Image Sensor Capacitor Structure With Air Gaps for Stable Capacitance
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Solution Overview
Problem
Image sensors with capacitors face challenges in maintaining stable electrical characteristics due to limited capacitance per unit area and unintended coupling capacitance, which affects their performance in applications such as digital cameras and medical micro-cameras.
Innovation Solution
The image sensor design incorporates a capacitor structure with a non-flat lower insulating film and air gaps in the upper insulating film, increasing the effective capacitance per unit area and reducing unintended coupling capacitance by conformally covering the non-flat surface of the lower insulating film and arranging air gaps around the capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the capacitor size is increased to increase capacitance per unit area, then the capacitance per unit area is improved, but the device area is increased
Solution Approach 1:
The lower insulating film is formed with a non-flat surface having concave-convex shapes in the vertical dimension, allowing the capacitor to utilize three-dimensional space rather than just a flat two-dimensional plane. This enables increased effective capacitance area without proportionally increasing the planar device footprint
Solution Approach 2:
The capacitor structure is nested within the non-flat lower insulating film topology, where the capacitor conforms to and fills the concave-convex patterns. This nesting approach maximizes the use of available space within the existing device area, effectively increasing capacitance without expanding the overall device footprint
2Area of stationary object
If the capacitor is placed close to other conductors to increase integration density, then the device area is reduced, but unintended coupling capacitance between the capacitor and conductors therearound is increased
Solution Approach 1:
Air gaps are introduced as intermediary spaces between the capacitor and surrounding conductors. These air gaps act as electrical isolators that reduce unintended coupling capacitance while allowing the capacitor to maintain close proximity to other conductors for high integration density. The air gap serves as a mediating element that enables close spacing without harmful electrical coupling
3Manufacturing precision
If the lower insulating film is made flat to simplify manufacturing, then the manufacturing precision is improved, but the capacitance per unit area is reduced
Solution Approach 1:
The lower insulating film is deliberately formed with non-flat curved surfaces including concave and convex patterns. This curvature increases the surface area available for capacitor formation, thereby increasing capacitance per unit area. The curved topology is achieved through controlled manufacturing processes that balance the complexity of forming non-flat structures with the benefit of increased capacitance
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 enhances the reliability of image sensors by increasing capacitance per unit area and reducing stress-induced defects, leading to improved performance and stability in capturing images.
Implementation Method 1
a capacitor arranged on the lower insulating film to contact the non-flat surface of the lower insulating film and conformally covering the non-flat surface of the lower insulating film along the contour of the non-flat surface of the lower insulating film
Implementation Method 2
at least one air gap having a side facing the at least one second surface of the lower insulating film in the horizontal direction and having a height defined by the upper insulating film in a vertical direction
Data Source
AI summary
An image sensor includes a lower insulating film arranged over a substrate and having a non-flat surface that has a concave-convex shape and includes a first surface, which extends in a horizontal direction parallel to a frontside surface of the substrate, and at least one second surface extending from the first surface toward the substrate, a capacitor arranged on the lower insulating film to contact the non-flat surface of the lower insulating film and conformally covering the non-flat surface of the lower insulating film along the contour of the non-flat surface of the lower insulating film, an upper insulating film covering the capacitor and the lower insulating film, and at least one air gap having a side facing the at least one second surface of the lower insulating film in the horizontal direction and having a height defined by the upper insulating film in a vertical direction.