Stacked Solid-State Image Sensor With Floating Diffusion Coupling
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Solution Overview
Problem
The existing solid-state imaging elements face challenges in securing sufficient space for pixel transistors, leading to reduced photoelectric conversion efficiency due to longer wiring lengths between stacked substrates.
Innovation Solution
A solid-state imaging element is designed with a configuration of three stacked substrates, where the first substrate includes a floating diffusion for temporarily holding electric signals from photoelectric conversion elements, and the second substrate features a multi-gate transistor connected to the floating diffusion, reducing wiring length and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If substrates are subdivided into separate substrates for photoelectric conversion elements and pixel transistors, then sufficient space for pixel transistors is secured, but wiring length increases and photoelectric conversion efficiency decreases
Solution Approach 1:
The patent transitions from planar substrate layout to three-dimensional stacked substrate architecture. By stacking the first substrate (with photoelectric conversion elements) and the second substrate (with pixel transistors) vertically, the patent achieves sufficient space for pixel transistors while maintaining short wiring lengths through vertical inter-substrate connections, thus resolving the contradiction between space requirement and wiring length.
2Area of moving object
If substrates are subdivided into separate substrates for photoelectric conversion elements and pixel transistors, then sufficient space for pixel transistors is secured, but photoelectric conversion efficiency decreases
Solution Approach 1:
The patent uses vertical stacking to separate photoelectric conversion elements and pixel transistors into different spatial layers, providing sufficient space for transistor operation while minimizing signal transmission distance through vertical connections, thereby maintaining high photoelectric conversion efficiency despite substrate subdivision.
Solution Approach 2:
The patent introduces floating diffusion regions as intermediary elements that directly connect photoelectric conversion elements on the first substrate to pixel transistors on the second substrate. This intermediary structure enables efficient signal transfer across substrates, reducing energy loss and maintaining high photoelectric conversion efficiency.
3Loss of energy
If wiring length between stacked substrates is reduced, then photoelectric conversion efficiency improves, but device complexity increases
Solution Approach 1:
The patent segments the imaging device into functionally distinct stacked substrates: the first substrate for photoelectric conversion elements and the second substrate for pixel transistors. This segmentation allows independent optimization of each substrate's layout, achieving short wiring lengths and high efficiency while managing complexity through modular design.
Solution Approach 2:
The floating diffusion regions serve multiple functions: they act as signal transfer intermediaries between substrates, provide charge storage capacity, and enable direct electrical connection without lengthy wirings. This multi-functionality reduces overall device complexity while maintaining high photoelectric conversion efficiency.
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 enhances photoelectric conversion efficiency by minimizing wiring length and allowing for a more compact design without increasing chip size, enabling higher pixel density and improved image quality.
Implementation Method 1
a photoelectric conversion element that converts incident light into an electric signal
Data Source
AI summary
A solid-state imaging element according to the present disclosure includes: a first semiconductor substrate that includes a floating diffusion that temporarily holds an electric signal output from a photoelectric conversion element; and a second semiconductor substrate that faces the first semiconductor substrate, in which the second semiconductor substrate includes a first transistor disposed on a side facing the first semiconductor substrate, the first transistor including: a channel extending along a thickness direction of the second semiconductor substrate; and a multi-gate extending along the thickness direction of the second semiconductor substrate and sandwiching the channel, and the multi-gate of the first transistor is connected to the floating diffusion.