JPH04291144A - Manufacture of solid electrolyte gas sensor - Google Patents

Abstract

PURPOSE:To obtain a method for manufacturing a compact sensor with an improved accuracy. CONSTITUTION:A solid electrolyte film 4 which is sandwiched by electrode films 5 and 6 is formed by repeating formation of a film and etching on an upper surface of a substrate 2. A lower surface of the substrate 2 up to a lower electrode film excluding a peripheral portion is eliminated by etching, thus forming a cavity 31. A pin hole 31 reaching the cavity 31 through an upper surface of the substrate 2 is formed by etching and a lower surface periphery portion of the substrate 2 is joined to a pedestal 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a solid electrolyte gas sensor,
In particular, the present invention relates to a method of manufacturing a limiting current type solid electrolyte gas sensor.

0002

[Prior Art] In this type of solid electrolyte sensor, electrodes are provided on both sides of a solid electrolyte exhibiting oxygen ion conductivity such as stabilized zirconia, and one electrode is brought into contact with exhaust gas and the other with the atmosphere. Oxygen sensors that measure the oxygen concentration in exhaust gas by generating an electromotive force between electrodes depending on the difference in oxygen ion concentration are often used in vehicles.

In this case, since the output voltage of the oxygen sensor changes suddenly around the stoichiometric air-fuel ratio, it is effective for detecting the stoichiometric air-fuel ratio, but is not suitable for controlling the air-fuel ratio at other ratios.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 60-252254, the electrode on the side that is in contact with the exhaust gas, which is the gas to be measured, is covered with a capsule provided with a small-diameter oxygen diffusion hole, and oxygen flows into the capsule through the diffusion hole. A limiting current type solid electrolyte sensor has been proposed that saturates the ion current (limiting current) by balancing oxygen molecules and oxygen molecules discharged to the outside via the solid electrolyte, and enables good detection over a wide concentration range. ing.

[0005]

[Problems to be Solved by the Invention] Incidentally, the diameter of the oxygen diffusion hole is an important factor that determines the performance of the sensor, but the capsule in the above-mentioned conventional sensor is often made of a ceramic material that is difficult to process. It is difficult to form small holes in such capsules with high accuracy in terms of productivity, and it is also difficult to miniaturize the sensor.

[0006] The present invention has been made to solve these problems, and it is an object of the present invention to provide a method for manufacturing a solid electrolyte sensor that can mass-produce small, highly accurate sensors.

[0007]

[Means for Solving the Problems] The manufacturing method of the present invention includes the steps of repeating film formation and etching on the upper surface of a substrate 2 to form a solid electrolyte film 4 sandwiched between upper and lower electrode films 5 and 6; A step of etching away the bottom surface of the substrate 2 up to the lower electrode film 5 except for the peripheral portion to form a cavity 31, and etching a pinhole 32 penetrating the top surface of the substrate 2 to reach the cavity 31. and a step of joining the lower peripheral edge of the substrate 2 to the pedestal 1.

In the manufacturing method of the present invention, the sensor is manufactured by film formation and etching, and since there is no mechanical manufacturing process such as drilling holes in ceramic, it is possible to mass-produce small-sized sensors with high precision.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. 1 and 2 show a micro gas sensor for oxygen detection manufactured by the manufacturing method of the present invention. In the figure, a substrate 2 made of silicon single crystal is bonded to a glass pedestal 1 via a bonding layer 11, and an insulating film 21 made of silicon oxide film (SiO2) is formed on the upper surface of the substrate 2. There is. A solid electrolyte membrane 4 made of stabilized zirconia or the like is buried approximately in the center of the insulating film 21.
Platinum electrode films 5 and 6 are formed on the upper and lower surfaces of. These electrode films 5 and 6 include a lead portion 51 made of platinum,
61, it is connected to an external circuit.

A cavity 31 is formed in the substrate 2 below the solid electrolyte membrane 4 in contact with the lower electrode membrane 5.
1 maintains communication with the outside through a pinhole 32 provided in the insulating film 21. This pinhole 32 makes the cavity 3
The introduction of the gas to be measured into the cavity 31 is restricted, and the cavity 31 and the pinhole 32 function as a diffusion restriction section that restricts the movement or diffusion of the gas to be measured to the lower electrode film 5 in contact with the cavity 31. Further, on the insulating film 21, a solid electrolyte film 4 is provided.
A heater film 7 is formed to cover the periphery of the heater film 7, and an end portion 71 of the heater film is connected to a power source (not shown).

Next, the manufacturing process will be explained with reference to FIGS. 3 to 5. In the step of FIG. 3(1), the surface of the silicon substrate 2 is thermally oxidized, and a SiO2 insulating film 2 of approximately 7000 Å is formed on the upper and lower surfaces of the substrate 2.
, 22. Next, a part of the SiO2 insulating film 21 on the upper surface of the substrate 2 is removed by a known photo-etching process. Here, for example, a photoresist is applied on the insulating film 21, the resist is hardened using a photomask depicting the patterning of the insulating film 21, and then a mixture of about 1:9 of hydrofluoric acid and ammonium fluoride is used. Insulating film 2
1 predetermined location is removed. Thereafter, the resist is removed by washing with running water.

In the step of FIG. 3(2), the insulating film 21
A platinum (Pt) film 51 with a thickness of about 1000 Å is formed on the upper surface by sputtering. Subsequently, in step (3), the Pt film 51 is removed by a photo-etching process except for the necessary portion, and the Pt film 51 is patterned to form the lower electrode film 5. Here, for example, argon ion milling method is used for etching the Pt film.

In the step shown in FIG. 3(4), the solid electrolyte film 4 is formed on the upper surface of the insulating film 21 and the lower electrode film 5. Examples of solid electrolytes include zirconia (ZrO2), calcium oxide (CaO), and yttrium oxide (Y2O3).
), ytterbium oxide (Yb2O3), etc. from several % to
A solid electrolyte membrane 4 having a thickness of about 5000 Å is formed by high frequency sputtering using stabilized zirconia added at a ratio of more than 10%. As a method for forming the solid electrolyte membrane 4, in addition to PVD (physical vapor deposition) such as sputtering,
Thin film formation methods such as CVD (chemical vapor deposition) or spin coating may also be used.

Further, in the step shown in FIG. 3(5), a Pt film 61 with a thickness of about 5000 Å is formed on the upper surface of the solid electrolyte membrane 4 by high frequency sputtering, and as shown in FIG. 3(3) above.
Patterning is performed in the same manner as in the step of , and the upper electrode film 6
(Fig. 4 (6)).

In the step shown in FIG. 4(7), the solid electrolyte membrane 4 at the pinhole formation location is removed using a photo-etching process. First, a photoresist is applied to the upper surface of the solid electrolyte membrane 4, and after the resist is hardened using a photomask, a portion of the solid electrolyte membrane 4 is removed by a reactive ion etching method using a chlorine-based gas. After that, the resist is removed. The insulating film 21 exposed by this,
The resist is patterned by a photo process, and then pinholes 32 are formed by reactive ion etching using fluorine gas. Pinhole diameter is approximately 30μm
do.

Next, in the step shown in FIG. 4(8), the solid electrolyte membrane 4
and silicon nitride (SiN) on the surface of the insulating film 22.
) Films 81 and 82 were formed to a thickness of 2000 Å by plasma CVD method.
Form to a thickness of . After removing the SiN film 82 and the insulating film 22 below the substrate 2 by a photo-etching process (FIG. 4(9)), in the step of FIG. 5(10),
The substrate 2 is etched from below using a potassium hydroxide (KOH) solution. At this time, the SiN film 82 and insulating film 22 remaining from the step of FIG. 4(9) are used as an etching mask. Also, the part removed in this process is the cavity 31.
becomes.

In the step of FIG. 5(11), the SiN film 81,
82 is removed by plasma etching using fluorine gas. In the process shown in FIG. 5 (12), the sensor element is mounted on the glass pedestal 1 using an airtight method such as soldering or anodic bonding.

FIG. 6 shows the operating principle of this micro gas sensor. The gas to be measured passes through the pinhole 32 and is introduced into the cavity 31 inside the sensor, but at this time, the pinhole 32 restricts the diffusion of the gas. On the other hand, the electrode film 5
, 6, oxygen gas in the gas to be measured is ionized at the electrode 5 (cathode), passes through the solid electrolyte membrane 4, reaches the electrode membrane 6 (anode), and is gasified again. When the current flowing between the electrodes 5 and 6 is measured here, the gas supplied to the electrode film 5 is restricted by the pinhole 32, so the current flows as shown in the formula below, and the limiting current as shown in FIG. Show characteristics.

[0019] Il: Limiting current R: gas constant D0: Oxygen diffusion coefficient T: Absolute temperature S: Area of pinhole P: Total pressure of gas to be measured Po2: Oxygen partial pressure in the measured gas l: Pinhole length

When the applied voltage is set to a constant value, the current value is detected in proportion to the gas concentration to be measured, as shown in FIG. Therefore, by measuring the value of the ion current flowing between the electrode films 5 and 6, the oxygen concentration in the gas to be measured can be detected with high accuracy.

[0021]

[Effects of the Invention] As described above, according to the manufacturing method of the present invention,
By using etching technology and thin film formation technology, it is possible to make the sensor ultra-miniaturized.Furthermore, by making the sensor ultra-miniaturized, the temperature of the solid electrolyte can be quickly adjusted with low power, resulting in reduced power consumption, fast response, and rise time. can be shortened. It also has excellent mass productivity.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a gas sensor.

FIG. 2 is a cross-sectional view of the gas sensor.

FIG. 3 is a cross-sectional view showing the manufacturing process of the gas sensor.

FIG. 4 is a cross-sectional view showing the manufacturing process of the gas sensor.

FIG. 5 is a cross-sectional view showing the manufacturing process of the gas sensor.

FIG. 6 is a diagram showing the operation of the gas sensor.

FIG. 7 is a diagram showing the limiting current characteristics of a gas sensor.

FIG. 8 is a diagram showing oxygen gas concentration and ion current value.

[Explanation of symbols]

1 Pedestal 2 Board 31 Cavity 32 Pinhole 4 Solid electrolyte membrane 5, 6 Electrode film 7 Heater membrane

Claims (1)

[Claims] [Claim 1] A step of repeating film formation and etching on the upper surface of the substrate to form a solid electrolyte film sandwiched between upper and lower electrode films; A solid electrolyte gas sensor comprising: forming a cavity by etching away; forming a pinhole through the upper surface of the substrate to reach the cavity; and joining the peripheral edge of the lower surface of the substrate to a pedestal. Production method.