MOSFET Radiation Sensor with Kapton Carrier and Self-Compensation
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Solution Overview
Problem
Current radiation sensors, particularly MOSFET and diode sensors, face challenges in achieving accurate and reproducible skin dosimetry due to packaging-related anisotropy and water equivalent depth (WED) issues, which lead to errors in radiation therapy, especially for applications like breast cancer treatment where steep dose gradients occur.
Innovation Solution
A radiation sensor design featuring a flexible polymeric carrier material, such as polyamide, that protects the semiconductor detector and provides a reproducible water equivalent depth, combined with a thermo-stabilization method using the source-substrate p-n junction to correct threshold voltage drift, ensuring accurate and temperature-independent dose measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MOSFET die is placed on Kapton tail with epoxy envelope for protection, then the sensor is protected from environmental conditions, but additional response anisotropy is introduced and WED becomes irreproducible
Solution Approach 1:
The invention removes the epoxy envelope and copper leads from the sensor packaging. The MOSFET die is directly mounted on the Kapton tail without epoxy, eliminating the source of anisotropy and WED variability while maintaining protection through the Kapton material itself.
Solution Approach 2:
The invention uses the Kapton tail as a flexible polymer carrier that provides both mechanical support and environmental protection. The thin film structure of Kapton replaces the bulky epoxy envelope, maintaining sensor protection while minimizing interference with radiation response and ensuring reproducible water equivalent depth.
2Temperature
If dual MOSFET sensors are used with different gate voltages to compensate temperature dependence, then temperature instability is compensated, but device complexity increases
Solution Approach 1:
The invention uses the MOSFET's own source-substrate p-n junction to generate a temperature-dependent voltage that automatically compensates for threshold voltage drift. The single MOSFET sensor serves its own temperature compensation needs through internal circuitry, eliminating the need for dual sensors and complex differential measurements.
3Measurement precision
If MOSFET gate oxide is made thin for high spatial resolution, then measurement of dose patterns with high spatial resolution is achieved, but sensitivity to environmental conditions increases
Solution Approach 1:
The invention removes the epoxy envelope that caused environmental sensitivity issues. By mounting the MOSFET die directly on Kapton without epoxy, the thin gate oxide structure is protected from moisture and contaminants while maintaining its high spatial resolution capabilities.
Solution Approach 2:
The Kapton tail provides a protective barrier against environmental conditions while maintaining a thin overall structure. This flexible polymer film protects the thin gate oxide MOSFET from environmental degradation without adding significant thickness that would compromise spatial resolution.
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 enables accurate and reproducible skin dose measurements with minimal anisotropy and WED variability, improving the reliability of radiation therapy by reducing errors associated with temperature changes and packaging-related issues.
Implementation Method 1
a thermo-stabilization method using the source-substrate p-n junction to correct threshold voltage drift
Implementation Method 2
The internal electric field produced by the p-n junction of the diode collects charge induced by radiation within the diffusion length
Implementation Method 3
A MOSFET operates by trapping a positive charge in the gate oxide proportional to the absorbed dose deposited in a gate
Data Source
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Figure 3A~5
Figure 6~7
AI summary
A semiconductor radiation sensor (100), comprising a substrate (102), a carrier material (104) mounted to the substrate (102), and a semiconductor detector (106) mounted to the carrier material (104). A radiation sensitive portion of the semiconductor detector (106) is oriented towards the carrier material (104) and generally away from the substrate (102), and the carrier material is adapted to transmit radiation to the radiation sensitive portion of the semiconductor detector (106). A dosimeter comprising the radiation sensor (100) and a method of manufacturing the radiation sensor (100) are also provided.