Photodiode Array With Lower Conductive Part for X-Ray Sensors
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Solution Overview
Problem
Photodiode arrays in X-ray sensors face challenges in achieving higher resolution and precision while maintaining a large saturated signal amount, as reducing pixel size decreases junction capacitance and dynamic range, and lowering bias potential reduces dark current but also signal output.
Innovation Solution
Incorporating a lower conductive part under the lower electrode with an insulating layer, creating an additional capacitive element parallel to the junction capacitor, which increases pixel capacitance and dynamic range without affecting light-receiving area or manufacturing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to achieve higher resolution, then measurement precision is improved, but junction capacitance decreases and dynamic range is reduced
Solution Approach 1:
The patent embeds an additional capacitive element within the existing pixel structure by introducing a lower conductive part beneath the lower electrode, separated by an insulating layer. This nested configuration allows the extra capacitance to be integrated without increasing the pixel's external dimensions, thereby maintaining high resolution while increasing junction capacitance and dynamic range.
Solution Approach 2:
The patent transitions from a two-electrode configuration to a three-layer capacitive structure by adding the lower conductive part in the vertical dimension. This dimensional extension creates an additional capacitor in parallel with the original junction capacitor, effectively increasing total capacitance without expanding the pixel area, thus resolving the contradiction between small pixel size and sufficient capacitance.
2Object-generated harmful factors
If bias potential is lowered to reduce dark current, then object-generated harmful factors are reduced, but signal output also decreases
Solution Approach 1:
The patent changes the electrical parameters of the pixel by introducing an additional capacitive element that modifies the RC time constant and charge storage capacity. This parameter change allows the system to maintain adequate signal output levels even at lower bias potentials, as the increased capacitance compensates for the reduced driving voltage, thereby reducing dark current without proportionally reducing signal output.
Solution Approach 2:
The patent creates a duplicate capacitive function by adding the lower conductive part and insulating layer configuration, which generates an additional capacitor parallel to the original junction capacitor. This copied capacitive element increases the total charge storage capacity, allowing the pixel to maintain signal output at lower bias potentials where dark current is reduced.
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 saturated signal amount, reduces noise, and maintains high precision while allowing for smaller pixel sizes, thus improving the dynamic range and reducing dark current effectively.
Implementation Method 1
a photoelectric conversion region between the upper electrode and the lower electrode
Implementation Method 2
an insulating layer between the lower electrode and the lower conductive part
Data Source
AI summary
A photodiode array includes a plurality of elemental devices arrayed on a substrate. Each of the plurality of elemental devices includes an upper electrode, a lower electrode, a photoelectric conversion region between the upper electrode and the lower electrode, a lower conductive part located lower than the lower electrode; and an insulating layer between the lower electrode and the lower conductive part. The lower conductive part at least partially overlaps the lower electrode with the insulating layer interposed therebetween when viewed planarly.