THE EFFECT OF HYDROGEN AND CARBON-MONOXIDE ON THE INTERFACE STATE DENSITY IN MOS GAS SENSORS WITH ULTRA-THIN PALLADIUM GATES

The admittance of 25 Å palladium-gate MOS capacitors with 125 Å of silicon dioxide has been studied as a function of hydrogen gas concentration and carbon monoxide gas concentration. The ultra-thin gate is a porous film, consisting of an array of partially connected islands. This MOS capacitor is sensitive to hydrogen (3 ppm to 1%) at room and elevated temperatures and to carbon monoxide (100 ppm to 10 000 ppm) at 150 °C. Using a bias scan conductance method at a fixed frequency, the interface state density (Nit) is determined at the surface potential corresponding to the peak in the conductance curve. It is shown that at the corresponding location in the bandgap, Nit increases with increasing concentrations of hydrogen, while Nit decreases with increasing concentrations of carbon monoxide. © 1990.