Thin Film Transistor Back-Channel Step for On-State Current
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Solution Overview
Problem
Existing thin film transistors (TFTs) face challenges in achieving high on-state current and on/off ratio, which are crucial for display device performance and power consumption, due to limitations in electric field distribution and semiconductor layer structures.
Innovation Solution
The introduction of a step portion in the back-channel portion of the semiconductor layer alleviates the electric field concentration, allowing for a higher on-state current and improved on/off ratio by creating a buffer layer with distinct side surfaces and curvature, enhancing charge flow and reducing off-state current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional semiconductor layer structure is used, then the manufacturing process is simple, but the on-state current and on/off ratio are insufficient
Solution Approach 1:
The semiconductor layer is segmented into multiple regions with different thicknesses: a first region with thickness d1 and a second region with thickness d2 (where d1 < d2). This segmentation creates different electric field distributions in each region, allowing the thinner first region to provide high on-state current while the thicker second region provides good off-state characteristics, thereby achieving high on/off ratio without excessive structural complexity
Solution Approach 2:
Different regions of the semiconductor layer are given different local properties through varying thickness. The first region (thinner) is optimized for high carrier transport and on-state current, while the second region (thicker) is optimized for charge confinement and off-state current suppression. This local quality differentiation allows each region to perform its specific function optimally, resolving the contradiction between performance and complexity
Data Source
AI summary
An object is to increase the on-state current of a thin film transistor. A solution is to provide a projection in a back-channel portion of the thin film transistor. The projection is provided so as to be off a tangent in the back-channel portion between a source or a drain and a channel formation region. With the projection, a portion where electric charge is trapped and a path of the on-state current can be apart from each other, so that the on-state current can be increased. The shape of a side surface of the back-channel portion may be curved, or may be represented as straight lines in a cross section. Further, a method for forming such a shape by performing one etching step is provided.