Hydrogen-sensitive I–V characteristics of metal–ferroelectric gas sensor device fabricated by sol–gel technique

A new type of metal–ferroelectric gas sensor device was fabricated on platinum-coated n-type silicon with an amorphous ferroelectric (Ba0.67Sr0.33)Ti1.02O3 (BST) layer of thickness 125 nm prepared by the sol–gel technique and annealed at temperatures ranging from 400 to 650°C. A layer of palladium 50 nm thick was deposited through an evaporation mask, and a layer of gold 400 nm thick was then deposited to provide the electrical contact. Measurements were made for the current–voltage characteristics and their time dependence before and after the introduction of hydrogen gas. The devices showed good hydrogen sensitivity of greater than 30 nA at the operating temperature range of 230–270°C. The I–V curve shift of 750 mV to 4.6 V was detected under the influence of 5–1042 ppm of hydrogen gas in air. The effects of bias voltage and operating temperature on the response and recovery times were studied. A model is also proposed in this paper to explain the key role played by the hydrogen ions at the metal–ferroelectric heterostructure interface and the related large Schottky barrier height-lowering phenomenon.