Stacked Image Sensor Bond Pad and Light Shield for Crosstalk Control
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Solution Overview
Problem
Current image sensors face challenges in optimizing the integration of pixel arrays and control circuitry for efficient light capture and signal processing, particularly in multi-chip stacked configurations, which can lead to issues like cross-talk and electrical charge dissipation.
Innovation Solution
The solution involves a method of forming an image sensor with a conductive light shield, color filter elements, opaque layers, planarization layers, microlenses, and anti-reflective coatings, along with trench formation and bonding techniques to enhance light shielding, reduce cross-talk, and improve electrical connectivity across stacked substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a stacked-die arrangement is used to increase pixel density and reduce device size, then the area of the image sensor is reduced, but cross-talk between adjacent pixels increases and electrical charge dissipation becomes difficult
Solution Approach 1:
The patent divides the image sensor into multiple separate dies stacked vertically, with each die containing a portion of the pixel array. This segmentation isolates the pixel circuits vertically, reducing lateral cross-talk between adjacent pixels while maintaining high pixel density. The bond pads on each die provide independent electrical connection points that facilitate charge dissipation without interfering with neighboring pixels.
Solution Approach 2:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional stacked configuration. By stacking multiple dies vertically along the z-axis, the patent increases pixel density without expanding the lateral footprint. This dimensional change separates pixel circuits vertically, reducing electromagnetic interference and cross-talk while providing multiple surfaces for charge dissipation through bond pads.
2Ease of operation
If circuitry is integrated within each pixel column for reading out image signals, then readout functionality is improved, but electrical charge accumulation increases and cross-talk is exacerbated
Solution Approach 1:
The patent extracts the charge dissipation function from the pixel circuitry by providing separate bond pads that extend to the surface of each die. These bond pads are specifically designed to dissipate electrical charge without interfering with the image signal readout circuitry. By separating the charge dissipation path from the signal readout path, the patent eliminates charge accumulation issues while maintaining readout functionality.
Solution Approach 2:
The bond pads serve as intermediary structures between the pixel circuits and the external environment. They provide a dedicated pathway for electrical charge to dissipate from the pixel circuits without interfering with the image signal readout process. The bond pads act as a mediator that separates the charge dissipation function from the signal processing function, preventing charge accumulation and cross-talk.
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 the image sensor's ability to capture light efficiently, reduces noise, and improves signal processing by mitigating cross-talk and electrical charge dissipation, leading to improved image quality and performance in electronic devices.
Implementation Method 1
The pixels in the image sensors may include photosensitive elements such as photodiodes that convert the incoming light into image signals.
Data Source
AI summary
An image sensor may include a sensor chip that is bonded to an application-specific integrated circuit (ASIC) chip. A bond pad for the image sensor may be formed in the ASIC chip and exposed through a trench in the sensor chip. The image sensor may include a conductive light shield at a periphery of the image sensor to shield optically black pixels. An opaque layer may be formed over the conductive light shield to mitigate reflections off the conductive light shield. An anti-reflective layer may be formed over the pixel array. The anti-reflective layer may have a different thickness over the pixel array than in the trench for the bond pad.