Stacked Image Sensor Transfer Gate Over Photodiode
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Solution Overview
Problem
Integrated circuits with image sensors face challenges in scaling to smaller sizes, leading to reduced photodiode voltage, increased noise, and degraded performance due to insufficient full well capacity and dynamic range, particularly when detecting visible light.
Innovation Solution
The integration of a photodetector with an impingement photodetector well and a base photodetector well, along with a transfer transistor overlying a buried insulator, eliminates the need for a reset transistor and allows for a larger photodetector size without competition for surface area, enhancing full well capacity and sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the image sensor is scaled to smaller sizes, then the overall area is reduced, but the photodiode area is reduced leading to reduced voltage, increased noise level, and reduced full well capacity
Solution Approach 1:
The patent moves the transfer gate from the lateral plane to the vertical dimension by forming it over the photodiode in a stacked configuration. This allows the transfer gate to occupy vertical space rather than competing for lateral area, enabling the photodiode to maintain its full lateral area for light collection while the transfer gate functions in the vertical dimension above it.
Solution Approach 2:
The patent segments the image sensor into distinct functional layers: the photodiode layer for light detection and the transfer gate layer for charge transport control. This segmentation allows each component to be optimized independently - the photodiode maximizes lateral area for full well capacity while the transfer gate is positioned vertically to provide precise control without occupying lateral space.
2Area of stationary object
If the photodiode area is reduced to scale down the image sensor, then the overall size is reduced, but the full well capacity and dynamic range are insufficient
Solution Approach 1:
The transfer gate is repositioned from a lateral arrangement to a vertical arrangement directly over the photodiode. This dimensional change allows the photodiode to maintain its maximum lateral area for charge collection while the transfer gate operates in the vertical dimension, eliminating area competition and preserving full well capacity.
Solution Approach 2:
The stacked configuration with transfer gate over photodiode creates a multi-functional vertical structure where the same lateral footprint serves both light detection (photodiode) and charge transport control (transfer gate) functions, maximizing the utility of each unit area.
3Adaptability or versatility
If multiple components (photodiode, transfer gate, reset gate) are integrated, then the functionality is complete, but they compete for surface area on the integrated circuit
Solution Approach 1:
The patent resolves component competition for surface area by transitioning from a two-dimensional lateral layout to a three-dimensional stacked layout. The transfer gate is positioned vertically over the photodiode, allowing multiple functional components to coexist within the same lateral footprint by utilizing vertical space.
Solution Approach 2:
The transfer gate is nested vertically above the photodiode, creating a compact stacked structure where components are arranged in layers rather than side-by-side. This nesting eliminates lateral area competition while maintaining all necessary functionalities.
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
This configuration enables efficient detection of visible light with improved signal-to-noise ratio and dynamic range, maintaining performance while reducing the overall size of the integrated circuit.
Implementation Method 1
Impinging a photodetector with an electromagnetic radiation source, such as light, produces an electrical current in the photodetector
Data Source
AI summary
Integrated circuits and methods of producing the same are provided. In an exemplary embodiment, an integrated circuit includes a photodetector, where the photodetector includes an impingement photodetector well and a base photodetector well. A transfer transistor overlies the photodetector, where the transfer transistor includes a transfer gate, a source, and a drain. A source contact is electrically connected to the source, and the source contact is also electrically connected to the photodetector.