Thin Film Transistor Doping Segmentation for Leakage Reduction
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Solution Overview
Problem
Thin film transistors (TFTs) in organic light-emitting display devices suffer from increased leakage current and off-current characteristics due to the short channel effect and hot electron effect caused by strong electric fields, which are exacerbated by the sharp doping density changes at the boundary between impurity regions and channel regions.
Innovation Solution
The design includes a thin film semiconductor device with a substrate, a first active pattern having a channel region, lightly doped region, and heavily doped region, where the first lower conductive pattern covers the channel region and the lightly doped region, and the first upper conductive pattern covers the channel region and lightly doped region, configuring a TFT and capacitor, respectively. This configuration reduces the strength of the electric field between the channel and heavily doped regions, thereby minimizing leakage current without increasing the number of mask processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a doping density sharply changes at the boundary between the impurity region and the channel region, then the electrical characteristics are improved, but a strong electric field is induced causing leakage current to increase and off-current characteristic to deteriorate
Solution Approach 1:
The impurity region is segmented into two distinct regions: a first impurity region with first doping density and a second impurity region with second doping density. This segmentation allows the doping density to change gradually rather than sharply at the boundary, reducing the strong electric field induction while maintaining effective impurity control in the semiconductor pattern.
Solution Approach 2:
Different regions of the impurity region are assigned different doping densities to achieve local optimization. The first impurity region has a different doping density than the second impurity region, allowing each region to serve its specific function: the first region provides strong impurity concentration near the channel for good electrical characteristics, while the second region provides a transition zone that reduces electric field strength at boundaries.
2Reliability
If the number of mask processes is increased to improve TFT electrical characteristics, then the off-current characteristic can be improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The first impurity region and the second impurity region are formed simultaneously in a single ion implantation process using one mask pattern. This merging of multiple doping regions into one process step achieves the desired gradual doping density transition without increasing the number of mask processes, thereby improving off-current characteristics while maintaining manufacturing efficiency.
Solution Approach 2:
The mask is designed in advance to define both the first impurity region and the second impurity region simultaneously. By performing the preliminary design of the mask pattern to include both regions, the complex doping profile is achieved in a single step, avoiding the need for multiple sequential mask processes.
Data Source
AI summary
Provided is a thin film semiconductor device such as an organic light-emitting display which includes a thin film transistor (TFT) having a lightly doped region. The thin film semiconductor includes a substrate, a first active pattern, a first lower conductive pattern, and a first upper conductive pattern. The first active pattern is disposed on the substrate and includes a channel region, a lightly doped region, and a heavily doped region. The first lower conductive pattern is disposed on the first active pattern and covers the channel region. The first upper conductive pattern is disposed on the first lower conductive pattern and covers the channel region and the lightly doped region.