JPH04276544A - Bonding type chemical sensor - Google Patents

Abstract

PURPOSE:To obtain sensors having the high nondefective product rate even in industrial mass production by achieving excellent reproducibility in a bonding type chemical sensor for detecting the samples such as gas, humidity and solvent. CONSTITUTION:A bonding type chemical sensor comprises an upper electrode 3, a first member 1 which is bonded to the upper electrode, a second member which is bonded to the first member and a lower electrode which is bonded to the second member. The first and second members are manufactured by a thin-film forming technology. Thus, the bonding interface between the first and second members becomes smooth. Therefore, the contact area is always constant, and the reproducibility is improved. Since the first and second members are the thin films, the entire chemical sensor become very thin and compact.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical sensor, and more particularly to a chemical sensor for sensing samples such as gases, humidity, and solvents.

0002

[Prior art] Conventionally, CO, Cl2, NOX, SO
Chemical sensors have been proposed to sense samples such as X, ozone, chlorofluorocarbons and other gases, humidity, alcohol, ether, acetone, toluene, gasoline, pentane, thinner and other solvents. For example, JP-A-62-9052
No. 9, Journal of the Chemical Society of Japan 1985 No. 6 No. 1154-1
159 pages, Journal of the Chemical Society of Japan 1987 No. 3rd 477th
Please refer to pages 483 to 483.

[0003] This type of chemical sensor is most commonly
As shown in FIG. 2, an upper electrode (3), a first member (1) made of a first substance bonded to the upper electrode, a second member (2) made of a second substance bonded to the first member, and The lower electrode (4) is connected to the second member, and the first member and the second
It has a structure in which the bonding interface with the member is exposed. The first member is a sintered body of copper oxide (CuO) or nickel oxide (NiO), which are p-type semiconductors, and the second member is a sintered body of zinc oxide (ZnO), which is an n-type semiconductor, or CVD. A ZnO thin film formed by the method (a type of vacuum thin film forming technology) is used in each case.

[0004] The mechanism by which this type of chemical sensor senses a sample has not yet been fully elucidated and is unclear, but it is necessary that the bonding interface between the first member and the second member be exposed. When a sample comes into contact with this exposed bonding interface, the electrical relationship between the first member and the second member changes. Therefore, this change is detected through the upper electrode joined to the first member and the lower electrode joined to the second member. The electrical information actually detected is current, voltage,
These include electrical resistance, rectification characteristics, and capacitance. When a sample is adsorbed to or detached from the bonding interface or its vicinity, carriers are injected from one side of the first member or the second member to the other, the carriers disappear, or the interfacial potential energy changes. , it is estimated that these electrical information can be obtained.

[0005] Journal of the Chemical Society of Japan 1987 No. 3rd 47th
According to pages 7 to 483, the detection mechanism of a chemical sensor formed by pressing a CuO sintered body, which is a p-type semiconductor, and a ZnO sintered body, which is an n-type semiconductor, is as follows: 1) Z
Lowering of the energy barrier on the nO surface 2) Current transport via the interface state caused by chemisorption of gas on the CuO surface proceeds independently or simultaneously.

[0006] Since electrical information is reproducible,
For known samples, the correlation between this information and the type and amount of the sample is measured. In this way, it is possible to measure this information about an unknown sample and sense the type and amount of the sample from the previously measured correlations. Conventional stand-alone sensors and catalyst-supported sensors that detect simple adsorption or internal diffusion lack sample selectivity, meaning they output the same electrical information for multiple types of samples. There were disadvantages such as (1) the need for regeneration treatment (for example, heating) when used repeatedly. On the other hand, this type of chemical sensor does not have these drawbacks, so there are great expectations for its practical use.

[0007]

[Problems to be Solved by the Invention] The present inventors have found that this type of chemical sensor has poor reproducibility, and therefore has a problem in that the rate of non-defective products is low when it is industrially mass-produced.

[0008]

[Means for Solving the Problems] As a result of intensive research, the present inventors have discovered that the cause of poor reproducibility is that the contact area between the first member and the second member is not uniform among individual sensors. We discovered that the reason for the nonuniform contact area was the surface roughness of the sintered body (irregular irregularities of several to tens of micrometers), and as a result of further research, we found that the contact area was not uniform. It was discovered that in order to make the area uniform, both members should be formed by a thin film forming technique such as vacuum evaporation, and the present invention was completed.

[0009] Therefore, the present invention firstly provides an upper electrode;
The first member is made of a first material and is bonded to the upper electrode, the second member is made of a second material that is bonded to the first member, and the lower electrode is bonded to the second member. 2
A bonded chemical sensor in which a bonding interface with a member is exposed, wherein the first and second members are both manufactured using a thin film forming technology.'' do.

0010

[Operation] When the first and second members are manufactured using vacuum thin film forming techniques such as vacuum evaporation, ion plating, sputtering, and CVD, electrodeposition, plating, spin coating, and spraying, the interface becomes smooth. It is presumed that the contact area will always be the same because the two members will maintain a bonded state even if they are not pressed together by external means.

Examples of combinations of the first substance constituting the first member and the second substance constituting the second member include, for example, a p-type semiconductor and an n-type semiconductor, an acid and a base, an oxidizing substance and a reducing substance, Examples include substances with a large ionization tendency and substances with a small ionization tendency. Examples of p-type semiconductors include NiO, CuO,
Cu2O, CoO, Cr2O3, MnO2, MnO
, MoO2, α-BiO3, p-Si, etc.
As the n-type semiconductor combined with this, for example, W
O3, ZnO, TiO2, BeO, SnO2, V
2O5, Fe2O3, CdO, SiC, In2O3
, ThO2, Al2O3, Nb2O5, Ta2
O5, BaTiO3, SrTiO3, PbCrO
3, n-Si, etc.

[0012] Examples of acidic substances include TiO2,
There are ZrO2, etc., and examples of basic substances combined with this include MgO, NiO, MgCrO4, etc. Examples of oxidizing substances include AlN, Zn
Examples of reducing substances that can be combined with O include CaO and Y2O3. For example, a thickness of about 1000 Å to 10000 Å is sufficient for both members.

[0013] Electrode materials include metals such as aluminum, gold, platinum, silver, copper, stainless steel, iron, rhodium, and indium, tin oxide, indium oxide, and ITO (indium oxide mixed with a small amount of tin oxide). etc. are used. In particular, the upper electrode often touches the sample, so
Gold and platinum, which have high corrosion resistance, are recommended. It is preferable that both the upper and lower electrodes be formed using a vacuum thin film forming technique.

[0014] Since the chemical sensor can sense by exposing the bonding interface to a sample, it is preferable that the length of the exposed bonding interface is longer than the contact area. Also, it is commercially advantageous to have a compact and long sensor as a whole. For this purpose, it is preferable to increase the length of the exposed bonding interface by forming one or more holes or grooves extending from the upper electrode to the second member or the lower electrode. This preferred sensor is claimed in claim 2.

[0015] A large number of holes may be provided in a dot matrix shape, and the grooves may be formed in a meandering or zigzag shape. In order to form holes or grooves, the diameter is preferably about several tens of microns or less, so it is preferable to use photolithography followed by etching technology (wet or dry) or a lift-off method. However, laser cutting or mechanical cutting methods may also be used. In this way, instead of first forming the sensor into a thin flat plate and then increasing the length of the exposed bonding interface by forming holes or grooves, vacuum using a mask such as mask evaporation can be used. A method may be adopted in which a sensor having a long exposed bonding interface is manufactured using thin film formation technology.

When the holes or grooves are small (fine), photolithography followed by etching techniques (wet or dry) or lift-off methods are often used; Since the second member is formed using vacuum thin film forming technology, it has the advantage that small (fine) holes and grooves can be formed accurately, and the length of the exposed bonding interface is always uniform. . This improves the reproducibility of the chemical sensor.

[0017] The sample is often corrosive, and even if a highly corrosion-resistant electrode material is used, there is a risk that the electrode, especially the upper electrode, will be corroded. As corrosion progresses, not only is there a risk that it will eventually disappear, but even a slight amount of corrosion, or even if there is no corrosion, just the adhesion of a sample will change the electrical resistance and adversely affect electrical information. Therefore, it is preferable to form a protective film on the electrode, especially the upper electrode. This preferred sensor is claimed in claim 3. Materials for the protective film include silicon oxide, niobium oxide, tantalum oxide, titanium oxide, zirconium oxide, magnesium fluoride, silicon nitride, titanium nitride, carbon thin film, diamond-like carbon thin film, diamond thin film,
Examples include silicon carbide and titanium carbide. It is sufficient that the thickness of the protective film is 0.01 to 100 μm. Therefore, the protective film can be formed using a thin film formation technique. It is preferable to manufacture all of the electrodes, the first and second members, and the protective film using thin film formation technology, since this reduces manufacturing costs. It is possible and preferred to form holes or grooves even after forming the protective film. The present invention provides a bonded chemical sensor characterized in that the two members are manufactured using thin film forming technology.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

[0019]

[Embodiment 1] This embodiment will be explained with reference to FIG. 1 (side view). A rectangular glass substrate (7) of 15 mm x 15 mm is prepared, and the entire surface is vacuum evaporated to a thickness of approximately 0.0 mm.
A lower electrode (4) was formed by depositing 1 μm of Al. Next, ZnO, which is an n-type semiconductor, was added in a similar manner to about 0.
The second member (2
) was formed.

Next, similarly, CuO, which is a p-type semiconductor, is
The first member (1) was formed by mask vapor deposition to a thickness of 0.5 μm. Finally, an upper electrode (3) was formed by depositing Al to a thickness of about 0.01 μm, thereby obtaining the chemical sensor shown in FIG. 1.

[0021]

[Embodiment 2] This embodiment will be explained with reference to FIGS. 3 to 5. (b) 15mm x 15mm rectangular glass substrate (7
) was prepared, a photoresist (8) was applied to the entire surface, a dot matrix negative pattern was projected and exposed, and then developed to form a dot matrix photoresist (8) pattern. Figure 3
The pattern is shown below. One resist dot is 30μ
It is a square of x30μ, and the dot spacing is also 30μ. (b) Next, Au was vacuum-deposited to a thickness of about 0.1 μm so as to cover the pattern portion, thereby forming a lower electrode (4). (c) Using a mask whose right end is closer to the left than the shape of the lower electrode (4), ZnO is deposited on the lower electrode (4) to a thickness of approximately 0.5 μm. Two members (2) were formed.

Similarly, CuO is placed on the second member (2).
The first member (1) was formed by mask vapor deposition to a thickness of 0.5 μm. Subsequently, Au is deposited on the first member (1).
The upper electrode (
3) was formed. At this time, only the pattern portion is sandwiched between the upper and lower electrodes. (d) Finally, place silicon oxide (SiO) on top of the upper electrode (3).
2) to a thickness of about 0.3 μm. Protective layer (7)
was deposited.

[0023] Here, the second member (2) and the first member (1
), the upper electrode (3), and the protective layer (7) had the same shape, so they were successively deposited using the same mask. (e) After this, all the resist dots (8) were lifted off. A square hole (9) is made at the lifted-off location. The dimensions of the hole are squares of 30μ x 30μ, and the area of the pattern portion is 25mm2.

In this way, FIG. 4 (plan view) and FIG.
A chemical sensor shown in (A-A' cross-sectional view) was manufactured. It actually works if external wiring (5), (6) is soldered to the upper electrode (5) and lower electrode (4), respectively, and a voltage is applied therethrough. FIG. 6 shows data obtained by measuring humidity at 23° C. with this chemical sensor. voltage 0.5
When the voltage was changed to volt (V), 1.0 V, and 1.5 V and measured three times, it was shown that the correlation between the output current value and the humidity was clearly linear (linear equation). Therefore, by having this output current value-humidity correlation curve as a calibration curve, unknown humidity can be calculated (sensed) from the output current value of the sensor.

Furthermore, as can be seen from FIG. 6, the change in current (sensitivity) due to humidity changes depending on the applied voltage, indicating that the sensing mechanism is different from the conventional single sensor. Therefore, sensitivity can be controlled by applied voltage. In addition, when we measured the current-voltage characteristics of this sensor in atmospheres with humidity of 2% (H) and 40% (H), we found that
As shown in FIG. 7, rectification was exhibited, and only the forward current increased or decreased in response to humidity. The reverse current was almost zero.

It should be noted that the sensor of Example 1 showed similar characteristics even when the protective film (7) was not formed.

[0027]

[Example 3] In Example 2, after forming the lower electrode (4) on the entire surface of the glass substrate (S), a dot matrix-like photoresist (8) pattern was formed, and then Example 2 and Similarly, the second member (2) and the first member (1)
A chemical sensor was fabricated by laminating the upper electrode (3) and the protective film (7), and finally lifting off the photoresist (8).

[0028] Therefore, in this sensor, the hole (9) reaches the protective film (7), the upper electrode (3), the first member (1), and the second member (2) (that is, it penetrates each layer). ) does not reach the lower electrode (4), and no hole (9) is formed in the lower electrode (4). This sensor also showed similar performance to Example 2.

[0029]

[Embodiment 4] In this example, a groove (10) is used instead of a hole (9).
Here is an example. A chemical sensor shown in FIG. 8 (plan view) was manufactured by the lift-off method in the same manner as in Example 2. Groove (1
9) The shape is a zigzag fold as shown in Figure 8,
Both the groove width and the groove interval are 10μ, and the total area of the grooves is 25mm2.

[0030]

Embodiment 5 In this example, holes were formed using an etching method instead of the lift-off method. The process of applying the photoresist (8) to the entire surface of the glass substrate is omitted, and the rest is carried out in the same manner as in Example 2 to form the lower electrode (4), the second member (2), the first member (1), and the upper part. The electrode (3) and the protective film (7) were laminated in this order. Then, a photoresist (8) was applied to the entire surface, and then a pattern inverted from the dot matrix negative pattern was projected and exposed, and then developed to form a photoresist (8) pattern. This pattern is shown in FIG. The protective film (7) is exposed through the opening of the resist (8) pattern.

Thereafter, the exposed protective film (7) is removed sequentially or several layers at the same time downwards by wet etching. For example, SiO2 of the protective film dissolves in hydrofluoric acid, and Al, CuO, and ZnO of the electrode dissolve in acid. As a result, a chemical sensor having a structure similar to that of Example 2 is obtained.

[0032]

Example 6 A chemical sensor was manufactured in the same manner as in Example 5, except that dry etching by ion beam irradiation (impact) was used instead of wet etching. Dry etching is more versatile than wet etching.

[0033]

As described above, according to the present invention, since both the first and second members are formed by vacuum thin film forming technology, the interface between the two members becomes a smooth plane, and both members can be formed by external means. Since the bonded state can be maintained even without crimping, chemical sensors can be manufactured with high reproducibility. Therefore, when chemical sensors are industrially mass-produced, the rate of non-defective products increases.

[0034] Also, compared to the conventional technology using a sintered body,
Since both the first and second members are thin films, the entire chemical sensor is extremely thin and compact.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of a chemical sensor according to Example 1 of the present invention.

FIG. 2 is a schematic side view of a conventional chemical sensor.

FIG. 3 is a schematic plan view of a photoresist (8) pattern of Example 2.

FIG. 4 is a schematic plan view of a chemical sensor of Example 2.

FIG. 5 is a sectional view taken along the line A-A' in FIG. 4;

6 is a graph showing data obtained by measuring humidity with the chemical sensor of Example 2. FIG.

7 is a graph showing current-voltage characteristics of the chemical sensor of Example 2. FIG.

8 is a schematic plan view of a chemical sensor of Example 4. FIG.

9 is a schematic plan view of a photoresist (8) pattern of Example 6. FIG.

[Explanation of symbols]

1 First member 2 Second member 3 Upper electrode 4 Lower electrode 5, 6 External wiring 7 Protective film 8 Photoresist 9 holes 10 groove

Claims (3)

[Claims] Claim 1: an upper electrode; a first electrode connected to the upper electrode;
Consisting of a first member made of a substance, a second member made of a second substance bonded to the first member, and a lower electrode bonded to the second member, the bonding interface between the first member and the second member is exposed. A bonded chemical sensor characterized in that both the first and second members are manufactured using a thin film forming technique. 2. One or more holes or grooves extending from the upper electrode to the second member or the lower electrode are formed, so that the length of the exposed bonding interface is increased. The junction type chemical sensor according to claim 1. 3. The junction type chemical sensor according to claim 1, wherein the upper electrode is covered with a protective film.