A 1.4-inch, 256Kpixels poly-Si TFT-LCD with integrated 8-bit digital data driver was designed with 4um design rule. And the digital data driver was fabricated. To get a high-density display, a serial digital data driver which has very narrow physical area was adopted. I proposed the paralIel-serial digital data driver. which accepts parallel digital data and processes serially digital data. To decrease the off current of pixel transistors, the offset structure using PR-reflow and multi-gate structure was adopted. I showed a shift register is operating at the speed of 2MHz and a serial DAC with poly-Si TFT's is fast enough to drive 8-bit gray image. One bit conversion time is 3us. I showed the serial digital data driver can be applied to 512 pixel-per-inch display even 4um design rule. Two groups of data drivers drive positive and negative polarity, respectively. For dot inversion display, the data drivers for positive polarity switch data lines every line time. This switching method gives low-power operation.