Collaborative Research: ASCENT: Wafer-Scale Sub-THz Reflectarray for Electrical Needle Beam Forming and Steering

In this ASCENT project, the team aims to develop a set of semiconductor technologies, including new device fabrication, large-scale heterogeneous integration, and robust beam-alignment system architectures, to achieve electrically controlled collimation of electromagnetic waves in sub-terahertz (sub-THz) frequency bands at low cost. Compared to the existing 5G wireless bands below 100 GHz, the sub-THz bands offer unprecedented wide bandwidth that can enable ultra-fast data rate for data center networking and wireless infrastructure, as well as high precision for radar and imaging. The electronic hardware developed in this project provides a highly desirable function for most sub-THz systems -- focusing the beam power within one degree in space (hence the term "needle beam" in the project title) with high-precision electronic control of the beam direction. The new hardware architecture enables wireless communication systems to achieve a high data rate up to 120 Gbps over a distance greater than one kilometer. It also enables radar imaging systems to achieve high-resolution sensing of the ambient environment, which is critical for all-weather safe operation of autonomous vehicles. In addition, this project not only provides extensive graduate researcher training in high-frequency circuit designs and advanced semiconductor manufacturing but also promotes STEM education through various programs. Needle beam forming at 140 GHz requires large (> 70x70 millimeter square) electronic phase-controlling surfaces with low signal loss at high frequencies. Therefore, transistors fabricated using advanced lithography are needed. Recent demonstrations of sub-THz reflectarray using either tiled complementary metal-oxide-semiconductor (CMOS) FinFET chips or chip package modules have excessively high fabrication and assembly costs. In this project, the team explores a new direct wafer-scale integration approach through low-temperature fabrications of custom metal-insulator-semiconductor-insulator-metal (MISIM) variable capacitance devices and high-efficiency sub-THz antennas on top of a foundry-processed integrated-circuit glass substrate. Without using any expensive advanced lithography, the devices can still achieve low-loss phase shifting of sub-THz signals, hence significantly reducing the cost of the needle-beam-forming system. The project also investigates new reflectarray circuits that perform self-correction of device defects and process variations, as well as new reflectarray transceiver architectures that enable compact overall system form factor and high-precision beam alignment. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.