Researchers Characterise Defects in Flexible Electronics, Improving Converter Reliability by 92 Percent

Researchers are addressing the vulnerability of analog-to-digital converters (ADCs) in emerging flexible electronic systems. Paula Carolina Lozano Duarte and Mehdi Tahoori from the Karlsruhe Institute of Technology, working with Sule Ozev from Arizona State University, have developed a novel framework to characterise defect sensitivity in Binary Search ADCs implemented using Indium Gallium Zinc Oxide (IGZO) and other unipolar technologies. This collaborative work is significant because it tackles a poorly understood issue, the impact of manufacturing defects in these promising thin-film technologies, which are crucial for applications like wearable sensors and health monitoring. Their hierarchical injection framework efficiently identifies critical circuit components susceptible to defects and enables targeted redundancy strategies, demonstrably improving fault tolerance from 60% to 92% under single defects and from 34% to 77.6% under multiple defects, with minimal area and power overhead.

The methodology combines detailed transistor-level simulations with system-level analysis, allowing researchers to efficiently explore a wide range of single and multiple defect scenarios across the entire conversion process.

By pinpointing the most sensitive circuit components, the team developed targeted redundancy strategies, selectively reinforcing only those areas prone to failure. This approach dramatically improves the ability of the ADC to function correctly even with manufacturing flaws, increasing fault coverage from 60% to 92% under single-defect conditions and from 34% to 77.6% when multiple defects are present.

Importantly, this improvement was achieved with a minimal increase in area overhead, only 4.2%, and a modest 6% rise in power consumption. Validated using IGZO thin-film transistors, the framework’s principles are broadly applicable to other emerging unipolar technologies, offering a pathway to robust and reliable flexible electronic systems.

The work demonstrates that proactive fault tolerance can be integrated into the design process, treating resilience as a key performance indicator alongside traditional metrics like speed and power efficiency. Multi-fault coverage demonstrated an even more substantial gain, rising from 34% to 77.6% under the same conditions. Systematic fault sensitivity analysis identified that early conversion stages are particularly susceptible to defects, concentrating vulnerability points regardless of ADC resolution.

This understanding enabled the development of targeted redundancy strategies, focusing on protecting only the most sensitive circuit components. The methodology employs a transistor-level defect characterisation combined with system-level propagation analysis, allowing for efficient exploration of both single and multiple fault scenarios.

This hierarchical approach facilitates straightforward extension to higher-resolution ADCs, where the fault space scales linearly with the number of comparison stages. Experimental validation using IGZO-TFTs confirmed the effectiveness of the fault-tolerant ADC designs. The framework accurately captures technology-specific failure modes and fault propagation, providing a comprehensive assessment of ADC robustness.

Quantifying the impact of defects on conversion accuracy revealed precise insights into the performance limitations of IGZO-based circuits. The methodology combines transistor-level defect characterisation with system-level fault propagation analysis, allowing for efficient exploration of both single and multiple fault scenarios across the ADC’s conversion hierarchy.

Defect injection was performed directly on IGZO-TFTs, modelling realistic manufacturing imperfections and their impact on circuit behaviour. This approach differs from traditional fault simulation, which often relies on simplified models and may not accurately capture the unique failure mechanisms present in unipolar technologies like IGZO.

Crucially, the work moves beyond simply identifying faulty components to pinpointing the most sensitive circuit elements. By tracing the propagation of faults through the Binary Search ADC’s cascaded structure, the research team identified components where defects have the greatest impact on conversion accuracy.

This granular understanding enabled the implementation of selective redundancy strategies, adding extra circuitry only to protect the most vulnerable parts of the design. The selective approach minimises area overhead and power consumption, critical considerations for resource-constrained flexible electronic systems.

Validation was performed on a 3-bit IGZO Binary Search ADC, representative of applications in personal health monitoring. The hierarchical nature of the simulation framework allows for scalability to higher-resolution ADCs, with the fault space increasing linearly with the number of comparison stages. This methodology is not limited to IGZO, but is applicable to all emerging unipolar technologies facing similar reliability challenges.

The Bigger Picture

Scientists are increasingly focused on flexible electronics as the next frontier in sensing and monitoring technologies. These devices promise to seamlessly integrate into our lives, from wearable health trackers to large-area environmental monitors. This work offers a crucial step forward by providing a systematic way to identify and mitigate the impact of these defects within analogue-to-digital converters.

The ingenuity lies in a hierarchical approach, moving from detailed transistor-level analysis to system-level performance prediction. This allows researchers to pinpoint the most vulnerable components and apply targeted redundancy, essentially building in backup systems only where they are needed. The relatively small increases in area and power consumption for substantial improvements in defect tolerance are particularly encouraging.

While the methodology is validated using IGZO, its broader applicability to other emerging materials is a key strength. Nevertheless, the simulations represent a simplified model of real-world defects. The precise nature of defects in these thin films can be complex, and accurately modelling their impact remains an ongoing area of research.

Future work will likely focus on refining these models and exploring more sophisticated redundancy schemes, perhaps even incorporating self-healing capabilities into the circuits themselves. Ultimately, this isn’t just about building more robust electronics; it’s about unlocking the potential of truly ubiquitous, reliable, and adaptable sensing systems.