The THz band (0.1 - 10 THz) holds several applications such as high-speed communication,3D imaging radars, and spectroscopy. A high-sensitivity receiver is crucial for fully utilizing this broad untapped spectrum. Advancements in silicon technologies now enable transistors with maximum oscillation frequency (fmax) beyond 400 GHz, enabling silicon THz ICs. This thesis presents two ultra-wideband low noise amplifiers in the THz band, designed using silicon technologies. Several key concepts are discussed, such as optimal bias selection, passive circuit modeling, bandwidth enhancement, circuit-EM co-simulation approaches, and THz probe-based testing. The first design is a 7-stage cascaded common-emitter LNA with more than 80 GHz of 3-dB bandwidth, covering the entire WR5 frequency band (140-220 GHz). It has a measured peak gain of 15.5 dB and a simulated NF of 6.8 dB at 180 GHz, with 46 mW DC power consumption, and is implemented in the IHP 130 nm SiGe BiCMOS process. The second design is a cascaded 12-stage common-emitter LNA with 45 GHz of 3-dB bandwidth, from 190 GHz to 235 GHz. This design achieves a peak gain of 216 GHz, a sub 10 dB noise figure, DC power consumption of 19.9 mW, and is implemented in GlobalFoundries 22nm FDSOI process.

The THz band, covering frequencies from 0.3 to 3 THz, has received considerable attention in recent years. Positioned between the RF and optical frequencies in the electromagnetic spectrum, this band exhibits properties of both and can enable several applications, such as high-speed wireless communication, high-resolution imaging, and spectroscopy. However, designing silicon-based THz integrated circuits is challenging mainly due to the limited maximum oscillation frequency (fmax) of transistors. Consequently, harmonic approaches using frequency multipliers are popular in THz design. The THz generation efficiency in this approach depends on the non-linearity of the device used in the frequency multiplier. Conventional devices have limited non-linearity, resulting in low output power and efficiency in THz sources, and high noise figures (NF) in THz receivers, ultimately making silicon-based THz systems inefficient.

This work introduces a novel approach for THz signal generation, utilizing PIN diodes in a silicon process. PIN diodes exhibit reverse recovery under a large-signal RF drive. This process, characterized by the diode abruptly switching a large current in a short duration, creates strong harmonics that extend into the THz band. Using PIN diodes as frequency multipliers, we design a highly efficient 400 GHz radiator that can produce a peak effective isotropic radiated power (EIRP) of +20.6 dBm. It achieves a radiated power of -5.8 dBm with 0.2% DC-to-THz radiation efficiency, marking the highest reported numbers above 320 GHz.

Expanding upon the PIN diode frequency multiplier, we demonstrate a fully integrated multi-Gbps wireless transceiver with on-chip antennas at 400 GHz. The transmitter uses a multiplier-last approach and has an EIRP of +17 dBm, consuming 84 mW DC power. The receiver, utilizing a fundamental-driven passive mixer architecture, achieves an NF of 25 dB while consuming 184 mW of DC power, marking the lowest reported NF above 320 GHz. Over-the-air data-transmission measurements are demonstrated, and for a 5 cm link, the transmitter supports a data rate of 10 Gbps (8 pJ/bit), while the transmit-receive system supports a data rate of 5 Gbps (36.8 pJ/bit for the receiver). This is the first demonstration of a fully integrated multi-Gbps wireless transceiver above 320 GHz in silicon.

Lastly, we present a novel complementary self-injection-locked (CSIL) radar architecture for low-power, high-accuracy THz phase sensing. The CSIL radar employs a self-injection mechanism within a coupled oscillator system and can estimate relative displacements within an unambiguous range of λ/4. Unlike conventional phase-sensing radars, CSIL eliminates the need for complex, power-hungry frequency synthesis, has autodyne operation, and is inherently immune to self-interference. The proposed radar operates at 232 GHz and is fabricated in a 65nm CMOS process. It achieves 20 μm static range accuracy—matching state-of-the-art performance—while consuming just 4.6 mW, 15–200× lower than prior works. Imaging results are also presented, showcasing its potential for low-power 3D imaging.