Junction Gate BCMD Pixel Sensor for Low Noise Imaging
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Solution Overview
Problem
Existing small pixel size junction gate BCMD image sensors face challenges in minimizing pixel size while maintaining high charge storage capacity, low dark current, and low noise, especially in back side illuminated configurations where vertical charge reset generates kTC noise and reduces light sensitivity.
Innovation Solution
The introduction of a junction gate BCMD transistor for vertical charge reset, which allows for high performance in both back side and front side illuminated image sensors, reducing pixel size while preserving charge storage capacity and avoiding kTC noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertical charge reset is used in back side illuminated sensors, then charge reset functionality is achieved, but light sensitivity is reduced and kTC noise is generated
Solution Approach 1:
The patent transitions from vertical charge reset (through the substrate thickness) to lateral charge reset (along the substrate plane). The reset transistor connects the photodiode to the readout circuitry through lateral pathways within the same substrate plane, eliminating the need for vertical charge transport through thick substrates. This dimensional change resolves the contradiction by achieving charge reset without compromising light sensitivity or generating kTC noise.
2Reliability
If multiple transistors are used per pixel for charge transfer and reset, then charge management capability is improved, but pixel size increases
Solution Approach 1:
The patent combines multiple transistor functions (charge transfer and reset operations) into a single integrated transistor structure. The readout circuitry performs both charge transfer from the photodiode and reset operations using shared circuit elements, reducing the transistor count from multiple discrete devices to a unified structure. This merging maintains charge management capability while significantly reducing pixel area.
Solution Approach 2:
The readout circuitry is designed with universal functionality to perform multiple operations (charge transfer, reset, and signal amplification) using the same hardware components. The circuit can dynamically switch between different operational modes without requiring separate dedicated transistors for each function, thereby reducing overall pixel size while maintaining full charge management capability.
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 the creation of small pixel image sensors with high well capacity, low dark current, and low noise, maintaining light sensitivity and anti-blooming capabilities, suitable for high-resolution imaging with minimal color aliasing and noise.
Implementation Method 1
The typical image sensors sense light by converting impinging photons into electrons that are integrated (collected) in sensor pixels
Implementation Method 2
The introduction of a junction gate BCMD transistor for vertical charge reset, which allows for high performance in both back side and front side illuminated image sensors, reducing pixel size while preserving charge storage capacity and avoiding kTC noise generation
Data Source
AI summary
The invention describes the solid-state image sensor array and in particular describes in detail the junction gate BCMD pixel sensor array that can be used in the back side illuminated mode as well as in the front side illuminated mode. The pixels generally do not need addressing transistors and the reset is accomplished in a vertical direction to the junction gate, so no additional reset transistor is needed for this purpose. As a result of this innovation the pixel maintains large charge storage capacity when its size is reduced, has low noise due to the nondestructive charge readout, and no RTS noise. The pixel interface generated dark current is also drained to the gate, so the image sensor array operates with very low dark current noise even at high temperatures. The junction gate also serves as a drain for the overflow charge.