Hafnia

Hafnia is the common name for hafnium oxide, a binary inorganic compound with the formula HfO2. It is a white to off-white solid with a very high melting point of about 2755°C and a density near 9.68 g/cm3. At room temperature hafnia crystallizes in the monoclinic form, with higher-temperature polymorphs (tetragonal and cubic) accessible as it is heated. Hafnia has a wide band gap of about 5.7 eV, and in thin films its dielectric constant can be around 25 depending on processing.

The name hafnia is closely related to hafnium, whose name derives from Hafnia, the Latin name for Copenhagen, where the element was discovered in 1923. Hafnium oxide does not occur as a pure natural mineral; hafnium is typically obtained as a byproduct of zirconium refining, and hafnia is usually produced synthetically as the oxide. Industrial production methods include oxidation of hafnium metal or hydrolysis of hafnium halides. Thin films of HfO2 are deposited by atomic layer deposition, chemical vapor deposition, or sputtering.

Applications of hafnia are predominantly in electronics as a high-k dielectric for semiconductor devices. It is used as a gate insulator in advanced CMOS transistors and in other capacitive structures, often in combination with silicon to replace silicon dioxide as devices scale down. Hafnia is also employed as a ceramic material and in optical coatings and UV-related applications. Doping with elements such as silicon, aluminum, or lanthanides can modify its phase stability and electrical properties.

Safety considerations are generally modest, as hafnia is chemically inert and hafnium oxide has low acute toxicity. Standard industrial hygiene practices apply to dust formation and handling of powders.