KR20040063050A - Module of humidity sensor equipped with heater and humidity sensing method thereof - Google Patents

Abstract

PURPOSE: A humidity sensor equipped with a heater and a method for measuring humidity by using the same are provided to expand life span of a humidity sensor module by effectively removing impurities penetrating into a humidity detecting layer. CONSTITUTION: A heater pattern is formed on an alumina substrate. Both ends of the heater pattern are formed with pads. Then, an insulation layer(53) is formed on an upper surface of the heater pattern in order to achieve uniform thermal conductivity. A lower electrode is formed on an upper portion of the insulation layer(53) and a pad is connected to the lower electrode. An inorganic humidity detecting layer is formed at an upper portion of the lower electrode. Then, an electrode is connected to one side of the heater pattern after forming a porous upper electrode(56) on an upper portion of the inorganic humidity detecting layer.

Description

Heat-absorbing humidity sensor module and humidity measurement method using same {MODULE OF HUMIDITY SENSOR EQUIPPED WITH HEATER AND HUMIDITY SENSING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a heater built-in humidity sensor module, and more particularly, to a heater built-in humidity sensor module and a method for measuring humidity using the same, which can be used for a long time in a high-temperature, high-humidity atmosphere or a harsh environmental condition having a large temperature change range.

Humidity sensors are used in various fields such as cultivation of vegetables in greenhouses, home appliances such as humidifiers and dryers and automatic cookers, and humidity control in automobiles and buildings.

Such a humidity sensor is classified into a thermistor type, a resistance type, a capacitor type, etc. according to its operation principle.

The resistance type or capacitor type mainly uses polymer as a moisture-sensing material, and can measure humidity by using resistance change between electrodes or capacitance change due to moisture adsorption into the polymer through proper electrode arrangement on both ends and top and bottom of the polymer. When described in detail with reference to the accompanying drawings, such a conventional resistance-type and capacitor-type humidity sensor and a method for manufacturing the same.

1A and 1B are perspective views illustrating a manufacturing process procedure of a conventional resistive polymer humidity sensor, forming two resistance patterns 2 and 3 on a substrate 1 as shown therein (FIG. 1A); Forming a polymer sensing layer 4 on the upper side of the two resistance patterns (2, 3) (Fig. 1b).

When the moisture sensor having such a structure absorbs moisture into the polymer sensing layer 4, the resistance components of the two resistance patterns 2 and 3 are changed to detect the change in humidity.

However, temperature is limited because the polymer is used as the polymer sensing layer 4, which is the moisture sensitive material. When the temperature of the organic polymer rises above 60 ° C., the deformation of the material occurs. May decrease the function of.

In addition, when exposed for a long time in an environment in which oil or other contaminants are generated, the surface of the sensing layer 4 is deteriorated, or the surface is blocked so that moisture cannot penetrate, and the moisture-sensitizing property is lowered.

In order to solve this problem, an inorganic material ceramic bulk type humidity sensor that can remove moisture or contaminants adsorbed on the surface of the moisture absorbent material by mounting a canal wire heater around the moisture absorber has been developed. Its response speed is slow, and packaging is difficult, and its application is extremely limited because of problems in reproducibility and uniformity.

2A to 2C are cross-sectional views illustrating a process of manufacturing a conventional capacitor-type polymer moisture sensor, and forming a lower electrode 22 having a predetermined area on the substrate 21 as shown therein (FIG. 2A); Forming a polymer sensing layer 23 on the lower electrode 22 (FIG. 2B); The upper electrode 24 is formed on the polymer sensing layer 23 (FIG. 2C).

The conventional capacitor-type polymer moisture sensor having the above structure detects a change in humidity by measuring a magnitude of capacitance that varies according to the amount of moisture introduced into the polymer sensing layer 23.

At this time, since the polymer is used as the moisture sensitive material, the problem of contamination and the limitation of the use temperature range are applied as described above.

Figure 3 shows the structure of a conventional thermistor type absolute humidity sensor, two thermistor elements 33, 34 separated from each other by the appropriate packaging (31, 32), one element enters the moisture (32) One side is designed to prevent moisture (31) from entering so that the absolute humidity value can be obtained by measuring the humidity by the resistance difference between the two thermistor element materials.

At this time, the material of the thermistor elements 33 and 34 is a material having a temperature characteristic of a negative temperature coefficient (NTC, NEGATIVE TEMPERATURE COEFFICIENT) or a positive temperature coefficient (PTC, POSITIVE TEMPERATURE COEFFICIENT).

As the negative temperature coefficient, a ceramic having semiconductivity is mainly used, and a metal such as Pt or Au is used as a material having a positive temperature coefficient.

The operating principle of the thermistor type is that the thermistor element 34 exposed to moisture in accordance with the change of ambient humidity in the state of heating the element temperature to about 200 ~ 300 ℃ by applying the applied voltage across the element deprives heat and the resistance becomes large. In addition, since the sealed element 33 has no change in resistance, the sealed element 33 is used as a compensating element, thereby converting a resistance difference between these elements into an electrical output to detect a change in humidity.

A signal processing method of the conventional thermistor-type absolute humidity sensor will be described with reference to FIG. 4.

4 shows a signal processing circuit of a conventional absolute humidity sensor, and as shown in FIG. 4, reference voltages corresponding to predetermined resistance ratios R1 and R2 from resistance brush circuits are inverted input terminals of an operational amplifier OP-AMP. A differential amplification circuit applied to the non-inverting input terminal of the operational amplifier and applying a measured voltage according to the resistance ratio between the thermistor elements SE1 and SE2 having a resistance component and inverting and amplifying the difference between the applied voltage values. Configure The variable resistor VR1 is used to finely adjust the resistance ratio of the thermistor elements.

Therefore, the output voltage Vo is generated according to the amplification degree R3 that is differentially amplified. The differential amplification using the operational amplifier is required because the resistance change of the thermistor elements SE1 and SE2 is insignificant. In order for the controller to recognize the difference in the voltage change caused by the insufficient resistance change, the difference is several hundred times. An amplifier to amplify is needed. Since this amplification also amplifies the noise, an expensive shield wire must be used.

As described above, the humidity sensor using the conventional polymer as the moisture sensitive material has a limited use temperature range of about 10 to 60 ° C., which limits its use range, and contaminants or moisture are adsorbed on the surface of the moisture sensitive film to shorten its lifespan. The absolute humidity and humidity sensor using the thermistor has to form two separate packages, which makes the manufacturing process complicated and requires a separate amplification circuit to amplify small resistance changes. There was a problem that an error occurs.

In view of the above problems, the present invention provides a compact, high-performance relative humidity humidity sensor having an integrated structure that can be used for a long time in a high temperature, high humidity environment or a severe temperature change, and a measured value compensated for environmental changes caused by ambient temperature and humidity using the same. It is an object of the present invention to provide a heater built-in humidity sensor module and a humidity measuring method using the same.

Figure 1a and Figure 1b is a perspective view of one embodiment manufacturing process of the conventional relative humidity sensor.

Figures 2a to 2c is another embodiment manufacturing process procedure perspective view of a conventional relative humidity sensor.

3 is a structure of a conventional absolute humidity sensor.

4 is a signal processing circuit of a conventional absolute humidity sensor.

Figure 5a to 5e is a perspective view of a manufacturing process of the present invention the humidity sensor.

Figure 6 is a structural top view of the present invention sensor module.

7 is a cross-sectional view of the present invention the sensor module.

8 is a signal processing circuit of the humidity sensor module of the present invention.

9 is a 200g continuous warming voltage output graph of the present invention the humidity sensor.

10 is a 200g continuous warming standardized value output graph of the humidity sensor of the present invention.

11 is a 300cc warming voltage output graph of the water humidity sensor of the present invention.

12 is a graph showing the 300cc standardized value of the water output of the humidity sensor of the present invention.

* Description of the symbols for the main parts of the drawings *

51: substrate 52: heater

53: insulating film 54: lower electrode

55: moisture sensitive film 56: upper electrode

70: humidity sensor 71: connecting pin

72: printed circuit board 73: upper case

74: lower case 75: signal line

In order to achieve the above object, the present invention is an impedance-changing relative humidity humidity sensor having an insulating film, a lower electrode, a porous inorganic moisture absorbing film, a porous upper electrode and pads for external connection on the heater pattern located on the substrate. Wow; External pins connected to pads of the relative humidity sensor; A printed circuit board supporting the external pins; Signal lines connected to the external pins and extended to the outside; And a case for sealing the entire surface of the structure except for the extension portion of the signal line and the opening for detecting humidity.

The relative humidity sensitivity sensor comprises: a heater part formed by placing two pad parts at each end on an alumina substrate; A planar insulating film positioned above the heater to perform insulation and uniform heat transfer; A lower electrode positioned on the insulating layer and connected to a new pad; A porous inorganic moisture sensitive membrane positioned on an upper front surface of the lower electrode; The upper electrode is positioned on the inorganic moisture-sensitive film and is connected to one of the heater pads.

The present invention relates to a method for measuring an impedance change of the humidity humidity sensor by connecting the inorganic relative humidity humidity sensor module equipped with a heater with a power supply through a resistance, wherein the heater of the relative humidity humidity sensor module is adsorbed for a predetermined time. Removing contaminated moisture or contaminants; Acquiring impedance by the voltage output of the relative humidity humidity sensor while supplying power with a pulse having a sufficient delay time; And averaging the detected impedance based on the impedance at a predetermined time to determine the relative humidity based on the averaged value.

When described in detail with reference to the accompanying drawings, the present invention as follows.

5A to 5E illustrate a manufacturing process procedure of one embodiment of the present invention, a method of forming a heater pattern 52 having pads at both ends thereof on an alumina (Al ₂ O ₃ ) substrate; Forming an insulating film (53) on the heater pattern (52) for insulation and uniform heat conduction; Forming a lower electrode (54) on the insulating film (53), and forming a pad connected to the lower electrode (54); Forming an inorganic moisture sensitive film 55 on the formed lower electrode 54; Forming a porous upper electrode 56 on the moisture sensitive film 55 and connecting an electrode to one end of the heater pattern 52.

Hereinafter, an embodiment of a built-in heater type humidity sensor configured as described above will be described in detail.

First, as shown in FIG. 5A, both ends of the heater pattern 52 are formed of Pt or RuO ₂ to remove moisture or contaminants adsorbed on a moisture sensitive material to be formed on the alumina (Al ₂ O ₃ ) substrate. It is configured in the form of a pad. The heater pattern 52 is heated when a constant voltage is applied, in which case the power consumption used is relatively small compared to the Kantal wire heater. The position of the pad to be formed may be different according to the embodiment.

Next, as shown in FIG. 5B, an insulating film 53 is formed on the heater pattern 52 to electrically insulate between the lower electrode 54 and the heater pattern 52 to be formed thereon. The heat generated by 52 can be evenly transferred to the lower electrode 54.

Next, as shown in FIG. 5C, a lower electrode 54 is formed of Pt or RuO ₂ on the insulating layer 53, and a pad connected to the lower electrode 54 is part of the heater pattern 52. It forms in the part different from a pad.

Next, as illustrated in FIG. 5D, an inorganic moisture sensitive film 55 is formed on the formed lower electrode 54, using a mixture of alumina (Al ₂ O ₃ ) and silica (SiO ₂ ) as a moisture sensitive material. Form. Since the moisture absorbent is a porous inorganic material, not a polymer, the use temperature range is wide and chemically stable. That is, because it has a heat resistance temperature of several hundred degrees, it can be used in a microwave oven or a gas oven.

Next, as illustrated in FIG. 5E, the porous upper electrode 56 is formed of Pt or RuO ₂ on the moisture sensitive film 55, and an electrode is connected to one end of the heater pattern 52.

Therefore, an embodiment of the present invention uses three electrodes, and the two pads formed on the heater pattern 52 may be applied with a ground potential and a heater driving voltage, respectively. Since the upper electrode 53 is connected to one of the pads of the heater pattern 52 and the lower electrode 54 is connected to its own pad, they are used as two electrodes of the relative humidity and humidity sensor. The unconnected one of the four pads shown is intended to match the external pin count and is practically meaningless. This can be omitted.

Since the formed sensor part is connected to the outside through a pad, proper packaging is required to apply the sensor part to an actual application product. Now, to describe the structure of the module including the relative humidity humidity sensor unit of an embodiment of the present invention formed as described above.

5 is a cross-sectional view of a module packaged according to the present invention, a relative humidity humidity sensor, and as shown, four pins 62 are connected to a printed circuit board 61, and the four pins 62 are connected to each other. And pads of the relative humidity humidity sensor unit 60 at the center are connected by a bonding wire. This may be connected to each pin by using an aluminum wire as in the packaging of a general semiconductor chip, or may be electrically connected by similar means.

Therefore, the relative humidity humidity sensor module of the present invention as in the above method can form a package using a general printed circuit board 61, the connection to the outside can also be variously configured using the pins 62. have.

FIG. 6 is a side cross-sectional view of the relative humidity humidity sensor module according to an embodiment, and the upper case 73 having an opening through which moisture can be introduced and an area through which the electrical signal line 75 can pass are shown in FIG. A general printed circuit board 72 is disposed in a sensor module sealed with a lower case 74, and four pins 71 are mounted on the printed circuit board 72, and the pins 71 Each pad of the humidity sensor unit 70 is connected. The pins 71 are connected to the electrical signal line 75 to receive power from the outside and provide a contact point of the internal sensor unit.

Although the relative humidity dehumidification sensor unit 70 is located in the air in the above embodiment, it is noted that it may be located on the substrate or on a predetermined support according to various embodiments.

Now, to configure a signal processing circuit using the present invention the relative humidity humidity sensor module.

7 is an embodiment of a simple signal processing circuit to which the present invention is applied, and as shown in FIG. 7, a relative humidity dehumidification sensor SE3 having one end grounded is connected to a power source through a resistor R _L , and the relative humidity dehumidification is performed. Through the contact between the sensor SE3 and the resistor R _L is configured to know the voltage applied to the relative humidity sensor (SE3).

Of course, the relative humidity humidity sensor module of the present invention may require a power line capable of supplying power to the heater in addition to such a circuit because a heater is built in, but this is obvious to the person skilled in the art, so only the circuit for measuring humidity is considered here. Do it.

As shown in the figure, the external circuit required in the case of using the relative humidity humidity sensor module of the present invention is simply a resistor R _L , and thus its configuration is very simple, and the output voltage (measured according to the value of the resistor R _L ) The voltage change width of Vout) is determined, which can be a voltage that can be used directly by the control unit sufficiently directly. Therefore, no amplification circuit is needed.

In the circuit configured as described above, when the power supply Vcc is applied, the output voltage Vout is output as a ratio of the resistance of the resistor R _L and the moisture sensor SE3, and the impedance of the moisture sensor SE3 is dependent on humidity. Greatly variable. The power supply Vcc is applied in the form of a pulse having a sufficient delay time as shown, and the output voltage Vout is valid only for a time T1 when the corresponding pulse power supply is applied. It is preferable that the measurement period T2 is about several Hz and the pulse voltage application time T1 is several Hz. This sufficient delay time improves sensitivity and reliability. It is also worth noting that only a positive power supply is used for the economical circuit configuration.

The impedance Z of the present invention can be obtained by the following equation.

Humidity can be obtained from this impedance value. Relative humidity measurement using this impedance value means that the humidity is lower if the current measured value is increased more than the previously measured value, and the humidity is increased if it is further reduced. This detects relative humidity changes. In addition to this method, the output voltage Vout may be used.

Subsequently, the actual measurement will show specific changes, but such a simple measurement may cause a significant deviation depending on the external environment, which is prominent when the ambient humidity or temperature is variable. When measured in a high humidity environment and measured in a low humidity environment, the voltage measured at the desired target humidity may be different, which is due to the measurement linearity of the humectant of the humidity sensor.

Therefore, in the present invention, the deviation is reduced by standardizing the value without using the impedance value as it is. This solves the problem that the eigenvalues differ from sensor to sensor and that voltage fluctuations are different depending on the measurement environment.

After the start of the measurement, take the impedance value at a certain point (T3), and then divide it by the measured impedance value. In the present invention, since it is for detecting the completion time of cooking in an application (for example, microwave oven or oven) that varies from low humidity to high humidity, when the impedance value is lowered based on the impedance value taken at a certain time point T3, the standardized value is Although intended to be large, it should be noted that these ratios may differ from one embodiment to another and may be weighted if necessary.

In this embodiment, the normalized value Z _N is as follows.

Now, practical measurement examples will be described to illustrate practical application examples of the present invention. This will clearly recognize the specific advantages of the present invention.

9 is a graph showing the 200g warming experimental data of measuring the output voltage by configuring the present invention relative humidity and humidity sensor module as shown in FIG. This is an example in which the present invention is applied to a microwave oven, and continuous experiments are shown according to the number of times.

For the first 10 seconds, a constant voltage is applied to the built-in heater to remove moisture or contaminants adsorbed on the humidity sensor module. This resets the humidity sensor to its optimal state for measurement.

Afterwards, when measured by applying a voltage having a predetermined frequency, it can be seen that the sensor signal is rapidly decreased in the vicinity of about 120 seconds after stabilization, rice warming, and moisture generation. In the case of continuous measurement, the graph can be seen that the measured value fluctuates while gradually moving toward the applied voltage (5V). For example, if you look at the point of 3V, if you measure one time (lowest graph) and the time of 3V is almost 120 seconds, if you measure 3 times (highest graph), the time of 3V is about 133 seconds. It can be seen that the deviation is more than seconds.

In addition, it can be seen that the voltage fluctuation range (about 4 V in this experiment) of the humidity sensor module of the present invention is very wide.

FIG. 10 is an experimental graph obtained by calculating impedance using the output voltage measured in FIG. 9 and normalizing it to T3 = 60 seconds. As shown in FIG. 9, an x-axis symmetrical graph is shown as using the ratio of impedance values. Note that since the value of T3 is 60 seconds, the previous value is shown in a graph after calculating the impedance value at T3 and can be ignored in actual measurement.

Since the present embodiment is based on the impedance measured at 60 seconds, the normalized value is 1 at 60 seconds in this case. It can be seen that the standardization value fluctuates rapidly in about 120 seconds.

Now, if you look at the deviation between one continuous measurement and three consecutive measurements, you can see that if the normalization value is 2 (that is, moisture is measured that cuts the impedance by half based on a 60-second state without moisture). ), You can see that the deviation is reduced to within 5 seconds.

FIG. 11 is a graph illustrating a measurement value of water warming, which is a more extreme case and may give a sudden change in the humidity environment. Here, the humidity is simply determined by the output voltage. It is a graph when the initial moisture environment is 29% RH, 50% RH, 73% RH at the same temperature (25 degrees), respectively.

As shown in the figure, when heating 300 cc of water in a microwave oven, the water starts to boil within 3 minutes when heated for about 3 minutes. As shown in the graph, the initial output voltage is almost the same, but the output of the humidity sensor varies considerably according to the humidity environment. In the case of high humidity, the output of the humidity sensor is greatly decreased from the beginning, and in the case of low humidity, the output gradually decreases. .

The time at which the output reaches 3V is 3V at 150 seconds at high humidity (73% RH) but 3V at about 215 seconds at low humidity (29% RH). That is, the time difference DELTA T1 reaches 65 seconds. This is fatal to the use of a humidity sensor for automatic cooking. If the measurement time error occurs about 65 seconds, too much cooking or too little cooking occurs. Of course, the timing of instructing the end of cooking after reaching a predetermined measurement value may be different according to various embodiments or the object of cooking, but it is impossible to uniformly cook the food due to the deviation. Of course, in other embodiments, the control accuracy is lowered.

Then, the deviation through the standardization method of the present invention.

FIG. 11 is a standardized graph using the output value of FIG. 10, based on 75 seconds. Again, the value before 75 seconds is a post operation value for graph display, which can be ignored in actual measurement.

Since the impedance value at the point of 75 seconds becomes a reference, the normalized value at that time becomes 1. When the standardization value is 2, the deviation is that in the high humidity (73% RH) environment, the standardization value is 2 at 135 seconds, and in the low humidity (29% RH) environment, the standardization value is 2 at the 165 seconds. It will shrink within seconds. Naturally, the standardized value for determining the target humidity may be changed in various ways, which may be different values depending on the food, the object to be measured, or the application example, and the deviation may be smaller.

Therefore, by using the relative humidity damping module of the present invention, the peripheral circuit can be simplified, the production cost of the module itself can be extremely reduced, and the standard deviation measurement method according to the present invention greatly improves the measurement deviation caused by the ambient environment conversion. can do.

As described above, the present invention can effectively remove moisture and contaminants that penetrate the moisture-sensitive film by using a heater on the relative humidity sensor and using a planar insulating film for even heat transfer, thereby extending the life of the humidity sensor module. have.

In addition, by using a porous inorganic moisture-sensitive film with a strong heat-resistance film, the use temperature range of the humidity sensor can be increased to expand its field of application, and external moisture easily reaches the moisture-sensitive film by using the porous upper electrode. It has the effect of improving the accuracy of the humidity, and by attaching the pin to the general printed circuit board to connect the humidity sensor, packaging can be done without using a separate package, thereby reducing the module manufacturing cost. have.

In addition, by using a single low-frequency square wave as a power source and connecting a resistor in series to directly use a damped sensor output, it is possible to reduce driving circuit configuration cost and increase measurement sensitivity.

In addition, by standardizing the measured impedance value based on the impedance value at a predetermined time, it is possible to reduce the measurement deviation caused by the change of the external environment, thereby improving the accuracy of the humidity.

Claims (7)

An impedance-variable relative humidity humidity sensor having an insulating film, a lower electrode, a porous inorganic moisture sensitive film, a porous upper electrode, and pads for external connection on a heater pattern positioned on a substrate; External pins connected to pads of the relative humidity sensor; A printed circuit board supporting the external pins; Signal lines connected to the external pins and extended to the outside; And a case sealing the entire surface of the structure except for the extension portion of the signal line and the opening for detecting humidity. The apparatus of claim 1, wherein the relative humidity sensor comprises: a heater part formed by placing two pad parts at each end on an alumina substrate; A planar insulating film positioned above the heater to perform insulation and uniform heat transfer; A lower electrode positioned on the insulating layer and connected to a new pad; A porous inorganic moisture sensitive membrane positioned on an upper front surface of the lower electrode; The built-in heater type humidity sensor module, characterized in that the upper electrode is located on the inorganic moisture-sensitive film and is connected to one of the heater pads. The method of claim 1, wherein the porous inorganic moisture-sensitive film is a heater built-in humidity sensor module, characterized in that the heat-resistant, chemically stable metal oxide ceramics, such as alumina or silica. The method according to claim 1, wherein the porous upper electrode is a heater embedded humidity sensor module, characterized in that the metal oxide, such as Pt or RuO ₂ . The method according to claim 1, wherein the pad and the external pins of the relative humidity sensor, the heater embedded humidity sensor module, characterized in that electrically connected using a bonding wire (bonding wire). A method of measuring an impedance change of the humidity sensor by connecting an inorganic relative humidity humidity sensor module equipped with a heater to a power supply through a resistance, wherein the moisture absorbed by operating the heater of the relative humidity humidity sensor module for a predetermined time or Removing contaminants; Acquiring impedance by the voltage output of the relative humidity humidity sensor while supplying power with a pulse having a sufficient delay time; And averaging the detected impedance on the basis of the impedance at a predetermined time to determine relative humidity based on the averaged value of the humidity. The method according to claim 6, wherein the averaging value is a ratio of impedance and impedance measured at a predetermined time, and when the averaging value is more than a predetermined value, it is determined that the target humidity is reached. Humidity measurement method using.