The Effect of SnO2 Mixture on a PVA-Based Thick Film Relative Humidity Sensor

Abstract

In this research, thick film technology has been used to design and fabricate relative humidity sensors with Polyvinyl Alcohol (PVA) as the sensing layer. The design was optimized to produce an ideal geometry according to the limitations of thick film technology. The sensor fabrication process used screen printing techniques on Alumina (Al2O3) substrate with Silver (Ag) as the electrode material. SnO2 was added to the PVA sensing layer with variations in the composition of 1:1 and 1:2. FTIR analysis showed that the addition of SnO2 did not affect the structure of the PVA, which indicated that there was no chemical reaction between PVA and SnO2. The deposition of the sensing layer was carried out using spin coating method, and the fabricated sensors were then tested by varying 5 humidity points inside a chamber with a hygrometer as a reference. Based on the test results, it was found that the sensors showed responses to humidity variation in the form of changes in resistance values. When the humidity in the chamber increased, the sensor resistance value decreased. The addition of SnO2 could reduce the relatively high resistance value of the PVA-based humidity sensor and also increase the sensor's time response to humidity variation. However, the humidity sensor's sensitivity decreased for the higher composition of SnO2. With this technique, a simple yet stable humidity sensor could be fabricated using thick-film technology with a wide range of potential applications.

Design and Fabrication of PVA-SnO2 Based Humidity Sensors

“…Adding metal oxides, such as SnO 2 , to PVA will not affect the polymer structure, as shown in previous studies [5]. The presence of metal oxides in the mix with PVA can affect sensor characteristics in two ways; a decrease in resistance value and an increase in response time when applied as a moisture-sensing layer.…”

“…The first sensing layer was prepared with PVA-SnO 2 with a ratio of 1:1 and 1:2. The composition of [5] is summarized in Table 1. The difference in paper [5][6] lies in the finger material using pure Ag (silver) metal, and this is intended to determine changes in resistance and sensitivity as well as the response time of the realized humidity sensor.…”

“…The composition of [5] is summarized in Table 1. The difference in paper [5][6] lies in the finger material using pure Ag (silver) metal, and this is intended to determine changes in resistance and sensitivity as well as the response time of the realized humidity sensor. The process of making the sensing layer by mixing it and then stirring it with DI water using a magnetic stirrer for 6 hours at 90°C until it is homogeneous.…”

“…The relative humidity (RH) unit is the ratio of the actual amount of moisture in the atmosphere to the amount of humidity it can hold at the same temperature and pressure. Unlike absolute humidity (AH), relative humidity depends on temperature and pressure [4][5][6].…”