Ferroelectric liquid crystal display device comprising gate-overlapped lightly doped drain structure

摘要

The present invention relates to a semiconductor device including a circuit composed of thin film transistors having a novel GOLD (Gate-Overlapped LDD (Lightly Doped Drain)) structure. The thin film transistor comprises a first gate electrode and a second electrode being in contact with the first gate electrode and a gate insulating film. Further, the LDD is formed by using the first gate electrode as a mask, and source and drain regions are formed by using the second gate electrode as the mask. Then, the LDD overlapping with the second gate electrode is formed. This structure provides the thin film transistor with high reliability.

主权项

1. A display device comprising:
a pixel circuit over a substrate, comprising:
a gate wiring over the substrate;a source wiring crossing the gate wiring;a first pixel and a second pixel adjacent to each other with the gate wiring interposed therebetween, the first pixel comprising: a pixel TFT comprising:
a first portion of a semiconductor layer comprising a channel formation region, a pair of LDD regions, a source region and a drain region;
a gate insulating film provided over the semiconductor layer; anda gate electrode provided over the gate insulating film, each of the pair of LDD regions comprising a first top portion overlapping with the gate electrode and a second top portion not overlapping with the gate electrode, a capacitor comprising a capacitor electrode, a second portion of the semiconductor layer overlapped with the capacitor electrode, and a portion of the gate insulating film overlapped with the capacitor electrode; wherein the gate electrode is a portion of the gate wiring, wherein the first portion of the semiconductor layer is overlapped with the source wiring, an insulating film comprising silicon nitride over the pixel TFT, wherein the gate electrode comprises a first conductive layer, a second conductive layer provided over the first conductive layer, and a third conductive layer provided over the second conductive layer, the third conductive layer being in direct contact with a side surface of the second conductive layer, a side surface of the first conductive layer, and the gate insulating film; wherein the first conductive layer and the third conductive layer each comprise a material selected from the group consisting of titanium, tantalum, tungsten and molybdenum, and wherein the second conductive layer comprises a material selected from the group consisting of aluminum and copper.