Microcavity Chemical Sensor for High-Concentration Optical Detection
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Solution Overview
Problem
Existing gas and liquid concentration measurement technologies face challenges in accurately determining high concentrations due to variations in path length and refractive index, leading to limited signal-to-noise ratios and difficulty in achieving short pathlengths, especially in non-dispersive infrared gas sensors.
Innovation Solution
A chemical sensor is developed with a semiconductor substrate and metal layers forming a cavity of less than 100 μm depth, incorporating an optical source and detector, allowing for precise measurement of concentration changes with improved signal-to-noise ratio through wafer-level or chip-level fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional gas cell with 1 cm optical pathlength is used, then the device structure is simple and easy to manufacture, but the measurement precision is poor due to limited signal-to-noise ratio for high concentration detection
Solution Approach 1:
The patent transitions from conventional macro-scale gas cells to micro-scale integrated sensors, utilizing vertical cavity depth reduction (to ≤100 μm) and horizontal planar integration of optical components. This dimensional scaling enables short pathlengths while maintaining manufacturability through standard semiconductor fabrication processes.
Solution Approach 2:
The patent integrates the optical source, detector, and gas cell into a single monolithic device structure. The optical source and detector are positioned in close proximity within the same substrate, eliminating the need for separate external components and simplifying the overall device architecture while achieving precise concentration measurements.
2Measurement precision
If the optical pathlength is reduced to improve signal-to-noise ratio for high concentration measurement, then the measurement precision improves, but the device complexity increases due to fabrication challenges
Solution Approach 1:
The patent replaces traditional mechanical machining methods for creating gas cell cavities with semiconductor fabrication processes. Standard photolithography and etching techniques are used to define cavity depths of ≤100 μm with high precision, leveraging the inherent capabilities of semiconductor manufacturing to achieve consistent, repeatable pathlengths across mass production.
Solution Approach 2:
The patent changes the fabrication parameter regime from macro-scale mechanical tolerances to micro-scale semiconductor process control. By specifying cavity depths in the range of ≤100 μm and using standard semiconductor fabrication parameters, the patent achieves precise pathlength control that is compatible with mass production while maintaining high measurement precision.
3Adaptability or versatility
If a non-dispersive infrared gas sensor with source and detector inside the gas cell is used, then the device integration is improved, but achieving short pathlengths becomes even harder due to required placement of components
Solution Approach 1:
The patent resolves the pathlength conflict by transitioning to a planar, two-dimensional integration scheme. The optical source and detector are positioned laterally adjacent to each other on the same substrate plane, with the light path traveling through a short vertical cavity depth (≤100 μm) rather than a long horizontal path. This dimensional reconfiguration enables both high integration and short pathlength simultaneously.
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 sensor achieves an 11-fold increase in transmittance change measurement sensitivity for gas concentrations and rapid response times, overcoming limitations of conventional gas cells by enabling accurate high-concentration detection with reduced variability and cost-effective mass production.
Implementation Method 1
Using Beer-Lambert law as seen below, transmittance (t) may be provided by: t=e−σnl where σ is the absorption cross-section of the target gas species, n is the concentration of the attenuating species and l is the path length of the beam of light through the gas cell
Implementation Method 2
Attenuated total reflection (ATR) is typically used to measure high concentrations for liquids by optical means
Data Source
AI summary
A chemical sensor that includes a first semiconductor substrate. The chemical sensor may also include a second semiconductor substrate. The chemical sensor may further include one or more metal layers between the first semiconductor substrate and the second semiconductor substrate such that the first and second semiconductor substrates and the one or more metal layers form a cell including a cavity, the cavity having a depth of any value equal to or less than 100 μm. The chemical sensor may also include an optical source. The chemical sensor may additionally include an optical detector such that light emitted by the optical source passes through the cell to the optical detector. The first and second semiconductor substrates and the one or more metal layers may also define at least one inlet for fluid to flow into the cavity and at least one outlet for fluid to flow out of the cavity.