3D-IC Stacked Event-Based Vision Sensor Fill Factor
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Solution Overview
Problem
Event-based vision sensors face limitations in quantum efficiency and fill factor due to the sharing of light-exposed area between photo-sensitive devices and circuitry, leading to reduced performance and unwanted effects from light exposure on non-photo-sensitive components.
Innovation Solution
The use of a Three-Dimensional Integrated Circuit (3D IC) stacking technique, where multiple wafers or dies are vertically stacked and interconnected, allowing photo-sensitive devices to be exposed to light while non-essential circuitry is shielded, and enabling different components to be fabricated using optimal IC processes, including non-silicon technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photo-sensitive devices and circuitry share the same light-exposed area in planar process, then device integration is achieved, but fill factor and quantum efficiency are reduced
Solution Approach 1:
The patent transitions from two-dimensional planar integration to three-dimensional stacked integration. Photo-sensitive devices are placed on a first substrate while circuitry is placed on a second substrate, with vertical interconnections (through-silicon vias, bump bonds, or wire bonds) connecting the layers. This dimensional change allows both photo-sensitive area and circuit functionality to coexist without competing for the same planar space, thereby maximizing fill factor while maintaining full device integration.
Solution Approach 2:
The patent segments the integrated device into separate functional layers: photo-sensitive devices on one substrate and circuitry on another substrate. This segmentation allows each component to be optimized independently for its specific function while maintaining electrical connectivity through vertical interconnections, resolving the conflict between integration and fill factor.
2Ease of manufacture
If circuitry is placed in the light-exposed area, then device integration is achieved, but performance is degraded due to unwanted light exposure effects
Solution Approach 1:
By moving circuitry to a separate vertical layer (second substrate) that is not directly exposed to light, the patent protects sensitive circuit components from unwanted light effects such as photo-generated noise and thermal effects. Light only interacts with the photo-sensitive devices on the first substrate, while circuitry operates in a shielded environment, maintaining high reliability and performance.
Solution Approach 2:
The patent introduces an intermediary structure (the second substrate) that physically separates light-exposed photo-sensitive devices from light-sensitive circuitry. This intermediary layer acts as a shield, allowing circuitry to function without direct light exposure while maintaining electrical connectivity through controlled vertical interconnections.
3Ease of manufacture
If all components are manufactured in the same IC process, then manufacturing simplicity is maintained, but component-specific optimization is limited
Solution Approach 1:
The patent segments the manufacturing process into separate fabrication steps for different substrates. Photo-sensitive devices can be manufactured using specialized processes (including non-silicon materials like GaAs) on the first substrate, while circuitry is manufactured using standard CMOS or other appropriate processes on the second substrate. This segmented approach allows each component to be optimized for its specific requirements while maintaining overall manufacturing feasibility through subsequent stacking and interconnection.
Solution Approach 2:
The patent enables the use of different materials for photo-sensitive devices and circuitry components. For example, photo-sensitive devices can be fabricated using compound semiconductor materials (GaAs, InP) on the first substrate to maximize quantum efficiency, while circuitry uses silicon-based CMOS on the second substrate. The heterogeneous material stack is then integrated through vertical interconnections, achieving component-specific optimization.
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 maximizes the fill factor and quantum efficiency by optimizing the distribution of components between wafers, reducing unwanted light effects on circuitry and allowing for improved performance and noise reduction, while enabling the use of best-suited technologies for each component.
Implementation Method 1
photodiodes of each pixel of the pixel array are in a first die
Data Source
AI summary
An event-based vision sensor is fabricated using an advanced stacking technique, known as Three-Dimensional Integrated Circuit, which stacks more wafers (or dies) and interconnects them vertically. The electronic integrated circuits of the sensor are then distributed between the two or more electrically connected dies.