Printed and flexible carbon nanotube macroelectronics

Abstract

In this dissertation, I present my work on the development of printed carbon nanotube (CNT) macroelectronics for large?area, low?cost and flexible electronic applications such as sensors, active?matrix?based displays, and electronic skin. Emerged as a solution?based and drop?on?demand patterning technique, printing eliminates high?vacuum environment and multi?stage photolithography needed in conventional micro?fabrication. Therefore, printing is very suitable for manufacturing large?area flexible electronics with low cost and rapid processing. The printing technologies we developed can be divided into two methods. ? One is top?contact self?aligned printing (SAP) for ultra?short?channel CNT thin?film transistors (TFTs). Using top?contact self?aligned printing, we addressed the following issues in fully printed TFTs. First of all, we have successfully downscaled the channel length of fully printed CNT TFTs to sub?micron, which is beyond the resolution of any existing printing technologies. As a result, we have achieved unprecedented on?current density ~4.5 ?A/?m of fully printed CNT TFTs with high on?off ratio ~10?. This may open up the door to fully printed high?performance TFTs for macroelectronic applications which need high current drive and high?speed TFTs, such as active?matrix backplanes for display. Also, using top?contact SAP, we eliminated the contact resistance caused by self?assembled monolayer (SAM) modification. Hence, the device performance was further optimized. Furthermore, our printing technique can be applied to other?materials?based systems like 2?dimensional materials, metal oxides and so on. Overall, we believe this platform is promising in producing high?performance fully printed TFTs. ? The other method is screen printing as a scalable and low?cost approach for fully printed CNT macroelectronics. Screen printing, with advantages of high throughput, cost effectiveness, and simplicity, are universally used in industry manufacturing. However, due to the lack of available metal, dielectric, and semiconductor inks in the past years, screen printing was hardly used in fabricating electronic devices. We made great efforts on developing new functional inks, optimizing device configurations, and modifying printing process. As a result, we have realized fully screen printed CNT TFTs with good electrical performance and mechanical flexibility. Furthermore, we developed fully printed CNT TFT backplanes and integrated them with different types of sensors. Finally, we have achieved fully screen printed active matrix electrochromic displays on flexible substrates. In this work, all the materials were formulated into screen printable ink and screen printing served as the unique patterning technique. This tremendously simplified the fabrication process and lowered the total cost of making such display. Therefore, our screen printing work can be very important for future fully printed large area and low?cost sensors, electronic skin, and displays. ? In addition to printed CNT macroelectronics, we have also studied the application of CNTs for ultraflexible electronics. Flexible thin?film transistors based on semiconducting single?wall carbon nanotubes are promising for flexible digital circuits, artificial skins, radio frequency devices, active?matrix?based displays, and sensors due to the outstanding electrical properties and intrinsic mechanical strength of carbon nanotubes. Nevertheless, previous research effort only led to nanotube thin?film transistors with the smallest bending radius down to 1 mm. We have realized the full potential of carbon nanotubes by making ultraflexible and imperceptible p?type transistors and circuits with a bending radius down to 40 ?m. In addition, the resulted transistors show mobility up to 12.04 cm� V?� S?�, high on?off ratio (?10?), ultralight weight (<3 g/m�), and good mechanical robustness (accommodating severe crumpling and 67% compressive strain). Furthermore, the nanotube circuits can operate properly with 33% compressive strain. On the basis of the aforementioned features, our ultraflexible p?type nanotube transistors and circuits have great potential to work as indispensable components for ultraflexible complementary electronics. ? This dissertation is presented with six chapters. Chapter 1 is an introduction of carbon nanotubes regarding the structure, electrical properties, and applications for micro/macroelectronics. For inkjet printed carbon nanotube electronics, top?contact self?aligned printing is presented in chapter 2 to downscale channel length of printed CNT TFTs to sub?micron. The resulted devices show unprecedented current density compared with reported fully printed nanotube TFTs. Chapter 3,4 are our screen printing work for fully printed CNT TFTs, printed nanotube backplanes, and fully printed active?matrix electrochromic display. Besides, we developed ultraflexible CNT macroelectronics which will be presented in chapter 5. The last chapter, chapter 6, is the summary and future direction of printed and flexible macroelectronics.