Solution-processed oxide semiconductors have emerged as a promising alternative to vacuum-deposited counterparts due to their cost-effectiveness, scalability, and compatibility with flexible substrates. Among these, indium-gallium-zinc oxide (IGZO) and zinc oxide (ZnO) are two of the most widely studied materials, often deposited via inkjet printing or spin-coating. These techniques enable large-area fabrication at lower temperatures, making them attractive for next-generation electronics. The performance of solution-processed oxide semiconductors depends heavily on precursor chemistry, annealing conditions, and the resulting film morphology, each of which introduces distinct trade-offs in electrical performance, stability, and uniformity.

Precursor chemistry plays a critical role in determining the quality of solution-processed oxide films. For IGZO, common precursors include indium nitrate, gallium nitrate, and zinc acetate dissolved in solvents such as 2-methoxyethanol or water. The choice of solvent affects the solubility of precursors and the viscosity of the ink, which in turn influences film uniformity during deposition. Additives like ethanolamine or acetylacetone are often used to stabilize the solution and prevent premature precipitation. Similarly, ZnO films are typically synthesized from zinc acetate dihydrate in methoxyethanol, with ethanolamine acting as a stabilizer. The hydrolysis and condensation reactions of these precursors form metal-oxygen-metal networks upon annealing, but residual organic species can degrade film quality if not fully removed.

Annealing is a crucial step in converting precursor solutions into functional semiconductor layers. Thermal treatment eliminates organic residues, promotes densification, and enhances crystallinity. For IGZO, annealing temperatures typically range from 300°C to 500°C, with higher temperatures improving carrier mobility but potentially damaging flexible substrates. In contrast, ZnO often requires lower annealing temperatures (150°C to 350°C), making it more suitable for plastic substrates. The annealing environment also matters; oxygen-rich atmospheres reduce oxygen vacancies, improving stability but sometimes lowering carrier concentration. Rapid thermal annealing (RTA) or microwave annealing can achieve similar results in shorter times, reducing thermal budget and enabling compatibility with temperature-sensitive materials.

The electrical performance of solution-processed oxide semiconductors is strongly influenced by film morphology and defect states. Spin-coated films tend to be more uniform than inkjet-printed layers, which can suffer from coffee-ring effects due to uneven solvent evaporation. However, inkjet printing offers superior patternability and material efficiency. Carrier mobility in solution-processed IGZO typically ranges from 1 to 10 cm²/Vs, compared to 10 to 50 cm²/Vs for sputtered films. This difference arises from higher defect densities, including oxygen vacancies and interfacial traps, in solution-processed layers. ZnO films exhibit similar trends, with solution-processed mobilities of 0.1 to 5 cm²/Vs versus 5 to 20 cm²/Vs for vacuum-deposited counterparts. Despite lower mobility, solution-processed oxides often show comparable on/off ratios (>10⁶) due to their amorphous or nanocrystalline nature, which reduces leakage currents.

Stability is another key consideration. Solution-processed oxides are more prone to environmental degradation, particularly from humidity, due to porous microstructures and residual hydroxyl groups. Passivation layers or polymer encapsulation can mitigate this, but they add complexity to fabrication. Bias stress stability is also inferior to vacuum-deposited films, with threshold voltage shifts often exceeding 1 V under prolonged gate bias. These instabilities stem from charge trapping at grain boundaries or interfacial defects, highlighting the need for improved precursor formulations and annealing protocols.

When comparing solution-processed and vacuum-deposited oxide semiconductors, several trade-offs become apparent. Vacuum methods like sputtering or pulsed laser deposition produce denser films with fewer defects, yielding higher mobility and better stability. However, they require expensive equipment, high-vacuum conditions, and rigid substrates, limiting their scalability. Solution processing, while less precise, enables roll-to-roll manufacturing and compatibility with flexible electronics. The lower thermal budget of solution techniques also allows integration with organic materials or layered heterostructures that would degrade under high-temperature vacuum processing.

Recent advances in precursor design have narrowed the performance gap between solution and vacuum methods. For example, combustion chemistry approaches using urea or acetylacetone as fuel reduce annealing temperatures by releasing energy during precursor decomposition. Aqueous routes employing zinc ammonium complexes yield ZnO films with mobilities approaching 10 cm²/Vs, rivaling some vacuum-deposited layers. Similarly, nanoparticle-based inks minimize shrinkage and cracking during annealing, improving film uniformity. Hybrid strategies, such as combining sol-gel precursors with nanoparticle dispersions, further enhance performance by balancing crystallinity and defect control.

In conclusion, solution-processed oxide semiconductors like IGZO and ZnO offer a compelling combination of low-cost fabrication and moderate performance, suitable for applications where high-throughput and flexibility outweigh the need for ultra-high mobility. Precursor chemistry and annealing conditions are pivotal in determining film quality, with ongoing research focused on optimizing these parameters to match the performance of vacuum-deposited counterparts. While challenges remain in stability and defect management, the scalability and versatility of solution processing make it a viable pathway for next-generation electronics.