Shared Active Pixel Sensor Area Reduction
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Solution Overview
Problem
Existing image sensors face challenges in minimizing pixel area while maintaining sensitivity, as regions other than the photodiode need to be minimized to increase sensitivity, and current sharing methods like 2-share or 4-share pixels are limited in reducing STI and floating diffusion areas.
Innovation Solution
A novel shared active pixel sensor structure is proposed, incorporating a shared photodiode with multiple signal nodes and gates, where the shared sense node is electrically connected to the photodiode, and transfer, reset, and source follower gates are strategically positioned to control and read photocurrent, allowing for reduced transistor numbers and pixel area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiode area is increased to improve sensitivity, then sensitivity is improved, but pixel area increases
Solution Approach 1:
Multiple photodiodes are merged into a single shared photodiode structure that serves multiple pixel units. The shared photodiode has multiple signal nodes (first signal node, second signal node, third signal node, fourth signal node) that can independently operate, allowing one photodiode to function as multiple pixels, thereby reducing the overall pixel area while maintaining sensitivity.
Solution Approach 2:
The shared photodiode is designed with multi-functionality to serve multiple purposes simultaneously. It can independently operate as multiple pixels through its multiple signal nodes, and shares readout circuits (transfer gates, source follower gates, reset gates) with multiple pixel units, achieving both area reduction and maintained sensing capability.
2Area of stationary object
If readout circuits are shared among multiple pixels to reduce pixel area, then pixel area is reduced, but device complexity increases
Solution Approach 1:
The shared photodiode is segmented into multiple independent signal nodes (first, second, third, and fourth signal nodes), each capable of independent operation. This segmentation allows the single photodiode to function as multiple independent pixels, reducing area while managing complexity through modular independent units.
Solution Approach 2:
The readout circuits including transfer gates and source follower gates are designed to dynamically switch between serving different signal nodes. The circuits can be selectively activated to read from different signal nodes at different times, providing flexible control that manages complexity while enabling multi-pixel functionality.
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 configuration minimizes pixel area, allows for high conversion gain, and enables the shared active pixel sensor to operate as multiple pixels, optimizing efficiency and sensitivity by strategically using signal nodes and gates to manage photocurrent.
Implementation Method 1
A photodiode is a semiconductor device for use as an image sensor
Data Source
AI summary
A shared active pixel sensor includes a first shared photodiode, a first shared sense node, a first transfer gate, a first shared reset gate and a first shared source follower gate. The first shared photodiode consists of a first signal node and a second signal node. The first shared sense node is electrically connected to the first shared photodiode. The first transfer gate is disposed between the first signal node and the first shared sense node so that the first signal node and the first shared sense node together serve as a source and a drain controlled by the first transfer gate. The first shared reset gate is electrically connected to the first shared sense node. The first shared source follower gate is capable of reading a photocurrent from the first shared photodiode.