Deep Diffused Photodiodes for Thin Wafer Structural Support
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Solution Overview
Problem
Existing thin wafer photodiodes face challenges in maintaining performance characteristics while being sturdy enough for handling and use, particularly in applications like computerized tomography, where they are prone to breakage due to high leakage current and noise.
Innovation Solution
The development of photodiode arrays with deep diffused p+ and n+ regions, integrated into a substrate with a passivation layer and an active high resistivity layer, providing structural support and minimizing cross-talk, radiation damage, and leakage current, while maintaining high sensitivity and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thin wafer photodiodes are made to improve sensitivity and reduce noise, then detection precision is improved, but strength and handling characteristics deteriorate causing breakage
Solution Approach 1:
The patent applies composite materials by integrating a thin active layer (for detection) with a support layer (for mechanical strength). The support layer is positioned adjacent to the active layer and provides structural reinforcement without interfering with the photodetection function. This composite structure enables the wafer to maintain both high detection precision and sufficient mechanical strength for handling.
Solution Approach 2:
The patent segments the wafer structure into functionally distinct layers: an active layer for photodetection and a support layer for mechanical reinforcement. This segmentation allows each layer to be optimized independently - the active layer can be made very thin for high sensitivity while the support layer provides the necessary mechanical strength, resolving the contradiction between detection precision and strength.
2Strength
If deep diffused p+ and n+ regions are added to provide structural support, then strength is improved, but device complexity increases
Solution Approach 1:
The support layer serves multiple functions simultaneously: it provides mechanical strength to prevent wafer breakage, acts as a structural foundation for the active layer, and helps with heat dissipation. By making the support layer multi-functional, the patent improves strength without proportionally increasing device complexity, as a single component accomplishes multiple objectives.
3Measurement precision
If thin wafer photodiodes are used to reduce noise, then measurement precision is improved, but reliability deteriorates due to excessive loss from breakage
Solution Approach 1:
The patent applies beforehand cushioning by incorporating a support layer that provides mechanical reinforcement before the wafer is subjected to handling stresses. This preventive measure ensures that the thin active layer is protected from breakage during manufacturing and operation, thereby improving reliability without compromising the noise-reduction benefits of the thin structure.
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 solution results in photodiode arrays with improved durability, low crosstalk, and high sensitivity, suitable for large diameter wafers, effectively addressing the issues of breakage and performance degradation in thin wafer photodiodes.
Implementation Method 1
charge carriers are created by light that illuminates the junction and reverse current is generated that varies with illumination
Implementation Method 2
Deep diffused thin photodiodes
Data Source
AI summary
This invention comprises photodiodes, optionally organized in the form of an array, including p+ deep diffused regions or p+ and n+ deep diffused regions. More specifically, the invention permits one to fabricate thin 4 inch and 6 inch wafer using the physical support provided by a n+ deep diffused layer and/or p+ deep diffused layer. Consequently, the present invention delivers high device performances, such as low crosstalk, low radiation damage, high speed, low leakage dark current, and high speed, using a thin active layer.