JP2860086B2 - Microcap for humidity sensor and humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a microcap for a humidity sensor and a humidity sensor to which a micromachining technique is applied.

[0002]

2. Description of the Related Art Conventionally, various types of moisture-sensitive elements or humidity sensors have been developed. Particularly, as a sensor for detecting relative humidity in an atmosphere, the electric resistance value or electric capacity of the moisture-sensitive material is different from that of the atmosphere. The following are mainly known using the change in response to moisture or water vapor in the inside. A sintered body of a metal oxide such as iron oxide (Fe ₂ O ₃ , Fe ₃ O ₄ ), tin oxide (SnO ₂ ) or a metal oxide film, a hydrophilic polymer film, a polymer electrolyte, and a fiber Examples thereof include those using a polymer, those using an electrolyte salt such as lithium chloride (LiCl), and those in which conductive particles or fibers such as carbon are dispersed in a hygroscopic resin or a hygroscopic polymer film. The above sensors have strengths and weaknesses in the detection humidity range, detection sensitivity and accuracy, response speed, reliability, environmental resistance, etc., respectively.However, for example, the atmosphere temperature suddenly increases, such as the atmosphere during operation in a microwave oven. In order to detect a slight change in water vapor in a changing environment, a change in relative humidity, which is a function of temperature, can be considered as follows. Therefore, there is a large problem in measuring humidity using the above humidity sensor.

That is, when it is assumed that the amount of water vapor in the detection atmosphere is constant and only the temperature of this atmosphere is increased, the relative humidity decreases due to the saturated water vapor pressure even when the amount of water vapor is constant. Furthermore, if the temperature rises sharply, it is expected that a slight increase in water vapor will be offset or decreased as a relative humidity as a relative humidity, and a result reflecting a substantial change in the amount of water vapor will be obtained. Has a major problem in detection.

[0004] Therefore, for humidity measurement of the environment as described above, absolute humidity detection which can directly detect the amount of water vapor is more advantageous than relative humidity detection.

[0005] As a means for detecting the absolute humidity (amount of water vapor), a measuring device to which microwave attenuation or infrared absorption by water vapor is applied has been conventionally used. Since these can directly detect water vapor by a physical method, it is advantageous for detecting a small change in water vapor even in an environment where the above-mentioned rapid temperature change is involved, but the configuration of the device including temperature compensation is Large and costly. In addition, there is a heat conduction type absolute humidity sensor using two thermistors 14 having uniform characteristics utilizing the difference in heat conductivity between wet air and dry air as shown in FIG. 7, and is small in size and excellent in environmental resistance. However, a satisfactory output was not obtained for a minute change in the amount of water vapor, and there was a problem in that the detection sensitivity was increased and the response was high.

Further, as shown in FIG. 8, a heat conduction type absolute humidity sensor makes full use of micromachining technology.
An absolute humidity sensor having a structure in which a sensitive film 15 using a thermistor material and an electrode 16 are formed on a microbridge 3 made of a thin insulating layer 2 on a substrate 1 made of Si to greatly reduce the heat capacity of the element has been developed. As shown in FIG. 7, a high-speed response and a high sensitivity are obtained as compared with a heat conduction type absolute humidity sensor having a structure in which two thermistors are suspended.

[0007]

However, the sensitive film 15 using the above-mentioned thermistor material has a problem in long-term reliability of the thermistor thin film, particularly in thermal stability, and the formation of the electrode 16 is necessary even in the fabrication process. And so on. In addition, it was not satisfactory because it had a problem in thermal stability in terms of high sensitivity characteristics.

The present invention has been made in view of the above circumstances, and has an improved detection sensitivity, low power consumption, high-speed response of characteristics, and a long-term stability microcap for a humidity sensor. And a humidity sensor.

[0009]

According to the present invention, there is provided a humidity sensor comprising:
In the microcap, the first recess and the second recess are common.
The semiconductor substrate is provided on one side of the semiconductor substrate, and is provided on one side of the semiconductor substrate.
The communicating portion that connects the direction side and the other side is the bottom of the first concave portion.
It is characterized by being provided in. In addition, the humidity
In the sensor microcap, one of the above-mentioned semiconductor substrates is used.
The opening of the first concave portion on the side is one side of the semiconductor substrate.
From the side to the communication section
And features.

The humidity sensor of the present invention is a humidity sensor having a detection-side sensitive film and a reference-side sensitive film provided on a semiconductor substrate, wherein the first concave portion of the humidity sensor microcap is provided on the detection-side sensitive film. , The second concave portion is sealed corresponding to the reference-side sensitive film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a sensor to which the microcap of the present invention is applied, for example, there is a humidity sensor. This humidity sensor is a heating film comprising a sensitive film in which a metal material having a large temperature coefficient of resistance is patterned into a shape having a predetermined resistance value on a concave portion of a substrate having the concave portion, and a heat-resistant insulating film covering the same. And at least two moisture-sensitive element structures configured to output a change in the amount of water vapor in the atmosphere around the heat generating film as a change in resistance due to a change in the amount of heat dissipated by the heat generating film. Each of the heat generating film bodies of these element structures is sealed by a microcap having a space of substantially the same volume, and a predetermined amount of water vapor is contained in the sealed space of the reference side element structure, or In a dry state, the sealed space of the detection-side element structure is configured to communicate with the outside, and the amount of water vapor in the detection-side sealed space is detected by an output based on a change in resistance between these element structures.

This moisture-sensitive element structure utilizes the fact that the thermal conductivity of air depends on the amount of water vapor contained in the air, and changes the amount of heat dissipated by the self-heating element due to the change in the thermal conductivity of the atmosphere. The absolute humidity can be detected based on a change in the element temperature (that is, a change in the resistance value of the self-heating element). Further, a humidity sensor using this moisture-sensitive element structure is provided with two moisture-sensitive element structures that are self-heated to a constant temperature, one of which (the first element) is exposed to the detection atmosphere, and the other (the second element). ) Is sealed in a constant humidity atmosphere or a dry atmosphere, and the first and second elements are caused by the self-heating temperature change of each of the first and second elements caused by the change in the thermal conductivity caused by the change in the amount of water vapor in the detection atmosphere. The configuration is such that the amount of water vapor can be detected without being affected by the ambient temperature using the differential output of the change in the resistance value of the element.

In general, in order to obtain a high-sensitivity output, it is important to obtain more heat dissipation from the element for the same change in the amount of water vapor. Here, the amount of heat dissipated by the element is expressed by the following equation.

Q = h (T−T ₀ ) A [q: heat dissipation (kcal / h), T: element temperature (° C.), A: element surface area (m ² ), h: thermal conductivity (kc
al / m · h · ℃) , T 0: ambient temperature (° C.)] Among these, to change the water vapor content change is a thermal conductivity h, A is a constant because the surface area. Therefore,
In order to increase the amount of heat dissipated q for the same change in the amount of water vapor,
It is beneficial to increase (T−T ₀ ), that is, to increase the element temperature T. However, simply raising the operating temperature of the device significantly increases the power consumption of the device,
This leads to a significant decrease in the thermal responsiveness of the device and, in turn, the moisture responsiveness to water vapor.

Therefore, in order to realize high-speed response, low power consumption, and high-temperature operation, it is important to reduce the heat capacity of the element, that is, to have an element structure capable of achieving sufficient thermal insulation of the element heat generating portion.

In this moisture-sensitive element structure, a substrate having a concave portion is used in order to reduce the heat capacity of the element.

The heat-generating film of this moisture-sensitive element structure is composed of a sensitive film made of a metal material having a predetermined resistance value and an insulating film covering the same. As the above-mentioned metal material, a material having a large resistance value change depending on temperature is advantageous. For example, Pt, Ni, etc. can be cited. In particular, a Pt material has excellent operating stability at high temperature and has ensured reliability. This is preferable in that it has unprecedented high sensitivity characteristics in the region.

An example of a structure in which the sensitive film has a predetermined resistance value is that a part of the film is finely processed into a zigzag (meandering) shape at a fixed width and at a predetermined interval.

In this moisture-sensitive element structure, the heat generating film is supported on the concave portion of the substrate. This supporting structure is, for example, a bridge-shaped, cantilever-shaped, or diaphragm-shaped one that can suppress heat conduction from the heat-generating film to the substrate and efficiently dissipate heat from the heat-generating film to the surrounding atmosphere. It may be.

The formation of the heating film composed of the above-mentioned sensitive film and the insulating film covering the same, and the supporting of the heating film on the substrate are performed by a film forming technique such as a thermal oxidation method, a sputtering method or a vacuum evaporation method, and lithography. This can be achieved by using a micromachining technique in a semiconductor process such as the one described above. For details, refer to the description of the embodiment described later.

Further, a humidity sensor for detecting absolute humidity can be constituted by using at least two or more of the above-mentioned humidity-sensitive element structures. In this case, one moisture sensitive element structure is configured to function as a detection side, and the other is configured to function as a reference side. The heat generating film of the element has a structure in which it is in constant contact with an atmosphere having a fixed amount of water vapor or a dry atmosphere so that the reference-side moisture-sensitive element structure can have a constant output, that is, a constant resistance value. In this configuration,
There is a structure in which the heat generating film is sealed in a space containing a predetermined amount of water vapor or in a space maintaining a dry state. On the other hand, the detection-side moisture-sensitive element structure is sealed in the same manner as the reference side, but this sealing is configured to communicate with the outside.
The sealing of the reference-side and detection-side moisture-sensitive element structures is as follows.
For example, a microcap for sealing is produced, and the microcap is bonded to a substrate so as to seal a predetermined heat generating film. For the production of the microcap, a micromachining technology such as an etching technology or a photolithography technology can be used as it is. The cap can be joined by a screen printing method, a coating method, a baking method, or the like. For details, refer to the description of the embodiment described later.

In this humidity sensor, it is preferable that the reference-side heating film and the detection-side heating film have the same supporting structure on the same substrate. In addition, at this time, the above-mentioned two heating film bodies are enclosed and sealed, and further, each heating film body is further individually sealed in the sealing, and pores are formed in the sealing on the detection side. It is preferable that the heat-dissipating elements be provided so as to be able to circulate with the outside, since the heat-dissipating state of both heating elements can be matched as much as possible, and the temperature dependency of the moisture-sensing characteristics can be matched.

In the sealing on the detection side, since the opening of the microcap is made narrower as it advances into the semiconductor substrate, the heat dissipation state of the detection-side sensitive film and the reference-side sensitive film is reduced.
Can be more consistent.

This humidity sensor is configured to be able to detect the amount of water vapor in the detection atmosphere by an output based on a change in resistance between the reference-side humidity-sensing element structure and the detection-side humidity-sensing element structure. As an example of this configuration, there is a configuration in which a bridge circuit is configured by the reference-side moisture-sensitive element and the detection-side moisture-sensitive element, and an unbalanced potential of the bridge circuit is detected as an output.

According to this humidity sensor, the heat generating film composed of the metal film having a large resistance temperature coefficient and the insulating film covering the metal film is supported on the concave portion of the substrate having the concave portion and having a low heat capacity. Therefore, conduction of the amount of heat dissipated from the heat generating film body generated by the predetermined resistance value to the substrate is suppressed, and most of the heat dissipation is determined by the amount of water vapor contained in the atmosphere around the heat generating film body. The change in the conductivity of the atmosphere due to the change in the amount of water vapor contained in the atmosphere is output as a change in the resistance value of the heating film body, and the amount of water vapor in the atmosphere is detected based on the change. It will be.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0027]

1A and 1B are explanatory views of the structure of a moisture-sensitive element structure, FIG. 1A is an explanatory view of a plan structure thereof, and FIG.
FIG. 2C is a cross-sectional configuration explanatory view taken along the line X ′, and FIG. As shown in FIG. 1, after a bridge-shaped thin-film insulating layer 2 is formed on a Si substrate 1, the crystal axis anisotropic etching of Si as the substrate 1 is performed, thereby etching the substrate 1-1 under the insulating layer bridge. A hollow structure is provided between the insulating layer bridge portions (hereinafter referred to as microbridges) 3 to provide an element structure excellent in thermal insulation, that is, low heat capacity, and a sensitive film 4 which is a thin film sensor material is provided on the microbridges 3 in a predetermined manner. A pattern is formed to have a resistance value, and a thin insulating layer 5 is laminated on the sensitive film 4 as a protective film.

The device structure forming process shown in FIG. 1 will be described below in detail. First, on a Si substrate 1 having a different chemical etching rate depending on the orientation of the crystal axis, SiO ₂ , Si ₃ N ₄ to be a lower layer of the microbridge 3 are provided. Alternatively, a thin insulating layer 2 such as Al ₂ O ₃ may be formed by thermal oxidation, sputtering,
It is formed by a vacuum evaporation method or a CVD method. In this embodiment, an SiO ₂ film is formed by a thermal oxidation method in consideration of prevention of generation of an etch pit during subsequent Si etching. At this time, SiO ₂ is simultaneously formed on the back surface and the side surface of the substrate, and is used as a mask for subsequent Si etching. Further, an Al ₂ O ₃ film was laminated by a sputtering method or an anodic oxidation method on the SiO ₂ film in view of the good adhesion of the sensitive layer and the insulating layer, the two layers of Al ₂ O ₃ / SiO ₂ An insulating layer 2 is formed. In this case, the insulating layer 2 may be made of SiO ₂ , Si ₃ N ₄ or Al ₂ , depending on the material of the sensitive film or the method of forming the insulating layer film.
It may have a single-layer structure of an O ₃ film. In consideration of the strength of the bridge and the like, a predetermined thickness of Si is left on the lower surface of the insulating layer of the microbridge 3 to form a cavity below the insulating layer, and has a two-layer structure in which the insulating layer and the Si layer of the substrate material are overlapped. It is also useful to form a bridge. In this case, B (boron) or the like is diffused or doped in advance at a high concentration on the surface of the bridge portion of the substrate to stop the portion at the time of anisotropic etching (chemical etching). When used as a layer, a bridge made of an insulating layer and a Si (B-doped) material can be formed as a result.

Next, a metal material such as Pt or Ni having a large temperature coefficient of resistance is formed on the insulating layer 2 by a sputtering method or a vacuum deposition method. The photosensitive film 4 is patterned on a predetermined portion by photolithography and dry etching or chemical etching so as to have a predetermined resistance value.
And In this embodiment, the sensitive film 4 is etched by dry etching using Pt having excellent chemical and thermal stability, and zigzag (meandering) as shown in FIG.
Patterned in shape. Thereafter, an upper insulating layer 5 serving as a protective film and as a mask for the subsequent Si etching is formed on the sensitive film 4 by a sputtering method, a vacuum deposition method, a thermal oxidation method, an anodic oxidation method, a CVD method or the like. In this method, an Al ₂ O ₃ film having excellent adhesion to Pt and good environmental resistance is formed by a sputtering method.

After the above steps, the substrate S under the lower insulating layer 2
A part of i is removed by etching, and a microbridge 3 composed of the upper and lower insulating layers 2 and 5 and the sensitive film 4 is manufactured. First, the upper and lower insulating layers are patterned into a bridge shape by etching using photolithography technology, chemical etching technology, and dry etching technology, and the Si substrate under the insulating layer is exposed. At this time, the upper insulating layer of the lead wire connection portion (pad portion) 6 to the Pt film is simultaneously etched to form a pad portion. As a specific method of etching, chemical etching using a phosphoric acid solution is used for the Al ₂ O ₃ film, and chemical etching and dry etching are used for SiO ₂ depending on the film thickness. In the pad portion, the upper Al
After etching the ₂ O ₃ film, the Pt film of the sensitive film is exposed,
There is a concern about the effect of etching the lower insulating layer (Al ₂ O ₃ / SiO ₂ ) in other parts, but the Pt film is an Al ₂ O ₃ film,
The pad 6 can be formed satisfactorily and hardly by any etching method of the iO ₂ film. From the exposed portion of the Si substrate thus obtained, E,
P, W solution (ethylenediamine-pyrocatechol-water)
Alternatively, the etching of Si in the preferential crystal axis direction proceeds by chemical etching using an alkali solution such as a KOH solution, that is, the Si under the insulating layer patterned into a bridge shape by the crystal axis anisotropic etching.
Is removed by etching to form a microbridge 3 composed of the sensitive film 4 and the upper and lower insulating layers 2 and 5. It is also effective to use a Si ₃ N ₄ film for the upper and lower insulating layers, and has the same characteristics as the Al ₂ O ₃ film. The upper and lower insulating layers are used as a mask for anisotropic etching, the etching is stopped when the (111) plane is exposed on the (100) Si substrate, and the etching depth is controlled by time.
FIG. 3 shows another explanatory diagram of the structure of the moisture-sensitive element structure.
FIG. 2A is a perspective view thereof, and FIG.
FIG. 2C is a cross-sectional configuration explanatory view taken along the line X ′, and FIG. As shown in FIG.
5 and cantilever 7 with patterning shape of sensitive film 4
The sensitive film 4 can also be formed on the insulating layer described above, and an element with slightly better mechanical strength but better thermal insulation can be manufactured.

The basic structure of the element is formed by the above steps, and the microbridge element and the cantilever element self-generate their respective Pt resistance portions (meandering-shaped patterning portions) (4 in FIG. 2) to a constant temperature. In addition, it is possible to detect steam as a change in the resistance value based on a change in the heat generation temperature due to a change in the amount of steam, which is practically useful depending on the application.

FIGS. 4A and 4B are explanatory views of another structure of the moisture-sensitive element structure, wherein FIG. 4A is a perspective view thereof, and FIG. 4B is a sectional structure explanatory view taken along line XX 'of FIG. (C) is the YY '
FIG. 4 is an explanatory diagram of a line cross-sectional configuration. A thin film insulating layer 2 'is formed on the Si substrate 1' and on the back and side surfaces of the substrate, and the thin film insulating layer 2 'on the back surface of the Si substrate 1' has a predetermined shape as a mask for anisotropic etching according to a pattern required for diaphragm formation. By performing anisotropic etching from the center of the back surface of the Si substrate 1 ′ where the thin film insulating layer 2 ′ is not formed, the central portion of the Si substrate 1 ′ becomes thinner,
A diaphragm 13 'having a two-layer structure of a thin film insulating layer and a Si substrate material is formed on the surface of the substrate 1'.
On the diaphragm 13 ', a sensitive film 4' made of a Ni thin film patterned into a predetermined shape (a meandering structure similar to that shown in FIG. 2) and dimensions is provided, and a protective film is further formed on the sensitive film. Thus, an element having the structure of the diaphragm 13 'is obtained.

The means for forming the stop layer on the substrate material of the diaphragm 13 'is obtained by doping B or the like at a high concentration in advance. Therefore, the diaphragm
It is formed by two layers of a doped substrate material and an insulating layer. Further, the thickness of the substrate material of the diaphragm 13 ′ does not necessarily need to be controlled by doping B or the like.
It is possible to control only by the anisotropic etching time, and furthermore, a structure may be employed in which all the substrate material in this portion is etched and the diaphragm is formed only by the insulating layer.

The diaphragm-type moisture-sensitive element thus obtained has a remarkable improvement in the thermal insulation of the sensitive film, that is, the reduction of the heat capacity of the element, as compared with the conventional heat-conduction-type moisture-sensitive element. However, the response characteristics are slightly inferior to those of a bridge or cantilever type element. However, considering the mechanical strength of the diaphragm, it is more advantageous than the bridge or cantilever type,
It has high sensitivity, high-speed response, and low power consumption, and is useful for application to use environments that require mechanical strength.

Next, the humidity sensor of the present invention has a structure in which the humidity sensing element structure shown in FIG. 1 has a structure for reducing the ambient temperature dependency of the steam sensing characteristics (humidity sensing characteristics) in order to make the steam sensing more accurate. Will be described.

FIGS. 5A and 5B are explanatory views of the configuration of an embodiment of the humidity sensor of the present invention. FIG. 5A is a perspective view of the humidity sensor, and FIG. is there.

In the humidity sensor of FIG. 5, a microbridge element (FIG. 1) or a cantilever element (FIG. 3) having the same characteristics is manufactured on the same substrate, and two microbridges 3, 3 or cantilevers 7, 7 are connected. At the same time, the device is hermetically sealed with a microcap 8 produced by anisotropically etching Si to form one device. However, a minute hole 11 through which water vapor can enter and exit is provided on the water vapor detection (sensor (hereinafter referred to as sensor)) side, and the reference (reference (hereinafter referred to as reference)) side does not have any water vapor as described above. Hermetically sealed. With the thus obtained sensor, two microbridge elements of the reference or the Pt resistor of the cantilever element and other fixed resistors, for example, a bridge circuit having the configuration shown in FIG. 6 is assembled to obtain an output (V _OUT ), thereby obtaining the ambient temperature. Noise factors for the output due to fluctuation or the like can be canceled, and only the output due to water vapor fluctuation can be obtained with high accuracy. That is, the temperature dependency of the humidity sensitivity can be corrected using the reference element. Hereinafter, the microcap manufacturing process, the sensor element, the method of bonding the reference element to the microcap, and the like of the element of this embodiment will be described in detail.

First, regarding the production of a sensor and a reference element (main element (hereinafter referred to as main element)), two microbridge elements or cantilever elements are formed as one unit (as in the above-mentioned element production of FIGS. 1 and 3). One body element is defined as one body element. Next, the microcap 8 is manufactured. The two cavities (recesses) 9 and 10 of the microcap are etched by etching the Si substrate on which the SiO ₂ film is formed on the entire surface of the substrate by thermal oxidation, and the minute water vapor on the sensor side is allowed to enter and exit. The SiO ₂ film is etched and patterned on the front and back surfaces of the substrate by photolithography and chemical etching or dry etching so that the holes 11 can be formed. Thereafter, the Si portion exposed by the etching of SiO ₂ is formed in the same manner as that of the main body element. P. W. Microcap 8 is obtained by anisotropic etching with an alkaline solution such as KOH. Finally, the microcap thus obtained is joined to the main body element to produce a moisture-sensitive element (FIG. 5). Concrete bonding is performed using a bonding medium 12 such as low-melting glass. That is, a low-melting glass is pattern-formed on the bonding pattern portion of the microcap by a screen printing method, a coating method, or the like, and is aligned with the main body element and fired and bonded in a furnace in an extremely low humidity atmosphere. In this way, the element whose bonding has been completed is mounted on a normal (known) TO package or the like, and wire-bonded to the pad portion 6 to obtain a final element. In the above description of the fabrication process, a single device has been described. However, in actual device fabrication, up to the bonding process, a body device and a microcap are fabricated in wafer units on which a plurality of devices can be simultaneously formed. A process of dividing two wafers simultaneously by dicing to form a single element is performed to improve mass productivity and reduce cost.
Using this element, a change in the amount of water vapor can be detected with high accuracy using the bridge circuit of FIG. The operation mechanism will be described below. A sensor side Pt resistor (R ₁ (≡Rs)) 18 and a reference side Pt resistor (R ₂ (≡≡Rr)) 19 are connected in series, and each Pt resistor self-heats to about 300 ° C. Turn on electricity. At this time, the current limiting resistor (R _L ) 1
7 to prevent overcurrent from flowing, R ₃ 20 and R ₄ 21
And an appropriate fixed resistor, and adjust the initial output of V _OUT 22 before measurement to the reference level. Therefore, R ₄ 21
It is desirable to use a variable resistor. If the amount of water vapor in the atmosphere changes in this state, the heat generation temperature of the Pt resistor 18 on the sensor side, which is affected by the water vapor, changes. Therefore, only the resistance value on the sensor side changes, and the balance of the bridge circuit is lost. A voltage output corresponding to the amount of water vapor is obtained at the _OUT section 22. On the other hand, if the ambient temperature changes,
The sensor side and the reference side receive the same heat-generating temperature fluctuation, so that both resistance values fluctuate. However, since the fluctuation amounts are the same, the output of the _VOUT section 22 remains at the reference level and no output fluctuation is recognized. The temperature dependency of the humidity characteristics is greatly reduced by correction, and highly accurate detection is possible. It is also superior in S / N of the humidity sensitive signal compared to the conventional packaged type, and suitable for obtaining high output by amplifying. I have.

Comparative Example FIG. 9 shows a comparison of humidity-sensitive output (sensitivity) under the same humidity condition. This is an ambient temperature of 40 ° C
Shows the characteristics when the absolute humidity is changed.
As the operation circuit, a known bridge circuit shown in FIG. 6 is used, and a microbridge type a using a Pt thin film according to the present invention as a sensitive film, a microbridge type a ′ using a Ni thin film as a sensitive film, and a thin film thermistor material 15 as a sensitive film. The characteristics of four types of micro-bridge type b (FIG. 8) and type c (FIG. 7) using two beat thermistors 14 were compared. The sensitivity is twice or eight times as high as that of the devices of types b and c.

As for the operating temperature of the device, the device operates at a temperature at which reliability is secured, which will be described later.
a ': about 300 ° C, b: about 150 ° C, c: about 200 ° C. Next, FIG. 10 shows a comparison between the characteristics of the humidity response speeds of the a and c types. The operating circuit and operating temperature are the same as those in the sensitivity comparison (FIG. 9).
This is the response characteristic of the circuit output when the ambient humidity is rapidly changed from 10 g / m ³ to 35 g / m ³ at ℃, where a is about 5 sec, c is about 50 sec, and the a-type element of the present invention is a conventional type. It has about 10 times faster response speed than c-type devices. Also, the power consumption of the device is several hundred meters for the c type.
In contrast to the case of W, the type a is as small as several tens of mW and achieves a significant reduction in power consumption.

Further, the high-temperature stability of each of the Pt thin film and the thermistor thin film is compared as reliability. FIG. 11 shows a,
Each of the b-type devices is about 4
00 ° C., illustrates a rate of change with respect to the initial value of the resistance value (R ₀₎ in the evaluation temperature 0 ℃ aging characteristics when allowed to stand by self-heating to about 200 ° C.. In the thermistor thin film b type device, R ₀ (resistance value) tends to increase and changes largely, whereas in the Pt thin film device a type device of the present invention, R ₀ (resistance value) is extremely stable and excellent in reliability. .

As described above, the insulating layer microbridge of the present invention
A moisture-sensitive element in which a Pt thin film is formed on a cantilever or diaphragm has excellent long-term reliability, and has unprecedented low power consumption, high-speed response, and high sensitivity characteristics.

The structure of the humidity sensing element used in the humidity sensor of the present invention has the following extremely useful characteristics in practical use.

(1) It can be applied to a heat conduction type absolute humidity sensor and can directly detect the amount of water vapor. This is more advantageous than the relative humidity detection particularly when measuring the humidity when the temperature of the detected atmosphere involves a sudden change. .

(2) The element structure using the microbridge, cantilever or diaphragm structure is excellent in thermal insulation of the sensitive film. That is, the heat capacity of the element is reduced as much as possible, and the sensitive film is made of a chemical such as Pt, Ni or the like. By using a thin film made of a material that is thermally stable and has a large resistance temperature coefficient, it is possible to achieve unprecedented stability, high sensitivity of water vapor detection, high-speed response, and low power consumption.

(3) Since water vapor is detected by a physical method, the device is stable against contamination and the like of the element surface and has good environmental resistance.

(4) The device can be manufactured in a batch process (wafer process) by an ordinary semiconductor process or its application process, and has excellent reproducibility and compatibility, and can be a low-cost device.

As described in detail above, this moisture-sensitive element structure is effective for detecting the absolute humidity, can be manufactured at low cost, has good environmental resistance, and has a greatly reduced heat capacity. It has many excellent characteristics, such as high sensitivity, high-speed response, and low power consumption operation.It is suitable for various applications and is extremely useful in practical use as a humidity sensor. It is intended to provide a humidity sensor suitable for application as a sensor or the like.

[0049]

The microcap for a humidity sensor according to the present invention.
According to this, it is possible to manufacture the semiconductor substrate in wafer units.
Excellent mass productivity, and has a detection side and a reference side
When used for a sensor, the thermal diffusion state between the detection side and the reference side is better.
The humidity sensor can be made inexpensively.
As well as greatly reducing the heat capacity of the humidity sensor,
Sensitivity, high-speed response, long-term stability, and low power consumption operation
Can be realized.

According to the humidity sensor of the present invention, in detecting the absolute humidity, the humidity sensor can be manufactured at low cost.
The heat capacity of the humidity sensor can be significantly reduced, high sensitivity, high-speed response, long-term stability, and low power consumption operation can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of a moisture-sensitive element structure.

FIG. 2 is a perspective view schematically showing a patterning shape of a sensitive film in a moisture-sensitive element structure.

FIG. 3 is a configuration explanatory view of another moisture-sensitive element structure.

FIG. 4 is a configuration explanatory view of still another moisture-sensitive element structure.

FIG. 5 is a diagram illustrating the configuration of a humidity sensor.

FIG. 6 is a circuit diagram showing an example of an operation circuit of the humidity sensor.

FIG. 7 is a diagram illustrating a configuration of a moisture-sensitive element using a conventional bead-type thermistor.

FIG. 8 is a diagram illustrating the configuration of a micro-bridge type moisture-sensitive element using a conventional thin-film thermistor.

FIG. 9 is a diagram illustrating a comparison of humidity sensitivity due to a difference in the structure of a moisture-sensitive element.

FIG. 10 is a comparative explanatory diagram of a moisture-sensitive response speed depending on a difference in the structure of a moisture-sensitive element.

FIG. 11 is a diagram illustrating a comparison of stability over time due to a difference in the structure of a moisture-sensitive element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Insulating layer 3 Micro bridge 4 Sensitive film 5 Insulating layer 6 Pad part 7 Cantilever 8 Micro cap 9 Cavity (sensor side) 10 Cavity (reference side) 11 Micro hole 12 Bonding medium 13 'Diaphragm

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Yoshiyoshi Shuji 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Yasuhiko Inami 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Nobuo Hashizume 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (56) References JP-A-63-263426 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) G01N 27/00-27/24

Claims (3)

(57) [Claims] A first concave portion and a second concave portion are provided on one side of a common semiconductor substrate, and one side of the semiconductor substrate is provided.
A communication part communicating between the first side and the other side is provided at the bottom of the first recess.
A microcap for a humidity sensor, wherein the microcap is provided. 2. A first concave portion on one side of the semiconductor substrate.
Opening from one surface side of the semiconductor substrate to the communication portion.
Claims characterized as becoming narrower as it progresses
Item 7. A microcap for a humidity sensor according to Item 1. 3. A detection-side sensitive film and a reference-side sensor on a semiconductor substrate.
3. The humidity sensor according to claim 1 , wherein the humidity sensor is provided with a membrane.
The first concave portion of the microcap for the detection side sensitive film
In addition, the second concave portions correspond to the reference-side sensitive films, respectively.
A humidity sensor characterized by being sealed.