Thin Film Transistor Substrate with Conductive Layer for Gray Scale
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Solution Overview
Problem
Thin film transistors used in display devices have a small s-factor, making it difficult to express gray scales effectively, particularly when applied as driving transistors.
Innovation Solution
A thin film transistor substrate design incorporating a conductive material layer between the substrate and active layer, connected to the source electrode, and a second thin film transistor with a larger s-factor for improved gray scale expression, featuring a conductive material layer overlapping the channel portion and a buffer layer for hydrogen blocking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin film transistor is designed with conventional structure to ensure on-off characteristics, then the s-factor is small, but it becomes difficult to express gray scale when applied as driving transistor
Solution Approach 1:
The patent applies different structural configurations to different transistor types within the same display device. The driving transistor includes a light shielding layer positioned to overlap the channel portion, while the switching transistor uses a conventional structure. This local differentiation allows each transistor type to be optimized for its specific function - the driving transistor achieves large s-factor for gray scale expression, while the switching transistor maintains small s-factor for on-off characteristics.
Solution Approach 2:
The patent changes the structural parameter of the driving transistor by introducing a light shielding layer that overlaps the channel portion. This parameter change (adding the overlapping light shielding layer) increases the electric field influence on the channel, thereby increasing the s-factor to enable gray scale expression, while keeping the switching transistor structure unchanged to preserve its on-off characteristics.
2Adaptability or versatility
If a light shielding layer is added to increase s-factor for gray scale expression, then gray scale capability improves, but device complexity increases
Solution Approach 1:
The light shielding layer serves multiple functions simultaneously: it shields light from reaching the channel portion (original function) and acts as an additional electric field control element that increases s-factor (new function). By making the light shielding layer serve dual purposes, the patent avoids adding separate components, thereby improving gray scale capability without proportionally increasing device complexity.
3Adaptability or versatility
If the light shielding layer overlaps the channel portion to increase electric field influence, then s-factor increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent merges the light shielding layer with the existing transistor structure such that the light shielding layer is integrated into the driving transistor fabrication process. By combining the light shielding function with the electric field control function in a single layer, the patent reduces the number of separate alignment operations needed, thereby reducing manufacturing precision requirements while still achieving the desired overlap with the channel portion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design enhances the s-factor of the second thin film transistor, enabling better gray scale expression in display devices by reducing the influence of the electric field and improving the switching characteristics of the first thin film transistor.
Implementation Method 1
a first buffer layer on the conductive material layer
Implementation Method 2
the conductive material layer is connected to the second source electrode and overlaps the second channel portion
Data Source
AI summary
A thin film transistor substrate is provided, which comprises a substrate, a first thin film transistor on the substrate, and a second thin film transistor on the substrate, wherein the first thin film transistor includes a first active layer having a first channel portion, a first gate insulating layer on the first active layer, a first gate electrode on the first gate insulating layer, a first source electrode connected to the first active layer, and a first drain electrode spaced apart from the first source electrode and connected to the first active layer, the second thin film transistor includes a conductive material layer on the substrate, a first buffer layer on the conductive material layer, a second active layer having a second channel portion on the first buffer layer, a second gate insulating layer on the second active layer, a second gate electrode on the second gate insulating layer, a second source electrode connected to the second active layer, and a second drain electrode spaced apart from the second source electrode and connected to the second active layer, and the conductive material layer is connected to the second source electrode and overlaps the second channel portion. Also, a display device comprising the thin film transistor substrate is provided.