Amorphous Silicon Photodiode Lag Reduction via Forward Bias
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Solution Overview
Problem
Computed Tomography systems with large flat panel digital x-ray detectors suffer from detector lag due to electron de-trapping from high density electronic defects, leading to non-uniform artifacts in reconstructed images, which existing correction methods like LED saturation and light distribution struggle to address effectively.
Innovation Solution
Applying a forward bias current periodically to the photodiodes to keep amorphous Silicon traps in a steady state, either for each frame or before image acquisition, effectively reducing photodiode gain and lag effects by filling trap states uniformly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LED saturation method is used to correct detector lag, then temporal artifacts are minimized, but mechanical construction is complicated and manufacturing costs increase
Solution Approach 1:
The patent extracts the LED components from the detector assembly, eliminating the need for integrated LED saturation correction hardware. Instead, software-based correction algorithms are applied to the raw detector data, removing the problematic mechanical elements while retaining the artifact correction benefit
Solution Approach 2:
The patent replaces the mechanical LED saturation system with a computational/software-based correction approach. The physical hardware (LEDs, light distribution mechanisms) is substituted with digital signal processing algorithms that correct temporal artifacts in the reconstructed images
2Reliability
If LED saturation method is used to correct detector lag, then temporal artifacts are minimized, but manufacturing costs increase
Solution Approach 1:
The patent removes the expensive LED components and light distribution hardware from the manufacturing process. By extracting these components, the bill of materials and assembly costs are significantly reduced while the software correction algorithm adds minimal manufacturing overhead
Solution Approach 2:
The patent replaces expensive, complex hardware (LEDs with precise optical coupling requirements) with inexpensive software algorithms. The computational correction method is far cheaper to manufacture and deploy than the hardware-based LED saturation system
3Reliability
If LED and light distribution are used for trap saturation, then detector lag is reduced, but x-ray beam interference occurs
Solution Approach 1:
The patent extracts the LED light sources and optical distribution system from the detector assembly, eliminating the source of x-ray beam interference. Without integrated LEDs and light guides in the detector path, x-ray beams can pass through without distortion or scattering from optical components
Solution Approach 2:
The patent replaces the physical LED light distribution system with a software-based correction approach that processes detector data computationally. This substitution eliminates the mechanical/optical components that would interfere with x-ray beam propagation while achieving the same goal of reducing detector lag
4Reliability
If forward bias current is applied periodically to photodiodes, then photodiode gain and lag effects are reduced uniformly, but additional control circuitry is required
Solution Approach 1:
The patent merges the forward bias control functionality into the existing TFT switching infrastructure. The same TFT network used for readout control is repurposed to apply forward bias currents, eliminating the need for separate control circuitry and reducing overall device complexity
Solution Approach 2:
The patent makes the TFT switching network multi-functional by using it for both readout control and forward bias application. This universal use of existing components achieves photodiode gain uniformity without adding dedicated control circuitry, as the TFTs serve dual purposes in the imaging sequence
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
Significantly reduces and uniformizes the photodiode gain and lag effects across exposures, minimizing artifacts in images and maintaining a consistent imaging system state, compatible with continuous x-ray exposure.
Implementation Method 1
A significant cause of the lag is related to the electron de-trapping resulting from the high density electronic defects in the energy band gap
Implementation Method 2
Radiation (e.g., alpha, beta, gamma, X-ray, neutrons, protons, heavy ions, etc.) strikes the scintillator and causes the scintillator to generate visible light
Implementation Method 3
The visible light strikes a phoiodiode and generates an electric current
Data Source
AI summary
A method for reducing gain and lag signals associated with trapped charges is described. Data is collected from a detector. A forward bias voltage is temporarily applied to the detector between collecting the data.