Photodiode Isolation Structure for Low Voltage Reset
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Image sensors face challenges in completely resetting photodiodes in low voltage environments, leading to image lag and ghost images due to residual charge, which degrades image quality and confuses image analysis algorithms.
Innovation Solution
The introduction of isolation structures within photodiodes, such as deep and shallow isolation structures formed using core and liner materials, alters electric field lines, reduces image lag by removing trapped charge and lowers the voltage required to extract image charge, thereby enhancing image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodiode structures are used in low voltage environments, then device complexity is reduced, but image lag occurs due to incomplete photodiode resetting
Solution Approach 1:
The isolation structure is divided into multiple segments including a deep isolation structure extending into the substrate and shallow isolation structures formed at different depths. This segmentation allows the structure to effectively remove trapped charge at various locations within the photodiode without requiring a single complex deep structure, thereby improving reset completeness while managing device complexity
Solution Approach 2:
The isolation structure acts as an intermediary element between the photodiode active region and the substrate. It provides a controlled interface that facilitates charge extraction and prevents charge trapping at the photodiode-substrate interface, enabling complete photodiode resetting in low voltage environments without directly modifying the photodiode itself
2Reliability
If isolation structures are introduced to remove trapped charge, then image lag is reduced, but manufacturing complexity increases
Solution Approach 1:
The isolation structure fabrication is merged with existing CMOS process steps. The deep and shallow isolation structures are formed using standard trench isolation, doping, and oxidation processes that are already part of the image sensor manufacturing flow, eliminating the need for additional specialized fabrication steps and maintaining ease of manufacture
Solution Approach 2:
The isolation structure uses standard materials and process parameters compatible with existing manufacturing. By forming isolation structures with conventional doping concentrations, trench depths, and oxidation conditions, the patent achieves effective charge removal without requiring changes to manufacturing parameters or processes
3Productivity
If higher voltage is applied to extract image charge, then charge extraction efficiency is improved, but power consumption increases
Solution Approach 1:
The isolation structure is pre-formed during manufacturing to create optimal electric field conditions for charge extraction. By establishing the isolation structure with appropriate geometry and material properties before operation, the photodiode can be efficiently reset at low voltages during normal operation without requiring high voltage pulses, thereby improving charge extraction efficiency while minimizing power consumption
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 implementation of isolation structures effectively reduces image lag, improving image quality by eliminating ghost images and reducing the voltage needed for charge extraction, making the technology cost-effective and efficient.
Implementation Method 1
alters electric field lines, reduces image lag by removing trapped charge
Data Source
AI summary
An image sensor includes a semiconductor material with a photodiode disposed in the semiconductor material. The image sensor also includes a transfer gate electrically coupled to the photodiode to extract image charge from the photodiode in response to a transfer signal. A floating diffusion is electrically coupled to the transfer gate to receive the image charge from the photodiode. At least one isolation structure is disposed in the photodiode, and the at least one isolation structure extends from a surface of the semiconductor material into the photodiode.