A method has been discovered to enhance the energy efficiency of 3D printing technologies for transistors.

The study published in the journal Nanosystems: Physics, Chemistry, Mathematics. The journal holds the First level of the national ranking system for scientific publications — the White List.

Laptops, smartphones, and other complex devices contain numerous electronic components, including transistors. Transistors enable the switching of individual elements within an electrical circuit, as well as amplifying or transforming electrical signals, for instance, into digital or audio formats.

The first transistor, measuring one centimeter, was created in 1947. Subsequent technological advancements have focused on miniaturizing devices. Modern transistors are now measured in nanometers. The most cost-effective and promising method for their production is three-dimensional inkjet printing. Special inks are required for printing. Firstly, they must remain in liquid form while passing through the printer's print head, and then quickly solidify when applied to the substrate. Secondly, it is essential for the hardened mass to selectively conduct electricity, meaning it must act as a semiconductor.

To meet these requirements, scientists from MIPT, SPbU, and YUUrGU, in collaboration with colleagues from Tajikistan, investigated the process of producing a complex oxide of indium, gallium, and zinc using the sol-gel method. Implementing this method involves first synthesizing a sol, then transforming it into a gel through drying and thermal treatment. A sol, or colloidal solution, is a liquid in which nanoparticles are distributed and can move freely.

It is well known that indium, gallium, and zinc bind ions and molecules of other substances, referred to as ligands, from solutions. The products of these reactions are various complexes, meaning compounds whose composition cannot be explained by the theory of chemical bond formation through shared electron pairs. The composition and properties of the complexes depend on the conditions under which the reactions are conducted. The scientists studied these dependencies and determined the conditions for synthesizing nanoparticles that are homogeneous in composition and represented by insoluble complexes of the aforementioned metals. In other words, a series of sols was obtained through intense mixing in a 1:3 ratio of aqueous solutions of metal salts and organic substances: citric and oxalic acids, ethylene glycol, glycerol, urea, and sucrose.

The transition from sol to gel was achieved by evaporating the liquid, during which the nanoparticles lost mobility and formed a spatial framework. Subsequently, the gel exhibited the properties of a solid body: lack of fluidity, retention of shape, strength, and elasticity. The gel was dried for 6–22 hours, gradually increasing the temperature from 100 to 500 degrees. After that, the dried gel, ground into powder, was sintered at 700–1450 degrees for 12–24 hours and cooled in air.

Using X-ray phase analysis, the scientists determined the chemical composition of the obtained samples, while their surfaces were examined using scanning and transmission electron microscopy methods. The difference between the methods lies in that scanning electron microscopy is designed to capture an enlarged image of the surface by reflecting a beam of electrons off it, whereas transmission electron microscopy does so by allowing a beam of electrons to pass through the sample.

It has been established that the use of ethylene glycol and glycerol, along with drying at 500 degrees, allows for the synthesis of X-ray amorphous compounds. Subsequent sintering at 700–900 degrees forms a layered structure in the samples, similar to that of the complex oxide of ytterbium and iron. The crystal lattice of the samples is rhombohedral. The lattice parameters depend on the composition and shape of the material, reaching their minimum values (a = 3.295 Å, c = 26.070 Å) when heated to 1450 degrees for 24 hours.

Microscopic investigations revealed that the obtained samples consist of agglomerates of nanoparticles lacking specific spatial organization. On the surfaces of the samples, there are clusters of particles measuring 20–30 nanometers, as well as areas comprised of smaller particles. It should be noted that more precise images were obtained using transmission electron microscopy.

“To date, there is no justification for the use of specific organic ligands for the synthesis of indium, gallium, and zinc complex oxide via the sol-gel method,” said Denis Vinnik, head of the laboratory of semiconductor oxide materials at MIPT. “The goal of our research was to find reagents that would allow for the production of nanoparticles of this oxide at the lowest possible temperatures.”

“While working with glycerol, we synthesized nanoparticles of the complex oxide of indium, gallium, and zinc at 500 degrees and determined the type and parameters of the crystal lattice of this oxide,” added Gleb Zirnik, junior researcher at the laboratory of functional oxide materials for microelectronics at MIPT.

The results obtained by the research group will enable the targeted selection of organic reagents for the synthesis of indium, gallium, and zinc complex oxide using the sol-gel method, thereby increasing the accessibility of transistor printing technologies by reducing energy costs.

The work was carried out with financial support from the Russian Science Foundation.