Global Shutter CMOS Sensor Doping for Complete Charge Transfer
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Solution Overview
Problem
Global shutter CMOS image sensors face challenges in transferring electrons from photodiodes to storage diffusion regions efficiently, especially with increased depth and pixel density, leading to electron loss and reduced image quality in near-infrared applications.
Innovation Solution
The implementation of non-uniform storage diffusion region doping, with varying doping concentrations in different rows of pixel units, and two-stage shallow layer ion implantation to reduce junction leakage and ensure complete electron transfer during row-by-row reading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiode depth is increased to improve near-infrared light absorption, then near-infrared sensitivity is improved, but electron transfer time increases and electron loss increases
Solution Approach 1:
The patent applies different doping concentrations to different row regions of the storage diffusion region. Specifically, the first doping concentration is applied to storage diffusion regions in earlier rows, while a second, higher doping concentration is applied to storage diffusion regions in later rows. This local differentiation optimizes electron transfer efficiency for each row's specific timing requirements, addressing the increased transfer time problem in deeper photodiodes without compromising near-infrared sensitivity.
Solution Approach 2:
The patent changes the doping concentration parameter of the storage diffusion region based on row position. By increasing the doping concentration in later rows compared to earlier rows, the patent optimizes the electrical properties of the storage diffusion region to facilitate faster and more complete electron transfer from deeper photodiodes, thereby reducing electron transfer time and minimizing electron loss while maintaining high near-infrared sensitivity.
2Measurement precision
If pixel density is increased to improve image resolution, then image quality is improved, but electron transfer completeness deteriorates
Solution Approach 1:
The patent implements different doping concentrations for different row regions within the pixel array. The first doping concentration is used for storage diffusion regions in earlier rows, while the second, higher doping concentration is used for storage diffusion regions in later rows. This local quality differentiation ensures that each row's storage diffusion region is optimized for its specific electron transfer requirements, maintaining high electron transfer completeness even as pixel density increases.
Solution Approach 2:
The patent introduces dynamic optimization by making the doping concentration dependent on the row position. This creates a gradient structure where later rows, which experience longer storage times and potentially greater electron loss, receive enhanced doping to improve their electron transfer reliability. This dynamic approach allows the system to maintain high image quality with increased pixel density while ensuring complete electron transfer across all rows.
3Ease of manufacture
If uniform doping concentration is used in storage diffusion region, then manufacturing simplicity is maintained, but electron transfer efficiency in later rows deteriorates
Solution Approach 1:
The patent divides the storage diffusion region into different doping zones based on row position. The first doping concentration is applied to storage diffusion regions in earlier rows, while the second, higher doping concentration is applied to storage diffusion regions in later rows. This local quality approach optimizes electron transfer efficiency for each row's specific requirements while maintaining a relatively simple manufacturing process through selective ion implantation.
Solution Approach 2:
The patent changes the doping concentration parameter across different row regions of the storage diffusion region. By implementing a doping gradient where later rows have higher doping concentrations than earlier rows, the patent improves electron transfer efficiency in rows that experience longer storage times and greater electron loss, while still maintaining manufacturing feasibility through controlled ion implantation processes.
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 effectively reduces electron loss and ensures complete transfer of carriers to floating diffusion regions, enhancing image quality even with increased pixel density and depth, particularly in near-infrared applications.
Implementation Method 1
two-stage shallow layer ion implantation to reduce junction leakage
Implementation Method 2
For the acquisition of near infrared light (with wavelength greater than 760 nm)... The intensity of four wavelengths varies with depth. In silicon, the depth at which blue light is attenuated to 1/e is about 0.42 um
Data Source
AI summary
The disclosure discloses a global shutter CMOS image sensor, which adopts non-uniform storage diffusion region doping to reduce the junction leakage at storage points, so as to ensure that with the increase of the depth of photodiodes and the increase of pixels, all carriers in rows read subsequently can be transferred to storage diffusion regions, the loss of the carriers in the storage diffusion regions is not caused when a global shutter transistor is turned on, and the carriers can be completely transferred from the storage diffusion regions to floating diffusion regions through second transfer transistors even if the number of rows of pixel units increases during reading-out row by row. The disclosure further discloses a method for making the global shutter CMOS image sensor.