Stanford University develops flexible, stretchable IC to successfully drive Micro LED screens

small wearable or implantable electronic devices can help monitor health and diagnose disease, but to do so, they must not aggravate or damage surrounding cells, be soft enough to not scratch and injure tissue, and bend and stretch with tissue when moving.

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

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

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

▲ Active matrix sensor arrays connected to human fingers. (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 hard and brittle silicon, the carbon nanotubes sandwiched between elastic materials have a fish network structure, making them continue to function when stretched and deformed. Transistors and circuits and stretchable semiconductor, conductor and dielectric materials are patterned onto the stretchable substrate.

Bao Zhenan said that this is the result of years of material and engineering research and development. It is not only necessary to develop new materials, but also to develop circuit design and manufacturing processes. There are many layers added together, if one layer does not work, you must start from the beginning.

In the latest demonstration, the researchers packed more than 2,500 sensors and transistors into a 1 mm² space 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 orientation of tiny shapes, or identify single words in a dotted word. According to the researchers, braille is usually only able to perceive one letter, and with such a high resolution, you can perceive an entire word, or even an entire sentence, with a single touch.

▲ A high-density array of transistors attached to a grain of white sesame, with 1,000 transistors on the 1 mm² area. (Source: Stanford University)

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

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

However, before commercialization, the team still faces some obstacles, such as changes in the electrical characteristics of the circuit caused by body and tissue movement. 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 to give robots closer to human sensing functions and safer work