Layered Image Sensor Pixel Layout for Accurate Noise Cancellation
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Solution Overview
Problem
In photoelectric conversion film layered image sensors, it is challenging to thoroughly transfer signal charge due to thermodynamic noise, particularly at fine pixel sizes of 3 μm or less, where feedback circuits are insufficient to cancel out noise accurately.
Innovation Solution
A solid-state imaging device is designed with a pixel circuit layout that includes a photoelectric conversion element above a substrate, a diffusion layer for an amplifier and reset transistor, and a charge accumulation node. The layout features a main signal line, a power line, and a feedback signal line, where at least one of the main signal line or the power line is disposed between the feedback signal line and the charge accumulation node, reducing line-to-line coupling capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pixel size is reduced to increase the number of pixels, then the productivity and resolution are improved, but the incident photon-to-current conversion efficiency is degraded due to interconnect layers
Solution Approach 1:
The patent moves the photoelectric conversion element from the substrate plane to a layered structure above the substrate. The photoelectric conversion film is formed on a transparent electrode layer that is positioned above the substrate, allowing light to incident from the front surface while separating the conversion function from the interconnect layers below.
Solution Approach 2:
A transparent electrode layer is introduced as an intermediary between the substrate and the photoelectric conversion film. This transparent electrode serves as both a support structure and an electrical connection medium, allowing light to pass through while providing electrical connectivity without blocking the incident light path.
2Measurement precision
If a feedback circuit is used to cancel thermodynamic noise, then the measurement precision is improved, but the device complexity increases and feedback errors occur due to coupling capacitance
Solution Approach 1:
The patent extracts and eliminates the problematic coupling capacitance by separating the feedback signal line from the charge accumulation node. The feedback signal line is routed through a different path that avoids direct capacitive coupling with the charge accumulation node, removing the source of feedback errors while maintaining the noise cancellation function.
Solution Approach 2:
An intermediate wiring structure is introduced to transmit the feedback signal without direct coupling to the charge accumulation node. The feedback signal is transmitted through an intermediate path that uses different routing layers or spatial separation, acting as a mediator that transfers the signal without creating harmful capacitive coupling.
3Area of stationary object
If the feedback signal line is placed close to the charge accumulation node, then the device area is reduced, but the line-to-line coupling capacitance increases causing noise errors
Solution Approach 1:
The patent resolves the proximity problem by using vertical separation through multiple wiring layers. The feedback signal line and charge accumulation node are positioned in different wiring layers, achieving spatial separation in the vertical dimension while maintaining compact horizontal layout. This layering approach reduces capacitive coupling without significantly increasing the pixel area.
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 effectively reduces random noise by minimizing line-to-line coupling capacitance, allowing for accurate cancellation of noise even at fine pixel sizes, thereby improving image quality.
Implementation Method 1
a photoelectric conversion element converting incident light into signal charge
Implementation Method 2
a charge accumulation node accumulating the signal charge
Data Source
AI summary
A solid-state imaging device includes: pixels arranged in a matrix; a vertical signal line provided for each column, conveying a pixel signal; a power line provided for each column, proving a power supply voltage; and a feedback signal line provided for each column, conveying a signal from a peripheral circuit to a pixel, in which each of the pixels includes: an N-type diffusion layer; a photoelectric conversion element above the N-type diffusion layer; and a charge accumulation node between the N-type diffusion layer and the photoelectric conversion element, accumulating signal charge generated in the photoelectric conversion element, the feedback signal line, a metal line which is a part of the charge accumulation node, the vertical signal line, and the power line are disposed in a second interconnect layer, and the vertical signal line and the power line are disposed between the feedback signal line and the metal line.