JPS5868661A - Device for measuring gas concentration - Google Patents

Abstract

PURPOSE:To enable to perform a high-temperature disinfection, by a method wherein a comparision electrode is adhered to a gate part of a pH-sensitive semiconductor sensor, the sensor is housed in a flexible tube, a lead wire is connected to a connector at the rear end of the tube, the inside of the tube is filled with an insulating resin, and the forward end is covered with a gas permeable film. CONSTITUTION:A comparision electrode 31 comprising Ag/AgCl is deposited to a gate part 22 of a pH-sensitive semiconductor sensor 2, and the gate part 22 is exposed at a forward end of a flexible polyester tube 40 to house the sensor 21 and a lead wire 45 for the sensor and the comparision electrode therein, a core wire 48 such as stainless steel is inserted for reinforcing, and the inside of the tube 40 is filled with an electric insulating resin 42 for curing. The lead wire 45 is then joined to a pin 47 for connector, the tube 40 and the pin 47 are set to a mold forming device, silicon resin is poured into for curing to form a connector part 49. After a part 46 is formed with PVC at the part 49, a forward end 43 is filled with a hydrophilic polymer such as PVC containing an electrolytic aqueous solution such as NaCl, and the whole periphery of the forward end of the tube 40 is covered with a gas permeable teflon film 44. This obtains a device which is used for measuring CO2 concentration in a living body, can perform a high- pressure steam disinfection, and is high-sensitive.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas concentration measuring device using a semiconductor hydrogen ion sensor having an insulated gate field effect transistor structure.

Measuring the concentration of gases such as carbon dioxide and ammonia gas is important in industrial applications. Also, medicine in recent years.

In the field of physiology, the measurement of gas concentrations in living organisms is beginning to be considered important. For example, in physiology,
- Measuring the concentration of carbon dioxide in cells provides important knowledge, and in medicine, continuous measurement of the concentration of carbon dioxide in the blood of anesthesia patients and patients in the recovery room for critically ill patients can help detect emergencies. It's helpful. For this purpose, a relatively small gas concentration measuring device that can be inserted into cells or blood vessels is required. The present inventors used the hydrogen ion concentration of semiconductors for the above purpose. A gas concentration measuring device was proposed in Japanese Patent Application Laid-Open No. 56-2546. As shown in FIG. This sensor is housed inside a single tube 40 with the gate part 22 of the FET located at the tip of the tube, and the sensor and...
- A lead wire 45 connected to the Ag CJ is extended along the tube, and an electrically insulating resin 10 is filled between the lead wire connection portion and the inner wall of the tube to close the tip of the tube, and further contains an electrolyte. A hydrophilic polymer 43 is coated over the gate sensitive membrane of the sensor and part of the Ag-AgCJ, and a gas permeable membrane 44 is coated thereon. This device eliminates the shortcomings of conventional glass electrodes and solid electrodes, such as increased electrical resistance due to miniaturization, and is particularly suitable for medical applications. However, this equipment often became completely unusable when exposed to severe conditions of A leakage, which caused problems with the tower.Therefore, it was necessary to develop equipment that could withstand high-pressure steam sterilization. or requested.

As a result of a detailed study of the condition of the above-mentioned device during high-pressure steam sterilization, the inventors of the present invention found that: (1) the connection between the sensor, Ag-kgcj, connector pin, and lead wire is likely to come off under high-temperature conditions, and (2) It was discovered that internal failure of the lead edge receiving tube is likely to occur, and the present invention was arrived at after thorough investigation. That is, in the present invention, a reference electrode is bonded close to the gate of a semiconductor hydrogen ion sensor, this sensor is housed in the tip of a tube, a connector is provided at the lateral end of this tube, and the sensor is The internal space formed by the lead wire connection of the reference electrode and the inner wall of the tube and connector is filled with an electrically insulating resin, and at least the entire circumference of the tip of the tube is covered with a gas permeable membrane. While forming an external space with the membrane, the gate sensitive membrane of the ion sensor, and the reference electrode,
This is a gas concentration measuring device in which the external space of C is filled with a hydrophilic polymer containing an electrolyte.

A feature of the present invention is that the sensor, reference electrode, and connector pin lead wire connecting portions are completely embedded in resin. These features have made it possible to significantly improve the durability of the device by preventing the joints of the lead wires from coming off or causing short circuits between the lead wires even under high-temperature conditions.

In the above device, it is preferable that a core wire for sleeve strength is further extended from the tip of the tube to between the connectors. Such a core wire can prevent the tube from deforming under high temperature conditions and improve the tensile strength in the tube direction. In addition, damage to the sensor can be prevented.Next, an embodiment of the device of the present invention will be described with reference to the drawings.

FIG. 2 is a plan view showing an example of the PH-sensitive semiconductor sensor 21 used in the gas concentration measuring device of the present invention. This sensor 21 is elongated and has a width of 0.4 cm and a length of 5 to 4 cm, and has a gate part 22 at one end, and a drain terminal 23 and a dozen terminals 24 at the other end. Reference numeral 22 indicates a drain diffusion region 26 and a drain diffusion region 27 in the silicon substrate 25, as shown in FIG.
, f are formed and the entire surface is sequentially covered with an oxide film 29 and a surface stabilizing film 30. This surface stabilizing film 30 is made of silicon nitride (85N4), at5 it ("ItO
One of the membranes such as tantalum pentoxide (Ta20g) can be used, and the sensor having the above-mentioned structure is sensitive to hydrogen ions.
FIG. 3 is a plan view showing an example of a comparison electrode 31 bonded onto a semiconductor ion sensor. This comparison electrode 31 is shown in FIG.
As shown in the BB sectional view in the figure, it is made of, for example, silver 52 and silver chloride 65.

The above -AgCJ can be produced by vapor deposition, plating, and electrolysis. However, since silver usually has poor adhesion to the surface stabilizing layer 30 of the ion sensor, it is preferable to provide an adhesive m34 between the silver and the surface stabilizing layer that adheres well to both. For example, when the surface stabilizing layer is made of silicon nitride, this adhesion@54 may include chromium, chromium copper,
Nickel etc. can be used. Reference numeral 2B is a channel block layer.The adhesive layer 54 and the ~-AgCj layers 52 and 55 provided on the silicon nitride layer 60 have a large impact on the stability and durability of the sensor. Therefore, the thickness of the adhesive layer 34 provided on the silicon nitride 50 is 100 mm.
~1,000K is preferable; if the thickness of the adhesive layer is less than 100λ, the adhesive effect on the adhesive side is insufficient.1 or 1,00
If it is 0k or more, not only will the deposition time of the adhesive layer be lengthened, but there will be no advantage, and it will be easily peeled off due to thermal strain. Furthermore, if the thickness of the first silver layer 52 and the silver chloride layer 53 provided on the adhesive layer are too thin, even if the sensor operates normally immediately after fabrication, measurement will become unstable after long storage. Drift is severe and it becomes impossible to use. In order to obtain sufficient durability, the thickness of the silver layer must be 5μ or more, Ag
It is preferable that the thickness of CNta is 1 μ or more.

~-AgO1 skin is 8 on the sensor surface when it falls down! sNa Hi
After a thin chromium layer is deposited on the chromium layer, a silver layer is deposited or plated on top of the chromium layer, and this is further electrolyzed in a NaCl solution using the Ag electrode as a liI electrode, so that the silver surface becomes chlorinated. can be used to prepare a ~-AgC-comparison electrode. In particular, when thickening the silver layer, it is preferable to first form a thin silver layer by vapor deposition and then form a sufficiently thick silver layer P11 by plating. In short, if the distance L (FIG. 5) between the gate part and the comparison electrode is large, noise due to induction will be easily picked up, so it is preferable that the distance between the gate part and the comparison electrode be 2 or less. At this distance of 2 cm or less, noise poses no practical problem. In order to prevent a short circuit between the lead wire connection portion of the comparison 1ull and the gate portion of the sensor, it is preferable that the comparison electrode has an m-long shape similar to the shape of the sensor.

FIG. 6 is a sectional view of essential parts showing the configuration of the gas concentration measuring device of the present invention. This sensor is made of polyethylene.

Polypropylene, polytetrafluoroethylene.

Silicone, nylon 11. A flexible tube 40 made of polyvinyl chloride, polyethylene terephthalate, etc., for example, a catheter, has a reference electrode ij+ shown in FIGS. 22 is exposed and accommodated in the tip opening of 1140. Each lead wire 45 connected to the reference electrode 31 and ion sensor 21 is insulated and passed through an insulated tube and connected to a connector pin 47 provided at the rear end. The opening at the tip of the insulating tube 40 is made to protrude slightly from the ion sensor 21fl in order to protect it from damage, and is cut out diagonally so that it can be easily inserted into a living body, for example. Then, the space formed by the lead wire connection portion of the ion sensor 21 and the comparison electrode 51, the insulating tube, and the inner wall of the connector is filled with electrically insulating resin 42 to close the insulating tube. In this case, epoxy, silicone, polyvinyl chloride, nylon, polyurethane, polypropylene, etc. can be used as the electrically insulating resin.

Gate section 22 of pH sensitive ion sensor 21 and comparison electrode 5
A hydrophilic polymer fi 43 containing an electrolyte that changes by absorbing gas is provided across both 10 and 10. The thickness of this polymer side is 1
The thickness of this polymer layer is preferably 10 μm or more. If the thickness of this polymer layer is 10 μm or more, the response speed becomes low, and if it is less than 1 μm, the signal becomes unstable. Therefore, the polymer layer must be very uniform.

The polymer used here has moderate water absorption (measured humidity: 57°C).
(more than 60%) and contains virtually no organic acid groups or base groups such as 0OOH groups, to put it mildly, it is 2mO! %
m9 or less (for all monomer units)
If the water absorption is low, the response speed will be low, and if it contains an organic acid or base group, the sensitivity will be decreased. Examples of such polymers include polyvinyl alcohol (hereinafter referred to as TPVA), cellulose, and polyhydroxyethyl methacrylate.

Examples include polyvinylpyrrolidone, agar, starch, and electrolyte polymers. These polymers may be co-combined with other monomers and may also contain oJWi agents, etc. Among these polymers, PVA is particularly excellent in terms of stability. The blood level of this PVA is 500-30
,000 is preferable・PVA polymer cha
During the in, there is a small amount of normal breasts as shown below.
In addition to the cohol unit (B), a terminal aldehyde group (A), a ketone group (C), and vinyl acetate 4i (D).

A CC=0 LH.

D E and carbonyl-containing he such as terminal carboxyl group (E)
Contains tero unrt. These hete
The terminal aldehyde group and getone group of the ro unit become an enol type by keto-enol isomerization, which acts as a weak acid group. Vinyl acetate groups are saponified to produce acetic acid. Further, the terminal carboxyl group acts as an acid as it is. In this way, all of these carbonyl-containing hetero units act as acid groups and cause a decrease in the sensitivity of the gas sensor.
For the gas sensor of the present invention, it is desirable to use a PV membrane in which the content of all of these carbonyl-containing betaro units is 2 moj% or less relative to the highest total unit. In addition, PVmuth may be a copolymer in which other O monomers such as vinylpyrrolidone and vinylene carbonate are copolymerized.
The ffi type has better stability against drying. As the above JjEl agent.

Ethylene glycol, diethylene glycol, trimethylolpropane, 5-methyl-1,3,5-pentanetriol, butanediol, triethylene glycol,
Dipropylene glycol, glycerin, polyhinylpyrrolidone, etc. can be used.7 Polymer content in the hydrophilic polymer single layer 45
(Ratio of polymer/(polymer + transport agent)) is preferably 50% or more and 95% or less in dry rice.If the polymer content is smaller than this, water absorption and shape retention will decrease. Compared to gates for long-term use and storage! The electrical contact between the poles is likely to break. When the content of the polymer exceeds 95%, the sensitivity and response speed tend to decrease when left in a dry state.Also, the electrolyte contained in this polymer layer tends to decrease the sensitivity when the concentration is low relative to the polymer. This is likely to occur and the signal becomes unstable. Also, if the concentration is high, the response speed will decrease. Therefore, it is necessary to contain the electrolytic solution to an extent that does not cause the above-mentioned troubles. For example, in the case of a carbon dioxide sensor, 0.01 to 1 mo of NaHOOs is added to the polymer.
A polymer layer containing such an electrolyte, which preferably contains 0.1 to 2 moJ of NaCj, is applied after being dissolved in a solvent that dissolves both the polymer and the electrolyte, such as water.

Alternatively, you can apply a solution of the polymer alone in advance, or if necessary, crosslink a single layer of polymer obtained by combining on the gate, immerse it in an electrolytic Wi bath solution, swell it, and then dry it. good. In either case, freeze-drying is preferable in order to maintain the thickness of the tube in an il-like state.
4. This polymer can be coated with a known gas permeable membrane. These include, for example, fluorocarbon resins such as Arashi coalescent copolymers such as tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, and chlorotrifluoroethylene, polyolefins such as polyethylene, polypropylene, and polypentene-11, and silicone resins. Particularly preferred among these are polytetrafluoroethylene and silicone resin; use of sfrtj produces a sensor with little change over time, and use of sfrtj yields a sensor with short response time. In terms of strength and response time, the thickness of the film is preferably 6 to 20 μm for fluororesins and olefin resins, and 50 to 500 μm for rubbers such as silicone resins.

Coating methods for the gas permeable membrane 44 include dipping, spraying, vacuum deposition, and ultraviolet light coating.

Methods such as plasma deposition and sputtering can be used. Gas permeation i! lI: The film needs to be uniform and thin in order to obtain a sufficient response speed. In particular, non-rubber-like polymers such as polytetrafluoroethylene, polyethylene, and polypropylene need to be thin films, and vacuum evaporation It is preferable to use a vapor phase method such as , ultraviolet light method, plasma method, or sputtering method. Furthermore, it is also possible to cover at least the gate region of the sensor with a gas-permeable tube with a closed end, and to fix the other end of the tube to the sensor in a fluid-tight manner. This method is a preferred method because it allows the gas sensor to be miniaturized in the case of an elongated sensor.

A reinforcing core wire 48 extends inside the tube from its tip to the connector to prevent deformation of the tube. This core wire only needs to have bending rigidity to the extent that the tube can be bent. For example, stainless steel wire, tungsten wire, molybdenum wire, titanium wire, etc. with a diameter of 0.05 to 0.20 square meters may be used.

Since the hydrophilic polymer layer of the device thus produced is dry, it will not work as it is, so the sensor is used after the hydrophilic polymer absorbs moisture and swells in water or water vapor. Even if this sensor is dried, it can be used again by immersing it in water for a long time, but it is preferable to store the sensor in water for use in III et al. No baseline drift, response speed, or 11 degree decrease occurs even after storage in water.

The sensor described above can then be measured by the circuit shown in FIG.
O is applied, and a constant current flows between the drain 26 and the source 27 by a constant current circuit 51. When a gas sensor or a measuring solution is inserted into a blood vessel, for example, the gas that has passed through the gas permeable membrane 44 is absorbed by the electrolytic solution contained in the hydrophilic polymer layer 46, changing the hydrogen ion concentration of the electrolytic solution, The interface potential of the gate portion 22 of the semiconductor sensor 21 exposed to the surface is changed. As the interfacial potential changes, the source potential Vs also changes. Therefore, by measuring the potential between the output terminal 52 and the comparison electrode 61, the hydrogen ion concentration of the polymer layer, or in other words, the gas concentration in the solution, can be determined. can be measured.

Example 1 A carbon dioxide concentration measuring device having the structure shown in the figure was prepared as follows. First of all, width 0.4m 111° length 5
■, pH sensor 21 with a thickness of 0.15■ and Ag/Ag'
The lead edge 45 is joined to the bonding part of the comparison electric tower 51, and the lead wire and core wire 48 are connected to each other with an inner diameter of 0.5 m and an outer diameter of 0.65 m.
Next, while vacuuming the opening on the connector side of the nylon catheter, suck the silicone resin liquid into the catheter from the opening on the side where the ion sensor is attached, and make sure that the silicone resin liquid is completely inside the catheter. When it is filled, stop the suction, and as shown in Figure 6, fix the FET so that everything other than the gate part of the FET is housed in the catheter, and leave it still until the silicone resin liquid solidifies. Care must be taken to ensure that the gate part and the tip of the reference electrode are not contaminated by the silicone resin liquid. After the silicone resin liquid has solidified, the connector side of the lead wire is joined to the connector bin 47 using a /A render, and the sensor storage catheter and the bottle are set in a molding machine for connector molding. Pour the pipe and harden it to mold the part corresponding to 1ζ in Figure 6. Next, fill the mold for molding the connector 46 with polyvinyl chloride resin and heat it to mold the part corresponding to 46 in Figure 6. to mold/
The tip portion 45 of the ion sensor thus created was
Blood rat% polyvinyl alcohol (degree of polymerization 1700.'7
(ft99.8%), 1% ethylene glycol in 57.

Immerse it in an aqueous solution containing 0, I MaNaHCO &, IM no Na (Jl) and remove the moisture by freeze drying after pulling it up. Next, cover this tip with a closed silicone rubber tube 44 of 10,000. By this, A device is completed, as shown in FIG. 6, in which the inside of the catheter and the inside of the connector are all filled with silicone resin reinforced with core wires.

When 20 devices created in this way were sterilized in 120°C ^pressure steam for 1 hour, the failure rate was 0% and no deformation of the catheter part occurred. Comparative Example Figure 1 A carbon dioxide concentration measuring device sensor as shown in the drawing was created, with a hollow space in the center of the catheter and inside the connector. In this case, the materials used were the same as in Example 1, but the silicone resin filling was limited to the ion sensor mounting part.

When 20 devices created in this way were sterilized in high-pressure steam at 120°C for 1 hour, the failure rate was 70%.
I failed. The main cause of the failure was a break in the solder part and a short in the lead wire part. In addition, the catheter parts of all ion sensors were significantly deformed.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional gas concentration measuring device, Figure 2 is a plan view of a semiconductor ion sensor, Figure 5 is a cross-sectional view taken along line A-A in Figure 2, and Figure 4 is a reference electrode bonded to the substrate surface. The top view of the ion sensor shown in Fig. 5 is B-BIIFrdi in Fig. 4.
Figure i, the sixth factor is a sectional view of the device of the present invention. Figure 7 is an electrical circuit diagram using the device of the present invention. Figure 1 Figure 2 Figure 4 Figure 6 Figure 7 Figure 71 44 43

Claims (1)

[Claims] 1. A reference electrode is glued close to the gate of a half-body hydrogen ion sensor, the sensor is housed in the tip of a tube, and a connector is attached to the rear end of the tube. The inner space formed by the lead wire connection part of the sensor and reference electrode and the inner wall of the tube and connector is filled with an electrically insulating resin, and at least the entire circumference of the tip of the tube is covered with a gas permeable membrane. A gas concentration measuring device characterized in that an external space is formed by this film, a gate sensitive film of an ion sensor, and a reference electrode, and this external space is filled with a hydrophilic polymer containing an electrolyte. 2. The gas concentration measuring device according to claim 1, wherein a reinforcing core edge is provided inside the tube and extends from the tip of the tube to the connector.