Review of recent trends in flexible metal oxide thin-film transistors for analog applications

Abstract

Thanks to the extraordinary advances flexible electronics have experienced over the last decades, applications such as conformable active-matrix displays, ubiquitously integrated disposable flexible sensor nodes, wearable or textile-integrated systems, as well as imperceptible and transient implants are now reachable. To enable these applications, specialized analog circuits able to transmit and receive data, condition sensors' parameters, drive actuators or control powering devices are required. High-performance sensor conditioning, driving and transceiver circuits on a wide range of flexible substrates are therefore extremely important to develop. However, the currently available materials and processes compatible with mechanically flexible substrates impose massive limitations in terms of large-area uniformity, device dimensions' shrinkability and circuit design, challenging the realization of flexible analog systems. Among state-of-the-art technologies employing low-temperature fabrication processes, thin-film transistors (TFTs) based on metal oxide semiconductors represent the potentially best compromise in terms of prize, performance, technology maturity and capacity to realize complex systems. This is why metal oxide TFTs are nowadays widely used for flexible, light-weight, transparent, stretchable and bio-degradable analog circuits and systems. Here, we review the current trends of flexible metal oxide TFTs for analog applications. First, an introduction is given, where current challenges and requirements related to the realization of flexible analog circuits and systems are analysed. Additionally, TFT performance parameters and configurations are briefly revised. Then, the recent advances in the field of flexible metal oxide TFTs for analog applications are summarized. In particular, all reported approaches to reduce the channel length and improve the AC performance are shown. Next, the current state of flexible metal oxide TFT-based analog circuits is shown, discussing n-type only and complementary circuit configurations. The last topic of the review covers systems based on flexible metal oxide analog circuits. Finally, a conclusion is drawn and an outlook over the field is provided.

Analog and Mixed Signal Circuit Design Techniques in Flexible Unipolar a-IGZO TFT Technology: Challenges and Recent Trends

“…To reduce channel length, non-planar TFT stack, such as such as vertical TFTs (VTFTs) or quasivertical TFTs (QVTFTs) have also been reported [50]- [54]. The use of different materials in the TFT stack and their effects on the electrical and mechanical performance of the device, along with the stability have been extensively investigated [55], [56]. The choice of the gate dielectric is an important factor for the performance of a TFT.…”

Atomic Structure Evaluation of Solution-Processed a-IZO Films and Electrical Behavior of a-IZO TFTs

“…However, as the production of the AOS film requires a process temperature of 500 °C or higher for the oxidation reaction, various attempts have been made to lower the process temperature by developing process techniques and chemical treatments [ 9 , 10 ]. In particular, developments of the chemical treatment such as metal–salt precursors, catalysts, and chemical chamber deposition contributed drastically to lowering the process temperature [ 11 , 12 , 13 , 14 ].…”

Performance Enhancement and Bending Restoration for Flexible Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors by Low-Temperature Supercritical Dehydration Treatment

“…Flexible and wearable electronics have drawn extensive attention in recent years. , Amorphous metal oxide semiconductor thin-film transistors (TFTs) based on amorphous indium gallium zinc oxide (a-IGZO) have been regarded as a promising candidate for next-generation flexible electronic applications such as transparent displays, , neuromorphic computing, solar cells, , or wearable sensors. , This is because a-IGZO possesses higher mobility than amorphous silicon (a-Si) and a lower processing temperature than the low-temperature polysilicon. − So far, magnetron sputtering has been regarded as a standard technique to deposit a-IGZO owing to its merit of high uniformity and its high quality of reproducibility . However, because of the structural defects generated by high-energy ion bombardment in the sputtering process, most of the obtained a-IGZO layers normally require additional thermal treatment at over 300 °C to achieve satisfactory semiconductor properties .…”