JPH05288705A - Sensor element - Google Patents

Abstract

PURPOSE:To improve the responsiveness of temperature detection by a method wherein a resistor for temperature detection is provided in a first recession of a first substrate and a resistor for temperature reference in a second recession, a part of the first recession is exposed, the second recession is covered with a second substrate and the capacity of the second recession is set to be larger than that of the first recession. CONSTITUTION:In the case when a humidity sensor S1 is placed in dry air, the amount of thermal dissipation from the sensor itself is small, and setting is made so that internal temperatures of two cavities 3 and 4 be balanced. When the sensor is placed in humid air, the amount of thermal dissipation becomes large in accordance with the quantity of water vapor in the air and the temperature of a microbridge 6 for humidity detection lowers. Although the surface temperature of the sensor and/both of the internal surface temperatures of the cavities 3 and 4 lower at the same time, the temperature is lowered only by thermal conduction from a silicon substrate, since a microbridge 5 for temperature reference is sealed hermetically. The capacity of a second recession is larger than that of a first recession, the wall thickness of the hermetically sealed cavity 3 is small and thereby the effect of thermal conduction is improved. Thereby the internal temperatures of the two cavities 3 and 4 can be balanced quickly and the responsiveness of humidity detection is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor element mainly used in a food cooking device such as a microwave oven and a microwave oven.

[0002]

2. Description of the Related Art As a conventional sensor element of this type,
A humidity sensor in which two microbridges made of thin film metal are arranged as a temperature reference (reference) resistance and a humidity detection resistance in a cavity of a silicon substrate (see, for example, JP-A-2-179459), or a thin film metal on a silicon substrate. A gas sensor in which a metal oxide gas adsorbent is formed by forming a microbridge (see, for example, “Nikkei Mechanical” No. 7-1, 1985) is known.

[0003]

In adopting such a sensor element in a food cooking device,
As a temperature bias, the gas / humidity sensing part of the device is about 30
An external circuit is added so that a current is caused to flow from 0 ° C. to 400 ° C. and self-heating occurs. The gas and humidity sensing accuracy of the sensor element is determined by the stability of this temperature bias, but it is expected that the environment in which the sensor element is set will be extremely severe.

That is, since the cooking device in which the sensor element is installed heats the food, the temperature of the cooking device itself largely changes at the beginning of cooking operation and at the end of the heating of the food, and further, it is directly exposed to steam or gas generated from the food. Therefore, temperature drift of the sensor element is unavoidable.

In particular, in the humidity sensor, it is an essential condition that the temperature characteristics of the temperature reference resistance and the humidity detection resistance bridge are the same, but the humidity detection resistance bridge is exposed to air containing moisture, so that it is a cavity. It also radiates heat itself, which causes a temperature difference with the cavity of the sealed temperature reference resistor bridge.

Further, since the temperature difference between the inner surfaces of the cavities of the two bridges varies depending on the temperature of the air to be measured and the ambient temperature, a temperature drift that adversely affects the detection accuracy of the sensor element is generated. Therefore, when adopting the sensor element, it is necessary to perform temperature compensation in consideration of this temperature drift.

Further, regarding the installation place of the sensor element in the cooking device, the place where the gas containing steam / gas from the food can be surely detected from the oven to the exhaust port of the cooking device case is extremely limited. Therefore, when each element is enclosed in an independent package, there are restrictions on the mounting location depending on the structure of the cooking device.

The present invention has been made in consideration of such circumstances, and provides a sensor element which has a good detection response, a high detection accuracy, and is easily installed.

[0009]

According to a first aspect of the present invention, in a sensor element configured to measure humidity by combining a temperature reference resistance and a humidity detection resistance, first and second recesses are formed on the surface. The first substrate having, the humidity detecting resistor provided in the first recess, the temperature reference resistor provided in the second recess, and a part of the first recess are exposed and the second recess is sealed. As described above, the present invention provides a sensor element including the second substrate that covers the first substrate, wherein the volume of the second recess is set to be larger than the volume of the first recess.

Further, the invention of claim 2 is a humidity sensor configured to measure humidity by combining a resistance for temperature reference and a resistance for humidity detection, and a gas for detecting gas by a gas adsorbent of metal oxide. A sensor element including a sensor, the first substrate having three recesses on the surface, a humidity detecting resistor provided in the first recess, and a temperature reference resistor provided in the second recess, A gas adsorbent provided in the third recess, and a second substrate that partially exposes the first recess and the third recess and covers the first substrate so as to seal the second recess.
A sensor element having a substrate is provided.

[0011]

In the invention of claim 1, when the sensor element is exposed to moist air, the volume of the second concave portion is larger than the volume of the first concave portion, so that the conductive heat dissipation effect from the outside causes both concave portions to be exposed. The temperature equilibrium of the inner surface is accelerated, and the responsiveness of humidity detection is improved.

In the invention of claim 2, since the humidity sensor and the gas sensor are integrated, the temperature stability of the humidity sensor is improved. That is, when the third recess is present on the same first substrate when exposed to humid air, the internal surface temperature drop of the first recess is mitigated by the conductive heat of the substrate, and therefore the humidity detection Accuracy is improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. This does not limit the invention.

Embodiment 1 FIG. 1 is a sectional view showing a sensor element (humidity sensor) according to Embodiment 1 of the present invention, FIG. 2 is a top view thereof, and FIG. 3 is a top view of a main part thereof. In the sensor element S1 of these figures, the cavity 3 and the cavity 4 are formed by the recess of the silicon substrate 1 and the recess of the sensor cap 2, and inside the cavity 3 and the cavity 4, the microbridge 5 for temperature reference and the humidity detection, respectively. A microbridge 6 for use is provided. The size of the cavity 3 in which the temperature reference microbridge 5 is sealed is the humidity detection microbridge 6
Is set to be larger than the size of the cavity 4 provided therein, and for this reason, the thickness of the cavity 3 from the surface of the sensor cap 2 is thin.

Reference numeral 7 denotes an opening provided in the sensor cap 2 so as to face the cavity 4, reference numerals 5a and 5b denote terminal electrodes connected to both ends of the temperature reference microbridge 5, and 6
Reference symbols a and 6b are terminal electrodes connected to both ends of the humidity detecting microbridge 6. Note that FIG. 3 shows the sensor cap 2 in order to show the pattern shape of each microbridge 5, 6.
The upper surface of the silicon substrate 1 after removing is shown.

FIG. 4 shows the inner surface temperature of the cavities 3 and 4 when the humidity sensor S1 of FIG. 1 is exposed to humid air. In the embodiment ((C) of FIG. 4), the humidity detection is performed. It can be seen that the temperature balance between the cavity 4 of the microbridge 6 for application and the cavity 3 of the microbridge 5 for temperature reference is improved as compared with the conventional example ((b) of FIG. 4). That is, when the humidity sensor S1 is placed in dry air, as shown in (a) of FIG. 4, the heat dissipation amount from the sensor itself is small, and the two cavity internal temperatures are set to be in equilibrium.

When placed in humid air, the temperature of the humidity detecting microbridge 6 decreases as the amount of heat dissipation increases in accordance with the amount of water vapor in the air. At the same time, both the surface temperature of the sensor and the internal surface temperature of the cavities 3 and 4 decrease, but since the temperature reference microbridge 5 is sealed, only the amount of heat conduction from the silicon substrate 1 decreases.
Furthermore, since the silicon thickness of the sealed cavity 3 is thin and the heat conduction effect is improved, the internal temperatures of the two cavities 3 and 4 can be quickly balanced.

FIG. 5 shows an example of a drive circuit for the humidity sensor S1. In FIG. 5, Rr represents the resistance of the temperature reference microbridge 5, and Rs represents the resistance of the humidity detection microbridge 6. R _L is a current limiting resistor for maintaining the temperature of about 400 ° C. due to self-heating of the two microbridge resistor portions. In addition, R ₁ and R ₂ are resistors R
R and Rs are fixed resistors that form a resistance bridge, and R ₃ and R ₄ are fixed resistors for determining the amplification factor when the minute voltage detected by the resistance bridge is amplified by the amplifier A.

When the two microbridges 5 and 6 which self-heat up to about 400 ° C. due to only heat dissipation according to the amount of water vapor in the air reach thermal imbalance, the humidity detection bridge resistance Rs in the circuit of FIG. The resistance is reduced due to heat dissipation, the voltage balance of the resistance bridge including the fixed resistances R ₁ and R ₂ is changed, and the input resistance R ₃ of the operational amplifier A is changed in voltage.

The operational amplifier A uses the voltage across R ₃ as R
_It is amplified by ₄ / R ₃ times and the voltage Vout is output. When the amount of water vapor in the air is constant and only the temperature of the air changes, the temperatures of the two microbridge resistors Rs and Rr change at the same time, so the voltage across the resistor R ₃ in the resistance bridge does not change. Therefore, this output voltage Vout corresponds only to the amount of water vapor in the air.

[0021] Figure 6 is a dry air moisture content of about 5 g / m ³ in air, in air with a moisture of about 40 g / m ^3,
It is a graph which shows the effect of this invention.

In this graph, the relationship between the temperature of the air when the humidity sensor detects the absolute humidity and the output voltage Vout of the operational amplifier A is shown. As described above, the two micro bridge resistances R are determined only by the amount of water vapor in the air.
When a temperature imbalance occurs in s and Rr, if the water vapor is constant in FIG. 6, a horizontal solid line graph is obtained.

However, in the conventional humidity sensor,
When the internal surface temperature of the cavity containing the two microbridges becomes unbalanced due to the temperature of the exposed air, the temperature of the humidity detecting microbridge 6, that is, the resistance Rs, is further dissipated in addition to the heat dissipation by the water vapor. Therefore, as shown by the broken line graph in FIG. 6, the circuit output voltage V
Out will have a value higher than the actual humidity.

FIG. 7 is a view corresponding to FIG. 1 showing a modified example of this embodiment. In this humidity sensor, the cavities 3 and 4 have the same size, and the outside of the sensor cap 2 is removed to reduce the cavity wall thickness. It is thin.

FIG. 8 is an exploded perspective view showing an example of a package for mounting the sensor element S1 according to the first embodiment. The sensor element S1 is mounted on the package base 8 and covered with a metal net cover 9. .. The mesh cover 9 is fixed to the package base 8 by the ring 10.

According to the first embodiment, the opening size in the cavity of the humidity detecting microbridge of the humidity sensor can be made relatively large. Therefore, the temperature equilibrium of the inner surfaces of the cavities of the two microbridges is accelerated, and the responsiveness of humidity detection is improved. Furthermore, in automated cooking with food heating and cooking equipment, steam and humidity generated from food are important information that indicates the cooking state of food, so using this humidity sensor, you can cook without losing the timing of the cooking finish. Can be terminated.

Embodiment 2 FIG. 9 is a sectional view of a sensor element showing Embodiment 2 of the present invention. In this sensor element S2, a gas sensor and a humidity sensor are provided on one silicon substrate.

The fabrication process of this element can be achieved by using the micromachining technique in the known semiconductor fabrication process.

In FIG. 9, cavities 13 and 14 are formed by the recess of the silicon substrate 11 and the recess of the sensor cap 12.
15 is formed, the humidity detecting microbridge 17 of the humidity sensor is provided in the central cavity 14, and the cavity 1 at both ends is formed.
5 and 16 are provided with a temperature reference microbridge 16 and a gas sensor microbridge 18 of the humidity sensor, respectively.

FIG. 10 shows the microbridges 16 and 1 with the sensor cap 12 removed from the sensor element S2.
It is a top view which shows the pattern of 7, 18, and the gas sensor microbridge 18 is arrange | positioned on the thin film heater 23 in piles. 16a and 16b are terminal electrodes connected to both ends of the microbridge 16, and 17a and 17b.
b is a terminal electrode connected to both ends of the microbridge 17, 18a and 18b are terminal electrodes connected to both ends of the microbridge 18, and 23a and 23b are terminal electrodes connected to both ends of the heater 23.

FIG. 11 is a top view of the sensor element S2, where 19 and 20 are two openings provided in the upper part of the cavity 14 (FIG. 9), and 21 and 22 are provided in the upper part of the cavity 15 (FIG. 9). There are two openings. Micro bridge 1
6, 17 and the heater 23 are resistors formed (patterned) of metal thin films, and the microbridge 18 is a resistor formed (patterned) of SnO ₂ thin film, and FIG. It is an equivalent circuit of an example.

FIG. 13 shows one of the three microbridges.
A graphical representation of the cavity internal surface temperature of 6, 17, and 18,
This shows the situation where the humidity sensor is temperature compensated by the gas sensor. That is, when the sensor element S2 is placed in odorless dry air, electric current is supplied to each of the three microbridges 16, 17 and 18 so as to stabilize at a preset temperature of about 400 ° C. It

Each of the cavities 15 and 14 of the gas sensor microbridge 18 and the humidity detecting microbridge 17 has an opening, but if the heat is dissipated to the extent that odorless / dry air is used as a medium, the temperature inside the cavity will decrease. Is almost the same as the cavity 13 of the microbridge 16 which is sealed.

When the sensor element S2 is placed in humid air, the temperatures of the gas sensor microbridge 18 and the humidity detection microbridge 17 decrease because the amount of heat radiated by water vapor in the air increases. At the same time, both the surface temperature of the sensor element S2 and the surface temperature of the inside of the cavity decrease, but comparing the decrease of the inside surface temperature of the cavity of the temperature reference microbridge, as shown in FIG. 1
When the temperature drift of 6 and 17 is minimized and an independent current supply is provided to safely maintain the detection sensitivity to odor, the bridge temperature returns quickly and the gas sensor micro as shown in FIG. The decrease in the temperature inside the cavity of the bridge 18 will be alleviated, and the compensation for the temperature inside the cavity of the microbridge 17 for humidity detection will be further improved. The sensor element S
2 can be mounted in a package as shown in FIG. 8 similarly to the sensor element S1 of the first embodiment.

In the automatic cooking in the food heating and cooking equipment, steam, moisture, odor, etc. generated from the food are important information indicating the cooking state of the food, and the operation is completed without missing the timing of the cooking finish. In order to do so, it is necessary to make the sensor multiple functions. According to the second embodiment, compared to the case where independent sensors for gas and humidity are adopted, both can be detected with the same mounting position, so that the sensor element can be easily installed on the cooking appliance. Further, since the humidity sensor can be temperature-compensated, the humidity can be detected with high accuracy regardless of the fluctuation of the environmental temperature of the sensor element.

[0036]

According to the present invention, the sensor element can be easily installed on the cooking device. In addition, it is possible to detect humidity with high responsiveness and accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a top view of the first embodiment.

FIG. 3 is a top view of a main part of the first embodiment.

FIG. 4 is a graph showing temperature characteristics with respect to the position of the inner surface of the silicon substrate cavity of Example 1.

FIG. 5 is a measurement circuit diagram applied to the first embodiment.

FIG. 6 is a graph showing the relationship between the air temperature detected by humidity and the output voltage.

FIG. 7 is a view corresponding to FIG. 1 showing a modified example of the first embodiment.

FIG. 8 is an exploded view of a package for mounting the sensor element of the first embodiment.

FIG. 9 is a sectional view of a second embodiment.

FIG. 10 is a diagram corresponding to FIG. 3 according to the second embodiment.

FIG. 11 is a diagram corresponding to FIG. 2 of the second embodiment.

FIG. 12 is an equivalent circuit diagram of the second embodiment.

FIG. 13 is a graph showing the temperature characteristics with respect to the position of the inner surface of the silicon substrate cavity of Example 2.

[Explanation of symbols]

 1 Silicon Substrate 2 Sensor Cap 3, 4 Cavity 5 Temperature Reference Micro Bridge 6 Humidity Detection Micro Bridge 7 Opening

Claims (2)

[Claims] 1. A sensor element configured to measure humidity by combining a resistance for temperature reference and a resistance for humidity detection, and a first substrate having first and second recesses on the surface,
The humidity detecting resistor provided in the first recess, the temperature reference resistor provided in the second recess, and the first substrate so as to expose a part of the first recess and seal the second recess. A sensor element comprising a second substrate for covering, wherein the volume of the second recess is set to be larger than the volume of the first recess. 2. A sensor element comprising a humidity sensor configured to measure a humidity by combining a temperature reference resistance and a humidity detection resistance, and a gas sensor for detecting a gas by a metal oxide gas adsorbent. A first substrate having three recesses on the surface, a humidity detecting resistor provided in the first recess, a temperature reference resistor provided in the second recess, and a temperature reference resistor provided in the third recess. A sensor element comprising: a gas adsorbent; and a second substrate that partially exposes the first recess and the third recess and covers the first substrate so as to seal the second recess.