Photodiode Light-Sensitive Area Proportion via Isolation Trenches
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Solution Overview
Problem
Conventional photodiodes have an inefficient distribution of light-sensitive and light-insensitive areas, limiting their effectiveness in converting light to electrical current.
Innovation Solution
A photodiode design with a high proportion of light-sensitive area to light-insensitive area is achieved by using a semiconductor structure with isolation trenches and vias, where the light-sensitive area forms at least 95% of the total frontside area, and the light-insensitive areas are minimized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodiode structure with passivation layer and isolation regions is used, then device reliability and electrical isolation are improved, but light-sensitive area proportion decreases
Solution Approach 1:
The photodiode is divided into multiple cells by isolation trenches, with each cell containing a via that segments the conductive path. This segmentation allows electrical isolation while minimizing the area occupied by isolation structures, thereby maintaining high light-sensitive area proportion while ensuring device reliability
Solution Approach 2:
The isolation mechanism is transitioned from a planar approach (isolation regions on the surface) to a three-dimensional approach (isolation trenches extending vertically with depth-to-width ratio of at least 5.0). This vertical isolation in another dimension effectively isolates electrical paths without consuming significant horizontal area, preserving the light-sensitive area proportion
2Reliability
If isolation regions are increased to reduce electrical crosstalk, then electrical isolation between cells is improved, but light absorption efficiency decreases
Solution Approach 1:
Each cell is segmented by isolation trenches that extend through the semiconductor layers, creating discrete electrical isolation zones. The vias within each cell further segment the conductive path, ensuring electrical isolation without requiring large isolation regions that would reduce light absorption area
Solution Approach 2:
The isolation trenches are strategically positioned only where electrical isolation is needed (between cells), while the majority of the cell area maintains high light sensitivity. The local application of isolation structures minimizes their impact on overall light absorption efficiency
3Reliability
If via size is increased to improve electrical contact, then electrical conductivity is improved, but light-sensitive area proportion decreases
Solution Approach 1:
The via dimensions are optimized with specific parameters: length-to-diameter ratio of at least 7.0 and controlled diameter to minimize light blockage. The via depth and diameter are carefully balanced to provide sufficient electrical conductivity while occupying minimal light-sensitive area, maintaining the 95% light-sensitive area proportion
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 enhances the photodiode's light absorption efficiency and reduces electrical crosstalk between cells, leading to improved performance in converting light to electrical current.
Implementation Method 1
A PIN diode typically exhibits an increase in its electrical conductivity as a function of the intensity, wavelength, and modulation rate of the incident radiation
Data Source
AI summary
A photodiode having an increased proportion of light-sensitive area to light-insensitive area includes a semiconductor having a backside surface and a light-sensitive frontside surface. The semiconductor includes a first active layer having a first conductivity, a second active layer having a second conductivity opposite the first conductivity, and an intrinsic layer separating the first and second active layers. A plurality of isolation trenches are arranged to divide the photodiode into a plurality of cells. Each cell has a total frontside area including a cell active frontside area sensitive to light and a cell inactive frontside area not sensitive to light. The cell active frontside area forms at least 95 percent of the cell total frontside area. A method of forming the photodiode is also disclosed.