Transparent Gate Electrode as Photolithographic Mask for TFTs
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Solution Overview
Problem
Current methods for preparing thin film transistors are complex and reduce transparency, feature size, and integration capabilities due to the need for multiple alignment operations and non-transparent masks, limiting the development of fully-transparent and flexible high-frequency electronic devices.
Innovation Solution
A method using a transparent conductive gate electrode layer as a photolithographic mask, with photoresist exposure through a transparent substrate, eliminating the need for additional masks and alignment, and combining self-aligned technology with roll-to-roll printing to create fully-transparent flexible thin film transistors with reduced feature size and increased integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography with multiple masks or concave/convex plates is used, then pattern alignment can be achieved, but the preparation process complexity increases and transparency is reduced
Solution Approach 1:
The patent merges the gate electrode function with the photolithographic mask function by using the transparent conductive gate electrode layer as the exposure mask. This eliminates the need for separate masks or concave/convex plates, reducing preparation process complexity while maintaining pattern alignment precision through self-aligned technology
Solution Approach 2:
The transparent conductive gate electrode layer serves multiple functions: it acts as both the functional gate electrode of the transistor and the photolithographic exposure mask. This multi-functionality reduces the number of additional components and steps required in the preparation process
2Device complexity
If a non-transparent gate is used as a photolithographic mask to reduce alignment procedures, then one mask set is saved, but full transparency of the device cannot be realized
Solution Approach 1:
The patent applies local quality by making the gate electrode transparent in the regions where light exposure is needed, while maintaining its electrical conductivity function. The transparent conductive material allows light to pass through for photolithography while still serving as the functional gate, achieving both transparency and functionality in different local regions
3Reliability
If roll-to-roll printing is used to fabricate flexible thin film transistors, then excellent device performance is achieved, but feature size is limited to greater than 100 nm
Solution Approach 1:
The patent replaces the mechanical alignment system of conventional photolithography with a self-aligned optical system. By using the gate electrode itself as the mask and exposing through the transparent substrate from the rear, the method achieves precise pattern definition without mechanical mask alignment, enabling smaller feature sizes while maintaining the benefits of roll-to-roll printing
4Manufacturing precision
If additional patterning process is used to separate electrodes of different thin film transistors in arrays, then electrode separation is achieved, but process complexity increases
Solution Approach 1:
The patent merges the electrode separation function with the main photolithography step by using the gate electrode pattern itself to define the separation regions. The self-aligned exposure process simultaneously creates the transistor patterns and separates adjacent transistors, eliminating the need for additional patterning steps
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 simplifies the preparation process, enhances transparency, and enables high-frequency and high-integration applications by reducing feature size and eliminating the need for additional masks, while maintaining excellent device performance with high transmittance and mobility.
Implementation Method 1
the transparent substrate has a transmittance higher than 60% to an exposure light beam
Implementation Method 2
the transparent conductive gate electrode layer has a transmittance lower than 5% to the exposure light beam
Implementation Method 3
a photoresist is exposed through a rear surface of a transparent substrate
Data Source
AI summary
The present invention provides a preparation method for a fully-transparent thin film transistor, wherein a transparent conductive gate electrode layer of the fully-transparent thin film transistor is used as a photolithographic mask, a photoresist is exposed through a rear surface of a transparent substrate, the transparent substrate has a transmittance higher than 60% to an exposure light beam, and the transparent conductive gate electrode layer has a transmittance lower than 5% to the exposure light beam. In the preparation method for a fully-transparent thin film transistor provided by the present invention, by using a self-aligned technology, the process complexity and the feature size of the device can both be reduced.