Radiation Detector Pixel With Dual Diodes For Dynamic Range
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Solution Overview
Problem
Current radiation detectors face limitations in dynamic range and signal-to-noise ratio (SNR), particularly in image sensing devices, where pixel binning compromises resolution and SNR, and there is a need for improved flexibility in image sensing arrays for varied applications.
Innovation Solution
A radiation detector with at least two diodes per pixel, where the first diode collects carriers only after the second diode exceeds its noise floor, utilizing different bias voltages and positions to optimize carrier collection, and employing semiconductor layers with varying resistivity to increase depletion layer depth, allowing independent readout of each diode for enhanced dynamic range and SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel binning is used to increase signal-to-noise ratio, then SNR is improved, but resolution is reduced
Solution Approach 1:
The pixel is divided into multiple independent photodiodes (first photodiode, second photodiode, third photodiode) with different collection regions and capacitances. Each photodiode can be independently controlled and read out, allowing selective use based on radiation conditions without requiring physical binning of adjacent pixels.
Solution Approach 2:
Different photodiodes within the same pixel are designed with different properties: the first photodiode has larger collection region for high radiation conditions, while the second and third photodiodes have smaller regions and lower capacitance for low radiation conditions. This local differentiation allows optimal performance across varying radiation levels.
2Device complexity
If a single diode is used per pixel, then device complexity is low, but dynamic range is limited
Solution Approach 1:
The system dynamically selects which photodiode to use based on radiation conditions. The control circuitry can switch between the first photodiode (larger collection region) for high radiation and the second/third photodiodes (smaller regions) for low radiation, enabling adaptive operation across a wide dynamic range.
Solution Approach 2:
Each pixel contains multiple photodiodes that can serve different functions: the first photodiode handles high radiation conditions, while the second and third photodiodes handle low radiation conditions. This multi-functionality within a single pixel structure expands the overall dynamic range without requiring multiple separate sensor arrays.
3Power
If the first diode collects carriers continuously, then signal strength is high, but noise floor increases
Solution Approach 1:
The first photodiode with larger collection region is activated only when radiation conditions warrant its use (excessive radiation levels). For normal or low radiation conditions, the system uses the second or third photodiodes with smaller collection regions, avoiding the excessive signal and associated noise from the larger photodiode.
Solution Approach 2:
The control circuitry acts as an intermediary that monitors radiation conditions and selectively activates appropriate photodiodes. This mediation ensures that the first photodiode (which would produce higher noise) is only used when necessary, while the second and third photodiodes handle conditions where lower noise is critical.
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 improves dynamic range and sensitivity by allowing the detector to operate effectively across a wider range of radiation conditions while maintaining high SNR, enabling flexible use in diverse applications through independent readout and adjustment of diode signals.
Implementation Method 1
image sensing devices that convert incident radiation into an electric signal
Implementation Method 2
each pixel normally consisting of a single diode which is employed to collect free carriers (ordinarily electrons) generated by radiation incident on the area corresponding to the pixel
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
Embodiments of the invention provide a radiation detector comprising a pixel, the pixel having a first diode arranged to collect radiation-generated carriers; a second diode arranged to collect radiation-generated carriers; switching components operable to permit independent readout of the first diode and the second diode, wherein the first diode has a higher node capacitance than the second diode.