Backside Lens-Integrated Photodetector for Optical Alignment
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Solution Overview
Problem
The challenge in optical communications is achieving efficient coupling of light into photodetectors (PDs) for high-speed operations, as the active area of PDs is very small, leading to low received light levels and misalignment issues, which compromise data recovery in optical receivers.
Innovation Solution
Integrating a focus lens on the backside of the PD die within the optical receiver package, allowing for improved alignment and reduced misalignment tolerance, enabling tighter accuracy and fewer discrete components, thus enhancing coupling efficiency and assembly yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the active area of the PD is made very small to achieve high-speed operation, then the speed increases, but the coupling efficiency of light deteriorates
Solution Approach 1:
A focus lens is introduced as an intermediary component between the optical input device and the PD. The lens focuses the optical signal onto the small active area of the PD, enabling efficient coupling despite the small detector size required for high-speed operation.
Solution Approach 2:
The focus lens is integrated on the backside of the PD die, utilizing the third dimension (depth) rather than increasing lateral dimensions. This allows the lens to be positioned optimally for focusing without increasing the planar footprint of the device.
2Speed
If the active area of the PD is made very small to achieve high-speed operation, then the speed increases, but the alignment tolerance deteriorates
Solution Approach 1:
The focus lens and PD are merged into a single integrated structure where the lens is formed on the backside of the PD die. This integration ensures precise alignment between the lens and the active area, eliminating alignment tolerance issues that would arise from using separate components.
Solution Approach 2:
The integrated focus lens acts as a mediator that bridges the optical input device and the small PD active area, providing robust alignment tolerance through its fixed positional relationship with the active area.
3Reliability
If a focus lens is used to improve coupling efficiency, then the coupling efficiency increases, but the device complexity increases
Solution Approach 1:
The focus lens is merged with the PD die by forming it on the backside of the same substrate. This reduces the number of discrete components from two separate elements (lens and PD) to a single integrated device, simplifying the overall structure while maintaining high coupling efficiency.
4Reliability
If a focus lens is used to improve coupling efficiency, then the coupling efficiency increases, but the manufacturing cost increases
Solution Approach 1:
The focus lens and PD are manufactured as a single integrated device on one die, eliminating the need for separate lens fabrication, handling, and assembly processes. This integration reduces manufacturing steps, material waste, and assembly costs while achieving high coupling efficiency.
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 integration of a focus lens on the backside of the PD die improves optical alignment, increases coupling efficiency, and reduces assembly costs by minimizing misalignment and discrete components, leading to improved performance and yield in optical receiver packages.
Implementation Method 1
a lens integrated at a second face of the PD die, the second face being opposite the first face, the second face to receive the optical input to be detected by the PD
Implementation Method 2
Photodiodes may be used as PDs to detect light by converting incident light into an electrical signal
Data Source
AI summary
Optical receiver packages and device assemblies that include photodetector (PD) chips having focus lenses monolithically integrated on PD die backsides are disclosed. An example receiver package includes a support structure, a PD die, and an optical input device. The PD die includes a PD, integrated proximate to a first face of the PD die, and further includes a lens, integrated on, or proximate to, an opposite second face. The first face of the PD die faces the support structure, while the second face (“backside”) faces the optical input device. The optical receiver architectures described herein may provide an improvement for the optical alignment tolerance issues, especially for high-speed operation in which the active aperture of the PD may have to be very small. Furthermore, architectures described herein advantageously enable integrating a focus lens in a PD die that may be coupled to the support structure in a flip-chip arrangement.