1. Field of the Invention
This invention relates to a semiconductor device having an integrated circuit constituted by thin-film transistors (hereinafter referred to as TFTs) and to a method of fabricating the same. The invention relates to, for example, an electro-optical device as represented a liquid crystal display panel and an electronic device mounting the electro-optical device as a part. In this specification, the semiconductor device generally stands for such devices that function by utilizing the semiconductor properties. Therefore, electro-optical devices, semiconductor circuits and electronic devices are all encompassed by the scope of the semiconductor device.
2. Related Art
Technology has been developed for fabricating thin-film transistors (TFTs) by using a thin semiconductor film (of a thickness of from about several nanometers to about several hundred nanometers). TFTs have been put into practical use as switching elements of the liquid crystal display devices and, in recent years, it is becoming possible to form a CMOS circuit and an integrated circuit on a substrate such as of a glass.
Active matrix liquid crystal display devices are becoming a main stream of liquid crystal display devices, by arranging pixel electrodes in the form of a matrix and by using TFTs as switching elements connected to the pixel electrodes, in order to meet the demand for realizing a highly fine picture quality. The active matrix liquid crystal display devices can be roughly divided into two; i.e., those of the transmission type and those of the reflection type. In particular, the liquid crystal display device of the reflection type, which does not use back light, has a merit that it consumes electric power in smaller amounts than the transmission-type liquid crystal display device, and is finding an increasing demand as a direct view-type display device for portable data terminals and video cameras.
The active matrix liquid crystal display device of the reflection type selects a state where an incident beam is reflected by a pixel electrode and is output to the outer side of the device and a state where the incident beam is not output to the outer side of the device by utilizing the optical modulation action of the liquid crystals, produces a bright display and a dark display, and, further, combines these displays to display a picture. In general, pixel electrodes in the liquid crystal display device of the reflection type are formed of an electrically conducting material having a high optical reflection factor such as of aluminum or silver.
In any way, the size of each pixel becomes inevitably more fine as the picture quality becomes more fine. As a result, the ratio of areas occupied by the TFT, source wiring and gate wiring increases in the pixel portion, and the numerical aperture decreases. In order to increase the numerical aperture of the pixels within a specified pixel size, therefore, it is essential to efficiently lay out the circuit elements necessary for constituting the pixel circuit.
This invention was derived in view of the above-mentioned problem, and has an object of providing an active matrix-type display device having a pixel structure in which a pixel electrode, a gate wiring and a source wiring are suitably arranged in a pixel portion, and which realizes a high numerical aperture without increasing the number of the masks or the number of the steps.
This invention has a structure in which TFTs are shut off the light without using a light-shielding film that forms a black matrix, and light leaking among the pixels is shut off. The above structure of this invention comprises;
a gate electrode and a source wiring over an insulating surface;
a first insulating film over the gate electrode and over the source wiring;
a semiconductor film over the first insulating film;
a second insulating film over the semiconductor film;
a gate wiring connected to the gate electrode over the second insulating film;
a connection electrode for connecting the source wiring and the semiconductor film together; and
pixel electrode connected to the semiconductor film.
Another invention has a constitution which comprises:
a first gate electrode, a second gate electrode and a source wiring over an insulating surface;
a first insulating film over the first and second gate electrodes and over the source wiring;
a first semiconductor film having a source region, a drain region and a channel-forming region over the first insulating film;
a second semiconductor film overlapped over the second gate electrode;
a second insulating film over the first and second semiconductor films;
a gate wiring connected to the gate electrode over the second insulating film;
a connection electrode for connecting the source wiring and the source region together; and
a pixel electrode connected to the drain region and to the second semiconductor film.
In this constitution of the invention, the end on one side of the pixel electrode is formed on the source wiring so as to also serve as a light-shielding film, enabling the pixel electrode to occupy an increased area in the pixel unit.
A further invention has a constitution which comprises:
a first step of forming a gate electrode and a source wiring over an insulating surface;
a second step of forming a first insulating film over the gate electrode;
a third step of forming a semiconductor film over the first insulating film;
a fourth step of forming a second insulating film over the semiconductor film; and
a fifth step of forming, over the second insulating film, a gate wiring connected to the gate electrode, a connection electrode for connecting the source wiring and the semiconductor film together, and a pixel electrode connected to the semiconductor film.
A further invention has a constitution which comprises:
a first step of forming a gate electrode and a source wiring over an insulating surface;
a second step of forming a first insulating film over the gate electrode;
a third step of forming a semiconductor film over the first insulating film;
a fourth step of forming a source region and a drain region over the semiconductor film;
a fifth step of forming a second insulating film over the semiconductor film; and
a sixth step of forming, over the second insulating film, a gate wiring connected to the gate electrode, a connection electrode for connecting the source wiring and the source region together, and a pixel electrode connected to the drain region.
A further invention has a constitution which comprises:
a first step of forming a first gate electrode, a second gate electrode and a source wiring over an insulating surface;
a second step of forming a first insulating film over the first and second gate electrodes;
a third step of forming, over the first insulating film, a first semiconductor film that overlaps over the first gate electrode and a second semiconductor film that overlaps over the second gate electrode;
a fourth step of forming a source region and a drain region in the first semiconductor film;
a fifth step of forming a second insulating film over the semiconductor film; and
a sixth step of forming, over the second insulating film, a gate wiring connected to the gate electrode, a connection electrode for connecting the source wiring and the source region together, and a pixel electrode for connecting the drain region and the second semiconductor film together.
According to the above steps, the end on one side of the pixel electrode is formed over the source wiring to form a pixel structure in which the source wiring also serves as a light-shielding film, enabling the pixel electrode to occupy an increased area in the pixel portion.