Oxide Semiconductor Transistor Doping for Stability
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Solution Overview
Problem
Current field-effect transistors using amorphous silicon or polycrystalline silicon for active layers face challenges in achieving high carrier mobility, stability, and reduced characteristic variations, particularly in large-screen liquid crystal displays, due to limitations in oxygen concentration control and process window narrowness.
Innovation Solution
A field-effect transistor with a monoclinic crystal compound n-type oxide semiconductor active layer, substitutionally doped with divalent, trivalent, tetravalent, pentavalent, or hexavalent cations, which eliminates the need for precise oxygen concentration control and reduces oxygen vacancies, enhancing lattice stability and property stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If oxygen concentration is precisely controlled during film forming to generate carrier electrons, then carrier mobility is improved, but the process window becomes extremely narrow and stability is reduced
Solution Approach 1:
The patent changes the fundamental parameter approach from precise oxygen concentration control to intentional oxygen deficiency control. By deliberately creating oxygen vacancies and compensating with donor dopants, the process window is widened while maintaining high carrier mobility and improving manufacturing stability.
Solution Approach 2:
The patent converts the harmful effect of oxygen vacancies (which cause instability) into a beneficial feature by intentionally creating controlled oxygen deficiencies and compensating them with donor dopants. This transforms the previously problematic oxygen vacancy into a controlled mechanism for carrier generation and mobility enhancement.
2Speed
If oxide semiconductor is in depression state to realize high mobility, then carrier mobility is improved, but the process window for normally-off becomes extremely narrow
Solution Approach 1:
The patent changes the doping mechanism from oxygen concentration control to substitutional doping with donor-type impurities. This allows independent control of carrier concentration through dopant selection and concentration, widening the process window while maintaining high mobility characteristics.
Solution Approach 2:
The patent introduces donor dopants as intermediary elements that mediate between the oxide semiconductor lattice and carrier generation. These dopant atoms substitute for metal atoms and provide excess electrons, enabling controlled carrier concentration without requiring precise oxygen concentration control.
3Ease of manufacture
If amorphous silicon or polycrystalline silicon is used for active layer, then manufacturing is easier, but carrier mobility is insufficient for high-speed operation
Solution Approach 1:
The patent uses composite material structure combining oxide semiconductor with donor dopant elements. This composite approach achieves high carrier mobility comparable to crystalline silicon while maintaining the manufacturing advantages of amorphous thin film deposition techniques.
Solution Approach 2:
The patent changes the material composition parameter by introducing donor dopants into the oxide semiconductor lattice. This compositional modification enables carrier mobility enhancement without requiring crystallization, maintaining the ease of manufacture of amorphous thin films.
4Speed
If LTPS-TFT is used to increase mobility, then carrier mobility is improved, but threshold voltage variations become large and mother glass size is limited
Solution Approach 1:
The patent changes the material phase from crystalline (LTPS) to amorphous oxide semiconductor with donor doping. This eliminates the need for excimer laser annealing and crystallization processes, reducing threshold voltage variations and enabling larger mother glass sizes while maintaining high mobility.
Solution Approach 2:
The patent converts the typically harmful effect of amorphous phase (lower mobility) into a benefit by combining it with donor dopant elements. This approach achieves high mobility without crystallization, eliminating the associated problems of threshold voltage variation and manufacturing complexity.
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 results in a high-quality field-effect transistor with increased process margin, reduced element variations, and improved mobility, enabling high-precision large-area image display with enhanced stability and reliability.
Implementation Method 1
the n-type oxide semiconductor is a monoclinic crystal compound, which is substitutionally doped with at least one dopant selected from the group consisting of a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, and a hexavalent cation
Implementation Method 2
introducing a sufficient amount of oxygen during formation of a film to eliminate precise control of an oxygen concentration, and reduce oxygen vacancy to enhance stability of lattice to thereby realize stability of properties in a later step
Data Source
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AI summary
A field-effect transistor, which contains: a gate electrode configured to apply gate voltage; a source electrode and a drain electrode, which are configured to extract electric current; an active layer formed of a n-type oxide semiconductor, provided in contact with the source electrode and the drain electrode; and a gate insulating layer provided between the gate electrode and the active layer, wherein the n-type oxide semiconductor is a triclinic crystal compound, a monoclinic crystal compound, or a trigonal crystal compound, each of which is substitutionally doped with at least one dopant selected from the group consisting of a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, and a hexavalent cation, and wherein a valence of the dopant is greater than a valence of a metal ion constituting the n-type oxide semiconductor, excluding the dopant.