X-ray Sensor Junction Termination with Floating Field Limiting Rings
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional X-ray detectors face challenges with junction termination designs that result in significant loss of active detector area, leading to 'dead' or 'blind' zones, which negatively impact image quality and are sensitive to high voltages and positive surface charge accumulation.
Innovation Solution
The proposed solution involves a spatially distributed junction termination using Floating Field Limiting Rings (FFRs) with specific distance constraints between the guard, FFRs, and the field stop, ensuring a uniform surface electric field distribution and reduced lateral extension of the termination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional junction termination designs (MFFR or JTE) are used to secure tolerance to positive surface charge and prevent breakdown, then the detector can sustain high voltages (400V-800V), but the active detector area is significantly reduced due to the large width (100-500 μm) required for the termination region
Solution Approach 1:
The junction termination is segmented into multiple discrete floating rings (first, second, and third rings) spaced at specific distances from each other, rather than using a continuous termination region. This segmentation allows the electric field to be distributed across multiple localized regions, reducing the overall lateral extension while maintaining breakdown protection.
Solution Approach 2:
The invention changes the geometric parameters of the termination structure by specifying precise distance relationships between rings (e.g., distance from guard to first ring is 5-15 μm, distance between first and second rings is 10-20 μm, etc.). These parameter optimizations enable compact spacing that reduces dead area while preserving the electrical field distribution needed for high voltage tolerance.
2Reliability
If the width of the junction termination is increased to reduce electric field strength at the surface and prevent breakdown, then the detector can withstand higher voltages, but the lateral extension of the termination increases, creating more dead areas in the detector matrix
Solution Approach 1:
The continuous termination region is divided into discrete floating rings spaced at optimized intervals. This segmentation concentrates the field-spreading function at specific locations rather than requiring a continuous wide termination region, thereby reducing the lateral extension while maintaining breakdown protection.
Solution Approach 2:
The invention transitions from a planar, two-dimensional termination approach to a three-dimensional spatial distribution of floating rings at different radial distances from the pixel center. This allows the termination function to be achieved in the radial dimension without increasing the lateral footprint in the pixel plane.
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 enhances the use of active detection area, balances electrical field peaks, and reduces sensitivity to positive surface charge, thereby improving the robustness and efficiency of the X-ray sensor.
Implementation Method 1
The function of the junction termination is to spread the electric field along the surface of the detector in order to reduce the electric field strength
Implementation Method 2
For maximum sensitivity the highly resistive n-type part of the detector that builds a so called drift region of the PiN diode structure must be totally depleted of charge
Implementation Method 3
the JTE uses the principle of charge neutrality between the dopant charge in the JTE under depletion negatively charged acceptors and in the n-type drift region also under depletion positively charged donors
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Disclosed is an X-ray sensor (1) having an active detector region comprising a plurality of detector diodes (2) arranged on a surface region (3) of the X-ray sensor (1) the X- ray sensor (1) further comprising a junction termination (4) surrounding the surface area (3) comprising the plurality of detector diodes (2), the junction termination (4) comprising a guard (5) arranged closest to the end of the surface region (3), a field stop (6) arranged outside the guard (2) and a number Nof field limiting rings, FLRs(7) arranged between the guard (5) and the field stop (6), wherein each of the FLRs (7) are placed at positions selected so that distances between different FLRs (7) and between the guard and the first FLR lie within an effective area, the effective area being bounded by the lines α = (10 +1,3 x (n-1)) μm and β= (5+1,05 x (n-1)) μm, and selected so that the distance between successive FLRs (7) is either constant or increases with increasing n where n denotes the index of the FLRs (7), and 1≤ n ≤ N. Also disclosed is method for constructing such an X-ray sensor (1) and an X-ray imaging system (100) comprising such an X-ray sensor (1).