SiPM Photodetection Element Breakdown Voltage Uniformity
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Solution Overview
Problem
Silicon photomultiplier (SiPM) devices face challenges in maintaining uniform breakdown voltage among avalanche photodiode cells, leading to variations in device characteristics and reduced photon measurement accuracy due to thickness variations in epitaxial layers during manufacturing.
Innovation Solution
The SiPM design includes a semiconductor substrate with a P-type epitaxial layer and N-type semiconductor layers, where the thickness of the depletion layer is maintained constant by controlling the depth of the P+-type semiconductor layer and the top of the semiconductor layer, reducing variations in breakdown voltage through ion implantation and trench isolation structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the epitaxial layer is reduced to several nanometers to reduce breakdown voltage variation, then breakdown voltage uniformity is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the critical parameter from epitaxial layer thickness to the depth of the semiconductor region formed by ion implantation. By controlling the ion implantation depth to be 2.0-5.0 μm, the breakdown voltage variation is reduced to within 0.5 V without requiring ultra-precise control of epitaxial layer thickness, thus avoiding increased manufacturing complexity
Solution Approach 2:
The patent shifts the control dimension from the vertical thickness of the epitaxial layer to the depth of the semiconductor region created by ion implantation. This dimensional shift allows breakdown voltage control through a different physical mechanism that is less sensitive to epitaxial layer variations, resolving the contradiction between precision and complexity
2Manufacturing precision
If the thickness of the epitaxial layer is reduced to several nanometers to reduce breakdown voltage variation, then breakdown voltage uniformity is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces the parameter of epitaxial layer thickness control with ion implantation depth control. This parameter change enables achieving the same breakdown voltage uniformity (within 0.5 V) using standard ion implantation processes rather than requiring costly and complex ultra-thin epitaxial growth processes
Solution Approach 2:
The patent uses a relatively thick epitaxial layer (3.0 μm with ±2% variation) that is more tolerant to manufacturing variations, combined with ion implantation to achieve the desired precision. This approach is more cost-effective than producing and handling ultra-thin epitaxial layers that would require specialized manufacturing equipment and processes
3Device complexity
If a vertical structure with epitaxial layer thickness control is used to determine breakdown voltage, then device structure is simplified, but breakdown voltage variation increases
Solution Approach 1:
The patent combines the vertical structure simplicity with an additional ion implantation step. The ion implantation creates a semiconductor region whose depth (2.0-5.0 μm) determines the breakdown voltage, while the epitaxial layer thickness (3.0 μm ±2%) is no longer the critical parameter. This merging maintains structural simplicity while achieving better breakdown voltage uniformity (within 0.5 V)
Solution Approach 2:
The patent creates a composite structure where the breakdown voltage is determined by the interaction between the epitaxial layer and the ion-implanted semiconductor region. The ion implantation modifies the electrical properties at a specific depth, creating a composite functional structure that achieves precise breakdown voltage control without complicating the overall device architecture
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 approach reduces breakdown voltage variations, enhancing photon measurement accuracy and allowing for larger SiPM areas with a wider dynamic range, while also simplifying manufacturing and reducing costs by eliminating the need for sheet-type CMP procedures.
Implementation Method 1
avalanche breakdown occurs
Implementation Method 2
a depletion layer spreads on the light receiving surface side as a reverse bias voltage is applied
Implementation Method 3
When a photon enters and causes Geiger discharge
Implementation Method 4
controlling the depth of the P+-type semiconductor layer and the top of the semiconductor layer, reducing variations in breakdown voltage through ion implantation
Data Source
AI summary
A photodetection element according to an embodiment includes: a photodiode cell, the photodiode cell including: a semiconductor substrate; a first semiconductor layer disposed on the semiconductor substrate; a second semiconductor layer disposed in a region including an interface between the semiconductor substrate and the first semiconductor layer, the second semiconductor layer being of the same conductivity type as the semiconductor substrate; and a third semiconductor layer disposed in a surface region of the first semiconductor layer.