Beyond CMOS

Beyond CMOS refers to the possible future digital logic technologies beyond the CMOS scaling limits which limits device density and speeds due to heating effects.
"Beyond CMOS" is the name of one of the 7 focus groups in ITRS 2.0 (2013) and in its successor, the International Roadmap for Devices and Systems.
CPUs using CMOS were released from 1986 (e.g. 12 MHz Intel 80386). As CMOS transistor dimensions were shrunk the clock speeds also increased. Since about 2004 CMOS CPU clock speeds have leveled off at about 3.5 GHz.
CMOS devices sizes continue to shrink – see Intel tick–tock and ITRS :
It is not yet clear if CMOS transistors will still work below 3 nm. See 3 nanometer.
Comparisons of technology.
About 2010 the Nanoelectronic Research Initiative (NRI) studied various circuits in various technologies.
Nikonov benchmarked (theoretically) many technologies in 2012, and updated it in 2014. The 2014 benchmarking included 11 electronic, 8 spintronic, 3 orbitronic, 2 ferroelectric, and 1 straintronic technology.
The 2015 ITRS 2.0 report included a detailed chapter on "Beyond CMOS", covering RAM and logic gates.
Superconducting computing and RSFQ.
Superconducting computing includes several beyond-CMOS technologies that use superconducting devices, namely Josephson junctions, for electronic signals processing and computing. One variant called rapid single-flux quantum (RSFQ) logic was considered promising by the NSA in a 2005 technology survey despite the drawback that available superconductors require cryogenic temperatures. More energy-efficient superconducting logic variants have been developed since 2005 and are being considered for use in large scale computing.