Stacked Image Sensor Pad Layout for Dark Current Uniformity
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Solution Overview
Problem
In solid-state imaging apparatuses with stacked semiconductor substrates, the difference in dark current between pixel circuits on electrode pads and those on dummy pads leads to noise in image data, reducing image quality.
Innovation Solution
The implementation of a configuration where first and second substrates are secured together with a bonding surface, featuring first and second pads connected by vias, ensures uniform hydrogen supply to pixel circuits, thereby equalizing dark current and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dummy pads are bonded to electrode pads to improve bonding strength, then bonding strength is improved, but dark current uniformity deteriorates causing noise in image data
Solution Approach 1:
The patent applies local quality by making the dummy pads electrically isolated from the pixel circuits through which they do not electrically connect to vertical signal lines. This local electrical isolation ensures that hydrogen supplied to dummy pads does not affect the dark current characteristics of adjacent pixel circuits, while still maintaining mechanical bonding strength across the entire bonding surface.
2Strength
If hydrogen is supplied uniformly to all pads, then bonding strength is improved, but dark current difference between pixel circuits on electrode pads and dummy pads occurs
Solution Approach 1:
The patent extracts the electrical connection function from the dummy pads by configuring them not to electrically connect to vertical signal lines or pixel circuits. This extraction allows dummy pads to serve their mechanical bonding purpose while preventing them from introducing harmful hydrogen to pixel circuits, thus resolving the conflict between bonding strength and image quality.
3Reliability
If the number of vias connected to dummy pads is increased to improve bonding, then bonding reliability is improved, but hydrogen supply to pixel circuits increases causing dark current noise
Solution Approach 1:
The patent applies equipotentiality by electrically connecting all dummy pads to the same potential (ground or power supply) through the substrate, making them electrically equivalent to pixel circuits without creating harmful potential differences. This configuration allows uniform hydrogen supply for bonding while preventing dark current noise by eliminating electrical potential differences that could cause charge accumulation.
Data Source
AI summary
There is provided an image sensor including a first substrate including a plurality of pixels and a plurality of vertical signal lines and a plurality of first wiring layers and a second substrate including a plurality of second wiring layers. The first and second substrates are secured together between the pluralities of first and second wiring layers. First pads are provided between one of the plurality of first wiring layers and one of the plurality of second wiring layers and second pads are provided between another of the plurality of first wiring layers and another of the plurality of second wiring layers. First vias and second vias connect the first pads and the one of the plurality of first wiring layers and the one of the plurality of second wiring layers together.