Back-Side Illuminated Imaging Device Capacitive Element Layout
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing imaging device structure with inter-line capacitance in the wiring layer limits the degree of freedom in wiring layout, restricting the design and performance of capacitive elements.
Innovation Solution
A back-side illuminated imaging device is designed with a capacitive element comprising a first and second metal electrode, where the second metal electrode is positioned closer to the substrate than the contact plug, allowing it to overlap the photoelectric conversion region, thereby increasing layout flexibility and reducing parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitive element is formed on a substrate, then the capacitance of the floating diffusion can be dynamically changed, but the size of the photoelectric conversion region is reduced
Solution Approach 1:
The capacitive element is moved from the substrate plane to the wiring layer above it, utilizing the third dimension (vertical space) to accommodate the capacitor without encroaching on the photoelectric conversion region area. This dimensional transition allows the capacitor to be formed in the wiring layer rather than competing for substrate space.
Solution Approach 2:
The capacitive element is nested within the wiring layer structure, specifically utilizing the space between wiring layers and around contact plugs. The capacitor is embedded in the interconnect structure rather than occupying separate substrate area, effectively nesting it within the existing device architecture.
2Area of stationary object
If a wiring layer is provided with an inter-line capacitance, then the capacitance can be formed without substrate space, but the degree of freedom of wiring layout is limited
Solution Approach 1:
The capacitive element is positioned at specific locations where it overlaps with contact plugs and photoelectric conversion regions, creating localized capacitance functionality. This local placement strategy allows the capacitor to be integrated at strategic points without constraining the overall wiring layout, as capacitors are only needed at specific nodes rather than throughout the entire wiring structure.
3Adaptability or versatility
If the second metal electrode is positioned closer to the substrate than the contact plug, then layout flexibility is increased, but parasitic capacitance may increase
Solution Approach 1:
The position of the second metal electrode is optimized by placing it closer to the substrate than the contact plug, which changes the geometric parameters of the capacitive element. This parameter adjustment increases the overlap area with the photoelectric conversion region, thereby increasing the useful capacitance value while the design manages parasitic effects through careful positioning.
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 the degree of freedom in wiring layout, allows for the formation of capacitive elements with larger capacitance without layout constraints, and reduces unnecessary capacitance, improving the imaging device's performance, especially at low illumination intensities.
Implementation Method 1
a substrate including a photoelectric conversion region
Implementation Method 2
a capacitive element connected to a floating diffusion via a switch element. In this imaging device, the capacitance of the floating diffusion can be dynamically changed
Data Source
AI summary
A back-side illuminated imaging device includes a substrate including a photoelectric conversion region, a contact plug connecting a wiring layer and the substrate, and a capacitive element including a first metal electrode and a second metal electrode disposed between the first metal electrode and the substrate. A distance between the second metal electrode and the substrate is shorter than a length of the contact plug. The second metal electrode overlaps at least a part of the photoelectric conversion region in a planar view with respect to a main surface of the substrate.