Stacked Image Sensor Via Layout for Uniform Dark Current
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Solution Overview
Problem
In solid-state imaging apparatuses with stacked semiconductor substrates, the difference in hydrogen supply to electrode and dummy pads leads to varying dark currents, causing noise in image data and reduced image quality.
Innovation Solution
The implementation of vias connected to both electrode and dummy pads ensures uniform hydrogen supply to pixel circuits, stabilizing dark current levels and improving bonding strength by allowing hydrogen to terminate dangling bonds uniformly across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dummy pads are bonded to each other to improve bonding strength, then bonding strength is improved, but dark current difference occurs between pixel circuits on electrode pads and dummy pads, causing noise in image data
Solution Approach 1:
The patent applies local quality by providing vias only at electrode pads and not at dummy pads. This creates a local difference in hydrogen supply mechanism: electrode pads receive hydrogen through vias to suppress dark current, while dummy pads do not have vias and thus do not supply hydrogen to underlying pixel circuits. This local differentiation resolves the contradiction by maintaining bonding strength through dummy pad bonding while preventing noise through selective via placement at electrode pads.
2Stability of the object's composition
If vias are provided at electrode pads to supply hydrogen uniformly, then dark current uniformity is improved, but device complexity increases due to additional via structures
Solution Approach 1:
The patent uses local quality by restricting via placement exclusively to electrode pad regions rather than uniformly distributing vias across the entire substrate. This localized approach achieves dark current uniformity for functional pixel circuits while avoiding the complexity of implementing vias throughout the entire device, including non-functional dummy pad areas.
Solution Approach 2:
The patent applies partial action by providing vias only where necessary (at electrode pads) rather than excessively providing them at all pad locations including dummy pads. This partial via implementation achieves the required hydrogen supply for dark current suppression in functional areas without the unnecessary complexity of adding vias to non-functional dummy pad areas.
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 approach enhances image quality by reducing noise due to consistent dark current levels and improves the bonding process, leading to more reliable and efficient image data acquisition.
Implementation Method 1
The reason why the difference in dark current occurs as described above is presumably because there is a difference between the amount of hydrogen supplied to the pixel circuit on the electrode pad and the amount of hydrogen supplied to the pixel circuit on the dummy pad
Implementation Method 2
first vias are connected to the one of the plurality of first wiring layers and the first pad provided on the first substrate and second vias are connected to the one of the plurality of second wiring layers and the first pad provided on the second substrate
Data Source
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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.