Rectangular InGaAs Photodiode for Wearable Biomarker Sensing
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Solution Overview
Problem
Existing optical sensors for wearable devices face challenges in accurately detecting low-concentration biomarkers like glucose, ethanol, and lactate due to high signal attenuation in human tissues and the inability to operate without thermoelectric coolers, which are impractical for wearable devices due to space and power constraints.
Innovation Solution
A photodiode with a rectangular active area sensitive to wavelengths between 1200 nm and 2400 nm, optimized for improved optical coupling and reduced Johnson noise, is used in conjunction with a temperature control mechanism that stabilizes operation temperature around body temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If extended InGaAs photodiodes are cooled to sub-zero temperatures by thermoelectric coolers, then Johnson noise is reduced and spectral responsivity is stabilized, but device complexity and power consumption increase significantly
Solution Approach 1:
The patent changes the operating temperature parameter from sub-zero (requiring thermoelectric coolers) to elevated temperatures (25-35°C). This parameter change is achieved through a specifically designed photodiode structure with optimized layer composition and geometry that maintains low Johnson noise and stable spectral responsivity at higher temperatures, eliminating the need for complex cooling systems
Solution Approach 2:
The patent extracts and removes the thermoelectric cooler component from the optical sensor system. By designing the photodiode to operate successfully at elevated temperatures, the cooling subsystem is completely eliminated, reducing device complexity, power consumption, and improving suitability for wearable applications
2Stability of the object's composition
If thermoelectric coolers are used to maintain low operating temperature, then spectral responsivity is stabilized, but space constraints and battery power consumption are violated
Solution Approach 1:
The operating temperature parameter is changed from low (requiring coolers) to elevated (25-35°C). The photodiode structure is specifically optimized with adjusted layer thicknesses and material composition to maintain stable spectral responsivity at these higher temperatures, eliminating the volume-consuming thermoelectric cooler
3Device complexity
If extended InGaAs photodiodes are operated at elevated temperatures without cooling, then device simplicity increases, but Johnson noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The photodiode structure parameters are changed to compensate for elevated temperature effects. This includes optimizing the active region thickness, adjusting the composition gradient in the InGaAs layers, and designing the contact structures to maintain low series resistance and high shunt resistance at 25-35°C operation, thereby keeping Johnson noise low without cooling
Solution Approach 2:
The photodiode is pre-designed and optimized during manufacturing to operate at elevated temperatures. The layer structure, material composition, and geometric parameters are predetermined to provide optimal noise performance and spectral responsivity at 25-35°C, eliminating the need for post-manufacturing cooling
4Measurement precision
If the photodiode active area is increased to improve optical coupling, then detection sensitivity improves, but device area and power consumption increase
Solution Approach 1:
The photodiode geometry parameters are optimized to achieve high optical coupling efficiency with a compact active area. This includes optimizing the active area shape (rectangular or substantially rectangular), adjusting the width and length dimensions, and designing the light-receiving surface profile to maximize light capture within a small footprint, thereby improving detection sensitivity without increasing device area
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 photodiode achieves a four-fold improvement in optical coupling and a 15-fold increase in signal-to-noise ratio, enabling reliable detection of biomarkers without the need for thermoelectric coolers, while maintaining high spectral responsivity and signal quality.
Implementation Method 1
a photodiode having a rectangular active area sensitive to wavelengths within the spectral range of 1200 nm to 2400 nm
Implementation Method 2
thermoelectric coolers reduce the temperature of the sensor, thereby reducing the thermally generated 'detector noise', also known as Johnson noise, which is directly proportional to the temperature, T, of the sensor
Data Source
AI summary
The present invention provides a photodiode for a wearable sensor system, the photodiode having a rectangular active area sensitive to wavelengths within the spectral range of 1200 nm to 2400 nm. The present invention also provides a wearable sensor system comprising the photodiode.