In this paper, we demonstrate that the large-area and high- aperture-ratio AM-LCDs can be realized by using planarization technology. Both a-Si:H TFT arrays and Cu-gate electrodes/buslines have been successfully planarized by low dielectric constant organic planarization polymer, benzocyclobutene (BCB). First, the impact of BCB interlayer thickness on vertical crosstalk, feedthrough voltage, and busline load capacitance is analyzed for the high-aperture- ratio pixel cell structure. For a given tolerance margin of crosstalk ratio, the pixel aperture-ratio decreases with an increase of interlayer dielectric constant, and such a reduction in aperture-ratio becomes more distinct in displays having a higher resolution. After the BCB passivation, there is no degradation in field-effect mobility and subthreshold swing for BCE type a-SI:H TFTs having different channel thicknesses and channel lengths. Finally, the electrical characteristics of Cu gate- planarized a-Si:H TFTs is presented. The device has a field- effect mobility of 0.73 cm2/V-s, a threshold voltage of 5.83, a subthreshold swing of 0.71 V/dec, and an ON/OFF- current ratio of 2.5 X 106. These results show that a combination of fully planarized Cu-gate lines and a-Si:H TFT-pixel arrays can be developed for large-area, high aperture-ratio, and high definition AM-LCDs.