Oxide Semiconductor TFT Gate Electrode Work Function Control
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Solution Overview
Problem
Thin film transistors using oxide semiconductors face challenges with heat resistance, lattice defects, and hydrogen impurities, leading to low resistance and negative threshold voltage, making it difficult to form P-channel transistors and complicating circuit configurations.
Innovation Solution
Incorporating a metal oxide layer in the gate electrode, specifically using metals like platinum, titanium, ruthenium, molybdenum, copper, tungsten, or nickel, to increase the work function difference with the oxide semiconductor, thereby increasing the threshold voltage without adding impurities to the channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If oxide semiconductor is used as active layer, then electron mobility is improved and high mobility is expected even at low temperature, but heat resistance is insufficient causing lattice defects and negative threshold voltage
Solution Approach 1:
The patent applies preliminary action by performing heat treatment in an oxygen atmosphere before the oxide semiconductor layer is fully formed. This pre-oxygenation prevents lattice defects and oxygen detachment during subsequent manufacturing processes, thereby maintaining the heat resistance while preserving the high electron mobility characteristics of oxide semiconductor.
Solution Approach 2:
The patent changes the parameter of oxygen concentration by introducing oxygen plasma treatment or oxygen atmosphere heat treatment. This parameter change ensures sufficient oxygen content in the oxide semiconductor layer, preventing the formation of lattice defects and maintaining positive threshold voltage, thus resolving the contradiction between heat resistance and electron mobility.
2Manufacturing precision
If doping is applied to change threshold voltage, then threshold voltage control is improved, but characteristics deterioration of thin film transistor occurs
Solution Approach 1:
The patent changes the parameter of work function by selecting specific metal materials for the gate electrode (such as tungsten, molybdenum, or their alloys). This material parameter change directly controls the threshold voltage through work function difference with the oxide semiconductor, achieving threshold voltage control without doping, thereby maintaining characteristics stability.
Solution Approach 2:
The patent extracts the doping process from the threshold voltage control method. Instead of adding impurities through doping, the invention uses the inherent work function difference between metal gate electrode and oxide semiconductor to control threshold voltage, thus avoiding characteristics deterioration caused by doping while achieving precise threshold voltage control.
3Reliability
If multi-element system material is used for active layer, then superior electric characteristics are achieved, but controlling element ratio becomes significantly difficult
Solution Approach 1:
The patent changes the parameter of sputtering conditions by controlling oxygen partial pressure, sputtering power, and gas flow ratios during film formation. These parameter changes enable precise control of element ratios in multi-element oxide semiconductor materials (such as IGZO), achieving superior electric characteristics while simplifying the manufacturing control process.
Solution Approach 2:
The patent applies feedback control by monitoring and adjusting sputtering parameters in real-time during film formation. By using oxygen partial pressure control and gas flow ratio adjustment, the system maintains optimal element ratios in the oxide semiconductor layer, ensuring consistent electric characteristics while easing manufacturing control difficulties.
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 allows for the enhancement of threshold voltage in thin film transistors without doping, simplifying the manufacturing process and stabilizing the electric characteristics, enabling the formation of N-channel transistors and preventing circuit complexity.
Implementation Method 1
Incorporating a metal oxide layer in the gate electrode, specifically using metals like platinum, titanium, ruthenium, molybdenum, copper, tungsten, or nickel, to increase the work function difference with the oxide semiconductor, thereby increasing the threshold voltage
Data Source
AI summary
A thin film transistor is provided. The thin film transistor includes a gate electrode, a gate insulating film, and an oxide semiconductor film, wherein at least a portion of the gate electrode includes a metal oxide. An electric device and a display device that include the thin film transistor are also provided in addition to a manufacture method.