Giuseppe Cantarella1, Júlio Costa2, Tilo Meister3, Koichi Ishida3, Corrado Carta3, Frank Ellinger3, Paolo Lugli1, Niko Münzenrieder1,2 and Luisa Petti1
Review of recent trends in flexible metal oxide thin-film transistors for analog applications
Flexible and Printed Electronics 2020, Vol. 5, No. 3
DOI: 10.1088/2058-8585/aba79a
1Faculty of Science and Technology, Free University of Bozen-Bolzano, 39100, Bozen, Italy
2Flexible Electronics Laboratory, University of Sussex, Brighton, BN1 9QT, United Kingdom
3Chair of Circuit Design and Network Theory, TU Dresden, 01069 Dresden, Germany
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.
Figure: Overview of published works on flexible metal oxide TFT based circuits, indicating the minimum channel length of the devices, the operation frequency of the circuits, the effective supply voltage used, as well as the total TFT count. Only integrated circuits are included.
Acknowledgments: This work was partially supported by the DFG FFlexCom Priority Programme, Germany, through projects WISDOM II and Coordination Funds, under Grants 271795180 and 270774198. This work was also partially funded with internal funding of the Faculty of Science and Technology of the Free University of Bolzano-Bozen (project ”EYRE” RTD Call 2019).
