Using Reliability Degradation Parameters To Drive Better Design Choices

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 Cadence’s 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 reliability workflow

The complete ADE 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!