KR101484540B1 - Flow sensor - Google Patents

Abstract

The present invention relates to a flow sensor to measure microflow at low speed in compared to a previous one. The flow sensor of the present invention comprises: a substrate (110) in a two-dimensional plane shape; a pair of electrodes (120) placed apart from each other in a first direction on the substrate (110); a CNT sheet (130) arranged on the substrate (110); and a sealing part (140) arranged to cover an upper part of the substrate (110) on which the electrodes (120) and the CNT sheet (130) are arranged.

Description

Flow sensor {Flow sensor}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor, and more particularly, to a flow sensor that improves performance so as to enable precise measurement up to a much slower speed than a conventional one.

Measuring the flow rate is a task that is widely required in various technical fields. The devices for measuring the flow rate are various structures and shapes to suit the flow rate and the characteristics of the fluid. There are a myriad of different types of flow measurement techniques depending on whether the flow rate is large or small, whether the fluid is liquid or gas,

In recent years, due to the development of semiconductor technology, minute size sensors have been developed and used, and a flow sensor for measuring a minute level flow rate is also used. Such flow sensors are generally made in the form of integrated circuits using semiconductor technology. In such a micro-level measurement technique, it is important to measure precisely how much slower the flow rate is.

As a technique for measuring a minute flow rate and a flow rate, there are a conventional method using a temperature difference between a heating part and a fluid using heat generated in a heating part, a method using a pressure loss generated from an orifice, A method of using a change in the frequency of light or ultrasonic waves in the light source is used. As a method of utilizing the temperature difference between the heating part and the fluid, there has been proposed a method of using the temperature difference between the heating part and the fluid as disclosed in Korean Patent Registration No. 0292799 ("Micro Flow Rate / Flow Rate Sensor with Membrane Structure and Method of Measuring Flow Rate / Flow Rate Using the Same ", 2001.03.27 Technology. In the above prior art, a cavity sealed with a membrane is formed on a silicon substrate, heat is radiated by a heater disposed on the membrane, and temperature changes in the upstream and downstream portions of the operating fluid due to heat emitted from the heater are detected by the upstream / A micro flow rate / flow rate sensor for measuring the flow rate and flow rate of a working fluid by measuring with a thermopile is disclosed.

However, in the case of the prior art, there is a problem that unnecessary structural complexity is increased, for example, a structure is required to apply heat separately. In order to solve such a problem, recently, a technique for measuring a minute flow rate using a carbon nanotube (CNT), which is a new material, has been developed. FIG. 1 is an example of the structure of flow sensors for measuring the existing minute flow rate using the new material.

1 (A) is a CNT-FET sensor, and its operation principle is as follows. A pair of electrodes are connected by a carbon nanotube wire, and a power is supplied to the carbon nanotube wire so that current flows through the carbon nanotube wire. A power source that supplies a reference voltage is also supplied to the substrate. When the fluid to be measured flows through the carbon nanotube in such a state, the fluid molecules of the fluid to be measured or the ions contained in the fluid to be measured are adsorbed on the carbon nanotube wire, thereby changing the electrical conductivity of the carbon nanotube wire. A change occurs in the current value flowing. In the CNT-FET sensor, the flow rate of the fluid to be measured can be measured by amplifying and outputting the current change. This structure and principle was introduced in the journal Nature Nanotechnology in 2007, and it is shown that low-speed measurement up to 20.83 mm / s is possible with this method. 1B is a silicon nanowire sensor, which operates on almost the same principle except that silicon nanowires are provided instead of carbon nanotube wires. These structures and principles are described in Nano Lett. And it is shown that low speed measurement up to 0.55 ~ 1.1mm / s is possible by this method.

It is relatively easy to measure the flow rate in the measurement of the minute flow rate, but it is difficult to measure the flow rate at a lower speed. As described above, along with the development of new materials, various technologies for more precisely measuring low-speed micro flow rate have been researched and developed, and efforts for further lowering the measurement limit have been made steadily. Particularly, the problems of existing researches such as the CNT-FET sensor and the silicon nanowire sensor described above are that it is relatively difficult to manufacture due to the nanowire which can not be made up to several tens of nanometers in width, There may arise problems such as durability.

1. Korean Patent Registration No. 0292799 ("Micro Flow Rate / Flow Rate Sensor with Membrane Structure and Method for Measuring Flow Rate / Flow Rate Using the Same", 2001.03.27)

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a method of measuring a minute flow rate And a flow sensor for measuring the flow rate of the fluid. It is still another object of the present invention to provide a flow sensor which is easier to manufacture than conventional methods, has durability against flowing water, and can improve the performance of the sensor.

According to an aspect of the present invention, there is provided a flow sensor comprising: a substrate in the form of a two-dimensional plane spreading along a first direction and a second direction perpendicular to the first direction; A pair of electrodes 120 spaced apart from each other in the first direction on the substrate 110; A CNT sheet 130 disposed on the substrate 110 so that both ends of the CNT sheet 130 are in contact with the pair of electrodes 120, ; A micro-channel 145 extending in a first direction and having a groove shape disposed at a position corresponding to the CNT sheet 130 is formed at a lower portion of the CNT sheet 130, A sealing portion 140 disposed to cover an upper portion of the substrate 110 on which the substrate 110 is disposed; And a pair of electrodes 120 that are generated by interaction between the CNT sheet 130 and the fluid to be measured flowing in the first direction through the microchannel 145, Signal may be used to measure the flow rate of the fluid to be measured.

At this time, the CNT sheet 130 is composed of non-metallic carbon nanotubes which are sensitive to flowing water, instead of using carbon nanotubes mixed with metallic and non-metallic properties used in the prior art. The electrode 120 may be made of chromium or gold. The sealing part 140 may be made of PDMS material.

Also, the method of manufacturing the flow sensor of the present invention is a method of manufacturing the flow sensor 100 as described above, comprising the steps of: disposing the substrate 110; Patterning a pair of electrodes (120) on the substrate (110); A carbon nanotube material layer is transferred between the pair of electrodes 120; Annealing the carbon nanotube material layer to form the CNT sheet 130; The sealing part 140 is disposed and fixed so as to cover the upper part of the substrate 110 on which the electrode 120 and the CNT sheet 130 are disposed; . ≪ / RTI > The step of annealing the carbon nanotube material layer includes spin coating the resin on the carbon nanotube material layer and irradiating UV light to the carbon nanotube material layer and the resin on the substrate 110 And forming the CNT sheet 130 by fixing.

According to the present invention, the structure is much simpler than the conventional sensor for measuring the minute flow rate, and the measurement can be performed at a much lower speed. More specifically, in the case of a method of heating a fluid to be measured among conventional micro-flow measuring systems, a heating unit, a structure for supplying power to the heating unit, a temperature sensor, and the like are required, and a type such as a CNT- There has been a problem in that the structure is complicated because the power must always be supplied to the circuit in order to measure the flow rate. On the other hand, the flow sensor of the present invention does not require a separate device such as a heating unit or a sensor for measuring other physical quantities, and does not require a structure corresponding to a power supply unit because it does not need a power supply. In addition, it is possible to construct a network type sensor that is not a conventional nanowire type, which is comparatively easy to manufacture, and the manufacturing cost can be reduced. That is, the flow sensor according to the present invention has a much simpler structure than any conventional flow sensor.

In addition, as a result of actual testing, the flow rate sensor of the present invention has a measurement low speed limit of several tens of mm / s in the case of a conventional CNT-FET sensor and a few millimeters per second in the case of a conventional silicon nanowire sensor, The limit is about 0.01 mm / s, which is a great effect that the precision can be increased several tens of times as compared with the conventional one. As described above, according to the present invention, it is possible to dramatically reduce the measurement limit while having a simpler structure than the conventional one.

In the present invention, since a carbon nanotube sheet in which carbon nanotubes are woven in a network form instead of using carbon nanotube wires is used, it is advantageous in that it is much easier to manufacture than a wire form And, of course, economical effects can be obtained that can further reduce the process steps and costs for fabrication.

Fig. 1 is an example of the structure of a flow sensor for measuring a conventional micro flow rate.
Fig. 2 shows a structure of the flow sensor of the present invention. Fig.
3 is a microscope photograph of a CNT sheet of the flow sensor of the present invention.
4 and 5 are flow velocity measurement results by the flow sensor of the present invention.

Hereinafter, a flow sensor according to the present invention will be described in detail with reference to the accompanying drawings.

Carbon nanotubes (CNTs) are substances that have a hexagonal shape consisting of six carbon atoms connected to each other to form a tube. The diameter of the tube is only a few to several tens of nanometers, which is called a carbon nanotube. Carbon nanotubes have the same electrical conductivity as copper and have the same thermal conductivity as natural diamond. Their strength is 100 times better than that of steel. Carbon fibers are cut by 1% transformation, while carbon nanotubes are 15% deformed And is capable of enduring even when it is used as a new material. Currently, it is researching and developing various ways of utilizing such carbon nanotubes in various fields.

One of the properties of such carbon nanotubes is high electric conductivity and good electron mobility. Thus, many researches have been made on utilization of the carbon nanotube as a transparent electrode material, a display device, a sensor device, etc. As described above with reference to FIG. 1, Micro-flow sensors have also been developed using nanotube wires.

However, since the carbon nanotubes have a very minute size as described above, it is difficult to arrange and arrange them in nanowire form, making the manufacturing process difficult. In addition, the structure in which the carbon nanotubes are arranged in the form of nanowires has a considerably high risk of being partially damaged by repetitive use. That is, in the case of the conventional flow sensor shown in FIG. 1, the device manufacturing process is difficult and the durability of the device itself is considerably low. Of course, the low-speed limits that can be measured also need to be further improved.

Fig. 2 shows the structure of the flow sensor of the present invention, and the structure and operation principle of the flow sensor of the present invention will be described with reference to Fig.

As shown in FIG. 2, the structure of the flow sensor of the present invention is a structure in which electrodes are connected to both sides of a CNT sheet. In order to clarify the direction, one direction of the CNT sheet plane is referred to as a first direction, and a direction perpendicular to the first direction on the CNT sheet plane is referred to as a first direction. At this time, as shown in FIG. 2, a pair of electrodes are brought into contact with both ends of the CNT sheet in the first direction, and the fluid to be measured flows along the first direction on the CNT sheet.

As described above, since carbon nanotubes have high electric conductivity and good electron mobility, when the fluid to be measured flows in contact with the carbon nanotubes, interaction occurs between the fluid substances to be measured and the electrons in the carbon nanotubes An electric signal is generated and detection is performed at the electrode. At this time, a constant relation is established between the flow rate of the fluid to be measured and the magnitude of the electric signal, and the flow rate of the fluid to be measured can be accurately measured by using this.

The structure of the flow sensor of the present invention will be described in detail with reference to FIG. The flow sensor 100 of the present invention includes a substrate 110, a pair of electrodes 120, a CNT sheet 130, and a sealing portion 140 as shown in FIG.

The substrate 110 is in the form of a two-dimensional plane spreading along a first direction and a second direction perpendicular to the first direction. The material of the substrate 110 may be glass, silicon, or the like widely used as a substrate of a general semiconductor component.

The pair of electrodes 120 are disposed on the substrate 110 in a first direction. 2, a portion of the electrode 120, which is connected to the CNT sheet 130, is spaced apart in a first direction. When the electrode 120 is connected to the outside (that is, The portion of the electrode 120 that is connected to the outside is shown as being spaced apart in the second direction, which is merely an arrangement for convenience, and it is natural that the portion where the electrode 120 is connected to the outside may be arranged in any direction . The electrode 120 may be made of a material having good electrical conductivity, and may be made of chromium or gold, which is generally used for electrodes.

The CNT sheet 130 has a planar shape in which a plurality of carbon nanotubes (CNTs) are networked. The CNT sheet 130 is formed on the substrate 110 so that both ends of the CNT sheet 130 are in contact with the pair of electrodes 120 . In the simplest case, since the CNT sheet 130 is in the form of a thin film, that is, a plane shape, the CNT sheet 130 formed in a square planar shape may be disposed so that both ends of the CNT sheet 130 in the first direction cover the electrode 120. As described above, when the fluid to be measured flows onto the CNT sheet 130 (that is, when the CNT sheet 130 and the fluid to be measured are in direct contact with each other), the electrons in the CNT sheet 130 reach the fluid Interact with molecules (eg water molecules) or ions contained in the fluid to be measured. In this process, electrons are attracted in a direction biased in one direction, so that a potential difference is generated, so that the electrode 120 can detect an electric signal.

In the present invention, a non-metallic carbon nanotube that exhibits a sensitive reaction (electrical signal) to the flowing water is used instead of the carbon nanotube mixed with metallic and non-metallic properties unlike the conventional research. In addition, non-metallic carbon nanotubes were fabricated on the substrate in a network type. In order to prevent loss of carbon nanotubes due to water flowing after the transfer, UV resin was coated on the carbon nanotubes to prevent loss. That is, the height of the non-metallic carbon nanotubes is about 100 nm. After the resin is impregnated to the lower end of the carbon nanotubes by about 50 nm or less using a spin coater, the portion is exposed to UV light for about 2 minutes, Was made to be fixed with a resin. FIG. 3 is an enlarged photograph of resin-coated non-metallic carbon nanotubes. In some of them, resin nanotubes are partially covered with resin as shown by arrows. Most of the carbon nanotubes are clearly classified into network types Can be confirmed.

In the present invention, the CNT sheet 130 is preferably made of non-metallic carbon nanotubes. It is well known that carbon nanotubes are classified into those having metallic properties and those having semiconducting properties (non-metallic properties) depending on the structure formed when carbon nanotubes are grown. In general, a mixture of metallic and semiconducting materials is used. For example, the ratio of metallic: semiconducting material is often about 6: 4. At this time, the CNT sheet 130 used in the present invention is formed by collecting only semiconducting carbon nanotubes. As a result, a high accuracy and high accuracy can be obtained as compared with a material mixed with metallic and semiconducting materials.

The sealing part 140 is formed at the lower part of the lower part of the microchannel 145 in the form of a groove extending in the first direction and disposed at a position corresponding to the position of the CNT sheet 130, And an upper portion of the substrate 110 on which the CNT sheet 130 is disposed. More specifically, the sealing part 140 is disposed to cover the substrate 110, and the micro-channels 145 in the shape of a groove are disposed at positions overlapping with the CNT sheet 130. Accordingly, a space is formed on the CNT sheet 130 by the microchannel 145, and the target fluid can flow into the space. That is, the microchannel 145 is a channel through which the fluid to be measured flows, and the microchannel 145 is disposed at a position overlapping the CNT sheet 130, So as to be able to flow. The sealing part 140 may be made of PDMS material.

A manufacturing method of the flow sensor 100 having such a structure can be performed as follows. First, the substrate 110 is disposed, and a pair of the electrodes 120 is patterned thereon. Next, a carbon nanotube material layer is transferred between the pair of electrodes 120 to form a pair of the electrodes 120 in contact with the carbon nanotube material layer.

Next, the carbon nanotube material layer is annealed to form the CNT sheet 130. As described above, the annealing process may be performed by spin coating a UV resin on the carbon nanotube material layer and irradiating ultraviolet rays.

Finally, the sealing part 140 is disposed and fixed so as to cover the electrode 120 and the substrate 110 on which the CNT sheet 130 is disposed.

Briefly, the flow sensor 100 of the present invention having such a structure is generated by interaction between the CNT sheet 130 and the fluid to be measured flowing in the first direction through the microchannel 145 And a flow rate of the fluid to be measured is measured using an electric signal detected by a pair of the electrodes 120. This will be described in more detail as follows.

4 and 5 are graphs showing flow velocity measurement results by the flow sensor of the present invention. In the graph, 'Flow on' indicates the moment when the measurement fluid starts to flow, and 'Flow off' indicates the moment when the measurement fluid stopped flowing.

When the fluid to be measured flows through the microchannel 145, fluid molecules of the fluid to be measured or ions contained in the fluid to be measured are randomly adsorbed on the CNT sheet 130. In this process, the electrons in the CNT sheet 130 are attracted from one side to the other, and the electrical signal is detected by the electrode 120 due to the potential difference generated. The flow rate measurement principle is based on the phenomenon that the electric signal generated by the reaction of the fluid with the carbon nanotube is proportional to the flow rate of the fluid. The measurement limit is determined based on when the signal to noise level (SNR) becomes 5 or less.

FIG. 4 clearly shows that there is a proportional relationship between the flow velocity of the fluid to be measured and the induced voltage of the generated electric signal. In particular, as shown in FIG. 4, highly reproducible results are obtained with respect to repetitive execution, so that the reliability of the measurement performance of the flow sensor 100 of the present invention is also high. Also, in FIG. 4, the blue graph shows the result when the water flows in the forward direction and the red graph shows the result when the water flows in the reverse direction, that is, the signal generated when the direction of the flow changes is also reversed The direction of the water flow can also be checked. FIG. 5 is a graph showing the relationship between the logarithmic value of the flow velocity and the voltage. It is seen from the graphs of FIG. 4 and FIG. 5 that the relationship between the flow rate of the fluid to be measured and the voltage of the electric signal A sublinear dependence is established. From these results, it can be seen that the flow rate of the fluid to be measured up to the level of 0.01 mm / s can be measured by using the flow sensor of the present invention.

As described above, the flow sensor of the present invention can accurately measure the flow rate by detecting an electric signal generated by flowing a fluid to be measured in a microchannel without requiring any separate power supply. This is a much simpler structure than the conventional micro-flow sensor including the heating unit and the temperature sensor described above, and is relatively simple in structure compared to the recently developed CNT-FET sensor or silicon nanowire sensor It has an advantage of being easy to manufacture.

More specifically, it is as follows. In the case of a CNT-FET sensor or a silicon nanowire sensor, a structure which is connected between the electrodes and in direct contact with the fluid to be measured is formed in a wire form. In the case of a conventional CNT-FET sensor, as described above, the flow velocity is measured by using the property that the electric conductivity of the wire changes due to adsorption of fluid molecules or ions on the wire. That is, in a conventional CNT-FET sensor, since the flow rate can be measured by using the difference between the original current value and the current value after the change of the electric conductivity, the power must be supplied for the flow rate measurement.

However, as described above, the flow sensor of the present invention measures the flow velocity by detecting a potential difference generated by the movement of electrons in the process of adsorbing the fluid to be measured while flowing on the CNT sheet, It is not necessary to provide even a power supply structure required for a conventional CNT-FET sensor or the like with a simple structure (network type), which is much simpler than the conventional one.

The flow sensor of the present invention also has the following advantages. As described above, in the case of a conventional CNT-FET sensor, since the property of changing the electric conductivity is used, the narrower the wire becomes, the more sensitive the change becomes, and the more precise measurement can be performed. On the other hand, if the fluid to be measured is continuously brought into contact with such a fine wire structure, there is a possibility that the wire itself is too fine structure to cause damage, and the risk becomes larger as the wire becomes thinner. In other words, in the case of conventional CNT-FET sensors, the sensitivity (ie, precision) may be increased as the wire becomes thinner, but the durability is lowered, so that it is impossible to improve the precision and durability at the same time.

However, in the flow sensor of the present invention, the structure contacting with the fluid to be measured is a CNT sheet in a planar form rather than a wire form, which is of course much more durable than a conventional wire structure, and is of course much easier to manufacture. In addition, as has been experimentally confirmed, when the flow rate sensor of the present invention has a measurement low-speed limit of 0.01 mm / s and a measurement low-speed limit of a conventional CNT-FET sensor is several to several tens mm / s It was confirmed that the precision was also greatly improved. That is, the flow sensor of the present invention can improve accuracy and durability at the same time as the conventional CNT-FET sensor.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It goes without saying that various modifications can be made.

100: Flow sensor (of the present invention)
110: substrate 120: electrode
130: CNT sheet 140: sealing part
145: Microchannel

Claims (6)

A substrate (110) in the form of a two dimensional plane spreading along a first direction and a second direction perpendicular to the first direction;
A pair of electrodes 120 spaced apart from each other in the first direction on the substrate 110;
A CNT sheet 130 disposed on the substrate 110 so that both ends of the CNT sheet 130 are in contact with the pair of electrodes 120, ;
A micro-channel 145 extending in a first direction and having a groove shape disposed at a position corresponding to the CNT sheet 130 is formed at a lower portion of the CNT sheet 130, A sealing portion 140 disposed to cover an upper portion of the substrate 110 on which the substrate 110 is disposed;
, ≪ / RTI >
(120) generated by interaction between the CNT sheet (130) and the fluid to be measured flowing in the first direction through the microchannel (145) And the flow rate of the target fluid is measured.
The method of claim 1, wherein the CNT sheet (130)
And a non-metallic carbon nanotube.
The method of claim 1, wherein the electrode (120)
Chromium, or gold.
2. The apparatus of claim 1, wherein the sealing portion (140)
PDMS material.
A method of manufacturing the flow sensor (100) of claim 1,
Disposing the substrate (110);
Patterning a pair of electrodes (120) on the substrate (110);
A carbon nanotube material layer is transferred between the pair of electrodes 120;
Annealing the carbon nanotube material layer to form the CNT sheet 130;
The sealing part 140 is disposed and fixed so as to cover the upper part of the substrate 110 on which the electrode 120 and the CNT sheet 130 are disposed;
Wherein the flow sensor comprises a plurality of flow sensors.
6. The method of claim 5, wherein the step of annealing the carbon nanotube material layer comprises:
Spin coating the resin on the carbon nanotube material layer; and
And forming the CNT sheet (130) by UV irradiation to fix the carbon nanotube material layer and the resin to the substrate (110).

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