Photolithography is at the heart of modern electronic chip making, technologies which power our cars, mobile phones, medical devices to name a few !

Pabitra Das (PhD), our next pathbreaker, works as R&D Engineer at X-FAB (France), one of the world’s leading specialty foundry groups for analog/mixed-signal semiconductor technologies.

Pabitra talks to Shyam Krishnamurthy from The Interview Portal about transitioning from a career in experimental (pure) physics to a career in the manufacturing industry (semiconductor physics).

For students, be open to experimenting with your knowledge, because you never know what is out there waiting for you !

Pabitra, Your background?

I was born and brought up in a small village in the then Midnapur district of West Bengal (now it’s in the Jhargram district). It is situated very close to the border of the neighboring state of Jharkhand. The region is remote and surrounded by forests, sometimes quite dense, and small hills. My father is a Maths teacher in a nearby school, he retired recently, and my mother takes care of the affairs at home.  I did my schooling until class ten from there. After that, I wanted to study general science for Higher Secondary. However, the village school didn’t have a science section, so I went to a school 30 kilometers from home. That was the first time I started to live out of home, which continues to date. I was always interested in doing something that is supported by logic and related to mathematics. So, it’s no wonder that I was interested in mathematics. I had no particular interest in Physics or Physical Science though I later pursued these subjects and am still pursuing them. But this changeover is a story that I will come back to later on.  

What did you do for graduation/ post-graduation?

I wanted to study basic science from the beginning. To some extent that motivation came from my father and a bunch of brilliant teachers that I came across. They always insisted on learning the fundamental aspects of anything. Somehow, I never prepared seriously for the Engineering Entrance Exams. Biology is nice, but I never liked it. The same story goes with Chemistry for me. So when applying for colleges I wanted to apply for Mathematics. Although, one thing was not clear to me then. I heard from my teachers that mathematics at college and higher level is very different from that at the school level. I remember one of them saying – that mathematics is too mathematical from time to time and if you don’t like too much abstract thinking you won’t like it for long. 

They also advised me to take Physics as a major which would have a substantial amount of math to handle, though more inclined towards physical problems. After thinking a bit I decided to opt for Physics as my major, and Mathematics and Chemistry with it (we used to call them pass subjects, you needed to obtain qualifying marks). My college was Ramakrishna Mission Vidyamandir, Belur Math, a fully residential degree college under Calcutta University. 

After that, my master’s was in general Physics with a specialization in Solid State Physics towards the second year of the master’s course. At that time Calcutta University didn’t have a semester system as it has now. 

I did my PhD in Physics (Experimental Physics) from Saha Institute of Nuclear Physics, Kolkata.

How did you end up in such an offbeat, unconventional and uncommon career?

I don’t have a short or one-sentence answer to this question. Still, to answer it briefly, I would say it’s the situation or events that made me choose my career instead of influencers or mentors. At least for me, that was and still is the case. I made my decisions depending on the situation, and so far it has worked out for good. 

I used to give private tuitions in Physics to undergraduate students when I was doing my master’s. Whereas I was doing this solely for financial reasons, I soon discovered that I enjoy explaining complicated ideas in easy words to students. I got hooked on teaching. And I thought I would enjoy it and maybe this will be a good career option, through a safe and secured government job in a school. Teaching in a college was still not in my mind, because most of the successful candidates had a PhD. 

So, I prepared for a school teacher job, and soon after my master’s, I got appointed as an assistant teacher in a government higher secondary school in Kolkata. A safe public job with a not-so-bad salary, and I was 23 at that time. Things could have ended then and there. But it didn’t happen. 

Soon I discovered that I was not enjoying teaching the same thing to the students repeatedly. Every day I wanted something new, but at the school level, it was a bit restricted. At least that’s what I found at that time (2005-06 timeframe). I asked myself, if I get bored in a few months, how could I do this job for the next 37 years? The answer was simple, I had to quit. Doing a PhD was an option, but at that time my girlfriend (now wife) was in Kolkata, and so I wanted to do a PhD in Kolkata. And I wanted to do it in some domain of experimental Physics. 

How did you plan the steps to get into the career you wanted? Or how did you make a transition to a new career? Tell us about your career path

This is how I applied for the entrance examination of the Saha Institute of Nuclear Physics, Kolkata and after a couple of interviews, I got selected. My second interview was not as good as the first one, and I was on the waiting list. But in the end, some of those on the first list went to other places and I got a chance to do my thesis. I resigned from my job as a school teacher and started a new phase of my career. 

As I said before, I was always interested in experimental Physics. However, when I joined my PhD, I didn’t have any idea about the topic of my research. On this front, the Saha Institute offered an excellent opportunity to experience and choose. The institute has a mandatory one-year Post MSc advanced course work. This course was there from the days of the great scientist Meghnad Saha. In this one year, you get exposed to different advanced aspects of theoretical and experimental physics. In another sense, it fills up the gaps of a master’s course and makes you prepared to handle a new problem on your own. During this one year, students have the opportunity to interact with different groups/labs working on various problems and decide on their own. As I had no predetermined topic in mind, during the coursework I became interested in experimental nanoscience. This is how at the end of my one-year post-MSc course work I started my PhD thesis work in a lab that was working on spectroscopic properties of semiconductor nanostructures. 

All those doing a PhD in experimental Physics in India will know that most of the time nothing works. For the first three years of my PhD, I was waiting for the electron microscope to be purchased and installed. These were frustrating times. You see your friends doing lab work, publishing papers, going to conferences, while nothing is ready for you to even start working in the lab. Anyway, nothing is permanent. My lab was ready one day and I started working. But these three and half years have taught me patience, persistence, and not to give up. Looking back, I feel grateful that I had gone through such a tough phase at the beginning of my research career. 

During my PhD, I worked on the optical properties of metal nanoparticles. I was doing spectroscopy of single metallic nanoparticles. It was quite a hot topic at that time and possibly the first such study in India in our lab. As exciting as it may sound, it was a very difficult experiment to do, and we had no prior experience. 

We were involved in understanding the fundamental aspects of the optical behavior of metals at the nanoscale level and more specifically at the individual nanoparticle level. Metals have the unique property of showing collective oscillations at the surface. This collective oscillation is called surface plasmon. At the nanoparticle level, this becomes more interesting. The optical properties of metal nanoparticles change drastically with shape, size, and the surrounding medium. Not only that, metal nanoparticles can confine light in a very narrow space (beyond the fundamental diffraction limit) making them an ideal candidate for photothermal applications. They have immense applications in various other fields like waveguides, sources, near-field optics, surface-enhanced Raman spectroscopy, data storage, solar cells, chemical sensors, and biosensors to name a few. 

We were studying their unusual properties at the single-particle level and how they change with size shape and surroundings. We were trying to have a better understanding through experiments as well as numerical simulations.

At that time, I contacted a person who I found from a pioneering paper in this field of research. I got some data and had no idea what was going on. We had a good conversation that lasted for the next few years. When that person came for a conference in India, I expressed my interest to work with him as a postdoctoral fellow in France. That was how I ended up at the University Paris Sud (University Paris Saclay now) in France one fine morning in October 2014. I worked in a university and CNRS combined research unit called Laboratoire de Physique des solides (in English Solid State Physics Laboratory). This laboratory is situated about 25 km south of Paris, amidst a beautiful lush green campus.  

Once again, the project I was assigned to was something that I had never worked on and involved quite a bit of instrumentation. It was a project that had started long before I joined, but never got its desired pace. With the help of some brilliant researchers and engineers, we successfully managed to build the instrumentation and start working. Often these types of development projects are not rewarding and you don’t publish a lot. Fortunately, I did some side projects and managed to keep the publication machine running. Things were going fine at CNRS after three years of repeated failures, we finally built something to work with. We planned to patent it. We were gathering data and analyzing them. Time was passing fast. 

The bad news was that my contract was about to end. And I was about to become unemployed again. Postdoctoral contracts are short-term contracts, and in France, it’s difficult to continue as a postdoc for long due to government rules. My initial choice was to go back to India. But I didn’t want a teaching job, so I applied at the research institutes and some IITs. However, things didn’t go as I expected. That’s a separate story and I don’t think I can talk positively about it, so let’s leave this chapter for the moment. The few private-sector jobs that I applied for in India were not responsive as well. So, there I was, applying anywhere and everywhere waiting for a break when I had only a few months of job left. During this phase, I got some postdoc offers but I was not willing to be in short-term contractual jobs anymore.  It was time to settle down by finding something long term. 

As I have already mentioned, during my postdoc, I did some side projects. One of them involved electron beam lithography. For those who are not familiar with this term, lithography means writing on stone (mostly Silicon or other wafers) with light (generally laser). You can draw a design on a surface with the help of lasers (photons) or electrons. And then through some smart chemical techniques, you can print or draw any geometry on a planar surface. When a laser is used, this is called Photolithography and when instead of a laser, an electron beam (as found in an electron microscope) is used, it is called electron beam lithography. Lithography is at the heart of modern electronic chip making, which I will come back to soon.  

So I had this skill of lithography, but I never thought this would help me in my next breakthrough. 

During this phase of job hunting, one fine afternoon, I was eating “dosa” at a south Indian restaurant in Paris and my phone vibrated. I checked and it was a message on Linkedin. A recruiter messaged me. She saw the lithography expertise in my Linkedin profile and told me she might have a job that fits my profile. We talked over the phone later that day, and I found the job interesting, but different from what I used to work on at that time. I sent her my CV, got interviewed by the company twice, “et voila” !! 

I got hired as an R&D engineer at X-Fab in the semiconductor industry. 

How did you get your first break?

As I mentioned above, my first break in the industry was through a recruiter in France who contacted me for an R&D profile in the industry

What were some of the challenges you faced? How did you address them?

What I understand in my scientific career so far is that most often our challenges are not technical. It doesn’t always come from work. At work, often we have others to help us with our expertise. Our problem often comes from within ourselves. So instead of addressing those technical problems (one I described later briefly), I will talk about the problems within ourselves. Our mindset. 

If you do a PhD, most often you are expected to either be a professor or a scientist in a university or research institute. This is something that we are told from our childhood and also deeply embedded in our society. However, academics doesn’t have enough jobs to hire all PhDs. So when you think of shifting from academia to industry, this thought in your mind is your biggest challenge. This is often fueled by family, friends, and close ones. I have seen many bright minds doing underpaid and undervalued jobs in academia. Often what they do is below average standard science, but they just can’t think of shifting careers because of this mindset. That’s why I always repeatedly say, be open, and explore things. There is always something interesting out there.

Where do you work now? Tell us about your work in semiconductors

At X-FAB, we make chips that are used in cars, mobile phones, and medical devices to name a few. And my job involves doing simulations in optics. So, yes, after hundreds of failed applications, I ended up somewhere that I didn’t even know about. More ironic is that for my whole academic life I didn’t like electronics and now I work in a place where I help make electronic chips. In my view, chip-making is more of Physics and Chemistry than Electronics. If you want to know more about chip-making, you may follow this.

How does your work benefit society? 

As I just said, I work with an organization that makes semiconductor chips. Today you will hardly find a thing that uses electricity and that doesn’t contain chips. They are everywhere. The mobile phone or the computer, your daily use appliances, cars…everything has chips inside for various functionalities. You would have heard of the recent problems in car manufacturing due to the chip shortage (click here for more on this), a sudden high demand, especially during the pandemic, something that the industry is not ready to deal with. Although chips are used everywhere, they are fabricated in some specialized factories called foundries. Foundries are one of the most expensive and most advanced labs in the world today. And their numbers are limited. You can’t imagine a modern world without chips. And as a part of an organization that is one of those very few who makes those chips, what I do is quite gratifying to me. 

Tell us an example of a specific memorable work you did that is very close to you!

It’s difficult to pick a single work or project that is very close to me. Different projects have different degrees of complexity associated. Resources also matter a lot. It’s not easy to compare one with the other. However, if there is one project that will remain very very close to my heart, it is my project during my postdoc. It was a proof of principle instrumentation by integrating an electron and laser beam synchronously. Theoretically, the idea was sound and we didn’t see any blocking point on the experimental realization. But then at the end of the day, theory is theory. The project was full of failures until the last moment. However tough it may be to digest those failures, we learned some precious lessons from them. It was the teamwork of a bunch of excellent Physicists and Engineers. Although I would have loved to work on this project for longer if I had to, this project is and will always remain very close to my heart.  If you want to know more about it, please click here

What we did was a pretty cost-effective alternative to exploring the same Physics using other expensive tools. Those interested may see my paper in the link above. 

Your advice to students based on your experience?

Do whatever you are doing with care. Don’t give up until the very dead end. Most often we are just a little away from success when we give up. If you have some pre-existing passion for something, go for it. If you don’t have one, don’t worry. Be open to trying. Someday you will certainly find something that you will love. Keep an open mind and be flexible. The world and job market are changing. The change is not linear and much faster than we can even think about. Be prepared for the change. Prepare yourself for the future. Future work will be more and more automation-dependent. So, everything that an intelligent machine can do, will be done by a machine. However, a machine can’t think (yet) out of the box. A machine is still decades away from being as creative as an average mind. Always try to be creative in what you do. There is little space for creativity in everything, however small it may be. Stay creative, you will thrive and success will just be the consequence of what you do. 

Last but not the least, always appreciate that the work you do, whatever it may be, isn’t done by you alone. Directly or indirectly, many people contribute. Never forget to acknowledge even the smallest of contributions.  

Future Plans?

As you may understand from what I have written so far, I take things whichever way they come to me. I never thought I would come this far from my village, though I still love to have surprises in life. Having said that, I do whatever I need to do with care and love. I find ways to love what I do. This might sound a bit strange but it’s exactly the opposite of always doing what you love. For the time being, I am navigating the industry, more specifically the semiconductor industry. It’s been a good journey so far including my shift from an academic background. I believe this quest will continue in the coming years. 

Well, let’s see..