Gas sensor and manufacturing method thereof

Abstract

A gas sensor and manufacturing method thereof. The gas sensor includes a substrate, a pair of electrodes disposed on the substrate, and a gas sensing thin film covering the electrodes, the gas sensing thin film is made up of carbon nanotubes and tin oxide.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a gas sensor and manufacturing method thereof. More particularly, the present invention relates to a gas sensor using carbon nanotubes and metal oxide as a sensing film. [0003] 2. Description of the Related Arts [0004] Naturally occurring gases such as carbon monoxide (CO), nitrogen oxides (NOx), hydrogen sulfide (H2S), or methane (CH4) can be hazardous to humans. These toxic gases are colorless and tasteless and cannot be easily detected by human senses. When the concentration of toxic gases in an environment exceeds an allowable range, symptoms of headache, dizziness, sickness, or even shock or death can result. Gas analyzers provide real-time monitoring of gas content in airtight or unventilated environments, providing timely notification when the concentration of toxic gases exceeds a threshold. [0005] Atomic / molecular absorption spectrometry, atomic / molecular fluorescence spectr...

AI Technical Summary

Benefits of technology

The present invention provides a gas sensor with high sensitivity, good repeatability, and rapid recovery rate at room temperature. The sensor solves the problem of conventional semiconductor metal oxide gas sensors that require heat desorption of the gas chemically absorbed on the oxide layer. The gas sensor is economic in preparation. The gas sensing thin film comprises carbon nanotubes and tin oxide, wherein x=1-2, and the ratio of carbon nanotubes and tin oxide is 0.001-5 wt %, preferably 0.001-0.05 wt %. The manufacturing method for the gas sensor involves application of a mixture of carbon nanotubes and an organic tin compound or tin oxide to the substrate to cover the pair of electrodes, and heat-treating or drying the substrate to obtain the gas sensing thin film comprising carbon nanotubes and tin oxide.

Problems solved by technology

These toxic gases are colorless and tasteless and cannot be easily detected by human senses.

When the concentration of toxic gases in an environment exceeds an allowable range, symptoms of headache, dizziness, sickness, or even shock or death can result.

These gas analysis instruments have the advantages of high accuracy, high sensitivity, and low detection limit; however, their application is limited due to a large profile with low portability, high power consumption, structural complexity, and high cost.

These gas sensors are applicable at room temperature, however, they have a short lifetime due to the corrosive property of the liquid electrolyte.

In addition, calibration of the sensor baseline is required since chemical buildup at the reference electrode may cause baseline drift.

Moreover, electrochemical gas sensors are usually costly.

However, heat desorption of the absorbed gases at 200 to 500° C. is required, and the sensitivity of the sensor is not satisfactory.

High throughput production cannot be easily achieved due to the requirement of vacuum equipment; the thermal treatment also increases the cost; in addition, the working temperature of the sensor is 200-500° C.

The process is complicated and costly due to noble metals and multiple heat treatments.

In addition, the gas sensor cannot be used at room temperature.

This preparation is costly due to the heat treatment, and the gas sensor also needs to be used at 280-400° C.

This gas sensor is costly and has to be used at 180-400° C.

The drawbacks of these gas sensors include low sensitivity, selectivity, and stability with gas.

Longtime operation at high temperatures may, however, causes irreversible changes in the electrical properties of metal oxides, leading to signal drift.

The heating requirement of these gas sensors also evokes several problems such as increased size of the gas sensor, power consumption, and temperature control.

Therefore, the cost of the gas sensor cannot be reduced.

The sensor detects CH4 and C3H8 at a lower temperature, such as 150° C. for CH4 and 190° C. for C3H8; however, ion beam sputtering and Pt or Pd electrodes are costly, and the working temperature cannot be reduced to room temperature.

However, the sensor still cannot be used at room temperature.

The above mentioned sensors have a common problem-unable to be used at room temperature; therefore, researchers are focusing on the study of a sensor with low working temperature.

The disadvantage of the sensor is the difficulty of controlling sensor temperature since the temperature of the sensor is increased by lightening time.

In addition, the design for light induction is complicated and the cost cannot be reduced.

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