Active Matrix Resistive Sensor Array With Reduced Dependence on TFT Channel Resistance

Large area active matrix sensor arrays for mapping of physical parameters like temperature or pressure, over an area employ a thin film transistor (TFT) to provide isolation and access to a specific sensor resistance. In the conventional single-TFT structure, the TFT channel resistance adds to the sensor resistance, resulting in loss of accuracy and sensitivity to process variations. An improved sensing scheme using a modified four-terminal TFT structure with an additional open-circuited contact is described, which removes the impact of TFT channel resistance completely without increasing process complexity and only a single additional column line in the active matrix structure. Two-dimensional numerical simulations were performed to establish the validity of this approach. Experimental results obtained with Pentacene organic semiconductor based top contact TFT show that sensor resistances that are less than 1% of channel resistance are measurable using the proposed approach. In addition to improved accuracy, an additional benefit of proposed TFT channel resistance independent sensing scheme is that it will allow a wider variety of both TFT and sensor materials to become potentially useful for the realization of high resolution large area sensor arrays.