Flexible Electronics

Chuan Wang | cwang@msu.edu | www.msu.edu/~cwang

 

The Flexible Electronics Group led by Prof. Wang is an interdisciplinary research program that links electrical engineering, materials science, physics, and chemistry. Our research falls in the area of flexible and stretchable electronics, which aims to have conventional electronic systems fabricated on ultrathin plastic or rubbery substrates. This new form factor could substantially expand the spectrum of potential applications. Examples include flexible displays, wearable electronics and sensors, implantable biomedical devices, and many more.

High-Performance Flexible Electronic Systems

Organic semiconductors and polymers are most widely used materials for flexible electronics and stretchable electronics. However, the main drawbacks of organic semiconductors are their inferior performance and susceptibility to oxygen and moisture. One-dimensional nanomaterials such as carbon nanotubes possess superior electrical properties and offer new entries into a wide range of novel electronic applications that are unattainable with conventional materials. Our group pioneered the field of nanomaterials-based flexible electronics and developed a robust platform for room-temperature solution-based processing of semiconducting carbon nanotube thin-film. Such carbon nanotube thin-film offers superior electrical properties and mechanical flexibility and can be used as the channel material for high-performance thin-film transistors (TFTs). The transistors obtained using our approach exhibit field-effect mobility up to 100 cm2/Vs, hundreds of times better than the performance achievable in other material platforms such as organic semiconductors.

Using the semiconducting carbon nanotube material platform, a wide range of large-scale flexible electronic systems have been demonstrated, including flexible integrated circuits, active-matrix organic light-emitting diodes (AMOLED) display, flexible image sensor with laminated x-ray scintillator for x-ray imaging, and interactive electronic skin (e-skin) that can provide spatiotemporal mapping of pressure stimuli.

As an example, in a recent paper published in Nature Materials, we have demonstrated the integration of transistors, circuits, OLEDs, and sensors (e.g. pressure, strain, temperature, and light sensors) on an ultra-thin substrate into a light-weight flexible system with sophisticated sensing and user-interactive functionalities. Such a flexible electronic system could conformably adapt to curved surfaces, and with the monolithically integrated sensing and displaying elements, the system could easily transform any surface into a smart interactive surface that could enable sophisticated human-surface interactions. It may find a wide range of applications in wearable electronic devices, interactive displays or input devices, and smart electronic wallpapers.

Fully-Printed Stretchable Electronic Systems

Fully-printed electronics is ideal for low-cost large-area fabrication without the need of conventional costly microfabrication tools used in the semiconductor industry. Our group has extensively explored various printable electronic materials (metal, semiconductor, and insulator) and has developed ink formulations to allow highly reproducible and uniform material patterning using inkjet printing or gravure printing technologies.

We have already made significant progress in the field of nanomaterials-based printed electronics by demonstrating fully-printed electronic devices including TFTs, sensors, and OLEDs with excellent performance on flexible and stretchable substrates. The printed transistors exhibit excellent performance for a fully printed process, with mobility and on/off current ratio up to ~ 10 cm2/Vs and 105, respectively. The aforementioned TFTs are further integrated into fully-printed logic circuits and active-matrix backplane - a key component for driving flat-panel displays. The use of fully printed transistors as switches for driving OLED displays has also been demonstrated. Owing to our proper design of flexible metallic, semiconducting, and insulating materials, extreme bendability and even foldability are achieved in our printed circuits. No measurable change in electrical performance was observed when the samples were folded to an extremely small curvature radius.

Additionally, our group is also working on developing printable electronic materials with superior stretchability and inter-layer adhesion for fabricating fully-printed integrated circuits on elastomer substrates. The aim is to develop stretchable electronic systems for applications in wearable electronic bandages or displays that can be easily stretched to larger size.