3D Stacked Image Sensor for Compact VIS-NIR-SWIR Imaging
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Solution Overview
Problem
Current image sensors cannot simultaneously image visual (VIS), near-infrared (NIR), and short-wave infrared (SWIR) spectral ranges using the same device, footprint, and readout circuitry, limiting their scalability and application in various fields.
Innovation Solution
A three-dimensional integrated circuit (3D-IC) is developed, where a SWIR sensitive sub-pixel is stacked on a VIS light sensitive sub-pixel, with shared readout circuitry and a metalens to focus incident light, enabling simultaneous or sequential imaging across all spectral ranges while maintaining superior dark noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If VIS and NIR pixels are implemented in cells in a side by side manner, then imaging capability in VIS and NIR spectral ranges is achieved, but device area increases and scalability is limited
Solution Approach 1:
The patent transitions from a two-dimensional side-by-side pixel arrangement to a three-dimensional stacked architecture. Multiple photodetector layers (VIS, NIR, SWIR) are stacked vertically on top of each other, sharing common readout circuitry. This vertical stacking enables multi-spectral imaging capability while maintaining a compact footprint, directly resolving the contradiction between imaging versatility and device area.
2Reliability
If separate readout circuitry is used for different spectral ranges, then imaging performance is optimized, but device complexity and footprint increase
Solution Approach 1:
The patent implements a universal readout circuitry design where a single set of readout circuits serves multiple photodetector layers detecting different spectral ranges (VIS, NIR, SWIR). The circuitry can selectively read out signals from different layers through control mechanisms, enabling one circuit system to perform multiple functions. This reduces device complexity and footprint while maintaining optimized imaging performance for each spectral range.
3Area of stationary object
If SWIR photodiode is stacked on VIS photodiode, then simultaneous imaging in VIS and SWIR is achieved with compact footprint, but manufacturing complexity increases
Solution Approach 1:
The patent divides the image sensor into separate functional layers, with each layer dedicated to detecting a specific spectral range (VIS layer, NIR layer, SWIR layer). Each layer can be independently optimized and manufactured using appropriate materials and processes, then stacked together. This segmentation approach manages manufacturing complexity by allowing specialized processes for each layer while achieving compact simultaneous multi-spectral imaging capability.
Solution Approach 2:
The patent employs composite material structures, including SiGe or Ge-on-Si photodiodes for SWIR detection stacked on standard silicon photodiodes for VIS detection. This composite approach allows each layer to use materials optimized for its specific spectral range, enabling simultaneous VIS and SWIR imaging in a compact footprint while managing manufacturing through established epitaxial growth techniques for the composite structures.
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 solution allows for simultaneous imaging of VIS, NIR, and SWIR spectral ranges using the same device, maintaining a compact footprint and readout circuitry, enhancing optical performance and reducing power consumption, suitable for applications in AR/VR, consumer, health, and security.
Implementation Method 1
The second pixels are sensitive in the short-wave infrared spectral range
Implementation Method 2
The first pixels are sensitive in the visual and/or near-infrared spectral range
Implementation Method 3
Another aspect relates to a metalens which can be added between two wafers to focus incident light, such as light with SWIR wavelength, onto the pixels
Data Source
AI summary
An image sensor, comprises a three-dimensional integrated circuit comprising a stack with at least a top-, a middle-, and a bottom-tier. The bottom-tier (BTR) comprises a first array of photodetectors, denoted first pixels (PD1), and the first pixels being sensitive in the visual and/or near-infrared spectral range. The middle-tier (MTR) comprises a second array of photodetectors, denoted second pixels (PD2), and the second pixels being sensitive in the short-wave infrared spectral range. The top-tier (TTR) comprises an application-specific integrated circuit, denoted ASIC, operable to read out the arrays of the first and second photodiodes (PD1, PD2).