Amrutha Sampath’s Contribution to Advancements in Electrical Fault Isolation Pioneering Novel Approaches to Semiconductor Stuck at Reset Hard Failures

In the intricate domain of semiconductor failure analysis, Amrutha Sampath has played a key role in the development of new methodologies for electrical fault isolation. Her recent work has focused on improving analysis techniques for stuck-at-reset hard failures, an area that has historically presented significant challenges for the semiconductor industry. This work supports the ongoing effort to establish more systematic and methodical approaches to these complex scenarios, with the goal of enhancing semiconductor reliability and testing.

The Challenge of Stuck-at-Reset Hard Failures

Hard failures, especially those classified as "Stuck at Reset" that remain insensitive to voltage, frequency, and temperature variations, represent some of the most challenging scenarios for semiconductor failure analysis engineers. These failures are characterized by devices that do not complete their boot-up sequence flow and fail predominantly on all tests, including basic JTAG operations. The primary challenge with such failures is the minimal diagnostic information available, as the devices do not respond to any external communication attempts.

Conventional electrical fault isolation methodologies often fall short when analyzing these failures. Techniques like Laser-Assisted Device Alteration (LADA) cannot be carried out due to the nature of the failure. While Photon Emission Microscopy (PEM) can identify differences between functional and failing devices, it typically reveals only the symptoms rather than the root cause, showing where intellectual property blocks are stuck in reset without indicating why.

Development of Synchronization Methodologies

Amrutha Sampath has made commendable contributions to the domain of electrical engineering with the introduction of two innovative methodologies aimed at addressing the challenges inherent in Laser Voltage Probe (LVP) analysis, particularly under stuck-at-reset scenarios:

1. Power Supply Modulation Technique: In this innovative approach, Sampath has adeptly developed a method that involves modulating power supply voltages within a meticulously crafted looping pattern. This technique enables effective optical probing of critical internal Power-on Reset (POR) signal transitions. By utilizing a custom-designed test setup, her methodology allows for the modulation of a specific power supply within the test loop while ensuring the uninterrupted operation of other connected supplies. This capability effectively alleviates the time constraints usually associated with complete power cycling. By synchronizing internal signals connected to the POR with a tester-generated trigger, her approach greatly enhances the accuracy of waveform acquisition related to the internally extracted POR signals.

2. Current Profile Synchronization: In cases where internal signals operate asynchronously to external test equipment, Sampath and her team developed a method using an external current probe to synchronize LVP to the device's internal state machine. By analyzing the current profile of particular supplies and using these measurements as trigger sources, she successfully synchronized LVP to internal clock edges, acquiring waveforms from critical signals that would otherwise be impossible to capture.


Real-World Impact Through Case Studies

The effectiveness of these methodologies has been demonstrated through case studies:

In one case involving a device from the edge of a wafer, conventional analysis methods revealed that the failing unit was stuck in the Power Down mode due to a Power Down (PDN) signal stuck at 0. This signal was driven by the POR, indicating the root issue was related to POR functionality. Using her power supply modulation technique, Sampath was able to isolate the failure to a specific power domain's POR that was not transitioning properly. Further analysis pinpointed a resistive/open via in the bias generator circuit, a defect that would have been extremely difficult to identify without her innovative methodology.

In another case involving devices failing after a specific test sequence in burn-in, Sampath's current profile study revealed that failing units were experiencing unexpected internal resets approximately every 200-250 microseconds. By using the current probe as a trigger source to synchronize with the internal clock, she was able to determine that although key fuse validation signals were asserting correctly, subsequent failures occurred during fuse reads, leading to internal resets. This analysis revealed that fuses were being inadvertently reprogrammed during specific test sequences, leading to boot failures and incorrect trim settings for the internal clock.

Impact on Semiconductor Failure Analysis

Amrutha Sampath's work contributes to the ongoing progress in semiconductor failure analysis. The methodologies support:

Enhanced debug capabilities for diagnosing complex boot sequence issues.

Improved test development through a deeper understanding of stuck-at-reset failures.

Providing insights to design teams for potentially improving testability and reliability.

Knowledge transfer within the semiconductor failure analysis community.

Future Outlook

Looking ahead, Sampath continues to refine and expand these methodologies to address increasingly complex semiconductor architectures. The growth of asynchronous design methodologies and complex boot sequences in modern semiconductors makes her work particularly relevant for next-generation devices.

Her vision includes developing automated approaches to implement these techniques, potentially incorporating artificial intelligence to identify patterns in current profiles that might indicate specific failure mechanisms, further streamlining the fault isolation process for stuck-at-reset failures.