National Yang Ming Chiao Tung University (NYCU) has been deeply committed to advanced transistor technology research. The research team, led by Professor Po-Tsun Liu from the Department of Photonics at NYCU, has developed “Ultra High-Density Heterogeneous Complementary Field-Effect Transistor Technology” this year to challenge the next-generation technology goal of angstrom-scale integrated circuits. This achievement offers hope for the continuous improvement of the density of integration of chip circuits, and the research results have been published in the internationally renowned academic journal Advanced Science in 2023.
National Yang Ming Chiao Tung University pioneers cutting-edge integrated circuit chip technology with ultra-high density of integration
This research, a component of the “Angstrom Semiconductor Initiative,” spearheaded by Professor Po-Tsun Liu, in collaboration with Yushan Fellow of the Ministry of Education, Professor Yue Kuo from Texas A&M, has focused on three key areas: materials, electronic devices, and circuits. Specifically, the research has innovated the development of complementary field-effect transistor technology (CFET), which is suitable for the application of monolithic three-dimensional integrated circuits (M3D-ICs).
According to Prof. Liu, the exponential growth of the semiconductor industry has resulted in an escalating demand for high-performance chips featured by high speed, high density of integration, and low power consumption. To overcome the physical limit of miniaturization, the concept of M3D-ICs was proposed. This involves vertically stacking multiple layers of transistor devices within a limited area, potentially surpassing Moore’s Law. In a recent project, a team of researchers from NYCU developed a novel nanometer-thick amorphous indium tungsten oxide (a-IWO) semiconductor channel layer. They successfully implemented a complementary inverter logic circuit, which uses a novel N-type amorphous indium tungsten oxide transistor, combined with P-type polycrystalline silicon thin-film transistor (poly-Si TFT).
The inverter circuit is known for its high voltage gain, low power consumption, and a high noise margin. By using a three-dimensional stacking structure, the inverter circuit significantly reduces the area used by devices, effectively enhancing the density of integration of transistor devices and circuits. In a recent study, the research team successfully integrated heterogeneous semiconductor channel materials: low-temperature polycrystalline silicon and indium tungsten oxide channel transistors, to create a CFET-based inverter circuit. This innovative development demonstrates the potential application of the technology in M3D-ICs.
“If we integrate this atomically-thin oxide transistor with front-end-of-line devices for three-dimensional integrated circuit technology, it could increase the density of transistors on the chip and enhance chip functionality to meet diverse product applications. Additionally, it could advance semiconductor technology and continue the trajectory of Moore’s Law,” said Prof. Liu. The three-dimensional integration technology of heterogeneous semiconductor devices allows CFET to achieve high voltage gain under low operating voltage, making it ideal for various low-power consumption applications such as AIoT smart networks, driver ICs, wearable electronics, display panels, and the metaverse-related industry chain. The CFET technology boasts higher energy efficiency, contributing to a low-carbon emission production chain, anticipating its future application in the semiconductor industry to realize the goal of a green semiconductor production chain.
Intensive Collaboration with Domestic and International Scholars and Industry
NYCU has been involved in the research of transistor technology since as early as 1964, being Taiwan’s first university equipped with a cleanroom. Over the years, NYCU has been establishing a comprehensive semiconductor research environment and resources. This includes the ongoing addition and updating of process and material analysis equipment. It is precisely because of these efforts that NYCU has achieved abundant accomplishments and publication outputs in the field of semiconductor research. The NYCU faculty actively engages in extensive collaborations with domestic and international scholars, industry partners, and government agencies to enhance research and development resources. Since 2020, Prof. Liu’s team has undertaken a forward-looking collaboration with TSMC, actively participating in the Joint Development Project (JDP) focused on the development of three-dimensional transistor technology. Additionally, they are involved in international collaborations with Professor Yue Kuo from Texas A&M University, Professor Peide Ye from Purdue University, and Academician Chenming Hu from the Academia Sinica.
Currently, a cross-university team is executing two phases of the “Angstrom Semiconductor Initiative,” with the guidance of Prof. Liu. This team primarily focuses on developing critical technologies for high-density integrated circuits in forward-looking Monolithic Three-dimensional Integrated Circuit (M3D-IC) technologies. This initiative aims to address critical challenges in the production technology of angstrom-scale devices and circuits to achieve the performance of 2030 equivalent 1-nm node in integration density and cost of logic and memory circuits.
International Research Collaboration: Bridging Students’ Gap Between Theory and Practice
Collaboration between on-campus faculty and industry plays a pivotal role in advancing research and technology within the field. Moreover, it offers students valuable insights into the latest technological developments in the industry, effectively bridging the gap between theoretical knowledge and practical application. Prof. Liu emphasizes, “This is why almost all graduate students from NYCU College of Electrical and Computer Engineering (ECE) secure job opportunities with Taiwan’s semiconductor industry giants even before graduation.”
In the concluding part of the interview, Prof. Liu shared his expectations for the students, placing particular emphasis on the importance of establishing a robust foundation in scientific knowledge. He underscored that every emerging technology is rooted in fundamental academic theories, and possessing this foundational knowledge would greatly contribute to students’ capacity to grasp various cutting-edge technologies in the future. Prof. Liu commended the students at NYCU for their strong academic aptitude and urged them to consistently enhance their innovative capabilities. Furthermore, he highlighted the university’s provision of financial support and diverse international exchange programs, encouraging students to capitalize on these opportunities. Participation in such programs, he noted, not only allows students to refine their communication skills and boost their confidence but also provides them with fresh knowledge that can inspire innovative ideas.
In his closing statements, Prof. Liu reiterated the profound significance of perseverance in research. Overcoming the inclination to “give up,” he emphasized, forms a sturdy foundation in academic pursuits and is the singular path to achieving success in one’s studies.
