Simulation of a randomly percolated CNT network for an improved analog physical unclonable function.

Carbon nanotube networks (CNTs)-based devices are well suited for the physically unclonable function (PUF) due to the inherent randomness of the CNT network, but CNT networks can vary significantly during manufacturing due to various controllable process conditions, which have a significant impact on PUF performance. Therefore, optimization of process conditions is essential to have a PUF with excellent performance. However, because it is time-consuming and costly to fabricate directly under various conditions, we implement randomly formed CNT network using simulation and confirm the variable correlation of the CNT network optimized for PUF performance. At the same time, by implementing an analog PUF through simulation, we present a 2D patterned PUF that has excellent security and can compensate for error occurrence problems. To evaluate the performance of analog PUF, a new evaluation method different from the existing digital PUF is proposed, and the PUF performance is compared according to two process variables, CNT density and metallic CNT ratio, and the correlation with PUF performance is confirmed. This study can serve as a basis for research to produce optimized CNT PUF by applying simulation according to the needs of the process of forming a CNT network.

Gate Capacitance Coupling of Double-Gate Carbon Nanotube Network Transistors.

Carbon nanotube (CNT) network channels constructed using a high-purity CNT solution for use in CNT thin-film transistors have the advantages of the possibility of requiring a low-temperature process and needing no special equipment. However, there are empty spaces between individual CNTs, resulting in unexpected effects. In this study, double-gate (DG) CNT network transistors were fabricated and measured in four different configurations to observe the capacitive coupling effects between the top gate (TG) and bottom gate (BG) in the DG structure. As a result, the electrical characteristics measured with the BG with a thicker gate oxide while floating the TG were similar to those measured with the TG with a thinner gate oxide. A comparison of the measured transfer curves showed that TG and BG were strongly coupled through the empty spaces in the channels. In addition, we evaluated the capacitance coupling effect due to changes in the CNT density, which is closely related to the empty space of the network channel. Finally, we proposed a method to determine the effective gate capacitance by considering the empty spaces between CNTs, which enabled the accurate evaluation of mobility. The effects of these materials were demonstrated by fabricating transistors using Al2O3, HfO2, and ZrO2 as TG oxide materials. By focusing on considerations based on the properties of CNT materials, our study provides valuable insights into accurate electrical modeling and potential advancements in CNT-based devices.

Wafer-scale striped network transistors based on purified semiconducting carbon nanotubes for commercialization.

Highly purified and solution-processed semiconducting carbon nanotubes (s-CNTs) have developed rapidly over the past several decades and are near-commercially available materials that can replace silicon due to its large-area substrate deposition and room-temperature processing compatibility. However, the more s-CNTs are purified, the better their electrical performance, but considerable effort and long centrifugation time are required, which can limit commercialization due to high manufacturing costs. In this work, we therefore fabricated 'striped' CNT network transistor across industry-standard 8 inch wafers. The stripe-structured channel is effective in lowering the manufacturing cost because it can maintain good device performance without requiring high-purity s-CNTs. We evaluated the electrical performances and their uniformity by demonstrating striped CNT network transistors fabricating from various s-CNT solutions (e.g. 99%, 95%, and 90%) in 8 inch wafers. From our results, we concluded that by optimizing the CNT network configurations, CNTs can be sufficiently utilized for commercialization technology even at low semiconducting purity. Our approach can serve as a critical foundation for future low-cost commercial CNT electronics.