Fig. 2: OEND operation.
From: Unravelling the operation of organic artificial neurons for neuromorphic bioelectronics
a OEND electrical characteristic accessed in voltage mode. A voltage ramp (\({V}_{{{{{{\rm{OEND}}}}}}}\)) is applied forward (red line) and backward (blue line), and the current \({I}_{{{{{{\rm{OEND}}}}}}}\) is measured. The four operating regions and the relevant circuit components in each region of operation are highlighted. b OEND circuit showing the internal voltages. c Gate-source voltage of transistor T1 (\({V}_{{{{{{\rm{GS}}}}}}1}\)) as a function of \({V}_{{{{{{\rm{OEND}}}}}}}\). T1 threshold voltage (\({V}_{{{{{{\rm{TH}}}}}}1}\)) is displayed. If \({V}_{{{{{{\rm{GS}}}}}}1}\ge {V}_{{{{{{\rm{TH}}}}}}1}\), T1 is turned OFF while if \({V}_{{{{{{\rm{GS}}}}}}1} < {V}_{{{{{{\rm{TH}}}}}}1}\), T1 is operated in a linear regime. Forward sweep (red line) and backward sweep (dashed blue line). The numbers refer to the four operating regions of the OEND, as highlighted in (a). d Source-gate voltage of transistor T2 (\({V}_{{{{{{\rm{SG}}}}}}2}\)) as a function of \({V}_{{{{{{\rm{OEND}}}}}}}\). If \({V}_{{{{{{\rm{SG}}}}}}2}\le |{V}_{{{{{{\rm{TH}}}}}}2}|\), T2 is in the OFF state and, if \({V}_{{{{{{\rm{SG}}}}}}2} > |{V}_{{{{{{\rm{TH}}}}}}2}|\) results that T2 is in saturation regime. e OEND characteristic accessed in current mode calculated with numerical simulations (line) and measured (symbols). A current ramp (\({I}_{{{{{{\rm{OEND}}}}}}}\)) is applied forward and backward, and the voltage \({V}_{{{{{{\rm{OEND}}}}}}}\) is measured. Forward and backward voltages are overlapped. The points \({{{{{{\bf{U}}}}}}}_{{{{{{\rm{ON}}}}}}}=({V}_{{{{{{\rm{ON}}}}}}},{I}_{{{{{{\rm{ON}}}}}}})\) and \({{{{{{\bf{U}}}}}}}_{{{{{{\rm{OFF}}}}}}}=({V}_{{{{{{\rm{OFF}}}}}}},{I}_{{{{{{\rm{OFF}}}}}}})\) define the negative resistance region (NRD).
