Image Sensor Unit Pixel With Deep Trench Isolation
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Solution Overview
Problem
Current CMOS image sensors face challenges in miniaturizing pixels to achieve high-resolution images while maintaining signal quality, as existing designs often result in electric and optical crosstalk between pixels, degrading the signal-to-noise ratio.
Innovation Solution
The implementation of a unit pixel design that includes a photoelectric conversion element, a transfer transistor, and a supplemental transistor, with deep trench isolation (DTI) to electrically isolate these components from adjacent pixels, minimizing the pixel area and reducing crosstalk by using a deep trench isolation (DTI) and shallow trench isolation (STI) to prevent signal interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If pixel area is miniaturized to increase resolution, then resolution is improved, but electric and optical crosstalk between pixels increases
Solution Approach 1:
The pixel structure is segmented into distinct functional regions separated by deep trench isolation. The photodiode, transfer transistor, and supplemental transistor are spatially separated and electrically isolated through the DTI structure, which divides the continuous substrate into isolated pixel units. This segmentation prevents crosstalk while maintaining miniaturization.
Solution Approach 2:
Deep trench isolation serves as an intermediary structure between adjacent pixels and between different components within a pixel. The DTI structure acts as a physical and electrical barrier that mediates the interaction between neighboring elements, blocking unwanted electrical and optical signals while allowing necessary signal transmission through controlled paths.
2Area of moving object
If number of transistors is reduced to minimize pixel area, then pixel area and power consumption are improved, but signal quality may deteriorate
Solution Approach 1:
The supplemental transistor is designed with multi-functionality to perform multiple roles within the pixel circuit. It can operate as a reset transistor, drive transistor, or select transistor depending on the operational mode, thereby providing comprehensive signal quality control with a single transistor component. This universal design maintains signal quality without requiring additional transistors that would increase pixel area.
3Object-affected harmful factors
If deep trench isolation is used to prevent crosstalk, then crosstalk is reduced, but manufacturing complexity increases
Solution Approach 1:
The deep trench isolation structure is nested within the existing pixel fabrication process flow. The DTI structure is formed by integrating additional processing steps into the standard CMOS fabrication sequence, where the trench isolation is created within the pixel structure during the formation of other components. This nesting approach incorporates the anti-crosstalk feature without requiring completely separate manufacturing processes.
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 effectively increases the resolution of the image sensor by minimizing pixel area and power consumption while enhancing signal quality by reducing crosstalk, thereby improving the signal-to-noise ratio and light receiving efficiency.
Implementation Method 1
a photoelectric conversion element configured to generate photocharge varying with the intensity of incident light
Data Source
AI summary
A unit pixel of an image sensor is provided. The unit pixel includes a photoelectric conversion element configured to generate photocharge varying with the intensity of incident light, a transfer transistor configured to transfer the photocharge to a floating diffusion in response to a transfer control signal, and a supplemental transistor connected to the floating diffusion. Because the unit pixel includes only one transistor in addition to the transfer transistor, the area of the unit pixel is minimized, and, as a result, the resolution of a pixel array is increased and the power consumption of the pixel array is decreased.