JPH0412230A - Semiconductor flow meter and micropump using this meter - Google Patents

Abstract

PURPOSE:To measure a very small flow rate with high accuracy by providing a check valve whose passage resistance is large in a low flow rate area, and whose passage resistance becomes small in a high flow rate area, and measuring a flow rate of a fluid, based on a detection output of a strain gage. CONSTITUTION:On the lower face of a silicon substrate 40, a diaphragm 42 for generating a stress corresponding to differential pressure of both faces of the substrate 40 is formed, and in the vicinity of the center of the diaphragm 42, a minute hole 44 tapered from the upstream side to the downstream side is formed. There diaphragm 42 and minute hole 44 can be formed with high accuracy by a unit of micron order by performing a crystal anisotropic etching treatment by using an alkali etching liquid to the substrate 40. Also, on the substrate 40, a check valve 60 is provided on the downstream side of the minute hole 44, and the valve 60 is formed so that the passage resistance becomes large in a low rate area, and the passage resistance becomes small in a high flow rate area. In such a state, by measuring a flow rate of a fluid, based on a detection output of a strain gauge 46, a very small flow rate can be measured with this accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor flowmeter suitable for measuring minute flow rates and a micropump using the same.

[Conventional technology] In order to realize the miniaturization of flow injection chemical analysis (FIA) systems, micro flow rates (several μ!/1 nm to several meters) have been developed.
A micropump and a sample injector have already been proposed to control the flow rate (17m1n) (Shōko et al. "Research on Medical Integrated Flow Injection Chemical Analysis System" 28th Japan ME Society Conference Japan See Liver &
BE (May, 1989)).

In order to improve the accuracy of the FIA, it is important to control the flow rate of the fluid with high precision, and for this reason, the flow rate of the fluid flowing through the flow path can be controlled over a wide range from a minute flow rate range to a high flow rate range.
Moreover, it is necessary to develop a flow meter that can measure with high precision.

As one of such flowmeters, a throttle flowmeter has been conventionally known. FIG. 6 shows a diagram of the principle of this throttle flowmeter, which restricts the flow path 10 through which fluid 100 flows]
2, the cross-sectional area of the flow path is partially reduced and a pressure difference is created before and after the cross-sectional area. Since this differential pressure has a predetermined correspondence relationship with the flow rate, the flow rate of the fluid 100 can be determined by measuring this differential pressure. One of the devices that are used in such throttle flowmeters is, for example, an orifice (Japan Society of Mechanical Engineers, Fluid Measurement Method, p. 174).
). A conventional flowmeter will be explained based on FIG. 7, taking this orifice as an example.

This flowmeter has an orifice 24 made of SUS or a material that is not corroded by the fluid to be measured, and this orifice 24 is sandwiched between flanges 22 and connected to a pipe 20. Inside the pipe 20, there is a channel 1 through which a fluid 100 flows.
0 is formed, and a pressure difference occurs before and after the orifice 24 depending on the flow rate. A pressure gauge 26 is connected to the pipe 20 to measure this differential pressure.

In this case, the differential pressure Δ generated before and after the orifice 22
The following relationship holds true between p and the flow rate q per unit.

Δf)-Kq2 (1) However, K is a value that depends on the density of the fluid 100, the shape of the orifice 24, the pipe 20, etc., and becomes a constant once the fluid 100 and the measurement system are determined.

In order to measure the flow rate of the fluid 100 with high precision, the pressure gauge 26 needs to detect a minute differential pressure (several mmHg), and for this reason, for example, a diaphragm type pressure sensor is often used.

FIG. 8 shows a characteristic diagram of a conventional flowmeter. In conventional flowmeters, the orifice 24. Since the shape of the tube 20 and the like is constant, the value of K shown in the above equation (1) is also constant. Therefore, the differential pressure Δp becomes a value proportional to the square of the flow rate q, and the rate of change in the differential pressure exhibits characteristics that are small in the low flow rate region and large in the high flow rate region.

[Problem to be solved by the invention] For this reason, conventional flowmeters have low sensitivity in low flow areas, and measurement accuracy in low flow areas, especially in minute flow areas, is extremely poor compared to measurement accuracy in high flow areas. There was a problem.

Further, since the pressure gauge 26 has a structure in which fluid accumulates inside, there is also a problem that purging is impossible or requires a long time for purging.

Furthermore, since the pressure gauge 26 is formed of a material completely different from components such as electronic circuits, there is a problem in that it cannot be integrated with various fluid control elements and electronic circuits.

[Object of the Invention] The present invention has been made in view of such conventional problems, and its purpose is to enable high-accuracy measurement of fluid flow rate even in a low flow rate region, especially in a minute flow rate region, and to enable the internal It is an object of the present invention to provide a semiconductor flowmeter that does not cause fluid to accumulate in the flowmeter, and can be integrated with various fluid control elements and electronic circuits as required, and can be applied to a microfluid control system.

Another object of the present invention is to provide a micropump that can accurately control even minute flow rates using the semiconductor flowmeter.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor flowmeter for measuring the flow rate of fluid flowing in a flow path, wherein one side is on the upstream side of the flow path and the other side is on the upstream side of the flow path. a semiconductor substrate installed so that its surface faces the downstream side of the flow path; a diaphragm formed on a part of the semiconductor substrate to generate stress due to a pressure difference between both sides of the substrate; A strain gauge that detects the generated stress, a microscopic hole formed in the diaphragm for fluid passage, and a flow path resistance provided downstream of the microscopic hole. and a check valve in which the strain gauge becomes small, and is characterized in that the flow rate of the fluid is measured based on the detection output of the strain gauge.

In this, the semiconductor substrate is formed as a substrate made of silicon crystal, the strain gauge is formed as a silicon diffused resistor, and the check valve is made of polycrystalline silicon, a part of which is fixed to the semiconductor substrate. It is preferable that

The semiconductor flowmeter of the present invention requires a particularly small structure in order to measure minute flow rates.

This can be achieved using silicon micromachining. That is, by using silicon crystal anisotropic etching, thin film CVD, etc., it is possible to form micron-order structures with high precision and good reproducibility. Therefore, by using such micromachining, it becomes possible to form the semiconductor flowmeter described above with high precision.

Further, in the semiconductor flowmeter of the present invention, it is preferable that the glass member forming the flow path and the silicon semiconductor substrate are anodically bonded.

Thereby, it becomes possible to connect the semiconductor flowmeter of the present invention to a structure forming a fine flow path with high precision and with high sealing performance maintained.

In addition, in order to achieve the above-mentioned objective, the micropump of the present invention includes a semiconductor substrate made of silicon crystal, and a first structure that is anodically bonded to both surfaces of the semiconductor substrate and forms a flow path between the semiconductor substrate and the semiconductor substrate. a glass member and a second glass member; a check valve made of polycrystalline silicon and located in the flow path and having a portion thereof fixed on the semiconductor substrate; and a check valve located in the flow path and having a portion fixed on the semiconductor substrate. A semiconductor flowmeter according to claim (1) provided above, and a diaphragm provided on the first or second glass member facing the flow path sandwiched between the semiconductor flowmeter and the check valve. , an actuator that reciprocates the diaphragm, the semiconductor flowmeter includes: the strain gauge is formed as a silicon diffusion resistor; the check valve is made of polycrystalline silicon, a portion of which is made of polycrystalline silicon; The actuator is driven based on the flow rate detected by the semiconductor flowmeter.

In a micropump formed in this way, it is necessary to extract the output signal of the semiconductor flowmeter from inside the flow path to the outside.
At this time, the sealing performance of the pump must not be compromised. To solve this problem, we need to form diffusion leads on the semiconductor substrate.
It is only necessary to input and output the above-mentioned signals.

principle of invention Next, the principle of the present invention will be briefly explained.

In the conventional throttle flowmeter, since the shape of the throttle part does not change, the value of K in the above equation (1) remains constant, resulting in a decrease in sensitivity in the low flow rate range. In the present invention, this problem can be solved by changing the flow path resistance of the constricted portion according to the flow rate.

]0 In other words, by increasing the flow path resistance in the low flow rate region and decreasing the flow path resistance in the high flow rate region, K in the above equation (1) can be reduced.
can be made a variable that increases as the flow rate decreases, making it possible to increase the sensitivity in the low flow rate region, especially in the minute flow rate region.

[Work] Next, the present invention will be explained in detail.

In the semiconductor flowmeter of the present invention, the degree of opening of the check valve changes depending on the flow rate, and the flow path resistance is large in the low flow rate region and small in the high flow rate region. Therefore, the value shown in (1) increases as the flow rate decreases, and the differential pressure generated on both sides of the check valve also increases.

As described above, the semiconductor flowmeter of the present invention can obtain sufficiently high sensitivity even in the low flow rate region, especially in the minute flow rate region, and as a result, it is possible to measure the fluid flow rate with high accuracy from the minute flow rate region to the high flow rate region. It becomes possible to measure with good responsiveness.

Further, in the semiconductor substrate of the present invention, the semiconductor substrate is formed as a substrate made of silicon crystal], the strain gauge is formed as a silicon diffused resistor, and the check valve is formed as a polycrystalline silicon. It is preferable that a portion of the semiconductor substrate be fixed to the semiconductor substrate. As a result, the semiconductor flowmeter of the present invention can be formed with high precision and good reproducibility in units of microns using silicon micromachining, etc., and can more accurately measure minute flow rates of fluids. It becomes possible to do so.

In particular, since a semiconductor substrate is used in the present invention,
It becomes possible to integrate a semiconductor flow meter and processing circuits for its output signals, etc. on a semiconductor substrate, making it extremely suitable for microfluid control systems.

Further, the semiconductor flowmeter of the present invention preferably has a structure in which a glass member forming a flow path and the silicon semiconductor substrate are anodically bonded. As a result, by anodic bonding of the semiconductor substrate and glass, a structure that constitutes a minute flow path,
It becomes possible to connect to the semiconductor flowmeter itself with high accuracy and while maintaining high sealing performance.

In addition, in the semiconductor flowmeter of the present invention, since the check valve also functions to prevent backflow, which is its original function, it is preferable to integrate it with a micro pump or the like as described in claim (2). This makes it possible to obtain a micropump whose configuration is simple and whose flow rate can be controlled with high accuracy.

In particular, by forming the micropump by anodic bonding between a semiconductor substrate and a glass member, it is possible to achieve high sealing performance, and it is possible to mount a fine flow channel network and fluid control element by silicon micromachining, and to It is extremely suitable to integrate the control system itself.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a semiconductor flowmeter that can measure minute flow rates with high sensitivity.

Furthermore, since the semiconductor flowmeter of the present invention is formed using a semiconductor substrate, the entire flowmeter can be miniaturized, manufacturing variations are small, it is suitable for mass production, and it is compatible with other fluid control elements. High-density integration] 3 is also possible.

Furthermore, the semiconductor flowmeter of the present invention achieves high reliability due to highly hermetic sealing by anodic bonding the semiconductor substrate and the glass member constituting the flow path, and allows for high-density integration with other fluid control elements. It is also possible to

Furthermore, by using the semiconductor flowmeter, it is possible to obtain a micropump that has a simple configuration and can control minute flow rates with high precision.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail based on the drawings.

First Embodiment FIGS. 1 and 2 show a preferred embodiment of the semiconductor flowmeter according to the present invention, and FIG. 1-1 is an explanatory diagram showing its planar configuration, and FIG. 1 is a schematic cross-sectional view taken along the line ■-■ in FIG.

The semiconductor flow meter of the embodiment is configured to measure the flow rate of a fluid 100 flowing in a flow path 32 formed using a pipe 30 along the direction indicated by an arrow in the figure. In this case, the tube 30 is made of glass.

The semiconductor pressure gauge of the embodiment includes an n-type (100) silicon substrate 40 installed so as to divide the tube 30 and block the flow path 32.
This silicon substrate 40 is anodically bonded to a tube formed using glass, thereby creating an airtight seal between the two.

A diaphragm 42 is formed on a portion of the lower surface of the silicon substrate 40 to generate stress according to the differential pressure between both sides of the silicon substrate 40. A thick plate portion is left near the center of this diaphragm 42, and a fine hole 44 tapered from the upstream side to the downstream side is formed in the center of the thick plate portion. These diaphragms 42. The micropores 44 can be formed easily and with high accuracy on the order of microns by subjecting the silicon substrate 40 to crystal anisotropic etching using, for example, an alkaline etching solution.

Four strain gauges 46 are formed in a thin portion of the diaphragm 42 to form a full bridge circuit, and convert the differential pressure generated on both sides of the silicon substrate 40 into a voltage signal and output it. The six strain gauges 46 are formed by selectively doping boron as an impurity from the surface of the diaphragm 42 and diffusing it to form a P-type semiconductor.
It is formed.

Further, on this silicon substrate 40, a diffusion layer functioning as a lead 48 is formed by diffusing boron using a similar method, and this lead 48 is connected to the strain gauge 46.
and an AI electrode 50 provided outside the flow path 32.

Further, the strain gauge 46. In order to protect the leads 48, an insulating layer 52 is formed over the entire surface of the silicon substrate 40. This insulating layer 52 is formed by coating silicon nitride using, for example, low pressure CVD.

The feature of the present invention is that the silicon substrate 4 formed in this way
0'' Second, a check valve 6 is located downstream of the microhole 44.
0 is provided, and the check valve 60 is formed so that the flow path resistance is large in the low flow range]-6 and small in the high flow range.

As a result, the constant K in equation (1) can be made a variable that increases as the flow rate decreases, making it possible to increase the sensitivity in the low flow rate range.

In the embodiment, the check valve 60 is made of polycrystalline silicon. The check valve 60 includes a ring-shaped fixing part 62 fixed to the silicon substrate 40, a valve seat part 64 that opens and closes the microhole 44, and a surface connecting the fixing part 62 and the valve seat part 64. It is made up of a plurality of beams 66 that determine the degree of opening.

When the flow rate is large, the beam 66 deforms greatly and the degree of opening becomes large, so that the flow path resistance of the check valve itself becomes small. Conversely, when the flow rate is low, the deformation of the beam 66 is small, so the opening degree is also small, and as a result, the flow path resistance of the check valve becomes large.

FIG. 3 shows experimental data for the flowmeter of this example. According to experiments, the length of one side of the micropore 44 is 100 μm,
The diameter of the valve seat part 64 is 1-50 μm, and the plate thickness of the beam 66 is 2 μm8.
The width is 200 μm, the length of the beam 66 is 150 μm, and the width is 300 μm.
Three types of flowmeters with different flow rates (μm and 600 μm) were manufactured, and the output of the strain gauge 46 with respect to the flow rate was measured.

As is clear from this measurement data, it can be understood that the semiconductor flowmeter of this example has a large output change rate on the low flow rate side and has a large measurement resolution. In particular, for a sample in which the length of the beam 66 is 150 μm, approximately 2 (g/c
A sensitivity of /) / (, cz i! 7m1n) was obtained, and the voltage output was about 20 μV/(μi' 7m1n).

Further, FIG. 4 shows actual measurement data regarding the backflow prevention function of the check valve 60. For pressure application in the opposite direction,
The check valve 60 functions so that its valve seat portion 64 closes the microhole 44 and prevents backflow. In the experiment, pressure was applied in the opposite direction of the flow path 32 using the three types of samples described above. As a result, the length of the beam 66 is 150 μm and 300 μm.
For sample No. m, it was confirmed that the check valve 60 completely stopped the flow and prevented backflow.

Note that in the semiconductor flowmeter of the present invention, the fine holes 44. Since the shape parameters of the check valve 60 are closely related to the sensitivity and the like as described above, it is necessary to design the check valve 60 according to the measurement range.

Second Embodiment FIG. 5 shows a preferred embodiment of a micropump formed using the semiconductor pressure sensor described above.

The micropump of the embodiment has first glass substrates 72 on both sides of the silicon substrate 40 to form a fine channel network.
and a second glass substrate 74 are hermetically bonded together by anodic bonding.

An inlet 76 and an outlet 78 connected to both ends of the flow path 32 are formed in the first glass substrate 72 .

In the embodiment, a check valve 60 was installed on the upstream side of the flow path 32, and a semiconductor flowmeter 110 was installed on the downstream side thereof.

This semiconductor flowmeter 11.0 is similar to that shown in the first embodiment, but uses a silicon substrate 40 as the single silicon substrate 40 shown in FIG. The structure is slightly different in that it eliminates the thick plate part and prevents liquid pooling.

A diaphragm 80 is formed on the first glass substrate 72 so as to face the flow path portion sandwiched between the check valve 60 and the semiconductor flowmeter 110, and the center portion of the diaphragm 80 is formed on the first glass substrate 72. It is fixed to a piezo actuator 84 supported on the substrate 72 using a fulcrum 82 .

Therefore, by applying an alternating current voltage to the piezo actuator 84, the piezo actuator 84 expands and contracts up and down, causing the glass diaphragm 80 to vibrate. When it comes time,
Due to the functions of the check valve 60 and the check valve 60 of the semiconductor flowmeter 110, the fluid 100 moves in the direction of the broken line arrow in the figure.

The flow rate at this time becomes a function of the maximum amplitude value of the voltage applied to the piezo actuator 84 and one frequency.

In the present invention, by controlling the maximum amplitude value 1 frequency of the voltage applied to the piezo actuator 84 based on the flow rate measured by the semiconductor flowmeter 110, the supply flow rate can be controlled with extremely high accuracy from a minute flow rate range to a high flow rate range. It becomes possible to realize a micropump that can

According to experiments, it has been confirmed that by controlling the frequency with the maximum amplitude value fixed at 100V, it is possible to control the flow rate below 20 μm 7 m1n. This upper limit is a restriction caused by the ability of the micropump, and the flowmeter does not impose any restrictions.

In this way, according to this embodiment, the semiconductor flowmeter 110
Utilizing the feature that it has a check valve 60 and can accurately measure minute flow rates, its configuration is simple,
Furthermore, it is possible to obtain a micropump that can control the flow rate with high accuracy from a minute flow rate to a high flow rate range.

Further, according to this embodiment, high sealing performance is achieved by anodic bonding the silicon substrate 40 and the first and second glass substrates 72 and 74, and fine flow path control is achieved by silicon micromachining. It will be understood that since a fluid control element can be mounted, it is extremely effective in integrating a fluid control system.

Furthermore, by using the silicon substrate 40 as in the semiconductor flowmeter and micropump of the embodiment, it is possible to mount a processing circuit from the output signal from the semiconductor flowmeter 110 on the silicon substrate 40. It also becomes possible to achieve high integration of the entire circuit and system.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible within the scope of the invention.

For example, the structure of the check valve 60 used in the present invention may be such that the opening degree can be adjusted according to the fluid flow rate.
Any structure can be used as needed.

Further, in the micro pump of the above embodiment, the diaphragm 80 is formed on the first glass substrate 72, but the present invention is not limited to this, and the diaphragm 80 is formed on the second glass substrate 74 as necessary. Alternatively, a diaphragm 80 may be formed on both glass substrates 72 and 74.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a preferred embodiment of the semiconductor flowmeter according to the present invention, FIG. 2 is a schematic cross-sectional view taken along the line ■-■ in FIG. 12, and FIG. 3 is a flow rate diagram of the present embodiment. FIG. 4 is a characteristic diagram showing the check characteristics of the check valve used in this example. FIG. 5 is a cross-sectional schematic diagram showing a preferred example of the micropump of the present invention. 6 is an explanatory diagram showing the general principle of a throttle flowmeter. FIG. 7 is a cross-sectional diagram of a conventional throttle flowmeter using an orifice. FIG. 8 is a diagram showing the flow rate of the conventional example. Differential pressure change 44...
- Microhole, 46... Strain gauge, 60... Check valve, 62... Fixed part, 64... Valve seat part, 6
6... Beam, 72... First glass substrate, 74... Second glass substrate, 80... Diaphragm, 84... Piezo actuator, 100... Fluid, 1]0... ·Flowmeter.

Claims (2)

[Claims] (1) A semiconductor flowmeter that measures the flow rate of fluid flowing in a flow path, the semiconductor substrate being installed so that one surface faces the upstream side of the flow path and the other surface faces the downstream side of the flow path. a diaphragm formed on a part of the semiconductor substrate to generate stress due to a pressure difference between both sides of the substrate; a strain gauge provided on the diaphragm to detect stress generated in the diaphragm; and a fluid formed in the diaphragm. a fine hole for passage; and a check valve that is provided on the downstream side of the fine hole and has a large flow path resistance in a low flow rate region and a small flow path resistance in a high flow rate region, and a detection output of the strain gauge. A semiconductor flowmeter characterized by measuring the flow rate of a fluid based on. (2) A semiconductor substrate made of silicon crystal, a first glass member and a second glass member that are anodically bonded to both sides of the semiconductor substrate and form a flow path between them and the semiconductor substrate, and made of polycrystalline silicon. , a check valve located in the flow path and partially fixed on the semiconductor substrate; and a semiconductor flowmeter according to claim 1, located in the flow path and provided on the semiconductor substrate. , a diaphragm provided on the first or second glass member facing the flow path sandwiched by the semiconductor flowmeter and the check valve; and an actuator that reciprocates the diaphragm, The flowmeter has a strain gauge formed as a silicon diffused resistor, a check valve made of polycrystalline silicon, and a part of which is fixed to the semiconductor substrate, and the semiconductor flowmeter detects The micropump is characterized in that the actuator is driven based on the flow rate.