Multi-junction Photodiode Depth Segmentation for High Sensitivity
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Solution Overview
Problem
Conventional CMOS image sensors are limited by the use of color filters and unsuitable for high sensitivity applications due to complex manufacturing processes, high production costs, and issues with spatial resolution and dark currents.
Innovation Solution
A semiconductor device with a multi-junction photodiode structure is developed, featuring specific stacked structures and doping concentrations to detect light of various wavelengths, integrated with CMOS logic processes, reducing dark currents and simplifying fabrication without increasing production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CMOS image sensors use color filters, then spatial resolution is maintained, but sensitivity for high sensitivity applications is reduced
Solution Approach 1:
The photodetector is divided into multiple junctions with different depth ranges, where each junction detects light within its specific depth range. This segmentation allows simultaneous achievement of high sensitivity across different wavelengths while maintaining spatial resolution through depth-selective detection.
Solution Approach 2:
The invention transitions from planar color filter-based wavelength separation to depth-based wavelength discrimination. By utilizing the vertical dimension (depth ranges of junctions) instead of lateral color filters, the system achieves both high sensitivity and spatial resolution.
2Adaptability or versatility
If multi junction structure is formed with additional silicon epitaxy processes, then wavelength discrimination capability is improved, but manufacturing complexity and production costs increase
Solution Approach 1:
The invention uses a single p-type epitaxial layer that serves multiple functions: it provides the base material for all junctions and enables wavelength discrimination through depth-controlled doping. This eliminates the need for multiple separate epitaxial growth processes for different wavelength regions.
Solution Approach 2:
The invention achieves wavelength discrimination by changing the doping concentration parameter at different depths within a single epitaxial layer, rather than creating multiple layers with different materials. This parameter-based approach simplifies manufacturing while maintaining versatility.
3Measurement precision
If isolation layers are added between photodiodes to prevent carrier diffusion, then spatial resolution is improved, but manufacturing complexity and production costs increase
Solution Approach 1:
The invention forms deep n-type well regions that extend sufficiently deep to act as carrier collection channels before carriers can diffuse laterally. This preliminary deep well formation prevents carrier diffusion into adjacent photodiodes without requiring additional isolation layers between pixels.
4Device complexity
If photodiodes are fabricated directly on substrate without epitaxy layers, then manufacturing complexity is reduced, but leakage current increases due to substrate defects
Solution Approach 1:
The invention introduces a p-type epitaxial layer as an intermediary between the n-type substrate and the photodiode junctions. This epitaxial layer acts as a mediator that isolates the active regions from substrate defects, thereby reducing leakage current while maintaining manufacturing simplicity.
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 multi-junction photodiode structure achieves high sensitivity and wavelength discrimination, enhancing detection capabilities while reducing dark currents and production complexities, making it suitable for various detection applications.
Implementation Method 1
the multi junction structure demonstrates different quantum efficiency in the photodiodes disposed at different depth for blue, green and red light
Implementation Method 2
the arsenic ion is implanted with a voltage of 1200 keV to form the junction in a depth of 1 μm
Data Source
AI summary
A multi junction photodiode for molecular detection and discrimination and fabrication methods thereof. The multi junction photodiode includes a substrate having first conductive type dopants, an epitaxial layer having the first conductive type dopants, a deep well having second conductive type dopants, a first well having the first conductive type dopants, a second well having the second conductive type dopants, a third well having the first conductive type dopants, and a first doped region having the second conductive type dopants. The epitaxial layer is disposed on the substrate. The deep well is disposed in the epitaxial layer. The first well having three sides connected to the epitaxial layer is disposed in the deep well. The second well is disposed in the first well. The third well having three sides connected to the epitaxial layer is disposed in the second well. The first doped region is disposed in the third well.