Stacked Electrode Structure for Oxide Semiconductor Contact Resistance
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Solution Overview
Problem
Existing thin film transistors face challenges in reducing contact resistance between oxide semiconductor layers and source/drain electrode layers, limiting material choices for these electrodes and affecting the upper temperature limit of processing.
Innovation Solution
A stacked-layer structure for source and drain electrode layers is implemented, using metals or alloys with work functions lower than the oxide semiconductor layer, such as indium, zinc, or yttrium, to form an optimal contact state, allowing for wider material choices and higher processing temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer source and drain electrode structure is used, then the device structure is simple, but the contact resistance between the oxide semiconductor layer and electrode layers is high
Solution Approach 1:
The source and drain electrode layers are divided into multiple sub-layers with different functions: a first electrode layer (Al, Mo, or W) providing low contact resistance, and a second electrode layer (Ru, Rh, Ir, or their alloys) providing heat resistance and oxidation resistance. This segmentation allows each layer to optimize its properties independently, achieving both low contact resistance and high reliability.
Solution Approach 2:
The electrode structure uses composite material design by stacking different metal layers. The first electrode layer uses metals with low work function (Al: 4.28 eV, Mo: 4.6 eV, W: 4.55 eV) to reduce contact resistance, while the second electrode layer uses heat-resistant metals (Ru, Rh, Ir) to withstand processing temperatures. This composite structure combines the advantages of different materials to solve the contradiction between contact resistance and structural simplicity.
2Reliability
If metals with low work function are used for source and drain electrodes, then contact resistance is reduced, but the upper limit of processing temperature is lowered
Solution Approach 1:
The electrode structure is segmented into two functional layers: the first layer (Al, Mo, or W) is optimized for electrical contact with low work function, while the second layer (Ru, Rh, Ir, or alloys) is optimized for thermal stability. This segmentation allows the low-work-function metal to provide low contact resistance without being directly exposed to high-temperature processing, as the second heat-resistant layer protects it.
Solution Approach 2:
The second electrode layer acts as an intermediary protective layer between the heat source and the first electrode layer. This intermediate layer with high melting point and oxidation resistance shields the low-work-function metal from direct thermal exposure, enabling the structure to withstand high processing temperatures while maintaining low contact resistance properties.
3Temperature
If high-heat-resistant materials are used for source and drain electrodes, then processing temperature limit is raised, but contact resistance increases
Solution Approach 1:
The electrode structure divides the functional requirements into two separate layers: the first layer specializes in providing low contact resistance through low work function metals, while the second layer specializes in providing heat resistance. This segmentation eliminates the need to compromise between these conflicting requirements in a single material.
Solution Approach 2:
The composite electrode structure combines metals with different properties in a stacked configuration. The first layer uses Al, Mo, or W for optimal electrical contact, while the second layer uses Ru, Rh, Ir, or their alloys for thermal stability. This composite design achieves both low contact resistance and high processing temperature capability that cannot be obtained with single materials.
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 effectively reduces contact resistance and allows for the use of high-heat-resistant materials, enhancing the electrical characteristics and reliability of thin film transistors.
Implementation Method 1
a thin layer, in the stacked-layer structure, is formed using a metal whose work function is lower than the work function of an oxide semiconductor layer or an alloy containing such a metal
Data Source
AI summary
An object is, in a thin film transistor including an oxide semiconductor layer, to reduce contact resistance between the oxide semiconductor layer and source and drain electrode layers electrically connected to the oxide semiconductor layer. The source and drain electrode layers have a stacked-layer structure of two or more layers in which a layer in contact with the oxide semiconductor layer is formed using a metal whose work function is lower than the work function of the oxide semiconductor layer or an alloy containing such a metal. Layers other than the layer in contact with the oxide semiconductor layer of the source and drain electrode layers are formed using an element selected from Al, Cr, Cu, Ta, Ti, Mo, or W, an alloy containing any of these elements as a component, an alloy containing any of these elements in combination, or the like.