Image Sensor Shielding Structure for Readout Node Capacitance
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Solution Overview
Problem
Conventional image sensors face challenges in achieving high light sensitivity due to parasitic capacitance in the readout node, which limits the signal voltage and increases noise, making it difficult to record high-quality images, especially in low-light conditions.
Innovation Solution
An image sensor with an electrically conductive shielding structure that surrounds the readout node and is set to a potential dependent on the voltage signal of the converter transistor, reducing the effective capacitance and thereby increasing the signal voltage and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the readout node capacitance is reduced to increase signal voltage, then light sensitivity is improved, but manufacturing precision becomes more difficult due to the need for precise capacitance control
Solution Approach 1:
The patent introduces a shielding structure as an intermediary element between the readout node and surrounding capacitive elements. This shielding structure, connected to a fixed potential, mediates the capacitive coupling and reduces the effective parasitic capacitance of the readout node without requiring direct modification of the readout node itself, thus avoiding manufacturing precision issues while achieving capacitance reduction
Solution Approach 2:
The patent replaces direct physical capacitance reduction (which would require precise mechanical/dimensional control) with an electrical field-based solution using the shielding structure. Instead of mechanically reducing the readout node size or capacitance, the invention uses electrostatic shielding principles to effectively reduce the parasitic capacitance through field manipulation, substituting a controllable electrical approach for a difficult-to-control physical approach
2Measurement precision
If shielding structures are added to reduce parasitic capacitance, then light sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent merges the shielding structure with existing pixel components, particularly integrating it with the readout node and surrounding transistor structures. The shielding structure is combined with the existing capacitive elements and interconnects, creating a multi-functional structure that provides both shielding and structural support, thereby reducing the net increase in device complexity
Solution Approach 2:
The shielding structure serves multiple functions: it reduces parasitic capacitance, provides electrostatic shielding, and can be integrated with existing pixel structures to serve as part of the readout circuitry. This multi-functionality justifies the added complexity by delivering multiple benefits from a single structural addition
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 shielding structure significantly reduces the effective capacitance of the readout node, leading to a substantial increase in light sensitivity by more than halving the noise, allowing for improved image quality in low-light conditions.
Implementation Method 1
The capacitance of the readout node is essentially a parasitic capacitance. The change in voltage caused by each electron is inversely proportional to the capacitance of the readout node.
Implementation Method 2
The respective pixel has an electrically conductive shielding structure that at least partially surrounds the readout node of the pixel and that is set or can be set to an electrical potential that depends on the voltage signal of the converter transistor
Implementation Method 3
Each pixel comprises at least: a photosensitive element to generate electric charge from incident light
Data Source
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AI summary
An image sensor for electronic cameras comprises a plurality of pixels for generating exposure-dependent signals, each pixel comprising at least: a photosensitive element to generate an electrical charge from incident light; a readout node; a transfer gate to selectively couple the photosensitive element to the readout node; a converter transistor to convert the charge present at the readout node into a voltage signal at a signal output; and a selector switch connected to the signal output of the converter transistor to selectively couple the signal output of the converter transistor to an associated readout line of the image sensor. Each pixel has an electrically conductive shielding structure that at least partially surrounds the readout node and is set or adjustable to an electrical potential that depends on the voltage signal of the converter transistor.