A 232-to-260GHz CMOS Amplifier-Multiplier Chain With a Low-Cost, Matching-Sheet-Assisted Radiation Package and 11.1dBm Total Radiated Power

Terahertz (THz) signal sources and radiators are essential for a variety of future applications, such as high-resolution radar imaging [1], molecular spectroscopy, and clocks [2], as well as high-speed or miniature-platform communications [3]. For over a decade, the growing interest in CMOS-based compact THz radiation sources has been driven by their small form factor and integration with other analog/digital systems. However, the total radiated power of prior CMOS THz sources was still only several mW, not only due to the limited $f_{\mathrm{m}\mathrm{a}\mathrm{x}}$ and breakdown voltages of the CMOS transistors, but also due to the inefficient on-chip radiation approaches. Front-side radiation, typically based on a patch antenna implemented using the CMOS BEOL, allows for low-cost packaging and reliable heat dissipation. However, the small metal and dielectric thicknesses cause low radiation efficiency $(\eta_{\mathrm{r}\mathrm{a}\mathrm{d}})$ and narrow radiation bandwidth $(f_{\mathrm{B}\mathrm{W}}/f_{0}) (\eta_{\mathrm{r}\mathrm{a}\mathrm{d}}\approx 25\%$ and $f_{\mathrm{B}\mathrm{W}}/ f_{0}\approx 5\%$ in the 200-to-300GHz band). To address these issues, back-side radiation is commonly adopted as an alternative, where the THz waves are radiated from, for example, slot and dipole antennas, into the silicon substrate and are eventually emitted from the back of the chip. However, due to the large dielectric constant contrast between the silicon $(\varepsilon_{\text{Si}}=11.9)$ and air $(\varepsilon_{\mathrm{a}\mathrm{i}\mathrm{r}}=1)$, the radiated waves undergo strong reflection at the silicon-air interface, and with a small outward angle of 17°, total internal reflection occurs. To alleviate this problem, cm-sized, high-resistivity silicon lenses affixed to the chip back have been used [1]. However, they dramatically increase the cost and size of the overall assembly. In this paper, we introduce a CMOS THz amplifier-multiplier chain array generating radiation between 232 and 260GHz. Instead of using a silicon lens, a patterned dielectric matching sheet is applied onto the flipped-chip back, which enhances the wave coupling from silicon to air and enables low-cost and planar packages. That, in conjunction with broadband gain-peaking power amplifiers built with a high-power RF FinFET (HyPowerFF) transistor technology in the CMOS process, enables a measured peak total radiated power of 11.1dBm.