Oxide Semiconductor Pixel Circuit for CMOS Image Sensor Threshold Compensation
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Solution Overview
Problem
CMOS image sensors face challenges in miniaturization, leading to increased difficulty in manufacturing transistors with uniform electrical characteristics, resulting in variation in threshold voltage and increased power consumption, which affects imaging quality, speed, and dynamic range.
Innovation Solution
The imaging device incorporates a pixel circuit with a photoelectric conversion element containing selenium and transistors made from oxide semiconductors, including In, Zn, and other metals, to compensate for variation in threshold voltage and reduce power consumption, enabling high-quality imaging with low noise and wide dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transistors are miniaturized to improve resolution, then imaging quality improves, but manufacturing precision deteriorates due to increased difficulty in reducing variation in electrical characteristics
Solution Approach 1:
The patent changes the material parameter of the transistor from conventional silicon-based semiconductors to oxide semiconductor materials (such as In-Ga-Zn-O). This material substitution fundamentally alters the electrical characteristics, providing transistors with threshold voltages that can be precisely controlled and maintained, thereby compensating for the manufacturing variations that occur during miniaturization.
Solution Approach 2:
The patent employs composite material structures in the pixel circuit, combining oxide semiconductor layers with other functional layers to create transistors with superior electrical stability. The oxide semiconductor layer is integrated with gate electrodes, insulating layers, and contact layers to form a composite structure that maintains uniform electrical characteristics even at reduced dimensions.
2Measurement precision
If data is written to capacitor for compensating threshold voltage variation by each imaging, then imaging quality improves, but power consumption increases and total imaging time becomes long
Solution Approach 1:
The patent performs threshold voltage compensation in advance by utilizing the inherent stability of oxide semiconductor transistors. The oxide semiconductor transistor maintains a stable threshold voltage over time and across operating conditions, allowing the compensation value to be determined once and stored in a capacitor. This preliminary compensation eliminates the need for repeated writing operations during subsequent imaging operations, thereby reducing power consumption and imaging time.
Solution Approach 2:
The oxide semiconductor transistor inherently maintains stable electrical characteristics without requiring active compensation mechanisms. The material's physical properties provide self-stabilization of the threshold voltage, reducing the need for external intervention through repeated capacitor writing operations. This self-service characteristic naturally reduces power consumption while maintaining imaging quality.
3Speed
If conventional silicon transistors are used for high-speed operation, then operation speed improves, but power consumption increases due to difficulty in reducing variation in electrical characteristics
Solution Approach 1:
The patent changes the transistor material from silicon-based semiconductors to oxide semiconductors, fundamentally altering the electrical parameters. Oxide semiconductor transistors exhibit lower off-state currents and more stable threshold voltages compared to silicon transistors. This parameter change enables high-speed operation with reduced power consumption because the stable characteristics reduce the need for frequent compensation operations and allow for more efficient switching behavior.
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 provides a CMOS image sensor with improved imaging quality, low power consumption, high sensitivity, and wide dynamic range, suitable for high-speed operation and low-cost manufacturing while maintaining high reliability.
Implementation Method 1
a photoelectric conversion element, wherein the photoelectric conversion element contains selenium in a photoelectric conversion layer
Data Source
AI summary
To provide an imaging device capable of obtaining high-quality imaging data. The imaging device includes a first circuit and a second circuit. The first circuit includes a photoelectric conversion element, a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, a first capacitor, a second capacitor, and a third capacitor. The second circuit includes an eighth transistor. The imaging device can compensate variation in threshold voltage of an amplifier transistor included in the first circuit.