Monolithic X-ray Detector Shielding Peripheral Circuits
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Solution Overview
Problem
Current X-ray imaging systems suffer from radiation damage to silicon-based image sensor arrays due to incomplete absorption of X-ray photons by scintillation layers, leading to limited system lifespan, high maintenance costs, and increased noise levels.
Innovation Solution
A buttable monolithic photodiode detector array with precision shielding of peripheral circuits from X-ray radiation using a common substrate and precision chip-on-board assembly, eliminating the need for wire bonding and reducing parasitic capacitances and inductances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the image sensor array is placed in the X-ray path to detect X-rays, then X-ray detection capability is improved, but radiation damage to the sensor array increases
Solution Approach 1:
The detector is divided into two separate chips: a photodiode array chip that is exposed to X-rays for detection, and a peripheral circuit chip that is shielded from X-rays. This segmentation allows the detection function to be maintained while protecting the sensitive peripheral circuits from radiation damage, thus resolving the contradiction between detection capability and radiation damage.
Solution Approach 2:
The peripheral circuits are extracted from the photodiode array and placed on a separate chip. By taking out the radiation-sensitive peripheral circuits from the X-ray path, the system maintains X-ray detection capability while eliminating radiation damage to the peripheral circuits.
2Ease of manufacture
If wire bonding is used to connect photodiode array to peripheral circuits, then electrical connection is achieved, but assembly cost and complexity increase
Solution Approach 1:
The photodiode array and peripheral circuits are merged into a single monolithic integrated circuit chip, eliminating the need for wire bonding or other inter-chip connections. This integration reduces assembly cost and complexity while improving connection reliability by removing intermediate connection interfaces.
3Reliability
If scintillation layer is placed on top of photodiodes to convert X-rays, then X-ray detection efficiency is improved, but X-ray photons are not completely absorbed causing radiation damage
Solution Approach 1:
The detector is segmented into a photodiode array chip that receives the full X-ray flux for efficient detection, while peripheral circuits are separated and shielded. This allows the photodiode array to operate at high detection efficiency without the peripheral circuits suffering radiation damage.
Solution Approach 2:
A lead shield is introduced as an intermediary element between the X-ray source and the peripheral circuits. The shield absorbs excess X-ray photons before they can reach and damage the peripheral circuits, while allowing the photodiode array to maintain high detection efficiency.
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
The solution extends the lifespan of X-ray detector systems, reduces assembly costs, improves reliability, and enhances noise and speed performance by effectively shielding sensitive components from radiation damage while maintaining high imaging resolution.
Implementation Method 1
X-ray sensitive scintillating materials, such as Gd2O2S:Tb (GOS), CsI(Tl), or CdWO4 have been used. These materials greatly enhance the detection efficiency of higher energy X-rays in silicon based sensor arrays through the ability of the scintillating materials to convert and emit visible light photons proportional to the X-ray energy and dose.
Implementation Method 2
The visible light photons are converted to electrical signals by a silicon based image sensor array, such as a Linear Photodiode Array (PDA). When the image sensor array is read out, the array sequentially produces a stream of electrical video signals from each photo-element with amplitudes proportional to the intensity of the X-ray pattern that impinges on the photo-elements.
Data Source
AI summary
A radiation damage resistant linear X-ray detector array system based on a unique buttable monolithic image sensor design and precision chip-on-board assembly technology includes at least one of the detector chips. Multiple chips of the image sensor may be butted end-to-end on a common printed circuit board to accommodate larger detection systems. A layer of scintillating material, such as Gd2O2S:Tb (GOS), CsI(Tl), or CdWO4, is placed on the image sensor to convert the impinging X-ray energies into visible light which can be detected efficiently by the image sensor array. A protective metal shield is fastened to the substrate to protect the sensitive circuits of the image sensor from X-ray radiation damage. A proper separation of sensitive circuits from the photodiode array on the sensor chip, coupled with precision registration of the sensor chips on the substrate, allows easy installation of the protective metal shield.