JP2001249040A - Fluid detecting sensor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the resistance value of a heater, to generate heat largely, to increase the Seebeck coefficient of a thermopile and to enhance the sensitivity of a fluid detecting sensor (a gas flow sensor) which is used to detect the flow rate of a fluid such as a gas or the like. SOLUTION: The heater 36 which is composed of polysiliocn is formed on the surface of a thin filmlike bridge part 35, and thermopiles 37, 38 are arranged on both sides of it. The thermopiles 37, 38 are constituted of thin wires composed of polysilicon and aluminum. The heater 36 and the polysilicon thin wires 41 of the thermopiles 37, 38 are doped with P (phosphorus) by an ion implantation operation or the like, and the doping amount of the heater 36 is set to be larger than that of the polysilicon thin wires 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid detection sensor and a method of manufacturing the same, and more particularly, to a fluid detection sensor including a heating element such as a heater and a temperature measuring element such as a thermopile, and a fluid detected by a change in the temperature detected by the temperature measuring element. The present invention relates to a fluid detection sensor for detecting the presence or absence of a fluid or a fluid flow rate and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIGS. 1 and 2 show a fluid detection sensor 1 having a conventional structure. Here, FIG. 2 shows a cross section taken along line AA of FIG. However, FIG. 1 shows a state in which a heater, a thermopile, and the like are exposed, and FIG. 2 shows a state in which the heater and the thermopile are covered with a protective film 10 or the like. In this fluid detection sensor 1, a concave gap 3 is formed on an upper surface of a silicon substrate 2.
The insulating thin film 4 is provided on the upper surface of the silicon substrate 2 so as to cover the gap 3, and a thin film bridge portion 5 is formed on the gap 3 by a part of the insulating thin film 4. . The bridge 5 is insulated from the silicon substrate 2 by the space (air) in the gap 3. Bridge part 5
Is provided with a heater 6 at the center thereof, and thermopiles 7 and 8 are respectively provided as temperature measuring elements at positions symmetrical with respect to the heater 6 (upstream and downstream). Also,
The silicon substrate 2 is covered with a protective film 10 so as to cover the heater 6 and the thermopiles 7 and 8.

The thermopiles 7 and 8 are made of BiSb / Sb
And a bridge 5
First thin line 1 made of BiSb across the edge of
1 and Sb are alternately wired, and the first and second thin wires 11 and 12 in the bridge portion 5 are formed.
A group of hot junctions 13 is formed by the connection points of the above, and a group of cold junctions 14 is formed by the connection point of the first thin wire 11 and the second thin wire 12 outside the bridge portion 5.

The numbers of the hot junctions 13 and the cold junctions 14 of the thermopiles 7 and 8 are each n, and the temperature of the hot junction 13 is Th,
Assuming that the temperature of the cold junction 14 is Tc, the thermopile 13
The output voltage (between both ends) V of the fourteenth voltage is expressed by the following equation (1). V = n · α (Th−Tc) (1) where α is a Seebeck coefficient.

[0005] The fluid detection sensor 1 is placed at a location where a gas flow occurs, and monitors the output of the upstream and downstream thermopiles 7 and 8 while applying a current to the heater 6 to generate heat. When there is no gas flow, the hot junction temperature of the upstream thermopile 7 and the hot junction temperature of the downstream thermopile 8 are equal due to the symmetry of the arrangement, so that the output voltage of the thermopile 7 and the output voltage of the thermopile 8 are different. Become equal. On the other hand, when the gas moves from the upstream side to the downstream side as shown by the arrow in FIG. 1, the hot junction of the thermopile 7 on the upstream side is cooled by the flow of the gas to lower the temperature, and its output is reduced. The voltage decreases. On the other hand, the heat of the heater 6 is transported to the downstream side by the gas, the temperature of the hot junction of the thermopile 8 on the downstream side rises, and the output voltage increases. In addition, since the difference between the hot junction temperatures of the thermopiles 7 and 8 increases as the flow rate of the gas increases, the flow rate of the gas can be measured based on the resulting difference between the output voltages of the thermopiles 7 and 8.

Next, the manufacturing process of the fluid detection sensor 1 will be described with reference to FIGS. 3 (a), 3 (b), 3 (c), 3 (d) and 4 (e), 4 (f).
(G) and FIG. 5 (h) (i) (j). All of the figures explaining these manufacturing processes are shown in FIG.
It shows a cross section along the -B line. Hereinafter, the manufacturing process will be described with reference to these drawings.

First, an insulating thin film 4 made of, for example, SiO ₂ is formed on both the front and back surfaces of the silicon substrate 2 by a thermal oxidation method or the like [FIG. 3A], and the upper surface of the insulating thin film 4 is formed by a sputtering method or the like. BiSb is deposited on the substrate to form a BiSb film 16.
Is formed [FIG. 3 (b)]. Next, doping is performed on the BiSb film 16 by an ion implantation method or the like [FIG.
(C)]. Further, BiSb is formed by photolithography.
The film 16 is etched to form a pattern of each of the first thin wires 11 of the heater 6, the thermopiles 7 and 8 with the BiSb film 16, and an oxide film 17 is formed on the surface of the patterned BiSb film 16 [FIG. d)].

Thereafter, a portion of the oxide film 17 covering the first fine wire 11 is etched at portions where the hot junction 13 and the cold junction 14 will be formed to form an opening 18 (FIG. 4E). Sb is deposited from above by sputtering or the like, and the Sb film is patterned by photolithography to form the second fine wires 12 of the thermopiles 7 and 8 (FIG. 4F).
At this time, each end of the second thin wire 12 is connected to each end of the first thin wire 11 through the opening 18 of the oxide film 17, and the thermopiles 7, 8 are connected by the first thin wire 11 and the second thin wire 12.
Is formed.

Next, both ends of the heater 6 and the thermopile 7,
At both ends of 8, a part of each oxide film 17 covering the first fine wire 11 and the heater 6 is etched to form an opening 19, and wire pads 9 and 15 are provided at both ends of the heater 6 and both ends of the thermopiles 7 and 8. [FIG. 4 (g)]. Then
For example, SiO ₂ is deposited on the entire substrate by a CVD method or the like to form a protective film 10 for protecting the wiring.
(H)].

After that, the protective film 10 is partially etched to expose the upper surfaces of the wire pads 9 and 15. At the same time, the protective film 10 and the insulating thin film 4 are partially removed by etching between the heater 6 and the thermopiles 7 and 8, and the insulating thin film 4 is also partially removed by etching to form an opening 20. To expose the semiconductor substrate 2 [FIG. 5 (i)]. Next, by etching the upper surface of the semiconductor substrate 2 from the opening 21, the cavity 3 is formed in the upper surface of the semiconductor substrate 2 and the bridge portion 5 is formed by the insulating thin film 4 (FIG. 5J).

[0011]

In the above-described fluid detection sensor, there are two factors that determine the sensitivity of the sensor. The two factors are the rising temperature of the heater as the heating element and the magnitude of the Seebeck coefficient of the thermopile as the temperature measuring element. That's it. The reason is,
As can be seen from the above equation (1), the higher the temperature of the heater, the higher the temperature of the hot junction, so the output voltage of the thermopile also increases, and the higher the Seebeck coefficient, the higher the output voltage of the thermopile. .

On the other hand, in a conventional fluid detection sensor,
One conductive wire of heater and thermopile (first thin wire)
Means that the same material is used and the doping amount is the same. A semiconductor material having a high Seebeck coefficient is used as the material, for example, BiSb is used. As a general property of such a semiconductor material, it has been found that when the doping amount is reduced, the Seebeck coefficient increases, but the resistivity also increases.

Therefore, in the conventional fluid detection sensor, if the doping amount is reduced and the Seebeck coefficient is increased to increase the sensitivity by increasing the output voltage of the thermopile, the resistivity of the heater increases because the doping amount is small. , Thereby increasing the resistance value of the heater. The heating temperature of the heater is determined by the power supplied to the heater,
Since there is a limit to the voltage that can be supplied to the heater, if the resistance value of the heater is too high, it is not possible to generate heat sufficiently, and the sensitivity of the fluid detection sensor is reduced. Conversely, when the doping amount is increased, the opposite occurs exactly, and the resistance value of the heater can be lowered, so that the heat generated from the heater is sufficient.However, the output voltage of the thermopile decreases due to the decrease in the Seebeck coefficient. As a result, the sensitivity of the fluid detection sensor deteriorates. Therefore, in the conventional fluid detection sensor, even if the doping amount is controlled, it is difficult to further improve the sensitivity of the fluid detection sensor.

The present invention has been made in view of the above-mentioned problems of the conventional example, and has as its object to provide a fluid detection sensor capable of improving sensitivity by controlling the doping amount. It is in.

[0015]

A fluid detection sensor according to the present invention has an insulating thin film at least partially supported in air by a substrate, and an impurity-doped film disposed on the surface of the air supporting portion of the insulating thin film. A heating element; and at least two contact potential difference measuring elements disposed on the surface of the insulating thin film with the heating element interposed therebetween and one of the conductive wirings doped with an impurity, forming the contact potential difference measuring element. An impurity doping amount of one conductive wiring and an impurity doping amount of the heating element are different from each other.

Another fluid detection sensor according to the present invention comprises: an insulating thin film at least partially supported in air by a substrate;
A heating element that is disposed on the surface of the aerial support portion of the insulating thin film and is doped with impurities; and a contact potential difference measurement that is disposed on the surface of the insulating thin film on one side of the heating element and one of the conductive wirings is doped with impurities. And a heating element, wherein an impurity doping amount of one of the conductive wires constituting the contact potential difference measuring element and an impurity doping amount of the heating element are different from each other.

In the present invention, the heating element is, for example, a heater using a resistor material. What is a contact potential difference thermometer?
The temperature is measured based on the contact potential difference between at least two types of conductive wirings, for example, a thermopile. Further, the material of the conductive wiring may be a metal material or a semiconductor material.

Further, in each of the above embodiments of the fluid detection sensor, the heating element and one conductive wiring constituting the contact potential difference measuring element are made of polysilicon.

Further, in each of the embodiments of the above-mentioned fluid detection sensors, an ambient temperature measuring resistor for measuring an ambient temperature is further provided, wherein the heating element and an impurity doping amount of the ambient temperature measuring resistor are further included. Are equal.

The method of manufacturing a fluid detection sensor according to the present invention includes the steps of: forming an insulating thin film on a surface of a substrate; forming a first material on the insulating thin film; Doping the entire surface; forming a heating element and one of the conductive wirings of the contact potential difference measuring element by patterning the first material; generating heat from the heating element or the first material; In the body area,
Further, the method is characterized by comprising a step of performing doping and a step of fabricating the other conductive wiring of the contact potential difference thermometer. Here, the further doping of the heating element or the region of the first material which becomes the heating element means that the doping may be performed before or after the patterning of the heating element. are doing.

[0021]

According to one aspect of the fluid detection sensor or the method of manufacturing the same according to the present invention, a contact potential difference measuring element is arranged on both sides of a heating element, and the other form is a contact potential difference measuring element disposed on one side of the heating element. It is one in which a warm body is arranged. In the case where the contact potential difference thermometer is provided on both sides of the heating element, there is an advantage that the fluid flow rate can be measured in both directions and the sensitivity is high in a low flow velocity range. The arrangement has an advantage that measurement can be performed even in a high flow velocity region.

In any of the fluid detection sensors, the Seebeck coefficient of the contact potential difference thermometer is set by making the impurity doping amount of one of the conductive wires constituting the contact potential difference thermometer and the impurity doping amount of the heating element different from each other. The resistance value of the heating element can be reduced without lowering the temperature, and the sensitivity of the fluid detection sensor can be further improved. Generally, the method of varying the impurity doping amount is as follows.
The effect can be obtained by reducing the impurity doping amount of one conductive wiring constituting the contact potential difference temperature measuring element and increasing the impurity doping amount of the heating element.

If polysilicon is used as one conductive wiring of the contact potential difference measuring element, the contact potential difference measuring element can be formed by combining it with aluminum or the like, and the workability is improved.

In the case where an ambient temperature measuring resistor for measuring the ambient temperature is provided, if the impurity doping amount of the ambient temperature measuring resistor and the impurity doping amount of the heating element are made equal, a heater is provided. Is easily maintained at a temperature higher than the ambient temperature by a certain temperature.

In the method of manufacturing a fluid detection sensor according to the present invention, the impurity doping of the heating element and the impurity doping of the contact potential difference measuring element are not separately performed, but the heating element is doped with impurities. Therefore, the time required for the doping process can be shortened.

[0026]

(First Embodiment) A fluid detection sensor (gas flow sensor) 31 according to an embodiment of the present invention.
6 and 7 are shown in FIGS. FIG. 7 shows a cross section taken along line CC of FIG. 6, and FIG. 6 shows a plane in which the thermopiles 37 and 38 are exposed by removing the protective film 40 and the like. In this fluid detection sensor 31, a concave void 33 widened upward is formed on the upper surface of a silicon substrate 32, and an insulating thin film 34 is provided on the upper surface of the silicon substrate 32 so as to cover the void 33. The bridge portion 35 in the form of a thin film is formed on the gap 33 by a part of the insulating thin film 34. The bridge 35 is insulated from the silicon substrate 32 by the space 33. On the surface of the bridge portion 35, a heater 3 made of polysilicon is provided at a central portion thereof.
6 are provided, and thermopiles 37 and 38 are provided as temperature measuring elements at symmetrical positions on the upstream side and the downstream side with the heater 36 interposed therebetween. Outside the bridge portion 35, a temperature measuring resistor 52 for sensing the ambient temperature is provided on the insulating thin film 34, and a silicon substrate is provided so as to cover the heater 36, the thermopiles 37, 38 and the temperature measuring resistor 52. 32 is covered with a protective film 40.

The thermopiles 37 and 38 are constituted by a thermocouple made of polysilicon / aluminum, and a first thin wire 41 made of polysilicon and a second thin wire made of aluminum are made to cross the edge of the insulating thin film 34. 42 are wired alternately and in parallel to form an insulating thin film 34.
A group of hot junctions 43 is formed by a connection point between the first thin wire 41 and the second thin wire 42 in the inside, and a cold junction 44 is formed by a connection point between the first thin wire 41 and the second thin wire 42 outside the insulating thin film 34. Make up a group.

Since the cold junction 44 is located on the silicon substrate 32 serving as a heat sink, the temperature does not easily change even when it comes into contact with a gas, but the hot junction 43 is a bridge portion floating from the silicon substrate 32. Since it is formed on 35, its heat capacity is small, and the temperature changes sensitively when it comes into contact with gas.

Outside the bridge portion 35 (on the upper surface of the silicon substrate 32), on the upper surface of the insulating thin film 34, a temperature measuring resistor 52 made of polysilicon is provided for measuring the ambient temperature.

Also in this fluid detection sensor 31, assuming that the number of the hot junctions 43 and the number of the cold junctions 44 of the thermopiles 37 and 38 are n, the temperature of the hot junction 43 is Th, and the temperature of the cold junction 44 is Tc, respectively. , 44 are expressed by the following equation (2). V = n · α (Th−Tc) (2) where α is a Seebeck coefficient.

Further, in the fluid detecting sensor 31, the temperature measuring resistor 52, the heater 36, the thermopile 37,
The first fine wires 41 are formed of the same material (polysilicon) and doped with impurities such as P (phosphorus). The impurity doping amount of the heater 36 is larger than that of the first fine wires 41. Is also getting bigger. For example, the heater 36 and the first fine wire 41 have a film thickness of 50.
In the case of 0 nm polysilicon, the first fine wire 41 is doped with P at a density of about 1 × 10 ²⁰ / cm ³ , whereas the heater 36 is doped with 4 × 10 ²⁰ / cm 3.
P is doped at a density of about ³ .

The output of the thermopiles 37 and 38 on the upstream side and the downstream side is also monitored in the fluid detection sensor 31 while applying a current to the heater 36 to generate heat. When there is no gas flow, the output voltage of the thermopile 37 is equal to the output voltage of the thermopile 38. However, when the gas moves from the upstream side to the downstream side in the direction indicated by the arrow in FIG. The hot junction 43 of the thermopile 37 on the side is cooled to lower the temperature, and the output voltage decreases. On the other hand, the temperature of the hot junction 43 of the downstream thermopile 38 increases due to the heat carried by the gas, and the output voltage increases. Therefore, the flow rate of air can be measured based on the difference between the output voltage values of the thermopiles 37 and 38. Further, as shown in this embodiment, thermopiles 37, 38 are provided on both sides of the heater 36.
In the case of the structure in which is disposed, the fluid flow rate (gas flow rate) can be detected even when the gas flows in the direction opposite to the direction of the arrow in FIG.

In addition, in the fluid detection sensor 31, since the impurity doping amount of the heater 36 is larger than that of the first fine wire 41, the resistance of the heater 36 can be reduced and the heat generation temperature of the heater 36 can be increased. be able to.
On the other hand, the impurity doping amount of the first fine wire 41 is
Since it is smaller than 6, the Seebeck coefficient can be increased. Therefore, the heat generation temperature of the heater 36 can be increased while using the thermopiles 37 and 38 having a high Seebeck coefficient, and the sensitivity of the fluid detection sensor 31 can be further improved.

The temperature measuring resistor 52 for measuring the ambient temperature is not necessary when the heater 36 is driven with the heat generation temperature constant regardless of the ambient temperature. When it is desired to drive the heater 36, the resistance value of the temperature measuring resistor 52 for measuring the ambient temperature is measured, and the measured resistance value is fed back to the heating temperature of the heater 36, so that the heating temperature of the heater 36 is a constant temperature than the ambient temperature. Can only be higher.

Reference numerals 39, 45 and 53 denote a heater 36, thermopiles 37 and 38, and a resistance temperature detector 52, respectively.
This is a wire pad for wire bonding.

Next, the manufacturing process of the fluid detection sensor 31 will be described with reference to FIGS. 8 (a), 8 (b), 8 (c), 8 (d) and 9 (e).
(F) (g) (h) (i) and FIG. 10 (j) (k)
This will be described with reference to (l) and (m). Each of the drawings describing these manufacturing processes shows a cross section along the line DD in FIG. 6A. Hereinafter, the manufacturing process will be described with reference to these drawings.

First, a silicon substrate 32 is formed by a thermal oxidation method or the like.
An insulating thin film 34 made of, for example, SiO ₂ is formed on both front and back surfaces (FIG. 8A), and polysilicon is deposited to a thickness of 500 nm on the insulating thin film 34 on the upper surface using a CVD method or the like. To form a polysilicon film 46 [FIG.
(B)]. Next, the entire polysilicon film 46 is doped with impurity atoms such as P by an ion implantation method or the like at a dose of 1 × 10 ²⁰ atoms / cm ³ by an ion implantation method or the like [FIG. 8C]. Further, after covering the entire surface of the polysilicon film 46 with the resist film 54, a window 55 is opened in the resist film 54 in the heater formation region 56a and the temperature measuring body formation region 65b of the polysilicon film 46 [FIG. ].

Through this window 55, impurities such as P
3 × 10 by ion implantation ²⁰Pieces / cm³Only
Additional injection is performed [FIG. 9 (e)]. Then, the resist film 5
4 is removed, the heater formation region 56a and the temperature measurement body formation
In the region 56b, the impurity concentration is 4 × 10²⁰Pieces / cm³When
And other areas (especially thermopile forming areas)
Has an impurity concentration of 1 × 10²⁰Pieces / cm³[Fig. 9
(F)].

Thereafter, the polysilicon film 46 is etched by photolithography, and the pattern of the first thin wire 41 of the heater 36, the temperature measuring resistor 52 for measuring the ambient temperature, and the thermopiles 37 and 38 is formed by the polysilicon film 46. Formed and patterned polysilicon film 46
Is thermally diffused. At this time, the polysilicon film 4
An oxide film 47 is formed on the surface of No. 6 (FIG. 9G).

As a result, of the heater 36, the resistance temperature detector 52, and the first thin wires 41 of the thermopiles 37 and 38 which are simultaneously patterned, only the impurity concentration of the heater 36 is increased.

Next, an opening 48 is formed by etching a part of the oxide film 47 covering the first fine wire 41 at the locations where the hot junction 43 and the cold junction 44 will be formed (FIG. 9H). Is deposited by sputtering or the like, and the aluminum film is patterned by photolithography to form the second fine wires 42 of the thermopiles 47 and 48 (FIG. 9 (i)). At this time, each end of the second thin wire 42 is connected to each end of the first thin wire 41 through the opening 48 of the oxide film 47, and the first thin wire 41 formed under the insulating thin film 47 and the second thin wire 42 are connected to each other. Thermopile 37 with thin line 42,
38 are formed.

Next, at both ends of the thermopiles 37 and 38, both ends of the heater 36 and both ends of the resistance temperature detector 52,
An opening 49 is provided by etching a part of the oxide film 47, and a metal material is deposited on both ends of the thermopiles 37, 38, both ends of the heater 36, and both ends of the resistance temperature detector to form respective wire pads 45, 39, 53. [FIG. 10 (j)].
Next, for example, SiO ₂ is deposited on the entire substrate by the CVD method or the like, and a protective film 40 for protecting the wiring is formed [FIG. 10 (k)].

Thereafter, the protective film 51 is partially etched to expose the upper surfaces of the wire pads 45, 39, 53. At the same time, between the heater 36 and the thermopiles 37 and 38, the protective film 21 is removed by etching, and the insulating thin film 34 is also partially removed by etching to form the opening 51.
Is formed, and the semiconductor substrate 32 is exposed from the opening 51 (FIG. 10 (l)). Next, the upper surface of the semiconductor substrate 32 is etched from the opening 51 so that the semiconductor substrate 3 is removed.
A gap 33 is formed in the upper surface of the second 2 and a bridge 35 is formed by the insulating thin film 34 (FIG. 10 (j)).

If the fluid detection sensor 31 is manufactured by additionally doping impurities in the heater formation region in this way, unnecessary doping processing time can be reduced, and a fluid detection sensor with good sensitivity can be manufactured efficiently. be able to.

(Second Embodiment) FIGS. 11 and 12 are a plan view and a sectional view showing the structure of a fluid detection sensor (gas flow sensor) 61 according to still another embodiment of the present invention. FIG. 11 shows a thermopile 37 after removing the protective film 40 and the like.
And a plane where the heater 36 is exposed. In the fluid detection sensor 61, the thermopile 37 is provided only on one side (upstream or downstream) of the heater 36 on the upper surface of the bridge section 35. According to such a structure, measurement can be performed in a higher flow velocity region than that according to the first embodiment.

FIG. 13 is a diagram showing a heater control circuit 62 used for the flow rate detection sensor 61 in which the thermopile 37 is disposed on the upstream side. This heater control circuit 62
Functions to automatically adjust the heat generation temperature of the heater 36 to a temperature higher than the ambient temperature detected by the resistance temperature detector 52 by a certain temperature. The heater control circuit 62 includes fixed resistors 63 and 64, voltage dividing resistors 65 and 66, an operational amplifier (differential amplifier circuit) 67, and a transistor 68. The fixed resistors 63 and 64 constitute a bridge circuit together with the heater 36 and the resistance temperature detector 52, and
The middle point of the resistor 3 and the resistance temperature detector 52 is connected to the inverting input terminal of the operational amplifier 67, and the middle point of the fixed resistor 64 and the heater 36 is connected to the non-inverting input terminal of the operational amplifier 67. The transistor 68 is inserted between the power supply and the fixed resistor 63, and the voltage dividing resistors 65 and 66 connected in series are connected between the base of the transistor 68 and the ground. The output of the operational amplifier 67 is connected to the middle point of the voltage dividing resistors 65 and 66.

The heater control circuit 62 is to maintain the thermal equilibrium state of the heater 36 at a certain temperature higher than the ambient temperature. For example, the heater control circuit 62 changes from a thermal equilibrium state in a no-wind state to a state in which gas flows. When the temperature of the heater 36 decreases, the potential of the non-inverting input terminal of the operational amplifier 67 decreases, drives the transistor 68, and repeats the operation of supplying the current and establishing the thermal equilibrium state again. The same applies when the ambient temperature changes. More specifically, in the heater control circuit 62, when the heat generation temperature of the heater 36 rises above the temperature at the time of equilibrium, the current output from the operational amplifier 67 increases. Voltage rises. As a result, the base current of the transistor 68 decreases, and the current flowing in the bridge circuit also decreases. As a result, the current flowing through the heater 36 decreases,
The exothermic temperature drops. Conversely, when the heat generation temperature of the heater 36 becomes lower than the temperature at the time of equilibrium, the current output from the operational amplifier 67 decreases, so the voltage at the midpoint of the voltage dividing resistors 65 and 66 decreases. As a result, the base current of the transistor 68 increases, and the current flowing in the bridge circuit also increases. As a result, the current flowing through the heater 36 increases, and the heat generation temperature of the heater 36 increases.

When the temperature of the resistance temperature detector 52 for detecting the ambient temperature rises above the temperature at the time of equilibrium, the current output from the operational amplifier 67 decreases.
The voltage at the midpoint between 5 and 66 decreases. As a result, the base current of the transistor 68 increases, and the current flowing in the bridge circuit also increases. As a result, the current flowing through the heater 36 increases, and the heat generation temperature of the heater 36 increases. Conversely, when the heat generation temperature of the resistance temperature detector 52 becomes lower than the temperature at the time of equilibrium,
Since the current output from the operational amplifier 67 increases, the voltage at the midpoint between the voltage dividing resistors 65 and 66 increases. as a result,
The base current of the transistor 68 decreases, and the current flowing in the bridge circuit also decreases. As a result, the current flowing through the heater 36 decreases, and the heat generation temperature of the heater 36 decreases.

The heater control circuit 62 automatically adjusts the temperature of the heater 36 by the above operation so that the heat generation temperature of the heater 36 is kept constant. When the temperature is lowered and the detection temperature of the resistance temperature detector 52 rises, the temperature of the heater 36 is also raised.

Next, conditions for maintaining the heat generation temperature of the heater 36 in the heater control circuit 62 as described above at a certain temperature higher than the temperature of the temperature measuring resistor 52 will be clarified. Now, let the resistance temperature coefficient of the heater 36 be βh and the resistance value of the resistance bulb 52 be βb. If the resistance value of the resistance temperature detector 52 is Rh at a certain ambient temperature, the resistance of the heater 36 is higher than that by a certain temperature and the resistance value is Rb, and the bridge circuit is in an equilibrium state, the following (3) ) Formula holds. However, R1 and R2 are two fixed resistors 63 and 64
Is the resistance value. R1 · Rh = R2 · Rb (3)

From this equilibrium state, the ambient temperature becomes ΔT (° C.).
Considering the case where the temperature rises only, the temperature of the resistance temperature detector is as follows: Rh (ΔT) = Rh (1 + βh · ΔT) (4) At this time, the temperature of the heater 36 also rises by the same amount, and the bridge circuit only needs to be balanced by the resistance value Rb (ΔT) = Rb (1 + βb · ΔT) (5). Should be satisfied. R1 · Rh (ΔT) = R2 · Rb (ΔT) (6) By substituting equations (4) and (5) into equation (6), R1 · Rh (1 + βh · ΔT) = R2 · Rb (1 + βb) .DELTA.T) (7) When the above equation (3) is applied to this equation, βh · ΔT = βb · ΔT (8) is obtained.

Therefore, it can be seen that if βh = βb, the condition is satisfied for an arbitrary temperature rise ΔT. Therefore,
Using the heater control circuit 62 as shown in FIG. 13, the resistance temperature coefficient βb of the resistance temperature detector 52 and the resistance temperature coefficient βh of the heater 36 are calculated.
It can be understood that if the values are equal, the heat generation temperature of the heater 36 can be controlled to a value higher by a certain temperature than the temperature detected by the resistance temperature detector 52. Since the resistance temperature coefficient of the semiconductor is determined by the doping amount, the heater 36 and the temperature measuring resistor 52 are manufactured in the same process, and if the doping amounts are made equal, the ambient temperature is measured by the temperature measuring resistor 52 and the heater 36 is measured. Can be adjusted to a value higher than the ambient temperature by a certain temperature.

[0053]

According to the fluid detection sensor of the present invention, by making the doping amount of the heating element and the doping amount of the contact potential difference measuring element different, the resistance of the heating element is reduced and the output of the contact potential difference measuring element is increased. And the sensitivity can be further improved.

[Brief description of the drawings]

FIG. 1 is a plan view showing a structure of a conventional fluid detection sensor.

FIG. 2 is a sectional view taken along line AA of FIG.

FIGS. 3 (a), 3 (b), 3 (c), 3 (d) are cross-sectional views for explaining a manufacturing process of the fluid detection sensor according to the first embodiment.

4 (e), (f) and (g) are continuation diagrams of FIG.

5 (h), (i) and (j) are continuation diagrams of FIG.

FIG. 6 is a plan view illustrating a structure of a fluid detection sensor according to an embodiment of the present invention.

FIG. 7 is a sectional view taken along line CC of FIG. 6;

8 (a), (b), (c) and (d) are cross-sectional views for explaining a manufacturing process of the fluid detection sensor according to the first embodiment.

9 (e), (f), (g), (h) and (i) are continuation diagrams of FIG.

10 (j) (k) (l) (m) are continuation diagrams of FIG. 9;

FIG. 11 is a plan view illustrating a structure of a fluid detection sensor according to another embodiment of the present invention.

FIG. 12 is a sectional view of the fluid detection sensor according to the third embodiment;

FIG. 13 is a diagram showing a heater control circuit used in the above fluid detection sensor.

[Explanation of symbols]

 Reference Signs List 32 semiconductor substrate 34 insulating thin film 35 bridge section 36 heater 37, 38 thermopile 52 resistance temperature detector

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaru Sasaki 10 Okayama Todocho, Ukyo-ku, Kyoto, Kyoto Prefecture (72) Inventor Kenichi Nakamura 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas (72) Inventor Tokudai Neda 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas Co., Ltd. F-term (reference) 2F035 EA02 EA08

Claims (5)

[Claims] An insulating thin film at least partially supported by air in a substrate, a heating element disposed on a surface of the air supporting portion of the insulating thin film and doped with impurities, and the insulating film sandwiching the heating element. At least two contact potential difference thermometers disposed on the surface of the thin film and having one conductive wire doped with an impurity, and an impurity doping amount of one of the conductive wires constituting the contact potential difference thermometer and the heating element Wherein the doping amounts of impurities are different from each other. 2. An insulating thin film at least partially supported by air in a substrate, a heating element disposed on a surface of the air supporting portion of the insulating thin film and doped with impurities, and an insulating film on one side of the heating element. A contact potential difference thermometer disposed on the surface of the thin film and having one of the conductive wires doped with an impurity; and an impurity doping amount of one of the conductive wires constituting the contact potential difference thermometer and an impurity doping of the heating element. A fluid detection sensor characterized in that the amounts are different from each other. 3. The fluid detection sensor according to claim 1, wherein the heat generating element and one of the conductive wirings forming the contact potential difference temperature measuring element are made of polysilicon. 4. The fluid detection sensor according to claim 1, further comprising an ambient temperature measuring resistor for measuring an ambient temperature, the impurity doping amount of the heating element and the ambient temperature measuring resistor. And a fluid detection sensor. A step of forming an insulating thin film on a surface of the substrate; a step of forming a first material on the insulating thin film; a step of doping substantially the entire surface of the first material; Forming a heating element and one of the conductive wirings of the contact potential difference temperature measuring element by patterning the first material; and further doping the heating element or a region of the first material which is to be a heating element. A method for manufacturing a fluid detection sensor, comprising: a step of forming the other conductive wiring of the contact potential difference measuring element.