X-ray Shielding in Photo Detector Diode Arrays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current X-ray detector arrays in CT scanners face issues with X-ray cross-talk and spurious back side illumination, leading to noise and ghosting in images, and existing shielding solutions are either ineffective or costly, such as using ceramic substrates which are expensive and expose CMOS circuitry to stray radiation.
Innovation Solution
Incorporating X-ray shielding materials like tungsten into the septa between photodiodes and on the back side of the array, using Chemical Vapor Deposition or sputtering methods, to create a comprehensive shield that prevents X-ray cross-talk and protects underlying processing circuitry, allowing for direct mounting of CMOS circuitry without additional substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ceramic substrates are used for shielding, then structural support and radiation shielding are provided, but cost increases and CMOS circuitry is still exposed to stray radiation
Solution Approach 1:
The substrate is segmented into multiple functional layers: a mechanical support substrate and separate shielding layers (tungsten or lead) positioned strategically between photodiodes and behind the array. This segmentation allows the support substrate to provide structural integrity while the dedicated shielding layers block stray radiation from reaching CMOS circuitry, resolving the contradiction between structural support and radiation protection.
Solution Approach 2:
Shielding materials (tungsten or lead) are introduced as intermediary layers between the photodiode array and the CMOS circuitry. These intermediary shielding layers absorb and block stray radiation before it can reach the sensitive CMOS circuits, effectively mediating the harmful interaction between radiation and electronics while maintaining system functionality.
2Object-affected harmful factors
If inter-scatter grids are placed in septa, then X-ray cross-talk is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The inter-scatter grid is extracted from the traditional position within the septa and repositioned to the back side of the photodiode array. This extraction simplifies the front-side structure and manufacturing process while maintaining the grid's primary function of blocking scattered X-rays from reaching adjacent photodiodes, thereby reducing cross-talk without the manufacturing complexity of integrating grids into septa.
Solution Approach 2:
The shielding approach is shifted from a lateral/dimensional approach (inter-scatter grids in septa) to a depth-based approach (shielding layers on the back side). By placing shielding material in the depth dimension behind the photodiodes, the patent achieves cross-talk reduction and stray radiation protection through a different spatial arrangement that simplifies manufacturing.
3Object-affected harmful factors
If additional shielding layers are added, then radiation protection is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The shielding function is merged with the substrate structure itself. The support substrate is designed to incorporate shielding layers (tungsten or lead) as integral parts of its construction, rather than as separate added components. This merging of structural support and radiation shielding functions reduces overall device complexity while maintaining effective radiation protection.
Solution Approach 2:
The support substrate is given multiple functions: it provides mechanical support for the photodiode array, serves as a mounting platform for CMOS circuitry, and incorporates shielding layers for radiation protection. This multi-functionality eliminates the need for separate dedicated shielding components, reducing device complexity while achieving comprehensive radiation protection.
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 effectively reduces noise and ghosting by blocking stray X-rays, eliminating the need for expensive ceramic substrates and providing comprehensive X-ray shielding while maintaining structural integrity and electrical connectivity.
Implementation Method 1
Incorporating X-ray shielding materials like tungsten into the septa between photodiodes and on the back side of the array... effectively reduces noise and ghosting by blocking stray X-rays
Implementation Method 2
using Chemical Vapor Deposition or sputtering methods, to create a comprehensive shield
Implementation Method 3
using Chemical Vapor Deposition or sputtering methods, to create a comprehensive shield
Data Source
AI summary
A front side illuminated photo detector array is shielded from X-ray cross-talk by filling the septa between individual photo detector diodes with a high atomic number material such as tungsten. The processing circuitry is also shielded from stray X-rays by a barrier such as tungsten placed between each photo detector diode and the processing circuitry. This barrier serves a dual role as shielding the processing circuitry from stray X-ray radiation and acting as the electrical contact between the detector diode and the circuitry.