Diode Radiation Sensor Layout for High Fill Factor Isolation
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Solution Overview
Problem
Radiation sensors, particularly diode radiation sensors with charge multiplication diodes, face inefficiencies due to the presence of isolation regions which reduce the fill factor, create dead edges, and disrupt photon incidence and surface continuity, leading to increased dark noise and reduced sensitivity.
Innovation Solution
The introduction of a third semiconductor layer doped with the same type as the second layer, positioned deeper in the substrate, forms a frame that directs charges towards the high electric field region, and a passivation layer with a high concentration of majority carriers is used to prevent electromagnetic interference, while a peripheral isolation region is designed to minimize substrate impact and maintain surface continuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolation region is introduced between adjacent microcells to provide electrical and optical isolation, then the isolation performance between cells is improved, but the fill factor of the microcells is reduced due to the dead edge formed by the necessary spacing
Solution Approach 1:
The invention moves the isolation region from the horizontal plane (affecting the fill factor) to the vertical dimension by extending the isolation region deeply into the substrate. This allows the isolation region to provide effective electrical and optical isolation between adjacent microcells while minimizing its impact on the horizontal active area, thus maintaining a high fill factor.
Solution Approach 2:
The invention introduces a passivation layer as an intermediary between the isolation region and the active substrate area. This passivation layer, positioned laterally adjacent to the isolation region, provides additional electrical isolation and prevents charge carrier leakage while maintaining surface continuity and not interfering with the optical path, thus improving isolation performance without reducing the fill factor.
2Reliability
If the isolation region is extended deeply into the substrate to improve isolation performance, then the electrical and optical isolation between cells is enhanced, but the complexity of the device structure and manufacturing process increases
Solution Approach 1:
The invention divides the isolation function into two distinct components: the isolation region extending vertically into the substrate for primary isolation, and the passivation layer positioned laterally for secondary isolation and charge carrier management. This segmentation allows each component to be optimized independently and simplifies the overall design and manufacturing process.
Solution Approach 2:
The passivation layer is positioned only in specific locations laterally adjacent to the isolation region, providing localized isolation and charge carrier management where needed. This local quality approach avoids the need for complex global modifications to the device structure and allows for simpler manufacturing processes.
3Manufacturing precision
If the second layer is spaced from the isolation region to form a virtual guard ring, then the electric field control at the edges is improved, but the sensitive area of each SPAD is reduced
Solution Approach 1:
The invention addresses the electric field control issue by extending the isolation region vertically into the substrate rather than increasing the horizontal spacing. This vertical extension provides effective electric field control at the edges while minimizing the impact on the horizontal sensitive area, thus maintaining a high fill factor.
Solution Approach 2:
The passivation layer acts as an intermediary that provides additional electric field control and charge carrier management at the edges of the active area. Positioned laterally adjacent to the isolation region, it helps control the electric field distribution without requiring increased horizontal spacing, thus preserving the sensitive area.
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 configuration enhances the fill factor, reduces the dead edge effect, improves charge multiplication efficiency, and decreases dark noise by effectively focusing charges and maintaining continuous surfaces, thereby increasing the sensor's ability to detect incident photons.
Implementation Method 1
a passivation layer with a high concentration of majority carriers is used to prevent electromagnetic interference
Implementation Method 2
a passivation layer with a high concentration of majority carriers is used to prevent electromagnetic interference
Implementation Method 3
a region with a high electric field E is created for generating the multiplier effect of the diode charge
Data Source
AI summary
A diode radiation sensor includes a substrate; a first layer of semiconductor material doped with a doping of a first type and provided on the front surface of the substrate; a second layer of semiconductor material doped with a doping of a second type of electrically opposite sign to the first type and provided at a first depth in the substrate, the first and the second layer forming a high electric field region therebetween; a third layer of semiconductor material doped with a doping of the second type and provided at a second depth in the substrate greater than the first depth; and a first isolation region provided peripherally to the substrate and extending deep in the substrate up to an intermediate area between the front and the rear surface of the substrate. A passivation layer is interposed between the lateral wall of the first isolation region and the substrate.