Temperature-Compensated Multi-Level CMOS Modulators Operating From 10 K to 300 K for Cryogenic Interconnects

This work presents temperature-compensated cryogenic complementary metal-oxide-semiconductor (CMOS) modulators operating over a 10 K to 300 K temperature range, suitable for intra- and inter-thermal cryogenic communications. Conventional metal-based coax cables suffer from a fundamental trade-off between thermal load and frequency-dependent attenuation, where lower thermal load results in higher electromagnetic attenuation. The recent surge in cryogenic high-performance computing and quantum computing has driven the demand for scalable cryogenic interconnect solutions. New techniques in optical fibers and millimeter-wave backscatter transceivers have demonstrated the ability to transport digital data between thermally isolated temperatures without the need for coaxial cables. Our new modulator can integrate (at the package or chip level) with millimeter-wave transmitters co-located on the same thermal condition while supporting bandwidth-efficient modulations such as multi-level pulse amplitude modulations. Based on this motivation, we implemented a current-steering 2-bit modulator in a 65-nanometer (nm) bulk CMOS process. The modulator achieves a data rate of 13 gigabits per second (Gb/s) while consuming 15.4 mW under a 1.2 V supply at 10 K, resulting in an energy efficiency of 1.18 picojoules per bit (pJ/b). In addition to previously demonstrated optical fibers and millimeter-wave backscatter, we implemented a 150 GHz (GHz) transmitter utilizing the same current-steering modulator scheme in a 28-nm CMOS process. We established contactless connections between thermally isolated systems operating at 10 K and 300 K, achieving a data rate of 8 Gb/s.