Establishing
ultimate spin current efficiency in graphene over
industry-standard substrates can facilitate research and development
exploration of spin current functions and spin sensing. At the same
time, it can resolve core issues in spin relaxation physics while
addressing the skepticism of graphene’s practicality for planar
spintronic applications. In this work, we reveal an exceptionally
long spin communication capability of 45 μm and highest to date
spin diffusion length of 13.6 μm in graphene on SiO
2
/Si at room temperature. Employing commercial chemical vapor deposited
(CVD) graphene, we show how contact-induced surface charge transfer
doping and device doping contributions, as well as spin relaxation,
can be quenched in extremely long spin channels and thereby enable
unexpectedly long spin diffusion lengths in polycrystalline CVD graphene.
Extensive experiments show enhanced spin transport and precession
in multiple longest channels (36 and 45 μm) that reveal the
highest spin lifetime of ∼2.5–3.5 ns in graphene over
SiO
2
/Si, even under ambient conditions. Such performance,
made possible due to our devices approaching the intrinsic spin–orbit
coupling of ∼20 μeV in graphene, reveals the role of
the D’yakonov–Perel’ spin relaxation mechanism
in graphene channels as well as contact regions. Our record demonstration,
fresh device engineering, and spin relaxation insights unlock the
ultimate spin current capabilities of graphene on SiO
2
/Si,
while the robust high performance of commercial CVD graphene can proliferate
research and development of innovative spin sensors and spin computing
circuits.