CMOS Image Sensor Buried Junction Layout for NIR Timing Resolution
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Solution Overview
Problem
CMOS image sensors with shallow p-n junctions face challenges in photon detection probability (PDP) and timing resolution due to the shallow placement of the p-n junction, which affects the detection of near-infrared radiation and the uniformity of photo-generated charge carrier transport.
Innovation Solution
A CMOS image sensor design with a second doped buried region of a first doping type disposed between a first doped buried region and a first well, creating a more centrally located depletion region deeper in the semiconductor substrate, improving PDP and timing resolution by evenly spacing photo-generated charge carrier creation locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the p-n junction is placed shallow in the semiconductor substrate, then the device complexity is reduced and manufacturing is easier, but the photon detection probability deteriorates and timing resolution worsens
Solution Approach 1:
The patent divides the buried region into multiple doped regions (first doped buried region, second doped buried region, third doped buried region) with different doping types and concentrations. This segmentation allows the depletion region to be extended deeper into the substrate while maintaining manufacturability through systematic doping processes, thereby improving photon detection probability without significantly increasing manufacturing complexity.
Solution Approach 2:
The patent applies different doping types and concentrations at different locations within the buried region. The first doped buried region has a first doping type, the second doped buried region has a second doping type opposite to the first, and the third doped buried region has the first doping type again. This local variation in doping quality creates an optimized depletion region profile that enhances photon detection probability while maintaining overall device manufacturability.
2Device complexity
If the p-n junction is placed shallow in the semiconductor substrate, then the device structure is simplified, but the timing resolution deteriorates due to non-uniform charge carrier transport
Solution Approach 1:
The patent segments the buried region into multiple doped regions with alternating doping types. This segmentation creates a more uniform electric field distribution and charge carrier transport path, improving timing resolution by ensuring uniformity in charge carrier creation and transport locations, while the segmented structure can be implemented using standard manufacturing processes without significantly increasing device complexity.
Solution Approach 2:
The patent changes the doping parameters (doping type, concentration, depth) across different buried regions to optimize charge carrier transport. By varying these parameters systematically, the patent achieves uniform charge carrier creation locations and improved timing resolution while maintaining a device structure that is still relatively simple and manufacturable.
3Reliability
If the depletion region is located deeper in the semiconductor substrate, then the photon detection probability improves, but the uniformity of charge carrier transport deteriorates
Solution Approach 1:
The patent divides the deep buried region into multiple doped regions with alternating doping types. This segmentation allows the depletion region to extend deeper into the substrate for improved photon detection probability, while the alternating doping structure maintains uniformity in charge carrier transport by creating consistent electric field conditions throughout the deep region.
Solution Approach 2:
The patent applies different doping types at different depths within the buried region. The first doped buried region, second doped buried region, and third doped buried region have alternating doping types, creating local variations that collectively maintain uniform charge carrier transport conditions throughout the deep depletion region, thereby improving photon detection probability without sacrificing transport uniformity.
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 design enhances photon detection probability and timing resolution by optimizing the depletion region's location, allowing for more uniform charge carrier transport and improved detection of near-infrared radiation.
Implementation Method 1
The image sensors comprise one or more photodetectors (e.g., photodiodes, phototransistors, photoresistors, etc.) configured to absorb incident radiation and output electrical signals corresponding to the incident radiation
Implementation Method 2
A second doped buried region having a first doping type is disposed in the semiconductor substrate between the first doped buried region and the first well, such that a depletion region is formed along the second doped buried region and the first well
Data Source
AI summary
In some embodiments, a photodetector is provided. The photodetector includes a first well having a first doping type disposed in a semiconductor substrate. A second well having a second doping type opposite the first doping type is disposed in the semiconductor substrate on a side of the first well. A first doped buried region having the second doping type is disposed in the semiconductor substrate, where the first doped buried region extends laterally through the semiconductor substrate beneath the first well and the second well. A second doped buried region having the second doping type is disposed in the semiconductor substrate and vertically between the first doped buried region and the first well, where the second doped buried region contacts the first well such that a photodetector p-n junction exists along the second doped buried region and the first well.