Photodetector Quantum Efficiency via Transparent Cathode
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Solution Overview
Problem
Conventional X-ray detector systems suffer from decreased quantum efficiency due to photon absorption by the metallic cathode, leading to inefficiencies and inaccuracies in image reconstruction.
Innovation Solution
A radiation detector module is designed with a photodetector fabricated over a scintillator substrate, where the scintillator emits optical photons that are absorbed by the photodetector, generating charge without obstruction by the cathode, and a planarizing layer is used to improve photon transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metallic cathode is used to electrically connect the detector to the scintillator, then electrical connection is achieved, but quantum efficiency decreases due to photon absorption by the cathode
Solution Approach 1:
The patent introduces an intermediary transparent conductive layer between the metallic cathode and the scintillator. This intermediary layer allows photons to pass through to the photodetector while still enabling electrical connection to the scintillator, thus resolving the contradiction between achieving electrical connection and minimizing photon absorption.
Solution Approach 2:
The patent applies different material properties to different layers: the cathode layer is made transparent in the optical range while maintaining electrical conductivity, and the organic photodetector layer is positioned to receive photons after they pass through the transparent cathode. This local differentiation of material qualities allows simultaneous achievement of electrical connection and photon transmission.
2Device complexity
If the photodetector is fabricated directly onto the TFT array with a metallic cathode, then device integration is achieved, but quantum efficiency is reduced
Solution Approach 1:
The patent employs composite material structure where the cathode is formed as a composite of transparent conductive oxide materials (such as ITO, IZO, or ZnO) that combine optical transparency with electrical conductivity. This composite approach maintains device integration while reducing photon absorption losses.
Solution Approach 2:
The patent changes the optical parameter (transparency) of the cathode material while maintaining its electrical conductivity parameter. By selecting transparent conductive oxide materials with appropriate bandgap energies, the cathode becomes transparent to the optical wavelengths emitted by the scintillator, thus reducing photon absorption while maintaining electrical connection.
3Ease of manufacture
If conventional scintillator-based detectors are fabricated with a metal cathode, then manufacturing is simplified, but quantum efficiency decreases by approximately 20%
Solution Approach 1:
The patent replaces the traditional metallic cathode structure with a transparent conductive oxide layer that can be deposited using similar thin-film deposition techniques (such as sputtering or chemical vapor deposition). This substitution maintains the ease of manufacturing through established processes while eliminating the harmful photon absorption effect of opaque metals.
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 quantum efficiency of the detector, reducing inefficiencies and inaccuracies in image reconstruction by minimizing photon loss and allowing the use of higher-efficiency scintillator materials.
Implementation Method 1
The scintillator substrate is configured to absorb radiation and emit optical photons in response to the absorbed radiation
Implementation Method 2
The photodetector is configured to absorb the optical photons emitted by the scintillator and generate charge in response to the absorbed optical photons
Data Source
AI summary
The present approach involves a radiation detector module with increased quantum efficiency and methods of fabricating the radiation detector module. The module includes a scintillator substrate and a photodetector fabricated on the scintillator substrate. The photodetector includes an anode, active organic elements, and a cathode. The module also includes a pixel element array disposed over the photodetector. During imaging, radiation attenuated by an object to be imaged may propagate through the pixel element array and through the layers of the photodetector to be absorbed by the scintillator which in response emits optical photons. The photodetector may absorb the photons and generate charge with improved quantum efficiency, as the photons may not be obscured by the cathode or other layers of the module. Further, the module may include reflective materials in the cathode and at the pixel element array to direct optical photons towards the active organic elements.