Biased Deep Trench Isolation for High-FWC Pixel Crosstalk Control
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Solution Overview
Problem
As image sensors are miniaturized, they face challenges with crosstalk and increased dark current rates due to smaller pixel cells, which affect resolution and performance, especially in low light conditions.
Innovation Solution
The implementation of frontside deep trench isolation (FDTI) and backside deep trench isolation (BDTI) structures in pixel cells, allowing for individual biasing of conductive materials to reduce charge transfer lag and enhance electric potential modulation, thereby improving full well capacity and near-infrared quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If image sensors are miniaturized to reduce size, then the sensor size is reduced, but crosstalk and dark current rates increase
Solution Approach 1:
The patent divides the isolation structure into two separate segments: frontside deep trench isolation (FDTI) and backside deep trench isolation (BDTI). Each segment performs a specific function - FDTI prevents crosstalk between adjacent pixel cells while BDTI reduces dark current generation. This segmentation allows independent optimization of each isolation function without compromising the other, thereby reducing harmful effects while maintaining miniaturized sensor size.
Solution Approach 2:
The patent introduces conductive materials within the deep trench isolation structures that act as intermediaries to modulate electric potential. These conductive materials create electric fields that actively suppress charge carrier diffusion (reducing crosstalk) and reduce dark current generation at the silicon surface. The intermediary conductive layer enables active control of harmful effects rather than passive isolation.
2Volume of moving object
If pixel cell sizes are reduced to maintain resolution in smaller sensors, then sensor size is reduced, but crosstalk between adjacent pixel cells increases
Solution Approach 1:
The isolation structure is segmented into frontside and backside components. The FDTI structure specifically addresses crosstalk by creating physical and electrical barriers between adjacent pixel cells on the frontside where light enters. This segmentation allows effective crosstalk prevention even when pixel cells are closely spaced to maintain resolution in miniaturized sensors.
Solution Approach 2:
Conductive materials deposited in the FDTI trenches serve as intermediaries that generate electric fields to control charge carrier movement. These electric fields prevent charge diffusion from one pixel cell to adjacent cells, effectively blocking crosstalk while allowing the pixel cells to remain closely spaced for high resolution in compact form factors.
3Measurement precision
If pixel cell sizes are reduced to maintain resolution, then sensor size is reduced, but dark current rates increase
Solution Approach 1:
The patent segments the isolation function into FDTI and BDTI, with BDTI specifically targeting dark current reduction. The backside deep trench isolation structure, combined with conductive materials, creates an electric field configuration that suppresses thermal generation of charge carriers at the silicon surface, thereby reducing dark current while allowing small pixel cell sizes for high resolution.
Solution Approach 2:
Conductive materials in the BDTI structure act as intermediaries that modulate the electric potential at the backside surface. This creates an electric field that reduces the probability of thermal generation events that produce dark current, enabling small pixel dimensions without sacrificing signal quality in low light conditions.
4Quantity of substance
If deep trench isolation structures are implemented with conductive materials, then full well capacity and near-infrared quantum efficiency increase, but device complexity increases
Solution Approach 1:
The complex isolation function is segmented into two manageable structures (FDTI and BDTI) with distinct purposes. This segmentation allows each structure to be optimized independently for its specific function, making the overall complex system more controllable and manufacturable while achieving high full well capacity and near-infrared quantum efficiency.
Solution Approach 2:
The deep trench isolation structures serve multiple functions simultaneously: they provide physical isolation between pixels, create electric fields for charge control, reduce dark current, and enhance near-infrared response. This multi-functionality reduces the need for separate structures for each function, thereby managing complexity while achieving multiple performance goals.
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 effectively reduces image lag and increases full well capacity and near-infrared quantum efficiency, enabling better performance in low light conditions and maintaining high resolution in smaller pixel cell sizes.
Implementation Method 1
modulating the electric potential of a photodiode (107) by applying a bias voltage to a conductive material (132, 162) in the deep trench isolation structure
Data Source
AI summary
A pixel cell includes a front deep trench isolation (FDTI) structure extending into a semiconductor material from a frontside. The FDTI structure isolates a first region of the semiconductor material from a second region of the semiconductor material. The FDTI structure includes a first conductive material coupled to receive a first bias voltage. A back deep trench isolation (BDTI) extends into the semiconductor material from a backside. The BDTI structure isolates the first region of the semiconductor material from the second region of the semiconductor material. The BDTI structure includes a second conductive material coupled to receive a second bias voltage. The FDTI structure and BDTI structure are at least partially aligned in a depthwise direction of the semiconductor material. A photodiode is disposed in the first region of the semiconductor material proximate to at least a portion of the FDTI structure and a portion of the BDTI structure.