Using Reliability Degradation Parameters to Drive Better Design Choices

22 Jul 2026 • 6 minute read

A circuit can look perfect on day one and still drift out of specification after months or years of electrical and thermal stress. That is the reliability problem in a nutshell: the design does not only need to work when devices are fresh; the design must continue to meet performance expectations as devices age.

A useful real-life analogy is a new car engine. A day-one test tells whether the engine runs today, but a reliability-minded test asks: how does the engine behave after heat, load, vibration, and years of use?

In ADE Assembler or Artist, reliability degradation parameters play a similar role: they help translate stress and aging data into measurable design signals, so users can decide whether the circuit still meets reliability expectations.

Why Reliability Degradation Parameters Are Needed

Reliability analysis is needed because degradation mechanisms such as Hot Carrier Injection (HCI), Negative Bias Temperature Instability (NBTI), Positive Bias Temperature Instability (PBTI), and self-heating can shift circuit behavior over time.

A fresh simulation shows the circuit at age = 0, while an aged simulation shows how the circuit behaves after degradation has been applied.

The key value of reliability degradation parameters is that they allow the designer to connect stress information to aged behavior.

Instead of only seeing whether the fresh design passes, the user can evaluate whether the design remains robust after stress-induced degradation.

What Adding Reliability Degradation Parameters Does

Adding reliability degradation parameters in the output setup pane using the relxexpr expression helps extract meaningful measurements from reliability reports.

Rather than manually searching through large report files, the user can fetch maximum, minimum, or count-based values for degradation-related fields.

Max: Find the worst-case value of a reliability parameter, such as maximum d_Vthsat.
Min: Find the minimum value of a reliability parameter, such as minimum trise in a filtered report.
Count: Count the number of devices or entries that violate a defined threshold.

Where This Fits in the ADE Reliability Workflow

The complete workflow starts with setting up reliability analysis, configuring fresh, stress, and aged tests, generating degradation reports, and then adding relxexpr outputs to evaluate design-level reliability metrics.

Step 1: Create the Reliability Setup

In ADE Assembler or Artist, create a reliability setup from the data view pane. The setup defines the analysis name and the Fresh, Stress, and Aged testbenches.

Step 2: Configure Fresh, Stress, and Aged Tests

Fresh simulation represents the no-degradation condition. Stress simulation generates degradation information. Aged simulation applies that degradation to evaluate post-stress circuit behavior.

Step 3: Set Reliability Options

Configure the reliability options needed for aging, modeling, degradation output, and report generation.

Step 4: Generate Reliability Reports

Reliability analysis can generate reports such as device characteristics degradation, device lifetime degradation, model parameter change, and self-heating results.

Step 5: Add a Reliability Expression Output

In the outputs setup tab, select Add new output → <testName> → Reliability expression. A new output row is added with output type set to relxexpr.

Step 6: Define the relxexpr Details

Double-click the details column and select the operation, field, and report. The operation can be max, min, or count. The field can be a report parameter such as d_Vthsat or trise. The report is the reliability report on which the operation is applied.

Step 7: Add a Specification

Use the Spec column to define the acceptable limit for the reliability expression. This enables pass/fail evaluation.

Step 8: Run or Re-evaluate Results

Run the simulation or re-evaluate an existing simulated history to populate the reliability expression values across sweeps and corners.

Viewing Results

After relxexpr expressions are defined in the output setup pane, the detail results view shows values for each reliability expression across sweeps and corners.

Users can click values to view the corresponding reliability report, making it easier to move from a summary metric to the detailed device-level data behind it.

Fresh outputs can appear disabled because no aging is applied in the fresh stage.
Stress outputs are fetched based on the defined relxexpr expressions.
Age outputs show values based on the defined relxexpr expressions after degradation is applied.
When a specification is assigned, each expression can be evaluated as pass or fail.

How This Helps the User

Faster failure triage: Users can identify maximum degradation, minimum margins, or violation counts without manually inspecting every report.
Clear pass/fail visibility: Specifications turn raw reliability values into actionable pass/fail indicators.
Better comparison across sweeps and corners: Reliability expressions make it easier to compare degradation behavior across design conditions.
Improved design confidence: The user can evaluate whether the design continues to meet reliability expectations after stress and aging effects are considered.
More useful thermal-aging insight: Expressions such as Max trise on Self-heating result help users quantify thermal behavior alongside device degradation.

Conclusion

Adding reliability degradation parameters in ADE Assembler or Artist is needed because modern IC reliability cannot be judged from fresh simulation alone.

By using relxexpr in the output setup pane, users can extract maximum, minimum, or count-based metrics from reliability reports, apply specifications, and evaluate pass/fail outcomes across sweeps and corners.

In short, reliability degradation parameters help transform reliability reports into design decisions!

Watch and Learn: Demo Video on Reliability Degradation Parameters!

To understand more about reliability degradation parameters, you can watch a small training bye video which shows this in action.

Working with Reliability Degradation Parameters using relxexpr (Video)

Look at our Training Bytes video channel that offers many helpful videos on how to run reliability analysis in Virtuoso Studio. All the related videos are linked together in a channel, so that you can easily access and watch, as many as you like.

Reliability Analysis in Virtuoso Studio (Video Channel)

Training Spotlight: Reliability Analysis in Virtuoso Studio

These concepts are covered in depth in the Reliability Analysis in Virtuoso Studio customer education course.

For the lecture, lab instructions, and a downloadable design, enroll in the online training courses of your interest on Reliability Analysis in Virtuoso Studio Training. Training is also available as a "Blended" or "live" class.

Digital Badge Available

You can become Cadence Certified once you complete the course (s) and share your knowledge and certifications on social media channels. Go straight to the course exam at the Cadence ASK and Learning portal.

Note: Some of the above links are accessible only to Cadence customers who have a valid login ID for the Cadence ASK and Learning portal.

The faster you finish your online training, the sooner you can claim your Digital Badge. Want to know how accelerated learning works? Our video walks you through the pre-quiz, navigation, and essential features. This is just the beginning. We're regularly adding new Accelerated Learning titles. Accelerated Learning courses are marked with this symbol in our Learning Maps.

Don't have an ASK account yet, some conceptual videos are even available on YouTube!

Explore the Cadence Customer Education Training Bytes and our YouTube Shorts for more videos.

Do You Have Access to the Cadence ASK Portal?

To find information on how to get an account on the Cadence ASK – Learning portal, check the Cadence ASK – Application Support and Knowledge page.

To stay up to date with the latest news and information about Cadence training and webinars, subscribe to the Cadence Training emails.

Cadence Customer Education Learning Maps provide a comprehensive visual overview of the learning opportunities for Cadence customers. Click on Learning Map to see all our courses in each technology area and the recommended order in which to take them. Wondering how to take an online class at your own pace? Come join us and learn from the Cadence Training offerings.

If you have questions about courses, schedules, online, public, or live on-site training, reach out to us at Cadence Training.

Related Resources

Happy reading!

Niyati Singh