A transistor has been made from linen thread, enabling the creation of electronic devices made entirely of thin threads that could be woven into fabric, worn on the skin, or implanted surgically for diagnostic monitoring. The flexible electronic devices could enable a range of applications that conform to different shapes and allow free movement without compromising function.
The thread-based transistors (TBTs) can be made into all-thread-based logic circuits and integrated circuits. The circuits replace the last remaining rigid component of many current flexible devices and when combined with thread-based sensors, enable the creation of completely flexible, multiplexed devices.
Most flexible electronics pattern metals and semiconductors into bendable structures or use intrinsically flexible materials such as conducting polymers. Compared to electronics based on polymers and other flexible materials, thread-based electronics have greater flexibility, material diversity, and the ability to be manufactured without the need for cleanrooms. The thread-based electronics can include diagnostic devices that are extremely thin, soft, and flexible enough to integrate seamlessly with the biological tissues that they are measuring.
Making a TBT involves coating a linen thread with carbon nanotubes, creating a semiconductor surface through which electrons can travel. Attached to the thread are two thin gold wires — a “source” of electrons and a “drain” where the electrons flow out (in some configurations, the electrons can flow in the other direction). A third wire, called the gate, is attached to material surrounding the thread so that small changes in voltage through the gate wire allow a large current to flow through the thread between the source and drain — the basic principle of a transistor.
An electrolyte-infused gel is used as the material surrounding the thread and connected to the gate wire. The gel is made up of silica nanoparticles that self-assemble into a network structure. The electrolyte gel (or ionogel) can be deposited onto the thread by dip-coating or rapid swabbing. In contrast to the solid-state oxides or polymers used as gate material in classical transistors, the ionogel is resilient under stretching or flexing.