Electrochemical carbon dioxide sensor for measuring $CO_2$ concentration in air has been fabricated by tape casting method. By using tape casting method, sensor fabrication process could be simple and easy compared with screen printing or other method. On the other hand, compromising heterojunction structure of the sensor which is composed of Na-$\beta$''-alumina (NBA) in contact with Yittria Stabilized Zirconia (YSZ) is highly risky procedure because of different thermal expansion and extraction coefficient between different material. Also, alumina substrate with printed heater pattern should also be attached to this structure which makes harder triple junction structure. In this study, the structural stabilization process by changing sensor structure and abrication
method. Also, after the establishment of sensor structure, various test has been put in to practice for comparing superiority of newly produced sensor. The most representative test field in this type of sensor is initial stabilization time test and long-term stability test.