TFT Active Layer Structure for Floating Body Suppression
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Solution Overview
Problem
Organic light emitting display devices face reliability issues due to the floating body effect, which causes threshold voltage shifts in thin film transistors, leading to degradation in transistor reliability.
Innovation Solution
A display device design with a specific active layer structure, including a channel region and conductive regions with varying dopant concentrations and thicknesses, and a method of fabricating this structure to reduce the floating body effect by recombining and dissipating carriers at grain boundaries, thereby stabilizing the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thin film transistor structure is used, then fabrication process is simpler, but threshold voltage shift occurs due to floating body effect
Solution Approach 1:
The active layer is segmented into multiple conductive regions (first conductive region, second conductive region, third conductive region) with different dopant concentrations and thicknesses. This segmentation allows carriers to be recombined and dissipated at grain boundaries between regions, preventing floating body effect and threshold voltage shift while maintaining manufacturing feasibility through a systematic multi-layer structure.
Solution Approach 2:
Different regions of the active layer are assigned different local properties: the first conductive region has higher first dopant concentration, the second conductive region has higher second dopant concentration, and the third conductive region has balanced dopant concentrations. This local quality variation creates grain boundaries that facilitate carrier recombination, solving the threshold voltage stability problem without requiring complete redesign of the fabrication process.
2Reliability
If multiple doping processes are used to achieve varying dopant concentrations, then threshold voltage stability is improved, but manufacturing complexity increases
Solution Approach 1:
The dopant concentrations are predetermined during the formation of each conductive region layer. The first doped layer, second doped layer, and third doped layer are prepared in advance with specific dopant concentrations, eliminating the need for multiple sequential doping processes. This preliminary action maintains threshold voltage stability while simplifying the manufacturing process.
Solution Approach 2:
The formation of conductive regions with varying dopant concentrations is merged into a single fabrication step where multiple doped layers are deposited simultaneously or in sequence without requiring separate doping processes. This merging of operations achieves the desired dopant concentration distribution while reducing manufacturing complexity and process time.
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 effectively reduces or eliminates the floating body effect, improving the reliability of thin film transistors and simplifying the fabrication process by omitting mask and doping steps, leading to enhanced display device performance.
Implementation Method 1
a first doped layer being disposed on the substrate in the first sub-conductive region, wherein in the first doped layer, a concentration of a first dopant is higher than a concentration of a second dopant that is different from the first dopant
Implementation Method 2
along with grain boundaries to recombine and dissipate carriers, reducing the floating body effect
Data Source
AI summary
A display device includes an active layer disposed on a substrate, the active layer including a channel region and a first conductive region, the first conductive region including a first sub-conductive region disposed on a first side of the channel region, and a second sub-conductive region disposed between the first sub-conductive region and the channel region. The first conductive region further includes a first doped layer disposed on the substrate in the first sub-conductive region, a second doped layer disposed on the first doped layer in the first sub-conductive region, disposed on the substrate in the second sub-conductive region, and a third doped layer disposed on the second doped layer in the first sub-conductive region and the second sub-conductive region.