The simulation of synaptic plasticity using new materials is critical in the study of brain-inspired computing. Devices composed of Ba(CF3SO3)2-doped polyethylene oxide (PEO) electrolyte film were fabricated and with pulse responses found to resemble the synaptic short-term plasticity (STP) of both short-term depression (STD) and short-term facilitation (STF) synapses. The values of the charge and discharge peaks of the pulse responses did not vary with input number when the pulse frequency was sufficiently low(~1 Hz). However, when the frequency was increased, the charge and discharge peaks decreased and increased, respectively, in gradual trends and approached stable values with respect to the input number. These stable values varied with the input frequency, which resulted in the depressed and potentiated weight modifications of the charge and discharge peaks, respectively. These electrical properties simulated the high and low band-pass filtering effects of STD and STF, respectively. The simulations were consistent with biological results and the corresponding biological parameters were successfully extracted. The study verified the feasibility of using organic electrolytes to mimic STP.
Long-term bidirectional frequency selectivity has been achieved in MEH-PPV/PEO–Nd3+cells, which suggests spike-rate-dependent plasticity learning protocol. It depends on pulse shape due to variation of ionic type.
Pt/Ca2+–polyethylene oxide/polymer poly[3-hexylthiophene-2,5-diyl]/Pt
devices were fabricated, and their pulse responses were studied. The
discharging peak, represented by the postsynaptic current (PSC), first
increases and then decreases with increasing input number in a pulse
train. The weight of the PSC decreased for low-frequency stimulations
but increased for high-frequency stimulations. However, the peak of
the negative differential resistance during the charging process varied
following the opposite trend. These behaviors suggested the ability
for transferring the signal bidirectionally, confirming the equivalence
between the ionic kinetics of our device and the transmitter kinetics
of one kind of synapse. A facilitation
(F)–depression (D) interplay
model corresponding to the ionic polarization and doping interplay
at the electrolyte/semiconducting polymer interface was adopted to
successfully mimic the weight modification of the PSC. The simulation
results showed that the observed synaptic plasticity was caused by
the great disparity between the recovery time constants of F and D (τF and τD). Moreover, such
an interplay could inspire the features of responses to post-tetanic
stimulations. Our study suggested a means to realize synaptic computation.
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