Dual-Facing BSI Image Sensor Stacking for Compact Camera Modules
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Solution Overview
Problem
Current mobile electronic devices with dual-facing camera capabilities often rely on two image sensors, which can be bulky and inefficient, lacking the advantages of backside-illuminated (BSI) image sensors such as shorter optical paths and higher quantum efficiency.
Innovation Solution
Integration of two BSI image sensors with a processor wafer using wafer-level stacking methods, where the processor is bonded between the two BSI image sensors, allowing for dual-facing radiation capture with optimized quantum efficiency and reduced size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two separate image sensors are used for dual-facing camera capability, then dual-facing image capture is achieved, but the device becomes bulky and inefficient
Solution Approach 1:
Two separate image sensors are merged into a single integrated sensor unit with dual photodiode regions, where the first photodiode region captures images from one direction and the second photodiode region captures images from the opposite direction. This consolidation maintains dual-facing functionality while reducing overall device volume and eliminating the need for two separate sensor assemblies.
Solution Approach 2:
The invention transitions from a planar arrangement of two separate sensors to a three-dimensional stacked architecture where photodiode regions are positioned at different depths within the substrate. This vertical stacking enables dual-facing capture capability while minimizing the horizontal footprint and overall device bulkiness.
2Ease of manufacture
If FSI image sensors are used, then manufacturing is simpler, but optical path length increases and quantum efficiency decreases
Solution Approach 1:
The invention inverts the traditional FSI architecture by implementing BSI (backside-illuminated) design where light enters through the back of the substrate rather than the front. This inversion allows light to reach photodiode regions without passing through metal stacks and other front-side structures, significantly reducing optical path length and improving quantum efficiency while maintaining manufacturing feasibility through adapted fabrication processes.
Solution Approach 2:
The invention changes the illumination parameter from front-side to backside illumination, fundamentally altering how light interacts with the photodiode region. This parameter change reduces the effective optical path length by eliminating obstructions in the light path and improves quantum efficiency by allowing direct light incidence on the photosensitive region.
3Reliability
If BSI image sensors are used, then quantum efficiency and resolution improve, but manufacturing complexity increases
Solution Approach 1:
The sensor is segmented into distinct functional regions: a first photodiode region for capturing images in a first direction and a second photodiode region for capturing images in an opposite direction. This segmentation allows each region to be optimized for its specific function while simplifying the overall structure compared to a monolithic design, making the BSI architecture more manufacturable.
Solution Approach 2:
The substrate serves multiple functions simultaneously: it acts as the structural support, the light entry window for BSI operation, and the medium for forming both the first and second photodiode regions. This multi-functionality reduces the need for additional separate components and simplifies the overall device structure, making the complex BSI design more manufacturable.
4Volume of moving object
If dual photodiode regions are integrated in a single substrate, then form factor is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The invention performs preliminary actions during the fabrication process by pre-defining the locations and orientations of the first and second photodiode regions within the substrate before final assembly. This preliminary structuring allows for controlled formation of multiple photodiode regions with precise spatial relationships, reducing the precision demands during later manufacturing stages.
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 configuration enables efficient dual-facing image capture with improved resolution and smaller form factor, leveraging the advantages of BSI image sensors while minimizing bulkiness and enhancing quantum efficiency.
Implementation Method 1
a photodiode region for accumulating an image charge in response to radiation incident upon a second side of the substrate
Data Source
AI summary
A device includes two BSI image sensor elements and a third element. The third element is bonded in between the two BSI image sensor elements using element level stacking methods. Each of the BSI image sensor elements includes a substrate and a metal stack disposed over a first side of the substrate. The substrate of the BSI image sensor element includes a photodiode region for accumulating an image charge in response to radiation incident upon a second side of the substrate. The third element also includes a substrate and a metal stack disposed over a first side of the substrate. The metal stacks of the two BSI image sensor elements and the third element are electrically coupled.