Image Sensor Pixel Separation Grid for Dark Current Reduction
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Solution Overview
Problem
As semiconductor image sensors become more integrated, the reduction in pixel size leads to increased defects due to dark current and charge accumulation at interfaces, particularly in CCD and CMOS image sensors, affecting their performance and efficiency.
Innovation Solution
The implementation of a pixel separation structure with a conductive grid layer surrounding each pixel, which includes sidewall insulating layers and a conductive layer, helps to prevent crosstalk from obliquely incident light, increases the light receiving area, and enhances quantum efficiency by applying a negative voltage or ground voltage through back side contacts connected to the conductive layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to increase integration, then productivity increases, but manufacturing precision deteriorates due to increased defects from dark current and charge accumulation
Solution Approach 1:
The pixel array is divided into individually isolated pixels using pixel separation structures. Each pixel is surrounded by separation structures that prevent charge accumulation and dark current interference from adjacent pixels, enabling high integration while maintaining low defect rates through electrical isolation of each pixel unit.
Solution Approach 2:
Pixel separation structures act as intermediary elements between adjacent pixels. These structures include insulating materials and conductive layers that mediate the electrical interaction between pixels, preventing harmful charge accumulation and dark current while allowing the pixels to function independently at high density.
2Productivity
If pixel size is reduced to increase integration, then productivity increases, but reliability deteriorates due to increased dark current and charge accumulation
Solution Approach 1:
By segmenting the pixel array into isolated units with separation structures, each pixel's electrical environment is controlled independently. This prevents charge accumulation and dark current from affecting neighboring pixels, maintaining signal quality and reliability even as integration density increases.
Solution Approach 2:
The pixel separation structures modify electrical parameters such as charge distribution and potential gradients between pixels. By controlling these parameters through insulating and conductive layers, the structures reduce dark current and prevent charge accumulation, thereby improving reliability without sacrificing integration density.
3Reliability
If pixel separation structure with conductive grid is implemented, then reliability improves by reducing defects, but device complexity increases
Solution Approach 1:
The pixel separation structures are merged with the interconnection layers and conductive grids that already exist in the image sensor. By combining multiple functions into unified structures, the patent reduces overall device complexity while maintaining the reliability benefits of pixel isolation and defect reduction.
Solution Approach 2:
The conductive grid and pixel separation structures serve multiple functions simultaneously: they provide electrical isolation between pixels, establish voltage references, reduce dark current, and integrate with existing interconnection schemes. This multi-functionality reduces the need for separate components, thereby lowering overall device complexity while improving reliability.
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 solution effectively reduces defects such as electrostatic discharge bruise defects, increases the fill factor, and enhances quantum efficiency by preventing charge accumulation and improving light absorption, thereby improving the overall performance of image sensors.
Implementation Method 1
An interconnection is electrically connected to the pixel separation structure and applied with the voltage having a negative voltage or a ground voltage
Implementation Method 2
A plurality of photodiodes is disposed in the substrate and arranged in a first direction and in a second direction intersecting the first direction in a planar view of the image sensor
Data Source
AI summary
A substrate includes a plurality of pixels arranged in a two-dimensional array structure and has a front side and a back side opposite to the front side. An interconnection is arranged on the front side of the substrate. An insulating layer, a color filter, and a micro-lens are arranged on the back side of the substrate. A pixel separation structure is disposed in the substrate. The pixel separation structure includes a conductive layer having a grid structure in a planar view of the image sensor and surrounds each of the plurality of pixels. A back side contact is vertically overlapped with and electrically connected to a grid point portion of the grid structure of the conductive layer of the pixel separation structure.