Tuning Ambipolarity of the Conjugated Polymer Channel Layers of Floating‐Gate Free Transistors: From Volatile Memories to Artificial Synapses

Abstract

Three-terminal synaptic transistor has drawn significant research interests for neuromorphic computation due to its advantage of facile device integrability. Lately, bulk-heterojunction-based synaptic transistors with bipolar modulation are proposed to exempt the use of an additional floating gate. However, the actual correlation between the channel's ambipolarity, memory characteristic, and synaptic behavior for a floating-gate free transistor has not been investigated yet. Herein, by studying five diketopyrrolopyrrole-benzotriazole dual-acceptor random conjugated polymers, a clear correlation among the hole/electron ratio, the memory retention characteristic, and the synaptic behavior for the polymer channel layer in a floating-gate free transistor is described. It reveals that the polymers with balanced ambipolarity possess better charge trapping capabilities and larger memory windows; however, the high ambipolarity results in higher volatility of the memory characteristics, namely poor memory retention capability. In contrast, the polymer with a reduced ambipolarity possesses an enhanced memory retention capability despite showing a reduced memory window. It is further manifested that this enhanced charge retention capability enables the device to present artificial synaptic characteristics. The results highlight the importance of the channel's ambipolarity of floating-gate free transistors on the resultant volatile memory characteristics and synaptic behaviors.

High-performance asymmetric electrode structured light-stimulated synaptic transistor for artificial neural networks

“…After the semiconductor layer has been irradiated by light, photogenerated excitons are generated in the bulk heterojunction film. Photoelectrons are more easily transferred to N2200 due to the higher LUMO of DPP-DTT and photohole accumulation in DPP-DTT, and the heterostructure of DPP-DTT/N2200/DPP-DTT forms a potential barrier similar to a quantum well, 37,38,71,72 allowing some electrons in the channel to be trapped and stored in the N2200, as shown in Fig. S5a (ESI †).…”

“…OFETs typically use symmetric electrodes and enable the transition from nonvolatile memories to artificial synaptic devices and photonic transistors by tuning the p-type/n-type semiconductor heterojunction structure. 37,38 However, photostimulated synaptic transistors based on symmetrical electrode OFETs have high energy consumption, limiting the application possibilities for building low-power artificial neural network systems. 39,40 Fortunately, OFETs with asymmetric electrodes generate a built-in electric field due to the difference in the source and drain work functions, which enables the fast separation of photogenerated carriers at the heterogeneous interface, enhancing performance and improving the response speed and sensitivity.…”

Reconfigurable Artificial Synapse Based on Ambipolar Floating Gate Memory

“…However, the organic materials and transistors suffer from low mobility and high drive voltage, reducing the switching speed and increasing the power consumption. 21 In addition, the charge trapping/detrapping process may cause the performance to degrade thermally over time owing to currentgenerated Joule heating, potentially leading to poor stability of the devices. 22,23 Herein, we implemented an artificial synaptic device using a WSe 2 /h-BN/MoTe 2 ambipolar floating gate (AFG) transistor structure exhibiting reconfigurable excitation and inhibition of synaptic functions.…”

“…In addition, by charge trapping at the dielectric interface, ambipolar conjugated polymer–TFTs exhibit volatile memory characteristics and synaptic behaviors. However, the organic materials and transistors suffer from low mobility and high drive voltage, reducing the switching speed and increasing the power consumption . In addition, the charge trapping/detrapping process may cause the performance to degrade thermally over time owing to current-generated Joule heating, potentially leading to poor stability of the devices. , …”

High-performance ambipolar field-effect transistors with a Ph-BTBT-10/PMMA/ZnO structure

“…Ambipolar field-effect transistors (FETs) have extensive application prospects in various emerging areas such as synaptic, 1–3 memory 4–6 and logic devices 7–9 due to their unique property of simultaneously transporting holes and electrons in conductive channels. 10,11 Zinc oxide (ZnO) as one of the representative metal oxide semiconductors has excellent properties, such as low cost, non-toxicity and high carrier mobility, and has been widely studied in FETs.…”