Oxide Semiconductor Pixel Circuit for CMOS Image Sensor Threshold Variation
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high-quality imaging data with uniform electrical characteristics, low power consumption, high-speed operation, and wide dynamic range due to variations in threshold voltage of amplifier transistors, especially as miniaturization increases and power consumption rises.
Innovation Solution
An imaging device is designed with a pixel circuit that includes transistors with oxide semiconductor active layers, specifically using In, Zn, and M (where M is Al, Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf) to compensate for variations in threshold voltage, incorporating a photoelectric conversion element and multiple transistors connected in a specific configuration to stabilize signal output and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If transistors are miniaturized to increase resolution, then imaging device resolution is improved, but variation in electrical characteristics of transistors increases
Solution Approach 1:
The patent changes the material parameter from conventional semiconductor to oxide semiconductor, which fundamentally alters the electrical characteristics to achieve extremely low off-state current and reduced threshold voltage variation, directly resolving the contradiction between miniaturization and electrical characteristic uniformity
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor layers with specific metal elements (In, Zn, M) to create transistors with superior electrical characteristics that maintain uniformity even at miniaturized dimensions
2Manufacturing precision
If data is written to capacitor by each imaging to compensate variation, then imaging quality is improved, but total imaging time increases
Solution Approach 1:
The patent performs threshold voltage compensation in advance by utilizing the inherent stability of oxide semiconductor transistors, eliminating the need for per-imaging capacitor writing and thus reducing imaging time while maintaining quality
3Manufacturing precision
If data is written to capacitor by each imaging to compensate variation, then imaging quality is improved, but power consumption increases
Solution Approach 1:
The oxide semiconductor transistors self-compensate for threshold voltage variation through their inherent material stability and low off-state current characteristics, eliminating the need for external compensation circuits and reducing power consumption
4Use of energy by moving object
If oxide semiconductor transistors are used to reduce power consumption, then power efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the semiconductor material parameter to oxide semiconductor, which inherently provides low power consumption through extremely low off-state current, while the manufacturing complexity is managed through established thin-film deposition techniques
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 high-quality imaging data with reduced power consumption, suitable for high-speed operation, wide dynamic range, and high resolution, while maintaining reliability and sensitivity, effectively addressing the challenges of transistor variation and miniaturization.
Implementation Method 1
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
Data Source
AI summary
An imaging device capable of obtaining high-quality imaging data is provided. 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. Variation in threshold voltage of an amplifier transistor (the fifth transistor) included in the first circuit can be compensated.