MOS hydrogen sensor with very fast response based on ultra-thin thermal SiO2 film

An MOS capacitor-type hydrogen gas sensor was fabricated with the structure of Ni/SiO2/Si by using conventional silicon wafer technologies. Grown by dry oxidation at 900°C, the thickness of the SiO2 film was only 24 Å. At 150°C, comparing to another MOS capacitor with 148 Å-thick oxide and otherwise identical configurations, this sensor showed much faster response speed (the time interval to reach half of the magnitude of the steady-state signal, or t50%, was only 4 s in response to 1% H2 without deduction of the delay from the gas delivery system), as well as enhanced signal magnitude (about two times of the former for 1% H2). Based on the hydrogen-binding to the traps in the bulk SiO2, a mechanism was proposed to explain the very short response time on the device with the ultra-thin SiO2. The gate leakage in the device is also discussed. The presented sensor demonstrates a promising step in designing low-cost H2 detectors with very fast responses.

Research highlights
► An MOS capacitor with a 24 Å-thick SiO2 film was fabricated.
► The device showed very fast response to H2 (4 s).
► The rapid response was attributed to the ultra-thin SiO2.