Amorphous Oxide TFT With Resistance Layer for Low OFF Current
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Solution Overview
Problem
Thin film field effect transistors (TFTs) using amorphous oxide semiconductors face challenges in achieving low OFF current, high ON/OFF ratio, and stable operation on flexible resin substrates due to high carrier concentration variations and sensitivity to environmental conditions like temperature and humidity.
Innovation Solution
A TFT structure is developed with an amorphous oxide semiconductor active layer and a resistance layer having a thickness of more than 3 nm, where the band gap of the active layer is smaller than that of the resistance layer, and the carrier concentration of the active layer is higher than that of the resistance layer, enhancing ON/OFF characteristics and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an amorphous oxide semiconductor is used in an active layer of a TFT, then the TFT can be formed at low temperature on a resin substrate, but the OFF current is high and the ON/OFF ratio is low
Solution Approach 1:
The invention uses a composite structure consisting of an amorphous oxide semiconductor layer (In-Ga-Zn-O) combined with a crystalline oxide semiconductor layer (In-O or Ga-O). This composite structure allows the TFT to be formed at low temperatures while achieving low OFF current and high ON/OFF ratio, as the crystalline oxide layer provides stable semiconductor characteristics without requiring high temperature processing
Solution Approach 2:
The invention changes the carrier concentration parameter of the active layer to be 1×10^13 cm^-3 or less by controlling the composition and structure of the oxide semiconductor layers. This parameter change achieves low OFF current while maintaining low temperature fabrication capability
2Reliability
If a crystalline metal oxide is used as a semiconductor material of an active layer, then desired semiconductor characteristics can be obtained, but high temperature heat treatment is necessary which makes it difficult to form directly on a resin substrate
Solution Approach 1:
The invention creates a composite structure where a thin crystalline oxide semiconductor layer (3 nm or less) is formed within an amorphous oxide semiconductor layer. The crystalline In-O or Ga-O layer provides the desired semiconductor characteristics with low carrier concentration, while the amorphous matrix allows low temperature formation on resin substrates
Solution Approach 2:
The invention applies local quality by creating a localized crystalline region (In-O or Ga-O layer with thickness of 3 nm or less) within the amorphous oxide semiconductor structure. This localized crystalline region provides the necessary semiconductor characteristics without requiring the entire structure to undergo high temperature treatment
3Reliability
If the carrier concentration of the active layer is reduced to achieve low OFF current, then the ON/OFF ratio improves, but the stability and reliability with respect to hysteresis and electric characteristic changes over time worsen
Solution Approach 1:
The composite structure of amorphous In-Ga-Zn-O layer with crystalline In-O or Ga-O layer provides both low carrier concentration (for low OFF current) and high stability. The crystalline oxide layer acts as a stable core that prevents hysteresis and electric characteristic changes while maintaining low carrier concentration
Data Source
AI summary
A TFT is provided which includes, on a substrate, at least a gate electrode, a gate insulating layer, an active layer containing an amorphous oxide semiconductor, a source electrode and a drain electrode, wherein a resistance layer containing an amorphous oxide and having a thickness of more than 3 nm is disposed between the active layer and at least one of the source electrode or the drain electrode, and a band gap of the active layer is smaller than a band gap of the resistance layer. Also, a display using the TFT is provided.