Stacked CMOS Photodiode Sub-PDs for Full Well Capacity
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Solution Overview
Problem
CMOS image sensors face a limitation in achieving high full well capacity (FWC), which restricts their ability to capture a wide dynamic range, especially in applications requiring ultra dim and bright scene capture with good quality, such as automotive and security applications.
Innovation Solution
The proposed CMOS image sensor design incorporates a top photodiode and a bottom photodiode with sub-photodiodes and sub-wells, allowing for increased junction capacitance and charge storage density, achieved through a layered structure and specific doping processes, enabling higher full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional single photodiode structure is used, then the device complexity is low, but the full well capacity is insufficient for high dynamic range applications
Solution Approach 1:
The photodiode is divided into multiple sub-photodiodes arranged in a stacked configuration within the same pixel area. This segmentation allows each sub-photodiode to contribute to charge storage capacity while maintaining a compact vertical structure, thereby increasing full well capacity without proportionally increasing lateral device complexity
Solution Approach 2:
The patent transitions from a conventional lateral photodiode arrangement to a vertical stacked configuration. By stacking sub-photodiodes in the vertical dimension rather than arranging them laterally, the design increases charge storage capacity within the same pixel footprint while managing structural complexity through vertical integration
2Quantity of substance
If the photodiode area is increased to improve full well capacity, then the charge storage density increases, but the pixel size increases reducing the number of pixels per sensor
Solution Approach 1:
The patent achieves higher charge storage density by stacking sub-photodiodes vertically within the same lateral pixel boundaries. This vertical stacking allows multiple photodiode junctions to occupy the same footprint area, increasing charge capacity without expanding the pixel's lateral dimensions
3Quantity of substance
If multiple photodiodes are stacked vertically, then the full well capacity increases, but the manufacturing precision requirements increase
Solution Approach 1:
The photodiode structure is segmented into multiple sub-photodiodes with distinct doping regions. Each sub-photodiode can be formed with controlled doping parameters, allowing precise charge storage characteristics to be achieved through modular doping processes rather than requiring a single complex doped structure
Solution Approach 2:
Different sub-photodiodes within the stacked structure can have different doping concentrations and profiles optimized for their specific functions. This local quality variation allows each sub-photodiode to be precisely manufactured with tailored electrical properties while maintaining overall structural integrity
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 enhances charge storage density and quantum efficiency, allowing the CMOS image sensor to capture a wider dynamic range, effectively addressing the need for improved FWC and dynamic range in various applications.
Implementation Method 1
A complementary metal-oxide-semiconductor (CMOS) image sensor has been widely applied to mobile applications
Data Source
AI summary
A photodiode (PD) of a complementary metal-oxide-semiconductor (CMOS) image sensor includes a top PD of a second type disposed in a first-type layer; and a bottom PD of the second type disposed in the first-type layer and below the top PD, the bottom PD including at least one sub-photodiode (sub-PD) of the second type connected to the top PD and at least one sub-well of the first type surrounded by the at least one sub-PD.