Oxide TFT Layer Stack for High-Mobility Mixed-Circuit Fabrication
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Solution Overview
Problem
Existing semiconductor devices with thin film transistors (TFTs) face challenges in achieving excellent electrical characteristics and efficient manufacturing processes, particularly in forming multiple types of TFTs with different structures on a single substrate without significantly increasing the number of manufacturing steps.
Innovation Solution
The proposed solution involves forming a stack of oxide semiconductor layers, where a metal thin film is first deposited on an insulating surface, followed by the formation of an oxide semiconductor layer. Oxidation treatment, such as heat treatment, is then applied to oxidize the metal thin film, creating a first oxide semiconductor layer with lower electrical resistivity. A second oxide semiconductor layer is subsequently formed, with the thickness of the second layer being greater than that of the metal thin film. This stack is used to manufacture thin film transistors with improved electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single oxide semiconductor layer is used in TFT manufacturing, then the manufacturing process is simple, but the electrical characteristics (field-effect mobility) are insufficient
Solution Approach 1:
The oxide semiconductor layer is divided into two distinct layers: a first oxide semiconductor layer with lower electrical resistivity and a second oxide semiconductor layer with higher electrical resistivity. This segmentation allows each layer to contribute different electrical properties, achieving excellent overall electrical characteristics including high field-effect mobility while maintaining a manageable layered structure.
Solution Approach 2:
Different regions of the oxide semiconductor structure are assigned different electrical properties through the two-layer configuration. The first oxide semiconductor layer provides high conductivity regions, while the second oxide semiconductor layer provides insulating regions, creating local quality variations that enhance overall device performance without requiring complex external structures.
2Adaptability or versatility
If multiple types of TFTs with different structures are formed on a single substrate, then device versatility is improved, but the number of manufacturing steps increases significantly
Solution Approach 1:
The two-layer oxide semiconductor structure serves multiple functions simultaneously: it can form different types of TFTs (depletion-type and enhancement-type) using the same basic layer configuration. By controlling the thickness and material composition of the first and second oxide semiconductor layers, various TFT characteristics can be achieved without requiring fundamentally different manufacturing processes, thus maintaining productivity while enhancing versatility.
Solution Approach 2:
Different TFT types are achieved by varying parameters such as the thickness of the first oxide semiconductor layer (5-20 nm), the thickness of the second oxide semiconductor layer (50-150 nm), and the material composition (In-Ga-Zn-O ratio), rather than changing the fundamental manufacturing process. This allows multiple TFT variants to be produced using the same manufacturing steps with adjusted parameters.
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 enables the fabrication of thin film transistors with excellent electrical characteristics, such as enhanced field-effect mobility, while also simplifying the manufacturing process by allowing multiple types of TFTs to be formed on a single substrate without a substantial increase in processing steps.
Implementation Method 1
oxidation treatment such as heat treatment is performed to oxidize the metal thin film partly or entirely
Implementation Method 2
oxidation treatment such as heat treatment is performed to oxidize the metal thin film partly or entirely
Data Source
AI summary
A semiconductor device which includes a thin film transistor having an oxide semiconductor layer and excellent electrical characteristics is provided. Further, a method for manufacturing a semiconductor device in which plural kinds of thin film transistors of different structures are formed over one substrate to form plural kinds of circuits and in which the number of steps is not greatly increased is provided. After a metal thin film is formed over an insulating surface, an oxide semiconductor layer is formed thereover. Then, oxidation treatment such as heat treatment is performed to oxidize the metal thin film partly or entirely. Further, structures of thin film transistors are different between a circuit in which emphasis is placed on the speed of operation, such as a logic circuit, and a matrix circuit.