Through-Electrode Insulation Layout for Low-Capacitance Image Sensors
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Solution Overview
Problem
The presence of a through electrode in semiconductor substrates of solid-state image sensors leads to increased electrostatic capacitance, which decreases conversion efficiency and pixel signal quality, and enlarging the distance between the electrode and substrate to reduce capacitance enlarges the element area.
Innovation Solution
The through electrode is designed with varying thickness and cross-sectional area of the insulating film and conductive portion across different sides of the semiconductor substrate, forming a taper or stepwise shape to minimize electrostatic capacitance without increasing the electrode's area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the through electrode is provided with a conductor and insulating film to transfer electric charge, then the photoelectric conversion element can be connected to the front surface, but the electrostatic capacitance between the through electrode and semiconductor substrate increases, decreasing conversion efficiency
Solution Approach 1:
The insulating film thickness is made non-uniform, being thicker at specific locations (e.g., near the photoelectric conversion element) and thinner at others. This local variation optimizes the balance between maintaining reliable electrical connection where needed and minimizing parasitic capacitance in other regions, thereby improving conversion efficiency while preserving connection reliability.
Solution Approach 2:
The patent changes the geometric parameter of the insulating film from uniform thickness to variable thickness. By adjusting the thickness parameter locally, the design reduces the electrostatic capacitance between the through electrode and substrate, directly addressing the conversion efficiency loss while maintaining the necessary connection functionality.
2Loss of energy
If the distance between the through electrode and semiconductor substrate is enlarged to reduce electrostatic capacitance, then the capacitance decreases, but the element area becomes large
Solution Approach 1:
Instead of uniformly increasing the distance between the through electrode and substrate across the entire element area, the patent applies local quality by varying the insulating film thickness locally. This allows the distance to be increased only where necessary to reduce capacitance, while maintaining compact dimensions in other critical areas, thus reducing electrostatic capacitance without significantly enlarging the overall element area.
3Loss of energy
If the through electrode is provided with varying insulating film thickness, then the electrostatic capacitance is reduced and pixel characteristics are improved, but the manufacturing complexity increases
Solution Approach 1:
The patent implements parameter changes by varying the insulating film thickness, which successfully reduces electrostatic capacitance and improves pixel characteristics. The manufacturing complexity increase is an accepted trade-off for achieving the performance improvement, as the non-uniform thickness can be achieved through standard semiconductor fabrication techniques such as selective deposition or etching processes.
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 electrostatic capacitance, improving pixel characteristics and maintaining a compact electrode size.
Implementation Method 1
electrostatic capacitance is generated between the through electrode and the semiconductor substrate
Data Source
AI summary
There is provided an image sensor including a semiconductor substrate having a first side and a second side and a photoelectric conversion element disposed at the first side of the semiconductor substrate. In addition, a through electrode is coupled to the photoelectric conversion element, where the through electrode includes a conductive portion and an insulating film. A thickness of the insulating film between the semiconductor substrate and the conductive portion at the first side of the semiconductor substrate is different than the thickness of the insulting film between the semiconductor substrate and the conductive portion at the second side of the semiconductor substrate.