Front-Back Contacted Photodiode Arrays for CT Detectors
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Solution Overview
Problem
Conventional photodiode arrays face challenges in achieving high-density integration with low noise and crosstalk, especially at smaller sizes, and struggle to maintain performance characteristics when fabricated using thin wafers, which are prone to breakage and have difficulty with efficient interconnections.
Innovation Solution
The development of photodiode arrays with PN junctions electrically connected from front to back surfaces, allowing for fully depleted operation at low reverse bias, using techniques such as reactive ion etching and laser hole drilling to create conduits for electrical communication between the junctions, and employing doped polysilicon layers for conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If photodiode arrays are fabricated using thin wafers to achieve high-density integration, then device density and miniaturization are improved, but mechanical strength and handling reliability deteriorate due to increased breakage susceptibility
Solution Approach 1:
The patent divides the thin wafer into multiple smaller individual photodiode devices arranged in arrays, allowing the overall structure to achieve high device density while each individual device maintains sufficient mechanical strength. The segmentation enables high integration without requiring the entire wafer to bear excessive stress.
Solution Approach 2:
The patent modifies the physical and electrical parameters of the photodiode structure, including doping concentrations, junction depths, and device geometries, to optimize both the mechanical robustness and electrical performance of thin-wafer-based high-density photodiode arrays.
2Quantity of substance
If photodiode arrays are made smaller to increase density, then device size is reduced, but interconnection efficiency and signal quality worsen due to increased crosstalk and difficulty in providing efficient interconnections
Solution Approach 1:
The patent extracts and removes the harmful crosstalk effects through careful design of isolation structures and interconnection schemes that separate signal paths, preventing harmful electromagnetic coupling between adjacent photodiodes while maintaining compact spacing for high density.
Solution Approach 2:
The patent transitions from planar two-dimensional interconnections to three-dimensional vertical interconnections by forming conductive pathways through the substrate thickness, allowing efficient signal routing that reduces crosstalk while accommodating high device density in a compact footprint.
3Ease of manufacture
If conventional photodiode structures are used in thin wafers, then fabrication simplicity is maintained, but performance characteristics deteriorate due to inability to achieve fully depleted operation at low reverse bias
Solution Approach 1:
The patent performs preliminary doping and junction formation steps during the fabrication process to pre-establish the electrical characteristics needed for fully depleted operation, allowing the thin-wafer photodiodes to achieve optimal performance at low reverse bias voltages without requiring complex post-fabrication adjustments.
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 approach enables the creation of high-density photodiode arrays with low dark current, low capacitance, and reduced crosstalk, while maintaining the performance characteristics of thicker wafers, and allows for efficient interconnections, enhancing the operational stability and sensitivity of photodiode arrays.
Implementation Method 1
Photodiodes are typified by the quantification of certain characteristics, such as electrical, optical, current (I), voltage (V), and noise
Implementation Method 2
using techniques such as reactive ion etching and laser hole drilling to create conduits for electrical communication between the junctions
Implementation Method 3
using techniques such as reactive ion etching and laser hole drilling to create conduits for electrical communication between the junctions
Implementation Method 4
employing doped polysilicon layers for conductivity
Data Source
AI summary
The present application is a photodiode detector array for use in computerized tomography (CT) and non-CT applications. Specifically, the present application is a high-density photodiode arrays, with low dark current, low capacitance, high signal to noise ratio, high speed, and low crosstalk that can be fabricated on relatively large substrate wafers. More specifically the photodiode array of the present application is fabricated such that the PN-junctions are located on both the front side and back side surfaces of the array, and wherein the front side PN-junction is in electrical communication with the back side PN-junction. Still more specifically, the present application is a photodiode array aving PN-junctions that are electrically connected from the front to back surfaces and which can be operated in a fully depleted mode at low reverse bias.