An organic synaptic circuit: toward flexible and biocompatible organic neuromorphic processing

Abstract

In the nervous system synapses play a critical role in computation. In neuromorphic systems, biologically inspired hardware implementations of spiking neural networks, electronic synaptic circuits pass signals between silicon neurons by integrating pre-synaptic voltage pulses and converting them into post-synaptic currents, which are scaled by the synaptic weight parameter. The overwhelming majority of neuromorphic systems are implemented using inorganic, mainly silicon, technology. As such, they are physically rigid, require expensive fabrication equipment and high fabrication temperatures, are limited to small-area fabrication, and are difficult to interface with biological tissue. Organic electronics are based on electronic properties of carbon-based molecules and polymers and offer benefits including physical flexibility, low cost, low temperature, and large-area fabrication, as well as biocompatibility, all unavailable to inorganic electronics. Here, we demonstrate an organic differential-pair integrator synaptic circuit, a biologically realistic synapse model, implemented using physically flexible complementary organic electronics. The synapse is shown to convert input voltage spikes into output current traces with biologically realistic time scales. We characterize circuit's responses based on various synaptic parameters, including gain and weighting voltages, time-constant, synaptic capacitance, and circuit response due to inputs of different frequencies. Time constants comparable to those of biological synapses and the neurons are critical in processing real-world sensory signals such as speech, or bio-signals measured from the body. For processing even slower signals, e.g., on behavioral time scales, we demonstrate time constants in excess of two seconds, while biologically plausible time constants are achieved by deploying smaller synaptic capacitors. We measure the circuit synaptic response to input voltage spikes and present the circuit response properties using custom-made circuit simulations, which are in good agreement with the measured behavior.

Impact of Planar and Vertical Organic Field‐Effect Transistors on Flexible Electronics

“…Quite recently, Hosseini et al developed a biologically realistic spiking synaptic circuit, namely differential-pair integrator synapse, using mechanically flexible and biologically compatible complementary organic electronics. [210] By fabricating DNTT-based POFETs on flexible polyimide substrates, the authors used an organic synapse to successfully demon-strate the conversion of somatic voltage spikes (time constants reaching in excess of 2 s) into linearly proportional output current. By applying input spikes of different frequencies, the authors showed synaptic circuit response, and concluded that synaptic time constants similar to the time constants of the neuron's membrane potential are crucial in distinguishing different temporal input spike patterns.…”

“…The performance of a ring oscillator is characterized by its high oscillation frequency and low stage delay (where circuit speed = 1/stage delay) to ensure implementation in next-generation sensing, clocking, or communication applications. [220] An example of a flexible Inverter VOFET [152] POFET [93,193] Oscillator POFET [90,93,193] Amplifier POFET [194,195] 4.2 Light-emitting devices OLED/AMOLED POFET [58,196] VOFET [144,197] Rollable displays POFET [58] Quantum-dot systems VOFET [144] Multiphoton emission OLEDs POFET [48] 4.3 Memory devices Floating gate POFET [87,198] Flash POFET [87] Ferroelectric VOFET [199,200] POFET [201] Optical VOFET [202] 4.4 Sensors Photo-/image sensors VOFET [88,[203][204][205] POFET [206,207] Biological sensors POFET [50,208] Neuromorphic systems POFET [209,210] VOFET [211] Gas sensors POFET [212] five-stage ring oscillator prepared on a flexible PEN substrate is shown in Figure 7f. [221] In a recent report that developed a bioinspired flexible artificial afferent nerve, organic ring oscillators were used to convert pressure stimuli into voltage pulses that oscillated at frequencies corresponding to the other circuit components.…”

Modulation of polyaniline memristive device switching voltage by nucleotide-free analogue of vitamin B12

“…Organic memristive devices and neuromorphic transistors are of special interest due to their unique set of characteristics, including relatively low operational voltage, mechanical flexibility, softness of devices, biocompatibility of materials, and ability to form three-dimensional structures [14][15][16][17]. In addition, they enable a variety of fabrication and processing techniques, ranging from spray-coating to inkjet and 3D printing, allowing fast and cost-effective production of devices [18][19][20][21].…”

Editorial: Focus on organic materials, bio-interfacing and processing in neuromorphic computing and artificial sensory applications

“…Mimicking spiking behavior is an important step towards artificial systems operating at the interface with biology. In Hosseine et al [3] the authors show a biologically realistic spiking synaptic circuit on a biocompatible flexible substrate.…”