APD Array Field Reduction Layer for High Fill Factor
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Solution Overview
Problem
Existing avalanche photodiode (APD) arrays face challenges in achieving a high fill factor and good position resolution due to the need for protective structures that reduce the effective signal collecting area and create dead regions between pixels.
Innovation Solution
The proposed APD array design features a homogeneous multiplication layer and a field reduction layer to ensure uniform amplification across the array, along with a novel pixel insulation structure that minimizes dead regions and enhances fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If protective structures are added to separate pixels, then electrical insulation between pixels is improved, but the effective signal collecting area is reduced and dead regions are created
Solution Approach 1:
The patent introduces a pixel insulation region filled with insulating material as an intermediary substance between adjacent n-doped anode regions. This insulating material acts as a mediator that provides electrical insulation between pixels without requiring large protective structures, thereby maintaining the effective signal collecting area while ensuring proper electrical isolation.
Solution Approach 2:
The patent applies localized p-doping in the pixel insulation region to create specific electrical properties only where needed. By concentrating the insulation function in specific regions rather than using extensive protective structures across the entire pixel area, the design achieves adequate electrical insulation while preserving the light-sensitive area.
2Measurement precision
If pixel size is reduced to improve position resolution, then spatial resolution is improved, but the fill factor decreases due to larger relative impact of protective structures
Solution Approach 1:
The patent segments the insulation function into a dedicated pixel insulation region with specific p-doping, separating it from the anode regions. This segmentation allows the protective/insulation structures to be minimized and optimized independently, enabling smaller pixel sizes with maintained fill factor since the insulation region does not need to extend far beyond what is necessary for electrical isolation.
Solution Approach 2:
The patent changes the doping parameters in the pixel insulation region (p-doping concentration) to optimize the balance between insulation effectiveness and area utilization. By adjusting doping parameters rather than relying on geometric dimensions of protective structures, the design achieves effective insulation with minimal impact on fill factor even as pixel size decreases.
3Reliability
If multiplication layer is made wider to reduce k factor and noise, then noise performance is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the pixel insulation function with the multiplication layer structure by implementing the multiplication layer within or as part of the pixel insulation region. This integration allows the multiplication layer to extend laterally without requiring separate protective structures, achieving the necessary width for low k-factor and noise performance while simplifying the overall device structure and manufacturing process.
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 achieves a high fill factor and good position resolution by ensuring homogeneous amplification and reducing signal losses at pixel boundaries, making it suitable for applications requiring high sensitivity and spatial resolution.
Implementation Method 1
Avalanche photodiodes use impact ionization of electric charge carriers for an amplification of the signal. The intrinsic amplification of the signal is effected by a multiplication layer 64 arranged between the drift region 63 and the anode region 61. Due to the higher p-doping, the electric field strength close to the pn junction is so much increased as compared to the field strength in the drift region that a multiplication of signal electrons occurs due to impact ionization
Implementation Method 2
In order to generate a sensor signal, the (signal) electrons that are generated must drift in the electric field in the drift region 63 towards the anode region 61 at the chip front side
Implementation Method 3
At the bottom side, which usually is regarded as chip front side, a heavily n-doped anode region 61 can be seen and at the opposed chip surface, which usually is regarded as chip backside, a heavily p-doped cathode region 62 can be seen. Due to the higher p-doping, the electric field strength close to the pn junction is so much increased
Data Source
AI summary
An avalanche photodiode array for detecting electromagnetic radiation comprises: a semiconductor substrate (100) having a first main surface (101) and a second main surface (102), which are opposite one another, a plurality of n-doped anode regions (1) formed at the first main surface (101) and separated from one another by pixel isolation regions (7), a p-doped cathode region (3) arranged at the second main surface (102) opposite the anode regions, a drift region (4) between the plurality of anode regions (1) and the cathode region (3), and a p-doped multiplication layer (2) arranged below the plurality of anode regions (1) and below the pixel isolation regions (7), and is characterized by an n-doped field reduction layer (9) arranged below the plurality of anode regions (1) and the pixel isolation regions (7) and above the multiplication layer (2).