Photodiode with Variable Space Charge Zone for Spectral Resolution
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Solution Overview
Problem
Existing photodiodes face challenges in achieving continuous, variable color resolution and high spectral resolution while maintaining a small area requirement, particularly in CMOS cameras, due to limitations in the expansion of the space charge zone and the complexity of integrating spectrally sensitive photodiodes into standard semiconductor processes.
Innovation Solution
A photodiode design featuring a p-n junction between doping regions of different types, with a highly doped and lightly doped layer, allows for variable expansion of the space charge zone through applied voltage, enabling continuous tuning of spectral sensitivity and color resolution, and includes a sink for minority charge carriers to improve resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spectral filters are used to achieve color resolution, then spectral sensitivity is improved, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent extracts the spectral filtering function from separate physical filter components and integrates it directly into the photodiode structure through wavelength-selective contact regions. This eliminates the need for separate spectral filters while maintaining spectral resolution, thereby reducing device complexity and manufacturing complexity.
Solution Approach 2:
The patent combines multiple functions (photodetection and spectral filtering) into a single integrated structure. The wavelength-selective contact regions serve both as electrical contacts and as spectral filters, merging what would traditionally be separate components into one unified device, thus reducing overall device complexity.
2Measurement precision
If multiple photodiodes with spectral filters are interconnected for color detection, then color resolution is improved, but area requirement increases
Solution Approach 1:
The patent segments the photodiode into multiple wavelength-selective contact regions, each responsive to different spectral ranges. This allows a single photodiode to perform the function of multiple filtered photodiodes, maintaining color resolution while reducing the total area required.
Solution Approach 2:
The patent creates a universal photodiode structure that can detect multiple spectral ranges simultaneously through its wavelength-selective contact regions. This multi-functional design eliminates the need for separate dedicated photodiodes for different color channels, significantly reducing area requirements.
3Reliability
If the space charge zone is expanded to improve detection effectiveness for long-wave radiation, then detection effectiveness is improved, but the range of adjustable expansion is limited by doping concentration
Solution Approach 1:
The patent introduces dynamically controllable impedance elements that allow real-time adjustment of the space charge zone expansion. This dynamic control mechanism enables the detection effectiveness to be optimized for different wavelengths during operation, overcoming the static limitations imposed by fixed doping concentrations.
Solution Approach 2:
The patent changes the electrical parameters (impedance) of specific regions to control the space charge zone expansion. By varying impedance rather than relying solely on doping concentration, the system achieves continuous adjustability of the space charge zone to optimize detection for different spectral ranges.
4Measurement precision
If discrete filters are fitted alternately above the photodiode structure for sequential spectral detection, then spectral range detection is improved, but response time increases due to sequential operation
Solution Approach 1:
The patent uses periodic switching of the impedance elements to sequentially activate different wavelength-selective contact regions. This periodic action allows rapid alternation between spectral ranges, achieving fast spectral detection that is much quicker than mechanical filter switching while maintaining spectral resolution.
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 design achieves a continuously variably tuneable color resolution and high lateral and spectral resolution with a small area requirement, suitable for high-resolution digital cameras, by varying the space charge zone expansion and using a sink to minimize disturbance currents.
Implementation Method 1
a photodiode embodied as a semiconductor diode including a p-n junction, in which electromagnetic radiation in the visible and adjacent spectral range is converted into electric current by using the internal photoelectric effect
Implementation Method 2
In the region of the p-n junction, a depletion layer, also called space charge zone, depleted of charge carriers is formed on account of diffusion and recombination processes, in which depletion layer an electric field prevails which provides for a separation of the charge carriers in the space charge zone
Data Source
AI summary
A photodiode comprises a semiconductor material having a p-n junction, the p-n junction being located between a first doping region of a first doping type and a second doping region of a second doping type, the second doping region comprising a highly doped layer and a lightly doped layer. A photodiode further comprises a voltage source being capable to apply a variable voltage between the first doping region and the lightly doped layer of the second doping region in order to vary the expansion of a space charge zone of the p-n junction.