Ask the Expert: Q&A with Process Engineers

Article By : Junko Yoshida

An in-depth interview with Arijit Raychowdhury, a professor at Georgia Tech, on where the electronics industry is heading, and what technologies engineers should be keeping abreast of.

EE Times and EDN are embarking on a series of regularly scheduled interviews with members of the EDN Editorial Advisory Board. One of our first guests is Arijit Raychowdhury, a professor in the School of Electrical and Computer Engineering at the Georgia Institute of Technology. He is a recipient of the 2018 IEEE/ACM “Innovator Under 40 Award” at the Design Automation Conference, where EE Times first met with him. Richard Quinnell, editor-in-chief of EDN, and Junko Yoshida, global co-editor-in-chief of Aspencore Media, joined in the conversation with Raychowdhury.

The new frontier of leading-edge IC design is packaging, according to Arijit Raychowdhury, an expert in digital and mixed-signal design who teaches VLSI courses at Georgia Tech.

Integration is the holy grail of VLSI design. Next-generation IC design lives or dies on the next feasible advance in integration. Historically, the VLSI community has depended on progress in process node technology to overcome the next fast-approaching bump on the road toward higher integration. But the times they are a-changing.

Arijit Raychowdhury

The chip industry understands that scaling in accordance with Moore’s Law has been slowing. The industry appears reluctant to confront an imminent upheaval in VLSI design — an unmistakable transition from process to packaging technologies.

Raychowdhury is one of few who have zeroed in on this trend. He told us packaging is an area process engineers must understand.

He cited AMD’s Zen processors and Intel’s Lakefield processors. Intel is using an advanced package integration technology called Foveros for its Lakefield chips, Raychowdhury noted. “AMD is using similar integration technology to combine 7nm CPU with 10nm I/O using package level integration. It helps improve system yield for them. Their flagship product for this is Zen 2,” he observed.

Others are notably taking similar approaches for package level integration. “Apple, Qualcomm are all pursuing this, and they are at different levels of maturity,” said Raychowdhury.

Put simply, leading CPU vendors looking to the future are “all about heterogeneous integration of the package.”

The emphasis on leading-edge IC design is shifting from the process to the packaging. The problem is that “there is very little understanding, at least in the U.S., about how this transition is going to happen,” according to Raychowdhury. He singled out TSMC as a company “doing a better job” of letting the industry know “what is on-die versus what is on package.”

During our interview, Raychowdhury stressed the importance of “connecting the dots” in the engineering world. Linking theories learned at school with designs in the real world is one obvious example. Knowing how the business of technologies connects with Wall Street valuation is another. While technical papers submitted at ISSCC or VLSI Symposia inform engineers about cutting-edge technology, there is a huge middle ground that must be explained between advanced tech papers and books that teach engineering basics. Raychowdhury pointed out that a key to bridging this critical gap is technical publications like EDN, along with news analysis on technology and business by EE Times.

Omni-Directional Interconnect (ODI) offers the highest density of several packaging options in Intel’s labs. (Source: Intel)

Our conversation took us from challenges in teaching EE courses in the pandemic era, to transistor scaling, new fields of expertise for next-generation VLSI designers to master, and what sort of engineering students are most likely to succeed in the real world.

Following is an excerpt of our conversation.

How do you teach in the pandemic era?

Junko Yoshida: Hi, Arijit. How are you? I see you at home. Is school still in session?

Arijit Raychowdhury: We just got [courses] done a day before yesterday. So, yeah, we moved to online classes in the middle of March. It’s been almost six weeks of online classes.

We have students from all over the place…you know, from China, from Vietnam… So, it’s crazy to hear from a student from the West Coast saying, “Oh, it’s a lot of work.”

Junko Yoshida: So, how do you teach online?

Arijit Raychowdhury: We video record the lectures, ahead of time and post them online. Then during normal class hours, we just log into bluejeans.com (video conference), Microsoft teams or some other video conference systems like that. Then we do a little more of a Q&A. I answer students‘ questions and all that, as opposed to going through the entire lecture. It has been okay. I mean, I wouldn’t say it’s that bad, but it’s been okay.

But I think now you’re seeing lots of students who don’t have proper Internet connections.

This could be a struggle even within this country right here. There are students in rural areas and they don’t have a stable Internet. And you know, we already have had tornadoes a couple of weeks back. And there were students in in southern Georgia whose houses suffered from some damages and in power outages… and it’s just a mess.

Junko Yoshida: Yeah. So, despite all the advances in technology, we are still at the mercy of nature, is that right?

Arijit Raychowdhury: In all sorts of ways. Yes.

Information gap

Richard Quinnell: So, over here at Aspencore, we are on a mission to discern a gap — between what our readers thought they’d already learned in school and what they have to do on the job. From your viewpoint, as an instructor, are you getting feedback from students such as, “Gosh, I wish I’d learned about that in school?”

Arijit Raychowdhury: That’s one thing students always mention. And this can be very specific to certain instructors as well.

Students are always interested in understanding how things they’ve learned in class apply to the real

Richard Quinnell (left), Arijit Raychowdhury(right above), Junko Yoshida (right below)

world. [They wonder] what products use which fundamental techniques, and what they’ve been taught. This is what we hear often in academia.

Some academics have moved to academia from the industry. They have a better understanding of what’s going on…I think students — undergraduates particularly — enjoy taking courses which have more implication on what the industry is doing and whether they can get jobs.

And then, there are some courses which are very fundamental. Like, we can’t stop teaching them Laplace transform or Fourier transform.

Richard Quinnell: So, these must be taught.

Arijit Raychowdhury: Right. But they sometimes find it hard to connect them to real-world applications. Students are always looking for “how does the theory connect to practice?”

You asked me about my connections with EDN. I’ve been reading EDN for, I don’t know, since 2001.

I used to work at TI long back before I went to grad school. So, the first design that I did from TI, it actually got this EDN innovation award. It was back in 2003. It wasn’t just me but our whole team got that award. Because it was the first award I actually got in my life, that was cool.

Hold and setup

Richard Quinnell: Speaking of EDN stories, one of the most popular articles is about “Setup and Hold Time.” Consistently, the basics of setup and hold time have been very popular.

Arijit Raychowdhury: Yes. Yes. [Nodding enthusiastically]

Richard Quinnell: So where could we get more of that kind of stuff out there?

Arijit Raychowdhury: I think that’s a perfect question. I agree. These days, in our VLSI course, I spend about 20 percent of my time just talking about setup and hold time. I did not understand how complex that was before I started working in the industry. And if you really want to understand what hold time is, and if you design a flip flop and a how do you clock the two stages of a flip flop so that you can get the best hold time.

So, these are the things that you only learn by building it and seeing how it works and then deploying it in millions and billions. We need to get someone to write about it. I think you need someone who understood first the theory, but also understands what going on in practice… This is exactly the kind of thing missing in books. It’s missing in most articles as well.

2D, 2.5D, 3D Integration

Richard Quinnell: In the academic world, it takes time for a book to be published. It takes time for a course to be developed to cover a technology. Are there things you see that you wish you had an opportunity to create a course for?

Arijit Raychowdhury: For example, look at technology today, and people are saying that transistor scaling probably is coming to an end, or whatever it means.

Technologically speaking, maybe scaling isn’t going as fast as we would want. But in terms of memory technologies, for example, or back end of line transistor technologies, I think there are lots of new things happening. The industry is moving very fast in that particular domain. And there are no good books because these are all the black magic that the industry talks about.

…Another trend that I see, which is not covered in books as well as it should be, is integration.

2D, 2.5D and 3D and all that. We all wonder: what does it mean then, and what are the different implications?

But [when it comes to discussions in the industry] it’s optimistic. They talk about layers and layers of transistors, which is never going to happen. Even if it’s technologically feasible, it’s just economically not feasible. Even for the short-term means of getting there — like the chiplet technologies that Intel has been working on. I don’t think there are good books on [that].

Transition from process to packaging

Richard Quinnell: Are there emerging technologies that you think we ought to be highlighting, or we should be bringing to people’s attention, or getting them prepared to be able to use?

There’s a lot of excitement about things like quantum computing, but in reality, quantum computing is a decade away. So, we are asking if there are things that are a little closer… so that we might say, hey, you know, in the next year or two, you might be called upon to work in this area, and here’s some background information to get you started.

Arijit Raychowdhury: I think one of those areas would be, process engineers now need to understand packaging. The way I look at that trend now, if you look at what AMD is doing with the Zen processor, or what Intel is doing with Lakefield… you see it’s all about heterogeneous integration of the package.

A lot of back-end engineers in these companies are now going to use their skills to build dense packages. I can see that happening.

Many of our research programs [at Georgia Tech] are industry-funded. So, I can see that those in the industry are asking us to look at these kinds of things… work from a design perspective as well as from a processing perspective.

There is very little understanding, at least in the US, about how this transition is going to happen. TSMC is probably doing a better job of making sure that people can understand that this is a smooth transition between what is on-die versus what is on package. And I think this would be one area where I would suspect people need to be ready very, very soon.

Most likely to succeed

Junko Yoshida: As a professor, when you see a student start work at TI, for example, what general knowledge you think he or she should have? What are the basics — other than a personal specialty — that he or she should absolutely know or seek to know? Any advice?

Arijit Raychowdhury: I feel like people who do well in the industry eventually have a broad understanding. Today I tell my students to take courses all across the board, not just courses in your area of research. A good example would be people who are doing process technologies. They need to understand physics and chemistry really well.

Device people really need to understand materials. If they don’t, it’s a problem. It’s harder for materials people to understand devices and technology.

Junko Yoshida: Materials people can’t learn devices? I think you’re biased, ha ha, but that’s okay.

Arijit Raychowdhury: I think understanding how basic chemistry works helps. Because as we change the paradigm, we are looking at new materials.

Similarly, I feel like a lot of circuit designers, particularly analog designers, who go into the industry do not have or have forgotten basic math and so on. So I think those things they have to relearn, once they go to TI or whatever company.

Sometimes they have the skill sets, but they do not necessarily have a boarder, general understanding of engineering — including math, physics and chemistry, which are often required.

Junko Yoshida: When you showed up at the doorstep at TI, you were the young guy. Did you already have a PhD at that time?

Arijit Raychowdhury: No.

Junko Yoshida: No? Okay. So when you showed up, what things did you wish you had studied before joining the company?

Arijit Raychowdhury with a microphone at DAC panel in 2018

Arijit Raychowdhury: I had all the background knowledge, but what I was missing was, I didn’t know how to connect the dots.

How is this particular subject material connected to that subject material? I think that’s something that you don’t learn in college, because you’re learning all these courses in separate semesters. At some point, all of these things need to click together. My first six or eight months of TI was essentially spent trying to understand how these different components are connected.

Universities now are trying to do more hands-on design-based courses in senior years and even for graduate students, which I think will help a lot.

Some people have the natural ability to hack things and write software and break things and put them back together. I think they are better engineers. They will be able to connect better when they enter the workforce.

So, I think more vertically integrated projects and courses are what is important.

New courses

Junko Yoshida: My last question. As you as you develop new courses for the next year, what are the things that you think will be must-teach topics?

Arijit Raychowdhury: I teach circuit courses. From our circuits’ perspective, I think a lot of students have gone down to the deep end. They’re just interested in, you know, understanding how [EDA] tools work.

Like, how do you know the different new options that Synopsys has come up with or new backend tools Cadence is producing… And they want to just do projects and get the skill set.

So, actually, I’m taking the fall semester off, and trying to build a new course I can use in the spring when go back. I want to teach the fundamentals. When grad students — and I mostly teach graduate students — graduate without having a good understanding of signal and noise, that’s a problem. And these are circuit designers.

In the VLSI space, we don’t have a lot of good fundamental courses. That’s mostly because of demand from the students. Students mostly want things that can help their skill set.

Yeah, they don’t really understand that it doesn’t take long to pick up those skills after you graduate.  They need more of fundamental understanding.

If you look at the VLSI curriculum — and this is common across the entire country — none of the schools are teaching fundamental VLSI circuit design.

Rich Quinnell/Junko Yoshida: Arijit, thank you so much for your time.

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