Abstract:
Disclosed are a gas sensor, and a method of manufacturing and using the same. The method includes: forming a detection material on a heater; coating an encapsulant on the detection material; and heating the heater to remove the encapsulant from the detection material when the gas sensor is operated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority from Korean Patent Application No. 10-2011-0104493, filed on Oct. 13, 2011, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a gas sensor, and more particularly, to a gas sensor for preventing an electrical property thereof from being changed by toxic gases, moisture or UV rays when the gas sensor is stored for a long time, and a method of manufacturing and using the same. 
     BACKGROUND 
     A semiconductor gas sensor is operated to determine a concentration of a detection gas by using a degree by which a resistance of a detection material such as a metal oxide, a polymer and a carbon nano tube is changed during an oxidation/reduction reaction of the detection gas and the detection material. To this end, the semiconductor gas sensor employs a dedicated heater for a smooth oxidation/reduction reaction of a detection gas and a detection material, and such a reaction is generated in a temperature section of 200 to 500 degrees Celsius. 
     An electrochemical gas sensor is operated to determine a concentration of a gas through a degree by which a current or an electromotive force is changed while the detection gas and a detection material such as an alkaline metal or an alkaline earth metal carbonate react each other at a high temperature to influence an ion conductivity of a solid electrolyte. 
     The semiconductor gas sensor or the electrochemical gas sensor employs a heater therein in terms of operation principle. The detection material used for the semiconductor gas sensor or the electrochemical gas sensor mainly includes a metal oxide, an alkaline metal carbonate, a carbon nano tube, graphene or a polymer. 
     However, a gas sensor according to the related art is known that sensitivity, selectivity and the like are influenced by humidity, that is, water molecules in the air (Jianwei Gong et al., Sensors and Actuators B 114(2006) 32-39). To solve this problem, a study for improving humidity stability of a gas sensor through a filter for adsorbing moisture to a gas inlet port or removing moisture from the gas inlet port while the gas sensor is packaged (U.S. Pat. No. 5,841,021). Such a filter technology helps remove moisture of a part of a gas sensor and secure stability of the gas sensor, deteriorates efficiency of the gas sensor in a situation where excessive moisture is present. And the filter has a limit in life when the filter is stored for a long time. Therefore, a process of replacing a filter after a predetermined time period is required to protect a gas sensor. 
     SUMMARY 
     The present disclosure has been made in an effort to provide a gas sensor for preventing an electrical property thereof from being changed by toxic gases, moisture or UV rays when the gas sensor is stored for a long time, and a method of manufacturing and using the same. 
     An exemplary embodiment of the present disclosure provides a gas sensor including: a heater; a detection material formed on the heater; and an encapsulant sealing the detection material. 
     Another exemplary embodiment of the present disclosure provides a method of manufacturing and using a gas sensor, including: forming a detection material on a heater; coating an encapsulant on the detection material; and heating the heater to remove the encapsulant from the detection material when the gas sensor is operated. 
     According to the exemplary embodiments of the present disclosure, by providing a gas sensor which coats a detection material with an encapsulant and removes the encapsulant from a detection material by using a heater installed therein shortly before the gas sensor is used, and a method of manufacturing and using the same, it is possible to secure stability during storage of the gas sensor, and to effectively utilize the gas sensor while excluding a poisoning phenomenon due to a long time storage of the gas sensor. 
     Further, according to the exemplary embodiments of the present disclosure, it is possible to replace a poisoned gas sensor and operate a reliable sensor node by providing a gas sensor which removes an encapsulant of a preliminary gas sensor by using a heater installed therein according to an encapsulant thermal decomposition command or an algorithm for removing the encapsulant from a server if a poisoning phenomenon of a gas sensor in operation is detected when a plurality of preliminary gas sensors are stored at sensor nodes by using an encapsulant, and a method of manufacturing and using the same. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view illustrating a structure of a gas sensor according to an exemplary embodiment of the present disclosure. 
         FIG. 2  is a process flowchart illustrating a method of manufacturing and using a gas sensor according to an exemplary embodiment of the present disclosure. 
         FIG. 3  is a view illustrating an application example of a gas sensor according to an exemplary embodiment of the present disclosure. 
         FIG. 4  is a graph for comparing detection characteristics of a general gas sensor and a gas sensor sealed by an encapsulant to formaldehyde. 
         FIG. 5  is a graph for comparing detection characteristics of a general gas sensor and a gas sensor from which an encapsulant is removed to formaldehyde. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawing, which form a part hereof. The illustrative embodiments described in the detailed description, drawing, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In describing the present disclosure, a detailed description of related known configurations and functions will be omitted when it may make the essence of the present disclosure obscure. 
       FIG. 1  is a sectional view illustrating a structure of a gas sensor according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 1 , a gas sensor according to the present disclosure includes a heater  110 , a detection material  120 , an encapsulant  130 , and the like. Here, the gas sensor may be a semiconductor gas sensor, an electrochemical gas sensor or the like. 
     The heater  110  is an alumina heater, and generates heat by using a voltage and a current applied thereto. The heater  110  according to the present disclosure may be used to coat the encapsulant  120  on the detection material  120  or to remove the encapsulant  130  from the detection material  120 . 
     The detection material  120  is formed on the heater  110  and is SnO 2 . Here, the detection material  120  detects the detection gas through a change in resistance, current, electromotive force or the like. 
     The encapsulant  130  is coated on the detection material to protect the detection material  120  from toxic gases, moisture, oxygen, UV rays and the like. Here, the encapsulant  130  is formed in the form of a film having a thickness of 100 to 200 μm. 
     The encapsulant  130  may be any one of a polymer such as poly(vinyl alcohol-co-ethylene), poly(vinylidene difluoride), poly(vinylidene dichloride), poly(vinylidene chloride-co-methylacrylate) and the like and inorganic particles such as aluminum oxide, silicon oxide, silicon nitride, aluminosilicate, metal nanoparticles, quantum dots, and the like, or a combination thereof. 
     Thus, when the gas sensor according to the present disclosure is operated, the heater  110  may be heated to a thermal decomposition temperature of the encapsulant  130  or higher to thermally decompose the encapsulant  130  while removing the encapsulant  130  from the detection material  120 . Accordingly, the detection material  120  is exposed to the detection gas such that the gas sensor is operated. 
       FIG. 2  is a process flowchart illustrating a method of manufacturing and using a gas sensor according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 2 , the detection material  120  is formed on the heater  110  through screen printing (S 210 ). 
     Next, the encapsulant  130  is coated on the detection material  120  through a method such as pressing, thermocompression binding, spin coating, drop coating, dip coating, spray coating, and the like (S 220 ). In this case, when the encapsulant  130  is coated through thermocompression binding, the encapsulant  130  may be heated to a glass transition temperature or higher (for example, 150 to 170 degrees Celsius) to be coated by using an external heater or an embedded heater  110  having therein. When the encapsulant  130  is coated through pressing or thermocompression binding, an encapsulant  130  in the form of a film having a thickness of 100 to 200 μm may be used. 
     When an operation of the gas sensor is required to detect a gas after the gas sensor is stored, the heater  110  is heated to a thermal decomposition temperature of the encapsulant  130  or higher (for example, 550 degrees Celsius) to thermally decompose the encapsulant  130  while removing the encapsulant  130  from the detection material  120  (S 230 ). Accordingly, the detection material  120  is exposed to the detection gas such that the gas sensor is operated. 
       FIG. 3  is a view illustrating an application example of a gas sensor according to an exemplary embodiment of the present disclosure. 
     A plurality of the gas sensors according to the present disclosure may be installed wirelessly or through wires in various environments for the purpose of monitoring the environments in measurement spaces. When the detection materials of the gas sensors are poisoned by toxic gases, moisture, UV rays and the like in such environments, the gas sensors may not be normally operated to fail to effectively monitor atmospheric environment information in the measurement spaces, acting as a serious failure factor of the entire atmosphere monitoring system. 
     Accordingly, as illustrated in  FIG. 3A , a plurality of gas sensors  320  are preliminarily mounted to sensor nodes, and the sensor nodes are sealed by encapsulants  322  to be protected from a poisoning factor in a measurement space. 
     As illustrated in  FIG. 3B , when the gas sensor  310  in operation is poisoned to show an abnormal behavior, one encapsulant  322  is removed from the preliminary gas sensor  310  according to an encapsulant thermal decomposition command or an algorithm for removing the encapsulant from a server to operate the gas sensor  310 . 
       FIG. 4  is a graph for comparing detection characteristics of a general gas sensor and a gas sensor sealed by an encapsulant to formaldehyde. 
     When a sensor resistance in an environment without formaldehyde is Ra and a sensor resistance during a measurement of formaldehyde is Rg, a sensitivity (%) of a gas sensor is defined as |Ra−Rg|/Ra*100. 
     As illustrated in  FIG. 4 , it can be seen that, in the case of a gas sensor  410  where a detection material is not sealed by an encapsulant, sensitivity is changed from 10% to 45% under a condition where formaldehyde of 0.2 ppm to 2 ppm is present. 
     It can be also seen that, in a gas sensor  420  where a detection material is sealed by an encapsulant, sensitivity is a value ranging from 0 to 5% regardless of a concentration of formaldehyde. Through this, it can be seen that an encapsulant protects a detection material from an exterior toxic gas. 
       FIG. 5  is a graph for comparing detection characteristics of a general gas sensor and a gas sensor from which an encapsulant is removed to formaldehyde. 
     Referring to  FIG. 5 , it can be seen that, in the case of a gas sensor  520  from which an encapsulant is removed, a general gas sensor  510  does not react formaldehyde at all when sealed by an encapsulant, whereas the gas sensor  520  shows a sensitivity performance of approximately ½ of that of the general gas sensor  510  after encapsulant is removed. The sensitivity performance is a level which does not matter at all in the gas sensor detecting formaldehyde. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.