Image Sensor Pixel Isolation for Crosstalk-Free Autofocus
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Image sensors face challenges in preventing crosstalk when providing an autofocusing function, as existing methods can cause light reflection and interference between adjacent pixels.
Innovation Solution
The image sensor design includes a first and second photodiode group, a floating diffusion region, and a power supply node with a barrier voltage, along with a device isolation layer, to prevent electric charges from migrating to the floating diffusion region and discharge them to a drain terminal, thereby limiting crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single photodiode group is used for both normal imaging and autofocusing, then device complexity is reduced, but crosstalk occurs between pixels due to light reflection and interference
Solution Approach 1:
The photodiode group is divided into two separate groups: a first photodiode group for normal imaging and a second photodiode group for autofocusing. This segmentation allows each group to be optimized for its specific function and prevents crosstalk by providing electrical isolation between the two functional areas.
Solution Approach 2:
The autofocusing function is extracted from the normal imaging path by creating a separate second photodiode group. This extracted structure is then isolated using a device isolation layer, removing the source of crosstalk while maintaining the autofocusing capability.
2Productivity
If photodiodes are placed adjacent to each other for high pixel density, then productivity is improved, but crosstalk increases due to light reflection between adjacent pixels
Solution Approach 1:
A device isolation layer is introduced as an intermediary structure between adjacent photodiode groups. This isolation layer acts as a mediator that allows high pixel density while preventing light reflection and electrical interference between neighboring pixels, thus eliminating crosstalk.
3Use of energy by moving object
If autofocusing pixels share a microlens for improved light collection, then sensitivity is improved, but crosstalk occurs due to light interference between unit pixels
Solution Approach 1:
Unit pixels within the second photodiode group share a common microlens for improved light collection, but are electrically segmented by individual device isolation layers. This allows optical sharing for sensitivity while maintaining electrical isolation to prevent crosstalk.
4Measurement precision
If transfer transistors are used to move electric charges to floating diffusion region for signal readout, then measurement precision is improved, but crosstalk occurs when charges migrate between adjacent pixels
Solution Approach 1:
The charge transfer path for the second photodiode group is extracted and redirected to a drain terminal instead of the floating diffusion region. This separate charge extraction path prevents crosstalk by ensuring that charges from autofocusing pixels do not migrate to the floating diffusion region used by normal imaging pixels.
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 ensures that the autofocusing function is provided without crosstalk, maintaining image quality and sensitivity comparable to normal pixel groups.
Implementation Method 1
The at least one transfer transistor of the second transfer transistor group is configured to have a barrier voltage applied thereto. The barrier voltage forms a potential barrier between the second photodiode group and the floating diffusion region.
Implementation Method 2
a first photodiode group including photodiodes and a second photodiode group including photodiodes, a first transfer transistor group including at least one transfer transistor connected to the first photodiode group
Data Source
AI summary
An image sensor includes a first photodiode group, a second photodiode group, a first transfer transistor group, a second transfer transistor group, a floating diffusion region of a substrate in which electric charges generated in the first photodiode group are stored, and a power supply node for applying a power supply voltage to the second photodiode group. A barrier voltage is applied to at least one transfer transistor of the second transfer transistor group. The power supply voltage allows electric charges, generated in the second photodiode group, to migrate to the power supply node, and the barrier voltage forms a potential barrier between the second photodiode group and the floating diffusion region.