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) | \(5 \, \textrm{pJ}\) | \(\sim \mathrm {ns{-}\upmu s}^{\Omega }\) | - |