Stanford University develops flexible, stretchable IC and successfully drives Micro LED screens

Small wearable or implantable electronic devices can help monitor health and diagnose disease, but this must be done without aggravating or damaging surrounding cells, soft enough to not scratch or damage tissue, and bent and stretched with tissue when moving.

Source: Stanford University

Stanford University has been studying skin-like stretchable electronic devices for more than a decade, and has finally developed a skin-like IC design and process that is five times smaller than the original version and 1,000 times faster. The research results were also recorded in the journal Nature on 3/13.

Researchers have shown that their flexible integrated circuits (ICs) can now drive Micro LED screens and detect braille arrays that are more sensitive than human fingertips.

Zhenan Bao, a professor of chemical engineering at Stanford University and senior author of the paper, pointed out that for the first time, stretchable integrated circuits have become small and fast enough to meet many applications, and are expected to make wearable sensors and implantable nerve and intestinal probes more sensitive, operate more sensors and reduce power consumption.

▲ An active matrix sensor array connected to a human finger. (Source: Stanford University)

The core of the circuit is a stretchable transistor, which is made of semiconductor carbon nanotubes and soft elastic electronic materials. Unlike silicon, which is hard and fragile, the carbon nanotubes sandwiched between elastic materials have a fish mesh structure, allowing them to be stretched and deformed. Can continue to function. Transistors and circuits and stretchable semiconductor, conductor and dielectric materials are patterned onto a stretchable substrate.

Bao Zhenan said that this is the result of many years of materials and engineering research and development. It is not only necessary to develop new materials, but also to develop circuit design and circuit manufacturing processes. There are many layers stacked on top of each other, and if one layer doesn't work, you have to start from scratch.

In the latest display, researchers packed more than 2,500 sensors and transistors in a space of 1 square millimeter to form an active matrix tactile array with more than ten times the sensitivity of a human fingertip. This sensor array can detect the position and direction of tiny shapes or recognize single words in Braille. According to researchers, when using Braille, only one letter is usually perceived. With such a high resolution, an entire word or even an entire sentence can be perceived with just a touch.

▲ A high-density transistor array attached to a white sesame seed has 1,000 transistors on an area of 1 square millimeter. (Source: Stanford University)

In addition, the researchers also used stretchable circuits to drive Micro LED displays with a refresh rate of 60 Hz. Previous versions could not generate enough current to achieve this goal because the stretchable circuits were small and not fast enough.

Can Wu, a postdoctoral researcher on the research team and co-lead author of the paper, pointed out that preliminary results show that our transistors can drive commercial displays commonly used in computer displays; the high-density, soft, and adaptable sensing array can allow us to have a wide range and high-resolution sensing of human signals, such as signals from the brain and muscles.

But before commercialization, the team still faced some obstacles, such as changes in the electrical characteristics of the circuit caused by body and tissue movements. The team is currently studying designs that can reduce these effects. Bao Zhenan said that this technology can also be used in soft robot technology, giving robots sensing functions closer to humans and making them safer at work.