Back-Side-Illumination Pulse Oximetry Sensor Using Infrared Light
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current pulse oximetry sensors cannot effectively utilize back-side-illumination techniques for SpO2 measurements due to the absorption of red light in the silicon substrate, and they often have aesthetically undesirable features like glowing red light, which is problematic for consumer products like ear buds that require a small form factor.
Innovation Solution
The use of two light emitting sources generating wavelengths outside the visible spectrum, such as 780 nm, which allows IR light to penetrate the silicon substrate effectively, and the optimization of the silicon substrate thickness to prevent red light absorption, along with the implementation of a trench and oxide passivation layer in the BSI chip, enables efficient IR light detection without the need for additional filtering and reduces the sensor's footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If back-side-illumination techniques are used for SpO2 measurements, then cost savings and footprint reduction are achieved, but red light is absorbed within the silicon substrate preventing effective measurement
Solution Approach 1:
The patent changes the wavelength parameter of the light source from red light (660 nm) to infrared light (780 nm or longer). This parameter change allows the light to penetrate through the silicon substrate in back-side-illumination configuration, resolving the absorption problem while maintaining cost savings and compact form factor benefits.
Solution Approach 2:
The patent introduces an infrared LED as an intermediary light source that bridges the gap between the silicon substrate absorption problem and the need for SpO2 measurement capability. The IR LED emits light at wavelengths that can penetrate silicon, enabling back-side-illumination to work for pulse oximetry.
2Reliability
If red LED is used for SpO2 measurement, then measurement capability is achieved, but aesthetically undesirable red light emission occurs
Solution Approach 1:
The patent changes the wavelength parameter from the visible red spectrum (660 nm) to the infrared spectrum (780 nm or longer). This parameter change eliminates the visible red light emission that causes aesthetic issues in consumer products while preserving the pulse oximetry measurement capability through IR light detection.
3Reliability
If red LED is used for SpO2 measurement, then measurement capability is achieved, but sensor footprint increases
Solution Approach 1:
By changing the light wavelength parameter to infrared, the patent enables back-side-illumination architecture which integrates the LED and photodiode more closely together. This parameter change allows the sensor to achieve SpO2 measurement capability with a smaller footprint suitable for earbud applications.
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 allows for cost-effective and compact pulse oximetry sensors that can accurately measure SpO2 and heart rate without the undesirable red light emission, providing a more aesthetically pleasing and efficient diagnostic solution.
Implementation Method 1
a light source that generates wavelengths outside of the visible spectrum, such as 780 nm, which enables IR light to penetrate the silicon substrate
Implementation Method 2
the light incident on a photodiode disposed above the trench
Implementation Method 3
the red light that SpO2 measurements require is absorbed within a relatively small penetration depth in the silicon substrate of the semiconductor device
Data Source
AI summary
Described are embodiments of methods for determining physiological data, such as vital signs, by using an optical diagnostic sensor, the method comprising receiving at a semiconductor material, which is located between a photodiode and a trench, an opening into silicon, or a backside wafer-level package (WLP) coating, light of a first wavelength and light of a second wavelength that are above the wavelength of red light, the semiconductor material acting as a filter that blocks wavelengths below the wavelength of red light; detecting, at the photodiode, light of at least one of the first wavelength or the second wavelength; and using the detected light to determine a vital sign.