Thin Film Transistor Impurity Diffusion Control
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Solution Overview
Problem
In organic light emitting display devices, polysilicon thin film transistors experience leakage current due to impurity diffusion into the channel region during the crystallinity process, affecting the electrical characteristics and display quality.
Innovation Solution
The design includes a thin film transistor structure with ohmic contact layers and a semiconductor having extrinsic regions with lower impurity concentration than the ohmic contact layers, and an intrinsic region between them, where the impurity is minimized from diffusing into the channel region by forming the semiconductor after the ohmic contact layers, reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polysilicon layer is formed with an ohmic contact layer and a crystallinity process is executed, then the electrical conductivity of the contact regions is improved, but impurity diffuses into the channel region causing leakage current
Solution Approach 1:
The semiconductor layer is segmented into distinct regions: a channel region with low impurity concentration and extrinsic regions adjacent to the ohmic contact layers. This segmentation prevents impurity diffusion from the ohmic contact layers into the channel region, eliminating leakage current while maintaining good electrical contact.
Solution Approach 2:
Different regions of the semiconductor layer are given different impurity concentrations tailored to their specific functions: the channel region has low impurity concentration for low leakage, while the extrinsic regions have higher impurity concentration for better contact with the ohmic contact layers.
2Ease of manufacture
If the semiconductor layer is formed before the ohmic contact layers, then the manufacturing process is simplified, but impurity diffuses into the channel region during crystallization
Solution Approach 1:
The ohmic contact layers are formed preliminarily before the semiconductor layer. This preliminary action allows the subsequent semiconductor layer to be deposited with controlled low impurity concentration in the channel region, preventing impurity diffusion issues while maintaining manufacturing efficiency.
Solution Approach 2:
The conventional sequence is inverted: instead of forming the semiconductor layer first and then the ohmic contact layers, the ohmic contact layers are formed first followed by the semiconductor layer. This inversion prevents impurity contamination of the channel region.
3Reliability
If the extrinsic region has high impurity concentration to match the ohmic contact layer, then good electrical contact is achieved, but impurity concentration in the channel region increases causing leakage
Solution Approach 1:
The semiconductor layer exhibits local quality variation with different impurity concentrations in different regions: high impurity concentration in the extrinsic regions for good contact, and low impurity concentration in the channel region for low leakage current.
Solution Approach 2:
The semiconductor layer is divided into functionally distinct segments: extrinsic regions for electrical contact and a channel region for current control, with appropriate impurity concentration in each segment.
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 prevents impurity diffusion into the channel region, thereby reducing leakage current and enhancing the display quality of organic light emitting devices by improving the electrical characteristics of the thin film transistors.
Implementation Method 1
ohmic contact layers formed in the openings and including a conductive impurity
Implementation Method 2
The impurity of the extrinsic region may be the same material as the impurity of the ohmic contact layer. The extrinsic region of the semiconductor may have the impurity at a lower concentration than that of the ohmic contact layer
Data Source
AI summary
A thin film transistor according to one or more embodiments of the present invention includes: an insulation substrate; a gate electrode formed on the substrate; a gate insulating layer formed on the gate electrode; a semiconductor formed on the gate insulating layer and having a pair of openings facing each other; ohmic contact layers formed in the openings and including a conductive impurity; and a source electrode and a drain electrode in contact with their respective ohmic contact layers. An organic light emitting device in accordance with an embodiment includes: a first signal line and a second signal line intersecting each other on an insulation substrate; a switching thin film transistor connected to the first signal line and the second signal line; a driving thin film transistor connected to the switching thin film transistor; and a light emitting diode (LED) connected to the driving thin film transistor.