Table 1 Comparison of the proposed synapse with prior works. \(^{\$}\)Calculated assuming SRAM cell area of \(\hbox {150F}^{2}\) in 28 nm technology and 8-bit weights. \(^{\Lambda }\)Calculated assuming 2T1R unit cell and 14nm technology for the access transistor as per14. \(^\Upsilon\)Based on fabricated \(\hbox {Ag/GeSe}_{3}\)/Ag device dimensions as per60. \(^{+}\)Based on 65nm technology for access transistor and cell area of \(\hbox {450F}^2\). \(^!\)Write energy calculated (\(\approx I^2 t_{pw} / G\)) assuming I\(_{prog}\) \(\sim\) 100 \(\upmu\)A, \(G \sim\) 1 \(\upmu\)S, and \(t_{pw} \sim\) 100ns, as per the parameters mentioned in50. &Learning energy reported at V= 0.5V59. \(^*\)Only coupling weights are PCM-based; eligibility computations are performed using a high-precision unit. Write energy is estimated roughly according to the values provided in49: I\(_{prog}\) = 700\(\,\upmu\)A, \(t_{pw}\) = 600ns, \(G = 10\, \upmu\)S. \(^\#\)Learning energy dominated by optical power60. \(^\otimes\) Limited by PCM device resistance drift rate. \(^\boxtimes\)Limited by Von-neumann style sequential computing. \(^\triangle\)Limited by Ag conductive filament relaxation dynamics. \(^\Omega\)Limited by thermal time constant.

From: NeoHebbian synapses to accelerate online training of neuromorphic hardware

 

Coupling weights

Eligibility

Per synapse area

Energy per timestep

Eligibility decay time constant

Maturity

Y. Demirağ et al.50

PCM conductance

PCM drift

\(12 \times 12 \, \upmu \textrm{m}^2\)

\(\sim 1 \, \textrm{nJ}^{!}\)

\(\sim \textrm{s}^{\otimes }\)

+

C. Frenkel et al.59

CMOS

CMOS

\(1200F^{2 \, \$}\) (0.94 μm2)

\(1.5-178 \, \textrm{nJ}^{ \& }\)

\(\sim \textrm{ms}^{\boxtimes }\)

++

T. Bohnstingl et al.49

PCM conductance

CMOS

\(5221F^{2 \, \Lambda }\) (1.02 μm2)

\(29 \, \textrm{nJ}^{*}\)

\(\sim \textrm{ms}^{\boxtimes }\)

+

S. G. Sarwat et al.60

PCM conductance

Optical response of PCM

\(5 \times 4.8 \, \upmu \textrm{m}^2 \, \Upsilon\)

\(\sim \textrm{mJ}^{\#}\)

\(\sim \mathrm {ns{-}ms}^{\triangle }\)

-

This work

ReRAM conductance

ReRAM local temperature

\(450F^2\) (1.9 μm2)

\(5 \, \textrm{pJ}\)

\(\sim \mathrm {ns{-}\upmu s}^{\Omega }\)

-