Advanced Organic Field-Effect Transistors with pn-Heterojunction beyond Von Neumann Device Architecture

In this presentation, we will introduce an antiambipolar transistor (AAT) as a key element for novel electronic device to overcome the limitation of conventional von Neumann architecture. The uniqueness of AATs is ascribed to their distinctive electrical properties; sharp increase and decrease in the drain current can be observed by monotonical increase in gate bias voltage. This characteristic Λ-shaped transfer curve is realized due to a pn-heterojunction formed around the center of a transistor channel. Particularly, negative differential transconductance (NDT), where the drain current decreases against increase in gate bias voltage, is the key property to yield various functionalities. By taking advantage of this character, we have been developing a variety of novel organic electronic applications.<br/>These kinds of innovative electronic device are particularly required in the field of organic electronics. Despite their various advantages, such as mechanical flexibility, light weight, solution processability, and cost-effectiveness, organic electronics have been recognized to have weak points in terms of integration density and data processing capability because of their incompatibility with conventional lithographic processes. Meanwhile, organic AATs appear to offer means to overcome such weaknesses, and thereby open a new frontier in the field of organic electronics.<br/>First, the fundamental mechanism of the carrier transport is discussed in terms of the characteristic device configuration. The essential part of the AATs is the pn-heterojunction at the transistor channels; thin films of a p-type and n-type organic semiconductors are partially overlapped. These films are contacted with respective metal electrodes (source and drain electrodes) to form a pn-heterojunction transistor. The carrier transport mechanism was analyzed by original measurement techniques: operando photoemission electron microscopy (operando-PEEM) and operando Kelvin probe force microscopy (operando-KPFM). These techniques allowed us to characterize carrier transport properties in the device operation status under bias voltage. Second, the ATT applications are introduced those are multi-valued (ternary and quaternary) logic circuits and reconfigurable logic circuits. Both are advantageous to increase integration density with less device elements. Other applications are logic-in-memory and artificial synaptic device. These were realized by combining AATs and non-volatile memory effects. These novel devices have a potential to overcome the weak point of the organic electronics and limitation of conventional von Neuman type devices. Therefore, we categorize these devices as beyond von Neumann type electronic devices.