TFT Substrate Gate Electrode Thickness Variation for Channel Control
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Solution Overview
Problem
The 4 mask process for manufacturing TFT array substrates faces challenges in controlling TFT channel length, leading to variations in TFT characteristics, display unevenness, and increased manufacturing costs due to difficulties in controlling resist film thickness uniformity and photolithography techniques, resulting in defects like stepped cuts in source lines.
Innovation Solution
A TFT substrate with a gate electrode having thick and thin film parts, along with a semiconductor active film, ohmic contact film, and electrode films, is manufactured using a method involving photolithography with two different exposure intensities to form precise resist patterns, allowing for accurate control of channel length and reduced variations in channel characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the 4 mask process with halftone exposure technology is used to reduce the number of photolithography processes, then manufacturing efficiency is improved, but it becomes extremely difficult to control the TFT channel length and resist pattern width
Solution Approach 1:
The patent changes the physical parameter of the gate electrode by forming a thickness difference between the first region (thicker) and the second region (thinner). This parameter change in the gate electrode structure enables the resist pattern width to be determined by the gate electrode thickness rather than by difficult-to-control halftone exposure, thereby achieving precise TFT channel length control while maintaining manufacturing efficiency
Solution Approach 2:
The gate electrode serves as an intermediary element that mediates between the photolithography process and the final TFT channel dimensions. By using the gate electrode thickness as the determining factor for resist pattern width, the patent introduces this intermediary structure that simplifies the control relationship and eliminates the need for precise halftone exposure control
2Device complexity
If halftone exposure technology is used to form resist patterns with different film thicknesses, then two photolithography processes can be combined into one, but resist film thickness uniformity and photolithography technique control become extremely difficult
Solution Approach 1:
The patent performs preliminary action by forming the gate electrode with a predetermined thickness distribution (first region thicker than second region) before the photolithography process. This preliminary structuring of the gate electrode eliminates the need for complex halftone exposure to create thickness variations, as the thickness difference is already established in the gate electrode itself
Solution Approach 2:
Instead of using photolithography to create the thickness difference (as in conventional halftone exposure), the patent inverts the approach by using physical deposition or other methods to directly form the gate electrode with the desired thickness distribution. This inversion of the process sequence simplifies the photolithography step and improves thickness uniformity
3Productivity
If the 4 mask process is used to manufacture TFT array substrates, then manufacturing steps are reduced, but TFT characteristic variations increase leading to display unevenness and defects
Solution Approach 1:
The patent changes the structural parameter of the gate electrode by introducing a thickness difference between regions, which directly affects the electrical characteristics of the TFT. This parameter change in the gate electrode enables more uniform TFT characteristics across the substrate while maintaining the simplified 4 mask manufacturing process
Solution Approach 2:
The patent applies local quality by creating different gate electrode thicknesses in different regions (first region vs. second region). This local variation in gate electrode structure allows for optimized TFT characteristics in different areas of the substrate, reducing overall characteristic variations and improving display uniformity
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 approach enhances productivity and performance by reducing variations in TFT characteristics, suppressing source-drain leakage current, and minimizing off-current, thereby improving display quality and manufacturing efficiency.
Implementation Method 1
forming a photoresist pattern by exposing the photoresist with use of a photomask pattern with two different levels of exposure intensity
Data Source
AI summary
There is provided a TFT substrate including a gate electrode having a thick film part and a thin film part with a smaller film thickness than the thick film part, a semiconductor active film formed above the thick film part and the thin film part of the gate electrode, an ohmic contact film formed on an inside of the semiconductor active film and on the semiconductor active film corresponding to the thin film part on an outside of the thick film part, and an electrode film constituting a source electrode and a drain electrode, having a planar shape identical to or on an inside of the ohmic contact film, and formed on the ohmic contact film.