Capping Layer Thickness for Light Cancellation in Display Devices
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Solution Overview
Problem
LCD display devices experience display defects due to leakage current caused by light incident on the switching element, which disrupts the switching operation and reduces reliability.
Innovation Solution
A display device design incorporating a capping layer with a thickness determined by the formula d1=(λ/2)×(1/2n), where λ is a visible wavelength and n is the ratio of refractive indices of the passivation layer to the capping layer, to achieve destructive interference and cancel incident light, thereby reducing leakage current. The capping layer is made of inorganic materials like silicon nitride, and the passivation layer can be a color filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin-film transistor is provided in the display panel with a semiconductor layer that protrudes from the source electrode and drain electrode, then the switching element can effectively control the image signal, but light incident on the protruding semiconductor layer causes bondings to disconnect and generates electron-hole pairs, resulting in photo leakage current and display defects
Solution Approach 1:
The patent applies destructive interference of light waves to convert the harmful effect of incident light into a beneficial outcome. By designing a capping layer with specific thickness (d1=(λ/2)×(1/2n)) and utilizing the refractive index difference between the passivation layer and capping layer, incident light undergoes destructive interference at the interface, canceling out the light energy that would otherwise generate photo leakage current. This transforms the harmful light incident on the semiconductor layer into a neutral or beneficial effect by preventing the light from reaching the semiconductor layer.
Solution Approach 2:
The patent changes the physical parameter of the capping layer thickness to a specific value determined by the formula d1=(λ/2)×(1/2n), where λ is the wavelength and n is the refractive index ratio. This parameter change enables the capping layer to function as an anti-reflection coating that minimizes light incidence on the semiconductor layer through destructive interference, thereby reducing photo leakage current while maintaining the switching element's effectiveness.
2Ease of operation
If the semiconductor layer is designed to protrude from the source electrode and drain electrode for proper transistor operation, then the transistor can effectively switch image signals, but this configuration exposes the semiconductor layer to incident light causing display defects
Solution Approach 1:
The patent introduces a capping layer as an intermediary structure between the passivation layer and the pixel electrode. This capping layer serves as a mediator that blocks incident light from reaching the protruding semiconductor layer while allowing the transistor to maintain its switching functionality. The intermediary capping layer with optimized thickness creates destructive interference that prevents light from causing display defects, thus resolving the contradiction between maintaining switching functionality and preventing display defects.
3Reliability
If a capping layer is added to reduce photo leakage current, then display defects are reduced, but the device structure becomes more complex
Solution Approach 1:
The capping layer serves multiple functions simultaneously: it acts as a protective layer for the underlying structures, provides the optical interference function to reduce photo leakage current, and maintains the structural integrity of the display panel. By assigning multiple functions to a single layer, the patent reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving reliable leakage current reduction.
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 leakage current, enhancing the reliability of the switching operation and minimizing display defects by ensuring that light is canceled at the interface between the passivation and capping layers, preventing it from reaching the semiconductor layer.
Implementation Method 1
a thickness of the capping layer is determined according to: d1=(λ/2)×(1/2n), where d1 denotes the thickness of the capping layer, λ denotes a wavelength within visible wavelength range, and n denotes a ratio of refractive indices of the passivation layer to the capping layer
Implementation Method 2
When light is irradiated onto a part of the semiconductor layer that protrudes from the line width of the source electrode and the drain electrode, bondings among the amorphous silicon molecules in the semiconductor layer are disconnected by the light energy, such that electron-hole pairs (e-h pairs) are formed
Data Source
AI summary
The display device includes: a substrate; a thin-film transistor disposed on the substrate; a passivation layer covering the thin-film transistor; a capping layer disposed on the passivation layer; and a pixel electrode disposed on the capping layer and connected to the thin-film transistor, wherein a thickness of the capping layer is determined according to: d1=(λ/2)×(1/2n), where d1 denotes the thickness of the capping layer, λ denotes a wavelength within visible wavelength range, and n denotes a ratio of refractive indices of the passivation layer to the capping layer.