Recently, iChEM Researcher Rong Cao, Professor at Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, have developed a facile strategy by which interpenetrated, crystalline metal-organic framework films were deposited onto conductive metal-plate anodes via in situ temperature-controlled electrochemical assembly. (Nature Commun. 2016, 7, 1-8. DOI:10.1038/ncomms11830). The resulting MOF thin films exhibit enhanced dielectric properties compared to their bulk powders MOFs. This study demonstrates the successful implementation of the rational design of metal-organic framework thin films on conductive supports with high-performance dielectric properties.

Exploitation of new high-k materials that allow for a proportional increase in the gate thickness is very important for the design of gate dielectric materials. Currently, conventional silicon-based electronics have been dominating as main dielectric materials; however, their relatively low dielectric constant and large static power dissipation limit their practical application. Inorganic hafnium dioxide (HfO₂) and zirconium dioxide (ZrO₂) have been widely studied as dielectric materials with high-k values. However, these materials are too brittle to be compatible with substrates, and the deposition techniques typically require high temperatures and expensive vacuum equipment. Organic polymers have deposited onto flexible plastic substrates to address this issue; however, organic polymers thin films typically suffer from low dielectric constants. Recently, organic and inorganic hybrid materials have emerged as a new type of electronic material that combines the distinctive properties of the high-k of metal oxides and the flexibility of organic molecules. However, one of the major challenges in the fabrication of these films is the low compatibility of the organic and inorganic components, which typically leads to the generation of defects in the resulting films and a significant decrease in device performance.

Prof. Cao’s research team based on a flexible ligand (1, 3, 5-tris[4-(carboxyphenyl)oxamethyl]-2, 4, 6-trimethylbenzene(H₃TBTC)), designed and synthesized a novel and interpenetrated MOF. Subsequently, they deposited the synthesized MOF onto conductive substrates via electrochemical techniques. It can be found that the dielectric constant of thin films was three times larger than their bulk powder MOFs. More important, as shown by the experiment test and theoretical calculation of the typical MOFs such as MOF-123 and MOF-246 couples, the interpenetrated structure can improve the dielectric constant of thin films. The measurement of mechanical properties and leakage current shows that the prepared thin films have a high mechanical properties and insulating properties.

This work was supported by the 973 Program, NSFC, "Strategic Priority Research Program" of the Chinese Academy of Sciences and 2011-iChEM post-doctor funding.

Paper link:
http://www.nature.com/ncomms/2016/160610/ncomms11830/full/ncomms11830.html