For the functionality of a touch screen, an essential component of a smartphone, a layer with a good electrical conductivity in a combination with optical transparency is needed. Nowadays, such layers are typically made with Indium tin oxide (ITO).
However, challenges for the industry are that the supply of indium is limited, that the ITO layer is expensive and fragile, and that the ITO manufacturing process is unfriendly for the environment. Therefore, the display industry is widely looking for alternative solutions.
New nanoprinting technology could bring such a solution. Conductive and optically transparent layers could be made by printing a mesh of wires. Obviously, such wires need to be very thin while offering a high conductivity. An additional benefit is that such printed wires are more suitable for use on flexible substrates, which fits well with the trend of introducing flexible displays. Printed wires with nanoscale dimensions, made using the novel process called Near-Field Electro-Hydrodynamic Nanowire Printing (ENP), promise to be the right choice for this. The introduction of printed solutions in the display industry fits well in the industry trend for adopting Additive Manufacturing processes.
The principle behind ENP is known for decades and is used for producing filters and non-wovens for the textile industry. By electrospinning, sub-micrometer thin wires can be produced. A typical electrospinning setup is configured by a syringe pump, high voltage supply, needle, and collector. Traditionally a rather chaotic random deposition of fibres is deployed on a relative far-field spinning distance of about 300mm and under 20K to 30K electrostatic voltage. Relatively new in the ENP process is the near-field printing at about 10 to 20 mm distance and voltages up to about 4 kV. This enables a controlled deposition of fibres for patterning and masking for a lithographic process or for direct deposition of functional materials.
Within the E-Nanoprint-Pro project, DoMicro, Coatema, microTEC, tec-V and TechToBizz cooperate on the development of a nanoprinter prototype, a desktop system for printing fibers in lines featuring nanoscale widths. The project is performed within the scope of the RocKET Reloaded program, a program for regional collaboration on key enabling technologies by German and Dutch companies. The program has been of great support for gathering the partners across borders, for getting an outlook on promising applications in the market, and for accelerating the project.
Close-up of the printhead in DM50 ENP platform
Next to the development of the prototype, the project partners are investigating a couple of promising applications that can be enabled by this new technology. An example of such an application is the printing of conductive wires for microfluidics devices. Printing such wires on a nanoscale allows significant miniaturization of such devices, which could enable the use of the device within the body. Furthermore, the project anticipates on the introduction of nanoprinting on an industrial scale.
Further promising applications in the industry are foreseen in electronics, life science, and energy. Examples include conductive electrodes for OLED displays as well as transistors on flexible substrates.
A major subject in the project is process development, which is required for bringing this very new printing process to a reliable and controllable level. Proper and stable process settings have been found during the course of the project for printing nanowires in a controllable way on conductive and isolating substrates.
PEO nanowires op Cu substrate. PEO nanowires on PET substrate
Line width ~20 µm, spacing 100 µm Line width ~12 µm, spacing 200 µm
These results show that the new nanoprinter is suitable for use in research laboratories with ambitions to study the deposition of advanced materials. Mid 2021, DoMicro is planning the market introduction of this first ENP nanoprinter.