KR101967420B1 - A sensor for nox using semiconductor and a manufacturing mehtod thereof - Google Patents

Abstract

The present invention relates to a NOx sensor using a semiconductor and a method of manufacturing the same, and more particularly, to a NOx sensor using a Schottky junction between a semiconductor and a metal and a manufacturing method thereof.
The present invention relates to an n-type GaAs substrate having an uneven region on at least a part of its surface; A metal layer Schottky-bonded to the uneven region; And an electrode for applying a voltage to the substrate.

Description

TECHNICAL FIELD [0001] The present invention relates to a NOx sensor using a semiconductor,

The present invention relates to a NOx sensor using a semiconductor and a method of manufacturing the same, and more particularly, to a NOx sensor using a Schottky junction between a semiconductor and a metal and a manufacturing method thereof.

At present, NO, NO ₂ , CO, and CO ₂ among air pollutants are mostly generated by combustion or ignition of petroleum materials, and detection technology for preventing and eliminating these toxic gases is absolutely necessary.

The Si-based micro-electron mechanical system (MEMS) is known to have excellent gas sensitivity efficiency and repeatability. However, the manufacturing complexity, low yield, and costly use of expensive equipment have caused economic problems. In addition, sensors based on new materials such as SiO2 and CNTs remain in the research stage, and it is difficult to maintain reproducibility and reliability.

Particularly, the technology development of semiconductor sensors showing selective response to a specific gas such as NOx is weak.

In Korean Patent No. 167852 granted to the Korean Institute of Energy Research, as shown in FIG. 1, a semiconductor detection material manufactured on an alumina substrate 2 having an Au electrode 3 and a Pt resistance heater wire 1 is printed Drying, and heat-treating a semiconductor gas sensor for detecting nitrogen oxide gas.

A problem to be solved by the present invention is to provide a new semiconductor type gas sensor.

Another object of the present invention is to provide a new semiconductor gas sensor having selectivity for NOx gas.

A further object of the present invention is to provide a new method for producing a semiconductor gas sensor having selectivity for NOx gas.

In order to solve the above problems, a gas sensor according to the present invention includes:

An n-type GaAs substrate having an uneven region on at least a part of its surface;

A metal layer Schottky-bonded to the uneven region; And

And an electrode for applying a voltage to the substrate.

In the present invention, the n-type GaAs substrate may be a substrate using Si, Te or the like as an impurity.

In the present invention, it is preferable that the n-type GaAs substrate has an impurity concentration (doping level) of the upper layer on which unevenness is formed so as to increase sensitivity of the gas sensor is higher than that of the lower layer. In the practice of the present invention, it is preferable that the impurity concentration of the upper layer is higher than the impurity concentration of the lower layer by 1 x 10 ¹⁸ atoms / cm 3 or more. In a preferred embodiment of the present invention, the impurity concentration of the lower layer of the n-type GaAs substrate may be about 1 × 10 ¹⁸ atoms / cm 3, the impurity concentration of the upper layer is preferably 2 × 10 ¹⁸ to 5 × 10 ¹⁸ atoms / cm 3, Lt; ¹⁸ > atoms / cm < 3 >.

In the present invention, the 'upper layer' refers to a depth of about 3 to 5 μm from the upper surface of the substrate.

In the present invention, the concavities and convexities of the GaAs substrate may have a sharp edge shape, for example, a cone shape. If the irregularities of the GaAs substrate are increased, the uniformity is reduced and the sensitivity range is reduced. If the roughness of the irregularities of the GaAs substrate is small, the sensitivity of the gas sensor may be decreased.

In the present invention, the Schottky junction metal may be Au, Pt, Pb, or AuZn, preferably Au metal. In the practice of the present invention, the Schottky junction metal may have a thickness of 100 nm or less, preferably 50 nm or less, and more preferably 10 to 20 nm. If the thickness of the Schottky junction metal layer is increased, the applied electric current can be overcorrected to the electrode surface and the Schottky property can not be exhibited if the thickness of the metal layer is lowered.

In the present invention, the electrode may include an upper electrode positioned on the upper surface of the n-type GaAs substrate and a lower electrode located on the lower surface of the substrate. The electrode may be made of AuZn or AuGe.

In the present invention, a reverse voltage is applied to the electrode, and the presence of the gas is measured by the change of the current generated when the specific gas contacts the surface of the irregularity. The reverse voltage applied to the electrode is preferably -10 V or more, more preferably -10 V to -30 V so as to exhibit high sensitivity. If the range of the reverse voltage is excessively large, the device active layer may be damaged and the device characteristics may not be exhibited. If the range of the reverse voltage is smaller than the above range, the degree of the gas reaction may become difficult to understand.

In the present invention, the gas sensor has a ratio of a current amount of a sensor in a state in which a specific gas is absent and a changed amount of current amount of the sensor in the presence of a specific gas (I _changed / I _initial ) is 5% or more, preferably 10% , More preferably at least 15%, and even more preferably at least 50%.

In the practice of the present invention, the gas sensor can be varied in current within 30 minutes, preferably within 20 minutes, and most preferably within 10 minutes after exposure to gas for effective operation, It can be a sensor that can be restored to the original amount of current within a short time.

In the present invention, the gas sensor can detect NOx gas, preferably NO ₂ , and can selectively detect NO, CO, CO 2 gas, and the like. The concentration of NOx in the measuring gas is preferably not less than 10 ppm, preferably not less than 50 ppm, more preferably not less than 70 ppm, even more preferably not less than 100 ppm so that the gas sensor can cause a change in the amount of current sufficient to detect the gas It is good.

According to an aspect of the present invention, there is provided an n-type GaAs substrate, comprising: an n-type GaAs substrate having an uneven region on at least a part of its surface;

A metal layer Schottky-bonded to the uneven region; And

And an electrode for applying a voltage to the substrate.

The present invention, in one aspect,

forming a high-concentration n-GaAs layer having a high concentration of impurities on an n-GaAs substrate;

Forming an electrode on upper and lower surfaces of the substrate on which the high concentration n-GaAs layer is formed;

Etching the upper surface of the substrate to form irregularities;

Forming a Schottky-bonded metal layer on an upper surface of the substrate;

The present invention also provides a method of manufacturing a semiconductor type gas detection sensor.

In the present invention, the irregularities of the GaAs substrate are formed by dipping the substrate in an acid solution, and the acid solution is composed of a mixture of sulfuric acid, nitric acid, and water.

In the present invention, an n-type GaAs layer having a doping level of 5 x 10 ¹⁸ atoms / cm 3 was deposited on a general GaAs substrate by using a MOCVD system in a thickness of about 10 μm or more. Nitric acid: pure = 5: 1: 5) for more than 30 seconds and then dried with N2 after pure cleaning.

In the present invention, a schottky contact was formed by depositing a thin Au film of about 20 nm thickness on the irregular surface of n-type GaAs using a thermal evaporator, and the specific NO ₂ gas was detected by forming the schottky contact.

The gas sensor according to the present invention is capable of selective detection of NOx, particularly NO _2. Also provided is a method of fabricating a sensor capable of NO ₂ gas detection by growing a 20 nm thick Au thin film on the irregular surface of n-type GaAs produced by a simple and effective mixed solution. The use of mixed solution shortened the process process.

In the present invention, the surface of the n-type GaAs layer grown by MOCVD is formed into a concavo-convex shape that is advantageous for gas detection by using a specific mixed solution (sulfuric acid: nitric acid: pure water) to produce a gas sensor advantageous for specific NO2 gas detection. Au thin films with a thickness of 20 nm or less were deposited on the irregular surface of n - type GaAs for the Schottky contact effect for NO2 gas detection, and the detection efficiency was increased.

1 is a simplified schematic representation of the structure of an n-type GaAs-based NO ₂ gas sensor fabricated from the present invention.
2 is a surface image (a) of the manufactured n-type GaAs-based NO2 gas sensor and a surface image of the n-type GaAs layer 4 on which the Au thin film 2 is formed.
3 is a voltage trace of the produced A1-1 and A1-2 sensors.
Figure 4 shows the characterization results for the 100 ppm NO ₂ of the produced n-type GaAs-based NO2 gas sensor (A1-1).
FIG. 5 shows the results of the characterization of 10 ppm NO ₂ of the manufactured n-type GaAs-based NO ₂ gas sensor (A1-1, A1-2).
FIG. 6 shows the analysis results of characteristics of the produced n-type GaAs-based NO ₂ gas sensor (A1-1, A1-2) for 100 ppm CO.
7 is a view for explaining the operation principle of the gas sensor according to the present invention.
8 is a perspective view of a conventional NOx sensor.

Hereinafter, the present invention will be described in detail with reference to examples. The following examples are intended to illustrate but not limit the present invention.

Example

Character analysis

1 is a simplified schematic representation of the structure of an n-type GaAs-based NO2 gas sensor fabricated from the present invention. In this structure, a high-concentration n-type GaAs layer 4 having a concentration of 5 × 10 ¹⁸ atoms / cm 3 or more was grown on an n-type GaAs substrate 5 by using an MOCVD vapor deposition apparatus, and AuZn and AuGe electrode materials were deposited on the upper electrode (1) and the lower electrode (6), respectively. The wafer with the electrodes formed thereon was etched in a mixed solution (sulfuric acid: nitric acid: pure water = 5: 1: 5) for about 30 seconds to obtain a roughened surface 3 favorable for gas detection.

A 20 nm thick Au thin film 2 was deposited on the n-type GaAs layer uneven surface 3 by thermal vapor deposition to form a Schottky contact. The gas and the reaction sensitivity can be known by the Schottky contact effect formed by the uneven surface and the bonding metal.

2 is a surface image (a) of the manufactured n-type GaAs-based NO2 gas sensor and a surface image of the n-type GaAs layer 4 on which the Au thin film 2 is formed. The sensor was a square model with a length of one side of 300 μm and an electrode with a branch attached to the top of the sensor was used to spread the current evenly. The irregular surface 3 of the n-type GaAs layer 4 formed by the mixed solution (sulfuric acid: nitric acid: pure water = 5: 1: 5) seems to rise around crushed craters of many needle- Holes are attracted to these needle-shaped models and are more sensitive to injected gases.

FIG. 3 is a current-voltage (I-V) characteristic curve of the manufactured sensor, showing normal Schottky diode characteristics.

Figure 4 shows the characteristic results for the 100 ppm NO ₂ of the produced n-type GaAs-based NO2 gas sensor. This result shows that a n-type GaAs-based NO2 gas sensor fabricated in a set capable of current-voltage application is installed inside a sealed case having a line in which a specific gas is injected and discharged, then 100 ppm NO2 gas is flowed, , -5V, -10V, and -30V, respectively. It was confirmed that NO 2, NO 2, CO, and CO ₂ gas were selectively injected into the n - type GaAs gas sensor.

Table 1 below shows the results of summarizing the degree of reaction according to the various reverse voltage changes under the injection of 100 ppm NO2 as shown in FIG.

Fig. 5 shows the reaction characteristics of a small amount of 10 ppm NO ₂ in the produced n-type GaAs-based NO ₂ gas sensor. At the time of confirmation, no normal gas response curve was observed until -20V reverse voltage application, but a normal gas response curve of 15% was observed at -40V reverse voltage.

FIG. 6 shows the result of analyzing the characteristics of the manufactured n-type GaAs-based NO ₂ gas sensor with respect to 100 ppm CO. Under the high COx gas volume (100 ppm) and high reverse voltage (-40 V) applied in conventional NOx, no gas response curve for Cox was observed. Therefore, it has been confirmed that the gas sensor fabricated in the present invention is a gas sensor that selectively reacts only with NOx gas

Claims (16)

An n-type GaAs substrate having an uneven region on at least a part of its surface;
A metal layer Schottky-bonded to the uneven region; And
And an electrode for applying a reverse voltage to the substrate,
Here, the n-type GaAs substrate is composed of an n-GaAs substrate layer and a high-concentration n-GaAs layer grown by MOCVD on the n-GaAs substrate layer,
Wherein the high concentration n-GaAs layer has an impurity concentration higher than that of the n-GaAs substrate layer by 1 x 10 ¹⁸ atom / cm ³ or more. delete The gas sensor according to claim 1, wherein an impurity concentration of the high concentration n-GaAs layer is 1 x ^{10 18} to 5 x 10 ¹⁸ atoms / cm ³ . The gas sensor according to claim 1, wherein the concavities and convexities are in the form of an edge. The gas sensor according to claim 1, wherein the Schottky junction metal is Au, Pt, Pb, or AuZn. The gas sensor according to claim 1, wherein the Schottky junction metal has a thickness of 10 to 20 nm. The gas sensor according to claim 1, wherein the electrode is an AuZn or AuGe electrode. delete The gas sensor according to claim 1, wherein the reverse voltage is a reverse voltage of -10V to -30V. The gas sensor according to claim 1, wherein the gas is NO ₂ . An n-type GaAs substrate having an uneven region on at least a part of its surface;
A metal layer Schottky-bonded to the uneven region; And
And an electrode for applying a reverse voltage to the substrate,
Here, the n-type GaAs substrate includes an n-GaAs substrate layer and a high-concentration n-GaAs layer grown by MOCVD in the n-GaAs substrate layer,
Wherein the concentration of the impurity in the high-concentration n-GaAs layer is higher than that of the n-GaAs substrate layer by 1 x 10 ¹⁸ atoms / cm ³ or more. forming a heavily doped n-GaAs layer having a high concentration of the impurity in the n-GaAs substrate by MOCVD, wherein the heavily doped n-GaAs layer is compared with the n-GaAs substrate on which the impurity concentration is high more 1x10 ¹⁸ atom / cm ³ or higher ;
Forming an electrode on upper and lower surfaces of the substrate on which the high concentration n-GaAs layer is formed;
Etching the upper surface of the substrate to form irregularities; And
Forming a Schottky-bonded metal layer on an upper surface of the substrate;
Wherein the gas detection sensor comprises: 13. The method of manufacturing a gas detection sensor according to claim 12, wherein the concave and convex portions of the GaAs substrate are made by immersing the substrate in an acid solution. 14. The method of claim 13, wherein the acid solution is a solution of a mixture of sulfuric acid, nitric acid, and water. delete 13. The method of claim 12, wherein forming the schottky contact is performed by depositing a thin Au film of 100 nm or less on the irregular surface of the n-type GaAs using a thermal evaporator.

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