Soft, Transparent Electronic Devices by High-throughput Process for Bio-inspired Artificial Sensing


Student thesis: Doctoral Thesis

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Award date20 Nov 2023


Soft electronics have gained widespread attention due to their vast emerging applications in wearable devices, epidermal electronics, bio-inspired sensors, conformable touch screen, flexible displays. Besides, the desire of next-generation electronic devices also drives the development of soft electronics towards high optical transparency, which is important for novel bio-medical applications such as contact lens sensors, smart glasses, and transparent neural interfaces. However, achieving fully soft and transparent electronics remains great challenging in both materials and integration strategies, since it requires all the components to possess excellent optical transparency, high mechanical stability, and high electrical performance at the same time. Thus, the research of soft and transparent electronics will lead to the development of a wide variety of new materials, novel system engineering, and novel optical applications. Moreover, research of advanced high-throughput technology that allowed low-cost and large-scale fabrication of soft transparent electronic devices also shows great importance in both academic community and industrial sector. In this thesis, we have comprehensively investigated soft and transparent electronics with the aim of achieving high-throughput fabrication. This thesis includes the development of soft and transparent electrodes for biomimetic tactile sensing, a soft and transparent electronic imaging system inspired by natural eyes, and a room-temperature fabrication method for transparent metal oxide films.

Our research begins with the soft and transparent electrodes, which are the very essential component of soft and transparent electronics. Transparent electrodes for soft electronics should fulfill the requirements of high optical transparency, high conductivity, stable mechanical performance, and low-cost fabrication. In this part, we introduce a low-cost and scalable method with precise pattern control for producing high-performance stretchable and transparent electrodes based on silver nanowires. Furthermore, flexible and transparent circuits with finely designed patterns were produced, which formed large-area flexible skin-integrated tactile sensor arrays.

Then, our research goes further to system-level soft and transparent electronics. Bio-inspired electronic eyes mimicking the natural light-sensing organs are highly attractive in next-generation miniaturized imaging systems. However, slow and equipment-intensive techniques are usually involved in fabrication of electronic eyes such as vacuumed-sputtering and high-temperature treatment. In this part, we develop an electronic eye system with a fully transparent artificial retina by a simple solution-based method at room-temperature. All the components of the artificial retina, including substrate, circuits and light-sensing units are soft and transparent, making it directly mounted on the curvy surface. It shows a reliable ultra-violet response and high transparence across the visible and near-infrared range, and hence allows the artificial retina to perceive light from all directions without weakening the photo-response. Furthermore, demonstrations of two kinds of electronic eye prototypes (concave and convex hemispheres) in a single device are realized.

Finally, our research takes on the challenge of addressing the most cut-edging problems in the field of soft transparent electronics, namely the low-temperature fabrication of solution-processed transparent metal oxide thin films. Throughout the history of flexible transparent electronics research, high transparency, flexibility, and rich material properties have made transparent metal oxides the dominant materials in this field. Unlike traditional silicon, metal oxides can be fabricated using low-cost, high-throughput solution-based methods, which could significantly facilitate the commercialization of the flexible transparent electronics. However, it usually needs high-temperature annealing above 400ºC to improve electrical performance and reliability of the solution-processed metal oxide films, which are also incompatible with flexible polymeric substrates. Meanwhile, to enable fully solution-processed metal oxide transparent electronics, efficient and high-resolution patterning method which is suitable for all kinds of metal oxides is still lacked. Thus, in this part, we come up with a universal printing process using plasmonic local heating for high-performance oxide thin films under room temperature. This process demonstrates high precision and uniformity, and we named it as plasmonic printing. We use femtosecond pulse laser to excite silver nanowire films and generate strong localized heat to condense the metal oxide film under room-temperature and ambient condition. We investigate the physical principles of the silver nanowires plasmonic local heating and precisely control the printing parameters to fabricate transparent metal oxide thin films electronics, including conductor, dielectric, semiconductors. All these transparent metal oxide thin films show high performance and uniformity comparable to the commercial metal oxide film by vacuumed process. Then, using this technology, we successfully print a fully metal oxide transistor array with a high density of 48400 transistor/cm2 by solution-process at room temperature, which is comparable to the best commercial display panels at present. Finally, we also realize the fabrication of solution-processed indium tin oxide film on flexible substrate.

In summary, we have made significant developments in soft and transparent electronics by high-throughput process for bio-inspired artificial sensing, including electrodes, system-level devices, and advanced fabrication technology. We believe that this thesis will open the new possibility for the low-cost and large-area fabrication of soft and transparent electronics and facilitate the next generation of soft transparent electronics era.