Active Matrix Substrate Multilayer Gate Insulator
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current top gate structure oxide semiconductor TFTs in active matrix substrates and display devices face challenges in reducing variation in TFT characteristics and improving reliability, as existing gate insulating layer structures do not sufficiently decrease threshold voltage shift (ΔVth).
Innovation Solution
A multilayer gate insulating layer with specific hydrogen to nitrogen atom ratios is used, where the lower layer H/N ratio is 1.5 or more and 5.0 or less, and the upper layer H/N ratio is 0.9 or more and 2.0 or less, with the lower layer ratio being larger, to improve the reliability of the TFTs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer gate insulating structure is used, then the structure is simple, but the threshold voltage shift (ΔVth) cannot be sufficiently decreased and reliability is insufficient
Solution Approach 1:
The gate insulating layer is divided into three distinct layers (first gate insulating layer, second gate insulating layer, and third gate insulating layer) with different hydrogen concentrations. This segmentation allows each layer to contribute differently to the overall performance: the first layer provides initial insulation, the second layer (with highest hydrogen concentration) actively suppresses threshold voltage shift, and the third layer provides additional insulation stability, collectively improving TFT reliability.
Solution Approach 2:
Different regions of the gate insulating structure are assigned different hydrogen concentrations to perform different functions. The second gate insulating layer specifically has the highest hydrogen concentration to target the suppression of positive charge accumulation at the oxide semiconductor interface, while other layers have varying hydrogen concentrations optimized for their respective positions and functions.
2Reliability
If existing gate insulating layer structures are used, then manufacturing is simpler, but variation in TFT characteristics cannot be sufficiently decreased
Solution Approach 1:
The invention controls and specifies the hydrogen concentration parameter for each gate insulating layer, with the second layer having the highest hydrogen concentration. By adjusting this critical parameter (hydrogen concentration distribution) during the formation process, the invention achieves reduced TFT characteristic variation and improved reliability while maintaining manufacturability through established thin-film deposition techniques.
3Power
If a top gate structure is used, then the gate insulating layer thickness can be decreased for high current supplying performance, but threshold voltage shift and reliability become critical issues
Solution Approach 1:
The gate insulating structure uses a composite of three insulating layers with different hydrogen concentrations, forming a multi-functional composite structure. This composite approach allows the thin gate insulating layer to maintain high current supplying performance while the specific hydrogen concentration distribution (particularly in the second layer) suppresses threshold voltage shift, resolving the reliability issue associated with thin-gate top-structure TFTs.
Data Source
AI summary
An active matrix substrate has pixel regions, and includes a substrate, pixel TFTs disposed to respectively correspond to the pixel regions, and pixel electrodes electrically connected to the pixel TFTs. The pixel TFTs are each a top gate structure TFT that has an oxide semiconductor layer, a gate insulating layer on the oxide semiconductor layer, and a gate electrode opposing the oxide semiconductor layer with the gate insulating layer therebetween. The gate insulating layer is formed of silicon oxide and includes a lower layer contacting the oxide semiconductor layer, and an upper layer on the lower layer. The lower layer H/N ratio of hydrogen atoms to nitrogen atoms in the lower layer is 1.5 to 5.0. The upper layer H/N ratio of hydrogen atoms to nitrogen atoms in the upper layer is 0.9 to 2.0. The lower layer H/N ratio is larger than the upper layer H/N ratio.