Optical characterizations of complete TFT–LCD display devices by phase modulated spectroscopic ellipsometry

A commercially available phase modulated spectroscopic ellipsometer (PMSE) has been used to characterize a full thin film transistor–liquid crystal display (TFT–LCD) structure, including the glass substrates coated with transparent conducting indium tin oxide (ITO) layers, the twisted liquid crystal (LC) layer sandwiched in between, and the amorphous silicon (a-Si) TFT device which controls the luminance of a pixel. Due to its unique optical design, PMSE presents an unparallel capability to measure very accurately ultra thin films on transparent substrates as often found in display applications. Results show that the ITO layer is inhomogeneous in depth, corresponding to a graded microstructure. In addition, strong uniaxial anisotropy was determined for the liquid crystal device over the entire measured spectral range. Finally, doping effects on the optical properties of the a-Si layer of the TFT device were also measured.