JP2002263458A - Gas-liquid separating membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas-liquid separating membrane for a diaphragm type chemical sensor, which is easily bonded to a sensor body even when the sensor is micronized, is adaptive to production, does not warp, keeps the rigidity and the satisfactory gas permeability and surely holds an internal liquid. SOLUTION: Two silicon substrates are bonded to each other. A gas- permeable pore is prepared by forming a submicron shallow groove concavely along the bonded surface on any of the bonded surfaces. Through-holes through which gas can entrance and exit are formed on each of the silicon substrates so that the through-holes on one silicon substrate are made to communicate with those on the other silicon substrate through the shallow groove. The vicinity of the part of the through-hole on any of the silicon substrates to be connected with the shallow groove is treated to have water repellence. Thereby, the objective gas-liquid separating membrane is obtained. As a result, the obtained gas-liquid separating membrane shows excellent gas permeability and excellent sensitivity, holds the internal liquid surely, keeps the rigidity and is adaptive to mass production.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas-liquid separation membrane that allows gas to permeate but blocks liquid permeation. More specifically, the present invention relates to a gas-liquid separation membrane that can be used as a diaphragm of various diaphragm sensors having a structure in which a detection electrode, a counter electrode, an electrolytic solution (internal solution), and the like are held.

[0002]

2. Description of the Related Art Conventionally, various sensors of a coulometric type and a constant potential electrolytic type having a centimeter size have been put to practical use. Especially, it is widely used for leak gas detection alarms, etc.
Tolerable concentration (ACGIH or recommended value by Japan Society for Occupational Health)
The sensor has the ability to quickly respond to low concentration gas in the vicinity.

[0003] These coulometric and potentiostatic gas sensors are more widely called electrochemical sensors and include a working electrode (detection electrode) inside a gas-liquid separation membrane (diaphragm) and a sensor body.
・ It has a structure that holds the internal liquid (electrolyte) together with the counter electrode. Here, the function of the gas-liquid separation membrane used as a diaphragm is to transport the component gas in the sample gas to be measured to the inside of the sensor and provide it for the electrochemical detection reaction, and to put the electrolytic solution essential for the reaction inside the sensor. It is to keep it closed. Various gas-liquid separation membranes have been used depending on the purpose. High-concentration (% order) oxygen sensors at the atmospheric level can be used for gas-liquid separation membranes with small pore size and porosity, and continuous membranes such as fluorine compounds and silicones utilizing intermolecular voids. Could be used.

On the other hand, in the case of a chlorine gas detection sensor, since the target gas is a toxic gas and is a gas having a low concentration on the order of ppb to ppm, it is necessary to secure a predetermined sensitivity and obtain a sufficient response speed. Is a so-called gas-liquid separation membrane having a large number of voids having an effective diameter of 1 micron or less (submicron) and having a porosity of 50-70%, which is produced by stretching a fluorine compound such as polytetrafluoroethylene. Porous membranes and the like have been used.

However, the sensor itself has become smaller and smaller, and for example, as disclosed in Japanese Patent Application No. 2000-132990, 5
The sensor body was formed by anisotropic etching on a silicon substrate like a sensor body obtained by processing the body of an electrode on a quartz glass block of about mm × 5 mm × 3 mm or an oxygen sensor described in Japanese Patent Publication No. 6-1254. In the case of the sensor body, since it is very small, if a porous membrane made by stretching an existing polytetrafluoroethylene or the like is used for the gas-liquid separation membrane, deflection etc. will occur, and the positional relationship between the detection electrode and the diaphragm will be minute. It is difficult to strictly control the size, and it is difficult to keep the distance between the diaphragm and the detection electrode constant. In the case of low concentration measurement, not only a problem occurs in accuracy, but also there are many difficulties in assembling work.

Therefore, the development of a gas-liquid separation film suitable for the material of such a new microsensor body such as glass or silicon wafer has become an issue.
A film material formed by piercing by epRIE (reactive ion etching) and a film material obtained by anodizing alumina to make it porous have been studied. For example, a through hole having a pore size of about 30 μm to about 100 μm can be formed in a silicon wafer having a thickness of 160 μm by DeepRIE. Further, a through hole having a pore size of about 0.03 μm can be formed in an alumina having a thickness of 10 μm by anodization.

[0007]

SUMMARY OF THE INVENTION The inventors of the present invention have developed a conventional stretch-formed gas-liquid separation membrane which is not made of a material such as polytetrafluoroethylene and has a pore size of φ160 μm on a silicon wafer having a thickness of about 160 μm by DeepRIE.
The one with a 30 μm through hole was made 1,1,1,3,
A method of using a reagent such as 3,3-hexamethyldisilazane to make it water-repellent by a silanization treatment and the like has been studied, and further studies have been made to reduce the pore size. As a method for directly penetrating pores into a silicon wafer or the like having a certain thickness, there is a method of punching holes by striking plasma-like ions on a substrate.

In the Deep RIE method (RIE is an abbreviation for reactive ion etching), since the surrounding substrate material is shaved by plasma-like ions, the pore diameter becomes larger than intended and the aspect ratio becomes lower. This is a method that can improve the problem. When drilling holes by striking plasma-like ions on the substrate, the surrounding substrate material is shaved to prevent the pore diameter from expanding beyond the intended hole diameter and lowering the aspect ratio. A method in which the material is formed around the pores while etching is performed, the aspect ratio is improved, and the method is relatively suitable for forming finer holes.

Even when this technique is used, when the aspect ratio is 20 and the thickness of the wafer is 100 μm, the diameter of the hole is the minimum diameter at which a hole of 5 μm can reach. Actually, the pore size used for the gas-liquid separation membrane is on the order of submicron, and if a pore size of submicron is to be drilled, a silicon wafer having a thickness of 10 micron will be used.
Difficulties have emerged in mechanical strength and retention stability, and it has been substantially difficult to produce a membrane with a small pore size on the order of submicrons suitable as a diaphragm for a chemical sensor for gas. Further, in order to provide the pores with a gas-liquid separation function, it is necessary to secure a predetermined pore diameter and to arrange a water-repellent substance around the pores.

[0010]

The inventors of the present invention have examined the point of the prior art, and have found that using a silicon substrate as a material, (1) it is mechanically robust and does not generate deflection, and (2) gas-liquid Estimation of the hole diameter, cross-sectional area (effective transmission area) and transmission distance of the gas path through which the gas can pass while maintaining the gas-liquid separation function to the extent that it can be used as a separation membrane. As a result of examining the grant method, etc.,
The present invention has been made.

The inventors have adopted a method of bonding two silicon substrates in order to improve the mechanical strength of the film. Further, as a path through which the gas passes, a fine gap was provided in the joint plane of the two layers, and a gas-liquid separation membrane was examined by regarding this as a hole diameter. In other words, two silicon substrates are joined together, and a shallow groove is formed along one of the joining surfaces along the joining surface, and the through holes provided in each silicon substrate are formed only through the shallow groove. In addition, the gas-liquid separation film is formed by making the vicinity of the portion connected to the recessed shallow groove of the through hole of one of the silicon substrates water-repellent.

In this method, (1) First, when a large number of micron-level through-holes are formed on two silicon substrates by using Deep RIE, when the two silicon substrates are overlapped, the through-holes of the two silicon substrates are connected to each other. Are formed so as to communicate with each other only by grooves which are not overlapped with each other and are concavely opened along the joining surface as shown in FIG.

(2) Next, in using a silicon wafer for a path through which gas gas-liquid selectivity is controlled and using a silicon wafer, a silicon wafer is formed instead of a conventional technique in which a hole penetrating a substrate is formed. A concave groove is formed by drilling on the flat surface. The method for perforating is as follows. 1) A stencil or the like patterned by laser processing or the like is pasted as a mask material on one surface of one of the two silicon substrates according to a predetermined design with a groove having a width, a length, and a shape. 2) ECR (ECR is an abbreviation for Electrocyclotron Resonance) etching is performed on the patterned portion by ion plasma. In the case of etching with argon ions, the opening rate in the depth direction of the groove can be controlled on the order of nanometers per minute. Therefore, by setting the etching time, the concave groove can be formed at a desired submicron level. It is quite possible to pierce with.

(3) Of the two silicon substrates, a silicon substrate having a shallow groove recessed on one surface is subjected to plasma CVD treatment or the like from the opposite side of the surface having the shallow groove recessed to form a through hole. The connection to the shallow groove made water repellent. (4) The two silicon substrates are joined by a known joining method with the surface having a shallow groove recessed on one surface as the joining surface. Here, the size, shape, and number of the through-holes are not particularly limited as long as the mechanical strength of the silicon substrate is not lost and the through-hole has an effective area enough to be used as a sensor diaphragm. .

Further, in the gas-liquid separation membrane of the present invention, the through holes provided in the two silicon films are elongated slit holes. In other words, a plurality of through holes are formed in one silicon substrate in the form of slits, and a plurality of shallow grooves are formed on one surface of the substrate between the elongated slits in a direction perpendicular to the slits. The silicon substrate is subjected to a water-repellent treatment by plasma CVD using a known method using vinylidene fluoride in the portion of the through-hole on the opposite surface where the shallow groove is not recessed. 2 for other silicon substrates
When the two substrates are stacked, a through-hole is provided in the shape of an elongated slit at a position that does not overlap with the elongated slit of one silicon substrate, and the surface with the shallow groove of one silicon substrate recessed is used as an overlapping surface, and both substrates are already Among known joining methods, joining was performed by an organic adhesive joining method which is a suitable method.

Although the basic structure and manufacturing method are the same as those of the gas-liquid separation membrane of claim 1, the gas permeable surface can be formed widely and the slit is elongated at right angles to the elongated slit as a through hole. When two silicon substrates are overlapped, the through-holes formed in each substrate are reliably communicated with the recessed shallow grooves, and the through-holes of both substrates are directly connected to each other. There is a characteristic that there is no danger of leakage due to overlapping. Since the gas-liquid separation film according to the present invention uses a silicon substrate as a material, the working electrode and the sensor body are also made of the silicon substrate, so that the bonding with the gas-liquid separation film when assembling the entire sensor can be performed by silicon-to-silicon bonding. Joining simplifies the manufacturing process.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing an embodiment of a diaphragm type chemical sensor obtained by bonding a silicon substrate using a gas-liquid separation membrane according to the present invention. In the diaphragm type chemical sensor in which the silicon substrate of FIG. 1 is bonded, the counter electrode 1 has a thickness of 300 μm.
Is formed by sputtering platinum on a silicon substrate using a stencil mask. The sensor body 2 is an internal liquid reservoir that stores an electrolyte therein. 500μ thickness
m silicon wafers are used. Working electrode 3 is 100
A slit is formed by anisotropic etching with potassium hydroxide on a silicon wafer of μm and penetrates the space where the electrolyte is stored and the gas-liquid separation part, and a platinum layer is sputtered on the wall of the penetration part using a stencil mask. It is formed as an electrode surface. The silicon substrate (1) 4 having a thickness of 100 μm is one of the two silicon substrates constituting the gas-liquid separation film, which has not been subjected to the water-repellent treatment.

Another silicon substrate (2) 5 having a thickness of 100 μm has a shallow groove recessed in the joint surface, and vinylidene fluoride is deposited on the slit-shaped through-hole from the surface exposed to the outside by a plasma CVD method. Water repellency treatment was performed by a known method. For the water pressure resistance when water repellency treatment is applied to micro air holes, theoretically, it is effective by stretching a fluorine compound such as polytetrafluoroethylene known as a gas-liquid separation membrane according to the following formula It is possible to make a comparative estimation with a so-called porous membrane having a porosity of 50 to 70% having a large number of voids at a level of 1 micron or less (submicron). Water pressure P = -2γCOSΘ (1 / w + 1 / h) γ Surface tension: 0.073 N / m in the case of water Contact angle: 110 ° w Width of hole h Width of hole

As for the size of the sensor, twelve sensor materials of each layer can be obtained from a silicon substrate having a square of 20 mm, and a sensor having a finished dimension of about 3 mm can be obtained.

FIG. 2 is a sectional view of a diaphragm type chemical sensor including a gas-liquid separation membrane. The gas-liquid separation membrane according to the present invention will be described in more detail with reference to FIG. 1, a counter electrode 1, a sensor body (internal liquid reservoir) 2, and a working electrode 3 correspond to FIG. A slit-shaped through hole 6 is formed in the silicon substrate (1) 4 constituting the gas-liquid separation film, and the silicon substrate (2) 5 constituting the other gas-liquid separation film has A slit-shaped through hole 7 is formed so as not to overlap with the through hole 6. The through holes 6 and the through holes 7 are communicated with each other by a shallow groove 8 (shown by a thick line) formed in a surface of the silicon substrate 5 that is joined to the silicon substrate (1) 4 by overlapping the slits. In this embodiment, the silicon substrate (1) 4
The slit-shaped through hole is 1.84 mm long
The width is 0.11 mm, and seven lines are formed at intervals of 0.27 mm. The slit-shaped through hole formed in the silicon substrate of the silicon substrate (2) 5 has a length of 4. 1.84 mm, the same width as 0.06 mm (60 μm), and the pitch is 4. 6 are formed at intervals of 0.27 mm in the same manner as described above, and when two sheets are overlapped, two pairs of slit holes are arranged so as not to overlap with each other, and among the known joining methods, suitable ones are used. Joining was performed using an organic adhesive joining method. This slit-shaped through hole is De
This is performed by the epRIE method (RIE is an abbreviation for reactive ion etching). Five concave shallow grooves of 1.84 mm in length and 0.29 mm in width (290 μm) are provided at right angles to the slit on the surface to be bonded to the silicon substrate (2) 5. Is processed as shallow as about 0.2 μm. According to ECR (ECR is an abbreviation for Electrocyclotron Resonance) etching,
Since the opening speed in the depth direction of the groove is on the order of nanometers per minute, it is possible with an accuracy of about 10 nm, and it is possible to stably form a gap for selectively transmitting gas and liquid. The gap thus formed has a width of 29.
A path length of 0 μm, a height of about 0.2 μm, and a gas passing through the through-holes is 25 μm, which corresponds to a half of a difference between slit widths formed in two upper and lower silicon substrates.
According to this embodiment, 60 holes having a gap width of 290 μm, a gap height of about 0.2 μm, and a path length of 25 μm are formed. The water pressure resistance of this gas-liquid separation membrane is about 250 KPa from the theoretical formula already described, and the gas-liquid separation performance is comparable to that of PTFE.

Using the thus-prepared gas-liquid separation membrane, this chemical sensor is filled with a 4.6 mol lithium bromide solution in the internal liquid, and the working electrode is -0.250 to -0.300 with respect to the working electrode.
The output current when applying V and exposing to 1 ppm of chlorine gas was 10 nA. Although the electrode was miniaturized, the output per unit area of the electrode was not inferior to that of the conventional electrode. Gas-liquid separation membrane, as a gas permeable membrane,
It was confirmed that it was working effectively.

[0022]

According to the present invention, (1) two silicon substrates having through holes formed thereon are superimposed, and a gas-permeable surface is subjected to submicron level surface etching with high accuracy on this joint surface. Since the through holes communicate with the narrow gap as a path through which the gas passes, and the water repellent treatment is performed in the vicinity of the through holes, the gas-liquid separation characteristics can be reliably provided. (2) Since the method for producing the gas-liquid separation membrane is based on the so-called semiconductor manufacturing technology, it can be easily joined to a fine sensor diaphragm, and mass production is possible. (3) Compared to the conventional method of forming a gas-permeable hole in a silicon substrate, a shallow groove through which a gas of a submicron level permeates is recessed in the surface of the substrate.
It is at a level of 00 μm, and there is no concern about bending or the like when it is joined to a sensor, and since it is used by laminating two sheets, it is structurally robust. And other effects can be confirmed.

According to the present invention, a gas-liquid separation film is manufactured by performing a known etching process for forming a submicron level shallow groove on one surface of a silicon substrate. Not only the silicon substrate but also a robust material having a flat surface and a material capable of forming shallow grooves on the surface at a submicron level, for example, a glass substrate or a polyimide film may be used. It is possible to produce a gas-liquid separation membrane. Further, it is also possible to produce a substrate in which a shallow groove is formed by a silicon substrate, and to select a glass substrate other than the silicon substrate, a polyimide film, or the like as a substrate to which the silicon substrate is bonded. In the second aspect, the slits are elongated in the two substrates, but are formed in a circular shape, and the shallow grooves to be recessed are formed radially from the center of the circumference. Design is possible. As a method of imparting water repellency in the vicinity of the through hole, in the embodiment of the invention, a method of depositing and introducing a water repellent compound such as vinylidene fluoride by a plasma CVD method or the like is employed,
The method is not limited to this method, and water repellency may be imparted by changing the geometric structure such as making the surface porous.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a diaphragm type sensor including a gas-liquid separation membrane according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a diaphragm sensor including a gas-liquid separation membrane according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Counter electrode 2 Sensor body (internal reservoir) 3 Working electrode 4 Silicon substrate (1) 5 Silicon substrate (2) 6 Through hole 7 Through hole 8 Shallow groove

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme Court ゛ (Reference) G01N 27/30 341J 27/46 316Z (72) Inventor Manabu Manabu Negishi 4-13-14 Kichijoji Kitamachi, Musashino City, Tokyo No. Within Toa DK Co., Ltd. (72) Inventor Hiroya Shimizu 4--13-14, Kichijoji Kitamachi, Musashino City, Tokyo Inside Toa DK Co., Ltd. (72) Inventor Yang Ming 1-1, Minami-Osawa, Hachioji-shi, Tokyo, Japan Inside the Faculty of Engineering, Tokyo Metropolitan University (72) Inventor, Seishiro Oya 705-1 Shimo-Imaizumi, Ebina City, Kanagawa Industrial Technology Research Institute (72 Inventor Zen Nakano 1-2-2 Namiki, Tsukuba, Ibaraki Pref., Ministry of Economy, Trade and Industry 4D006 GA32 MA03 MA08 MB10 MB16 MC02X NA31 NA45 NA54 PC38 PC80

Claims (2)

[Claims] 1. A method comprising: bonding two silicon substrates; forming a shallow groove in one of the bonding surfaces along the bonding surface; A gas-liquid separation membrane characterized in that the gas-liquid separation membrane is made to be water-repellent in the vicinity of the connecting portion of the through hole of one of the silicon substrates to the recessed shallow groove. 2. A silicon substrate, wherein one silicon substrate has a plurality of through-holes formed in a plurality of elongated slits, and a plurality of shallow grooves formed on one surface of the substrate between the elongated slits in a direction perpendicular to the slits. When two were overlapped on another silicon substrate, a through-hole was provided in an elongated slit shape at a position that did not overlap with one slit, and a shallow groove of one silicon substrate was recessed. 2. The substrate according to claim 1, wherein the two substrates are joined with the surfaces as overlapping surfaces, and a water-repellent treatment is applied to the vicinity of a through hole of one silicon substrate and a portion connected to the recessed shallow groove. Gas-liquid separation membrane.