Photo TFT Reverse-Bias Driving for Stable In-Cell Touch Sensing

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Solution Overview

Problem

In-cell touch panels experience reduced reliability and sensitivity due to decay of photo-induced current over time, especially under varying illumination conditions, leading to incorrect touch event determination.

Innovation Solution

A novel photo element and driving method featuring a capacitor, charge thin-film transistor, photo thin-film transistor, and switch thin-film transistor, where high and low voltages are applied to gate lines to maintain a reverse-biased stress on the photo thin-film transistor, preventing threshold voltage increase and current decay.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of stationary object

If the photo element is operated under long-term illumination, then the touch panel can continuously detect touch events, but the photo-induced current decays leading to reduced reliability and sensitivity

Engineering Contradiction:

Improvecontinuous operation timeVSAvoidphoto-induced current stability

Core Design Contradiction:

Duration of action of stationary objectVSReliability

Solution Approach 1:

The patent applies preliminary action by introducing a compensation voltage generation mechanism that proactively counteracts the threshold voltage shift before it significantly degrades photo-induced current. The compensation voltage is generated in advance based on the accumulated threshold voltage shift and applied to restore the photo-induced current to its initial level, preventing reliability degradation before it occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the electrical parameters of the photo element by dynamically adjusting the gate voltage to compensate for threshold voltage shift. The compensation voltage is calculated based on the relationship between accumulated threshold voltage shift and photo-induced current decay, and applied to restore the photo-induced current to its initial level, thereby maintaining reliability under continuous operation.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the photo element is operated at high illumination levels (outdoor conditions), then the touch panel can detect touch events in bright environments, but the photo-induced current decays rapidly reducing accuracy

Engineering Contradiction:

Improveillumination condition adaptabilityVSAvoidtouch event detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent implements feedback by continuously monitoring the photo-induced current and comparing it with the initial current level. The difference (threshold voltage shift) is fed back to generate a compensation voltage that is applied to restore the photo-induced current. This closed-loop feedback mechanism ensures accurate touch event detection across varying illumination conditions including outdoor environments.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent adjusts the gate voltage parameter dynamically based on the measured threshold voltage shift. The compensation voltage is calculated as a function of the threshold voltage shift and applied to restore the photo-induced current to its initial level, thereby maintaining measurement precision across different illumination conditions including high illumination outdoor environments.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the photo element operates in dark environments, then the photo-induced current remains stable, but the touch panel cannot detect touch events in low-light conditions

Engineering Contradiction:

Improvephoto-induced current stabilityVSAvoidillumination condition adaptability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the gate voltage parameter to compensate for threshold voltage shift in dark environments. By applying the compensation voltage calculated from the threshold voltage shift, the photo-induced current is restored to its initial level, enabling the touch panel to detect touch events accurately in low-light conditions while maintaining the stability characteristic of dark environment operation.

Inventive Principle:

Principle #35Parameter changes

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

The solution maintains reliable photo-induced current and signal-to-noise ratio, ensuring accurate touch event determination even under long-term illumination and varying environmental conditions.

Implementation Method 1

a photo thin-film transistor for inducing a photo-induced current

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS20110063252A1Photo Element and Driving Method Thereof and Liquid Crystal Display

Publication Date: 2011.03.17 HANNSTAR DISPLAY CORP

AI summary

A photo element includes a capacitor, a switch thin film transistor (TFT), a charge thin film transistor, and a photo thin film transistor. A voltage is charged to the capacitor through the charge TFT, and the output voltage of the capacitor is read through the readout line. The photo-induced current will affect the output voltage of the capacitor; therefore it is employed to determine whether the photo element is touched. Later, a reverse-biased voltage is applied to the photo TFT, such that the threshold voltage and sensitivity of the photo TFT can be maintained.