Modeling Excess Base Current in Irradiated Bipolar Junction Transistors
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Solution Overview
Problem
Traditional methods for qualifying commercial-off-the-shelf (COTS) bipolar junction transistors (BJTs) for space systems are costly and inaccurate due to radiation-induced total ionizing dose (TID) effects, which cause permanent damage and require expensive and inefficient testing processes.
Innovation Solution
A method is developed to model excess base current in irradiated BJTs by quantifying defect-related electrostatic effects such as charged interface traps and surface potential, allowing for improved prediction of TID response, enabling faster and lower-cost qualification of COTS components for space systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional qualification testing is conducted for COTS bipolar transistors in space systems, then reliability of the qualification process is improved, but cost and time consumption increase significantly
Solution Approach 1:
The patent applies preliminary action by developing and validating a predictive modeling framework before actual space deployment. The model uses pre-characterized defect parameters (interface trap density, oxide charge density) to predict TID response, allowing qualification decisions to be made before expensive and time-consuming radiation testing is performed. This enables faster part qualification while maintaining reliability through the model's ability to accurately predict radiation-induced base current increases.
2Measurement precision
If comprehensive radiation testing is performed on every COTS component, then measurement precision of TID response is improved, but cost increases prohibitively
Solution Approach 1:
The patent applies copying by creating a mathematical model that replicates the complex radiation response behavior of bipolar transistors. Instead of physically testing every component, the model copies the essential physics of TID effects (interface trap generation, oxide charge accumulation) to predict base current increases. This virtual copy allows accurate TID response assessment without the prohibitive cost of physical radiation testing for every COTS component.
Solution Approach 2:
The patent substitutes the mechanical/physical radiation testing system with a computational modeling system. The model replaces actual radiation exposure with mathematical calculations based on defect physics, using equations that predict base current increase as a function of interface trap density and oxide charge density. This substitution maintains measurement precision while dramatically reducing qualification costs.
3Ease of manufacture
If COTS components are used in space systems, then ease of manufacture and cost are improved, but reliability under radiation exposure deteriorates
Solution Approach 1:
The patent applies feedback by using the predictive model to assess COTS component suitability for space applications. The model takes as input the actual measured defect parameters from specific COTS transistors and provides feedback on their expected TID response. This feedback mechanism allows engineers to identify which COTS components meet space radiation requirements and which do not, enabling informed selection decisions that maintain both ease of manufacture and reliability.
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 accurately predicts the TID response of BJTs, facilitating the qualification or disqualification of COTS components for space systems, thereby reducing costs and improving accuracy in part qualification processes.
Implementation Method 1
radiation induces a large increase in bipolar base current, which can create so-called total ionizing dose (TID) effects
Implementation Method 2
quantifying and utilizing defect-related electrostatic effects (e.g., charged interface traps on surface potential and carrier concentration at bipolar base surface)
Data Source
AI summary
The disclosure describes a method for modeling excess base current in irradiated bipolar junction transistors (BJTs). The method includes quantifying defect-related electrostatic effects of a BJT device to help improve accuracy in predicting an irradiated excess base current of the BJT device. The method can be adapted to model the excess base current of a lateral P-type-N-type-P-type (LPNP) BJT device in depleted and/or accumulated surface potential states. The predicted excess base current may be used to qualify or disqualify the BJT device or an electrical circuit including the BJT device for use in a space system(s) as a commercial-off-the-shelf (COTS) component. By modeling the excess base current based on quantifying and utilizing the defect-related electrostatic effects, it may be possible to accurately predict a total-ionizing-dose (TID) response of the BJT device, thus enabling faster and lower-cost qualification of a COTS component(s) for use in the space system(s).