Pinned Photodiode Avalanche Region for Low Light Signal Amplification
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Solution Overview
Problem
Current CMOS image sensors face challenges in amplifying low light intensity signals without introducing additional noise, as increasing the breakdown voltage to enable avalanche photodiode operation requires complex circuitry and reduces fill factor, and existing solutions like electron-multiplication require high voltage capabilities and worsen fill factor.
Innovation Solution
A pinned photodiode pixel architecture is developed where a third externally biased potential creates an avalanche region between doped regions, allowing signal amplification without additional circuitry and maintaining pixel fill factor, by decoupling the avalanche photodiode from the CMOS pixel and readout circuitry ground potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If avalanche photodiode operation is implemented by increasing breakdown voltage, then signal amplification is achieved, but device complexity increases and fill factor decreases
Solution Approach 1:
The photodiode structure is segmented into multiple doped regions (first doped region, second doped region, third doped region) with different doping types and concentrations. This segmentation creates distinct functional zones within the photodiode, allowing avalanche multiplication to occur in specific regions while maintaining simplicity in others, thereby achieving signal amplification without increasing overall device complexity
Solution Approach 2:
Different doped regions are assigned different doping concentrations and types to create localized properties. The first doped region has a first doping concentration, the second doped region has a second doping concentration, and the third doped region has a third doping concentration. This local quality variation enables avalanche breakdown to occur at controlled locations with specific voltage thresholds, achieving amplification without requiring complex external circuitry
2Power
If electron-multiplication is used to achieve avalanche amplification, then signal amplification is achieved, but fill factor worsens
Solution Approach 1:
The avalanche multiplication function is merged directly into the photodiode structure itself by integrating multiple doped regions within a single device. This eliminates the need for separate external multiplication circuitry or additional gates, thereby achieving signal amplification while maintaining a large fill factor as the photodiode occupies the full pixel area without requiring extra components
3Power
If high voltage capability is implemented for avalanche operation, then signal amplification is achieved, but device complexity increases
Solution Approach 1:
The invention achieves avalanche multiplication by changing the doping concentration parameters within the photodiode structure rather than requiring high voltage external biasing. By adjusting the doping concentrations in different regions (first, second, and third doping concentrations), the breakdown voltage is engineered to occur at lower, more practical voltage levels that are compatible with standard CMOS processes, eliminating the need for process modifications
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 solution enables signal amplification with improved sensitivity for low light detection without affecting the fill factor or requiring complex circuitry, allowing for efficient low-light imaging without the need for high bias potentials, thus enhancing the signal-to-noise ratio.
Implementation Method 1
amplification of the signal itself... can be engineered by choosing the appropriate doping concentrations of the p and n side of the junction... the same avalanche principle can also be utilized as an amplification process when biased just below the breakdown voltage
Implementation Method 2
pinned photodiode (PPD)... eliminates or limits several noise sources... by avoiding interaction of signal electrons with the silicon surface
Data Source
AI summary
Described herein is a pinned photodiode pixel architecture (100) having a p-type substrate (110) which is independently biased with respect to a pixel area (180) to provide an avalanche region (230) between an n-type region (130) and a p-type region (120) formed on the substrate (110). Such a pinned photodiode pixel (100) can be used in imaging sensors that are used in low light level conditions.