Diverse Synaptic Plasticity Induced by the Interplay of Ionic Polarization and Doping at Salt-Doped Electrolyte/Semiconducting Polymer Interface

Abstract

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.

Modulation of Response Patterns by Loading-Rate-Dependent Interface Polarization and Doping

“…Under conditions of negative bias 0 V → −2 V → 0 V (red line), the current hysteresis curve possesses a substantially larger current amplitude with the disappearance of the NDR peak. Similar results in Figure a have been observed in our previous studies. − ,, Apparently, the heterojunction is naturally rectified along the Ca Tf 2 -PEO/P3HT orientation. Since Figure f shows no space charge region without voltage loading, the energy alignment would be dynamically regulated under external field.…”

“…Therefore, the ions tend to dope into the P3HT layer to release the stress and finally lead to a reduction of space charge region and internal field. This phenomenon would be more distinct with a train of stimuli applied, which is the source of frequency selectivity and other signal-manipulating properties. , The accumulation and release of interface stress is hard to be examined because of our sandwich structure. However, some studies support structure and volume variations accompanied by ionic migrations.…”

Implantable Organic Artificial Synapses Exhibiting Crossover between Depressive and Facilitative Plasticity Response

“…Indeed, at higher frequencies (≥500 Hz), Γ = 0, σ = +∞, L F →+∞, ρ = 1, leading to I F = 0. Thus, in the absence of inductive contributions, only depressive mono-exponential STP decay can be elicited and Equation ( 8) becomes [17,29,37,38]…”

“…In an aqueous environment, the slow kinetics is inherent to the ion displacement in the electrolyte at the interface with the active OMIEC. A number of neuromorphic devices were demonstrated in aqueous electrolytes, from switchable nonvolatile memory elements [14] to devices emulating the main synaptic signal processing features, like spike-timing-dependent-plasticity, [15,16] shortterm-plasticity (STP), [17,18] and long-term-potentiation. [7,[19][20][21] These functions are the basis of processing, memorization, and learning mechanisms in the human brain.…”

Implementing a Type of Synaptic Coupling between Excitatory and Inhibitory Cells by Using Pt/Poly(3,4-ethylenedioxythiophene):Polystyrenesulfonate/HfOx/Pt Memristive Structure

“…The chemical synapse communicates one-way through neurotransmitters, resulting in a time delay in the signal conversion. Several memristors have demonstrated to simulate the Ca 2+ flux and transmission of neurotransmitters in chemical synapses. ,,, On the basis of these artificial chemical synapses, scientists have emulated the neural phenomena of learning and various complex synaptic plasticity. ,− Moreover, the memristor-based circuits or arrays have been fabricated to simulate various synaptic processes for neuromorphic computing applications. − …”