JP3065862B2 - Flow rate detecting device and flow rate detecting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate detecting apparatus for measuring a flow rate of a gas, liquid, atomized fluid (atomized fluid), solid powder fluid or the like to which a diamond thin film is applied.

[0002]

2. Description of the Related Art The types of conventionally known flow detecting devices are roughly classified into a thermal detecting device and a mechanical detecting device. Thermal detectors measure flow by detecting the temperature of a detector section that varies with flow. This method has little effect on the device under test and can operate at a relatively high speed, but has a problem in the reaction with the device under test or sensitivity. The mechanical detection device uses a mechanical action (for example, pressure of a fluid) and has excellent sensitivity and reaction speed, but has a mechanical limit, and has a problem that an influence on an object to be measured occurs.

[0003] Generally, sccm is used as a unit of the flow rate. It indicates how much fluid (expressed in cm ³ ) per minute passes through a given cross-section of the fluid, in units of cm ³ / minute. For example, if the flow velocity is 2cm
/ Min fluid flowing through a 10cm ² pipe
In the cross section of the pipe, 2 × 10 cm ³ of fluid per minute will pass and the flow rate will be 20 sccm.

[0004] Various thermal detectors have been reported with the aim of improving sensitivity and reaction. For example, there have been known ones in which the accuracy is improved by integrating the semiconductor device into a silicon wafer and integrating it with an IC, and attempts to improve the sensitivity by integrating the semiconductor device with a pressure sensor.

In each of these methods, the flow rate detector portion has a thermistor structure, the detector portion is locally heated, and the amount of heat carried by the fluid from the detector is read by a thermistor function to determine the flow rate. It is something to be converted. Also, in order to detect the amount of heat carried away by the fluid sensitively, the thermistor portion is usually made as small as possible, and its heat capacity is usually made small.

A thermistor is an element utilizing the property that the electric resistance of a substance changes in accordance with a change in temperature, and an element using a metal or a semiconductor is well known. In actual measurement, the temperature of the thermistor portion is measured by the thermistor function, the amount of heat carried away by the fluid is calculated therefrom, and the flow rate of the fluid is calculated based on the amount of heat carried away by the fluid. Then, if the flow velocity is obtained, the flow rate is calculated.

As a conventional flow rate detecting device, a P or N type silicon semiconductor formed on a silicon substrate is used as a thermistor, and the thermistor is heated by an appropriate method in order to increase the amount of heat carried by the fluid. The configuration was adopted.

[0008] [Problems of the prior art] However, when silicon is used as a substrate, heat cannot be supplied to the thermistor portion satisfactorily due to the problems of thermal conductivity and specific heat of the silicon, and the silicon is carried away from the thermistor portion to a fluid. The calorific value could not be measured accurately.

For example, if the distance between the thermistor portion and the heating element that heats the thermistor portion is increased, heat cannot be supplied to the thermistor portion properly, and once the heat of the thermistor portion is carried away by the fluid, the thermistor portion is cooled. Will be done. In the measurement of the flow rate, for example, when a constant flow rate is flowing, the output from the thermistor must be constant, and even when the constant flow rate flows, the temperature of the thermistor part decreases over time. If it does, the output will not be constant. That is, accurate flow rate measurement cannot be performed.

If a heating element is provided close to the thermistor in order to efficiently heat the thermistor, an excessive amount of heat is supplied to the thermistor.
Then, the minute amount of heat carried away by the fluid cannot be accurately measured due to the huge amount of heat supplied from the heating element. This is because the temperature of the thermistor does not accurately reflect the amount of heat carried away by the fluid,
This is because it is greatly affected by the heating element.

Therefore, in the conventional flow rate detecting device using a silicon thermistor, the positional relationship or the thermal relationship between the thermistor portion and the heating element is finely adjusted so that the amount of heat is not insufficiently supplied to the thermistor portion but excessively supplied. Instead, it had a structure that seemed to realize such a delicate state. However, the appropriate amount of heat to be supplied to the thermistor portion greatly changes depending on the flow rate, and the above-mentioned delicate state also changes with the flow rate. Therefore, in reality, a compromise structure must be obtained at an appropriate location in view of the measurement flow rate range and the measurement accuracy. As a result, the flow measurement range was narrowed, and the flow measurement accuracy had to be reduced to some extent.

A narrow flow rate measurement range means that the ratio between the maximum flow rate and the minimum flow rate that can be measured is small, that is, the dynamic range is narrow.

If the heating element of the thermistor is heated to a high temperature (for example, 100 ° C. or higher) in order to increase the sensitivity as much as possible, there is a serious problem that it is impossible to measure the flow rate of hydrochloric acid or gasoline having a high risk of ignition. Was. In particular, flammable fluids such as gasoline (whether gas or liquid,
In the case of a mist or a powder, heating at a high temperature is dangerous, and a material having low sensitivity must be used.

Further, the conventional flow rate detecting device using a thermistor requires a protective film such as a silicon oxide film in order to protect the thermistor portion, the heating element, and their metal wiring from corrosion by a fluid. However, the protective film has been a factor that reduces measurement accuracy. In this case, it is conceivable to form a protective film with a material having a high thermal conductivity and a small specific heat in order to reduce the influence of measurement.However, as the protective film, the thermal conductivity and specific heat of the thermistor portion and the heating element are considered. If different materials are used, heat reflection or refraction occurs at the interface between the protective film and the thermistor portion due to the difference in thermal conductivity and specific heat, which also lowers measurement accuracy.
Due to the factors described above, in reality, only a minimum sensitivity of about 1 sccm (minimum flow rate that can be measured) and a response speed of about 0.5 sec have been practically used.

[0015] Further, the conventional flow rate detection device cannot achieve both the detection sensitivity and the detection response speed. That is, when the detection sensitivity is increased, the response speed is decreased, and when the response speed is increased, the detection sensitivity is decreased.

[Object of the Invention] From the above background, the present invention does not require high heating, can measure a minute flow rate, can achieve both high sensitivity and high-speed response, and has a large dynamic range. It is an object of the invention to provide a detection device.

[Background of the Invention] Considering the relationship between the temperature directly detected by the thermistor and the amount of heat carried away by the fluid from the thermistor portion, if the temperature of the fluid is assumed to be constant, the flow rate must be accurately measured by the thermistor portion. Concludes that it is necessary for the temperature of the thermistor portion to depend only on the amount of heat carried away by the fluid. This, in other words, requires that the temperature of the thermistor section be determined to balance the amount of heat carried away by the fluid. Therefore the temperature of the fluid,
For accurate flow measurement at a constant flow rate, the thermistor portion needs to be in thermal equilibrium and have a temperature determined by the flow rate.

The above relationship is quantitatively expressed by the following equation (1). In the following, W is the amount of heat generated per unit time by which the thermistor itself generates heat, G is the thermal conductivity of the material forming the thermistor portion, K is the heat conduction coefficient related to the amount of heat carried away by the fluid, It is proportional to u to the power of 1/2. That is, this K is calculated using the flow velocity u and the proportionality constant K ₀ as K =
K ₀と u. T is the temperature of the thermistor portion, and T ₀ is the temperature of the fluid.

[0019]

(Equation 1)

In the above equation (1), the term K (T−T ₀ ) represents the amount of heat per unit time taken by the fluid from the thermistor portion per unit time. Equation 1 is an equation showing the energy balance in the thermistor section. If the thermal equilibrium state as shown in Equation 1 is realized, the temperature of the thermistor section is determined so as to balance the amount of heat taken from the thermistor section by the fluid. Means that What is important here is that the temperature of the thermistor portion is uniquely determined by the flow rate if the flow rate is constant and the thermal equilibrium state represented by Equation 1 is realized in the thermistor portion.

Here, W can be predetermined as the heat value of the thermistor itself. For example, if the relationship between the current flowing through the heating element for heating the thermistor and the amount of heat generated in the thermistor portion is known, the amount of heat generated per unit time can be determined in advance. However, as described above, in the conventional flow rate detection device using silicon, W cannot be accurately determined due to low thermal conductivity and high specific heat. That is, even if the amount of heat generated by the heating element is accurately determined, it is difficult to determine the amount of heat generated in the thermistor due to poor heat conduction to the thermistor.

In the model represented by the above equation 1, what is actually measured is T−T ₀ . That is, T is measured from the output from the thermistor portion and the temperature T _{0 of the} fluid itself is separately measured.
Is measured. Here, if the calorific value W and the constant G at the thermistor portion are determined, K is determined from Expression 1, and if K is determined, the flow velocity u of the fluid is determined from the relational expression of K = K ₀ √u. Once determined, the flow rate will be determined.

Considering the operation model as described above, there are several methods for improving the sensitivity and resolution of the flow rate detector. Here, sensitivity refers to how small a flow rate can be measured, and resolution refers to how small a flow rate change can be measured.

The low flow rate means that the amount of heat K (T
−T ₀ ) is relatively small. Further, the small change in the flow rate means that the change in the amount of heat K (T-T ₀ ) carried by the fluid from the thermistor portion is small.

In order to increase the sensitivity and the resolution, a method of increasing the heat value W of the thermistor portion is considered. In order to obtain high sensitivity and resolution, a faithful temperature change of the thermistor corresponding to a minute flow rate change is required. To detect a temperature change, the larger the change, the easier it is to detect. That is, the temperature T of the thermistor portion corresponding to the change in the flow rate
The larger the value of, the higher the sensitivity and resolution can be obtained. For the above-described reasons, in the conventional flow rate detecting device, the amount of heat K (T-T ₀ ) carried away by the fluid by heating the thermistor portion and making the temperature T of the thermistor portion higher than the temperature T ₀ of the fluid. And increased the sensitivity.

However, as shown in Equation 1,
It is important that a state in which the amount of heat carried away from the thermistor portion by the fluid and the amount of heat generated by the thermistor portion are balanced (thermal equilibrium state) is realized, and a state in which Equation 1 is not satisfied (non-equilibrium state) In (2), since the temperature T of the thermistor does not show a value reflecting the flow rate of the fluid, no matter how much T is increased, high sensitivity and high resolution cannot be obtained.

Further, as is apparent from Equation 1, if the value of the thermal conductivity G of the thermistor portion is large, the value of T-T ₀ cannot be increased, and the sensitivity is lowered.

However, when the value of the thermal conductivity G of the thermistor portion is large, the temperature change of the thermistor portion in accordance with the change in the amount of heat taken by the fluid becomes faster, so that the response speed becomes faster. Here, a time constant τ given by τ = C / (G + K) is introduced as a parameter indicating the response speed of the thermistor. τ means that the smaller the value, the faster the response speed. Here, C is the heat capacity of the thermistor portion, and G and K are the aforementioned constants. As is apparent from this equation, to increase the response speed, C should be reduced and G should be increased. Also, if the flow rate is large, the flow velocity u is high, so that K becomes larger from the relational expression of K = K ₀ √u, and it can be seen that the response speed also becomes faster. In the conventional flow rate detection device,
The heat capacity of the thermistor portion is made as small as possible in order to increase the response speed by reducing the value of C.

However, as described above, if G is increased, the sensitivity is reduced. That is, as a fundamental problem, a problem that high sensitivity and high-speed response speed are incompatible with each other and cannot be compatible is explained.

The fact that a conventional flow rate detecting device using a silicon thermistor cannot have a large dynamic range can be explained as follows using Expression 1. For example, when measuring a fluid with a large flow rate,
Since a large amount of heat is carried away by the fluid from the thermistor portion, if the heat capacity of the thermistor portion is small, the thermistor portion will not be able to hold a heat amount corresponding to the amount of heat carried away, and Expression 1 will not be established. Specifically, the temperature of the thermistor portion gradually decreases, and the temperature T of the thermistor portion does not accurately reflect the flow rate. However, there is a problem that the heat capacity C of the thermistor cannot be increased unnecessarily in order not to lower the response speed.
Also, in order to quickly replenish the amount of heat to the thermistor part,
A method of bringing the heating element close to the thermistor portion and rapidly replenishing the amount of heat is conceivable. In this case, when the flow rate is high, the amount of heat K (TT) carried away by the fluid is removed.
₀ ) and the calorific value W are satisfied, but when the flow rate is low and the flow rate is small, the term of the calorific value K (T−T ₀ ) taken by the fluid becomes extremely small. As a result, there is no balance with W having a value, and as a result, Expression 1 does not hold.

Conversely, when the flow velocity is small and the flow rate is small, the amount of heat carried away from the thermistor portion is small. Therefore, the thermistor portion is heated as high as possible, and the amount of heat is given to the thermistor portion so as not to break the state of Equation (1). What should be done. More specifically, appropriate conditions are set by delicately setting a positional relationship between the thermistor portion and the heating element, and an appropriate thermal isolation between them.

Then, equation 1 always holds, and T
Since possible to increase the difference between T ₀ and can detect a degree of minute flow rate and the change. However, when the flow rate suddenly changes in a direction of increasing, the term of K (T−T ₀ ) increases according to the change of the flow rate. Therefore, if the amount of heat is not supplied to the thermistor portion so as to follow the change, the expression 1
Does not hold. However, as described above, the thermal balance is set so as to be suitable when the flow rate is small, that is, when the value of the term K (T−T ₀ ) is small. In this case, the amount of heat applied to the thermistor layer is set. Cannot follow the change in the term K (T−T ₀ ). In this way, the thermal equilibrium state represented by Expression 1 is broken, and accurate flow rate measurement cannot be performed.
Specifically, even if the flow rate suddenly changes from a very small flow rate to a large flow rate, and then the flow rate is stabilized with the large flow rate, the thermal balance in the thermistor portion is lost, so that the temperature T of the thermistor gradually increases over time. And the output from the thermistor is as if the flow rate is changing.

[0033]

As described above, the problem with the conventional thermal flow rate detecting device is that the condition for satisfying the formula 1 in the thermistor portion is limited, and the formula 1 follows the change in the flow rate. This is not always the case. Formula 1
Does not hold because the amount of heat K (TT) carried away by the fluid
_{This is because} an appropriate amount of heat corresponding to ₀ ) is not supplied to the thermistor portion.

[0034]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for forming a thermistor portion on the surface of a diamond thin film, and using the diamond thin film as a heat storage layer for supplying heat to the thermistor portion. It is characterized in that a thermal equilibrium state in which Expression 1 holds is realized, and the temperature of the thermistor portion is determined by a value that always reflects the flow rate of the fluid.

[First Invention] The first invention of the present invention is a flow rate detecting device using a diamond thin film, wherein the diamond thin film has a layer having a thermistor function on its surface. The gist of the present invention is a flow detection device.

In the first invention, it is appropriate to use a diamond thin film produced by a gas phase method. In addition, the conductivity type of the diamond thin film is not particularly limited, and one having one conductivity type by an appropriate doping method may be used. Examples of the layer having a thermistor function include platinum formed by a sputtering method or the like, an alloy of platinum and another material, and a layer generally formed of a material having a thermistor function. Also, by doping the diamond thin film with an impurity imparting one conductivity type, a layer having a thermistor function can be formed on the surface of the diamond thin film, and this layer can be used as a thermistor portion. Here, the thermistor function refers to a function capable of detecting temperature and its change by measuring the resistance of a material that changes with temperature.

What is important in the present invention is that a layer having a thermistor function is formed on a diamond thin film which responds thermally at a high speed, so that the diamond thin film has a thermal role. That is, it is a principle feature of the present invention that the fluid and the thermistor exchange heat quantity through the diamond thin film.

Further, as defined in the second invention, a layer having a thermistor function is formed on one surface of the diamond thin film, and the other surface is brought into contact with a fluid whose flow rate is to be measured. It is possible to realize a configuration in which the layer having the thermistor function on which the electric wiring and the like are formed is not corroded or deteriorated by the fluid. In particular, it is a great feature that diamond, which is the most resistant to corrosion, can be used as a protective film.

[Third Invention] A third aspect of the present invention is a flow rate detecting device using an intrinsic or substantially intrinsic diamond thin film, wherein the diamond thin film has a layer having a thermistor function on its surface. The layer is formed on the initial crystal growth surface of the diamond thin film, and the final crystal surface of the diamond thin film is configured as a surface in contact with a fluid; is there.

In the third aspect of the present invention, the initial crystal growth surface of the diamond thin film refers to the surface where crystal growth of the diamond thin film starts to grow. For example, when a diamond thin film is grown on a substrate, the surface where the substrate and the diamond thin film are in contact is the initial crystal surface. In addition, the crystal growth termination surface means a surface on which crystal growth has been completed, that is, a surface exposed on the surface after film formation. The final stage of crystal growth has a rough surface with many irregularities, and by bringing this surface into contact with a fluid, the heat exchange efficiency can be increased. Of course, the unevenness is minute and does not affect the flow velocity of the fluid.

By adopting the structure of the third aspect, the usefulness of the second aspect is obtained in that the fluid and the layer having the thermistor function do not come into direct contact with each other, and at the same time, the efficiency of heat exchange with the fluid is increased. And the usefulness that the accuracy of the flow rate detection can be improved.

[Fourth Invention] A fourth invention of the present invention relates to a flow rate detection device using an intrinsic or substantially intrinsic diamond thin film, wherein the diamond thin film has a layer having a thermistor function on its surface. The gist of the invention is a flow rate detecting device, wherein the diamond thin film has a larger heat capacity than the layer.

The fourth aspect of the present invention is a matter necessary for making a diamond thin film function as a heat storage layer and supplying a required amount of heat to a thermistor portion (a portion where a layer having a thermistor function is formed) at a high speed. is there. If the heat capacity of the diamond thin film is smaller than the heat capacity of the thermistor portion, the temperature of the diamond thin film determined according to the amount of heat taken from the fluid of the diamond thin film is greatly affected by the temperature of the thermistor portion having a larger heat capacity,
The temperature of the diamond thin film does not become a temperature that accurately reflects the flow rate. That is, accurate flow measurement cannot be performed. Of course, if the heat capacity of the diamond thin film is too large with respect to the heat capacity of the thermistor portion, the responsiveness of the diamond thin film with respect to heat will decrease, and the sensitivity of measuring the flow rate will decrease.

[Fifth invention] A fifth invention of the present invention relates to a flow rate detection device using a diamond thin film, wherein the diamond thin film has a plurality of layers having a thermistor function on its surface and a heating element. A plurality of layers having the thermistor function have a function of detecting a thermal gradient formed in the diamond thin film by the heating element, and the flow rate detection device is characterized in that.

The diamond thin film is not uniformly heated by the heat generated by the heating element, but is in a state of thermal equilibrium (meaning that the state is thermally balanced, that is, a state of thermal balance, depending on the distance from the heating element and the flow of the fluid). ), The temperature differs depending on the location of the diamond thin film, and a thermal gradient exists between the portions having different temperatures. Of course, the state of the thermal gradient changes according to the change in the flow rate. Therefore, information on the flow rate can be obtained by detecting this thermal gradient. The function of detecting a thermal gradient refers to a function of detecting a temperature of a different portion of the diamond thin film and calculating a thermal gradient from the temperature difference.

[Sixth Invention] A sixth invention of the present invention relates to a flow rate detection method using a flow rate detection device having a layer having a thermistor function formed on the surface of a diamond thin film and a heating element. Heating the heating element with an AC waveform,
A flow rate detection method, wherein a flow rate of a fluid flowing in contact with the diamond thin film is calculated by arithmetically processing an output from the layer having a thermistor function obtained as a result of the heating. It is.

[Seventh Invention] A seventh invention of the present invention relates to a flow rate detecting method using a flow rate detecting device having a plurality of layers having a thermistor function formed on the surface of a diamond thin film and a heating element. The diamond thin film is brought into contact with a fluid, a thermal gradient formed on the diamond thin film by the heating element is measured, a flow rate of the fluid is obtained from a magnitude of the thermal gradient, and the flow rate is determined from a direction of the thermal gradient. The gist of the present invention is a flow rate detection method characterized in that a flow direction of a fluid is obtained, and a change in the flow rate is obtained from a way of changing the thermal gradient.

Obtaining the flow rate of the fluid from the magnitude of the thermal gradient means calculating the flow rate from the magnitude of the thermal gradient formed according to the flow rate of the fluid. Obtaining the direction in which the fluid flows from the direction of the thermal gradient utilizes the effect that the direction of the thermal gradient is determined by the direction in which the fluid flows. Obtaining the change in the flow rate from the manner of the change in the thermal gradient means calculating the change in the flow rate from the change in the thermal gradient reflecting the flow rate.

In the above invention, it is extremely useful to form a layer having a thermistor function on one surface of the diamond thin film and make the other surface contact with a fluid. This is because it is possible to use the thermal function of the diamond thin film and at the same time to realize a configuration in which the wiring and the like formed on the layer having the thermistor function are not corroded or deteriorated by the fluid.

The present invention makes use of the inertness, high thermal conductivity (up to 20 W / cm deg), and low specific heat (1.8 J / cm ³ deg), which are characteristics of diamond. Inert means that it is stable to a number of corrosive fluids, that is, it does not corrode.

FIG. 1 shows an example of a basic flow rate detecting device utilizing the present invention. A cross section taken along line AA ^′ in FIG. 1A is FIG. 1B, and a cross section taken along line BB ^′ is FIG. 1C. In FIG. 1, a heating element (11), a pair of electrodes (10) for supplying current to the heating element, a thermistor layer (12) functioning as a flow detector, and a pair of thermistor layers (12) for obtaining an output from the thermistor layer (12). A metal electrode (15) is formed on the diamond thin film (13). Here, the heating element (11) and the thermistor layer (12)
Although a metal electrode is provided for both the heating element (11) and the thermistor layer (12), when a metal material is used, it is not necessary to provide wiring directly to the heating element and the electrode.

The thermistor layer (12) needs to function as a thermometer with high sensitivity. In FIG. 1A, the diamond thin film 13 is exposed between the heating element 11 and the thermistor layer 12, and as shown in FIG. This is because it has a structure in which the thermistor layer (11) and the thermistor layer (12) are separated by a groove. This structure
The heating element (11) is not in direct contact with the thermistor layer (12), but is thermally connected through the diamond thin film (13).

The diamond thin film (13) has a thickness of about 10 μm formed by the CVD method. And, utilizing platinum formed on the surface by a sputtering method.
A thermistor layer (12) having a thickness of about 1 μm is formed. The heating element (11) is also formed of the same material as the thermistor layer. As described above, the flow rate detecting device shown in FIG. 1 is composed of a thin film thermistor layer (12) using platinum having a thickness of about 1/100 of the thickness of the diamond thin film (13). It has a structure provided with a heater (11).

There are various places where the flow rate detecting device is used, and therefore, the temperature T _{0 of the} fluid may change in a short time. As described above, in the measurement of the flow rate, the difference between the temperature T of the flow rate detector and the temperature T _{0 of the} fluid is important, but the temperature T ₀ of the fluid has changed due to a change in the temperature of the environment. In this case, the value of T−T ₀ will change,
Such as when to be particularly measured value or a minute change in T-T ₀ would change in large measurement errors or sensitivity appears. Therefore, a method of detecting a flow rate that does not depend on a change in ambient temperature is required.

As a method for addressing this problem, the present invention is characterized in that the thermistor, which is a flow rate detector, is subjected to AC heating. In this case, since the amount of heat consumed in the thermistor portion is modulated by the frequency ω as represented by Wexp (iwt), Equation 1 is changed to Equation 2 below.

[0056]

(Equation 2)

Here, ΔT / Δt is a minute change in the temperature of the thermistor portion, C is the heat capacity of the thermistor portion, G is the thermal conductivity of the thermistor portion, and K is the heat indicating the heat carried away by the fluid. It is a conduction coefficient. That is, the symbols common to Expression 1 have the same meanings as in Expression 1. In the method using the AC heating, ΔT is measured by the output of the thermistor, K is obtained from Expression 2, and K is further obtained.
= K ₀ √u, and the flow rate is calculated. ΔT measured by the flow rate detection device is represented by the following Expression 3.

[0058]

(Equation 3)

Note that τ is the aforementioned time constant defined by τ = C / (G + K).

[0060]

The operation obtained by adopting the configuration of the present invention using the apparatus shown in FIG. 1 which is an example of a flow detector utilizing the present invention will be described below. As shown in FIG. 1, in the present invention, platinum is used in the same manner as the thermistor layer (12) using platinum on a diamond thin film (13) having low specific heat and high thermal conductivity, which is the base of the flow rate detection device. Heating element (1
(1) to achieve uniform and high-speed heat conduction between the components of the apparatus. Diamond has a thermal conductivity 10 times or more higher than that of silicon, and the diamond thin film of the present invention is not merely a substrate on which the thermistor layer (12) is formed, but is sensitive to the amount of heat taken away by the fluid. Has the function of acting.

In the flow detecting device as shown in FIG. 1, only the thermistor layer (12) has a temperature sensor function, and the other portions function as good heat conductors in a sense. In the example shown in FIG. 1, the surface indicated by (17) is in contact with the fluid (16), and the flow of heat from the heating element (11) deprived of the fluid (16) is caused by the thermistor of the diamond thin film (13). Layer (12)
And the surface on which the heating element (11) is provided is the surface on the back side (arrow
(17).

In actual operation, the heat generated by the heating element (11) is carried away by the fluid (16) at the portion (17) of the diamond thin film (13) in contact with the fluid (16), resulting in (1) The temperature T of the thermistor layer (12) determined by the equation is determined.

Platinum has a low Debye temperature of 240 K and a specific heat of 0.132 J / cm ³ K. Therefore thermistor layer (12)
Has a very low heat capacity. Therefore, a high-speed response can be obtained.

As shown in FIG. 1, the diamond thin film (13)
When the thermistor layer (12), which is a flow rate detector, is formed by stacking it, a 10-μm-thick diamond thin film (13), which is 100 times thicker than the 0.1-μm-thick thermistor layer (12), accumulates heat. Acts as a layer. For example, if the amount of heat K (T−T ₀ ) taken by the fluid from the thermistor layer greatly changes, conventionally, it is not possible to cope with the situation change and Expression 1 cannot be established.
When the configuration as shown in FIG. 1 is adopted, the diamond thin film (13)
Quickly supplies the amount of heat to the thermistor layer (12) in response to the change in the amount of heat K (T−T ₀ ), so that Expression 1 is quickly satisfied, and a situation where the temperature of the thermistor depends on the flow rate is realized at high speed. . That is, the diamond thin film (13), which is a heat storage layer,
Acts as a fast responsive heat source. Diamond thin film as described above is extremely high thermal conductivity since they have (~20W / cmdeg) and very low specific heat (1.8J / cm ³ deg), the thermistor layer from above of the diamond thin film (13) (12) Heat flow into the air is rapid.

The thermal storage layer composed of the diamond thin film (13) acts passively, supplies an appropriate amount of heat to the thermistor layer (12) according to the situation, and always obtains the thermal equilibrium state represented by the equation (1). It acts to correct the deviation from.
Specifically, the fluid (16) and the thermistor layer (12), and furthermore, the fluid (16) and the heating element (11) are formed by a diamond thin film (13) having much higher thermal conductivity than the fluid (16). Thermally connected. Therefore, when heating is performed by the heating element (13), the thermistor layer (12) becomes a diamond thin film that is a heat storage layer.
It is efficiently heated through (13). Also, a diamond thin film that is about 100 times thicker than a thermistor layer (13)
Has a heat capacity about 100 times that of the thermistor layer (12). Therefore, even if the flow rate of the fluid (16) is slightly increased or greatly increased, the thermistor layer (12) is quickly removed from the diamond thin film (13) in response to the flow rate change.
Is supplied with the optimal amount of heat for realizing the thermal equilibrium.
Is satisfied at a high speed.

When the flow rate decreases rapidly, the heat capacity of the thermistor layer (12) is extremely small.
(12) responds fast. Moreover, at this time, the heat storage layer composed of the passively acting diamond thin film (13) does not supply an unnecessary amount of heat to the thermistor layer (12) to break the thermal equilibrium state. This is because the function as the heat storage layer is to act so that a thermal equilibrium state is established between the diamond thin film (13) and the thermistor layer (12) provided in a laminated manner.

For example, in this case, as the amount of heat carried away by the fluid from the thermistor layer (12) decreases, the amount of heat required by the thermistor layer (12) to maintain thermal equilibrium decreases. Since the diamond thin film (13) is thermally connected to the thermistor layer (12) and acts to maintain thermal equilibrium in the thermistor layer (12), in this case, the thermistor layer (12)
The optimal amount of heat required by the diamond thin film (1
From 3), it is supplied to the thermistor layer (12).

As described above, the diamond thin film (1
By the action of the heat storage layer constituted by 3), a thermal equilibrium state, that is, a situation where Equation 1 is always satisfied without being affected by a change in the flow rate, is realized.
The temperature (12) accurately reflects the temperature of the fluid (16), and as a result, the flow rate can be accurately measured.

The operation of each component when the structure shown in FIG. 1 is employed can be described as follows.

As shown in Expression 1, the sensitivity of the flow rate detecting device is proportional to T−T ₀ , which is the difference between the temperature T of the thermistor and the temperature T ₀ of the fluid. Here, consider the case where heat is taken from the surface (17) of the diamond thin film (13) by the fluid (16). Then the surface (17) of the diamond thin film (13) becomes fluid (16)
Since loses heat, the surface (17) becomes a value close to the temperature T ₀ of the fluid (16). At this time, the amount of heat taken up by the fluid is rapidly replenished from the diamond thin film (13), which is a heat storage layer, according to the amount, so that the temperature of the portion of the diamond thin film (13) in contact with the thermistor (12) varies greatly. And fluid (1
6) Quickly stabilizes at a temperature dependent on the amount of heat deprived. That is, in this case, the temperature of the diamond thin film (13) is set to a temperature determined by the flow rate of the fluid (16).

At this time, the surface of the diamond thin film (13)
Since heat is gradually removed from (17) by the fluid, a thermal gradient as shown by an arrow (18) occurs in the diamond thin film (13) (the temperature increases in the direction of the arrow), and the thermistor layer The difference between the temperature T of (12) and the temperature T _{0 of the} fluid can be increased. Of course, the situation where Equation 1 is satisfied is established by the action of the diamond thin film (13) described above.

Therefore, the sensitivity of the flow rate detecting device can be substantially increased as discussed above using Equation (1). That is, the same effect can be obtained as in the case where the thermal conductivity G is apparently reduced in Expression 1. Of course, the above state is realized at a high speed in response to a change in the flow rate, so that a high sensitivity can be realized and a high-speed response can be realized.

Further, in the present invention, the heat capacity of the thermistor portion itself can be extremely reduced, so that a faster response can be realized. Specifically, a value sufficiently close to 20 W / cmK, which can be expected from the physical properties of diamond itself, can be obtained as the thermal conductivity of the flow rate detector portion, and the heat capacity of the thermistor portion can also be reduced to about 20 μJ / K. . Therefore, in the time constant τ = C / (G + K) which is a parameter indicating the above-described response speed, the thermal conductivity G can be increased and the heat capacity C can be reduced, so that τ can be reduced and a high-speed response can be achieved. Becomes G =
If 20 Wcm / K and C = 20 μJ / K, τ ≒ 10 ⁻⁶
Seconds are approximated.

By adopting the structure of the present invention as described above, it is possible to obtain high sensitivity obtained when it is assumed that thermal conductance is apparently reduced, and also it is possible to obtain high-speed response. In addition, it is possible to achieve both conventional and conflicting matters.

The above operation is achieved by forming a thermistor layer (12) as a flow rate detector and a heating element (11) on a diamond thin film (13) as shown in FIG. This is made possible by increasing the heat capacity of the diamond thin film (13) as the heat storage layer with respect to the heat capacity of (12). Therefore, the diamond thin film that is the heat storage layer
If the heat capacity of (13) is not large compared to the heat capacity of the thermistor layer (12), the diamond thin film (13) will
Since it does not function as a heat storage layer that reacts rapidly in response to the temperature change of (12), a predetermined effect cannot be obtained.

In the above description, a structure in which a heating element and a thermistor layer are provided on one surface of a diamond thin film serving as a heat storage layer, and a fluid flows on the other surface, the back surface, has been described. However, the same discussion can be applied to a configuration in which a fluid flows on the surface side on which the heating element and the thermistor layer are provided, and a predetermined effect can be obtained.

Further, since a thermal gradient is also formed in a direction parallel to the surface of the diamond thin film, a plurality of thermistor portions are formed so as to detect the thermal gradient, and a diamond thin film is formed by the plurality of thermistor portions. The thermal gradient is detected, and the flow rate, the change in the flow rate, and the direction of the flow rate can be simultaneously measured based on the information on the thermal gradient. In this case, the flow rate is calculated from the magnitude of the thermal gradient,
The flow rate change can be calculated from the change in the thermal gradient, and the direction in which the fluid flows can be calculated from the direction of the thermal gradient.

Further, in the case of the example of FIG.
By making the surface (17) in contact with the fluid (16) of (13) a rough surface in the crystal growth by the CVD method, the surface (17) is made into a surface having minute unevenness to substantially increase its surface area. Thus, it is possible to realize a structure in which the fluid (16) efficiently removes heat from the surface (17). The structure in which the rough surface of the diamond thin film is in contact with the fluid is expressed by the following equation (1).
In this case, the value of K (T−T ₀ ), which is a term indicating the amount of heat carried away by the fluid, is increased, which substantially increases the sensitivity in detecting the flow rate.

This is because the surface in contact with the substrate (for example, a silicon substrate) on which the diamond thin film is to be crystal-grown is smooth, and the surface on the opposite side, that is, the surface exposed when the diamond thin film is formed, has fine irregularities (up to 100 °). Degree). In this case, the thermistor portion, the heating element, the electrode, the wiring, and the like are formed on a smooth surface, which is useful in terms of ease of production.

Further, by measuring the temperature change of the detector portion, that is, the thermistor portion which fluctuates in accordance with the change of the heat generating portion, using the AC driving heating as shown in the equation 2, the temperature change of the measurement environment is obtained. Independent measurement can be performed. That is, in order not to measure the temperature change of the fluid or the temperature change of the measurement environment, heat that constantly changes AC is generated in the thermistor portion, and ΔT / Δt, which is the temperature change in the thermistor portion in a short time, is measured. From the value, the amount of heat carried away by the fluid can be detected without being affected by the temperature of the fluid or the temperature of the environment.

[0081]

【Example】

[Embodiment 1] In this embodiment, platinum is formed on a surface of a diamond thin film having a thickness of 10 μm by a sputtering method, and this platinum layer is used as a layer having a thermistor function.

First, an intrinsic or substantially intrinsic diamond thin film is vapor-phase synthesized on a silicon substrate by a low-pressure CVD method. This diamond thin film is formed without artificially containing impurities such as nitrogen and boron, and has a specific resistance of 10 ¹⁰ to 10 ¹⁵ Ωcm.

In the vapor phase synthesis, a Whistler mode CVD method using a magnetic field is used. The film formation conditions were as follows: a film formation substrate temperature of 800 ° C., a reaction chamber pressure of 0.25 Torr, and a microwave input of 4 KW. Film. As a source gas used for the film formation, a mixed gas of a methane-based gas and hydrogen mixed at a ratio of CH ₃ OH: H ₂ = 1: 4 is used. The film formation time is 24 hours, and a diamond thin film having a thickness of about 10 μm is formed on a silicon substrate.

The diamond thin film formed on the silicon substrate can be obtained as a diamond thin film only by peeling off the silicon substrate. At this time, a diamond thin film alone can be easily obtained by using a method of mechanically separating the substrate, a method of melting the substrate with hydrofluoric acid or the like.

Then, this diamond thin film is 5 mm × 5 mm
And set in a sputtering apparatus. This sputtering apparatus does not particularly use a sputtering gas, and sputter-deposits platinum on the surface of a diamond thin film with an applied voltage of about 1.2 kV. The platinum film thickness is 1000Å (0.1μ
m). During this sputtering, the target substrate is
Heated to 500 ° C.

In this embodiment, since the platinum metal layer is used as the thermistor layer, the resistance is adjusted by the thickness. Specifically, it was 1 kΩ. Of course, this value is set according to the embodiment.

The platinum thermistor obtained in this example is
3000 could be obtained as the thermistor parameter.
The thermistor parameter is a parameter indicating a change in resistance that occurs when the temperature rises by one degree.

Thus, a thermistor layer composed of a platinum layer was formed on the surface of the diamond thin film.

Further, in order to form the structure as shown in FIG. 1, simultaneously with the process of forming the thermistor layer, a heating element for keeping the thermistor layer in a heated state is formed of platinum constituting the thermistor layer. The heating element is formed by changing the area of the platinum layer and setting its resistance to about 100 Ω. Specifically, by the patterning process,
The thermistor layer and the heating element may be formed, and the area of the heating element may be determined so that the resistance of the heating element is about 100 Ω.

Referring to FIG. 1, the platinum layer is patterned so that the part (12) becomes a thermistor layer and the part (11) becomes a heating element layer. Are simultaneously formed.

As described above, a flow rate detecting device was completed by forming a platinum layer having a thickness of about 0.1 μm as a thermistor layer on the surface of a diamond thin film having a thickness of 10 μm.

An example in which the diamond thin film having the above-mentioned platinum layer is made to function as a flow rate detecting device in the system shown in FIG. 2 will be described below. In FIG. 2, a nitrogen gas (N ₂ ) (42) is introduced into an electromagnetic valve (44) through a flow meter (43), and flows into a box (40) provided with a flow detecting device (41) of the present embodiment. This box is provided with a gas outlet along the flowing direction, and is designed so that there is no stagnation of gas in the box. In this case, the nitrogen gas as the fluid to be measured flows in contact with the thermistor layer (formed on the surface of (41)). As described above, the flow rate detection device (41) has a thickness of 0.1 μm
A thick platinum layer is formed as a thermistor layer.

In the measurement, the platinum layer as the thermistor portion was not particularly heated, and the electromagnetic valve (44) was taken out from the oscillator of the lock-in amplifier (48) through the modulator (45).
It is driven by a signal of Hz, and the flow of nitrogen gas is changed by alternating current.
Then, the maximum flow rate change is detected by the flow rate detection device (41). In detecting the flow rate, the current flowing from the power supply (46) to the thermistor portion on the surface of the diamond thin film of the flow rate detection device (41) is detected as a voltage by a 1 MΩ resistor (47),
By recording with a lock-in amplifier (48) or an oscilloscope (49), a change in the flow rate is measured as a change in the output current from the thermistor portion. At the same time, the flow rate of the nitrogen gas is accurately measured by the calibrated flow meter (43). With the above experimental apparatus, it is possible to obtain a correlation between the output (output as a voltage) from the thermistor composed of the platinum layer and the flow rate.

FIG. 3 shows an example of the correlation between the nitrogen gas flow rate and the output voltage obtained by the system shown in FIG. FIG. 3 shows that the output increases linearly with an increase in the flow rate (N ₂ gas). In this case, the flow rate detection device (41) is not particularly heated and is considered to be kept at the same temperature as the nitrogen gas.Therefore, the output here is a thermistor composed of a platinum layer provided on the surface of the diamond thin film. The part is cooled slightly by the flow of nitrogen gas,
It is understood to indicate that a certain temperature corresponding to the flow rate has been reached. Of course, at this time, it is considered that the diamond thin film played a significant role in thermal performance.

From the above experimental results, it is confirmed that the diamond flow rate detector maintained at the same temperature as the nitrogen gas normally operates as the flow rate detector. Further, when the sensitivity at this time is calculated based on the data obtained from FIG. 3 using the specific heat of nitrogen gas of 1.03 J / gK, it is calculated to reach 2 × 10 ⁻⁴ cal. This means that the amount of heat of about 2 × 10 ^-4 cal deprived from the thermistor can be detected.
This value is comparable to the sensitivity of a 25 μm fine alumel-chromel thermocouple, and is several hundred times more sensitive than the published silicon flow detector.

In a conventional flow rate detecting device using a silicon thermistor, there is no example in which high sensitivity as in the present embodiment was obtained without any heating. Due to the action of a thermistor part that responds quickly to the outflow of heat from the air, and a diamond thin film that acts as a heat storage layer that quickly realizes the state of balance of heat expressed by Equation 1 in response to changes in the amount of heat taken by the fluid from the thermistor It is considered to be.

FIG. 4 shows the output from the thermistor when the flow rate measuring device (41) is heated to 1 to 7 degrees at a fluid temperature of about 300K. At this time, to heat the thermistor portion, the flow rate detector (41) is heated by a heater (not shown), and the flow rate detector (4) at that time is heated.
The temperature of 1) was measured. The measurement was performed with the flow rate fixed at 50 sccm. As is apparent from FIG. 4, it is understood that the output can be increased and the sensitivity can be increased by holding the detector in a heated state. That is, in FIG. 3 in which the flow rate detector (41) is not heated, the output was about 0.1 mV or less when the flow rate was 50 sccm, but as is clear from FIG. It can be seen that by heating (about 307 K) about 7 ° C. to the temperature of the fluid (about 300 K), the output can be increased to less than about 0.8 mV. That is, by heating the temperature of the flow detection device about 7 degrees higher than the temperature of the fluid, it can be seen that the sensitivity could be increased about eight times in this case as compared with the case where the flow detection device was not heated.

Therefore, by heating several tens of degrees further,
It is expected that a flow rate of about several sccm can be detected.

As described above, the sensitivity of the flow rate detecting device can be increased by about 10 times by heating only a few degrees, as described above, because of the large capacity that thermally responds quickly to the thermistor portion. This is probably due to the action of the diamond thin film serving as the heat storage layer. That is, an appropriate amount of heat is supplied from the diamond thin film to the platinum layer, which is the thermistor portion, so that the balance equation shown in Expression 1 is satisfied. It is considered that this is because the temperature of the thermistor portion is kept in an equilibrium state.

[Embodiment 2] In actual use, a flow rate detecting device is used under various environmental conditions such as high temperature and low temperature.
For example, -2 when used in the engine
It must operate in the range of 0 ° C. to over 100 ° C., and a measurement method that is not affected by such a temperature change is required.

Therefore, in the present embodiment, the above-mentioned problem is reduced by driving the heating element incorporated in the flow rate detecting device by AC driving and extracting only an output signal that fluctuates in accordance with the change. In the measurement of this embodiment, the heating element is driven by an alternating current. The detection of the flow rate is performed by using an integrator of the output signal from the thermistor layer and the reference signal.

In this embodiment, an example is shown in which, in the flow rate detecting device shown in FIG. 1, the flow rate measurement independent of the temperature change of the fluid is performed by driving the heating element (11) by AC. 1 is basically the same as the fabrication method of the flow rate detection device described in Embodiment 1, except that the thermistor layer (12) and the heating element ( 11) is made separately by the parning process. As described above, the resistance of the thermistor layer (12) is 1 kΩ and the resistance of the heating element (11) is 100 Ω.
The area is set so that

The measuring apparatus according to the present embodiment shown in FIG. 6 will be described below. Nitrogen gas (81), which is the fluid to be measured, was provided with a flow rate detection device having a thermistor layer (12) made of platinum and a heating element (11) formed on the surface of the diamond thin film (13) by sputtering. It flows inside the box (86) in the direction of the arrow in the figure. Although not shown, the nitrogen gas flow rate is accurately measured by a separate flow rate detector, and the nitrogen gas is flown in parallel on the surface opposite to the surface of the thermistor layer (12). The surface on which the thermistor layer (12) was formed was coated with an organic resin so as not to come into direct contact with the fluid. Therefore, the thermistor layer (12) is a diamond thin film
The structure is affected by the amount of heat taken by the nitrogen gas as a fluid via (13). In addition, it is important that the flow rate detecting device is thermally insulated from the installation base by an organic resin having a low thermal conductivity or the like so that heat does not flow out. This is because the function of the diamond thin film (13) as a heat storage layer is ruined. In this example, polyimide was used as a material for thermally insulating the flow rate detector.

An AC current is supplied to the heating element (11) from an AC power supply (85) through a pair of electrodes (10). A bias current is applied to the thermistor layer (12) from a bias power supply (87), and an output signal from the thermistor layer (12) is applied to a pair of electrodes (1).
It is output from 5) and amplified by the amplifier (88). The output signal related to the flow rate from the thermistor layer (12) amplified by the amplifier (88) is multiplied by the reference signal from the AC power supply (85) by the multiplier (89) and amplified by the integrator for amplification (800). Is done. The output signal related to the flow rate from the thermistor layer (12) and the reference signal from the AC power supply (85) are multiplied by the multiplier (89) and amplified by the integrator for amplification (800). This is for obtaining the relationship between the drive waveform for driving (11) and the output from the thermistor layer (12).

The measuring method and the measurement result will be described below. 8 and 9 show the thermistor layer (1) when the heating element (11) is AC-driven and heated with a rectangular wave having a width of 10 s.
Measure the output of 2), the horizontal axis is time, and the vertical axis is thermistor layer (1
An output waveform is shown as an output indicating the temperature in 2). In FIGS. 8 and 9, (100) and (110) indicate the time during which the heating is being performed, and (101) and (111) indicate the time during which the heating is not being performed and the natural cooling is performed. 8 and 9, the signal is processed so that the output increases as the temperature of the thermistor layer (12) increases. Therefore, it can be said that the higher the output, the higher the temperature of the thermistor layer (12) is. FIG. 8 shows the case where nitrogen gas is not flown, and FIG. 9 shows the case where nitrogen gas is flown at a flow rate of 1 m / s.

A comparison between FIG. 8 showing the case where the flow velocity is zero and FIG. 9 showing the case where the flow velocity is 1 m / s shows that the output indicative of the temperature of the thermistor portion is reduced by about 0.1 mV due to the flow of the nitrogen gas. . That is, it can be seen that the temperature of the thermistor layer (12) has decreased. Also, from FIG. 9, it can be seen that the temperature of the thermistor layer (12) is constant as shown by Expression 1 if the flow rate is constant. That is, it can be seen that the thermal equilibrium state as shown by the equation 1 is maintained.

FIG. 9 shows that the thermistor layer (12) is at a certain temperature, which is affected by the temperature of the environment, for example the temperature of the fluid (16). Therefore, if the temperature of the environment is always constant, accurate flow rate measurement can be performed, but if the temperature of the environment fluctuates during flow rate measurement,
The output of the thermistor layer (12) indicated by the vertical axis in FIG. 9 fluctuates. However, in FIG. 9, the heating time (11
Considering the difference (112) in the output of the thermistor layer between (0) and the non-heating time (111), the difference in the output indicated by (112) in FIG. 9 should not depend on the temperature of the environment. This is because, at the time represented by (111) and (110), the temperature of the thermistor layer indicated by the output from the thermistor layer includes the temperature of the environment and the output. If) is taken, the output of the environmental temperature is also deducted to zero and is not included in (112).

Actually, the heating element has a pulse waveform or an AC waveform having a higher frequency than those shown in FIGS.
(11) is heated to obtain a waveform corresponding to FIG. If the flow rate does not change and the environmental temperature does not change, the temperature of the thermistor does not change, and in that case, a waveform as shown in FIG. 9 is obtained.

However, if the environmental temperature does not change and the flow rate changes, a waveform having a gradually different area over time is obtained. Then, by calculating the area of the waveform, the temperature of the thermistor portion is calculated, and the flow rate is further calculated. The change in temperature is calculated by calculating the change in the area of the waveform, and the change in the flow rate is calculated based on the change.

Here, even if the environmental temperature changes, the principle is the same. That is, the area of the waveform shown in FIGS. 8 and 9 and the change of the area with respect to time do not depend on the temperature of the environment as described above.

As described above, even if there is a change in the temperature of the measurement environment, it is possible to accurately measure the temperature of the thermistor and its change in accordance with the amount of heat carried away from the thermistor by the AC drive heating. Therefore, the flow rate and its change can be accurately measured.

FIG. 7 shows the relationship between the flow rate of nitrogen gas measured by the above-described AC drive heating and the output voltage from the thermistor layer (12). In FIG. 7, the vertical axis represents the output voltage, and the horizontal axis represents the flow rate (cm / s) ^1/2 . The unit of the horizontal axis is (cm
/ s) ^1/2 in order to clarify the correlation between the flow velocity and the output voltage.

In FIG. 7, since the horizontal axis represents the half flow of the flow velocity, the maximum flow rate of the nitrogen gas fluid measured in this case is approximately 25 ² × S (cm ³ / s), where S is the cross-sectional area of the fluid. Indicated by It can be seen from FIG. 7 that the measured minimum flow rate is 1 × S (cm ³ / s) or less.
This means that three or more digits were obtained.

In the flow rate detecting device using the conventional silicon thermistor, the AC drive heating did not work effectively. That is, there is no mechanism that follows the temperature change of the thermistor portion and realizes the equilibrium condition as shown by the equation 1 at high speed in the conventional apparatus. Even if you flow a certain amount of flow,
Since an equilibrium state following AC drive heating is not realized,
The output of the thermistor does not reflect the flow rate,
Therefore, the flow rate could not be accurately detected from the output of the thermistor portion.

If the thermal equilibrium in the thermistor portion is always maintained, the higher the frequency of the AC drive heating, the higher the measurement accuracy is expected. However, since diamond is not completely resistant to heat, there is actually an upper limit of the driving frequency such that Equation 1 always holds. According to preliminary experiments and calculations, it is considered that several tens of Hz can be used as the upper limit. However, in the conventional flow rate detection device using a silicon thermistor, considering that the AC drive heating itself is difficult, the flow rate measurement that is not affected by the temperature of the environment by the AC drive heating is very useful.

Further, the frequency and the waveform in the AC drive heating can be appropriately determined according to the use form and the measurement accuracy.

[Embodiment 3] This embodiment is an example of a practical flow rate detecting device in which four flow rate sensors utilizing the thermistor function are formed on the surface of a diamond thin film. The device functions as a vector flow meter that can simultaneously obtain information about the direction and flow rate of fluid flow.

The flow detecting device shown in FIG. 5 has a size of 4 mm square as a whole, and includes four sensor portions formed of a thermistor layer (75). In FIG. 5, (7
7) is a diamond thin film having a thickness of about 10 μm which becomes a base of the flow rate detection device. Further, (75) is a thermistor layer made of platinum, (74) is a pair of metal electrodes for detecting a current flowing through the thermistor layer (75), and sandwiches the thermistor layer (75) at the base of an isosceles triangle. It is arranged. Also (7
6) is a heating element formed simultaneously with the thermistor layer. (78) is an amplifier that amplifies the signal, (701) is a differential amplifier that amplifies the difference between the input signals, and (79) is a heating element.
A power supply for supplying a current for heating (76), and a bias power supply for supplying a current to the thermistor (75) through the electrode (74) are provided at (700). And thermistor layer (75) and heating element (7
6) are connected by a diamond thin film (77) acting as a heat storage layer.

In FIG. 5, the portion serving as the heating element (76) has a sheet resistance of 10 to 100 Ω / cm ² . That is, the heating element (76) generates Joule heat by passing an electric current. Also in this example, the thickness of the diamond thin film was 10 μm, and the thickness of the thermistor layer was 0.1 μm. Other manufacturing methods and manufacturing conditions were the same as those in Example 1.

In actual use, the AC drive heating shown in Embodiment 2 is useful. In use, the fluid is caused to flow on the surface of the diamond thin film (77) on the back side of the flow rate detecting device shown in FIG.

The diamond thin film (77) has four heating elements (7
It is heated to the required temperature (usually 2 to 3 degrees with respect to the temperature of the fluid) by 5), and even when the fluid is not flowing by this heating element, a thermal gradient is formed in the plane direction. Have been. Here, when the fluid flows on the surface of the diamond thin film (77) on the back side of the apparatus shown in FIG. 5, the shape of the thermal gradient formed on the surface of the diamond thin film (77) changes. That is, since the temperature of the portion that first comes into contact with the fluid tends to be lower, the thermal gradient is reformed according to the direction and the flow rate of the fluid. For example, in FIG. 5, it is assumed that a fluid is flowing from the right side of the drawing. Then, since the amount of heat taken by the fluid from the right half of the diamond thin film (77) shown in the figure is larger than the amount of heat taken from the left half, it is formed by the heating element (75) in the diamond thin film (77). The state of the thermal gradient is different between the right part and the left part of the diamond thin film (77). In the apparatus shown in FIG. 5, the fact that the state of the thermal gradient formed on the diamond thin film (77) is different at the left and right sides of the drawing means that the difference between the outputs of the thermistor layers (75) arranged in the left and right directions is natural. Will come out.

In the above state, the bias power supply
A change in current flowing from the transistor (700) to the thermistor layer (75) through the electrode (74) is amplified by the amplifier (78), and the differential component is further amplified by the differential amplifier (701). By measuring the differential component of the output of each thermistor layer (75), the state of the thermal gradient formed on the diamond thin film (77) can be known. Then, the flow rate and its direction are measured from the state of the thermal gradient. At the same time, the flow rate change can be known by measuring the change in the thermal gradient. In this embodiment, 4
The outputs from the thermistor portions are detected by two differential amplifiers, and the outputs from the two operating amplifiers are compared. By comparing the outputs from the two operating amplifiers, the thermal gradient can be measured not only in the vertical and horizontal directions of FIG. You can know the state of. The thermal gradient formed on the diamond thin film is determined by the method of measuring the flow rate, the method of providing the heating element, the number and arrangement of the thermistor portions, and these may be determined as needed. For example, if one wants to know the state of the thermal gradient more precisely, the direction of the thermal gradient is 2
One or more thermistor portions may be provided. If it is desired to measure the thermal gradient only in the required direction, a plurality of thermistor portions may be formed on a line in that direction, and the output from the thermistor may be processed.

As described above, by measuring the state of the thermal gradient formed by the heating element on the diamond thin film with a plurality of thermistors, the direction, flow rate, and change in flow rate of the fluid can be simultaneously known. Of course,
As described in the first and second embodiments, the operation is performed with high speed, high sensitivity, and high dynamic range.

In the apparatus shown in FIG. 5, the fluid does not flow on the surface on which the metal electrode (74) and the metal wiring (not shown) are provided (that is, the surface on the near side of the paper), but on the back side thereof. Flows through the surface of the diamond thin film (77), so that the diamond thin film, which is the most stable material, can act as a heat exchange part, a heat storage layer, and even a protective layer, even when detecting the flow rate of corrosive gas. The apparatus can be used without worrying about corrosion of metal electrodes and metal wiring.

When manufacturing a flow rate detector having a structure as shown in FIG. 5, the roughened side of the diamond thin film is used as the surface in contact with the fluid, and the thermistor layer, the electrodes, and the heating element are formed on a smooth surface. By forming, the easiness of manufacturing the device and the improvement of the sensitivity can be measured at the same time.

As described above, the diamond thin film formed on the silicon substrate has a smooth surface at the interface with the silicon substrate, and the exposed surface on the opposite side has a rough surface. Using this, a thermistor layer, electrodes, and a heating element are formed on the smooth surface of the diamond thin film separated from the silicon substrate, and the rough surface behind the surface is in contact with the flow rate, so that the surface area of the heat exchange portion Can be increased, and the heat exchange efficiency with the flow rate can be increased.

This embodiment is an example of a practical flow rate detecting device. The arrangement and number of the thermistor layers as the sensor portion, and the arrangement and shape of the electrodes are adapted to the actual measurement environment and measurement conditions. The arrangement and shape of the heating element can be selected as appropriate. Particularly, in the above description, the thermistor portion and the heating element portion are formed on the same surface side because the thermistor portion and the heating element portion are formed in the same process. Even if it is formed separately from the portion, the function as a heat storage layer of the diamond thin film can be obtained, and a high-performance flow rate detection device can be obtained. Also, the signal processing method between the sensors is not limited to the method shown in the present embodiment, and a method suitable for actual use can be used as appropriate.

Further, the embodiments of the present invention are not limited to the forms shown in the above embodiments. For example, in the above embodiment, the thickness of the diamond thin film and the thickness of the portion to be the thermistor layer were set to about 100: 1, and the heat capacity ratio was set to about 100: 1. May be determined in a timely manner according to the difference between the two or the environment in which the flow rate detection device is used, the measurement accuracy, the measurement sensitivity, the method of use, and the like. In addition, the method and conditions for forming the diamond thin film may be appropriately selected for implementation. Further, the material and manufacturing method of the thermistor layer may be selected according to the embodiment.

[0129]

In the conventional flow rate detector, there was a problem of a two-pronged trade-off that the response speed decreases when trying to obtain high sensitivity, and the sensitivity decreases when trying to increase the response speed. By forming a layer having a thermistor function on the surface of a diamond thin film serving as a heat storage layer, which is a configuration of the present invention, the thermal equilibrium condition in the thermistor portion, which is an important condition in flow rate detection using the thermistor, is always changed according to a change in flow rate. It can be realized at high speed and the flow rate at that time can be accurately measured with high sensitivity, high speed response and high dynamic range.

Further, by using the AC drive heating,
The flow rate can be measured without being affected by the temperature of the environment.

Further, since it has a structure that makes full use of the physical properties of diamond material such as high thermal conductivity and low specific heat, it is possible to obtain a material resistant to long-term deterioration.

Further, the flow rate detecting device of the present invention has a feature of high stability in addition to the above-described features, and can obtain high sensitivity by heating the fluid only a few degrees.
It can be replaced with a conventional flow rate detection device as a gasoline flow rate detector for automobiles and the like. Another advantage is that it is resistant to various corrosive gases. Further, it is also very useful for measuring the flow rate of a fluid, which has conventionally been difficult to measure because of the danger of ignition.

[Brief description of the drawings]

FIG. 1 shows a schematic cross-sectional view and a plan view of a flow rate detection device using a diamond thin film.

FIG. 2 shows an arrangement of an apparatus used in Example 1.

FIG. 3 shows a correlation between the flow rate of the nitrogen gas and the output of the flow rate detection device in the first embodiment.

FIG. 4 shows a correlation between an output and a heating temperature when the flow rate detection device is in a heating state in the first embodiment.

FIG. 5 shows a flow rate detection device according to a third embodiment.

FIG. 6 illustrates a flow rate detection device according to a second embodiment.

FIG. 7 shows a relationship between a flow rate and an output in the second embodiment.

FIG. 8 shows an output waveform at zero flow rate when AC drive heating is performed in Example 2.

FIG. 9 shows an output waveform at a flow rate of 1 m / sec when AC drive heating is performed in Example 2.

[Explanation of symbols]

 10 Electrode 11 Heating element 12 Thermistor layer 13 Diamond thin film 16 Fluid 17 Surface in contact with fluid 40 Box 41 Flow rate detector 42 Nitrogen gas 43 Flow meter 44 Electromagnetic valve 45 Modulator 46 Power supply 47 1 MΩ resistor 48 Lock-in amplifier 49 Oscilloscope 86 Box 85 AC power supply 81 Nitrogen gas 87 Bias power supply 88 Amplifier 89 Multiplier 800 Integrator for amplification 74 Electrode 75 Thermistor layer 76 Heating element 77 Diamond thin film 78 Amplifier 79 Power supply for heating element 700 Bias power supply 701 Differential amplifier

Continuation of the front page (56) References JP-A-63-252224 (JP, A) Sensors Applications for Synthetic Polycrystalline Line in Thin-Film Diamond, Sensors and Materials (346, 329, 1991). ) Surveyed field (Int.Cl. ⁷ , DB name) G01F 1/68-1/699 G01P 5/12

Claims (6)

(57) [Claims] 1. A flow sensing device using a diamond film having a thermistor portion on a surface of said diamond thin film,
The back surface of the diamond thin film is disposed in contact with a fluid, and in the thermistor portion, W = K (T−T ₀ ) + G (T−T ₀ )
······ Formula 1 (where W is the unit time at which the thermistor generates heat)
The amount of heat, K, is the heat related to the amount of heat carried by the fluid
Transfer coefficient, T is the temperature of the thermistor part, T ₀ is the fluid temperature
G is the thermal conductivity of the material forming the thermistor part.
Satisfies the following conditions: 2. A method according to claim 1, wherein the diamond film flow rate detecting device comprising a this <br/> to have a large heat capacity than the thermistor portion. 3. A flow sensing device using a diamond film having a thermistor portion on a surface of said diamond thin film, wherein the thermistor portion is formed on the crystal growth initial surface of the diamond film, said diamond and the crystal growth end surface of the thin-film is contact with the fluid
Disposed in the thermistor part, Equation 1] _{W = K (T-T 0} ) + G (T-T 0) ····
······ Formula 1 (where W is the unit time at which the thermistor generates heat)
The amount of heat, K, is the heat related to the amount of heat carried by the fluid
Transfer coefficient, T is the temperature of the thermistor part, T ₀ is the fluid temperature
G is the thermal conductivity of the material forming the thermistor part.
Satisfies the following conditions: 4. A flow rate detecting device using a diamond thin film has a plurality of thermistor portion on a surface of said diamond thin film, a heating element, a rear surface of the diamond film is disposed in contact with the fluid , W = K (T−T ₀ ) + G (T−T ₀ ) in the plurality of thermistor portions.
······ Formula 1 (where W is the unit time at which the thermistor generates heat)
The amount of heat, K, is the heat related to the amount of heat carried by the fluid
Transfer coefficient, T is the temperature of the thermistor part, T ₀ is the fluid temperature
G is the thermal conductivity of the material forming the thermistor part.
Is satisfied, and the plurality of thermistor portions have a function of detecting a thermal gradient formed in the diamond thin film by the heating element.
Flow rate detecting apparatus characterized by being. A 5. A thermistor portion formed on the diamond thin film table surface, a heating element, wherein the back surface of the diamond thin film is placed in contact with fluid, said at a plurality of thermistors portions, Equation 1] W = K (T−T ₀ ) + G (T−T ₀ )
······ Formula 1 (where W is the unit time at which the thermistor generates heat)
The amount of heat, K, is the heat related to the amount of heat carried by the fluid
Transfer coefficient, T is the temperature of the thermistor part, T ₀ is the fluid temperature
G is the thermal conductivity of the material forming the thermistor part.
Represented) is satisfied, a flow rate detection method using the flow rate detecting device, by the heating element is heated by an AC waveform and processing the output from the resulting thermistor portion of the heating, before Symbol flow rate detection wherein the Turkey to calculate the flow rate of the flow body. Includes a plurality of thermistors portions having 6. one conductivity type formed on the diamond film table surface, a heating element, a rear surface of the diamond film is disposed in contact with the fluid, the plurality of thermistor portion in, [number 1] _{W = K (T-T 0} ) + G (T-T 0) ····
······ Formula 1 (where W is the unit time at which the thermistor generates heat)
The amount of heat, K, is the heat related to the amount of heat carried by the fluid
Transfer coefficient, T is the temperature of the thermistor part, T ₀ is the flow body temperature
G is the thermal conductivity of the material forming the thermistor part.
Represented) is satisfied, a flow rate detection method using the flow rate detector, a thermal gradient is formed in the diamond film by the heating element is measured by the plurality of thermistor portion, said from the magnitude of the thermal gradient Obtaining a flow rate of the fluid, obtaining a flow direction of the fluid from the direction of the thermal gradient, and obtaining a change of the flow rate from a way of changing the thermal gradient.