Investigation of Curtain Mura in TFT–TN panels after COG ACF process

We have utilized a transmission ratio (TR) between curtain-shaped (Curtain) Mura and non-Mura zones as a key parameter to characterize the optical appearance of Curtain Mura occurred on a 13.3-in TFT–TN panel (Mura sample) after bonding process to place silicon-based driver-IC chips on one of the panel substrates using anisotropic conductive film as a binder (COG ACF process). Our measured TRs of the Mura sample at zero applied voltage were in good agreement with calculated TRs using optical parameters of the Mura sample derived from the measured Stokes parameters of the liquid crystal (LC) medium in that sample. We conclude that the occurrence of Curtain Mura is dominant by the stress-induced change in the twist angle, less sensitive and insensitive to the corresponding induced changes in the cell gap and pretilt angle of the in-panel-LC medium, respectively. By simulation, we also point out a way to reduce the occurrence of Curtain Mura by designing the cell gap for a 90°-twsit TN panel to satisfy the condition of Gooch–Terry first minimum.

► Transmission ratio is a key parameter to characterize the Curtain Mura.
► Curtain Mura is dominant by the stress-induced change in the twist angle.
► Curtain Mura is less sensitive to the changes in the cell gap.
► Curtain Mura is insensitive to the changes in the pretilt angle.
► Cell gap designed at Gooch–Tarry first minimum is effective to reduce Curtain Mura.