In this Progress Report we provide an update on recent developments in inkjet printing technology and its applications, which include organic thin-film transistors, light-emitting diodes, solar cells, conductive structures, memory devices, sensors, and biological/pharmaceutical tasks. Various classes of materials and device types are in turn examined and an opinion is offered about the nature of the progress that has been achieved.

Inkjet Printing—Process and Its Applications

Efforts to adapt and extend graphic arts printing techniques for demanding device applications in electronics, biotechnology and microelectromechanical systems have grown rapidly in recent years. Here, we describe the use of electrohydrodynamically induced fluid flows through fine microcapillary nozzles for jet printing of patterns and functional devices with submicrometre resolution. Key aspects of the physics of this approach, which has some features in common with related but comparatively low-resolution techniques for graphic arts, are revealed through direct high-speed imaging of the droplet formation processes. Printing of complex patterns of inks, ranging from insulating and conducting polymers, to solution suspensions of silicon nanoparticles and rods, to single-walled carbon nanotubes, using integrated computer-controlled printer systems illustrates some of the capabilities. High-resolution printed metal interconnects, electrodes and probing pads for representative circuit patterns and functional transistors with critical dimensions as small as 1 μm demonstrate potential applications in printed electronics.

High-resolution electrohydrodynamic jet printing

Solution-deposited metal oxides show great potential for large-area electronics, but they generally require high annealing temperatures, which are incompatible with flexible polymeric substrates. Combustion processing is now reported as a new low-temperature route for the deposition of diverse metal oxide films, and high-performance transistors are demonstrated using this method.

Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing

We demonstrate inkjet printing as a viable method for large-area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to ∼95 cm2 V–1 s–1, as well as transparent and conductive patterns, with ∼80% transmittance and ∼30 kΩ/□ sheet resistance. This paves the way to all-printed, flexible, and transparent graphene devices on arbitrary substrates.

/pdf/inkjet-printed-graphene-electronics-57uspbuxaf.pdf

Inkjet-printed graphene electronics.

We demonstrate ink-jet printing as a viable method for large area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-Methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to~95cm^2V^(-1)s(-1), as well as transparent and conductive patterns, with~80 % transmittance and~30kOhm/sq sheet resistance. This paves the way to all-printed, flexible and transparent graphene devices on arbitrary substrates

Ink-Jet Printed Graphene Electronics

The manufacture of silicon semiconductor devices involves complicated photolithography and expensive machinery, so many researchers are seeking alternative semiconductor materials that can be handled by simple processes such as spin-coating or printing. Organic semiconductors are the most promising candidates but they still lack performance and reliability. Shimoda et al. have taken a different approach, printing a silicon transistor itself, not a substitute. They successfully fabricated polycrystalline silicon transistors by spin-coating a novel liquid precursor. This solution-based approach can also be adapted for ‘ink-jet’ printing of transistors. The development of a process whereby silicon can be prepared from a liquid allows the printing of semiconductor devices directly from solution. The use of solution processes—as opposed to conventional vacuum processes and vapour-phase deposition—for the fabrication of electronic devices has received considerable attention for a wide range of applications1,2,3,4,5,6,7, with a view to reducing processing costs. In particular, the ability to print semiconductor devices using liquid-phase materials could prove essential for some envisaged applications, such as large-area flexible displays. Recent research in this area has largely been focused on organic semiconductors8,9,10,11, some of which have mobilities comparable to that of amorphous silicon11 (a-Si); but issues of reliability remain. Solution processing of metal chalcogenide semiconductors to fabricate stable and high-performance transistors has also been reported12,13. This class of materials is being explored as a possible substitute for silicon, given the complex and expensive manufacturing processes required to fabricate devices from the latter. However, if high-quality silicon films could be prepared by a solution process, this situation might change drastically. Here we demonstrate the solution processing of silicon thin-film transistors (TFTs) using a silane-based liquid precursor. Using this precursor, we have prepared polycrystalline silicon (poly-Si) films by both spin-coating and ink-jet printing, from which we fabricate TFTs with mobilities of 108 cm2 V-1 s-1 and 6.5 cm2 V-1 s-1, respectively. Although the processing conditions have yet to be optimized, these mobilities are already greater than those that have been achieved in solution-processed organic TFTs, and they exceed those of a-Si TFTs (≤ 1 cm2 V-1 s-1).

Solution-processed silicon films and transistors.

There are provided a silicon-film-forming composition containing silicon particles and a dispersion medium and a method for forming a silicon film by forming a coating film of the silicon-film-forming composition on a substrate and subjecting the coating film to instantaneous fusion, a heat treatment or a light treatment. According to the composition and the method, a polysilicon film with a desired thickness which may be used as a silicon film for a solar battery can be formed efficiently and easily.

Composition for forming silicon film and method for forming silicon film

It is an object of the present invention to provide a high order silane composition that contains a polysilane having a higher molecular weight than conventionally, this being from the viewpoints of wettability when applying onto a substrate, boiling point and safety, and hence in particular enables a high-quality silicon film to be formed easily, and also a method of forming an excellent silicon film using the composition. The present invention attains this object by providing a high order silane composition containing a polysilane obtained through photopolymerization by irradiating a solution of a photopolymerizable silane or a photopolymerizable like-liquid silane with ultraviolet light. Moreover, the present invention provides a method of forming a silicon film comprising the step of applying such a high order silane composition onto a substrate.

High order silane composition, and method of forming silicon film using the composition

We have developed a liquid precursor that can be used in a solution process to form n-type doped silicon films. This precursor is based on phosphorus-doped hydrogenated polysilane synthesized by photo-copolymerizing cyclopentasilane and white phosphorus. By spin-coating this precursor, we have prepared n-type amorphous silicon films and polycrystalline silicon films with resistivities of 6.5–27 Ωcm and 2.0–10 mΩcm, respectively.

https://iopscience.iop.org/article/10.1143/JJAP.46.L886/pdf

Spin-on n-Type Silicon Films Using Phosphorous-doped Polysilanes

A silane polymer is disclosed which has a larger molecular weight in view of boiling point, safety, and wetting property in case when it is applied to a substrate. In particular, a composition is disclosed which enables to form a good silicon film easily. A composition for forming a silicon film is disclosed which contains a silane polymer obtained by irradiating a photopolymerizable silane compound with light in a specific wavelength range for causing photopolymerization thereof. A method for forming a silicon film is also disclosed wherein such a composition is applied to a substrate and then subjected to heat treatment and/or photo treatment.

Haruo Iwasawa

Papers

Solution-processed silicon films and transistors.

Composition for forming silicon film and method for forming silicon film

High order silane composition, and method of forming silicon film using the composition

Spin-on n-Type Silicon Films Using Phosphorous-doped Polysilanes

Silane polymer and method for forming silicon film