Low frequency noise characteristics of resistor- and Si MOSFET-type gas sensors fabricated on the same Si wafer with In₂O₃ sensing layer

By analyzing the Low Frequency Noise (LFN) characteristics of the resistor-type and the Si metal oxide semiconductor Field Effect Transistor (FET)-type gas sensors fabricated on the same wafer, the intrinsic device noise and the additional noise generated from the gas reaction are systemically examined. Sensing material, n-type Indium-Oxide (In₂O₃) film, is deposited using the radio frequency magnetron sputtering method. Unlike the FET-type gas sensor, the LFN characteristics of the resistor-type gas sensor are affected by the deposition condition of the sensing material. It is shown that the FET-type sensor has at least 10 times less LFN power than the resistor-type gas sensor despite its smaller size. Gas to Air Noise Ratio (GANR) is introduced as a new figure of merit to evaluate and compare the LFN characteristics during the gas reaction in both resistor- and FET-type gas sensors with the sensing layer prepared by different process conditions. The GANRs of the resistor-type sensors range from ∼2 to 4, which demonstrates that the reaction between the gas molecules and the sensing material generates a fluctuation that exceeds the intrinsic noise of devices. However, the FET-type gas sensors have a constant value of GANR (∼1) regardless of the operation region, showing that the FET-type gas sensors have better performance in terms of noise.