Response Comparison of Resistor- and Si FET-Type Gas Sensors on the Same Substrate

The response characteristics of a field-effect transistor (FET)-type gas sensor are compared with those of the resistor-type gas sensor fabricated on the same Si substrate. Both types of gas sensors have the same sensing material prepared by the same process. Indium oxide (In
₂
O
₃
) film is adopted as a sensing material to sense NO
₂
gas. The two types of gas sensors have different response characteristics depending on the operating condition. The resistor-type gas sensor shows relatively constant response at all operating currents, and the Si FET-type gas sensor shows high response in the subthreshold region. Both types of sensors have the highest response at 105 °C, and the current of the Si FET-type gas sensor can change up to ~ 3.8×10
⁴
times at 500 ppb of NO
₂
gas, which is ~8.15 times higher than that of the resistor-type gas sensor. In addition, when the pre-bias method ( V
_pre
= -3 V) is applied to the Si FET-type gas sensor, the response of the Si FET-type sensor overwhelms that of the resistor-type sensor over the entire measurement temperature and concentration range.