Publications

An ultra-stable time-keeping device is presented, which locks its output clock frequency to the rotational-mode transition of polar gaseous molecules. Based on a high-precision spectrometer in the sub-terahertz (THz) range, our new clocking scheme realizes not only fully electronic operation but also implementations using mainstream CMOS technology. Meanwhile, the small wavelength of probing wave and high absorption intensity of our adopted molecules (carbonyl sulfide, 16O12C32S) also enable miniaturization of the gas cell. All these result in an "atomic-clock-grade" frequency reference with small size, power, and cost. This paper provides the architectural and chip-design details of the first proof-of-concept molecular clock using a 65-nm CMOS bulk technology. Using a 231.061-GHz phase-locked loop (PLL) with frequency-shift keying (FSK) modulation and a sub-THz FET detector with integrated lock-in function, the chip probes the accurate transition frequency of carbonyl sulfide (OCS) gas inside a single-mode waveguide, and accordingly adjusts the 80-MHz output of a crystal oscillator. The clock consumes only 66 mW of dc power and has a measured Allan deviation of 3.8 × 10^−10 at an averaging time of tau = 1000 s.

A new type of broadband link enabling extremely high-speed chip-to-chip communication is presented. The link is composed of fully integrated sub-mmWave on-chip traveling wave power couplers and a low-cost planar dielectric waveguide. This structure is based on a differentially driven half-mode substrate integrated waveguide supporting the first higher order hybrid microstrip mode. The cross-sectional width of the coupler structure is tapered in the direction of wave propagation to increase the coupling efficiency and maintain a large coupling bandwidth while minimizing its on-die size. A rectangular dielectric waveguide, constructed from Rogers Corporation R3006 material, is codesigned with the on-chip coupler structure to minimize coupling loss. The coupling structure achieves an average insertion loss of 4.8 dB from 220 to 270 GHz, with end-to-end link measurements presented. This system provides a packaging-friendly, cost effective, and high performance planar integration solution for ultrabroadband chip-to-chip communication utilizing millimeter waves.