Thin Film Transistor Semiconductor Layer Segmentation
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Solution Overview
Problem
Thin film transistors with polycrystalline silicon layers face issues with high OFF current due to lack of potential barriers between electrodes, leading to increased contact resistance and insufficient ON current, necessitating voltage limitations to maintain performance.
Innovation Solution
A display device structure featuring a transparent substrate with thin film transistors including a gate electrode, source and drain electrodes, a first semiconductor film, an insulation film, and second and third semiconductor films with the third film providing an ohmic contact and higher resistance than the second, allowing for improved current control and reduced OFF current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an impurity silicon layer is used to cover the polycrystalline silicon layer and electrodes, then OFF current is suppressed by preventing hole passing, but contact resistance increases due to narrow connecting portion resulting in insufficient ON current
Solution Approach 1:
The semiconductor layer is divided into two distinct layers: a first semiconductor layer (polycrystalline silicon) for channel formation and a second semiconductor layer (amorphous silicon) for electrode contact. This segmentation allows each layer to perform its specialized function - the first layer controls electron flow while the second layer provides low-resistance ohmic contact with the electrodes, resolving the contradiction between suppressing OFF current and maintaining sufficient ON current.
Solution Approach 2:
Different regions of the semiconductor structure are given different material properties. The first semiconductor layer uses polycrystalline silicon with specific crystalline structure for channel control, while the second semiconductor layer uses amorphous silicon for optimal electrode interface properties. This local differentiation of material quality enables simultaneous achievement of low OFF current and low contact resistance.
2Reliability
If the area where drain electrode, source electrode and semiconductor film are connected is increased to lower contact resistance, then ON current is sufficiently ensured, but OFF current cannot be suppressed at high drain voltage due to strong electric field concentration at drain-electrode-side edge portion
Solution Approach 1:
The semiconductor structure is segmented into two functional layers where the second semiconductor layer (amorphous silicon) specifically addresses the electrode interface region. This layer provides extended contact area for low contact resistance while its material properties prevent electric field concentration at the drain edge, thus enabling high ON current without increasing OFF current at high voltages.
Solution Approach 2:
The second semiconductor layer acts as an intermediary between the metal electrodes and the first semiconductor layer. It provides a transition zone that ensures good electrical contact (low contact resistance) while preventing direct electric field concentration at the drain edge, thereby mediating between the conflicting requirements of low contact resistance and OFF current suppression.
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 structure effectively manages ON and OFF currents while minimizing manufacturing costs by reducing contact resistance and suppressing OFF current even at higher voltages.
Implementation Method 1
the third semiconductor film is connected with the source electrode and the drain electrode by an ohmic contact
Implementation Method 2
a first semiconductor film which is stacked between the gate electrode, and the source electrode and the drain electrode so as to control an electric current which flows between the source electrode and the drain electrode
Data Source
AI summary
A display device including a transparent substrate, and a plurality of thin film transistors formed on the transparent substrate, wherein each of the thin film transistors have a gate electrode, a source electrode and a drain electrode, a first semiconductor film, an insulation film, a second semiconductor film, and a third semiconductor film. The third semiconductor film is connected with the source electrode and the drain electrode by an ohmic contact, and the second semiconductor film is formed below the third semiconductor film and has a resistance higher than resistance of the third semiconductor film.