Biased Deep Trench Isolation for Image Sensor Dark Current
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Solution Overview
Problem
Image sensors face noise issues due to dark current, which degrades their performance, especially in low-light conditions, and existing technologies have not effectively addressed this problem.
Innovation Solution
A deep trench isolation (DTI) structure is introduced in the image sensor, biased with a DTI bias voltage to create an electric field that reduces dark current and noise, improving image sensor performance by isolating photodiodes and extending into peripheral regions of the semiconductor layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deep trench isolation structure is introduced to reduce dark current, then noise is reduced and image quality is improved, but device complexity increases
Solution Approach 1:
The isolation structure is divided into multiple discrete deep trenches spaced apart from each other, rather than using a continuous isolation layer. Each trench is filled with isolation material and can be independently biased, allowing the structure to be segmented into functional units that collectively reduce dark current while maintaining manufacturability
Solution Approach 2:
The isolation approach transitions from a planar two-dimensional isolation layer to a three-dimensional deep trench structure that extends vertically into the semiconductor substrate. This dimensional change creates isolation barriers at depth rather than at the surface, effectively blocking dark current paths without requiring complex lateral patterning
2Object-affected harmful factors
If DTI structure extends into peripheral regions to maximize dark current reduction, then noise minimization is improved, but manufacturing precision requirements increase
Solution Approach 1:
The deep trenches are strategically positioned at specific locations where dark current generation is most problematic, such as around photodiode perimeters and in high-surface-area regions. Rather than uniform distribution, the trenches are placed locally where they provide maximum benefit, reducing overall dark current while minimizing the total number of trenches required
Solution Approach 2:
The deep trenches are formed and filled with isolation material before final device assembly and biasing. This preliminary structuring allows subsequent biasing circuits to be simplified, as the physical isolation framework is already in place. The trenches are prepared in advance to receive bias voltages that will be applied during device operation to maximize dark current suppression
3Object-affected harmful factors
If multiple isolation layers are used to completely block dark current paths, then dark current reduction is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Multiple deep trenches are arranged in continuous or overlapping patterns that collectively form an uninterrupted isolation barrier around photodiodes and other sensitive structures. The trenches are spaced and sized so that their combined effect creates a continuous dark current blocking path, eliminating the need for additional isolation layers while maintaining effective dark current suppression
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
The biased DTI structure effectively minimizes dark current and noise, enhancing image sensor performance by reducing unwanted signal contributions and improving image quality, especially in low-light conditions.
Implementation Method 1
biased with a DTI bias voltage to create an electric field that reduces dark current and noise
Data Source
AI summary
An image sensor includes photodiodes disposed in a pixel region and proximate to a front side of a semiconductor layer. A backside metal grating is formed in a backside oxide layer disposed proximate to a backside of the semiconductor layer. A deep trench isolation (DTI) structure with a plurality of pixel region portions and an edge region portion is formed in the semiconductor layer. The pixel region portions are disposed in the pixel region of the semiconductor layer such that incident light is directed through the backside metal grating, through the backside of the semiconductor layer, and between the pixel region portions of the DTI structure to the photodiodes. The edge region portion of the DTI structure is disposed in an edge region outside of the pixel region. The edge region portion of the DTI structure is biased with a DTI bias voltage.