Parallel Voltage Limiter for Electromigration Tester DUT Protection
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Solution Overview
Problem
Electromigration testers often fail to prevent catastrophic thermal damage to devices under test due to insufficient speed in disconnecting stressing currents, and existing solutions for limiting compliance voltage are impractical due to the rarity of power supplies with low voltage and high output current.
Innovation Solution
Incorporating a voltage limiter in parallel with the device under test (DUT) in a circuit with a controlled current source, where the limiter allows current to flow only when the voltage across the DUT would exceed a maximum voltage, thereby limiting the voltage to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stressing current is disconnected quickly to prevent thermal damage, then the DUT is protected from catastrophic damage, but the electromigration tester cannot act sufficiently fast
Solution Approach 1:
The voltage limiter is pre-configured in parallel with the DUT before the electromigration test begins. When the voltage across the DUT reaches the predetermined maximum voltage Vmax, the voltage limiter automatically activates to clamp the voltage, preventing thermal damage without requiring fast disconnection of the stressing current. This preliminary setup allows the system to respond instantly to voltage thresholds.
2Reliability
If the compliance voltage is limited to a low level to preserve post-test failure analysis capability, then thermal damage is prevented, but sufficient degradation cannot be sustained
Solution Approach 1:
The voltage limiter is configured with a predetermined maximum voltage Vmax that is carefully selected to balance two requirements: it is low enough to preserve post-test failure analysis capability by preventing catastrophic thermal damage, yet high enough to sustain sufficient electromigration degradation for meaningful testing. This parameter optimization allows both objectives to be achieved simultaneously.
3Reliability
If a power supply with very low voltage and high output current is used to limit voltage drop across DUT, then voltage is limited to preserve failure analysis, but such power supplies are uncommon and difficult to make
Solution Approach 1:
Instead of using a specialized low-voltage high-current power supply, the invention introduces a voltage limiter as an intermediary component connected in parallel with the DUT. This voltage limiter clamps the voltage across the DUT to a maximum value Vmax, effectively limiting the voltage drop without requiring the entire power supply system to be designed for low voltage. Standard high-voltage power supplies can be used, and the voltage limiter handles the voltage limitation function, making the system much more practical and easier to manufacture.
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 solution effectively prevents catastrophic thermal damage during electromigration tests while maintaining test accuracy and sensitivity, allowing for multi-DUT stressing with a single current source without significant additional constraints.
Implementation Method 1
Once the DUT sustains significant damage due to electromigration, its resistance and dissipated power may increase dramatically to the point where the thermal damage can be catastrophic
Data Source
AI summary
An electronic device under test (DUT) may be incorporated into a circuit having a voltage limiter connected in parallel with the DUT. The circuit includes a controlled current source having an output current connected in series with the DUT. The voltage limiter is characterized in that, when the output current is such that the voltage across the DUT (Vdut) would exceed a particular maximum voltage Vmax, without the voltage limiter in place, at least a portion of the output current flows through the voltage limiter, so as to limit Vdut to be less than or equal to Vmax. When the output current is such that Vdut would be less than or equal to Vmax, current does not flow through the voltage limiter. The circuit may include a plurality of DUTs, each DUT connected in series with the output current of a controlled current source, with a voltage limiter connected in parallel with each DUT.