UNCD films

First, the main difference between NC and UNCD films has to be considered. The decrease of the crystal grain size from NC to UNCD films increases the number of grain boundary interfaces. This also results in a decrease of thermal conductivity and an increase of the optical absorption of UNCD films compared to NC films. At the same time, the friction coefficient of UNCD films is lower than that of NC films. Both types of CVD films can be used for MEMS (microelectromechan-ical systems), NEMS (nanoelectromechanical systems), and also for electrochemical applications. " DND is applied as an abrasive for ultrafine mechanical polishing of hard surfaces of materials. Present-day polishing compositions based on detonation ND offer the possibility of obtaining... 

The film-thickness uniformity has been more difflcult to optimize when UNCD films are grown using MPCVD systems powered by microwaves of 2.45 GHz. 

Fig. 2 (a) Schematic procedures for growth of UNCD films on Si-simulating microchips (b) Cross-section SEM picture of encapsulating UNCD film grown with 1% H2 in Ar/CILt plasma showing the UNCD conformal hermetic coating covering the Si substrate... 

Fig. 3 Optimization of UNCD film-thickness uniformity via position on the substrate holder in the MPCVD system...

Fig. 4 Raman spectra of UNCD films grown with different H2 percentage in the Ar/CHa gas mixture used to grow UNCD films (a) 20%, (b) 10%, (c) 2%, and (d) 0%. All curves have been normalized against the intensity of the peak around 1590 cm . UNCD films were grown in the ANL group (Reproduced from Ref. [40] with permission from Wiley)...

Fig. 5 Visible Raman spectra of UNCD films deposited at different temperatures (Reproduced from Ref [41] with permission from American Institute of Physics)...

SEM analyses on UNCD films deposited with different hydrogen percentages are shown in Fig. 7. Results showed that the incorporation of hydrogen leads to dramatic changes to the UNCD film microstructure. The more hydrogen incorporated, the... 

Fig. 7 SEM imaging and analysis of UNCD films grown with different hydrogen contents in the Ar/CHt plasma, showing the microstructure changes induced by hydrogen incorporation into the films. The best microstructure is for 1% Ha in the plasma, since this is the densest, thus the most hermetic for liquid penetration (Reproduced from Ref. [40] with permission from WUey])...

The comparisons of the microstructures of UNCD thin films deposited at different temperatures are shown in Fig. 8. The growth rates estimated from the corresponding SEM cross-section images shown in Fig. 8 are 0.2 p.m/h at 400 C and 0.25 fim/h at 800°C, which indicates that the growth of UNCD films with the Ar rich/CH4 plasma chemistry is less temperature dependent. 

The results shown in Fig. 8 indicate that the UNCD films deposited at 400 C have similar microstructures to those of the films deposited at higher temperatures. These films are very dense and pinhole-free (Fig. 9). Three different scales are given to provide thorough views of the films from microstmcture to macrostmcture. The SEM images of the very dense UNCD films indicate that they are good candidate materials as hermetic coatings. 

To characterize the electrochemical performance of the hermetic UNCD films, cyclic voltammetry tests were performed, using three electrodes in a potentiostat (Solartron 1287A Solartron Analytical). Phosphate-buffered saline (PBS) was used as the electrolyte. A platinum rod was used as the counter electrode. An Ag/AgCl electrode was used as the reference electrode. 

Fig. 15 Measurement of CMOS-device performance before and after coating with UNCD film, for four hours at 400° C. There is negligible change in the electrical parameters of the CMOS device after UNCD deposition, demonstrating that the Argonne-patented UNCD growth process is compatible with CMOS devices (200 mm CMOS wafers were supplied by S. Pacheco (Freescale) and the electrical characterization was performed by Prof. Z. Ma s group at University of Wisconsin-Madison)...

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