Stacked Silicon Optical Sensor for Multi-Wavelength Oximetry
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Solution Overview
Problem
Current wearable devices with optical heart rate sensors face challenges in achieving high fidelity and efficient blood oxygen saturation monitoring, particularly at low temperatures and in environments with motion artifacts, due to limitations in skin penetration and energy consumption, especially when using visible light, which affects the accuracy and reliability of pulse oximetry.
Innovation Solution
A photoplethysmography (PPG) sensor system utilizing stacked silicon optical sensor chips with different thicknesses to effectively detect green, red, and infrared signals, allowing for simultaneous operation in both visible and near-infrared wavelengths, thereby enhancing skin penetration and reducing energy consumption while maintaining a small form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If visible light (green wavelength) is used for PPG sensing, then the perfusion index is maximized and motion artifacts are reduced, but skin penetration depth is limited and performance at low temperatures deteriorates
Solution Approach 1:
The patent combines multiple silicon optical sensor chips with different thicknesses (15μm, 50μm, 100μm) into a single stacked sensor system. This merging allows the system to simultaneously capture light at different penetration depths, effectively combining the advantages of shallow penetration (high PI, low motion artifacts) and deep penetration (low temperature performance) of visible light sensors.
Solution Approach 2:
The patent transitions from a single-plane sensor to a multi-layer stacked sensor architecture with varying thicknesses. By adding the dimension of depth variation through different chip thicknesses, the system can selectively sense light at multiple penetration depths, resolving the contradiction between shallow and deep skin penetration requirements.
2Measurement precision
If multiple separate sensors are used to cover different wavelengths, then measurement accuracy is improved, but device area and complexity increase
Solution Approach 1:
The patent merges multiple sensor functions into a single stacked sensor package. By stacking silicon sensor chips of different thicknesses, the system achieves multi-wavelength sensing capability in a compact form factor, avoiding the need for separate sensor modules for each wavelength and thereby reducing overall device area and complexity.
Solution Approach 2:
The stacked silicon sensor system serves multiple functions simultaneously: it acts as a multi-wavelength detector, provides depth-resolved sensing, and enables both reflectance and transmittance measurement modes. This multi-functionality eliminates the need for separate dedicated sensors for each function, reducing device area.
3Adaptability or versatility
If silicon sensor chips with different thicknesses are stacked, then skin penetration and wavelength filtering are improved, but device complexity increases
Solution Approach 1:
The patent changes the physical parameter of silicon chip thickness to achieve wavelength-selective sensing. By fabricating sensor chips with specific thicknesses (15μm, 50μm, 100μm), each chip naturally filters different wavelengths based on silicon's absorption characteristics, enabling versatile wavelength detection without complex optical filters or tuning mechanisms.
Solution Approach 2:
The patent segments the sensing function across multiple chips with different thicknesses, where each segment (chip) handles a specific wavelength range. This segmentation allows independent optimization of each chip's thickness for its target wavelength range, achieving versatile detection while maintaining relatively simple individual chip 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
The solution enables more accurate and reliable blood oxygen saturation monitoring with improved skin penetration and reduced energy consumption, providing robust SpO2 values even in challenging conditions, such as low temperatures and motion artifacts, by leveraging the absorption properties of silicon to filter wavelengths and combine signals from multiple sensors.
Implementation Method 1
stacked silicon optical sensor chips having different thicknesses... leveraging the absorption properties of silicon to filter wavelengths
Implementation Method 2
a photodetector (PD) to track any light intensity variation... and transforms it into a photogenerated current
Data Source
AI summary
A stacked photoplethysmography (PPG) sensor for oximetry is capable of sensing simultaneously, with optimal area and quantum efficiency, PPG signals using a plurality of emission wavelengths without the need for time division multiplexing.