Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2002-03-20
2003-08-12
Jackson, Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S071000, C349S044000
Reexamination Certificate
active
06605827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electrooptical substrate device for an electrooptical apparatus, such as a liquid-crystal apparatus, of a so-called TFT active-matrix drive scheme for active-matrix-driving pixel electrodes by thin film transistors (hereinafter “TFTs”). The invention also relates to a manufacturing method for the same, an electrooptical apparatus including such an electrooptical substrate device, an electronic apparatus having such an electrooptical apparatus, and a manufacturing method for a substrate device.
2. Description of Related Art
In this type of an electrooptical substrate device, pixel-electrode-switching TFTs are respectively provided on a plurality of pixel electrodes that are arranged in a matrix form. Each TFT is turned on each time a scanning signal is applied to the gate electrode thereof, to write an image signal onto the pixel electrode through the TFT.
Particularly, N-channel TFTs, having as carriers high-mobility electrons, are used to enable control by the TFTs having a high-performance transistor characteristic when effecting pixel-switching control. Recently, as the drive frequency of an electrooptical apparatus increases, the N-channel TFTs having high-mobility electrons as carriers are still being used in order to cope with the higher driving frequency.
On the other hand, in order to perform a higher level of driving, such as high-frequency driving, there is a need to further enhance the performance of such a pixel-switching TFT. For this reason, it is proposed to apply the SOI (Silicon On Insulator) structure, or SOI art, in the semiconductor manufacturing technology to an electrooptical substrate device of that kind. Specifically, a single-crystal semiconductor layer is formed by bonding or the like on an insulating layer of quartz or sapphire formed on a substrate, to fabricate transistors on the single-crystal semiconductor layer. The application of such an SOI art makes it possible to fabricate single-crystal silicon TFTs that are higher in performance than the amorphous-silicon or polysilicon TFTs on an electrooptical substrate device.
SUMMARY OF THE INVENTION
However, where an SOI structure is adopted, the N-channel MOS TFT has a tendency to build up holes as surplus carriers in the channel region during the operation thereof. According to the research by the present inventor, this is due to a parasitic bipolar phenomenon resulting from a substrate float effect, because in the SOI structure, an insulator layer is arranged below the channel region. In this phenomenon, in the case of the N-channel MOS TFT, the electrons, of among the electron-hole pairs caused due to impact ionization within a drain depletion layer, directly flow into the drain. However, the holes are built up, as surplus carriers, in the vicinity of the source beneath the channel, to raise the channel potential and further promote impact ionization. As a result, the accumulation amount of surplus holes increases to increase the drain current in an avalanche-effect fashion.
Accordingly, in the n-channel MOS TFT adopting an SOI structure, a need exists to provide a body contact to remove such surplus carriers. More specifically, a portion of a semiconductor layer needs to be extended from the channel region in order to remove surplus carriers, and to place a surplus-carrier-removing conductor layer in contact with that extended portion. This causes a problem of complication in the overlying structure on a substrate and in the manufacturing process. Furthermore, such a body contact makes it difficult to fabricate TFTs within a limited region of non-opening area in each pixel not contributing to actual display in the image display region. There is also a problem of interference with the broadening of the opening area of each pixel.
The present invention addresses the foregoing problem, and provides each pixel with comparatively high performance transistors suited to broaden the opening area in each pixel, and provides an electrooptical substrate device enabling bright, high-quality image display, a manufacturing method for the same, an electrooptical apparatus including such an electrooptical substrate device, an electronic apparatus having such an electrooptical apparatus, and a manufacturing method for a substrate device to be suitably used in such an electrooptical apparatus.
An electrooptical substrate device of the invention that addresses the foregoing problem includes: on a substrate, an insulator layer; and an N-type single-crystal semiconductor layer formed on the insulator layer, and including a P-type source region, a P-type drain region and a channel region; a gate electrode formed on the single-crystal semiconductor layer in the channel region through a gate insulating film; a scanning line connected to the gate electrode; a data line connected to one of the source region and the drain region; and a pixel electrode connected to the other of the source region and the drain region. A P-channel transistor is architected by the single-crystal semiconductor layer, the gate insulating film and the gate electrode to switch-control the pixel electrode.
The use of the electrooptical substrate device of the invention makes it possible to architect an electrooptical apparatus that is capable of being active-matrix-driven by switch-controlling the pixel electrodes due to the transistors connected to the scanning and data lines. In the electrooptical substrate device of the invention, particularly an N-type single-crystal semiconductor layer is formed on an insulator layer, to architect P-channel transistors on a so-called SOI substrate. The P-channel transistor, having holes as carriers, is generally inferior in transistor performance to the N-channel transistor correspondingly to its low mobility. However, because of being formed on an SOI substrate, it is made to be not inferior in its transistor performance to the MOS transistor configured using, for example, polysilicon or amorphous silicon as a semiconductor layer. Namely, the P-channel transistor on the SOI substrate provides sufficiently high transistor performance to switch-control the pixel electrode. Conversely, despite being formed on the SOI substrate, because it is of the P-channel type, the parasitic bipolar effect due to a substrate float effect as noted before is practically not a problem, which is different from the case with the N-channel type. This is considered to be because the P-channel transistor is low in the impact ionization ratio of holes. For this reason, there is no need for the P-channel transistor to perform the removal of surplus carriers required in practical use in the N-channel transistor as noted before. Consequently, a structure does not need to be fabricated to remove such surplus carriers in each pixel, correspondingly enabling an increase in the opening ratio in each pixel. At the same time, there is no complication incurred in the overlying structure of each pixel and in the manufacturing process. This ultimately results in realizing an electrooptical substrate device that is capable of being switch-controlled or active-matrix-driven by the transistors having comparatively high performance to display a bright, high-quality image.
In one form of an electrooptical substrate device of the invention, the transistor is a P-channel MOS (Metal Oxide Silicon) transistor.
In this form, because the P-channel MOS transistor is provided on the substrate, a conductor layer does not have to be provided to remove the carriers built up in the semiconductor layer during operation, which is different from the N-channel MOS transistor. Because the P-channel transistor is a transistor made up on the SOI substrate, sufficiently high transistor performance is obtained in switch-controlling the pixel electrode.
Another form of an electrooptical substrate device of the invention further includes an interlayer insulating film formed on the gate electrode, a source electrode formed by a P-type conductor layer on the interlayer insulating film and c
Jackson Jerome
Seiko Epson Corporation
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