Stacked APD Photodetector Layout for Low Crosstalk and Dark Count
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Solution Overview
Problem
Avalanche photodiodes (APDs) face issues with crosstalk and dark count rate (DCR) due to light emission in high-electric-field regions and dark current generation at interfaces, which affect their sensitivity and accuracy in photon detection.
Innovation Solution
The implementation of a sensor design with a hole accumulation region between the well region and the isolation region, electrically connected to the anode, and an insulating material around the anode, to reduce crosstalk and dark current, enhancing photon detection efficiency and reducing DCR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a through-hole is formed to penetrate the substrate to extract the anode pad, then the anode pad can be accessed for bonding, but the mechanical strength of the substrate is reduced and bonding pads may be exposed to external environment
Solution Approach 1:
The patent transitions from a planar pad layout to a three-dimensional stacked architecture where the anode pad is positioned on the rear surface of the substrate. This dimensional change allows pad access without requiring through-hole penetration, thereby maintaining substrate integrity while achieving the necessary electrical connection accessibility for bonding operations.
2Ease of manufacture
If bonding pads are exposed on the substrate surface, then electrical connection can be established, but the pads are susceptible to external environmental factors and contamination
Solution Approach 1:
The patent inverts the conventional arrangement by positioning the bonding pads on the rear surface of the substrate rather than the front surface. This inversion allows the pads to be electrically connected while remaining protected from external environmental factors and contamination, as they are not exposed on the operational front surface of the device.
3Area of moving object
If the substrate area is reduced to miniaturize the sensor, then device size is reduced, but the bonding pads may become too close or overlap
Solution Approach 1:
The patent employs three-dimensional stacking to separate cathode and anode pads into different spatial planes. The cathode pad remains on the front surface while the anode pad is positioned on the rear surface, allowing both pads to be accommodated within a compact footprint without overlap or excessive proximity, thus enabling miniaturization while simplifying the effective pad layout.
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 effectively reduces crosstalk and dark count rate, improving the sensitivity and accuracy of APDs by isolating pixels and minimizing dark current, thereby enhancing the overall performance of the photodetector.
Implementation Method 1
a first avalanche photodiode (21) including a first cathode region (101) and a first anode region (105)
Implementation Method 2
a first avalanche photodiode (21)
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A sensor, comprising a first substrate (41) including a first semiconductor layer (310) including a first avalanche photodiode (21) including a first cathode region (101) and a first anode region (105); and a first isolation region (108), a first wiring layer (41, 311) including a first wiring; a first via (104), wherein the first cathode region (101) is electrically connected to the first wiring through the first via (104); a second wiring; and a second via (106), wherein the first anode region (105) is electrically connected to the second wiring through the second via (106); and a second substrate (42) stacked on the first substrate, the second substrate including a second wiring layer (42, 610) including a third wiring directly bonded to the first wiring; and a fourth wiring directly bonded to the second wiring; and a second semiconductor layer (610), wherein the first anode region (105) is disposed between the first cathode region (101) and the first isolation region (108).