Nanocrystalline Diamond as a Dielectric for SOD Applications
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1039-P13-02
Nanocrystalline Diamond as a Dielectric for SOD Applications Mose Bevilacqua1, Niall Tumilty1, Aysha Chaudhary1, Haitao Ye1, James E Butler2, and Richard B Jackman1 1 London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, United Kingdom 2 Gas/Surface Dynamics Section, Naval research laboratories, 4555 Overlook Ave. St., Washington, WA, DC 20375 ABSTRACT
Nanocrystalline diamond (NCD) has been grown on oxide coated silicon wafers by microwave plasma assisted chemical vapour deposition using a novel seeding technique followed by optimised growth conditions, and leads to a highlydense form of this material with grain sizes around 100nm for films approximately 1.5 microns thick. The electrical properties of these films have been investigated using Impedance Spectroscopy, which enables the contributions from sources characterised by differing capacitances, such as grain boundaries and grain interiors, to be isolated. After an initial acid clean the electrical properties of the film are not stable, and both grain boundaries and grains themselves contribute to the frequency dependant impedance values recorded. However, following mild oxidation grain boundary conduction is completely removed and the films become highly resistive (>1013 ohm/sq). This is most unusual, as conduction through NCD material is more normally dominated by grain boundary effects. Interestingly, the AC properties of these films are also excellent with a dielectric loss value (tan δ) as low as 0.002 for frequencies up to 10MHz. The dielectric properties of these NCD films are therefore as good as high quality free-standing (large grain) polycrystalline diamond films, and not too dissimilar to single crystal diamond, and are therefore ideally suited to future ‘silicon-on-diamond’ applications. a)
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INTRODUCTION
There is considerable interest in the use of diamond as a semiconductor for the fabrication of high performance electronic devices [1]. There are also potentially important passive uses for diamond within electronics; for example, as a more thermally effective insulator layer than SiO2 within ‘silicon-on-insulator’ (SOI) technologies [2]. The use of Chemical Vapour Deposition (CVD) methods for the formation of homoepitaxial diamond films is well-established [3]. However, such films are limited in area by current available diamond substrates. Attempts to grow CVD diamond on non-diamond substrates such as silicon lead to polycrystalline materials whose properties are strongly influenced by the presence of numerous grain boundaries [4]. Whilst one approach to overcome the grain boundary problem is the growth of films with ever-increasing crystal sizes, leading to reduction of grain boundary densities, such films become unreasonably thick and not suited for integration with microscale and nanoscale device technology.
Nanocrystalline
diamond (NCD) films, where the grains are less than 100nm in diameter, can be produced with film thicknesses of
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