Nanocrystalline diamond for Micro-Electro-Mechanical Systems (MEMS)

This project aims to develop high frequency, high quality factor Micro-Electro-Mechanical Systems (MEMS) from Nanocrystalline Diamond (NCD). NCD offers superior performance to silicon for MEMS due to its extreme Young's modulus, but it is also compatible with silicon CMOS technologies, offering a key advantage over other potential MEMS materials. High performance NCD growth and planarization will be optimised for MEMS applications. The realisation of continuous, smooth, pin hole free NCD over large areas exhibiting bulk diamond properties will enable a multitude of applications at drastically reduced cost to currently available bulk diamond technologies. The resulting material will have applications outside the MEMS field such as in tribology, optical coatings, electrochemical electrodes (when doped with boron), heat spreading etc. The development of clean room processing technologies of NCD will allow the fabrication of new devices and result in new ideas exploiting this novel material.

MEMS, biochips, and micro/nano-sensors are one of the fastest growing technology areas, with sales of more than $2.5 billion in 2007 growing to more than $7 billion in 2010. MEMS accounted for the bulk (82.8%) of the microsensor market in 2007. Radio Frequency (RF) MEMS is the principle driving force behind this growth, growing an average 46% between 2008 and 2011 and is predicted to be a billion dollar market by 2012 (Source: Yole Développement). RF MEMS are micron-sized replacements for the dozens of discrete components that make up filters etc in radios and mobile phones. These devices can also be tunable, adding functionality at the same time as reducing power consumption and ultimately cost.

It is clear that mobile telephony is a significant new RF MEMS market as well as aerospace and defense. With some 5 billion mobile phone connections worldwide, the energy consumption of mobile communication devices and base stations is a real concern. The base stations of such systems consume typically between 750W and 3000W. In the UK there are over 52,000 such base stations, consuming power levels somewhere between 39 and 156 megawatts. In Germany the mobile telephony network is estimated to consume the energy production of a moderate size nuclear power station. It is envisioned that the introduction of RF-MEMS into base stations and ultimately mobile handsets will drastically reduce the overall power consumption of the network and extend the range of the overcrowded frequency spectrum. Thus it will have both technological and societal/environmental impacts. In other sectors such as aerospace and defense it is essential for the UK to have its own RF-MEMS technology, as access to US MEMS is subject to ITAR restrictions. This creates a real limit on the technology currently available for HF products in the UK.

The vast majority of MEMS are actually hybrid technologies and thus the integration of diamond is not significantly different from the integration of other MEMS materials. Diamond also offers the possibility of monolithic integration with CMOS, as nanocrystalline diamond can be grown below 400C without detrimental effects on the silicon transistors. Even poly-silicon cannot offer this benefit as growth temperatures are usually of the order of 600C. Thus diamond offers superior integration possibilities than silicon itself due to the possibility of lower temperature growth.

The establishment of a high quality NCD growth facility at Cardiff will have a positive influence on the UK's already world-renowned diamond reputation. In fact, NCD is one of the few areas in the diamond field where the UK does not dominate, and thus the bolstering of this area is timely indeed. There are many applications of NCD besides MEMS, such as electrochemistry (waste water treatment, bio-sensing etc), tribology (hard, low wear and low friction coatings), transparent optical coatings, heat spreaders etc [2]. Thus the development of NCD growth and processing for MEMS will result in material of multiple uses and therefore other projects will certainly be facilitated by this capability. It is envisioned that the foundation of state of the art NCD material growth facilities will act as a seed corn for future funding within the EU FP7 program in collaboration with such laboratories as CEA (Saclay, France) and the Walter Schottky Institute (Munich, Germany).

The publication of results from high performance RF-MEMS from NCD will draw significant attention to the material from the RF sector, which without this incubation, it is unlikely that UK companies would start to develop diamond MEMS themselves. The UK is the leading producer of CVD diamond, Element6 being the largest diamond CVD operation worldwide (letter of support attached).