Dual Gate Oxide TFTs for Threshold Voltage Stabilization
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Solution Overview
Problem
The reliability of liquid crystal display (LCD) panels is compromised due to variances in the threshold voltage of thin-film transistors (TFTs) caused by aging or manufacturing processes, leading to abnormal operation as they fail to turn off at the specified voltage, affecting image production.
Innovation Solution
The implementation of a display apparatus with dual gate electrodes for TFTs, where the second gate electrode is electrically connected to the first gate electrode, and an oxide semiconductor active layer is used, enhancing the control over the TFTs to prevent threshold voltage degradation and ensure reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single gate electrode configuration is used for TFTs, then the device structure is simple and manufacturing is easier, but the threshold voltage becomes unstable due to aging and manufacturing variances
Solution Approach 1:
The gate electrode is divided into two separate gate electrodes (first gate electrode and second gate electrode) that can be independently controlled. This segmentation allows independent optimization of each gate's function - the first gate controls the main current flow while the second gate stabilizes the threshold voltage, thereby improving reliability without requiring complex integrated structures
Solution Approach 2:
The insulating layer between the first and second gate electrodes acts as an intermediary that electrically isolates the two gates while allowing both to control the same active layer. This intermediary structure enables the second gate to function as a stabilizing element that compensates for threshold voltage shifts without directly interfering with the primary switching function of the first gate
2Productivity
If inspection-use TFTs are used to control display signals, then quick inspection of the display panel can be performed, but the TFTs may cause image failures due to threshold voltage degradation
Solution Approach 1:
The inspection-use TFTs are equipped with dual gate electrodes that segment the control functions - one gate for switching during inspection and another gate for stabilizing threshold voltage. This ensures that even after aging or manufacturing variances, the inspection TFTs maintain stable threshold voltages and continue to provide reliable inspection signals without causing image failures
Solution Approach 2:
By introducing a second gate electrode, the patent changes the electrical parameters of the inspection-use TFTs, specifically enabling independent control of threshold voltage. This parameter change allows the TFTs to maintain stable operating characteristics throughout the inspection process and prevents threshold voltage degradation from affecting image quality
3Reliability
If the gate terminals of inspection-use TFTs are connected to negative DC voltage to turn them off, then electrical connections among data lines are prevented, but the TFTs cannot be reliably turned off due to threshold voltage variance
Solution Approach 1:
The gate control is segmented into two independent gates, allowing the second gate to be specifically used for threshold voltage stabilization while the first gate handles switching. This segmentation enables more precise control of the off-state by using the second gate to counteract threshold voltage shifts, ensuring reliable turn-off without requiring overly complex voltage control schemes
Solution Approach 2:
The dual gate structure provides a form of feedback control where the second gate can compensate for threshold voltage drift caused by aging or manufacturing variances. By monitoring the effective threshold voltage through the device's electrical characteristics and adjusting the second gate voltage accordingly, the system maintains reliable off-state control
Data Source
AI summary
This disclosure provides a display apparatus which includes a substrate, first TFTs, scan lines and data lines connected to the first TFTs, and second TFTs for controlling inspection-use display signals; wherein each of the second TFTs includes: a first gate electrode disposed on the substrate; a first insulation layer disposed on the first gate electrode; an active unit disposed on the first insulation layer and having a source electrode electrically connected to one of the data lines, an active layer including an oxide semiconductor, and a drain electrode; a second insulation layer disposed on the active unit; and a second gate electrode disposed on the second insulation layer; wherein the first TFTs, the scan lines, and the data lines are disposed in a display area on the substrate, and the second TFTs are disposed in an area other than the display area on the substrate.