Image Sensor Pixels With Vertical Storage Gate For Global Shutter
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Solution Overview
Problem
Global shutter mode in image sensors faces challenges with image distortion and signal transmission due to varying integration times across rows, necessitating improvements in photocharge management and signal processing.
Innovation Solution
The proposed solution involves a pixel design with a photo diode, storage diode, and vertical gate structures for controlled photocharge transfer, along with deep trench isolation and light shielding to optimize photocharge accumulation and transfer, ensuring uniform integration times and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If global shutter mode is used to eliminate image distortion, then image quality is improved, but signal transmission and integration performance deteriorate
Solution Approach 1:
The pixel is divided into functionally independent regions: a photo diode for photocharge generation, a storage diode for photocharge storage, and a floating diffusion for signal readout. This segmentation allows the photo diode to accumulate photocharges during a first period while the storage diode holds previously accumulated photocharges, enabling uniform integration times across all rows without the image distortion problems of rolling shutter mode.
Solution Approach 2:
A storage diode is introduced as an intermediary component between the photo diode and the floating diffusion. The storage diode temporarily holds photocharges and allows controlled transfer to the floating diffusion through a transfer gate, decoupling the photocharge accumulation process from the signal readout process. This intermediary structure enables global shutter operation with uniform integration times while maintaining reliable signal transmission.
2Reliability
If photocharges are accumulated in the photo diode during a first period, then signal transmission is improved, but image distortion occurs due to varying integration times
Solution Approach 1:
The pixel structure separates photocharge accumulation (photo diode during first period) from signal readout (floating diffusion), with the storage diode enabling uniform integration timing across all rows. This segmentation allows simultaneous photocharge generation in all pixels during the same time period, eliminating the row-by-row timing variations that cause image distortion in rolling shutter mode.
3Measurement precision
If deep trench isolation and light shielding are added to optimize photocharge management, then noise is reduced, but device complexity increases
Solution Approach 1:
Deep trench isolation structures are extracted and positioned between adjacent pixels and around the storage diode to physically separate and electrically isolate different pixel elements. This extraction of isolation structures to specific critical locations effectively blocks charge leakage and reduces crosstalk noise between pixels, achieving noise reduction through targeted structural additions rather than comprehensive complexity.
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 image sensor performance by minimizing image distortion, improving signal transmission, and reducing noise, while also decreasing power consumption through optimized electric potential and voltage usage.
Implementation Method 1
a photo diode that is configured to accumulate photocharges generated therein corresponding to incident light
Data Source
AI summary
Pixels of image sensors are provided. The pixels may include a photo diode configured to accumulate photocharges generated therein corresponding to incident light during a first period, a storage diode configured to store photocharges accumulated in the photo diode and a storage gate configured to control transfer of the photocharges accumulated in the photo diode to the storage diode. The storage gate may include a vertical gate structure extending toward the photo diode.