First transistors made of nanocrystal ‘inks’ produced

Posted Jun 8, 2017 by Tim Sandle
To design transistors to be built into flexible or wearable applications, researchers from the University of Pennsylvania have developed a process using nanocrystal “inks.”
Because this process works at relatively low temperatures  many transistors can be made on a flexibl...
Because this process works at relatively low temperatures, many transistors can be made on a flexible backing at once.
University of Pennsylvania
The production of transistors is a complex process and it needs a specialized environment (high temperature) and sophisticated equipment (capable of producing a high vacuum). To make the process of producing transistors faster, cheaper and more reliable, researchers have developed a method of sequentially depositing components in the form of liquid nanocrystal “inks.”
A further advantage with the process is that it will allow electrical components to be built into flexible or wearable applications. This is because the lower-temperature process is compatible with a wide array of materials and it can be applied to larger areas. This fits in with the design specifications for wearable electronics.
Transistors are key to electronic devices; the transistor is the fundamental building block of electronics, being used to build circuits capable of amplifying electrical signals. Transistors are also used to switch signals between the binary notations of 0s and 1s, which lies at the heart of digital computation. Transistor fabrication is a highly complex process, however, requiring high-temperature, high-vacuum equipment. Transistors are composed of a semiconductor material, typically with at least three terminals for connection to an external circuit.
With the process of developing nanocrystal-based field effect transistors, these were created onto flexible plastic backings using a technique called spin coating. Longer-term 3-D printers will be used. The method starts by taking nanocrystals with the electrical qualities needed for a transistor. These crystals are dispersed in a liquid, creating nanocrystal inks. In all four different inks were created:
A conductor (silver),
An insulator (aluminum oxide),
A semiconductor (cadmium selenide)
A conductor combined with a dopant (a mixture of silver and indium), which determines.whether the device transmits a positive or negative charge.
Each ink is a type of colloid, similar to the ink found in an inkjet printer. The researchers developed the means to lay these inks down onto a surface to form functional transistors.
The new process is described in the journal Science, with the supporting paper titled "Exploiting the colloidal nanocrystal library to construct electronic devices."