(Invited) High Performance Fully Solution Processed Transistors Towards Flexible Sustainable Electronics
Authors: Bermundo Juan Paolo , Corsino Dianne , Hanifah Umu , Uraoka Yukiharu 
Published: November 2022

The shift towards a human-centered society promotes greater interconnectedness between people and the digital space. Modern devices such as displays and sensors in which thin-film transistors (TFT) are key materials have crucial roles in the next-generation society because displays are used as both information terminals and interface for human-device interactions while sensors gather data. Furthermore, there is growing interest in neuromorphic devices which aim to mimic the human brain’s efficiency in simultaneously processing and memorizing information to address the von Neumann bottleneck pervasive in modern computing architecture [1]. Amorphous oxide semiconductors (AOS) have gained attention as excellent materials for TFT [2], memory [3], sensing [4], and neuromorphic [5] applications for their superb combination of electrical performance and transparency. Currently, AOS devices are still mainly fabricated using vacuum process. To achieve high throughput and cost-effective production of numerous ubiquitous devices necessary in the next-generation society, an alternative fabrication process is needed.
Solution process is an exceptional candidate because of its: (i) efficient production with cost-effective equipment, (ii) large material utilization (low waste) since it can be an additive process compared to vacuum process (high waste), and (iii) low temperature processability for flexible applications in healthcare, energy, and electronics. However, solution process still has major issues such as inferior performance and reliability compared with vacuum process. Several processes have been developed to address these issues but are mostly focused on improving performance and usually limited to a single solution processed device layer – the channel or gate insulator [6]. Thus, many still opt for vacuum process or a single solution processed layer as a compromise. For truly high throughput fabrication, all device layers should be fabricated by solution process. In reality, fully solution-processed TFTs are challenging to fabricate, have dismal performance (mobility (μ) < 1 cm2/Vs), and poor reliability. Therefore, high temperature (>400 °C) process and exotic materials are required for decent μ <10 cm2/Vs which precludes their use in high performance flexible device applications [7].
Here, we present how photo-assisted methods through UV treatment and excimer laser annealing (ELA) can selectively transform AOS regions at low substrate temperatures [8]. Consequently, a single AOS film acts as both the semiconductor channel and conducting electrode to realize fully solution processed TFTs with μ of ~40 cm2/Vs (see Fig. 1) [9]. We also show how alternative methods can be used to enhance the performance and stability of fully solution processed TFTs on rigid/flexible substrates. In particular, how low temperature processes such as light, plasma, and material design of functional materials enable high throughput solution processing of flexible electronic devices.
Acknowledgment
This research was supported by JSPS Kakenhi Grant no. 22K14291.
References
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[7] S. J. Lee et al ACS Appl. Mater. Interfaces 8, 12894 (2016)
[8] J. P. Bermundo et al ACS Appl. Mater. Interfaces 10, 24590 (2018)
[9] D. Corsino et al ACS Appl. Electron. Mater., 2, 2398 (2020)

Figure 1