Design of THz Radiators in Nanometer CMOS

In the frequency spectrum, the THz range is located between the millimeter wave and the far field infrared spectrum. There are numerous possible applications in the THz range such as medical/security imaging, spectroscopy, and communication. In these applications, THz signal sources are needed to provide the output signal in a transmitter or provide the LO signal in a heterodyne transceiver. CMOS technologies have the advantage of low cost in volume production and full integration with digital circuits, thus attracting intensive research interest on designing THz circuits in CMOS technologies.

The output power of signal sources need to be high enough to fulfill the requirement of the system. Besides high output power, beam-steering ability of a signal source is also essential as it can replace the bulky and slow mechanical beam-steering approaches. This work focuses on pushing the output power of CMOS THz radiators to higher level and exploring the beam-steering capability
of THz radiator arrays.

In this work, modeling of active device interconnections, design of passive devices and on-chip antennas are introduced in detail. Concept of free-space power combining and phased array are introduced. Topologies for THz signal generation and phase control are investigated.

A new EM-simulation-based modeling method is proposed to develop a lumped model representing the transistor interconnect parasitics. This method can extract parasitic including capacitance, inductance, and resistance, thus making it suitable for circuit design at very high frequency range. The accuracy of the developed model is verified by the measurement of the 0.53-THz radiating
source.

A 525-to-556-GHz radiating source with a dielectric lens antenna is designed and fabricated in 28-nm CMOS. The dielectric lens is designed, fabricated, and mounted on top of the chip to enhance the on-chip antenna performance.

A 510-to-545-GHz radiating source with a novel SIW harmonic power extractor is designed and fabricated in 40-nm CMOS. The SIW harmonic power extractor is co-designed with the tripler. The SIW harmonic power extractor enhances harmonic power generation, performs harmonic power extraction, and provides suppression of unwanted harmonic leakage. It is the first time that an on-chip
SIW has been co-designed with active circuits. This chip achieves the largest frequency tuning range among the silicon signal generators above 0.5 THz.

A 0.53-THz subharmonic injection-locked phased array based on an injection-locked oscillator chain is designed and fabricated in 40-nm CMOS. Thanks to this architecture, the phase error in the phased array is compensated without introducing power variation. This technique enables accurate beam steering with a 60° scan range at 0.53 THz. To increase the output power and DC-to-THz efficiency of the phased array at 0.53 THz, a novel 6-stage triple-push oscillator is proposed to generate the output signal. Compared with a conventional
triple-push oscillator, it reduces layout constraints, improves signal balance, and enhances output power by at least 3 dB. This work is the first silicon phased array above 0.45 THz.

A 0.59-THz beam-steerable coherent radiator array is designed and fabricated in 40-nm CMOS. In order to increase the output power, a large-scale coherent radiator array is needed. In this work, a compact coupling structure is proposed to build a scalable coherent radiator array with beam-steering capability. This work achieves the highest radiated power in all the reported silicon signal sources
above 0.35 THz.