High-temperature electrical behavior of nanocrystalline and microcrystalline diamond films
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P.B. Kosel Department of Electrical, Computer Engineering and Computer Science, University of Cincinnati, Cincinnati, Ohio 45221 (Received 14 February 2008; accepted 11 July 2008)
Chemical vapor deposition of diamond has opened up new applications in microelectronics, microelectromechanical systems (MEMS), and coating technologies. This paper compares and contrasts the high-temperature electrical behavior of microcrystalline versus nanocrystalline diamond films. Through-thickness current–voltage characteristics between room temperature and 823 K are presented for a series of films synthesized with different gas phase concentrations of nitrogen and argon. One set of samples was characterized by measurements between room temperature and 823 K and a second set by two-step thermal cycling from room temperature to 573 and 823 K. It was found that with increasing nitrogen concentration (up to 0.1% N2), the resistivity slightly increased followed by a decrease at higher concentrations. Activation energies and barrier heights were in general lower for the more defective films. These results in conjunction with material characterization indicated that more defective diamond films were synthesized at higher nitrogen concentrations in the gas phase.
I. INTRODUCTION
Diamond has exceptional physical properties such as the highest packing density, thermal conductivity, and hardness, along with a high band gap and breakdown voltage.1 The combination of these properties makes diamond a unique material with the potential to stimulate new developments in a wide range of technologies. Since the first commercial synthesis of diamond by the highpressure and high-temperature (HPHT) method by the General Electric Company in the early 1950s, a significant effort has been invested in synthesizing diamond films for high-technology applications. One such envisaged application is high-temperature electronics. High-temperature electronics, though a niche area, is projected to have a market value of $900 million by the year 2008.2 Diamond with its aforementioned properties would be a suitable candidate for applications in harsh environments. A significant stumbling block in the realization of high-temperature diamond electronics has been the inability to produce heteroepitaxial diamond films. To date, heteroepitaxy yields polycrystalline diamond films whose properties differ significantly from their
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0330 2774
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 10, Oct 2008 Downloaded: 16 Mar 2015
single-crystal counterparts. The defective nature of the polycrystalline diamond films effectively degrades a host of physical properties, which are essential to their application in high-temperature electronics. Therefore, it is imperative to study the behavior of polycrystalline diamond films at high temperatures to better understand and hence predict their behavior. Further, the recent development of “nanocrystalline” diamond films using argon
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