Structure and humidity sensing properties of barium strontium titanate/silicon nanoporous pillar array composite films

A composite thin film with regular pillar array structure was fabricated by applying a coating of barium strontium titanate (Ba0.7Sr0.3TiO3, or BST) to freshly prepared silicon nanoporous pillar array (Si-NPA) substrate. Capacitive humidity sensors were made based on this BST/Si-NPA thin film and the corresponding sensing properties were investigated. Experimental results showed that the sensor exhibited high sensitivity, fast response time and good stability. The capacitance increment was over 4400% of its initial value at relative humidity (RH) increased from 11 to 95% at 100 Hz signal frequency. The response time for both the RH-increasing and decreasing processes was ~ 42 s. The humidity sensing curves of fresh sensors aged for 9, 57 and 100 days exhibited an ideal coincidence. Both the pillar-like array structure and the thin film composition should play an important role in the improvement of sensing performance.