Bio‐Inspired Adaptive Sensing through Electropolymerization of Organic Electrochemical Transistors

Abstract

for converting ionic signals into electronic ones thanks to the unique property of organic mixed ionic-electronic conductors (OMIECs). [4] Ionic concentration from an analyte or ionic currents from electroactive cells can be efficiently sensed/probed and amplified, thus making OECTs attractive sensors. [5] In the perspective of neuromorphic engineering, the same devices are capitalizing on the possibility to engineer devices where ion-electron coupling can be used to implement various synaptic plasticities, from short-term to long-term memory effects. [3,[6][7][8][9] These two aspects have been so far mostly developed independently from each other. In contrast, synapses in biology are combining sensing capabilities with plastic properties to provide some essential aspects of biocomputing. Through their adaptation properties, synapses are enhancing/depressing relevant/irrelevant signals from neurons. They also provide a rich set of non-linear operations to process the spike signals from neural cells. [10] As sensors, synapses are converting chemical signals from sensed neurotransmitters into transduced post-synaptic electric signals as ionic concentration modulation. Such ambivalence existing in biology is the natural example of a non-Von Neumann computing architecture that embeds highly complex biochemical sensing at all nodes in its network, and demonstrates reciprocally the power of the local adaptation of a sensing array that programs according to its environment.In this paper, we show how OECTs can combine these two important features for bio-signal sensing and processing. The corner stone of OECTs behavior is the transconductance, which couples ionic signals to electronic ones. [11] Transconductance can be well described by the coupling between: i) volumetric ionic capacitance allowing for a very large effective surface of interaction between the analyte and the polymer; and ii) efficient electronic transport along the π-conjugated organic chains. Several works have demonstrated routes for optimizing transconductance through either volumetric capacitance or electronic mobility tuning. [12,13] Notably, side-chain engineering on the conductive backbone of the polymer have been recently proposed as a promising chemical engineering route. [14] Here, we show how electropolymerization can be used to adapt post-fabrication of these two intrinsic parameters of OECTs (i.e., volumetric capacitance and electronic mobility) and how this technique Organic electrochemical transistors are considered today as a key technology to interact with a biological medium through their intrinsic ionic-electronic coupling. In this paper, the authors show how this coupling can be finely tuned (in operando) post-microfabrication via the electropolymerization technique. This strategy exploits the concept of adaptive sensing where both transconductance and impedance are tunable and can be modified on-demand to match different sensing requirements. Material investigation through Raman spectroscopy, atomic force microscopy, and scanning ele...

Polymer‐based neuromorphic devices: resistive switches and organic electrochemical transistors

“…Other than the spin coating technique used in the studies mentioned above, electropolymerization is one major method of fabricating OECT devices. [108][109][110][111][112] The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer originated in early studies in conductive polymers [113][114][115] and has continued to be used as an effective method to obtain polymer films in a position-selective way, including forming dendric conductive networks. 109,110 In addition, modified EDOT derivatives (Fig.…”

Mixed Ionic-Electronic Transport for PEDOT:PSS-Based Zero-Gated Organic Electrochemical Transistors Using Impedance Spectroscopy and Micro-Raman Imaging

“…Essentially, the OECT operates via ion injection (usually using an electrochemical bias application) from an electrolyte solution toward the channel based on an OMIEC material leading to a change in the oxidation state of the conjugated polymer and thus altering the electronic transport. – Efforts to unravel mixed ionic-electronic transport mechanisms have been addressed by computational simulation studies, where most frequently, ionic and electronic transport are treated separately, i.e., ionic transport is computed in large polymeric systems using classical molecular dynamics , and electronic transport is computed in smaller oligomeric systems using first-principles calculations . However, recent literature has just addressed mixed ionic-electronic transport mechanisms simultaneously and other studies have also provided interesting insights on swelling and ionic injection processes for OMIEC channel materials comprising OECT devices. – Experimentally, insights on mixed ionic-electronic transport mechanisms in OMIECs based on impedance spectroscopy studies have been addressed separately, i.e., in the in-plane configuration for OMIECs , and in the out-of-plane configuration for OMIECs comprising OECT devices. – The use of impedance spectroscopy has also been a key to boosting frequency-dependent transconductance experiments relevant to bioelectronic applications. – In addition, some recent studies are being focused on establishing a link between structural and mixed ionic-electronic transport properties based on the characterization of OMIEC materials under operation conditions in OECT devices . For instance, X-ray and neutron reflectivity studies on PEDOT:PSS have revealed that the swelling-driven microscopic rearrangement of the conducting PEDOT-rich cores in the PSS matrix strongly influences the electrical charge transport. , A recent study performed by a combination of electrochemical quartz microbalance, X-ray scattering, and spectrochemical techniques has shown that infiltration of the hydrated dopant ions into the OMIEC material irreversibly changes the polymer structure and negatively impacts the efficiency, reversibility, and speed of charge generation .…”

Sputtered Electrolyte‐Gated Transistor with Modulated Metaplasticity Behaviors

“…[ 37,38 ] The unique ion‐mediated conductance modulation makes it ideal for mimicking the neurotransmitter‐mediated synaptic weight modulation because ions are also the carrier in brain neuro functions. [ 39–44 ] EGTs with various types of electrolytes were studied for mimicking synaptic metaplasticity behaviors. John et al.…”

“…[37,38] The unique ion-mediated conductance modulation makes it ideal for mimicking the neurotransmittermediated synaptic weight modulation because ions are also the carrier in brain neuro functions. [39][40][41][42][43][44] EGTs with various types of electrolytes were studied for mimicking synaptic metaplasticity behaviors. John et al emulated homeostatic synaptic metaplasticity behaviors on 2D transition metal di-chalcogenide (MoS 2 ) transistors gated with ion liquids.…”