Oxide Semiconductor Light Sensor for Optical Touch Screens
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Solution Overview
Problem
Conventional touch screen apparatuses face difficulties in sensing inputs at increased distances due to the need for direct touch, and light-sensing devices like amorphous silicon TFTs have insufficient light current changes, leading to delayed sensing and increased parasitic capacitance in larger optical touch screen systems.
Innovation Solution
A light-sensing apparatus using a pixel array with oxide semiconductor transistors, where each pixel includes a light sensor transistor and a switch transistor, connected in series, with a gate driver providing sequential gate voltages and a signal output unit receiving light-sensing signals, allowing for improved sensitivity and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If amorphous silicon TFT is used as light-sensing device, then device can be manufactured with existing processes, but light current change is insufficiently large
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical characteristics to achieve larger light-induced current changes while maintaining compatibility with existing thin-film transistor manufacturing processes
2Measurement precision
If charges are accumulated in capacitor for predetermined period of time, then light sensing signal can be generated, but sensing time is delayed
Solution Approach 1:
The patent extracts and eliminates the capacitor component from the light-sensing pixel circuit, using the oxide semiconductor transistor's inherent ability to accumulate charges during the light sensing period without requiring a separate capacitive storage element, thereby reducing sensing delay
3Area of stationary object
If size of optical touch screen apparatus increases, then direct touch capability is improved, but parasitic capacitance increases
Solution Approach 1:
The patent changes the transistor material parameter to oxide semiconductor, which has superior electrical characteristics including lower off-state current and smaller capacitance, thereby reducing parasitic capacitance effects as the display size increases
4Device complexity
If gate line is connected to light sensor transistors in same row, then circuit design is simplified, but light sensor transistors cannot be reset during signal output period
Solution Approach 1:
The patent segments the gate line connections by row, connecting each light sensor transistor to a different gate line, which enables independent control and resetting of each row's light sensor transistors during the signal output period of other rows
Solution Approach 2:
The patent implements periodic resetting of light sensor transistors by applying reset signals to gate lines in a sequential manner that coincides with the signal output periods of respective rows, ensuring proper reset timing without interfering with ongoing signal readout
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 enables faster and more accurate light sensing with a larger size optical touch screen apparatus, reducing power consumption and simplifying the driving circuitry, while maintaining a high on/off current ratio, thus enhancing the overall performance and usability of optical touch screens.
Implementation Method 1
a light sensor transistor configured to sense light
Data Source
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AI summary
A light-sensing apparatus in which a light sensor transistor in a light-sensing pixel is formed of an oxide semiconductor transistor for sensing light, a method of driving the light-sensing apparatus, and an optical touch screen apparatus including the light-sensing apparatus. The light-sensing apparatus includes a light-sensing pixel array having a plurality of light-sensing pixels arranged in rows and columns, and a plurality of gate lines which are arranged in a row direction and respectively provide a gate voltage to the light-sensing pixel. Each of the light-sensing pixels includes a light sensor transistor for sensing light and a switch transistor for outputting a light-sensing signal from the light sensor transistor, and gates of the light sensor transistors of the light-sensing pixels arranged in an arbitrary row are connected to a gate line arranged in a row previous or next to the arbitrary row.