Low Temperature Polysilicon Layer Edge Thickness Control

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Solution Overview

Problem

Current low temperature polysilicon technologies face issues with increased mask requirements and production cycles due to light shielding layer processes, and are prone to photo-induced leakage current, affecting display performance with issues like crosstalk and contrast reduction.

Innovation Solution

A method for manufacturing a low temperature polysilicon layer involving a substrate with buffer layers, patterning to form channel and doped regions, and using an island-shaped photoresist layer with halftone masks to reduce edge thicknesses and minimize photon absorption, thereby reducing photo-induced leakage current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If a light shielding layer is added to reduce photo-induced leakage current, then photo-induced leakage current is reduced, but the number of masks required increases and production cycle is extended

Engineering Contradiction:

Improvephoto-induced leakage currentVSAvoidnumber of masks

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent extracts and removes the light shielding layer from the thin film transistor structure. By eliminating this layer along with its associated mask process, the invention reduces the total number of masks from 7-9 to 5-6 while maintaining acceptable photo-induced leakage current performance through alternative structural designs of the polysilicon layer

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention merges the light shielding function into the polysilicon layer structure itself through specific thickness variations and doping configurations. The polysilicon layer is designed with different thicknesses in different regions (thinner at edges, thicker in center) to provide both structural function and optical control, eliminating the need for a separate light shielding layer

Inventive Principle:

Principle #5Merging (Combining)

2Object-generated harmful factors

If a light shielding layer is added to reduce photo-induced leakage current, then photo-induced leakage current is reduced, but production cycle is extended

Engineering Contradiction:

Improvephoto-induced leakage currentVSAvoidproduction cycle

Core Design Contradiction:

Object-generated harmful factorsVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention performs preliminary optimization of the polysilicon layer structure during the main fabrication process. By pre-designing the polysilicon layer with specific thickness variations and doping profiles, the light shielding function is built-in from the start, eliminating the need for subsequent light shielding layer deposition and mask processes that would extend the production cycle

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If the polysilicon layer has uniform thickness, then manufacturing is simpler, but photo-induced leakage current is excessive

Engineering Contradiction:

Improvepolysilicon layer fabricationVSAvoidphoto-induced leakage current

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by creating non-uniform thickness distribution within the polysilicon layer. The layer is designed with thinner regions at the edges and thicker regions in the center, with each region having different thickness optimized for its specific function. This local variation reduces photon absorption in critical areas while maintaining structural integrity and electrical performance

Inventive Principle:

Principle #3Local quality

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

This approach reduces the number of masks needed, shortens production cycles, and decreases photo-induced leakage current, enhancing display performance by minimizing photon absorption and recombination of electron-hole pairs.

Implementation Method 1

the island-shaped photoresist layer is exposed and developed by a halftone mask to form the island-shaped photoresist layer, the halftone mask has an opaque region and a light transmissive region

Methodology Applied

Scientific EffectPhotoresist exposure and development: Photopolymerisation

Implementation Method 2

etching the edge of the channel region and at least one portion of the low doped regions such that thicknesses of the edge of the channel region and the at least one portion of the low doped regions are less than a thickness of another position of the polysilicon layer

Methodology Applied

Scientific EffectEtching: Ablation

Data Source

PatentUS11101387B2Low temperature polysilicon layer, thin film transistor, and method for manufacturing same

Publication Date: 2021.08.24 WUHAN CHINA STAR OPTOELECTRONICS TECH CO LTD

AI summary

A low temperature polysilicon layer, a thin film transistor, and a method for manufacturing same are provided. The low temperature polysilicon layer includes a substrate, at least one buffer layer, and a polysilicon layer. The polysilicon layer is disposed on the at least one buffer layer. The polysilicon layer includes a channel region, two low doped regions disposed on two sides of the channel region, and two high doped regions disposed on an outer side of the low doped regions. Thicknesses of an edge of the channel region and at least one portion of the low doped regions are less than a thickness of another position of the polysilicon layer.