X-Ray Sensor Junction Termination With Asymmetric Field-Limiting Rings
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Solution Overview
Problem
Conventional X-ray detectors suffer from inefficiencies in junction termination designs, leading to loss of active detector area and uneven electric field distribution, which affects image quality and detector longevity.
Innovation Solution
A novel X-ray detector design utilizing a specific configuration of Field Limiting Rings (FLRs) with carefully selected distances between the guard, field stop, and FLRs, ensuring a balanced and even spread of electric field peaks, thereby reducing the number of FLRs required while maintaining a large active detection area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional junction termination designs (MFFR or JTE) are used to ensure tolerance to positive surface charge and prevent junction breakdown, then detector reliability is improved, but active detector area is reduced due to large termination width (100-500 μm)
Solution Approach 1:
The junction termination is segmented into multiple discrete field limiting rings instead of a continuous wide termination region. This segmentation allows the electric field to be controlled at specific locations while reducing the overall lateral extent of the termination structure, thereby preserving more active detector area while maintaining reliability.
Solution Approach 2:
The invention changes the geometric parameters of the field limiting rings (spacing, radius, doping concentration) to optimize the electric field distribution. By adjusting these parameters, the termination can provide adequate field control with a much smaller lateral dimension than conventional designs, increasing the active detector area.
2Duration of action of stationary object
If wide junction termination (100-500 μm) is used to spread electric field and prevent breakdown, then detector lifetime under irradiation is extended, but detector complexity increases due to additional structures (guard rings, field plates)
Solution Approach 1:
The invention extracts and eliminates unnecessary components from the conventional termination structure. By using a simplified field limiting ring design without guard rings or field plates, the detector lifetime is maintained through proper field control while the device complexity is reduced.
Solution Approach 2:
The field limiting rings perform multiple functions simultaneously: they control the electric field distribution, prevent junction breakdown, and provide tolerance to positive surface charge accumulation. This multi-functionality reduces the need for separate protective structures, simplifying the overall detector design while extending detector lifetime.
3Stability of the object's composition
If multiple field limiting rings with small spacing are used to control electric field distribution, then electric field uniformity is improved, but active detector area is further reduced due to occupation of space by rings
Solution Approach 1:
The field limiting rings are positioned asymmetrically with non-uniform spacing optimized for the specific detector geometry and electric field requirements. This asymmetric arrangement achieves adequate field uniformity with fewer rings and smaller overall termination width, preserving more active detector area compared to symmetric evenly-spaced designs.
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
The proposed design achieves a well-balanced electric field distribution, increases the active detector area, and enhances the detector's tolerance to positive surface charge, thereby improving image quality and extending the detector's lifespan.
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 and to secure the tolerance to the positive oxide charge
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. This requires applying a voltage of at least 300 Volts for a 500 - 550 μm thick n-type region
Implementation Method 3
The X-ray source emits X-rays, which pass through a subject or object to be imaged and are then registered by the X-ray detector system
Data Source
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AI summary
The proposed technology provides 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 comprises a junction termination (4) surrounding the surface region (3) comprising the plurality of detector diodes (2). The junction termination (4) comprises a guard (5) arranged closest to the end of the surface region (3), a field stop (6) arranged outside the guard (5) and at least two field limiting rings, FLRs (7) arranged between the guard (5) and the field stop (6), wherein a first FLR (7) is arranged at a distance Δ1 from the guard (20) selected from the 10 interval [4 μm; 12 μm], a second FLR (72) is arranged at a distance Δ2 from the first FLR (7) selected from the interval [6.5 μm; 14 μm], and wherein the distance Δ2 is larger than the distance Δ1. The proposed technology also provides a method for constructing such an X-ray sensor and an X-ray imaging system (100) comprising an X-ray detector system (20) that comprises at least one such X-ray sensor (1).