Researchers develop novel form of hafnium oxide

7 February 2012 LONDON – Researchers at the University of Cambridge have developed a novel form of hafnium oxide, a compound used at the leading-edge of integrated circuit production and being investigated for use in novel non-volatile memory prototypes. The…

7 February 2012

LONDON – Researchers at the University of Cambridge have developed a novel form of hafnium oxide, a compound used at the leading-edge of integrated circuit production and being investigated for use in novel non-volatile memory prototypes.

The university is now looking for partners to help it make money from licensing companies to use the material.

A research team working under Andrew Flewitt in the Department of Engineering at the university has developed a novel form of hafnium oxide (HfO2) with a dielectric constant higher than 30 compared with the conventional value of 20 to 25 for amorphous and crystalline forms of the compound. The novel form of the material is expected to find use in plastic electronics, high-volume semiconductor manufacturing, optical coatings and for the creation of more efficient solar cells.

Hafnium oxide is best known for its use in high-K metal gate (HKMG) stacks within the transistors of nanoelectronic manufacturing processes. The increased dielectric constant should enable further device miniaturization as well as opening up possibilities for next generation electronic and optoelectronic devices, the research group said.

Andrew Flewitt with higher-k hafnium oxide film

The key to progress made by Flewitt and his team is the adoption of a refinement of conventional sputtering called as HiTUS (High Target Utilization Sputtering). The material is produced using a room-temperature, high-deposition rate process, making it suitable for plastic electronics and high-volume semiconductor manufacturing.

Metal oxides are usually produced on substrates by sputtering, a process by which some of the atoms of an electrode are ejected as a result of bombardment by heavy positive ions. However, it is difficult to control precisely the energy of the deposition process, and hence the material properties such as defect density.

The use of HiTUS has allowed the creation of alternative amorphous form of hafnium oxide, according to the research team, with a higher dielectric constant than the previously known form.

Hafnium oxide forms in a number of different crystalline and polycrystalline structures: monoclinic, cubic and orthorhombic. However, for electronics work amorphous hafnium oxide is desirable as polycrystalline grain boundaries act as conduction paths through the material and reduce the resistivity. Until now amorphous hafnium oxide has had dielectric constant of around 20.

“Most people thought that all amorphous hafnium oxide had to exist in the monoclinic-like phase,” said Flewitt, in a statement. “What we’ve shown is that it can exist and does exist in a cubic-like phase. This is similar to amorphous carbon, where you can get diamond-like properties out of amorphous carbon material.”

Amorphous dielectrics are more homogenous than other forms, allowing improved uniformity from one device to another, and the absence of grain boundaries results in higher effective resistivity, as well as less optical scatter.

Cambridge Enterprise, the University’s commercialization group, said it is seeking partners for collaborative development and licensing of the material.