Geiger Mode Diode Matrix for X-Ray Detection
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Solution Overview
Problem
Current electromagnetic radiation detection devices, such as Flat Panel Detectors (FPDs) for X-ray imaging, are limited by low Detection Quantum Efficiency (DQE) at low doses of incident radiation, requiring high exposure doses for high-quality images, especially for sensitive subjects, and are also limited in speed and quality in applications like virtual reality and cargo scanning.
Innovation Solution
The device employs avalanche multiplication in Geiger mode diodes with a segmented structure and high-resistance quenching resistors to generate a high charge pulse per photon, allowing for improved DQE and reduced exposure doses, enabling high-quality large-area imaging with lower doses and faster frame rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional amorphous silicon diodes are used in FPDs, then the device structure is simple and manufacturing is easier, but the Detection Quantum Efficiency (DQE) is low at low radiation doses
Solution Approach 1:
The detector is divided into a matrix of individual pixel sensor circuits, with each pixel containing segmented photodiodes (e.g., 2x2 or 4x2 segments). This segmentation allows independent avalanche multiplication in each segment, significantly boosting the charge signal from single photons while maintaining manageable device complexity through modular architecture
Solution Approach 2:
The operating mode of the photodiodes is changed from linear mode to Geiger mode (avalanche breakdown mode). This parameter change transforms the diodes into highly sensitive single-photon detectors where a single photon can trigger an avalanche multiplication producing thousands of electron charges, dramatically improving DQE at low doses
2Measurement precision
If high dose levels are used to achieve high-quality X-ray images, then image quality is improved, but the exposure risk to subjects increases
Solution Approach 1:
The patent converts the typically harmful high radiation dose requirement into a benefit by using the avalanche multiplication effect in Geiger mode diodes. Each incident photon triggers an avalanche that produces thousands of electron charges, effectively amplifying the weak signal from low-dose radiation into a strong, detectable signal, thereby enabling high-quality imaging at low exposure levels
Solution Approach 2:
By changing the operating parameter of the photodiodes to Geiger mode (above breakdown voltage), the system achieves ultra-high sensitivity where single photons generate large charge pulses (several thousand electrons). This parameter change allows the detector to extract maximum information from minimal radiation doses, reducing exposure risk while maintaining image quality
3Measurement precision
If conventional photodiodes with conversion gain below unity are used, then the device is simpler, but the charge signal per photon is insufficient for high-quality detection
Solution Approach 1:
Each pixel is divided into multiple photodiode segments (e.g., 4 segments per pixel), with each segment independently biased in Geiger mode. This segmentation enables each segment to function as a single-photon avalanche detector, generating large charge signals that are then read out through shared readout circuits, achieving high signal strength without proportionally increasing readout complexity
Solution Approach 2:
The patent introduces avalanche multiplication as an intermediary process between photon detection and charge signal generation. The Geiger mode diodes act as mediators that amplify single-photon events into large charge pulses (thousands of electrons), bridging the gap between weak optical signals and the electrical readout system
4Productivity
If sequential addressing scheme is used in active matrix FPDs, then the device complexity is reduced, but the frame rate and acquisition speed are limited
Solution Approach 1:
The pixel array is segmented into multiple independently addressable units with their own switching transistors and readout paths. This segmentation enables parallel or pipelined readout architectures where multiple rows or columns can be read simultaneously or in overlapping time windows, significantly increasing frame rate without requiring a complete redesign of the addressing scheme
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 solution enhances image quality by reducing exposure doses and blurring due to patient or object movement, while improving detection efficiency and speed in medical and non-medical applications, including CT, PET, SPECT, Digital Radiography, and security imaging.
Implementation Method 1
Each of the diode segments generates a charge signal in response to electromagnetic radiation incident on the FPD. The reverse voltage bias is above the breakdown voltage of the diode segments, so that the diode segments operate in an avalanche multiplication Geiger mode.
Implementation Method 2
Optical light photons from the phosphor that reach photodiodes within respective pixel circuits are converted into single electron-hole pairs
Implementation Method 3
Typical scintillation materials used in X-ray imaging are phosphors such as structured Cesium Iodide (CsI(Tl)) and Gadolinium OxySulfide (Gd 2 O 2 S(Tb))
Data Source
Figure 1~3
Figure 4~5
Figure 6(a)~6(e)
AI summary
An electromagnetic radiation detection device (1) comprises a matrix having a plurality of N rows divided into a plurality of M columns of cells (2), each cell comprising a plurality of diode segments (3) responsive to electromagnetic radiation incident on said device (1). A scan driver (4) provides a plurality of N scan line signals to respective rows of said matrix, each for enabling charge values from cells (2) of a selected row of said matrix to be read. A reader (5) reads a plurality of M variable charge value signals from respective columns of said matrix, each corresponding to a cell (2) within a selected row of said matrix. Each diode segment (3) is connected to a drive voltage sufficient to operate each diode segment (3) in avalanche multiplication Geiger mode; and connected in series with an avalanche quenching resistor (8) to said reader.