuration of the present invention. When the heat-generating resistor 5 is heated, a tensile stress is generated according to the average coefficient of thermal expansion of the entire film forming the membrane 4. In addition, due to the asymmetry of the film configuration, a difference in the coefficients of thermal expansion occurs between the upper layer and the lower layer, so that a bending stress eb is generated. During bending deformation, the compressive stress is generated on the inner circumferential side, while the tensile stress is generated on the outer circumferential side. Because the heat-generating resistor 5 is subjected to bending deformation on the inner circumferential side, i.e.,Located on the side of the upper layer at the midpoint of the membrane thickness 4, the compressive stress ebm acts on the stress caused by the bending stress eb. The stress esm of a heating element is a value obtained by subtracting the tensile stress es from the compressive stress ebm. As a result, the tensile stress of the heating element can be reduced, the expansion and contraction of the heating element associated with temperature changes can be suppressed, and the resistance change of the heating element due to expansion and contraction can be reduced.

[0035] In the present embodiment, a heat sensor device 1 is created which includes: a substrate 2 with an opening 2a; and a membrane 4 with a structure in which a lower stacked film 3a, a heat-generating resistor 5 and an upper stacked film 3b are stacked such that they bridge the opening 2a, wherein a film thickness of the lower stacked film 3a is greater than a film thickness of the upper stacked film 3b, an average coefficient of thermal expansion of the lower stacked film 3a is greater than an average coefficient of thermal expansion of the upper stacked film 3b, the lower stacked film 3a contains several films 14a, 15a and 14c with different coefficients of thermal expansion, and the film 15a with the largest coefficient of thermal expansion among the several films 14a, 15a and 14c is formed below a thickness center of the lower stacked film 3a.

[0036] According to the embodiment configured as described above, the heat-generating resistor 5 is located on the side of the upper layer at the midpoint of the thickness of the membrane 4, because the film thickness of the lower stacked film 3a is greater than the film thickness of the upper stacked film 3b. Furthermore, because the average coefficient of thermal expansion of the lower stacked film 3a is greater than the average coefficient of thermal expansion of the upper stacked film 3b, bending deformation of the membrane 4 occurs when the heat-generating resistor 5 is heated. Therefore, in addition to the tensile stress due to thermal expansion of the membrane 4, a compressive stress due to bending deformation of the membrane 4 also occurs on the side of the upper layer at the midpoint of the thickness of the membrane 4.As a result, the tensile stress on the heat-generating resistor 5, which is located on the side of the upper layer at the midpoint of the thickness of the membrane 4, is reduced by the compressive stress ebm due to the bending deformation of the membrane 4. This effect suppresses the plastic deformation due to thermal expansion of the heat-generating resistor 5 and reduces the resistance change of the heat-generating resistor 5, thus ensuring that the measurement accuracy of the heat sensor device 1 can be maintained over a long period.

[0037] Additionally, a silicon oxide film and a silicon nitride film are formed alternately on the lower stacked film 3a, wherein the film thickness T1 of the silicon oxide film 14a as the bottom layer of the lower stacked film 3a is smaller than the film thickness T3 of the silicon oxide film 14c as the top layer of the lower stacked film 3a.

[0038] As a result, the silicon nitride film 15a, which has a large coefficient of thermal expansion, is located closer to the side of the lower layer from the midpoint of the thickness of the lower stacked film 3a. In this configuration, the side of the lower layer of the lower stacked film 3a expands significantly when the heat-generating resistor 5 is heated, thereby increasing the bending moment acting on the membrane 4 and further increasing the bending stress generated in the membrane 4.

[0039] Additionally, the upper stacked film 3b contains a silicon oxide film and a silicon nitride film, the film thickness of the silicon nitride film 15c contained in the upper stacked film 3b being less than the film thickness of the silicon nitride film 15a contained in the lower stacked film 3a. As a result, the coefficient of thermal expansion of the upper stacked film 3b can be further reduced, and the coefficient of thermal expansion of the lower layer of the membrane 4 can be increased. In this configuration, the lower layer of the lower stacked film 3a expands significantly when the heat-generating resistor 5 is heated, thus increasing the bending moment and generating a greater bending stress in the membrane 4.

[0040] Because the heat-generating resistor 5 is arranged between the two silicon nitride films 15c and 15a, oxidation of the heat-generating resistor 5 can be prevented. Second embodiment

[0041] A second embodiment according to the present invention is described below. The same configurations as those of the first embodiment are given the same reference numerals, but their descriptions are omitted.

[0042] In the present embodiment, a configuration is described in which several silicon nitride films are provided on the lower stacked film 3a. Fig. Figure 7 illustrates a cross-sectional structure of the sensor element 1. The lower stacked film 3a is formed on the substrate 2. The lower stacked film 3a has a configuration in which silicon oxide films and silicon nitride films are stacked alternately. 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, obtained by thermal oxidation of a Si substrate, are formed in the order of the lower layer. The silicon oxide films 14a to 14c and the silicon nitride films 15a and 15b can be formed by a CVD process. The heat-generating resistor 5, the heating temperature sensor 7, the upstream temperature sensors 8a and 8b, and the downstream temperature sensors 9a and 9b are formed on the lower stacked film 3a. The upper stacked film 3b is formed on these layers.On the upper stacked film 3b, a silicon oxide film 14d, a silicon nitride film 15c, and a silicon oxide film 14e are formed in order from bottom to top. The silicon oxide films 14d to 14e and the silicon nitride film 15c can be produced by a plasma-CVD process.

[0043] In the present embodiment, the silicon oxide film and the silicon nitride film are used as the materials of the upper stacked film 3b, although the materials are not limited to these films. Furthermore, in the present embodiment, the average coefficient of thermal expansion of the upper stacked film 3b can be configured such that it does not exceed the average coefficient of thermal expansion of the stacked film 3a. Therefore, it is not necessary to use two types of films, such as a silicon oxide film and a silicon nitride film, as the silicon oxide film alone can be used.

[0044] Furthermore, in the present embodiment, the silicon oxide film and the silicon nitride film are used for the lower stacked film 3a, although materials with different coefficients of thermal expansion can also be used in addition to these films. For example, aluminum nitride or the like can be used instead of a silicon nitride film.

[0045] Fig. Figure 7 is a cross-sectional view illustrating deformation when the heat-generating resistor 5 of the sensor element 1 is in Fig. 5 is heated. Here, in the lower stacked film 3a, the film thickness T1 of the silicon oxide film 14a on the side of the bottom layer and the film thickness T3 of the silicon oxide film on the side of the top layer are configured such that they satisfy T1 < T3. As a result, the silicon nitride films 15a and 15b, which have a large coefficient of thermal expansion, are located closer to the side of the bottom layer than the midpoint of the thickness of the lower stacked film 3a. In this configuration, the side of the bottom layer of the lower stacked film 3a expands significantly when the heat-generating resistor 5 is heated, thereby increasing the bending moment acting on the membrane 4, which in turn further increases the bending stress generated in the membrane 4.

[0046] In the present embodiment, a more effective configuration is described below.

[0047] In the Fig. Figure 8 illustrates that the lower stacked film 3a is formed when the film thickness of the silicon oxide film 14b inserted between the several silicon nitride films is T2, and T3 > T2. As a result, the silicon nitride film 15b is formed on the side of the lower layer, and when the heat-generating resistor 5 is heated, the side of the lower layer of the lower stacked film 3a expands significantly, increasing the bending moment acting on the membrane 4, thus further increasing the bending stress generated in the membrane 4.

[0048] Next, in the present embodiment, a configuration is described in which the effect of the present invention can further be obtained for several silicon nitride films contained in the lower stacked film 3a. Fig. 9 illustrates. In Fig. 9 is the thickest silicon nitride film 15a among the several silicon nitride films 15a and 15b contained in the lower stacked film. That is, the thickness of silicon nitride film 15b is reduced by the thickness of silicon nitride film 15a. As a result, it is possible to increase the expansion of the side of the lower layer when the heat-generating resistor 5 is heated without changing the combined thickness of the silicon nitride films of the entire film. In this configuration, the side of the lower layer of the lower stacked film 3a expands significantly when the heat-generating resistor 5 is heated, thereby increasing the bending moment acting on the membrane 4, thus further increasing the bending stress generated in the membrane 4.

[0049] Next, a configuration is described in the present embodiment in which the effect of the present invention can further be obtained for the silicon nitride films contained in the upper stacked film 3b. Fig. In the upper stacked film 3b, the upper stacked film contains a silicon oxide film 14d and 14e and a silicon nitride film 15c, the film thickness of the silicon nitride film 15c contained in the upper stacked film 3b being less than the film thickness of the silicon nitride films 15a and 15b contained in the lower stacked film 3a. As a result, the coefficient of thermal expansion of the upper stacked film 3b can be further reduced, and the coefficient of thermal expansion of the lower layer of the membrane 4 can be increased. In this configuration, the lower layer of the lower stacked film 3a expands significantly when the heat-generating resistor 5 is heated, thus increasing the bending moment and generating a greater bending stress in the membrane 4.

[0050] In the present embodiment, the configuration described includes two silicon nitride films contained within the lower stacked film 3a. However, the effect of the present invention can also be achieved with a configuration containing three layers. If any one of the silicon nitride films contained within the lower stacked film 3a is extremely thin, this thin silicon nitride film will have a negligible effect on the overall membrane expansion. Therefore, such a remarkably thin film (e.g., down to 20 nm or 1 / 10 or less of the total film thickness of the entire silicon nitride) need not be considered.

[0051] In the present embodiment, at least two silicon nitride films are formed on the lower stacked film 3a, wherein the film thickness T2 of the silicon oxide film 14b inserted between the two silicon nitride films 15a and 15b of the lower stacked film is smaller than the film thickness T3 of the silicon oxide film 14c of the uppermost layer of the lower stacked film 3a.

[0052] According to the present embodiment, which is configured as described above, the silicon nitride film 15b is formed on the side of the lower layer, the side of the lower layer of the lower stacked film 3a expands to a great extent when the heat-generating resistor 5 is heated, and the bending moment acting on the membrane 4 increases, so that the bending stress generated in the membrane 4 can be further increased.

[0053] Furthermore, in the (in Fig.Figure 9 illustrates a modification of the present embodiment in which the film thickness Tn1 of the bottom silicon nitride film 15a is the greatest among the multiple silicon nitride films 15a and 15b contained in the lower stacked film 3a. As a result, it is possible to increase the expansion of the side of the bottom layer when the heat-generating resistor 5 is heated without changing the combined thickness Tn1 + Tn2 of the silicon nitride films 15a and 15b of the entire film. In this configuration, the side of the bottom layer of the lower stacked film 3a expands significantly when the heat-generating resistor 5 is heated, thereby increasing the bending moment acting on the membrane 4 and further increasing the bending stress generated in the membrane 4.

[0054] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, which include various modifications. The embodiments described above have been described in detail, for example, to present the invention in an easily understandable manner and are not necessarily limited to those with all the described configurations. In addition, a part of a configuration of another embodiment can be added to a configuration of a particular embodiment, and a part of the configuration of a particular embodiment can be deleted or replaced by a part of another embodiment. List of reference symbols 1 sensor element (heat sensor device) 2 Substrat 2a Opening 3a lower stacked film 3b top stacked film 4 Membran 5 heat-generating resistor 6 Airflow 7 Heating temperature sensor 8a, 8b Temperature sensor on the upstream side 9a, 9b Temperature sensor on the downstream side 10, 11, 12 temperature-sensitive resistor 13 Electrode contact area 14a, 14b, 14c, 14d, 14e silicon oxide film 15a, 15b, 15c silicon nitride film 16 amplifiers 17 transistors 18 amplifiers

Claims

[1] Heat sensor device comprising: a substrate with an opening; and a membrane with a structure in which a lower stacked film, a heat-generating resistor and an upper stacked film are stacked in such a way as to bridge the opening, where the film thickness of the lower stacked film is greater than the film thickness of the upper stacked film, and the average coefficient of thermal expansion of the lower stacked film is greater than the average coefficient of thermal expansion of the upper stacked film. The lower stacked film contains several films with different coefficients of thermal expansion, and a film with the largest coefficient of thermal expansion among the multiple films below a thickness center of the lower stacked film is formed. [2] Heat sensor device according to claim 1, wherein a silicon oxide film and a silicon nitride film are formed alternately in the lower stacked film, and The film thickness of the silicon oxide film of a bottom layer of the lower stacked film is less than the film thickness of the silicon oxide film of a top layer of the lower stacked film. [3] Heat sensor device according to claim 2, wherein at least two silicon nitride films are formed in the lower stacked film, and a film thickness of a silicon oxide film inserted between two silicon nitride films of the lower stacked film is smaller than a film thickness of the silicon oxide film that is the top layer of the lower stacked film. [4] Heat sensor device according to one of claims 1 to 3, wherein the upper stacked film contains a silicon oxide film and a silicon nitride film, and the film thickness of the silicon nitride film contained in the upper stacked film is smaller than the film thickness of the silicon nitride film contained in the lower stacked film. [5] Heat sensor device according to claim 3, wherein the film thickness of a silicon nitride film of the bottom layer is greatest among several silicon nitride films contained in the lower stacked film.

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