Oxide Semiconductor TFT Substrate With Alkaline Etching
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Solution Overview
Problem
Conventional TFT substrates for liquid crystal displays face challenges in reducing manufacturing process steps, achieving high display quality, and maintaining display performance, particularly due to difficulties in forming auxiliary capacitance and using oxide semiconductor materials that are prone to etching by acidic solutions used for metal films.
Innovation Solution
A thin film transistor substrate with a matrix array of pixels, featuring a semiconductor film, source and drain electrodes, a gate electrode, auxiliary capacitance electrodes, and a manufacturing method that reduces photolithography steps to three, using an oxide semiconductor material and a specific etching process with an alkaline developer to pattern the semiconductor and metal films without damaging the oxide semiconductor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxide semiconductor material is used as the active layer to achieve higher mobility and improved display performance, then the display quality is improved, but the material becomes easily dissolved by acidic solutions used for etching metal films
Solution Approach 1:
The patent changes the chemical parameter of the etching solution from acidic to alkaline (pH change). The alkaline developer solution selectively etches the metal films (Cr, Ti, Mo, Ta, Al, Cu) while leaving the oxide semiconductor material intact, as oxide semiconductors are resistant to alkaline solutions. This parameter change resolves the contradiction by enabling metal film etching without damaging the oxide semiconductor active layer.
2Device complexity
If the photolithography steps are reduced to three times to decrease manufacturing complexity, then the manufacturing process is simplified, but it becomes difficult to form the auxiliary capacitance structure
Solution Approach 1:
The patent merges the formation of the auxiliary capacitance electrode with the source line and drain electrode in the same metal film layer. By forming these structures simultaneously in one photolithography step rather than separately, the auxiliary capacitance can be created without increasing the number of photolithography steps, thus resolving the contradiction between process simplification and capacitance formation capability.
Solution Approach 2:
The metal film layer serves multiple functions: it forms the source electrode, drain electrode, source line, and auxiliary capacitance electrode all in one layer. This multi-functional design allows the auxiliary capacitance to be integrated without requiring additional dedicated layers or steps, maintaining process simplicity while enabling capacitance formation.
3Reliability
If conventional metal films (Cr, Ti, Mo, Ta, Al, Cu) are used for source and drain electrodes to ensure good electrical contact, then the electrical performance is improved, but the metal films are etched away along with the oxide semiconductor by acidic solutions
Solution Approach 1:
The patent changes the chemical environment from acidic etching to alkaline etching. The alkaline developer solution provides selective etching of metal films while preserving the oxide semiconductor material, maintaining both the electrical performance of the metal electrodes and the integrity of the semiconductor active layer.
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 solution enables high-performance TFT substrates with improved display quality and reduced manufacturing complexity, maintaining high mobility and resistance to photo carrier generation, thus enhancing display stability and contrast without increasing the manufacturing process steps.
Implementation Method 1
the oxide semiconductor material as thus described has advantages of being etchable by a mild acidic solution such as oxalic acid or carboxylic acid... However, the oxide semiconductor material is also dissolved with ease by an acidic solution normally used at the time of etching a typical metal film
Data Source
AI summary
Provided is a thin film transistor having a semiconductor film disposed in a plurality of portions on a substrate, a source electrode and a drain electrode which are disposed, on a semiconductor film, in contact with the semiconductor film while being spaced from each other, and a gate electrode which is disposed across the source electrode and the drain electrode via a gate insulating film; an auxiliary capacitance electrode which is disposed on the semiconductor film while in contact with the semiconductor film; a source line which has the semiconductor film in a lower layer, extends from the source electrode; a gate line which extends from the gate electrode; a pixel electrode which is electrically connected to the drain electrode; and an auxiliary capacitance electrode connecting line which electrically connects the auxiliary capacitance electrodes to each other in the adjacent pixels.