Active Device Substrate Protrusion for Channel Size Control
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Solution Overview
Problem
The existing methods for forming thin film transistors on substrates with protrusions result in variations in channel size due to instability in applying photoresist materials, leading to inconsistent electrical characteristics and making mass production challenging.
Innovation Solution
The active device substrate features a protrusion with a concave-convex structure, where the photoresist layer is formed to cover and pattern the conductive layer, with the convex portion defining the gap between electrodes, allowing precise control of channel size and reducing variations in electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the channel length is reduced to increase the W/L ratio, then the on-current increases, but the channel length can only be reduced to about 3.5 μm due to limitation of existing exposure and development processes
Solution Approach 1:
The patent introduces a protrusion structure that adds vertical dimension (height) to the substrate surface. By forming the thin film transistor on this protrusion, the channel width can be increased in the horizontal direction while maintaining a reasonable channel length, thus increasing the W/L ratio without being limited by the 3.5 μm exposure process constraint
Solution Approach 2:
The substrate is segmented into a protrusion region and a flat region. The protrusion structure separates the channel formation area from the surrounding areas, allowing independent control of channel dimensions. This segmentation enables precise definition of channel width through the protrusion geometry while maintaining adequate channel length
2Power
If the channel width is increased to increase the W/L ratio, then the on-current increases, but the component layout area increases substantially resulting in loss of the aperture ratio
Solution Approach 1:
By utilizing the vertical dimension through the protrusion structure, the patent achieves increased channel width without proportionally increasing the horizontal footprint. The protrusion allows the channel to extend in width while confining the overall component layout area, thereby preserving aperture ratio while increasing on-current
3Manufacturing precision
If the thin photoresist material is applied on the substrate and protrusion to form the thin film transistor, then the channel size can be defined, but the variations in tape angle and process stability result in large variation in electrical characteristics
Solution Approach 1:
The protrusion structure serves as a self-aligned feature that automatically defines the channel boundaries. The photoresist material applied on the protrusion naturally conforms to the protrusion geometry, and the etching process uses the protrusion itself as a mask, eliminating the need for precise tape angle control and reducing process variability
Solution Approach 2:
The protrusion structure is formed beforehand to pre-establish the channel geometry. This preliminary action of creating the protrusion with precise dimensions allows subsequent photoresist application and etching to proceed with minimal variability, as the critical dimensions are already defined by the protrusion structure rather than relying on photoresist application precision
Data Source
AI summary
An active device substrate including a substrate and an active device is provided. The active device includes a protrusion, a gate disposed on the protrusion, a semiconductor layer, a gate insulation layer disposed between the gate and the semiconductor layer, a first electrode and a second electrode electrically connected to the semiconductor layer. The protrusion has a first upper surface, a second upper surface, an inner surface and an outer surface. The inner surface and the first upper surface define a concave portion. The inner surface, the second upper surface and the outer surface define a convex portion. The semiconductor layer is disposed on the first upper surface, the inner surface, the second upper surface and the outer surface. The first electrode is disposed on at least one portion of the outer surface. The second electrode is disposed in the concave portion of the protrusion.