Photodiode Fluid Sensor Cavity Structure for Higher LOC Sensitivity
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Solution Overview
Problem
Current lab-on-chip (LOC) structures with fluid sensors, such as FET-based sensors, face a need for improved sensitivity in detecting and characterizing chemical species in fluids.
Innovation Solution
A semiconductor structure incorporating a photodiode-based fluid sensor with a well region, trench, and multiple semiconductor layers, including a first intrinsic semiconductor layer lining the trench and a second semiconductor layer with different conductivity extending laterally, forming a PIN photodiode, where surfaces of the second semiconductor layer are exposed within a cavity to interact with fluids, enabling enhanced sensitivity through concurrent illumination and fluid exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FET-based sensors are used in lab-on-chip structures, then fluid sensing capability is achieved, but sensitivity is insufficient
Solution Approach 1:
The patent replaces the electrical field-based FET sensing mechanism with an optical field-based photodiode sensing mechanism. The photodiode detects fluid composition through optical absorption, providing superior sensitivity compared to the electrical field interaction in FET-based sensors.
Solution Approach 2:
The patent creates a localized fluid reservoir cavity that concentrates the fluid sample in direct contact with the photodiode's light-sensitive surface. This localized configuration maximizes the interaction between light and fluid, enhancing detection sensitivity at the specific sensing location.
2Measurement precision
If a trench structure is created to expose semiconductor layer surfaces for fluid contact, then sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent segments the device into distinct functional regions: a well region for the photodiode, a trench structure for fluid access, and a capped cavity for fluid reservoir. This segmentation allows each region to be optimized independently while maintaining overall functionality.
Solution Approach 2:
The patent implements a nested structure where the fluid reservoir cavity is formed within the trench, which itself is etched into the well region of the semiconductor substrate. The dielectric cap then covers this nested cavity, creating a compact multi-level structure that maximizes fluid exposure while minimizing overall device footprint.
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-based fluid sensor achieves improved sensitivity by generating an output current proportional to light and fluid interaction, allowing for precise determination of fluid composition and characterization.
Implementation Method 1
causing the photodiode to be illuminated... sensing an output current of the photodiode in response to the concurrent illumination of the photodiode and fluid flow into the cavity
Data Source
AI summary
Disclosed is a semiconductor structure with a photodiode including: a well region with a first-type conductivity in a substrate, a trench in the well region, and multiple conformal semiconductor layers in the trench. The semiconductor layers include a first semiconductor layer, which is, for example, an intrinsic semiconductor layer and lines the trench, and a second semiconductor layer, which has a second-type conductivity and which is on the first semiconductor layer within (but not filling) the trench and which also extends outside the trench onto a dielectric layer. An additional dielectric layer extends over and caps a cavity that is at least partially within the trench such that surfaces of the second semiconductor layer are exposed within the cavity. Fluid inlet/outlet ports extend to the cavity and contacts extend to the well region and to the second semiconductor layer. Also disclosed are methods for forming and using the semiconductor structure.