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Microelectromechanical Systems from Nanocrystalline Diamond

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Diamonds are microelectronics' best friend

Diamonds do not have to be large to be valuable, at least to scientists. Nanocrystalline diamond (NCD), superior to silicon for use in microelectromechanical systems (MEMS), was exploited in novel MEMS devices, attracting large industrial investment.

Industrial Technologies

The resistance of diamond to elastic (reversible) shape changes under loading (high Young's modulus) makes possible very-high–frequency resonators with high-quality factors. Conveniently, NCD is also compatible with silicon complementary metal oxide semiconductor technology, a key advantage over many other MEMS materials. Scientists launched the EU-funded project 'Microelectromechanical systems from nanocrystalline diamond' (DIAMEMS) largely to optimise NCD growth and planarisation. The ability to produce smooth and continuous NCD covering large areas and exhibiting bulk diamond properties could significantly reduce the price of current applications relying on bulk diamond. It could also open the door to new applications outside the MEMS field, such as tribological coatings. Optimised nucleation and chemical vapour deposition at relatively low temperatures (400 degrees Celsius) led to uniform NCD films with thicknesses of 30 nm. Planarisation to very-low–roughness values via chemo-mechanical polishing resulted in a high-profile publication. Integration of aluminium nitride (AlN), a ceramic widely used in microelectronics, was accomplished in two different ways. The first more traditional method growing AlN on the polished NCD surface led to surface acoustic wave devices (often used as high-frequency filters or oscillators) operating at frequencies in excess of 15 GHz. As high-precision pressure sensors capable of withstanding harsh environments, their presentation resulted in investment by a very large telecommunications company. This approach resulted in three more publications. The second method manipulated the voltage difference between the surface of the NCD seeds and the bulk deposition solution (zeta potential). Removing the planarisation step reduces costs considerably. This approach led to demonstration of high-frequency MEMS. A total of six publications resulted from work on AlN and NCD. Doping or addition of impurities such as boron can transform NCD from one of the best electrical insulators to a superconductor. Investigations exploiting this phenomenon with MEMS led to demonstration of a superconducting nanoresonator and yet another publication. DIAMEMS fully demonstrated the utility of nano-scale diamond in electronic devices, opening the door to major cost reductions in a number of fields. As seen by major industrial investment in continued development, the outcomes will have important socioeconomic impact.

Keywords

Nanocrystalline diamond, microelectromechanical systems, MEMS, planarisation, superconductor

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