JPH04186153A - Planer type ion sensor - Google Patents

Abstract

PURPOSE:To make easy constructing a sensor of integrated type and facilitate mounting for installation of a flow cell by forming separately a semiconductor base board and a base board for formation of ion sensitive film, and afterward consolidating them at mounting. CONSTITUTION:A polymide film 4 is formed through patterning process on a glass epoxy base board 2 provided with Cu wiring 1 on the surface of an ion sensor as object of this invention, and in the center of the patterned polyimide film an opening is formed to serve for formation of ion sensitive films 3. A plurality of sensitive films 3 are put separately as covering the wiring 1 in this opening part. The potential generated in the sensitive films 3 at measurement is conducted through a through hole 5 provided in the base board 2 to a plurality of FETs in a semiconductor chip 10 mounted on the rear of the base board 2. These FETs 9 are connected to an external measuring circuit through a drain 12 and a source 13. Thus the FETs 9 are protected perfectly from the measuring liquid by performing mounting to the surface opposite the sensitive films 3, and connection with the external measuring circuit can be made on the rear surface.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to measurements of electrolyte concentrations in blood in clinical tests, electrolyte concentrations in rivers and foods in environmental measurements, etc. This invention relates to the structure of an ion sensor that measures electrolyte concentration.

[Conventional technology]

Conventional methods for measuring ion concentration in solutions include ion-selective electrodes. The basic structure of this ion-selective electrode is to adhere various ion-sensitive membranes to the tip of the electrode body.
The electrode body is filled with an electrolyte solution, and the silver/silver chloride electrode is immersed in the electrolyte solution. In recent years, many ion-sensitive field-effect transistors (TSI"IETs) using semiconductors have been announced for the purpose of downsizing and integrating these ion-selective electrodes. For example, Analyteka Chemiriki Acta, 159 (1984) No. 47, which made it possible to measure many types of ion components simultaneously by separately forming four types of ion-sensitive membranes on each of the two field-effect transistors. Discussed on pages 62-62. This 15FET has an element structure in which an ion-sensitive film is directly formed on an insulated gate. Insulated game 14sFET like this
The problem was deterioration of the gate insulating film due to alkali ions and halogen ions in the solution. In order to improve this, the part of the ion-sensitive membrane that comes into direct contact with the solution and the field-effect Lancistor gate are placed on the semiconductor substrate apart from each other, and a conductive material is used to connect them. There is a Gate-ISFET, which is Senzas An 1~ Actuators 4. (1,9
1983) pages 291- to 298 (Se
nsors and actuators II, (1
9B3) pp29], -298). In addition, the l5FE'r of consideration is mounted on the flow cell.
However, wire bonding for electrical connection between the 15FIET and an external measurement circuit had to be performed from the same surface of the semiconductor chip on which the ion-sensitive film was formed. For this reason, mounting has become complicated in order to sufficiently protect parts other than the ion-sensitive membrane from the solution. In order to facilitate mounting, there is one in which an electrode terminal portion for connection with an external 11Tl constant circuit is provided on the back surface of a semi-1D board. This is a preview of the 4th International Conference on Isospherical Element Sensors and Actuators (1987), pages 7211i to 729.
Page (Proceedings of Tbe4thIn
ternatjona1. Conference
on 5olid-3L, atCSensor, s
and Actuators (1987) pp7
26-729). It has a structure in which a hole is drilled through it from the back side to the front side using an anisotropic etching method, and a conductive material is deposited on the side of the hole.

[Problem to be solved by the invention]

In a structure in which external connection electrode terminals are provided on the back side of a semiconductor substrate by anisotropic etching, the shape of the hole widens on the back side, and the size of the opening is at least equal to the thickness of the semiconductor substrate. Put it away. For this reason, as the number of elements in the 15FET increases, the area occupied by the electrode terminals increases, and it is therefore necessary to increase the area of each sensor chip. For this reason, the number of sensor chips that can be obtained from one Si wafer is limited. At the same time, when the sensor chip area is limited, the number of electrode terminals is limited, which limits integration. Furthermore, since the field-effect transistor is on the same surface as the ion-sensitive film, there are restrictions on its placement on the semiconductor substrate in order to protect it from the solution. Similarly, even if the surface can be protected, when each sensor is cut out from the semiconductor wafer, S'' is electrically exposed on the cut side surface, so there is a problem that protection processing is required.

An object of the present invention is to provide an ion sensor structure that allows easy integration of the ion sensor and easy implementation for incorporating into a flow cell.

[Means to solve the problem]

In order to achieve the above object, an insulating substrate on which an electrocardiographic material was wired was used instead of forming an ion-sensitive film on the semiconductor substrate. Here, this wiring was provided on both sides of the insulating substrate, and conduction was established on both sides through through holes. The wiring was coated with an ion-sensitive membrane on the surface that would come into contact with the solution. A semiconductor substrate on which a field effect transistor was formed was mounted on the opposite side.

The gate of the field-effect transistor was connected to the wiring on the back side, which was connected to the wiring coated with the ion-sensitive film on the front side.

Furthermore, multiple types of ion-sensitive films were separately formed on the surface of the insulating substrate to coat the wiring so that multiple types of ions could be measured simultaneously. A semiconductor substrate on which field-effect transistors corresponding to the number of wires were integrated was mounted on the back surface of the insulating substrate.

In order to further reduce the impedance of the output from this field effect transistor, a semiconductor substrate was used in which an operational amplifier using a field effect transistor as an input stage transistor was integrated.

In the analyzer, a part of the flow cell was opened to expose a part of the inside of the flow channel so that it could be easily incorporated into the flow cell through which the measurement sample solution flows.

The structure was such that this exposed flow path contacted only the ion sensor J1L: membrane portion of the sensor substrate.

[Effect]

A semiconductor substrate on which a field-effect transistor was formed and a substrate on which an ion-sensitive film was formed were separately formed and later integrated by mounting. This allows the semiconductor to be mounted on the opposite side of the ion-sensitive membrane, and the field effect transistor can be completely protected from the measurement solution. Furthermore, since the field effect transistor is placed on the back side, connection to an external measurement circuit can be made directly from the back side. In addition, the wiring coated with the ion-sensitive membrane is connected to the wiring on the back side through a through hole provided in the insulating substrate, so that the potential generated by the ion-sensitive membrane depending on the ion concentration in the solution can be applied to the gate 1 of the field effect transistor on the back side. can be conveyed to.

Even when the sensor is integrated, there is no need to make holes in the semiconductor chip, so there is no need to take up a large area. For this reason, it has become possible to integrate a large number of field effect type I-transistors on a single semiconductor chip without any limitations. This allows simultaneous measurement of many types of ions.

By integrating an operational amplifier that uses not only a field effect transistor on a semiconductor substrate but also a field effect transistor as an input stage transistor, the output impedance is lower than that of a single field effect transistor. I can do it.

This makes it possible to obtain high-quality sensor signals that are not affected by external electrical signal noise.

[Implementation example]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows the surface of a planar ion sensor. A glass epoxy substrate 2 with copper wiring 1 was used.

A polyimide film 4 was patterned onto the glass epoxy substrate 2 so that an opening was formed in the center of the glass epoxy substrate where the ion-sensitive film was to be formed. Four types of ion-sensitive films 3 were separately coated on the copper wiring in the openings of the polyimide film. In order to transmit the potential generated in the ion-sensitive membrane during measurement to a field effect transistor mounted on the back side of the substrate, a through hole 5 was provided in the glass epoxy substrate and wiring was connected to the back side.

FIG. 2 shows the cross-sectional structure of the ion-sensitive membrane portion.

A copper wiring 1 was formed on a glass epoxy substrate 2, and chromium 6 was formed on the second wiring. Furthermore, silver 7 and silver chloride 8 were laminated on top of the chromium. Polyimide was formed around the silver chloride. An ion sensitive film 3 was formed in the opening of this polyimide, and was formed separately from other ion sensitive films formed on the same substrate.

FIG. 3 shows the back side of the planar ion sensor. Wiring is connected from the surface through through holes. A semiconductor chip 10 on which a field effect transistor 9 was formed was mounted on this surface.

Here, four field effect transistors were integrated into the semiconductor chip. A copper wiring extending from the surface was connected to the gate electrode 11 of this field effect transistor by a honda wire. The first drain 2 and source 13 of the field effect transistor 9 were connected to an external measurement circuit connection terminal 15 through bonding wires.

Figure 4 shows the structure of the flow cell. A flow path 17 was formed in the flow cell body 16. An opening 18 is provided in this flow cell body, and a flow path exposed portion 1 where a part of the flow path is exposed.
9 was formed. A groove was formed to surround the exposed portion of the flow path, and an O-ring 20 was fitted therein. The planar ion sensor shown in FIGS. 1 to 3 is attached to the opening. O-
The link prevents the measurement solution from leaking to other parts, and allows the part where the ion-sensitive membrane is formed to come into contact with the complete solution 41 that has passed through the tube 23. Insert the sensor first,
The sensor was fixed to the flow cell hotel r- using a sensor holding plate 1-21 and a fixing screw 22. The output of the planar ion sensor is input to an external measurement circuit through a lead wire 24. The flow cell in which the planar ion sensor was mounted in this way was installed in an analyzer, and the response characteristics of the sensor were investigated. The results are shown in FIGS. 5 and 6. Figure 5 shows the pH sensor integrated into the planar ion sensor.
Indicates H response. A linear response was obtained between pH 2 and pH 10, with a sensitivity of 56 mV/pH. FIG. 6 shows the ion responses of the Na sensor, I sensor, and CI sensor. Ion concentration 100 m m o
], / ] to Q, 1. A linear response was obtained in the range of 2 mmol/]. The sensitivity of each sensor is 51 mV/pNa for the Na sensor and 58.5 mV/p for the Na sensor.
K, CI sensor was -54, mV'/pCI.

〔Effect of the invention〕

According to the present invention, an ion-sensitive membrane portion in contact with a solution;
Separate the semiconductor chip that forms the field effect transistor that converts the response of the ion-sensitive membrane into an electrical signal,
Moreover, since it can be placed on the opposite side of the sensor substrate, it is easier to protect it from the solution.

In addition, since there is no need to drill holes from the front to the back of the semiconductor substrate using anisotropic enochink to obtain the sensor output from the back side of the sensor, it is possible to integrate more sensors on the sensor substrate with a limited area. became. Furthermore, by integrating an operational amplifier with a field effect transistor in the input stage to a run transistor on a semiconductor chip, the impedance of the sensor output signal can be lowered and the sensor output signal can be made more linear.

The flow cell to which the planar ion sensor is attached has a structure in which the flow path is partially open, so it can be inserted into the opening and used without leaking the solution. An insulating layer is formed on the surface of the planar ion sensor on which the ion-sensitive membrane is formed, with only the ion-sensitive membrane part open [''], thereby preventing deterioration of the wiring parts other than the ion-sensitive membrane part on the surface over the long term. be able to.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the front surface of the planar ion sensor of the present invention, FIG. 2 is a structural diagram of the ion-sensitive membrane portion of the planar ion sensor, FIG. 3 is a diagram showing the back surface of the planar ion sensor, and FIG. The figure is a structural diagram of a flow cell for a planar type ion sensor, and Figure 5 shows the flow cell for a planar type ion sensor.
Figure 6 shows the pH response of the 1-T sensor.
FIG. 3 is a diagram showing the ion response of the sensor. 1. Copper wiring, 2. Glass epoxy substrate, 3. Ion sensitive film, 4. Polyimide, 5. Through hole, 6.
Chromium, 7 Silver, 8 Silver chloride, 9 Field effect type 1 helangister, 10 Semiconductor chip, 11
Electrode to Ge 1, 12-1 Nirein, 13- Source,
4. Bonding wire, 15. External measurement circuit connection terminal, 16 Flow cell body, 17. Channel, 18 Opening, 19 Channel exposed section, 20. O-ring, 21 Sensor holding plate, 22. Stiffness No. 1st item 2nd town Fig. 4 , 5 Fig. θ・3 Fig. 3

Claims (1)

[Claims] 1. An ion sensor that measures the ion concentration of a liquid uses an insulating substrate on which a wiring pattern is formed so as to establish conduction on both sides through through holes, and one side of the insulating substrate has a plurality of ions. An electrode coated with a sensitive film is wired, a plurality of field effect transistors (FETs) are mounted on the back side of the insulating substrate, the electrode is connected to the gate of each FET, and the wiring is connected to an external measurement circuit. A planar type ion sensor characterized in that: is provided on the back side of the surface on which the ion-sensitive membrane is formed. 2. A planar ion sensor characterized by using a semiconductor chip in which a plurality of field effect transistors according to claim 1 are integrated on one semiconductor substrate. 3. The field effect transistor according to claim 1,
A planar ion sensor characterized in that an operational amplifier using a field effect transistor is used at least in an input stage, and a field effect transistor at a non-inverting input of the operational amplifier is connected to an electrode on which an ion sensitive film is formed. 4. A solution flow path is formed in the insulator, and a part of the flow path is opened to provide an opening, and the portion where the ion-sensitive membrane of the planar ion sensor according to claim 1 is formed and the opening. A flow cell characterized by being brought into contact with. 5. A planar type ion insulating substrate according to claim 1, characterized in that an insulating layer patterned so that only the portion covered with the ion-sensitive film is open is formed on the surface on which the electrode coated with the ion-sensitive film is formed. sensor.