Did you know that the performance of the smartphones we rely on every day is powered by tiny semiconductor chips? The pursuit of higher-performance semiconductors continues to drive intense innovation across the field. At the forefront of this effort is Professor Changsik Yoo, a leading figure in advancing next-generation semiconductor technologies.

After earning his Ph.D. in analog circuit design from Seoul National University, Professor Yoo built a distinguished career spanning both academia and industry, including roles as a researcher at Samsung Electronics, a professor at Hanyang University, and a founder of a fabless company. Most recently, he served as a Vice President in the Memory Business at Samsung Electronics, where he led DRAM development and next-generation memory technologies.

Having accumulated extensive expertise in semiconductor design across both industry and academia, he joined the Department of Semiconductor Convergence Engineering at Sungkyunkwan University this March. Let us hear his story as he begins a new chapter of teaching and research at SKKU.

| What led you to join the Department of Semiconductor Convergence Engineering at Sungkyunkwan University?

After completing my Ph.D., I worked at the Memory Business of Samsung Electronics for four years. I then spent 18 years teaching students at the Department of Electronic Engineering at Hanyang University. While I was on sabbatical at Samsung Electronics, I received an offer to return to the company, which led me to serve for five years as Vice President of the DRAM Development Division.

Following this experience, I joined the Department of Semiconductor Convergence Engineering. I hope that the experience I have gained from both industry and academia will contribute to strengthening industry–academic collaboration at SKKU.

| Could you introduce your research area, including circuit design?

My research field is analog circuit design. Many people ask why we continue to study analog circuits in what is now considered a digital era. However, the light, sound, and touch that we perceive are fundamentally analog in nature. These signals are converted into digital information for processing and then converted back into analog signals for us to experience.

For example, the DRAM I developed at Samsung Electronics stores information in digital form as “0” and “1.” However, the internal processes of reading and writing that data rely on highly sophisticated and complex analog circuit technologies. Therefore, regardless of how far digital technology advances, analog circuits remain a fundamental core of semiconductor systems.

About five years ago, during my time at Hanyang University, I conducted research supported by the Samsung Future Technology Development Program, exploring new approaches to implementing analog circuits. This research utilized time-based information and statistical techniques and was published in ISSCC and international journals.

▲ Professor Yoo’s paper published at ISSCC

| Having worked in the semiconductor field for over 30 years, what do you find most appealing about this field?

The semiconductor field encompasses various areas, including devices, processes, and design. My focus is on circuit design, which plays a role in bringing theoretical concepts in electrical engineering into real-world implementation.

One of the most fascinating aspects of this field is the ability to see theories come to life and function in actual systems.

About a decade ago, when I served as a program committee member at ISSCC, there was a discussion on whether analog circuit designers would remain relevant in the future. At the time, there were concerns that analog circuits might become obsolete due to the rapid advancement of digital technologies.

Looking back now, those concerns were unnecessary. In fact, the demand for analog circuit designers has significantly increased. I hope that more students will pursue careers in this field.

| You returned to Samsung Electronics after 18 years in academia. Could you tell us about the projects you led and their outcomes?

I worked in the DRAM Development Division within the Memory Business at Samsung Electronics. The DRAM products we developed are used in smartphones, laptops, and computers, as well as in servers such as those operated by Google, which support services like YouTube and AI platforms.

During my five years there, both the speed and density of DRAM improved by approximately twofold. More recently, I worked with my team on defining the standards for LPDDR6 and DDR6 through JEDEC, the global semiconductor standardization organization.

In particular, for LPDDR6, we successfully completed both standardization and product development simultaneously, achieving the world’s first implementation. The results were presented at ISSCC this February, and the product is expected to be adopted in smartphones to be released next year.

▲ Professor Yoo presenting on DRAM-related research

| Achieving both high performance and low power consumption in semiconductor design is known to be a very challenging technical task. What was the most difficult problem you encountered, and how did you overcome it?

Capacitors, which are widely used in analog circuits, occupy a large silicon area, which increases chip size and cost. This makes it difficult to achieve low-cost designs.

During the Samsung Future Technology Development Program, I addressed this issue by leveraging time-domain information. Capacitors integrate voltage, and voltage-controlled oscillators (VCOs) also integrate voltage to generate phase information. By exploring the similarities between these two mechanisms, I was able to significantly reduce circuit area.

High performance, low power consumption, and low cost are the key goals of semiconductor development. However, it is extremely difficult to fully achieve all three simultaneously. Ultimately, the success of a product depends on how well one finds the optimal balance among these factors.

| You also conducted research abroad, including at ETH Zurich and Silicon Image. How did these experiences influence your research philosophy?

After completing my Ph.D., I worked as a postdoctoral researcher at ETH Zurich for about 16 months. At the time, Korea’s global standing was much lower than it is today, yet my doctoral research was highly recognized, allowing me to gain valuable international experience.

At ETH, I was particularly impressed by how systematically graduate research labs were operated. Administrative staff and technical personnel handled support tasks, allowing graduate students to focus entirely on research. Even the ability to take extended summer vacations was striking. Based on those impressions, I made a conscious effort to build a research environment at Hanyang University where the labs I supervised could focus entirely on research.

Later, during my first sabbatical at Hanyang University, I worked at Silicon Image for one year. At that time, we faced an issue where intermittent defects appeared during final field testing—occurring only once in thousands of tests. After overcoming this challenge, I realized the critical importance of thorough validation at the design stage.

While it is difficult to fully replicate such real-world production challenges in academic research, I emphasize to students the importance of anticipating potential issues and designing with those possibilities in mind.

| What research areas are you currently interested in exploring?

The limits of DRAM scaling are gradually approaching. Despite extensive research on alternative memory technologies, my conclusion so far is that future DRAM will ultimately still be DRAM. In other words, we have yet to find a technology that can replace DRAM. The challenge now is how to develop DRAM that offers higher bandwidth and capacity required by AI systems, while also achieving lower power consumption and cost —and as of now, no one has the definitive answer.

Based on my experience at Samsung Electronics, I hope to work with students at Sungkyunkwan University to find answers to these challenges. In addition, I plan to conduct research on various analog and mixed-signal circuits, particularly as scaling trends push supply voltages lower and existing circuit technologies approach their limits.

| Lastly, do you have a message for SKKU students?

I am truly delighted and excited to be working with the outstanding students of Sungkyunkwan University. I will do my best to share my experience and knowledge with you, so please feel free to reach out whenever you need guidance. My lab door is always open, and both phone calls and emails are welcome.

Interview: Kim Eunseo