X-Ray Sensor Field Limiting Ring Layout for Larger Active Area
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Solution Overview
Problem
Conventional X-ray detectors face challenges with junction termination designs that result in a significant loss of active detector area, leading to 'dead' or 'blind' areas, which negatively impact image quality, and are not adequately tolerant to positive surface charge accumulation under X-ray exposure.
Innovation Solution
The proposed solution involves a configuration of Field Limiting Rings (FLRs) with specifically selected distances between them and the guard ring, ensuring a well-balanced and even spread of electric field peaks, thereby reducing the lateral extension of the junction termination and increasing the active detection area while maintaining uniform electric field distribution and tolerance to surface charge.
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 the detector can sustain high voltages (300V-800V), but the lateral extension of the termination structure (100-500 μm) causes significant loss of active detector area
Solution Approach 1:
The patent applies local quality by implementing a non-uniform doping concentration profile within the junction termination extension region. The doping concentration varies laterally, being higher near the guard ring and decreasing towards the outer edges, which optimizes the electric field distribution locally to prevent breakdown while minimizing the overall termination area.
Solution Approach 2:
The patent changes the doping concentration parameter as a function of lateral position within the termination region. By gradually varying the doping concentration rather than using a uniform value, the electric field is better controlled, allowing for a more compact termination structure that preserves more active detector area while maintaining reliability.
2Strength
If the width of the junction termination is increased to spread the electric field and prevent breakdown at high voltages, then the detector can sustain 300V-800V, but this creates larger 'dead' or 'blind' areas in the detector matrix
Solution Approach 1:
The patent implements local quality through a spatially varying doping concentration in the junction termination extension, where the doping level is highest near the guard ring and decreases towards the outer boundaries. This creates an optimized electric field distribution that prevents breakdown at critical locations while reducing the overall lateral extension of the termination region.
Solution Approach 2:
The patent applies asymmetry by using an non-uniform doping profile that is asymmetric with respect to the lateral position within the termination region. The doping concentration is deliberately higher near the guard ring where the electric field stress is greatest, and lower towards the outer edges, creating an asymmetric distribution that optimizes breakdown protection while minimizing dead area.
3Reliability
If traditional junction termination structures with guard rings and floating field rings are used to collect leakage current and prevent edge effects, then detector reliability is improved, but the lateral extension (100-500 μm) reduces the effective detection area
Solution Approach 1:
The patent extracts or removes the traditional floating field rings and guard ring structures from the detector design. Instead of using separate discrete rings, the invention integrates the termination function into a continuous junction termination extension region with a graded doping profile, eliminating the need for additional ring structures that would consume active detector area.
Solution Approach 2:
The patent merges the functions of the guard ring, floating field rings, and junction termination extension into a single integrated structure. The junction termination extension region performs multiple functions simultaneously: it spreads the electric field, suppresses leakage current, and provides gradual voltage transition, eliminating the need for separate ring structures.
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 active detector area, maintains uniform electric field distribution, and extends the detector's lifespan by reducing sensitivity to positive surface charge accumulation, resulting in improved image quality and longer detector life.
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
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. Since some materials absorb a larger fraction of the X-rays than others, an image is formed of the subject or object.
Data Source
AI summary
Disclosed is an X-ray sensor having an active detector region including detector diodes on its surface. The X-ray sensor further includes a junction termination surrounding the surface region including the detector diodes. The junction termination includes a guard arranged closest to the end of the surface region, a field stop outside the guard and at least two field limiting rings, FLRs arranged between the guard and the field stop. A first FLR is arranged at a distance Δ1 from the guard selected from the interval [4 μm; 12 μm], a second FLR is arranged at a distance Δ2 from the first FLR 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 including an X-ray detector system that includes such X-ray sensor.