Capacitive humidity sensors based on PVA/CAB compound film with potassium acetate-enhanced sensitivity

This paper presents a capacitive humidity sensor utilizing compound sensitive film based on polyvinyl alcohol (PVA). PVA is a water-soluble polymer structuring with a lot of hydrophilic groups, so PVA film has the problem of hydrolysis due to its long-term exposure to high-humidity environment. In the novel capacitive humidity sensor, a layer of cellulose acetate butyrate (CAB) covered on PVA humidity sensitive layer acts as protective layer, and improves linearity of the sensor simultaneously. In order to improve the sensitivity of the humidity sensor, potassium acetate is mixed in PVA film. SEM images show that a number of uniform microporous structures take place in PVA film due to the introduction of potassium acetate, the humidity sensitive layer is completely covered by CAB film. The fabricated novel capacitive humidity sensors exhibit a good linear capacitive data response ( $\mathrm{R}^{2}=0.8515$ ) with a high sensitivity of 1.41pF/%RH over a wide relative humidity range of 10%RH to 90%RH, and have good repeatability, fast response and recovery times over 25%RH to 75%RH. Combined with the excellent biodegradability of PVA and CAB, this humidity sensor has broad application prospects such as respiratory monitoring, agricultural production and so on.