Guide to Rad-hard vs. Rad-tolerant

By Patrice Parris, Chief Technology Officer, VORAGO Technologies.
December 20, 2023

Rad-hard vs. Rad-tolerant: A Complete Guide

Radiation damage poses a significant threat to electronics in the harsh environment of space. High radiation levels can cause catastrophic damage to electronic components.  This can result in mission failure, financial losses totaling millions or billions of dollars, and months or years of lost time. Aerospace engineers designing components for space missions can protect against these radiation effects by using a rad hard MCU.

What is radiation-hardening?

Put simply, radiation hardening makes electronic components resistant to damage caused by radiation exposure. When you take an integrated circuit and put it in high radiation environments such as space, it is exposed to high energy radiation that passes through the semiconductor body. Some of the energy of the incident radiation is transferred into the semiconductor, creating mobile charge. The currents resulting from this charge can flow into circuit nodes which lead to circuit malfunction, either instantly or over time. Radiation hardening is the process in which specialized techniques are used to create a semiconductor IC which is resistant to the effects of the resulting charge and currents so that energetic strikes on the circuit do not impact its functioning correctly.

Two prominent classes of radiation hardening are Radiation Hardening By Design (RHBD), which uses special design libraries and devices, and Radiation Hardening By Process (RHBP), which often uses specialized, often expensive, semiconductor fabrication processes.  VORAGO’s patented HARDSIL® technology uses cost-effective, high-volume manufacturing to harden any commercially designed semiconductor component for extreme environment operations.

Definitions of Rad-hard vs Rad-tolerant

Radiation-hardened and radiation-tolerant components offer varying levels of radiation protection from high levels of ionizing radiation. The difference between rad-hard versus rad-tolerant is a matter of degree of robustness against or resistance to these radiation effects.

What are radiation tolerant electronics?

Radiation-tolerant electronics offer a middle ground between commercial components and radiation-hardened components. Rad-tolerant components can tolerate more radiation doses and/or fluxes than standard consumer electronics, but they tolerate lower radiation exposure than radiation hardened devices.

Usually, these parts were not purposefully made to be radiation-tolerant. They were typically made for another application, such as automotive or medical, but turned out to have a higher level of radiation tolerance which makes them useful for space applications.

Levels of Radiation Protection

Rad-hard Radiation Protection

Radiation-hardened components are the gold standard for space missions and other applications involving extreme radiation doses. Rad-hard components protect against significant levels of radiation. Although there is no absolute guarantee, radiation-hardened parts help to ensure a very low chance of malfunction over the course of a mission.

Rad-tolerant Radiation Protection

Radiation-tolerant electronics are less sensitive to the passage of radiation than commercial electronics, but not nearly as resilient as their radiation-hardened counterparts. Importantly, there is no industry standard definition of “radiation-tolerant” – so some rad-tolerant parts offer substantially better radiation performance than commercial electronics, but others may not be much stronger than a commercial part. Radiation energy thresholds and fluxes for instantaneous disturbance and cumulative doses before malfunction are all much lower with radiation-tolerant parts than radiation-hardened, so there’s a much higher chance of malfunction over the course of the mission.

Can Rad-tolerant Components be Upgraded to Rad-hardened Status?

It is not possible to retroactively radiation-harden semiconductor components – they come out of the fab either radiation-hardened or not. Sometimes, components are fabricated “accidentally” radiation-tolerant with a higher level of radiation performance than commercial integrated circuits.

That said, upscreening – the process of selecting from among a batch of ICs and components those capable of enough radiation resistance to be labelled “rad-tolerant” and possibly acceptable for a sub-set of possible missions – is intended to lessen the chances of malfunction in a radiation tolerant part as much as possible.

Upscreening of Radiation-Tolerant Components

Not every rad-tolerant part is obtained by upscreening. When a supplier upscreens, they are promising the customer that they will screen out the weaker parts and only sell the strongest, most radiation-capable parts from that batch. However, this still comes with some level of risk and engineers working with radiation-tolerant parts must be cognizant of this risk that radiation can cause those components to malfunction during the planned mission. To counter this risk, engineers will build systems around radiation-tolerant parts in a way that allows the system to reset and wipe the slate clean if an error is detected.

Benefits and Drawbacks for Each

Functionality

Radiation-tolerant parts can provide access to some functionality, such as high-performance computing, that is currently limited or unavailable on most radiation-hardened components. This is likely to change as the industry is actively working to increase the scope of functionality associated with radiation-hardened components.  For example, VORAGO’s patented HARDSIL® technology can be applied to advanced CMOS nodes to create rad-hard ICs which expand the range of functionality and performance available.

Chance of Malfunction

While radiation-hardened parts are very unlikely to malfunction, radiation-tolerant parts are more susceptible to mission radiation levels and engineers must assume some likelihood that a rad-tolerant part will fail during the planned mission. Missions requiring a high degree of confidence in the resilience of components would be best served by radiation-hardened components.

Engineers working with radiation-tolerant components need to build fault-tolerant systems so that, when operations of those ICs are corrupted by radiation, the system recognizes something has gone wrong and resets itself.

Even in fault-tolerant systems, there is still some level of risk. For example, an SEL event could cause enough irreversible damage within a rad-tolerant IC in milliseconds that the IC will never function correctly again even after one or more full resets. Therefore, rad-tolerant ICs are usually and most appropriately used in missions with lower radiation energies and fluxes in hopes that the more benign mission conditions will allow the IC to operate throughout the mission without any errors that can’t be recognized and corrected by the system.

Cost Differences

Creating a rad-hard IC using RHBD requires additional design collateral and design time while conventional RHBP often uses specialized, expensive semiconductor manufacturing processes so they are typically more expensive to build than commercial or rad-tolerant ICs.  VORAGO’s proprietary HARDSIL® leverages cost-effective, high-volume semiconductor fabrication methods with standard commercial design methods in order to minimize the cost difference between commercial and HARDSIL® rad-hard ICs.

Rad-tolerant parts can offer a cost-effective option for some situations where a lower level of radiation protection is acceptable to the mission.  However, this apparent savings in cost between the rad-hard and rad-tolerant IC needs to be balanced against the increase in the total cost of the system driven by the additional fault tolerance needed to support the use of rad-tolerant component(s) instead of rad-hardened equivalents. 

Availability of Parts

Traditionally, it was more difficult to acquire radiation-hardened parts because the process to design and manufacture rad-hard components was slow, expensive, and cumbersome. VORAGO is working to remove this barrier by leveraging HARDSIL® to bring a broader range of radiation-hardened components to the market.

Testing Standards

There are recognized tests and quality standards defined by the Defense Logistics Agency (DLA), European Space Agency (ESA) and others to classify a component as “radiation-hardened”. These include published, well-known standards such as the MIL standard.

Conversely, there are no specific standards to classify a part as “radiation-tolerant”. Radiation tolerance has more involved testing than basic consumer parts, but the part is called rad-tolerant because it can’t meet the standards required to be called “radiation-hardened”. Thus, the definition of what is “rad-tolerant” is based on what the market accepts for the part rather than a clear-cut set of qualification standards.

Recent Advancements

Radiation-tolerant components are not generally a focus for research and advancement, as they are mostly created as incidental outputs from development for other applications.

In the world of radiation-hardened components, recent advancements have focused on limiting the impact of Single Event Latchup (SEL), Single Event Upsets (SEUs) and Single Event Transients.

There have also been some recent developments with FPGAs in space, as people are using TMR in FPGA fabric.

Ongoing Research Initiatives

VORAGO is at the forefront of the next generation of radiation hardened components, working to design new rad-hard ICs that will support a broad range of Aerospace and Defense applications, particularly as the industry advances the use of Artificial Intelligence and Machine Learning. Additionally, VORAGO is working on putting HARDSIL® into smaller nodes that will improve availability of high performance computing in radiation hardened components.

How to Find a Reliable Manufacturer or Supplier

As discussed, testing and qual standards are more stringent for radiation-hardened components than for radiation-tolerant parts. Some components, such as QML parts, require extra testing above and beyond the basics for traditional radiation-hardened parts. 

When a supplier tells you their part is radiation-hardened or radiation-tolerant, you want to understand exactly how they are getting to that determination. Inquire about their test methods, and which qualification standards they are following. Doing the upfront research to ensure you are getting the right components to meet the specialized requirements of your mission will save you time, money and headache.  Reputable suppliers will expect and welcome these questions.

A few good questions to ask include:

·       What facilities did you use for testing?

·       What dose rates did you use?

·       What standards did you use to measure those numbers (for radiation hardening classification)?

VORAGO Technologies is the only pure-play, Rad-hard Arm® company. For over 15 years, we have led the industry in providing radiation-hardened components and extreme-temperature solutions for Aerospace, Defense and Industrial projects around the globe.

Let us help you Achieve Your Mission. For more information, please fill out this form or send us an email at info@voragotech.com.