3D-Stacked SPAD Pixel Layout for Quench Circuit Miniaturization
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Solution Overview
Problem
Current SPAD pixels face challenges in miniaturization due to the complexity of miniaturizing the quench circuit, which limits the reduction in surface area.
Innovation Solution
A method of manufacturing SPAD pixels involving a stack of layers with molecular and hybrid bonding, where the SPAD is bonded to a quench circuit and a data processing circuit, with the quench circuit being formed within a semiconductor layer and etched to create distinct regions, allowing for miniaturization by separating components and optimizing interconnection networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the quench circuit is integrated in the same level as the SPAD, then the surface area is reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent transitions from planar integration to three-dimensional stacking, placing the quench circuit in a separate level above the SPAD. This vertical dimensionality change allows both components to coexist without increasing surface area, while the bonding interface manages the complexity of integration.
Solution Approach 2:
The pixel is divided into distinct functional levels: the SPAD in the first level and the quench circuit in the second level. This segmentation separates the photon detection function from the signal quenching function, allowing each to be optimized independently while reducing overall surface area through vertical stacking.
2Area of stationary object
If the quench circuit is placed in a separate level, then the surface area is reduced, but the bonding process becomes more complex
Solution Approach 1:
A bonding interface with metal pads and interconnection structures serves as an intermediary between the SPAD level and the quench circuit level. This intermediary layer facilitates electrical connections and mechanical bonding while managing the complexity of the multi-level integration process.
Solution Approach 2:
The quench circuit level is positioned directly above the SPAD level in a nested vertical configuration, with the bonding interface embedding the electrical connections between levels. This nesting approach compactly integrates multiple functional layers within a small footprint.
3Productivity
If molecular bonding is used to bond the levels, then the integration density is improved, but the manufacturing precision requirements increase
Solution Approach 1:
Metal pads and bonding structures are pre-formed on both the SPAD level and the quench circuit level before the actual bonding process. This preliminary preparation establishes precise alignment references that guide the molecular bonding process, ensuring accurate registration of the stacked levels.
Solution Approach 2:
Traditional mechanical bonding methods are replaced with molecular bonding techniques that rely on chemical adhesion at the interface. This substitution enables stronger, more reliable bonds between levels while allowing for precise alignment through the interaction of bonding surfaces at the molecular level.
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 enables the miniaturization of SPAD pixels by separating the SPAD, quench circuit, and data processing circuit, reducing the overall surface area while maintaining efficient photon detection and data processing capabilities.
Implementation Method 1
bonding, on the first level, by molecular bonding, a stack of layers comprising a semiconductor layer
Implementation Method 2
the second and third levels are bonded by hybrid bonding
Data Source
AI summary
An electronic device includes a stack of a first level having a SPAD, a second level having a quench circuit for said SPAD, and a third level having a circuit for processing data generated by said SPAD. A method for making the device includes: a) forming of the first level; b) bonding, on the first level, by molecular bonding, of a stack of layers including a semiconductor layer; and c) forming the quench circuit of the second level in the semiconductor layer.