CMOS Image Sensor Light Shielding Film Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The parasitic capacitance caused by light shielding films in CMOS image sensors interferes with the operation of pixel circuits, affecting the performance of photoelectric conversion apparatuses, particularly by reducing signal gradation at low luminance and increasing dark noise.
Innovation Solution
A photoelectric conversion apparatus design that includes a light shielding film with specific portions covering the charge holding and gate electrodes, where the distance between the film and the gate electrode's upper surface is greater than the distance between the film and the semiconductor layer, reducing parasitic capacitance while maintaining effective light shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the light shielding film is increased in area or disposed close to the semiconductor layer to increase light shielding performance, then light shielding performance is improved, but parasitic capacitance is added to the gate electrode
Solution Approach 1:
The light shielding film is divided into multiple portions: a first light shielding film portion covering the charge holding portion and a second light shielding film portion covering the gate electrode. This segmentation allows each portion to be optimized independently - the first portion can be positioned close to the semiconductor layer for effective light shielding, while the second portion is positioned at a greater distance to minimize parasitic capacitance on the gate electrode.
Solution Approach 2:
Different regions of the light shielding film are positioned at different distances from the semiconductor layer. The first light shielding film portion is disposed close to the semiconductor layer to maximize light shielding effectiveness, while the second light shielding film portion is disposed at a greater distance from the gate electrode to minimize parasitic capacitance. This local differentiation resolves the contradiction between light shielding performance and parasitic capacitance reduction.
2Object-affected harmful factors
If the light shielding film is disposed close to the gate electrode to improve light shielding, then light shielding is enhanced, but operation of the pixel circuit is interfered with due to parasitic capacitance
Solution Approach 1:
The light shielding film is segmented into distinct portions with different positioning strategies. The second light shielding film portion that covers the gate electrode is positioned at a greater distance compared to the first light shielding film portion. This segmentation enables the gate electrode region to have reduced parasitic capacitance while other regions maintain effective light shielding, thereby preserving pixel circuit operation reliability.
3Object-affected harmful factors
If the light shielding film area is increased to prevent light from entering the charge holding portion, then light shielding performance is improved, but parasitic capacitance is added to the gate electrode
Solution Approach 1:
The light shielding film exhibits local quality variations in its positioning. The first light shielding film portion has a different distance relationship with the semiconductor layer compared to the second light shielding film portion's distance relationship with the gate electrode. This local differentiation allows the overall light shielding performance to be maintained while specifically reducing parasitic capacitance in the gate electrode region.
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 design reduces parasitic capacitance, enhancing the signal-to-noise ratio and improving the operating speed of pixel circuits, leading to better image quality and reduced dark noise.
Implementation Method 1
The light shielding film includes a first portion covering the charge holding portion and a second portion covering an upper surface of the gate electrode
Implementation Method 2
a charge holding portion configured to hold electric charge generated in the photoelectric conversion portion
Implementation Method 3
a photoelectric conversion portion, a charge holding portion configured to hold electric charge generated in the photoelectric conversion portion
Data Source
AI summary
A photoelectric conversion apparatus includes a semiconductor layer including a photoelectric conversion portion, a charge holding portion configured to hold electric charge generated from the photoelectric conversion portion, and a charge detection portion to which the electric charge held by the charge holding portion is transferred. A gate electrode of a transistor and a light shielding film including a first portion covering the charge holding portion and a second portion covering an upper surface of the gate electrode are disposed above the semiconductor layer. The distance between the second portion of the light shielding film and the upper surface of the gate electrode is greater than the distance between the first portion of the light shielding film and the semiconductor layer.