The joint research group of Hu Youfan-Peng Lianmao of the School of Electronics has made important progress in the research of high-speed flexible circuits

In recent years, flexible epidermal electronic systems have shown important application value and broad prospects
in the fields of personalized medicine, intelligent diagnosis and health monitoring.
Flexible systems require high-speed flexible circuits to achieve real-time information analysis or build wireless communication modules for new applications, so the research of high-speed flexible integrated circuits has attracted widespread attention
.
At present, limited by the performance of existing flexible electronic devices, there are still severe challenges
in achieving high-performance, high-speed flexible integrated circuits.

Recently, Associate Professor Hu Youfan-Professor Peng Lianmao Joint Research Group of Associate Professor Hu Youfan and Key Laboratory of Nanodevice Physics and Chemistry of Ministry of Education, School of Electronics, Peking University, used carbon nanotube network thin films as semiconductor materials, making full use of the advantages of high mobility and good mechanical properties of carbon nanotube materials, and realized high-performance flexible transistors
through size reduction.
The constructed flexible carbon nanotube transistors with submicron channel lengths can achieve high open-state current of 187μAμm-1 and large transconductance of 123.
3μSμm-1, which can meet the performance requirements
of building ^{high-performance} flexible integrated circuits.
After hundreds of bends, the performance of the device has not changed significantly, showing excellent flexibility and meeting the requirements
of environmental applications on the surface of organisms.
This work shows that the contact resistance of the device (approximately 180 kΩ per carbon tube) remains unchanged during size reduction and is comparable to the contact resistance value of the device on a hard substrate, thus indicating that the limit reduction of flexible carbon tube transistors can have comparable performance
to devices on hard substrates.

Figure 1.
a) Schematic diagram of flexible device and circuit processing flow; b) Flexible devices and circuits are placed on the surface of the contact lens; c) Diagram of device transfer characteristics in bending test of the device

The research group built a ring oscillator on an ultra-thin flexible substrate to characterize the speed of
flexible devices after size reduction.
The constructed ring oscillator achieves an operating frequency of up to 356MHz at an operating voltage of 2.
6V, which is equivalent to a single-stage gate delay of 281ps
.
This work realizes for the first time a high-speed flexible integrated circuit with sub-nanosecond gate delay based on flexible devices, and fully demonstrates the application potential
of flexible carbon nanotube transistors in the field of high-speed, low-power flexible circuits.

Figure 2.
a) Sub-nanosecond delay ring oscillator output spectrogram; b) Comparison of flexible ring oscillators based on various material systems

With the support of the National Natural Science Foundation of China and the National Key Research and Development Program, the above work was published in Nature on November 8 with a paper entitled "Carbon nanotube-based flexible high-speed circuits with sub-nanosecond stage delays" Communications, 13, 6734）； Long Guanhua, a doctoral student at the School of Electronics, Peking University, and Jin Wanlin, a master's student, are co-first authors, and Hu Youfan and Peng Lianmao are co-corresponding authors
.
This series of achievements fully demonstrates the great advantages and application prospects of carbon nanotube materials in flexible integrated circuits, which is expected to be used to build a next-generation personalized diagnosis and treatment and health monitoring platform, and will play an important role
in promoting the advanced medical diagnosis system in the future.