Contactless Functionality Inspection of Flat-Panel-Display Pixels and Thin-Film Transistors by Capacitive Coupling

A fast and thorough detection of structural and functional defects of flat-panel displays, large-area image detectors, and printed electronics requires a contactless and flexible inspection technique. Moreover, to accelerate the development of new products and to increase yields, efficient device characterization including the analysis of single component functionality and testing under operating conditions is essential. In this contribution, a contactless inspection method solely based on capacitive coupling is used to analyze pixel and thin-film transistor (TFT) functionality of active-matrix liquid crystal and electrophoretic display backplanes. Employing a capacitively coupled sensor, the measurement of the evolution of the pixel electrode voltage during TFT operation (switching) yields display flicker and TFT parameters, such as TFT on- and off-currents, TFT threshold, and intrinsic capacitance. To confirm the measurement results, the pixel voltage was also measured with an active voltage probe brought into contact with the pixel electrodes under test.