Oxide Semiconductor Gate Stack With High-Work-Function Barrier
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Solution Overview
Problem
Existing semiconductor devices face challenges in maintaining high threshold voltage and electrical conductivity due to oxygen removal from oxide semiconductors, especially when using materials with lower work functions as gate electrodes, leading to fluctuations in Fermi levels and decreased performance.
Innovation Solution
Incorporating a conductor with a higher work function between the gate electrode and the second gate insulating film to prevent oxygen removal from the oxide semiconductor, while using a material with higher electrical conductivity for other gate electrode portions to maintain conductivity and suppress threshold voltage decreases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a material with lower work function is used as gate electrode, then electrical conductivity is improved, but oxygen is removed from oxide semiconductor causing threshold voltage to decrease
Solution Approach 1:
A conductor layer with higher work function than the oxide semiconductor is introduced as an intermediary between the gate electrode and the oxide semiconductor. This intermediary layer prevents oxygen diffusion from the gate electrode to the oxide semiconductor, thereby maintaining the threshold voltage while allowing the use of highly conductive materials for the gate electrode.
2Reliability
If gate electrode material with higher conductivity is used, then electrical conductivity is improved, but Fermi level fluctuation occurs leading to performance degradation
Solution Approach 1:
The conductor layer with higher work function acts as a barrier that stabilizes the Fermi level at the interface between the gate electrode and oxide semiconductor. By preventing direct contact and oxygen exchange, it eliminates Fermi level fluctuations that would otherwise occur with highly conductive gate electrode materials.
3Reliability
If conductor with higher work function is added to prevent oxygen removal, then threshold voltage is maintained, but device complexity increases
Solution Approach 1:
The gate electrode structure is segmented into multiple layers: a gate electrode layer for electrical conductivity and a conductor layer with higher work function for oxygen barrier functionality. This segmentation allows each layer to perform its specific function optimally while maintaining overall device reliability.
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 semiconductor device effectively maintains high threshold voltage and electrical conductivity by using a high work function conductor to prevent oxygen removal and utilizing a conductive material for the gate electrode, thereby enhancing overall performance and stability.
Implementation Method 1
Incorporating a conductor with a higher work function between the gate electrode and the second gate insulating film to prevent oxygen removal from the oxide semiconductor
Data Source
AI summary
A semiconductor device according to an embodiment includes a first conductor, a first oxide semiconductor, a first insulator, a second conductor, a third conductor, and a fourth conductor. The first oxide semiconductor contacts, at one end, the first conductor, and extends in a first direction intersecting a surface of the first conductor. The first insulator surrounds a side surface of the first oxide semiconductor. The second conductor and the first oxide semiconductor interpose the first insulator therebetween. The third conductor contacts another end of the first oxide semiconductor. The fourth conductor extends in a second direction intersecting the first direction, and contacts a second conductor on a side opposite to the first insulator. The second conductor is of a material with a higher work function than a material of the fourth conductor.