JPH0374943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a humidity detection element for a so-called dew point hygrometer that measures the humidity in an atmosphere based on dew point temperature.

[Conventional technology]

As a hygrometer for detecting the humidity in the atmosphere, one using a hygroscopic material such as ceramic or polymer is already known. Such a hygrometer utilizes the fact that the resistance value or capacitance value of a moisture absorbent body changes depending on the humidity in the atmosphere.

However, although the hygrometer with this type of configuration is characterized by an extremely simple configuration, contaminants from the atmosphere adhere to the hygroscopic body during use.
The disadvantage was that the physical properties of the hygroscopic material changed, resulting in a lack of long-term stability. Therefore, depending on the usage environment, the output value error often reaches a non-negligible level in one to two months.

On the other hand, a dew point hygrometer is well known as a hygrometer that does not have such problems, and specifically has the following configuration.

In other words, the surface of a cooler such as a Peltier cooler is made into a mirror surface, and when water droplets form on this mirror surface, fogging of the mirror surface is detected as a change in light reflectance. It detects dew point temperature. If you know the dew point temperature,
Since the saturated water vapor pressure at a certain temperature is uniquely determined, the water vapor pressure, that is, the absolute humidity of the atmosphere can be known. Note that if you want to know the relative humidity, you can calculate it by further detecting the temperature of the atmosphere.

This dew point hygrometer utilizes the condensation phenomenon of water molecules, which is a phase change in response to water temperature, and does not utilize changes in the physical properties of the sensor element in response to humidity, so it cannot be used for long periods of time. Even when used in an atmosphere with many pollutants, measurement output is unlikely to be distorted.

In recent years, the Delft University of Technology in the Netherlands has attracted attention for their research on using an element that integrates a water droplet detection sensor and a temperature sensor in a dew point hygrometer that uses the Peltier effect. The published literature is
P. P. L. Legtain, Solid State Humidity Sensors, Sensors and Actuators (PPL)
REGTIEN，Solid−state humidity sensors，
Sensors and Actuators, 2 (1981/82) 85−
95.).

This dew point hygrometer is an element that integrates a temperature sensor and a water droplet detection sensor by providing a water droplet detection sensor consisting of comb-shaped electrodes facing each other on a silicon substrate on which a temperature sensor is formed. By placing the sensor on top of a Peltier cooler, it is possible to detect the formation of water droplets in the atmosphere through the cooling of the Peltier effect, and also to measure the temperature at the time of water droplet formation.

In other words, the generation of water droplets causes a sudden change in the electrical capacitance between opposing comb-shaped electrodes, so the cooling action of the Peltier cooler is controlled to maintain the point at which this capacitance changes rapidly, that is, the dew point. The dew point temperature in the dew point state is detected using a temperature sensor formed on a silicon substrate.

[Problem that the invention seeks to solve]

This dew point hygrometer is new in that it uses an element that integrates a water droplet detection sensor and a temperature sensor on the same substrate using IC technology, but it also requires a Peltier cooler to cool the entire element. ,
A large operating current is required to cool the entire device, and the power consumption of the cooler is also large. Furthermore, the heat generated by the cooler must be efficiently dissipated, and there are many restrictions on the design of the entire sensor section including the cooler. Therefore, such a dew point hygrometer is not suitable as a hygrometer that is widely and easily used.

[Means for solving problems]

The humidity detection element of the present invention was made in view of the above problems, and includes a Peltier cooling means in which the cooling part is concentrated in the center of the humidity detection element, and a temperature sensing part is provided near the cooling part. Cooling temperature detection means and water droplet detection means for detecting water droplets adhering to the upper part of the cooling section are formed on a substrate from which the central portion has been removed.

[Effect]

Since the cooling part of the Peltier cooling means is concentrated in the center of the humidity detection element from which the substrate has been removed,
This cooling section is thermally insulated, allowing local cooling with a weak current, and the humidity of the atmosphere can be measured from the outputs of the cooling temperature detecting means and the water droplet detecting means.

〔Example〕

Hereinafter, the present invention will be explained in detail along with examples and manufacturing steps.

FIG. 1 is a perspective view of an embodiment of the present invention during manufacture.

The substrate 20 is made of a metal such as stainless steel or a material such as a single crystal silicon wafer. On this substrate 20, first, a silicon nitride (Si ₃ N ₄ ) film having good moisture resistance is formed to a thickness of about 6000 Å as an insulating layer 22 using a plasma CVD apparatus.

Next, the thickness of the first Peltier metal 24, the first thermocouple metal 28, and the resistance temperature detector 32 is 2μ.
A thin film of P-type lead tellurium (PbTe) is formed on the insulating layer 22 by vapor deposition.

Then, by photolithography, this P-type tellurium lead thin film was formed into the first Peltier metal 24 shown in FIG.
The pattern of first thermocouple metal 28 and resistance temperature detector 32 is selectively etched.

That is, the first Peltier metal 24 is
The first thermocouple metal 28 extends from the periphery to the center like the first Peltier metal 24. It is a band-like pattern.

Further, the temperature measuring resistor 32 is patterned around the surface of the insulating layer 22 so as to surround the first Peltier metal 24 and the first thermocouple metal 28 . Note that this resistance temperature detector 32 functions as a room temperature detection means.

Next, a silicon nitride film is formed as an insulating layer 22 on the surface patterned with the first Peltier metal 24 and the like as described above using a plasma CVD apparatus.
It forms to a thickness of about 3000 Å.

Thereafter, by selectively etching this silicon nitride film using a photolithography technique, a contact hole for a joint between the first Peltier metal 24 and the second Peltier metal 25 to be formed later, and a first A contact hole is created for a joint between the second thermocouple metal 28 and the second thermocouple metal 29 that will be formed later. These contact holes are
Formed at the ends of first Peltier metal 24 and first thermocouple metal 28 .

Next, a thin film of n-type tellurium lead with a thickness of about 2 μm, which will become the second Peltier metal 25 and the second thermocouple metal 29, is placed on the insulating layer 22 including the contact hole.
It is generated by vapor deposition on the entire upper surface.

Thereafter, selective etching is performed using a photolithography technique so that the pattern of the second Peltier metal 25 and the second thermocouple metal 29 shown in FIG. 1 is obtained.

That is, the second Peltier metal 25 connects the central end of the first Peltier metal 24 (the contact hole is formed in the upper part) and another Peltier metal 25 adjacent to the first Peltier metal 24. The first Peltier metal 24 is patterned in a band shape so as to be connected to the peripheral side end (a contact hole is also formed in the upper part).

However, one of the plurality of second Peltier metals 25 has only one end connected to the first Peltier metal 24.
The other end becomes one electrode part of a Peltier cooling means to be described later. Also, one of the plurality or first Peltier metals 24,
Only one end is joined to the second Peltier metal 25, and the other end becomes the other electrode part of the Peltier cooling means.

By this patterning, the first Peltier metal 24 and the second Peltier metal 25 are alternately and continuously connected and electrically integrated to constitute a Peltier cooling means.

That is, among the joints between the first Peltier metal 24 and the second Peltier metal 25, those located at the center of the substrate 20 are referred to as the first joint group 26, and those located at the periphery are referred to as the second joint group. In the case of the joint group 27, passing a current in a predetermined direction causes the first joint group 26 to absorb heat and the second joint group 27 to generate heat. Using this endothermic effect, the first
This makes it possible to cool the central part of the element where the group of joints 26 are concentrated.

The second thermocouple metal 29 has a band-like pattern extending from the central end of the first thermocouple metal 28 in which the contact hole is formed to the peripheral portion in parallel with the first thermocouple metal 28. First thermocouple metal 28
The junction between the thermocouple metal 29 and the second thermocouple metal 29 is the temperature sensing part 30.
The other end portions of both metals serve as electrode portions of a thermocouple serving as cooling temperature detection means.

Subsequently, the insulating layer 2 is again applied so as to cover the Peltier cooling means, the room temperature detection means, and the cooling temperature detection means.
By forming a silicon nitride film with a thickness of approximately 6000 Å using a plasma CVD device, and selectively etching the silicon nitride film using photolithographic technology, each of the Peltier cooling means, cooling temperature detection means, and room temperature detection means is formed. A contact hole is formed in the electrode part.

Thereafter, a thin metal film of aluminum or the like having a thickness of approximately 1 μm is formed by vapor deposition over the entire surface including the contact holes on the insulating layer 22, and this thin metal film is selectively etched using a photolithography technique to form a second layer.
The pads 34a and 34b of the Peltier cooling means and the pad 3 of the cooling temperature detection means as shown in the perspective view of the figure.
5a, 35b, pads 36a, 3 of room temperature detection means
6b and the water droplet detection means 33 are patterned.

As can be seen from the perspective view of FIG.
3a and 33b are opposed to each other so as to mesh with each other to form a flat capacitor.

Next, a silicon nitride film with a thickness of about 6000 Å is formed on both the front and back surfaces of the device using a plasma CVD device. This is because silicon nitride is an extremely stable material and is therefore used as a protective film.

Then, using a photolithographic technique, the silicon nitride film at the center of the back side of the substrate 20 is selectively removed by plasma etching to form an opening, and the substrate 20 is further etched down to the insulating layer 22 through this opening. FIG. 3 is a sectional view showing the state at this time, and it can be seen that a recess 21 is formed in the center of the substrate 20 by etching from the back surface of the substrate 20.

As a final step, as shown in the schematic perspective view of FIG.
By selectively etching a part of the peripheral part of the electrode 33a by photolithography, a through hole 23 communicating between the element surface and the recess 21 is formed, and the electrodes 33a,
Bonding pad openings for connection with external circuits are formed at 33b, . . . , 36a, 36b. Note that this through hole 23 is formed to eliminate a pressure difference between the air in the recess 21 and the atmosphere in contact with the upper surface of the insulating layer 22. Thereafter, the substrate is diced, cut into individual chips, and predetermined packages are formed.

Through the above steps, the humidity detection element of this example is manufactured.

Although the recesses 21 are formed by etching from the back surface of the substrate 20, it is also possible to apply a microbridge structure realized by anisotropic etching of a silicon substrate, as shown in the perspective views of FIGS. 5 and 6. It is.

Further, the patterns of the first Peltier metal 24 and the second Peltier metal 25 are limited to the patterns of the embodiments as long as the first joint group 26, which is a cooling part, can be concentrated in a predetermined place. Needless to say, it is not.

Further, in this embodiment, the Peltier cooling means 2 is the first
The first Peltier metal 24 and the second Peltier metal 25 are alternately connected to form one series circuit, but it is sufficient that at least one series circuit is formed; A series circuit connected in parallel may also be used.

Furthermore, depending on the metal used, the joint between the first Peltier metal 24 and the second Peltier metal 25 may not be an ohmic junction but a semiconductor junction (for example, a shotgun junction). In such a case, if electrical connection is made through a third metal such as nickel, generation of Joule heat in the cooling section can be suppressed, and a decrease in cooling capacity can be prevented.

Furthermore, it is preferable that the first thermocouple metal 28 and the second thermocouple metal 29 be made of the same materials as the first Peltier metal 24 and the second Peltier metal 25, respectively, as in this embodiment. Although this is practical due to ease of use, it is not limited to this.

Further, the temperature measuring resistor 32, which is a room temperature detection means,
As will be described later, this is an unnecessary element when measuring absolute humidity. Even when measuring relative humidity, it is possible to use a separate room temperature detector, so it is not necessarily necessary to integrally form it on the humidity detection element.

Another example of integrally forming the room temperature detection means with the humidity detection element is to use a silicon single crystal wafer with integrated diodes as the substrate, and utilize the temperature dependence of the forward voltage of the diodes. There are things etc.

Further, the cooling temperature detecting means does not necessarily have to be composed of a thermocouple, but can also be composed of, for example, a temperature-measuring resistor.

Next, the circuit configuration when the humidity detecting element of this embodiment is actually used as a dew point hygrometer will be explained based on the block diagram of FIG.

A portion surrounded by a dashed line is a humidity detection element 1, which includes a Peltier cooling means 2, a water droplet detection means 3, a cooling temperature detection means 4, and a room temperature detection means 5.

The current generating circuit 6 is a circuit that supplies the necessary current to the Peltier cooling means 2.
This circuit determines the cooling capacity of the

The water drop detection circuit 7 directly connects to the water drop detection means 3.
This is a circuit that detects changes in impedance, and determines the presence or absence of water droplets by detecting this change. That is, the presence or absence of water droplets is detected by utilizing the fact that the capacitance of the capacitor constituting the water droplet detection means 3 changes greatly due to adhesion of water droplets.

In the temperature difference detection circuit 8, a thermocouple serving as the cooling temperature detection means 4 detects an electromotive force generated based on the difference between the cooling section and the room temperature in the Peltier cooling means 2, and detects the difference between the cooling section and the room temperature from this electromotive force. This is a circuit that detects temperature differences.

The room temperature detection circuit 9 is connected to the temperature-measuring resistor 32 as the room-temperature detecting means 5, and has a function of detecting the room temperature Ta from the resistance change of the temperature-measuring resistor 32.

The microcomputer 10 is connected to a current generation circuit 6, a water droplet detection circuit 7, a temperature difference detection circuit 8, and a room temperature detection circuit 9 via a bus 12, and generates a current depending on the presence or absence of water droplets detected by the water droplet detection circuit 7. It has a function of controlling the circuit 6 and calculating absolute humidity and relative humidity using the temperature difference ΔT detected by the temperature difference detection circuit 8 and the room temperature Ta detected by the room temperature detection circuit 9. .

The interface 11 is connected to the microcomputer 10 and has a function of sending information regarding dew point temperature, absolute humidity, relative humidity, etc. from the microcomputer 10 to an external device (not shown).

Next, regarding the operation of the dew point hygrometer configured in this way, the microcomputer 1 shown in FIG.
This will be explained according to the flowchart executed by 0.

First, the microcomputer 10 instructs the current generating circuit 6 to cause the maximum current to flow through the Peltier cooling means 2 (step 101).

When a current flows through the Peltier cooling means 2, a Peltier effect occurs in the joint groups 26 and 27. That is, an endothermic action occurs in the first joint group 26, and an exothermic action occurs in the second joint group 27.

The first joint group 26 is concentrated in the center of the humidity detection element 1, and is formed in a thin film layer whose front and back surfaces are exposed to the air, so that it is thermally insulated. There is. Therefore, cooling of the vicinity of the first joint group 26, that is, the cooling section, can be achieved with an extremely small amount of current.

On the other hand, the second joint group 27 is connected to the humidity detection element 1
The heat generated by the heat generation is immediately transmitted to the inside of the substrate 20 because it is dispersed around the periphery of the substrate 20 and formed in a thin film layer that is in close contact with the substrate 20 . Therefore, there is almost no temperature rise in the vicinity of the second joint group 29, and the first
This has no effect on the cooling effect of the joint group 26 at all.

Therefore, the cooling section located in the center of the humidity detection element 1 is quickly cooled down to below the dew point temperature, and the water droplet detection means 3 formed above this cooling section is further cooled down to below the dew point temperature. A dew condensation phenomenon appears on the insulating layer 22, and water droplets adhere.

As described above, the water droplet detection means 3 is composed of two electrodes 33a and 33b that are separated from each other and are opposed to each other. Therefore, when a water droplet adheres to the insulating layer 22, the dielectric constant increases and the impedance between the electrodes 33a and 33b increases. will drop sharply.

The water droplet detection circuit 7 detects the change in the impedance of the water droplet detection means 3, and the microcomputer 10 knows the presence or absence of water droplets from the output of the water droplet detection circuit 7 (step 102).

The water droplet detection circuit 7 excites the water droplet detection means 3 with, for example, an oscillation pulse of a constant period, converts the impedance value of the water droplet detection means 3 into a corresponding voltage value using an integrating circuit, and converts this voltage value into a predetermined voltage value. A conceivable configuration is to use a comparator to detect the presence or absence of water droplets by comparing the level.

By cooling the cooling part of the Peltier cooling means 2 with the maximum current, water droplets adhere within a predetermined time, and when the water droplet detection circuit 7 detects this, the microcomputer 10 reduces the cooling current by N% (step 105). . At this time, if water droplets do not adhere even after a predetermined period of time has elapsed, the atmospheric condition is outside the measurement range, and a display signal to that effect is output (steps 103, 104).

After reducing the cooling current by N%, the presence or absence of water droplets is determined again after a predetermined time has elapsed (step
106). Even if the cooling current decreases, the water droplet detection circuit 7
When the microcomputer 10 continues to issue a signal indicating that there are water droplets, the microcomputer 10 further reduces the cooling current by N% (step 105), and through this circulation, the cooling capacity of the Peltier cooling means 2 is gradually reduced. .

Due to the reduction in the cooling capacity of the Peltier cooling means 2, water droplets no longer adhere, and furthermore, the water droplets begin to disappear due to evaporation.

When the water droplet detection circuit 7 detects the disappearance of water droplets, the cooling current is increased by M (<N)% to increase the cooling capacity and return to the dew point temperature at which water droplets begin to adhere (step 107).

When the water droplet detection circuit 7 detects the adhesion of water droplets (step 108), the microcomputer 10 detects the temperature difference ΔT between the cooling section and the room temperature detected by the cooling temperature detection means 4 and the room temperature Ta detected by the room temperature detection means 5.
are read via the temperature difference detection circuit 8 and the room temperature detection circuit 9, respectively (steps 110 and 111).

In addition, in the cycle of increasing the cooling current by M% (steps 107, 108, 109), if the cooling current reaches the maximum, it means that the atmospheric condition is outside the measurement range. A display signal to that effect is output (step 104).

The cooling temperature detection means 4 includes the temperature sensing section 3 as described above.
thermocouple 28,2 with 0 placed approximately in the center of element 1;
9, and the other ends of the thermocouples 28 and 29 are placed on the periphery of the element 1, that is, on the substrate 20, not on the recess 21, so this temperature difference ΔT is determined by the temperature value of the substrate 20 at room temperature and the Peltier cooling. This is the difference value from the temperature value of the cooling section of the means.

The room temperature detection means 5 includes the resistance temperature detector 3 as described above.
2, the room temperature value is detected by converting the change in resistance value due to room temperature change into a voltage value by flowing a minute current.

When the microcomputer 10 reads the temperature difference ΔT and the room temperature Ta, it calculates Td=Ta−ΔT (step 112). This Td is the dew point temperature of the cooling section of the Peltier cooling means 2.

Not shown in the microcomputer 10
In the ROM, the well-known graph of the relationship between atmospheric temperature and saturated steam pressure shown in FIG. 9 is tabulated by function approximation. Therefore, room temperature
Once Ta and the dew point temperature Td are determined, the microcomputer 10 can use this table to determine the saturated water vapor pressures Pa and Pd at the indoor temperature Ta and the dew point temperature Td.

Absolute humidity is defined by this saturated water vapor pressure Pd,
Since relative humidity is defined as Pd/Pa, all humidity values can be found by calculation (step
113).

The microcomputer 10 controls the dew point temperature Td,
Absolute humidity Pd and relative humidity Pd/Pa are output to external equipment (step 114).

In the steps of the above flowchart, a method has been shown in which the cooling current is gradually decreased by N% from the maximum value, and after the dew condensation phenomenon disappears, the cooling current is gradually increased by M% to achieve the dew point. and,
The idea was to find the approximate dew point temperature by setting the value of N larger than the value of M, and then to find the precise dew point temperature in order to improve responsiveness. The dew point temperature may be determined by gradually decreasing the temperature and using the temperature data at the time when the dew condensation phenomenon occurs. Furthermore, the cooling current may be increased from the maximum value, or the duty ratio may be effectively changed.

Further, in the above embodiment, two electrodes 33 facing each other are used as the water droplet detection means, but moisture sensing elements such as Zn ₃ (PO ₄ ) ₂ or Zn ₃ whose characteristics change rapidly due to adhesion of water droplets are used. (PO ₄ ) ₂ and LiPO ₄ may also be used.

〔Effect of the invention〕

As explained above, according to the humidity detecting element of the present invention, the first heat sensitive means has the cooling part concentrated in the central part of the humidity detecting element, and the second heat sensitive means has the temperature sensitive part located near the cooling part. Since the temperature difference detection means consisting of a heat sensitive means and the water droplet detection means for detecting water droplets adhering to the upper part of the cooling section are integrated on the substrate from which the central portion is removed, the cooling section is thermally insulated. Only necessary parts can be locally cooled rapidly with a weak current, and the humidity of the atmosphere can be measured with an extremely fast response speed from the outputs of the second heat-sensitive means and the water droplet detection means.

Further, since only a local part of the element is cooled, the air to be cooled is also localized and there is less thermal disturbance of the air to be measured, making it possible to measure humidity in a narrow space. Furthermore, cooling only a local part of the element means that other parts of the element are not cooled and are kept at room temperature, thus
A room temperature sensor can be integrated on the device as required.

Furthermore, like general ICs, it can be produced in large quantities at one time, so it is very inexpensive despite having all the detection functions necessary for humidity detection.

[Brief explanation of drawings]

1 and 2 are both perspective views of one embodiment of the present invention during manufacture, FIG. 3 is a sectional view of one embodiment of the present invention during manufacture, and FIG. 4 is an embodiment of the present invention. 5 and 6 are perspective views showing other methods of forming the recessed portions of the substrate. FIG. Block diagram, No. 8
The figure is a flowchart showing the operation of the microcomputer, and FIG. 9 is a graph showing the relationship between ambient temperature and saturated steam pressure. 1... Humidity detection element, 2... Peltier cooling means,
3, 33... Water droplet detection means, 4... Cooling temperature detection means, 5... Room temperature detection means, 24... First Peltier metal, 25... Second Peltier metal, 26... First joint group, 30... Temperature sensing Department.

Claims (1)

[Claims] 1. A water droplet detection means, a temperature difference detection means, and a cooling means are provided on a substrate, the cooling means is composed of a thin film layer having a plurality of thin film-like Peltier elements, and the heat generating joint of the plurality of Peltier elements is The heat-absorbing joints of the plurality of Peltier elements are located at the periphery of the thin film layer, and the heat-absorbing joints of the plurality of Peltier elements are located adjacent to each other in the central cooling part of the thin film layer, and the periphery of the thin film layer is bonded to the substrate and A central portion of the Peltier elements is separated from the substrate, all heat-absorbing joints and all heat-generating joints of the plurality of Peltier elements are formed on the same surface, the water droplet detection means is located on the cooling means, and the temperature The difference detection means includes a first one located in the center of the cooling means.
and a second heat sensitive means located at the periphery of the thin film layer.
A humidity detection element comprising a heat sensitive means.