Pinning Layer Voltage Control for Image Sensor Crosstalk
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Solution Overview
Problem
Conventional CMOS image sensors face issues with unstable pinning layer potential leading to non-uniform surface pinning and increased dark current due to floating pinning layers, resulting in crosstalk between pixels.
Innovation Solution
The introduction of a voltage supply unit to apply a predetermined voltage to the pinning layer of the photodiode during depletion, ensuring stable surface pinning and uniform potential across all pixels, thereby preventing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the pinning layer is left floating to simplify the structure, then device complexity is reduced, but surface pinning becomes non-uniform and dark current increases
Solution Approach 1:
A voltage supply unit is introduced as an intermediary component between the power source and the pinning layer. This unit actively supplies predetermined voltage to the pinning layer during the depletion period, ensuring uniform surface pinning across all pixels while maintaining overall system reliability.
Solution Approach 2:
The electrical parameter (voltage) of the pinning layer is actively changed and controlled. By supplying a predetermined voltage to the pinning layer during depletion, the invention transforms the floating, unstable voltage state into a controlled, uniform voltage state, thereby achieving consistent surface pinning and reducing dark current.
2Reliability
If additional voltage supply components are added to stabilize pinning layer potential, then surface pinning uniformity improves, but device complexity increases
Solution Approach 1:
The voltage supply unit serves as a minimal intermediary that bridges the power source and pinning layer. It provides the necessary voltage control without introducing complex circuitry, adding only the essential components needed to stabilize pinning potential while maintaining simplicity.
Solution Approach 2:
The voltage supply unit is designed to automatically supply voltage to the pinning layer during the depletion period based on control signals, eliminating the need for manual adjustment or complex control mechanisms. The system self-regulates to maintain uniform surface pinning.
3Ease of manufacture
If the pinning layer voltage is not controlled, then manufacturing process is simpler, but dark current increases due to non-uniform surface pinning
Solution Approach 1:
The invention changes the electrical parameter (voltage) of the pinning layer from an uncontrolled floating state to a controlled predetermined voltage state. This parameter change ensures uniform surface pinning, which directly reduces dark current generation while maintaining manufacturing simplicity through the use of standard voltage supply circuits.
Solution Approach 2:
The voltage supply unit continuously supplies the predetermined voltage to the pinning layer throughout the depletion period, ensuring continuous and stable surface pinning. This continuous voltage supply prevents fluctuations that would otherwise lead to non-uniform pinning and increased dark current.
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 stabilizes surface pinning and reduces dark current by maintaining uniform voltage across pinning layers, enhancing reset signal uniformity and preventing crosstalk between pixels.
Implementation Method 1
a voltage supply unit connected to the pinning layer to apply a predetermined voltage to the pinning layer when the pinned photodiode is depleted
Implementation Method 2
a CMOS image sensor converts colliding photons into electrons collected in a sensor pixel to detect light
Implementation Method 3
the first shallow p+ doping region 104a serving as the pinning layer prevents the depletion region 109 from being expanded to an interface (that is, the surface of a silicon epi-layer) between silicon and silicon dioxide, thereby blocking a dark current from being generated
Data Source
AI summary
Disclosed are a pinned photodiode having and electrically controllable pinning layer and an image sensor including the pinned photodiode. A predetermined voltage is applied to the pinning layer for the depletion duration of the photodiode in the image sensor, so that stable surface pinning is acquired and the uniform surface pinning is achieved between pixels.