JPS63128247A - Metal/insulator/semiconductor capacitor type gaseous oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain a gaseous oxygen sensor which permits easy prepn. and has excellent long-term stability by laminating a solid electrolyte layer which dissociates oxygen molecules to oxygen ions on a thin film-like insulating layer formed on a semiconductor substrate. CONSTITUTION:The insulating layer 12 is formed on the silicon substrate 10. The insulating layer 12 consists of an SiO2 oxide film 14 and an Si3N4 insulating film 16. The solid electrolyte layer 18 is laminated on the insulating film 16. The layer 18 consists of a Y2O3 or CaO-doped ZrO2 film. A metal electrode 20 is provided atop the layer 18. Platinum, palladium, etc., which have the high catalytic effect for the dissociation reaction to dissociate gaseous oxygen to oxygen ions at a room temp. are preferable as the electrode 20. The gaseous oxygen in the atmosphere is dissociated to ions at the boundary between the electrode 20 which catalyzes the reaction to dissociate the gaseous oxygen to oxygen ions and the layer 18. The electromotive force corresponding to the gaseous oxygen partial pressure in the atmosphere is generated when the dissociation attains equal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxygen gas sensor using an i-conductor for measuring the partial pressure of oxygen gas in a gas.

7. [Prior art] When measuring the partial pressure of oxygen gas in gas or liquid,
Clark type oxygen electrodes are widely used. In recent years, there has been a strong demand for the development of compact oxygen sensors in the medical field. Therefore, in order to meet this demand, for example, IEEE TRANSACTIONON BIOM
EDICAL ENGINEERING, VOL,
BME-22, Na4°G in JULY1975,
“MiniaturizedEle” by EDF, N, etc.
ctorode for 0n-Line P○
z Measurements", efforts are being made to miniaturize Clark-type oxygen electrodes by making full use of semiconductor technology.

[Problem that the invention seeks to solve]

However, the above-mentioned glue and Lark type oxygen electrodes have a structure in which silicon is formed into a container shape, an electrolytic solution is placed in the container, and the container is sealed with an oxygen permeable film (Teflon film). Therefore, when manufacturing such an oxygen electrode, a process different from the conventional process for manufacturing semiconductor elements and semiconductor parts is required, and the problem was how to maintain compatibility with the conventional manufacturing process. Also, Clark type oxygen electrode.

There was a problem.

The present invention has been made in order to eliminate the drawbacks of the prior art, and provides a metal/insulator/semiconductor capacitor type oxygen gas sensor that can be easily manufactured using conventional manufacturing processes and has excellent long-term stability. With the goal.

[Means for solving problems]

The present invention provides a thin insulating film formed on a semiconductor substrate;
A metal / This is an insulator/semiconductor capacitor type oxygen gas sensor.

[Effect]

In the present invention configured as described above, oxygen gas in the gas (atmosphere) dissociates into ions at the interface between the solid electrolyte layer and the metal electrode that catalyzes the reaction of dissociating into oxygen ions, and this dissociation reaches equilibrium. Then, an electromotive force is generated according to the partial pressure of oxygen gas in the atmosphere. This electromotive force changes the carrier concentration on the surface of the silicon substrate provided via the insulating layer.

Therefore, the capacitance-voltage characteristics of a capacitor configured as a metal/insulator/semiconductor change in the voltage axis direction depending on the oxygen gas partial pressure, and by measuring this change, the oxygen gas partial pressure in the atmosphere ( oxygen concentration) can be detected.

Further, in the present invention configured as described above, since an electrolytic solution and an oxygen permeable membrane are not used, it can be easily manufactured by a method similar to that used for manufacturing semiconductor integrated circuits. Furthermore, the electromotive force described above is based on the dissociation equilibrium of oxygen gas, and an oxygen gas sensor that does not affect the electrodes and can operate stably over a long period of time can be obtained. Moreover, in the present invention, since an insulating layer is interposed between the silicon substrate and the solid electrolyte layer, there is no need to consider impedance, and the device can be operated at room temperature.

〔Example〕

Preferred embodiments of the metal/insulator/semiconductor capacitor type oxygen gas sensor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of a metal/insulator/semiconductor capacitor type oxygen sensor according to the present invention.

In FIG. 1, reference numeral 10 is a silicon substrate, which is a semiconductor substrate. An insulating layer 12 is formed on top of this silicon substrate 10. The insulating layer 12 is made of Si
It consists of a 0g oxide film 14 and a 5isN insulating film 16. A solid electrolyte layer 18 is laminated on the 51 g N4 insulating film 16. This fixed electrolyte layer 18 can be made of, for example, zirconia (ZrOz), zirconia doped with YfLOa, or zirconia doped with Ca 2 O. A metal electrode 20 is provided on the upper surface of the solid electrolyte layer 18. The metal electrode 20 is preferably one that has a high catalytic effect on the dissociation reaction that dissociates oxygen gas into oxygen ions at room temperature; for example, it is made of a noble metal such as platinum, palladium, iridium, or gold, or a laminated layer of some of these metals. Preferably, it is made into a metal or an alloy.

An insulating layer 1 is provided between the silicon substrate 10 and the solid electrolyte layer 18.
In order to operate the above-mentioned metal/insulator/semiconductor capacitor type oxygen gas sensor with 2 interposed with high sensitivity at room temperature, the materials and layer thicknesses of the solid electrolyte layer 18 and the metal electrode 20 must be carefully considered. There is a need to. Solid electrolyte layer 1
In order to improve the electrical characteristics of the metal/insulator/semiconductor capacitor, the thickness of the capacitor 8 is preferably as thin as 5000 Å or less. The solid electrolyte layer 18 is
A material with high oxygen ion conductivity at room temperature (Zr
Oz doped with Y2O3, ZrOz doped with Ca
Doped with O, etc.) is preferable. However, the material forming the solid electrolyte layer 18 does not necessarily have high oxygen ion conductivity, and in this case, the solid electrolyte layer 18 may be formed thin.

The metal electrode 20 is preferably made of the above-described material, and in order to efficiently dissociate oxygen molecules on the electrode,
Since the metal electrode 20 is porous or does not use an oxygen film, it can be manufactured at low cost using semiconductor integrated circuit technology, and a small and easy-to-use oxygen gas sensor can be obtained. Furthermore, it can be integrated into a single chip with other semiconductor sensors, signal processing circuits, etc., and a multifunctional oxygen gas sensor can be manufactured. Further, the oxygen gas sensor of the above embodiment can measure oxygen partial pressure at room temperature, and can significantly extend its service life compared to the conventional Clark type oxygen gas sensor.

FIG. 2 is a sectional view showing a second embodiment of the invention. In this embodiment, a channel stopper 22 is provided in a portion of the silicon substrate 10 other than the portion immediately below the metal electrode 20 and at the boundary with the 5iOz oxide film 14 to prevent the formation of a depletion layer or an inversion layer. . This channel stopper 2
2, it is possible to eliminate crosstalk between elements integrated on one chip.

FIG. 3 is a sectional view showing a third embodiment of the present invention. The embodiment shown in FIG.
Using a SO8) substrate, a part of the silicon epitaxial layer on the sapphire substrate 24 is etched to form a silicon island 26, and a 5iOz oxide film 14,5 is formed on the silicon island 26.
iaN4 insulating film 16, solid electrolyte layer 18. Metal electrode 20
are sequentially laminated. In this way, if an SO8 substrate is used.

Sensor elements, signal processing circuits, etc. integrated on one chip can be electrically separated from each other.

In the embodiment shown in FIG. 4, the 5isN4 insulating film 16 is omitted and the solid electrolyte layer 18 is formed directly on the SiOx oxide film 14. By doing so, the number of man-hours can be reduced. In addition, Fig. 2.

Also in the embodiment shown in FIG. 3, the 51 g N4 insulating film can be eliminated.

Specific Example A 5iOz oxide film 1 with a thickness of 500 on a silicon substrate 10.
4 and 1000 5iaN4 insulating films 16 were formed as the insulating layer 12, and a solid electrolyte layer 18 was formed on the 5isN4 insulating film 16 using Zr0 doped with 8 mol% of Y2O3.
1000 Z films were formed by sputtering. Thereafter, a metal electrode 20 is formed using a sputtering method.
A platinum layer of 0.000 mm was formed to obtain the oxygen gas sensor shown in FIG.

The oxygen gas sensor of the example thus obtained was placed in a dark box, oxygen gas or a mixed gas of oxygen and nitrogen was introduced into the dark box, and the oxygen gas partial pressure in the atmospheric gas was changed.
The output of the sensor was measured.

The measurement results are shown in FIGS. 5 and 6.

FIG. 5 shows the measurement results of capacitance-voltage characteristics in 1-atm oxygen gas or nitrogen gas. The measurement frequency was IMHz, and curve a represents the capacitance-voltage characteristics measured in oxygen gas and curve a in nitrogen gas. The flat band voltage in oxygen gas shifts in the positive direction compared to the flat band voltage in nitrogen gas.

FIG. 6 is a plot of the relationship between the flat band voltage and the oxygen partial pressure when the oxygen partial pressure in the atmosphere is changed, and the oxygen partial pressure on the horizontal axis is on a logarithmic scale. The flat band voltage varied depending on the oxygen partial pressure, and its slope was 11 mV/Pot.

FIG. 7 shows the time-dependent changes in response to 1 atm oxygen and nitrogen between the oxygen gas sensor of the example and the conventional Clark type oxygen electrode, and compares the long-term stability of both sensors. Taking the initial response of both sensors as 100%, we measured how the relative sensitivity changed over time. The oxygen gas sensor of the example obtained a response with a reproducibility of within ±5% even after 100 hours, whereas the Clark type oxygen electrode had a sensitivity that was lower than the initial 50%.
%. Therefore, it can be seen that the oxygen gas sensor of the example has excellent long-term stability.

FIG. 8 shows that the solid electrolyte layer 18 of the embodiment shown in FIG. 1 is made of Zr0z doped with 8 mol% of CaO.
These are the results of measuring the relationship between the flat band voltage and oxygen partial pressure of a sensor formed to a thickness of 1,000 people. The flat band voltage depends on the oxygen partial pressure, and its slope is 9
mV/P O2.

FIG. 9 shows the results of measuring the relationship between the flat band voltage and oxygen partial pressure of a sensor in which the solid electrolyte layer 18 of the example shown in FIG. 1 was formed as a 1000 LaFa film. The flat band voltage varied depending on the oxygen partial pressure, and its slope was 10 mV/P Ox.

〔Effect of the invention〕

As described above, according to the present invention, by using a solid electrolyte, it is possible to obtain an oxygen gas sensor that can be manufactured using conventional semiconductor integrated circuit technology and has excellent long-term stability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a metal/insulator/semiconductor capacitor type oxygen gas sensor according to the present invention, FIG. 2 is a sectional view of an embodiment in which a channel stopper is formed on a silicon substrate, and FIG. A cross-sectional view of an embodiment using a silicon-on-Savior substrate, FIG.
FIG. 5 is a cross-sectional view of an embodiment in which the N4 insulating film is omitted, and FIG. Figure 6 is a diagram showing the relationship between the flat band voltage and oxygen partial pressure according to the example in which the characteristic curve in Figure 5 was obtained, and Figure 7 is a diagram showing the relationship between the example and the Clark type oxygen electrode. Comparative characteristic diagram of long-term stability, Figure 8 shows Ca
A characteristic diagram showing the relationship between the flat band voltage and oxygen partial pressure of an example having a solid electrolyte layer made of Zr0z doped with O. FIG. 9 is a characteristic diagram showing the relationship between flat band voltage and oxygen partial pressure of an example having a solid electrolyte layer made of LaFa. FIG. 10... Silicon substrate, 12... Insulating layer, 18...
- Solid electrolyte layer, 20...metal electrode.

Claims (1)

[Claims] 1. A thin film-like insulating layer formed on a semiconductor substrate, a fixed electrolyte layer laminated on this insulating layer and dissociating oxygen molecules into oxygen ions, and a fixed electrolyte layer provided on top of this fixed electrolyte layer. and a metal electrode that catalyzes the dissociation reaction. 2. The metal/insulator/semiconductor capacitor type oxygen gas sensor according to claim 1, wherein the insulating layer is composed of a SiO_2 film and a Si_3N_4 film. 3. The metal/insulator/semiconductor capacitor type oxygen gas sensor according to claim 1 or 2, wherein the solid electrolyte layer is made of a ZrO_2 film doped with Y_2O_3 or CaO. 4. The metal/metal material according to claim 1 or 2, wherein the solid electrolyte is a LaF_3 film.
Insulator/semiconductor capacitor type oxygen gas sensor. 5. The metal/insulator/insulator according to any one of claims 1 to 4, wherein the metal electrode is made of any one of platinum, palladium, iridium, or gold. Semiconductor capacitor type oxygen gas sensor.