Oxide Thin-Film Transistor Buffer Layer for Stable Off Current
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Solution Overview
Problem
Thin film transistors face issues with increased off current and negative shift of the threshold voltage, and achieving ohmic contact between the oxide semiconductor layer and the source/drain electrode layers, which affects their performance and reliability.
Innovation Solution
An inverted staggered thin film transistor structure is implemented, featuring a buffer layer with a metal oxide layer over the oxide semiconductor layer, and conductive layers with higher oxygen concentration, which acts as a protective layer to prevent impurity incorporation and ensure ohmic contact by diffusing oxygen through thermal treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional thin film transistor structure is used, then the device can be manufactured with standard processes, but off current increases and threshold voltage shifts negatively
Solution Approach 1:
A buffer layer is formed over the oxide semiconductor layer before forming the source and drain electrode layers. This preliminary structural preparation prevents impurity incorporation into the oxide semiconductor layer during subsequent manufacturing steps, thereby preventing off current increase and threshold voltage shift while maintaining compatibility with standard manufacturing processes
Solution Approach 2:
The buffer layer acts as an intermediary protective structure between the oxide semiconductor layer and the source/drain electrode layers. It prevents direct contact and impurity transfer from the electrodes to the semiconductor layer, resolving the contradiction by maintaining reliability without requiring complex manufacturing changes
2Reliability
If the oxide semiconductor layer is directly contacted by source and drain electrodes, then the manufacturing process is simplified, but ohmic contact is not achieved
Solution Approach 1:
The buffer layer is preliminarily formed with conductive properties through specific material selection and formation processes. This preliminary preparation enables ohmic contact between the source/drain electrodes and oxide semiconductor layer without requiring additional complex contact optimization steps
Solution Approach 2:
The buffer layer's electrical conductivity is optimized by controlling its composition and formation parameters. By adjusting these parameters, the buffer layer achieves the appropriate conductivity level to form ohmic contacts while maintaining its protective function, thus improving contact quality without excessive structural complexity
3Productivity
If impurity incorporation is allowed during manufacturing, then the manufacturing process is faster, but off current increases and threshold voltage shifts
Solution Approach 1:
The buffer layer is formed in advance to create a protective barrier before electrode formation steps. This preliminary protection allows subsequent manufacturing steps to proceed without special precautions against impurity contamination, maintaining manufacturing speed while preventing electrical characteristic degradation
Solution Approach 2:
The buffer layer serves as an intermediary barrier that blocks impurity diffusion from the manufacturing environment and electrode materials into the oxide semiconductor layer. This mediation allows fast manufacturing processes to be used without compromising the electrical characteristics stability
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 structure effectively prevents off current increase and threshold voltage shift, while achieving ohmic contact and enhancing the overall performance and reliability of the thin film transistor.
Implementation Method 1
a metal oxide layer which is provided over a middle portion of the oxide semiconductor layer
Implementation Method 2
acts as a protective layer to prevent impurity incorporation and ensure ohmic contact by diffusing oxygen through thermal treatment
Implementation Method 3
a buffer layer is provided over an oxide semiconductor layer and a source electrode layer and a drain electrode layer are provided over the buffer layer
Data Source
AI summary
In a thin film transistor, an increase in off current or negative shift of the threshold voltage is prevented. In the thin film transistor, a buffer layer is provided between an oxide semiconductor layer and each of a source electrode layer and a drain electrode layer. The buffer layer includes a metal oxide layer which is an insulator or a semiconductor over a middle portion of the oxide semiconductor layer. The metal oxide layer functions as a protective layer for suppressing incorporation of impurities into the oxide semiconductor layer. Therefore, in the thin film transistor, an increase in off current or negative shift of the threshold voltage can be prevented.