Thin Film Transistor Gate Insulator Hydrogen Control
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Solution Overview
Problem
Thin-film transistors using oxide semiconductor layers, such as IGZO, face challenges in maintaining stable threshold voltage under stress conditions like light irradiation and bias voltage, leading to reliability issues in display devices.
Innovation Solution
A thin-film transistor with a gate insulator layer having a hydrogen concentration of 4 atomic % or lower, composed of In, Zn, and Sn, and formed using specific plasma CVD conditions to enhance stress stability, including controlling temperature, power density, and gas flow ratios to reduce hydrogen content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an oxide semiconductor layer is used to achieve high carrier mobility and low temperature film formability, then the transistor can be applied for next generation displays with large size, high resolution, and high-speed drive, but the threshold voltage shifts under stress conditions such as light irradiation and bias voltage application, leading to poor reliability
Solution Approach 1:
The patent changes the chemical composition parameters of the gate insulator layer by incorporating aluminum oxide (Al2O3) in specific proportions (5-50 atomic %) into the silicon oxide matrix. This compositional parameter change modifies the insulator's properties to reduce hydrogen content and improve stress stability, thereby resolving the contradiction between high-speed operation and reliable threshold voltage stability
Solution Approach 2:
The patent creates a composite gate insulator layer combining silicon oxide (SiO2) and aluminum oxide (Al2O3) in a specific ratio. This composite material structure leverages the advantages of both materials: SiO2 provides good insulating properties while Al2O3 contributes to reduced hydrogen content and improved stress resistance, thereby maintaining threshold voltage stability under stress conditions while preserving high carrier mobility
2Reliability
If hydrogen concentration in the gate insulator layer is reduced to less than 6×10^20 atoms/cm³ to suppress hydrogen diffusion into the oxide semiconductor layer, then the threshold voltage shift is suppressed and electric characteristics are improved, but the manufacturing process complexity increases due to specific plasma CVD conditions
Solution Approach 1:
The patent modifies the plasma CVD process parameters by adjusting the gas composition (adding Al-containing gas such as TMA or TEA), temperature (200-400°C), and pressure conditions to directly form a gate insulator layer with inherently low hydrogen content and specific Al2O3 composition. This parameter optimization achieves the desired hydrogen concentration (<6×10^20 atoms/cm³) and stress stability without requiring additional post-processing steps or complex multi-layer structures
Solution Approach 2:
The patent introduces aluminum oxide (Al2O3) as an intermediary material within the gate insulator layer that acts as a barrier to hydrogen diffusion into the oxide semiconductor layer. This intermediary substance prevents hydrogen from reaching the semiconductor layer, thereby suppressing threshold voltage shift and improving reliability while maintaining a relatively simple single-layer or dual-layer gate insulator structure
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 provides excellent switching properties and stress stability, with minimal threshold voltage shift under negative bias and light irradiation, improving the reliability of display devices.
Implementation Method 1
the diffusion of hydrogen into the oxide semiconductor layer is suppressed by allowing the insulator layer in contact with the oxide semiconductor layer to be an oxide insulator layer having a reduced hydrogen concentration
Implementation Method 2
when such an insulator layer having a reduced hydrogen concentration is formed by a plasma CVD method, a gas in which hydrogen is not contained in its molecular structure is needed to be selected and used as the deposition gas
Data Source
AI summary
Provided is a thin film transistor which is provided with an oxide semiconductor thin film layer and has a threshold voltage that does not change much due to light, a bias stress or the like, thereby exhibiting excellent stress stability. A thin film transistor of the present invention is provided with a gate electrode, an oxide semiconductor layer composed of a single layer which is used as a channel layer, an etch stopper layer to protect a surface of the oxide semiconductor layer, a source-drain electrode, and a gate insulator layer arranged between the gate electrode and the channel layer. The metal elements constituting the oxide semiconductor layer comprise In, Zn and Sn. The hydrogen concentration in the gate insulator layer in direct contact with the oxide semiconductor layer is controlled to 4 atomic % or lower.