Amorphous Selenium Radiation Detector Biasing

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Solution Overview

Problem

Conventional planar radiation detectors using amorphous selenium-based radiation-induced-charge or light-induced-charge conversion films experience reduced sensitivity, particularly when taking static radiographic images, due to electron trapping and ghost phenomena, especially when the upper electrode is negatively biased.

Innovation Solution

The use of a planar radiation detector with a radiation-induced-charge or light-induced-charge conversion film formed mainly of amorphous selenium or its alloy, with a residual oxygen concentration of 35 ppm or lower, and additional features such as controlled halogen and alkali metal doping, to prevent sensitivity reduction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional amorphous selenium-based radiation-induced-charge conversion film is used with negative bias on upper electrode, then electron trapping occurs and ghost phenomenon appears, but sensitivity is reduced

Engineering Contradiction:

Improvestability of charge distributionVSAvoidsensitivity

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the electrical bias configuration from negative bias to positive bias on the upper electrode. This parameter change prevents electron trapping in the through region while maintaining stable charge distribution, thereby eliminating the ghost phenomenon and preserving sensitivity in static radiographic imaging

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional biasing approach by applying positive bias instead of negative bias to the upper electrode. This inversion reverses the electron flow direction, preventing electron accumulation in the through region and eliminating the ghost phenomenon that occurs with conventional negative biasing

Inventive Principle:

Principle #13The other way round (Inversion)

2Productivity

If halogen concentration is suppressed to enhance responsiveness in dynamic radiography, then electron trapping is reduced, but sensitivity lowering still occurs according to raw material lots

Engineering Contradiction:

Improveresponsiveness in dynamic radiographyVSAvoidsensitivity stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the bias configuration parameter from negative to positive, which fundamentally alters charge carrier behavior. This change makes the system insensitive to variations in halogen concentration and raw material lots, providing stable sensitivity across different production batches while maintaining responsiveness

Inventive Principle:

Principle #35Parameter changes

3Productivity

If alkali metal doping is performed to reduce electron trapping, then responsiveness in dynamic radiography is enhanced, but sensitivity lowering still occurs

Engineering Contradiction:

Improveresponsiveness in dynamic radiographyVSAvoidsensitivity stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the bias configuration from negative to positive, which addresses the root cause of sensitivity instability. This parameter change eliminates the need for alkali metal doping to prevent electron trapping, providing stable sensitivity across different doping levels and production lots while maintaining responsiveness

Inventive Principle:

Principle #35Parameter changes

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 effectively suppresses the ghost phenomenon, enhancing sensitivity by maintaining low residual oxygen and halogen concentrations, and optimizing alkali metal content, thereby improving image quality in static radiography.

Implementation Method 1

an X-ray-induced-charge conversion film, which is sensitive to X rays, is used, and a distribution of electric charge produced in the X-ray-induced-charge conversion film by X rays

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

another type of planar radiation detector in which a fluorophor converts X rays into visible light, and a thin selenium film is used as a light-induced-charge conversion film

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS7745796B2Planar radiation detector using radiation-induced-charge conversion film of amorphous selenium

Publication Date: 2010.06.29 FUJIFILM CORP

AI summary

In a planar radiation detector having a substrate; a charge-collection electrode; a radiation-induced-charge conversion film formed mainly of amorphous selenium; and an upper electrode which transmits radiation, or in a planar radiation detector having a substrate; a charge-collection electrode; a light-induced-charge conversion film which is formed mainly of amorphous selenium and generates electric charge when the light-induced-charge conversion film is irradiated with visible light which has passed through an upper electrode; the upper electrode which transmits the visible light emitted from a fluorescent layer; and the fluorescent layer formed of a fluorescent material which converts a radiation carrying image information into the visible light, the radiation-induced-charge conversion film or the light-induced-charge conversion film is formed of amorphous selenium or amorphous selenium alloy and has a residual oxygen concentration of 35 ppm or lower.