Shield Line Reduces Parasitic Capacitance in Solid-State Image Pickup Pixels
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Solution Overview
Problem
Solid-state image pickup apparatuses face color mixing issues due to parasite capacitance between floating diffusion areas and signal output lines of adjacent pixels, leading to signal interference and image quality deterioration.
Innovation Solution
Incorporating a shield line between the wiring of one pixel and the signal output line of an adjacent pixel, forming the signal output line to detour the floating diffusion area, and increasing the width of certain wirings to reduce parasite capacitance, with a capacitance ratio of Cp/Cfd of 1.4% or less to minimize color mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the floating diffusion area is positioned close to the signal output line of an adjacent pixel, then the area utilization is improved, but the parasitic capacitance between the floating diffusion area and the signal output line increases causing color mixing
Solution Approach 1:
A shield line is introduced as an intermediary element positioned between the floating diffusion area and the signal output line of the adjacent pixel. This shield line acts as a mediator that reduces the parasitic capacitance coupling between these two structures, allowing them to be positioned closer together without causing color mixing. The shield line is connected to ground potential to provide an electrostatic shield that minimizes the capacitive interference.
Solution Approach 2:
The problem is solved by transitioning from a two-dimensional planar layout consideration to a three-dimensional structure. The shield line is positioned in a different spatial layer or dimension between the floating diffusion area and the adjacent pixel's signal output line, creating vertical or lateral separation that reduces parasitic capacitance while maintaining horizontal compactness for area efficiency.
2Object-affected harmful factors
If the shield line is added to reduce parasitic capacitance, then the color mixing is reduced, but the device complexity increases
Solution Approach 1:
The shield line is merged with existing ground structures or power supply lines in the pixel array, eliminating the need for completely separate shielding infrastructure. By combining the shield line function with existing conductive elements that are already present in the pixel structure, the complexity increase is minimized while still achieving the parasitic capacitance reduction.
Solution Approach 2:
The shield line serves multiple functions: it acts as an electrostatic shield to reduce parasitic capacitance, provides a reference ground potential, and can be integrated with existing ground networks. This multi-functionality reduces the need for additional dedicated structures, thereby limiting the increase in device complexity.
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
Effectively reduces parasite capacitance and color mixing, maintaining acceptable image quality by limiting the capacitance ratio, thereby preventing significant image quality deterioration and ensuring minimal observable color mixing.
Implementation Method 1
a parasite capacitance may be generated between the FD area and the signal output line, thereby resulting a color mixing between the adjacent pixels
Data Source
AI summary
The invention is to reduce a color mixing resulting from influences of adjacent pixels. The invention provides a solid-state image pickup apparatus including plural pixels each including a PN junction area constituting a photoelectric conversion area, a floating diffusion area for holding a charge outputted from the PN junction area, an amplifying transistor for amplifying the charge in the floating diffusion area, and a wiring for connecting at least the floating diffusion area, a gate electrode of the amplifying transistor and a resetting MOS transistor, and a signal output line for outputting signals from the amplifying transistors, the apparatus including shield lines between the wiring of one pixel or the floating diffusion area and the wiring of one pixel and the signal output line of another adjacent pixel.