On-Chip Radiation Dosimeter Using Buried Oxide Layer
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Solution Overview
Problem
Existing radiation monitoring technologies, such as Geiger counters and TLDs, are either expensive or provide only after-the-fact radiation exposure data, while semiconductor radiation detectors face challenges in maintaining threshold voltage stability during CMOS processing and ionizing radiation exposure in supply chains.
Innovation Solution
A semiconductor device with an on-chip FDSOI radiation dosimeter is fabricated, featuring a buried oxide layer that enhances radiation sensitivity, allowing for accurate real-time tracking of radiation exposure by measuring changes in threshold voltage, and is integrated into CMOS chips to monitor radiation history and ensure device performance and security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Geiger counters or ionization detectors are used for radiation monitoring, then real-time radiation dose information is available, but the devices are relatively expensive
Solution Approach 1:
The patent employs a semiconductor-based radiation dosimeter that can be fabricated using standard CMOS processing techniques, making it significantly cheaper than traditional Geiger counters or ionization detectors. The dosimeter uses a simple transistor structure with oxide layers that can be manufactured at scale using existing semiconductor fabrication processes, enabling cost-effective real-time radiation monitoring.
Solution Approach 2:
The invention replaces the mechanical/electronic complex systems of Geiger counters and ionization detectors with a solid-state semiconductor device. The radiation detection function is achieved through electrical field effects in a transistor structure, substituting complex mechanical scanning and signal processing systems with a compact semiconductor-based threshold voltage measurement approach.
2Ease of manufacture
If TLDs are used for radiation monitoring, then the devices are comparatively inexpensive, but real-time dose information is not available and only after-the-fact determination is possible
Solution Approach 1:
The patent replaces the thermal stimulation mechanism of TLDs with an electrical field effect mechanism. Instead of requiring heat application to release trapped charge and generate light signals, the invention uses voltage application to modulate the transistor threshold voltage, enabling direct electrical readout of radiation dose information in real-time.
Solution Approach 2:
The invention utilizes the phase transition-like effect of charge trapping and de-trapping in the oxide layer. When voltage is applied to the transistor gate, trapped charges are released, causing a measurable shift in threshold voltage that corresponds to the accumulated radiation dose, enabling real-time monitoring without thermal stimulation.
3Duration of action of stationary object
If FET radiation detectors are used to track total radiation dosage, then long-term charge retention is achieved, but holes trapped in SiO2 during CMOS processing cause threshold voltage shifts and device performance degradation
Solution Approach 1:
The patent divides the oxide layer into distinct functional regions: a radiation-hardened lower oxide layer that prevents charge trapping during CMOS processing, and a radiation-sensitive upper oxide layer that enables long-term charge retention for dosimetry. This segmentation allows the device to maintain performance stability while achieving the desired long-term charge retention capability.
Solution Approach 2:
The invention applies different quality characteristics to different parts of the oxide structure. The lower oxide layer is engineered to be radiation-hardened with minimal trap states, while the upper oxide layer is designed with appropriate trap density for long-term charge retention. This local differentiation resolves the contradiction between processing stability and dosimetry functionality.
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 provides accurate, real-time radiation monitoring and long-term tracking of radiation dosage, enhancing device reliability and security by differentiating between active and dosimeter transistors, and enabling verification of processing steps and supply chain integrity.
Implementation Method 1
the wafers being processed are subject to various types of ionizing radiation sources during various processing steps
Implementation Method 2
Electron-hole pairs are created in the silicon (Si) wafer being processed by the energy released by the ionizing radiation
Implementation Method 3
A charge may be induced in a buried oxide (BOX) layer of the FDSOI radiation detector by radiation exposure and trapped by voltage applied to a back gate contact or body contact
Data Source
AI summary
A semiconductor device includes a first field effect transistor (FET) located on a substrate; and a second FET located on the substrate, the second FET comprising a first buried oxide (BOX) region located underneath a channel region of the second FET, wherein the first BOX region of the second FET is configured to cause the second FET to have a higher radiation sensitivity that the first FET.