We introduce a gas sensor platform consisting of resistive sensor, thin film transistor (TFT) type sensor, and Si-based field effect transistor (FET) type sensor fabricated on the same wafer. The FET type sensor has a horizontal floating gate interdigitated with the control gate. The schematic structures of these gas sensors are shown in Fig. 1. These gas sensors can be fabricated using only 5 masks. The sensing layer of these sensors is a 15nm thick n-type ZnO film prepared using atomic layer deposition (ALD) in the final process step. Although these sensors have the same sensing material, they have different sensing characteristics because of different sensing mechanisms. Our group has reported the studies of resistive- and FET-type gas sensors having ALD ZnO sensing layer previously [1], [2]. Fig. 2 shows the transfer (I-V) characteristics of these sensors. These sensors have different sensing characteristics when exposed to 500 ppb of oxidizing gas, NO2. When exposed to NO2 gas, the currents of resistive- and TFT-type gas sensors are decreased [2]. On the other hand, the drain current of the FET-type gas sensor increases when exposed to NO2 gas [1], [2]. As a result, the difference in response of these sensors can be used as a fingerprint to more accurately detect the target gas in the gas sensor platform composed of three types of gas sensors.
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