JPH06103285B2 - Semiconductor gas detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered body of a gas sensitive semiconductor containing SnO ₂ , ZnO or the like as a main component and enclosing a single metal wire coil into a bead shape, and heating the metal wire coil. The present invention relates to a semiconductor gas detection element used as an electrode for detecting a change in electric resistance of a sintered body.

[0002]

2. Description of the Related Art A gas-sensitive semiconductor causes a change (in many cases, a decrease) in electric resistance value when placed in a test gas atmosphere. At that time, in order to change the gas adsorption / desorption rate and the resistance value with a practical size, it is usually used at a temperature considerably higher than room temperature (often 300 ° C. or higher). Therefore,
A practical gas detection element using a semiconductor includes some heating means for raising the temperature of the semiconductor.

Furthermore, it goes without saying that some kind of electrode is provided to detect a change in the resistance value of the semiconductor. Thus, semiconductors gas detecting element,
Generally they are both equipped with a heater resistance value change detecting electrodes.

As a semiconductor gas detecting element that performs such two functions by a single metal wire coil, there is a type shown in FIG.

In FIG. 4, 1 is a metal wire coil, 2 is a sintered body of a gas sensitive semiconductor, and 3 is a metal pin. The operation of this semiconductor gas detecting element will be described below.

The semiconductor gas detecting element is heated by passing an appropriate current through the metal wire coil 1. Also,
The change in the resistance value of the sintered body 2 is detected as a resistance value at both ends of the metal wire coil 1, that is, a combined change in the resistance value of the combination of the metal wire coil 1 and the sintered body 2. Hereinafter, this combined resistance value will be referred to as a sensor resistance value R.

Now, the resistance value of only the metal wire coil 1 is R _C ,
The resistance value R _C of the metal wire coil 1 is effectively applied to the portion of the sintered body 2.
Assuming that the resistance value of the parallel resistance of R is R _S , the sensor resistance value R is

[0008]

[Equation 1] Becomes This is illustrated in FIG. The presence of the test gas is detected as a change in the resistance value R _S of the sintered body 2 due to the test gas as a change in the sensor resistance value R according to the equation (1).

[0009]

The wire used for the metal wire coil 1 as the heater and electrode as described above is excellent in heat resistance, corrosion resistance and electrical contact with the sintered body 2. Conventionally, Pt wire is used. However, the Pt wire has a problem that the specific resistance is not sufficiently large and therefore the detection sensitivity is insufficient.

It is an object of the present invention to provide a semiconductor gas detection element using a Pt alloy wire which can have a higher detection sensitivity without significantly changing the corrosion resistance and the like as compared with the Pt wire.

[0011]

A semiconductor gas detecting element according to the present invention has a bead-like structure in which a single metal wire coil is wrapped with a sintered body of a gas sensitive semiconductor, and the metal wire coil is heated. In the gas detection element used as the heater for the heater and the electrode for detecting the change in the electric resistance value, the metal wire coil is
It is composed of a Pt alloy wire containing any one of h, Ir and Ni in the range of 5 to 30%.

[0012]

In the present invention, as the metal wire coil, Rh,
Since the Pt alloy wire in which the content of one of Ir and Ni is 5 to 30% is used, the specific resistance can be increased and the gas detection sensitivity can be improved as compared with the Pt wire alone without significantly changing the corrosion resistance. .

[0013]

EXAMPLE A semiconductor gas detecting element of the present invention has a metal wire coil containing 5 to 3 of any one of Rh, Ir and Ni.
The Pt alloy wire is 0%. Hereinafter, examples of the present invention will be described by dividing the specific resistance and the temperature coefficient of resistance of the metal wire.

(A) Specific resistance of the metal wire rod In order to extract the change in R _S due to the test gas as the change in the sensor resistance value R as large as possible, it is desirable that R _S be smaller than R _C. However, since it is not so easy to reduce the resistance value of the sintered body 2, it is necessary to make R _C as large as possible in order to properly balance R _C and R _S. Therefore, the wire diameter of the metal wire coil 1 may be reduced or the number of turns may be increased, but there is a limit to that.

Therefore, in the present invention, instead of pure Pt wire,
For example, if a Pt alloy wire containing Rh is used, as shown in FIG. 1, at 400 ° C., the specific resistance ρ _C (400 ° C.) of the wire is R
When the h content is 5 to 30%, it is 25% or more of pure Pt,
It can be seen that at 20%, it increases by nearly 40%. Thus, by using the Pt-R h alloy wire suitable Rh content,
There is an advantage that the existence of the test gas is used as a sensor output and is taken out more efficiently.

[0016] The above Pt- although a was the case of R h alloy wire, this addition may be used alloy wire, such as Pt-Ir, Pt-Ni. Table 1 below summarizes the specific resistance ρ _C (20 ° C.) at 20 ° C. of the Pt alloy wire used in the present invention.

[0017]

[Table 1] (10 ^-5 Ωcm) (b) Temperature coefficient of resistance of metal wire When a change in the sensor resistance value R is detected by applying a constant voltage or a constant current to the gas detection element, the change in the sensor resistance value R Correspondingly, the power consumption of the gas detection element changes, causing the temperature of the gas detection element to change. Order to suppress this temperature change, in order to reduce the power consumption changes may be made smaller to R _C compared to R _S but based on R _S changes due to the test gas as evidenced by the previous discussion when too small Since the change in R becomes small, the sensitivity of the so-called gas detection element becomes low. Therefore,
R _C cannot be simply reduced. Also, R _C
Is appropriately large, the larger the resistance temperature coefficient of R _C , the more the power consumption of the gas detection element is affected. Therefore, it is desirable to use a wire rod having a small temperature coefficient for the metal wire coil 1.

However, the temperature coefficient of resistance of Pt is much larger than that of a heating wire such as a nichrome wire (a base metal wire such as a nichrome wire cannot be used in terms of corrosion resistance). Therefore, in order to reduce the temperature coefficient of resistance α without significantly changing the corrosion resistance and the like, as a wire material of the alloy wire coil, for example, Rh is used.
It is effective to use a Pt-R h alloy wire containing.

As shown in FIG. 2, the temperature coefficient of resistance α (0 to 100 ° C.) increases as the content of R h with respect to Pt increases.
Decreases first and then increases again. Content of 5 to 70%, α
Value is about 55% of pure Pt wire, and the content is 10-60
% Is 50% or less of the pure Pt wire. If the temperature of the gas detection element is 400 ° C. and the gas to be detected lowers the temperature by 100 ° C. (that is, reaches 300 ° C.), the resistance value R _C of the metal wire coil 1 is shown in FIG. Decrease as there is (R _C (300 ° C) / R _{C in the} figure)
(Expressed at 400 ° C.). Is a 15.4% reduction if Pt wire is about 11.5% in the Rh content of 5 to 65% of the Pt-R h line, the content of 10-15%, suppressed within approximately 10% Has been. Therefore, a suitable R
If the h content Pt-Rh line is used, it is possible to suppress a change in the temperature of the gas detection element due to the presence of the test gas.
Even when a small amount (for example, 0.1%) of a suitable oxide such as ZrO ₂ or TiO ₂ is dispersed and added, the effect of alloying is the same.

Although the above is the case of the Pt-Rh alloy wire, other alloy wires such as Pt-Ir and Pt-Ni can also be used. Table 2 below shows Pt used in the present invention.
The temperature coefficient of resistance α of the alloy wire is shown together.

[0021]

[Table 2] (× 10 ⁻⁴ / ° C.) Advantages described in (1) and (2) above and Rh content of 3
Considering from the point that workability deteriorates when it exceeds 0%, R
It seems that the practical range of the h content is 5 to 30%. In addition , a similar effect was obtained with a Pt alloy wire containing 5 to 30% of either Ir or Ni .

[0022]

As described in detail above, according to the present invention, in a semiconductor gas detecting element having a bead-like structure in which a single metal wire coil is wrapped with a sintered body of a gas sensitive semiconductor, a heater / electrode for heating is also used. Since a Pt alloy wire containing any one of Rh, Ir, and Ni in an amount of 5 to 30% was used instead of the pure Pt wire as described above, the heat resistance of the metal wire coil
With the advantage that the existence of the test gas can be more sensitively taken out as the sensor output without changing the corrosion resistance etc.
It has an advantage that a change in power consumption of the gas detection element in a gas atmosphere can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between Rh content and specific resistance with respect to Pt for explaining the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the content of Rh and the temperature coefficient of resistance α.

FIG. 3 Rh content and resistance of metal wire coil of 300 ° C.
It is a figure which shows the relationship between and the ratio in 400 degreeC.

FIG. 4 is a schematic configuration diagram of a main part showing an example of a conventional semiconductor gas detection element.

FIG. 5 is an equivalent circuit diagram of FIG.

[Explanation of symbols]

 1 Metal wire coil 2 Sintered body 3 Metal pin

Claims (1)

[Claims] 1. A gas having a structure in which a single metal wire coil is wrapped in a sintered body of a gas sensitive semiconductor to form a bead, and the metal wire coil is used as a heater for heating and an electrode for detecting electric resistance value change. In the detection element, the metal wire coil is made of any one of Rh, Ir and Ni in an amount of 5 to 30%.
2. A semiconductor gas detecting element, characterized in that it is composed of a Pt alloy wire contained in the range of.