Marked Cofuel Tuning of Combustion Synthesis Pathways for Metal Oxide Semiconductor Films

Abstract

tors (TFTs) because of their high optical transparency, large electron mobility, mechanical flexibility, and high electrical uniformity over large areas. [1] During the past few years, multiple display manufacturers have implemented large-scale production of active-matrix organic lightemitting diode and liquid crystal displays driven by amorphous indium gallium zinc oxide (a-IGZO) TFTs. [2] While currently the IGZO TFTs are being fabricated using conventional sputtering and subtractive photolithographic processes, a-MO semiconductors are potentially solutionprocessable and printable, which should reduce fabrication costs and enable TFT array/circuit printing on flexible plastic substrates. [3] However, solution routes to high-performance amorphous as well as polycrystalline MO films typically require high temperature annealing (>400 °C) of the printed/coated MO precursor films to effect sufficient metal-oxygen-metal (M-O-M) lattice densification and impurity elimination for acceptable charge transport and TFT performance stability. [4] In pioneering studies, complementary lowthermal budget processes have reduced film processing temperatures to as low as 150-250 °C, depending on the particular MO. [5] However, the electron mobilities achieved at these low temperatures (150-250 °C) for technologically relevant IGZO devices on 300 nm SiO 2 /Si wafers are far lower (1-3 cm 2 V −1 s −1 ) than those achieved for Ga-free compositions. Low temperaturefabricated MO TFTs typically suffer from inferior bias-stress stability (large threshold voltage shifts), which is currently the greatest obstacle to their commercialization. Furthermore, although some low-thermal budget processes have provided a significant stepping stone in MO performance evolution, they also have limitations. For example, deep ultraviolet processes accelerate the degradation of plastic substrates and must be carried out under inert atmosphere to prevent reactive/toxic ozone formation, [5b] while approaches based on metal alkoxide precursors require labor-intensive, costly syntheses of unstable organometallic precursors for all required metal ions. [6] Another approach to low-temperature MO semiconductor film processing is combustion synthesis (CS), which has traditionally employed an exothermic reaction between an oxidizer and a fuel in a liquid metal-organic precursor formulation. [5d,7] Thin-film combustion synthesis (CS), driven by the exothermic reaction of liquid fuel+oxidizer+metal precursors is an important methodology for growing smooth, transparent, amorphous, and polycrystalline metal oxide (MO) films at low temperatures. In optimized MO CS precursors, the fuel combines a primary coordinating ligand [e.g., acetylacetone (AcAcH)] with an additional cofuel. Several studies suggest a structure-property relationship between the resulting MO film composition/microstructure and macroscopic charge transport characteristics. However, the structural and compositional details of solution-phase precursors remain poorly defined. Here a diverse serie...

Photonic curing of solution-deposited ZrO2 dielectric on PEN: a path towards high-throughput processing of oxide electronics

“…In the solution-combustion method, fuel and oxidizer included in the chemical precursors provide some of the energy required for the formation of metal-oxide bonds, reducing the amount of thermal energy required to convert the precursors to oxides 13,16 . Conversion of combustion films still requires heating the substrate and film to a relatively high temperature of 250-300°C [17][18][19] for at least 20 min plus additional time for heating and cooling. This is repeated for each layer of oxide deposited; typically, multiple layers for each material (conductor, semiconductor, or dielectric) are required.…”

Trends in Low‐Temperature Combustion Derived Thin Films for Solution‐Processed Electronics

“…In an investigation, a range of co-fuels has been employed with primary acetylacetone. [65,66] The improvement in the amount of heat energy liberated from the exothermic reaction (ΔH exo ), due to the presence of co-fuels, is greater . Adapted with permission.…”

“…In an investigation, a range of co‐fuels has been employed with primary acetylacetone. [ 65,66 ] The improvement in the amount of heat energy liberated from the exothermic reaction (Δ H exo ), due to the presence of co‐fuels, is greater than those with only acetylacetone. Also, various co‐fuels obey a linear relationship between Δ H exo and TFT μ (Figure 16b).…”

“…Also, various co‐fuels obey a linear relationship between Δ H exo and TFT μ (Figure 16b). [ 66 ] Note that excess co‐fuel in the system can act adversely and reduce the performance of TFTs due to carbonaceous impurity. Moreover, the precursors without a primary fuel also show exothermic combustion response; the presence of an organic solvent serves the purpose of fuel as well.…”

“…(Note: Sor: sorbitol, Gly: glycine, VC: l-ascorbic acid, Ery: erythritol, Glu: glucose, Xyl: xylitol, Suc: sucrose). Adapted with permission [66]. Copyright 2019, Wiley-VCH.…”