From Coulter's Vision to Silicon's Precision: An Odyssey of Microfabrication at IIT Bombay

Could the same principle that revolutionized blood tests evolve to sequence DNA? It's a journey we explored at IIT Bombay. Wallace Coulter's groundbreaking method, using merely a needle and cellophane tape, set a precedent for simplicity and ingenuity in medical diagnostics. Inspired by his spirit, our team in the Microelectronics Group set out to refine this principle using advanced microfabrication techniques. This is our story of exploration, from glass to silicon, and the setbacks that fueled our breakthroughs.

The Initial Challenge: Navigating Material Limitations

Our venture began with a straightforward goal: to create a precise microscale hole in an insulator for blood cell sizing. Glass seemed the obvious start. However, its brittleness and the limitations of conventional drilling techniques quickly became apparent. Moving to grinding with a diamond bit allowed for greater control, but we struggled to achieve sub-100 micron precision consistently.

Breakthroughs and Setbacks

Ceramics offered greater durability for the substrate. We explored CO2 laser drilling in collaboration with the Space Application Center Ahmedabad, employing a jet assist to mitigate slag formation. While this improved results, the remaining irregularities in hole geometry and surface finish proved unsatisfactory for our application.

The breakthrough came with an unexpected material: glass epoxy PCBs. Overcoming the challenges of high-speed microscale drilling was a defining moment. For optimal material removal and hole quality, a critical balance must be maintained between the cutting speed and the mechanical integrity of the drill bit. Smaller diameter bits require increased angular velocity (RPM) to achieve the cutting velocity. However, as we pushed the drilling process to its limits to achieve this high RPM, we discovered a crucial lesson: exceeding the safe operating range of the drilling machine itself could lead to significant damage beyond just broken drill bits.

The Importance of Understanding Process Limits

This experience underscored the importance of thoroughly understanding any chosen process's limitations and inherent variability. Operating at the edge of a process invariably leads to unreliable system performance. Sensitivity analysis or critical parameter analysis, while valuable tools for later root cause identification, can be time-consuming and expensive to uncover what could have been foreseen with a deeper understanding of the process during selection.

Getting Things Done Wisely

A fundamental leadership skill is prioritizing and getting things done efficiently within a limited time and budgetary constraints. This experience at IIT Bombay highlighted the importance of balancing the urgency to achieve results with the need for a thoughtful and measured approach. Understanding process limitations allows for better decision-making, avoiding costly mistakes, and ultimately leading to a smoother path towards achieving goals.

Silicon and the Quest for Precision

The move to silicon was a leap into semiconductor fabrication, promising unmatched precision with anisotropic etching. Yet, constraints like lacking LPCVD nitride forced us to rethink our etching solutions. Our team's tenacity led to using ethylene diamine and pyrocatechol (EDP), enabling selective etching of silicon with the available oxide mask. Handling these hazardous chemicals emphasized the delicate balance between progress and the need for rigorous safety protocols in research environments.

A Note on Obsolescence

Interestingly, this etching solution, while effective, highlighted the obscurity and obsolescence of some of the chemicals we relied upon. In discussions with colleagues at the Stanford Nanofabrication Facility, it became evident that pyrocatechol was largely unheard of, a testament to the evolving landscape of microfabrication materials and methods.

The Collaborative Spirit of IIT Bombay

This journey would not have been possible without the invaluable guidance of Prof. Lal, our dedicated faculty, and the exceptional students at IIT Bombay. Their collective expertise and unwavering curiosity fostered an environment where innovation thrived.

Reflections on the Journey

Our odyssey was a testament to persistence, adaptability, and the enduring spirit of innovation. Beyond the technical details, it reinforces the vital role of collaboration. It reminds us that even the most ambitious goals can be reached through determination and the relentless pursuit of knowledge.

The lessons learned at IIT Bombay went far beyond microfabrication techniques. The trust in first principles, the willingness to boldly tackle any challenge, and the tenacity to see projects through to completion left an indelible mark on us. Such clarity of thought and unwavering belief in the fundamentals is a rare gift, far exceeding the scope of formal education. We are forever grateful for the opportunity to learn, grow, and forge our character within the nurturing environment of IIT Bombay.

The journey was exhilarating, and the triumphant closure was the micrograph revealing gleaming planes that marked a successful anisotropic etch! That image made its way into my PhD thesis and later a paper, celebrating this journey more than any other outcome.

Let this story remind us of the power of building upon the legacies of those who came before. Whether you're a scientist, an engineer, or simply passionate about progress, the lessons learned at IIT Bombay can inspire us all.

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