Top Gate Thin-Film Transistor Light Blocking Film Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Top gate type polysilicon TFTs experience increased off current and threshold voltage shift due to the electric field generated by the light blocking layer, leading to display irregularities and increased manufacturing costs from the need for additional electrode steps to fix the potential of the light blocking layer.
Innovation Solution
A thin-film transistor design where the light blocking film is divided across the channel region, shielding the drain and source regions but not the channel, eliminating the need for an electrode to apply a fixed potential and reducing the influence on the channel region, thereby suppressing photo leak current without affecting the channel's potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light blocking layer is formed to cover the channel region to suppress photo leak current, then photo leak current is reduced, but an electric field is generated between the light blocking layer and the polysilicon film causing channel formation, threshold voltage shift, and increased off current
Solution Approach 1:
The light blocking layer is divided into two separate regions: a first light blocking layer covering the source region and a second light blocking layer covering the drain region, with a gap between them that exposes the channel region. This segmentation allows selective shielding of the source and drain regions while leaving the channel region uncovered, thus suppressing photo leak current without generating unwanted electric fields in the channel.
Solution Approach 2:
Different regions of the device are treated differently regarding light blocking. The source and drain regions are covered with light blocking layers to suppress photo leak current, while the channel region is intentionally left uncovered to avoid electric field interference. This local differentiation optimizes both photo leak suppression and electrical performance.
2Object-affected harmful factors
If a light blocking layer is formed covering the channel region, then photo leak current is suppressed, but additional electrode steps are required to apply fixed potential to the light blocking layer, increasing manufacturing complexity and cost
Solution Approach 1:
The light blocking function is extracted from a continuous layer and implemented only where needed (source and drain regions), leaving the channel region exposed. This eliminates the need for additional electrodes to control the light blocking layer's potential, as the segmented structure naturally avoids creating unwanted electric fields in the channel region.
3Ease of manufacture
If the light blocking layer potential is not fixed, then manufacturing is simpler, but threshold voltage fluctuates due to electric field effects on the channel region
Solution Approach 1:
By segmenting the light blocking layer into separate source and drain regions with a gap exposing the channel, the design achieves both manufacturing simplicity and threshold voltage stability. The segmented structure prevents electric field formation in the channel region, eliminating the need for potential fixation while maintaining precise threshold voltage control.
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
This design effectively reduces photo leak current and prevents threshold voltage fluctuations, enhancing display performance and reducing manufacturing costs by eliminating the need for additional electrode steps.
Implementation Method 1
a light blocking film that is arranged not to superimpose on the channel region and arranged such that the light blocking film overlaps, at least, a part of each of the two regions doped with impurity at low concentration
Data Source
AI summary
The present invention provides a thin-film transistor manufactured on a transparent substrate having a structure of a top gate type crystalline silicon thin-film transistor in which a light blocking film, a base layer, a crystalline silicon film, a gate insulating film, and a gate electrode film arranged not to overlap at least a channel region are sequentially formed on the transparent substrate; wherein the channel region having channel length L, LDD regions having LDD length d on both sides of the channel region, a source region, and a drain region are formed in the crystalline silicon film; the light blocking film is divided across the channel region; and interval x between the divided light blocking films is equal to or larger than channel length L and equal to or smaller than a sum of channel length L and a double of LDD length d (L+2d). Thereby, the cost for manufacturing the thin-film transistor is low, and the photo leak current of the thin-film transistor is suppressed.