Chemical solution deposition (CSD) is one of the most common processes for the fabrication of thin films, specifically oxide films <ref>Handbook of Sol-Gel Science and Technology: Processing, Characterization, and Applications – Volume 1: Sol-Gel Processing. Hiromitsu Kozuka, Sumio Sakka. Kluwer Academic Publishers. Norwell, MA 2005</ref>. It consists of the deposition of a solution onto a surface during which chemical reactions occur in order to synthesize the desired material. The final crystalline material is achieved after a heat treatment. CSD was originally developed in the mid 1980s <ref>Robert W. Schwartz Chemical Solution Deposition of Perovskite Thin Films Chem. Mater. 1997, 9, 2325-2340</ref>. Fukushima and Budd were two of the early engineers who studied the CSD process and made important findings <ref>Chemical Processing of Ceramics 2nf Ed. Burtrand Lee and Sridhar Komarneni. Taylor and Francis, Boca Raton, FL, 2005, 714-742</ref>. They showed that it was possible to achieve bulk material properties in ferroelectric thin films made by this process ^[2,3]. CSD consists of three main processing steps <ref>K. Knoth, S. Engel, C. Apetrii, M. Falter, B. Schlobach, R. Huhne, S. Oswald, L. Schultz, B. Holzapfel. Chemical solution deposition of YBa₂Cu₃O_7-x coated conductors. Current Opinion in Solid State and Materials Science. 2006,10, 205-216</ref>.

A. Synthesis of the Precursor Solution: Combining the essential chemical ingredients required for the formation of the desired phase and appropriate to the chemical process chosen; all the necessary cations that are required to synthesize the material must be present in a homogeneous solution ^[3]

B. The Coating or Deposition Process: Creating the homogeneous precursor layers on the desired substrate

C. Heat Treatments: Converting the homogeneous, amorphous as deposited layers into the final crystallized phase

There are many advantages CSD has over other thin film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), sputtering, or molecular beam epitaxy (MBE). In chemical solution deposition, control of the exact composition on a molecular level (local stoichiometry) is possible ^[1,3]. It is easy to incorporate multiple elements into the solution, which is a large advantage when processing complex oxide films <ref>Second-Generation HTS Conductors. Amit Goyal. Kluwer Academic Publishers: P. Clem. Solution Deposition of YBa₂Cu₃O_7-d Coated Conductors. 2005</ref>. CSD is one of the simplest and least expensive thin film fabrication processes because typically no vacuum system or elaborate deposition chamber is required. Low temperature synthesis of the thin films is possible as well as being able to coat a large deposition area ^[1,5]. The vaporization or ionization of the solutions is not required for deposition. It produces films of high purity and good homogeneity ^[1]. CSD is a process which can be modified quickly in order to synthesize a new material system that may not have been studied in a thin film form ^[3].

CSD also has some disadvantages compared to conventional thin film processing. It is difficult to deposit layers less than 30nm thick. Usually only polycrystalline films are grown with this method. It is more difficult to grow oriented or epitaxial films ^[3]. CSD is generally not found in manufacturing.

A. Synthesis of the Precursor Solution

There are multiple routes that can be taken to prepare the chemical solution. CSD can be separated into different categories. For the preparation of ferroelectric materials the three categories include metal-organic decomposition (MOD), sol-gel, and chelation ^[3]. According to some scientists chelation is categorized as a form of the sol-gel method because it is quite similar ^[4]. Therefore the sol-gel process can be subcategorized into different routes depending on the exact chemistry involved. Modified versions include the chelate process, the nitrate-citrate route, and the Pechini method ^[4]. Each CSD route can be characterized by the chemical reaction and the type of precursors used to make the solution.

Most CSD solutions are created using metal-organic compounds as the main source of cations. Before discussing the different CSD routes, a quick explanation of the different metal-organic precursors used will be given. The main solution precursors can be divided in to three classes ^[3].

a.