Substrate Bias Amplification of a SiC Junction Field Effect Transistor with a Catalytic Gate Electrode

The drain current-voltage (Id-VD) characteristics of a chemical gas sensor based on a catalytic metal insulator silicon carbide field effect transistor (SiC-FET) were measured in H2 or O2 ambient while applying negative substrate bias, Vsub, at temperatures up to 600 deg C. An increase in the negative Vsub gives rise to an increase of the drain voltage at a given drain current level, which can be used to adjust the device baseline. In addition, we found that the difference in drain voltage between H2 and O2 ambient at a given drain current level (the gas response to H2) increases for an increased negative substrate bias. By modifying an equation for the drain current in a SIT (static induction transistor), the influence of substrate bias on the amplification factors, mu and eta, was estimated using the temperature dependence of the Id-VD characteristics. From this, the effect of substrate bias on the gas response to hydrogen was calculated. It was clarified that the increase in the gas response caused by the negative substrate bias is due to a substrate bias dependence of the amplification factor of the short channel device.