Wavelength Selective Photodiode Using Shorted Junctions
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Solution Overview
Problem
Silicon photodiodes are sensitive to a wide range of wavelengths, making it desirable to limit the collected signal to a narrower wavelength band, but optical band filters add fabrication cost and complexity to semiconductor devices.
Innovation Solution
A semiconductor device with a photodiode featuring a stack of p-n junctions, where at least one junction is electrically shorted to prevent signal current from being sensed by an external detection circuit, allowing signal current from a desired wavelength range to be selectively sensed, using metal silicide or other conductive materials for shorting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical band filters are formed over the photodiodes to limit the collected signal to a narrower wavelength band, then the wavelength selectivity is improved, but the fabrication cost and device complexity increase
Solution Approach 1:
The photodiode is divided into multiple p-n junctions stacked vertically at different depths. Each junction is responsible for detecting a specific wavelength range, with shallower junctions detecting shorter wavelengths and deeper junctions detecting longer wavelengths. This segmentation eliminates the need for optical band filters while achieving wavelength-selective detection through the natural depth-dependent absorption characteristics of silicon.
Solution Approach 2:
The patent transitions from lateral wavelength filtering (using optical band filters over the photodiode surface) to vertical wavelength discrimination (using stacked p-n junctions at different depths). By exploiting the third dimension (depth) of the semiconductor structure, the patent achieves wavelength selectivity without adding lateral complexity or optical filtering layers.
2Measurement precision
If optical band filters are formed over the photodiodes to limit the collected signal to a narrower wavelength band, then the wavelength selectivity is improved, but the fabrication cost increases
Solution Approach 1:
The photodiode is divided into multiple p-n junctions stacked vertically at different depths. Each junction is responsible for detecting a specific wavelength range, with shallower junctions detecting shorter wavelengths and deeper junctions detecting longer wavelengths. This segmentation eliminates the need for optical band filters while achieving wavelength-selective detection through the natural depth-dependent absorption characteristics of silicon.
Solution Approach 2:
The silicon material itself is used to provide wavelength-selective detection through its inherent depth-dependent light absorption properties. Different wavelengths are naturally absorbed at different depths within the silicon substrate, allowing the material to serve its own wavelength filtering function without requiring additional optical filter layers or complex fabrication processes.
3Measurement precision
If multiple p-n junctions are stacked to detect different wavelength ranges, then the wavelength selectivity is improved, but the device structure becomes more complex
Solution Approach 1:
The patent transitions from lateral wavelength filtering (using optical band filters over the photodiode surface) to vertical wavelength discrimination (using stacked p-n junctions at different depths). By exploiting the third dimension (depth) of the semiconductor structure, the patent achieves wavelength selectivity without adding lateral complexity or optical filtering layers.
Solution Approach 2:
The stacked p-n junction structure serves multiple functions simultaneously: it provides wavelength-selective detection, maintains electrical connectivity through the semiconductor substrate, and utilizes the natural optical absorption properties of silicon. This multi-functional design achieves wavelength selectivity without requiring separate optical filter components or complex interconnect 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
This approach allows for selective signal current collection from a desired wavelength range, reducing the complexity and cost associated with optical band filters while maintaining sensitivity, by strategically configuring and depth-selecting p-n junctions within the photodiode.
Implementation Method 1
signal current from incident light on the photodiode which generates electron-hole pairs across the connected junction
Data Source
AI summary
A semiconductor device contains a photodiode which has a plurality of p-n junctions disposed in a stack. Two contact structures on the semiconductor device are connected across at least one of the junctions to allow electrical connection to an external detection circuit, so that signal current from incident light on the photodiode which generates electron-hole pairs across the connected junction may be sensed by the external detection circuit. At least one of the junctions is electrically shorted at the semiconductor device, so that signal current from the shorted junction may not be sensed by the external detection circuit.