OLED TFT Back Channel Protection Insulating Film
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional thin film transistors in organic light emitting diode (OLED) displays suffer from back-channel effects due to overetching, which degrade off-state, swing, and saturation characteristics, and shift the threshold voltage, making them unsuitable for current-driven displays.
Innovation Solution
The implementation of a thin film transistor structure with a back channel protection insulating film, either a photosensitive organic or organic/inorganic hybrid film, formed on top of a laminated high-crystallinity and low-crystallinity semiconductor layer, which reduces fixed charge and prevents overetching, ensuring improved transistor characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional thin film transistor structure with laminated high-crystallinity and low-crystallinity semiconductor layers is used, then manufacturing process is simplified, but overetching occurs during ohmic contact film removal causing back-channel effects that degrade transistor characteristics
Solution Approach 1:
An etch stopper layer is introduced as an intermediary between the ohmic contact film and the semiconductor layers. This layer mediates the etching process by stopping the etchant before it reaches the semiconductor layers, preventing overetching and back-channel effects while maintaining the simplified laminated semiconductor structure
Solution Approach 2:
The etch stopper layer is formed in advance before the ohmic contact film is processed. This preliminary action ensures that when subsequent etching occurs to remove or pattern the ohmic contact film, the semiconductor layers are already protected, preventing damage and maintaining transistor characteristics
2Reliability
If the ohmic contact film is completely removed to improve contact properties, then electrical contact is enhanced, but the active semiconductor layer is exposed to overetching and back-channel effects occur
Solution Approach 1:
The etch stopper layer serves as a protective intermediary that allows the ohmic contact film to be removed or patterned without exposing the semiconductor layers to harmful overetching. This enables complete removal of the ohmic contact film for improved electrical contact while the etch stopper layer prevents the generation of back-channel effects by blocking the etchant
3Productivity
If high carrier mobility is achieved through high-crystallinity semiconductor layers, then light emission efficiency is improved, but the layers become more susceptible to overetching and fixed charge accumulation
Solution Approach 1:
The etch stopper layer acts as a protective intermediary that shields the high-crystallinity semiconductor layers from overetching during ohmic contact film processing. This allows the high-carrier-mobility layers to maintain their superior light emission efficiency without being exposed to the harmful effects of overetching and fixed charge accumulation
Data Source
AI summary
An organic light emitting diode display includes a thin film transistor on a substrate (1). The thin film transistor includes a gate electrode (2), a gate insulating film (3) that covers the gate electrode (2), a first semiconductor film (4) provided on the gate insulating film (3), a second semiconductor film (5) provided on the first semiconductor film (4), a back channel protection insulating film (7) and an ohmic contact film (8) provided on the second semiconductor film (5), and source/drain electrodes (9). A crystallinity of the first semiconductor film (4) is higher than that of the second semiconductor film (5). The back channel protection insulating film (7) is formed as one of an organic insulating film and an organic/inorganic hybrid insulating film. The thin film transistor has excellent off-state characteristics, swing characteristics, and saturation characteristics.