JP2735423B2 - Humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor having improved detection sensitivity and detection response.

[0002]

2. Description of the Related Art In recent years, various sensors have been developed and used in various fields. For example, a microwave oven, which is a home electric appliance, is one example, and a temperature sensor and a humidity sensor are used. An example of a humidity sensor that is commonly used, include the structure shown in FIG. In this figure, the first and second temperature sensing elements are provided independently of each other.
As the first and second temperature sensing elements, for example, thermistors are used. In order to detect humidity with two temperature-sensitive elements, it is necessary to expose one side to the outside atmosphere and to reversely shield the other side from the outside atmosphere. The need for such a structure is based on the humidity detection principle. In other words, both thermistors generate heat by themselves, so that both thermistors have substantially the same temperature in the same environment. If one of the thermistors is capable of detecting a temperature change in the external atmosphere and the other is isolated from the external atmosphere so as not to be affected by the temperature change of the external atmosphere, the difference between the two detection values, that is, both thermistors, Is a value related to the absolute humidity in the atmosphere. This means that the thermistor exposed to the external atmosphere detects a change in the heat transfer coefficient due to a change in humidity as a change in the resistance value of the heat-sensitive resistor provided to the thermistor. A change in the heat transfer coefficient due to a change in the temperature of the atmosphere is detected as a change in the resistance value of the heat-sensitive resistor provided therein.

Because of the above detection principle, one of the thermistors in the humidity sensor shown in FIG. 5 has a hole 1a for communicating with the external atmosphere in order to detect the humidity in the external atmosphere. A metal cap 1 having a plurality of openings is mounted, and a metal cap 2 having a closed structure is mounted on the other thermistor to shut off the external atmosphere. These thermistors are mounted on the hermetic seal 3a. Further, since the thermistor which is cut off from the external atmosphere is used for temperature compensation of the other thermistor, both thermistors mounted on the hermetic seal 3a are held on the metal soaking plate 3 so that the temperatures of both thermistors become equal. Have been.

[0004]

However, in such a conventional humidity sensor, since a temperature sensing element such as a thermistor is provided independently, each of them is individually sealed with a metal cap. And the number of components is large. In order to maintain the accuracy of detecting humidity, both thermosensitive elements must have the same thermal responsiveness. Therefore, metal caps of the same shape are used. It is best to place such a metal cap directly in an external atmosphere, so that use of such a metal cap sacrifices humidity detection sensitivity and responsiveness. The present invention has been made to solve such a problem of the conventional humidity sensor. Two temperature-sensitive elements having different structures are formed on the same substrate, and the sealing of these temperature-sensitive elements is performed. It is an object of the present invention to provide a humidity sensor using a metal cap or mesh having good communication with an external atmosphere.

[0005]

According to the present invention, in order to achieve the above object, a first and a second temperature sensing element are integrally formed on the same substrate, and the first temperature sensing element is connected to an external atmosphere. The second temperature sensing element has a hermetically sealed structure so as to be shielded from an external atmosphere, and the substrate is mounted on a metal hermetic seal. Humidity sensor which is configured to be self-heated to substantially the same temperature, and detects an absolute humidity based on a change in a detection value in the first and second temperature sensors based on a change in humidity in an external atmosphere. The hermetic seal is sealed with a metal cap having an opening for communicating with an external atmosphere, and the thermosensitive element is sealed.
The child forms a bridge structure . The first and second temperature sensing elements are integrally formed on the same substrate, and the first temperature sensing element has a structure capable of detecting humidity in an external atmosphere. Has a hermetically sealed structure so as to be shielded from an external atmosphere, the substrate is mounted on a metal hermetic seal, and the first and second temperature sensing elements are configured to be self-heated to substantially the same temperature. , a humidity sensor for detecting absolute humidity based on the change of the detected value of the first and second temperature sensitive elements based on humidity change in the ambient atmosphere, the first second temperature sensitive
For the device, a SiO ₂ film was formed on the entire surface of the substrate by thermal oxidation
Two cavities in the cap by etching into the Si substrate and
A small hole through which water vapor can enter and exit on the sensor side can be formed.
Photolithography technology and chemical
SiO ₂ by etching or dry etching technology
Etch the film and remove the exposed Si portion in the same way
By anisotropic etching with an alkaline solution
It is characterized by being sealed with the obtained bridge structure cap .

[0006]

The humidity sensor of the present invention constructed as described above has a first temperature-sensitive element having a structure capable of detecting the humidity in the external atmosphere on the same substrate and a sealed structure for isolating from the external atmosphere. Since the second temperature sensing element is integrally formed, the heat uniformity between the two elements is very excellent. Therefore, a metal cap having a plurality of holes or a metal mesh can be used as a cap for preventing electrical corrosion of a lead wire caused by vapor condensation. Even if such a cap is used, the thermal uniformity is good as described above, so the thermal responsiveness of both thermosensitive elements is always the same, and the detection accuracy and responsiveness are improved without lowering the detection sensitivity. Can be done.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B are views showing the element structure of a humidity sensor according to the present invention, wherein FIG. 1A is a perspective view thereof, and FIG. 1B is a sectional view taken along line XX ′. The humidity sensor shown in the figure has a bridge structure cap 7 in which a microbridge element 4 or a cantilever element 5 having the same characteristics is formed in the same substrate and two microbridges or cantilevers are simultaneously subjected to Si anisotropic etching. It is hermetically sealed to form one element. Micro holes 6 are formed on the microbridge side so that water vapor in the external atmosphere can enter and exit, and the cantilever side has a hermetically sealed structure so as to completely prevent the entrance and exit of water vapor in the external atmosphere. From the output terminal of the sensor having such a structure, only the signal due to the fluctuation of water vapor is output with high accuracy. The humidity sensor having such a structure is manufactured as follows. First, regarding the manufacture of the sensor as the first temperature-sensitive element and the reference element as the second temperature-sensitive element,
One microbridge element 4 or cantilever element 5 is formed on the same substrate 10 to form one main body element as one unit. Next, the cap 7 is manufactured so that two cavities 8 and 9 of the cap 7 and micro holes 6 through which water vapor can enter and exit from the sensor side can be formed by etching a Si substrate having an SiO ₂ film formed on the entire surface of the substrate by thermal oxidation. Next, 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. Thereafter, the Si portion exposed by the etching of SiO ₂ is anisotropically etched with an alkaline solution in the same manner as the main element. Finally, the cap 7 thus obtained and the body element are joined to produce a temperature-sensitive element. Specifically, this bonding is performed using a bonding medium 11 such as glass having a low melting point.
That is, a glass 11 having a low melting point is formed in a pattern on the joining pattern portion of the cap by a screen printing method, a coating method, or the like. The element completed in this manner is mounted on a known TO package or the like, and wire-bonded to the electrode portion 12 to form a final element. Using this element, changes in water vapor are detected with high accuracy. The temperature sensing element uses a platinum thin film resistor, and the temperature sensing part has a bridge structure in order to improve heat generation efficiency. The size of this humidity sensor is about 5 mm square, and the temperature uniformity between the two temperature sensing elements is very excellent. Also, the reason why the above gap is provided is that since the detection target is humidity, it is necessary to always consider the electrolytic corrosion due to dew condensation, and it is necessary to limit the arrival of humidity to the sensor part to some extent.

FIGS. 2 to 4 show various embodiments of the humidity sensor according to the present invention. FIG. 2 shows a state where the humidity sensor is mounted on a hermetic seal. The humidity sensor 13 is attached to a hermetic seal 15 as shown in the figure, and is connected to a lead wire portion 16 attached to the hermetic seal 15 by a wire 14. Then, as shown in FIG. 3, a metal cap 17 having a plurality of holes 17a is attached to the hermetic seal 15 so as to cover the humidity sensor 13. Further, instead of the metal cap 17, as shown in FIG.
Is attached. Since the metal mesh 18 does not have a mountability with the hermetic seal 15 by itself, the metal mesh 18 is attached by the mesh press fitting 19. By adopting such a structure, even if a metal cover is attached to the humidity sensor 13, the cover has no relation to the detection accuracy and the responsiveness of the humidity sensor 13, so that a very high precision detection is possible. Can be done quickly. Conventionally, in order to match the thermal responsiveness of the temperature sensing elements on both sides, there was a restriction on the above-described gap structure due to the structure.
In the sensor of the present invention, since the sensor portion has excellent heat uniformity, it can be sealed with a metal cap depending on the installation conditions of the sensor and the required response, and the cap has a plurality of holes as described above. It is possible to use ones that are open or meshed. This mesh type has been confirmed to have sufficient reliability even when used in a microwave oven, and when responsiveness is important, a mesh type is used, and when cost is important, a metal cap type is used. Can be used separately.

[0009]

As is apparent from the above description, according to the present invention, two temperature-sensitive elements having different structures are formed on the same substrate, and these temperature-sensitive elements are sealed with an external atmosphere. Since the thermal responsiveness of both thermosensitive elements is always the same, the detection accuracy and the responsiveness can be improved without lowering the detection sensitivity because the heat responsiveness is achieved by using a metal cap or mesh having good communication.

[Brief description of the drawings]

FIG. 1 is a diagram showing an element structure of a humidity sensor according to the present invention, wherein (A) is a perspective view thereof, and (B) is a cross-sectional view taken along line XX ′ of (A).

FIG. 2 is a state diagram when the humidity sensor according to the present invention is mounted on a hermetic seal.

FIG. 3 is a diagram showing a first embodiment of a metal cap of the humidity sensor according to the present invention.

FIG. 4 is a view showing a second mode of the metal cap of the humidity sensor according to the present invention.

FIG. 5 is a structural diagram of a conventional humidity sensor.

[Explanation of symbols]

 4: Micro bridge element (first temperature sensing element) 5: Cantilever element (second temperature sensing element) 6: Hole 7: Cap 8, 9: Cavity 10: Substrate 11: Bonding medium 12: Electrode section 13: Humidity Sensor 14: Wire 15: Hermetic seal 16: Lead wire 17: Perforated metal cap 18: Metal mesh 19: Mesh presser

Claims (2)

(57) [Claims] A first temperature sensing element integrally formed on the same substrate, wherein the first temperature sensing element has a structure capable of detecting humidity in an external atmosphere; The temperature-sensitive element has a hermetic structure so as to be shielded from the external atmosphere, the substrate is mounted on a metal hermetic seal, and the first and second temperature-sensitive elements are self-heated to substantially the same temperature. A humidity sensor configured to detect absolute humidity based on a change in a detection value in the first and second temperature sensing elements based on a change in humidity in the external atmosphere, wherein the hermetic seal has a communication hole to the external atmosphere. together are sealed with a metal cap is opened, the temperature sensing
A humidity sensor, wherein the elements constitute a bridge structure . A first temperature sensing element integrally formed on the same substrate, wherein the first temperature sensing element has a structure capable of detecting humidity in an external atmosphere; The temperature-sensitive element has a hermetic structure so as to be shielded from an external atmosphere, the substrate is mounted on a metal hermetic seal, and the first and second temperature-sensitive elements are self-heated to substantially the same temperature. is configured, a humidity sensor for detecting absolute humidity based on the change of the detected value of the first and second temperature sensitive elements based on humidity change in the external atmosphere, said first
The second temperature sensing element is composed of a SiO ₂ film over the entire surface of the substrate by thermal oxidation.
Two caps by etching on the Si substrate with
The shape of the cavity and the micro hole on the sensor side where water vapor can enter and exit
Photolithography technology on the front and back of the substrate
Technique and chemical etching or dry etching technology
The SiO ₂ film is etched, and the exposed Si portion is
Perform anisotropic etching with an alkaline solution
And sealed with the bridge structure cap obtained by
And humidity sensor, characterized in that are.