Superconducting nano-mechanical diamond resonators

In this work we present the fabrication and characterization of superconducting nano-mechanical resonators made from nanocrystalline boron doped diamond (BDD). The oscillators can be driven and read out in their superconducting state and show quality factors as high as 40,000 at a resonance frequency of around 10 MHz. Mechanical damping is studied for magnetic fields up to 3 T where the resonators still show superconducting properties. Due to their simple fabrication procedure, the devices can easily be coupled to other superconducting circuits and their performance is comparable with state-of-the-art technology.     

Diamond surface micromachining technology

Diamond is a wide bandgap semiconductor material with high mechanical strength and thermal stability, and therefore is an ideal candidate for micro electromechanical devices. In this paper, diamond surface micromachining technology used for fabricating diamond film devices is reported. Boron-doped diamond films were used as structure layer, and polysilicon films were used as sacrificial layer. After dry etching of diamond films using an oxygen-ion beam under an aluminum mask and wet etching of polysilicon films by KOH solution to release the microstructures, diamond-film beam resonators and tuning-fork-like resonators were fabricated. The technical problems encountered in surface micromachining technology are discussed.     

Effect of deposition temperature and quality of free-standing diamond substrates on the properties of RF sputtering ZnO films

Highly c-axis oriented ZnO film is often deposited on diamond substrates by RF magnetron sputtering and widely used for high frequency surface acoustic wave (SAW) devices. Deposition temperature is a key factor affecting the quality of the ZnO film. Different quality polished free-standing diamond films prepared by DC Arc Plasma Jet were used as the substrates to deposit ZnO films at different temperatures. Effect of the deposition temperature and the quality of the diamond films on the properties of the ZnO films were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that highly c-axis oriented ZnO films can be much easier deposited on the optical-grade diamond films with < 111> preferred orientation than the tool-grade diamond films with < 220> preferred orientation. The optimal deposition temperature is 200 °C for highly c-axis oriented and lower roughness ZnO films. Acoustic phase velocity of more than 10,000 m/s for the SAW devices based on the ZnO/optical-grade free-standing diamond films was obtained.     

Raman scattering,AFM and nanoindentation characterisation of diamond films obtained by hot filament CVD

In this work, structure and mechanical properties of diamond films fabricated by HFCVD on silicon substrates with nanodiamond seeding were investigated. Raman spectroscopy was used to characterise the diamond phase content, crystalline quality and source of stresses in these films. Topography, hardness and Young's modulus were studied by scanning force microscopy (SFM) and nanoindentation methods. It has been ascertained that for the diamond films grown on silicon substrates with nanodiamond seeding hardness and crystalline quality is higher than for films on scratched silicon. The diamond films demonstrate Raman upshift with respect to natural diamond, indicating presence of internal compressive stress. It was shown that various types of impurities and defects induce compressive stresses in the diamond grains.     

The properties of free-standing diamond films after plasma high temperature treatment of the rapid heating

The plasma treatment of rapid heating was introduced for increasing fracture strength of free-standing diamond films. The effects of plasma high temperature annealing treatment on surface morphology, internal stress, vacancy defects, impurities and fracture strength of free-standing diamond films were investigated by scanning electron microscopy (SEM), Raman, positron annihilation technique (PAT) and mechanical property testing. It showed that the fracture strength of the diamond films increases up to 70% for lower fracture diamond films with treating temperature (1500-1600 °C). The graphitization in surface and interior of diamond films would be produced by high temperature treatment more than 1700 °C. Fracture strengths of diamond films could be enhanced after high temperature treatment and the main factor of that was compressive stress state in diamond films induced by graphitization. The impurity of N was segregated and integrated with vacancy cluster to become [N-V]⁰ and [N-V]⁻.     

Oxidation behaviour of high quality freestanding diamond films by high power arcjet operating at gas recycling mode

Oxidation may cause degradation of mechanical, thermal and optical properties of freestanding CVD diamond films at elevated temperatures, and thus may impose severe technical limitations for applications of freestanding diamond films. In the present investigation oxidation behaviour of high quality freestanding diamond films prepared by high power d.c. arc plasma jet operating at gas recycling mode has been studied. It was found by thermogravimetry that the diamond films started to oxidize at approximately 650 °C, whilst the rate of oxidation increased substantially with increasing temperatures. Experimental observations confirmed that grain boundaries were the most preferred site for oxidation damage. Detailed studies were made on the influence of high temperature oxidation on the optical, thermal, and mechanical properties of high quality freestanding diamond films. Our results demonstrated that the high quality freestanding films prepared by high power d.c. arcjet can be safely used below 800 °C for a short time period of 180 s, which is more than enough for certain important IR applications.     

Dielectric property of thick freestanding diamond films by high power arcjet operating at gas recycling mode

Dielectric property of thick freestanding diamond films prepared by high power arcjet operating at gas recycling mode was measured by the high voltage electric bridge method at low frequencies (r.f.) and the wave guide resonance method at high frequencies (microwave). It was found that, with increasing frequencies, dielectric loss of freestanding diamond films increased at low frequencies, but decreased at high frequencies, with a maximum located at approximately 3 MHz. Measurements of dielectric loss of the freestanding diamond films at a microwave frequency of 5.2 GHz showed a strong dependence on the growth parameters such as substrate temperature and methane concentration. It was found that dielectric loss decreased with increasing substrate temperature, and increased with an increasing methane concentration in the feed gases. It is suggested that dielectric loss is closely related with the quality level of freestanding diamond film samples, as demonstrated by the results from Raman and SEM observations. Non-diamond carbon in the diamond films was found responsible for the increase in dielectric loss. Nitrogen was intentionally introduced into the Ar–H₂–CH₄ gas stream for diamond deposition to investigate the effect of impurities. It was shown that nitrogen addition to the feed gases seriously deteriorated the dielectric property of the resultant diamond films. This is again in agreement with our experimental observations by Raman and SEM, in that the addition of nitrogen also seriously deteriorated the quality of the diamond film. Mechanisms for the dielectric behaviour of the diamond films were discussed in detail.     

Investigation of nitrogen addition on hydrogen incorporation in CVD diamond films from polycrystalline to nanocrystalline

The effect of nitrogen addition in the gas phase on hydrogen impurity incorporation into CVD diamond films was investigated. A series of thick diamond films of different morphology and quality ranging from large-grained polycrystalline to fine-grained nanocrystalline were deposited on silicon wafers using a 5 kW microwave plasma assisted CVD system. They were obtained only by changing the small amount of oxygen and nitrogen addition while keeping all other input parameters the same. Bonded hydrogen impurity in these diamond films was studied by using Fourier-transform infrared spectroscopy. It was found that with increasing the amount of nitrogen addition in the gas phase, the produced diamond films from large-grained polycrystalline gradually shift to fine-grained nanocrystalline and their crystalline quality is drastically degraded, while the amount of incorporated hydrogen impurity in the diamond films increases sharply. The role of nitrogen additive on diamond growth and hydrogen incorporation is discussed. These results shed light into the growth mechanism of CVD diamond films ranging from polycrystalline to nanocrystalline, and the incorporation mechanism of hydrogen impurity in CVD diamonds.     

High-quality homoepitaxial diamond (100) films grown under high-rate growth condition

We present advantages of high-power microwave plasma chemical vapor deposition (MPCVD) in homoepitaxial diamond film deposition. Diamond films grown at comparatively high growth rate of 3.5 μm/h showed intense free-exciton recombination emission at room temperature. The free-exciton decay time of the diamond film at room temperature, 22 ns, was much longer than that of type-IIa single crystal, indicating electronically high quality of the homoepitaxial films. Dislocation-related emissions were locally observed, a part of which created by mechanical polishing process was successfully removed by surface etching process using oxygen plasma. Another advantage of the high-power MPCVD is effective impurity doping; boron-doped diamond films with high carrier mobility and high carrier concentration were reproducibly deposited. An ultraviolet photodetector fabricated using the high-quality undoped diamond film showed lower noise equivalent power as well as higher photoresponsivity for ultraviolet light with better visible-blind property, compared to those of standard Si-based photodetectors. The high-power MPCVD is, thus, indispensable technique for depositing high quality diamond films for electronic devices.     

Polishing of diamond thick films by Ce at lower temperatures

An efficient coarsely polishing and thinning method for CVD diamond films is achieved using solid or molten rare earth—Ce at the lower temperatures such as 700 °C for 2 h and 820 °C for 0.5 h. The factors affecting the surface roughness (Ra) and the rate of removal of diamond films are discussed thoroughly in this paper. In addition, the polishing mechanism is investigated primarily. The results show the content of diamond on the surface of the polished films has increased to a certain extent due to the etching out of impurities mostly at the grain boundaries and the FMHW of diamond Raman peak for polished diamond films has a visible increase. A large number of diamond films may be polished simultaneously at the temperatures lower than reported previously without noticeable contaminants on the polished surfaces of diamond films.     

Diamond films grown by a 60-kW microwave plasma chemical vapor deposition system

In order to use chemical vapor deposition (CVD) diamond films for electronic devices, it is necessary to establish technologies for producing diamond wafers with controlled quality. Most of existing diamond CVD systems are, however, designed primarily for laboratory use. To cross the technological gap between the commercial production and the laboratory experiments, the current CVD technologies of diamond must be scaled up and upgraded. Development of large-scale diamond deposition processes was undertaken by using a microwave plasma CVD system, equipped with a 915-MHz, 60-kW generator for generating a large-size plasma. Polycrystalline diamond films were deposited from a hydrogen/methane gas mixture with typical gas pressures and substrate temperatures of 80–120 torr and 800–1050°C, respectively. It was found that depending on the growth conditions, the deposited films have various surface morphologies. Some of the samples have well-defined {111} and {100} facets of up to tens of micrometers in size. The Raman spectra had an intense main peak due to diamond at 1333 cm⁻¹ without a trace of non-diamond carbon. The film quality in terms of Raman spectra was relatively uniform across the samples of 100 mm in diameter. Both 〈111〉 and 〈001〉 textured diamond films were obtained by selected growth conditions.     

On the two-phonon absorption of CVD diamond films

It is well known that the absorption coefficient of diamond in the two-phonon region is constant, for example at 2000 cm^{− 1}, the absorption coefficient is 12.3 cm^{− 1}. This means that the infrared absorbance in the two-phonon region is proportional to the thickness of the samples, which is generally used as standard to normalize the infrared absorption spectra of diamond samples according to their thickness. This is true for natural and HPHT synthetic single crystal diamond. However for polycrystalline or nanocrystalline CVD diamond films, we found that the situation may be different. For high quality thick CVD diamond films of thickness > 150 μm, the infrared absorbance in the two-phonon region is proportional to its thickness. While CVD diamond films of equal thickness but of different quality show variable absorbance in the two-phonon absorption region in terms of thickness. Our investigation on this observation primarily indicates that the grain size of CVD diamond films has influence on the two-phonon absorption. In this work, we present this new result and discuss the mechanism of this phenomenon in the light of the growth mechanism of CVD diamond.     

Experimental study of nucleation and quality of CVD diamond adopting two-step deposition approach using MPECVD

Effects of the deposition conditions on quality and nucleation density of CVD diamond were investigated using a microwave plasma enhanced chemical vapor deposition (MPECVD) method with methane-hydrogen gas mixtures. Diamond films were deposited at pressures of 665–4000 Pa, temperatures of 660–950 °C, and methane concentrations of 0.5–5 vol.%. Deposited diamond films were characterized by scanning electron microscopy, field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Diamond quality and nucleation density significantly affected by the deposition pressure, substrate temperature, and methane concentration. The findings of this work were discussed in terms of the effects of deposition conditions on the plasma composition. A two-step deposition approach was applied to improve nucleation density and quality of CVD diamond films. Polycrystalline diamond films were grown using the two-step deposition process changing a combination of parameters in the two steps. Growth and quality of the deposited diamond films were improved altering the deposition pressure and substrate temperature in the two steps.     

Incorporation of hydrogen in diamond thin films

In this investigation, diamond thin films with grain size ranging from 50 nm to 1 µm deposited using hot filament chemical vapor deposition (HFCVD) have been analyzed by elastic recoil detection analysis (ERDA) for determining hydrogen concentration. Hydrogen concentration in diamond thin films increases with decreasing grain size. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that part of this hydrogen is bonded to carbon forming C–H bonding. Raman spectra also indicated the increase of non diamond phase with the decrease in crystallite size. Incorporation of hydrogen in the samples and increase of hydrogen content in nanocrystalline sample are discussed. Large separation between filament and substrate used for the synthesis of nanocrystalline film helped to understand the large incorporation of hydrogen in nanocrystalline diamond films during growth. The study addresses the hydrogen trapping in different samples and higher hydrogen concentration in nanocrystallites by considering the synthesis conditions, growth mechanisms for different grain sized diamond films and from the quality of CVD diamond films.     

Towards facile fabrication of photonics components from inorganic and hybrid sol-gel films. Preparation and optical properties characterization

New trends towards development of integrated optics and miniaturization of photonic devices require fabrication of miniaturized photonic components. Fabrication of waveguiding films with designed optical properties is a fundamental process for production of planar integrated devices.We report here preparation of thin layers based on TiO₂ precursor (TET – titanium(IV) ethoxide) and SiO₂ precursors, namely inorganic (TEOS – tetraethyl orthosilicate) or organically modified (GLYMO ? 3-glycidoxypropyltrimethoxysilane) as candidates for potential application in the planar integrated circuits.The thin layers were deposited on soda-lime glass substrates using the sol-gel method and dip-coating technique and processed at relatively low temperature (up to 300 °C). Several parameters e.g. a) the type of SiO₂ precursor, b) the presence of complexing agent for TET and c) heat treatment temperature were tested for their influence on thickness and refractive index of the obtained films.Furthermore, a few series of sol-gel films activated with luminescent dye (Rhodamine B) was fabricated. The influence of the above-listed parameters on luminescent properties of the films was characterized because of lack of systematic study in the literature in this aspect. Moreover, a spectrum of the light at the output of a chosen luminescent dye-doped waveguiding film excited by laser source was investigated.In addition, the subject of our investigations were films prepared at 200 °C with various amounts of TET and organically modified SiO₂ precursor in concentration range not presented before. Their optical properties such as homogeneity and values of optical band gap of TiO₂ clusters were explored. For selected samples the waveguide properties including the optical losses were evaluated. For the first time, hybrid films with presented composition and refractive index in range of 1.59–1.71 were used for patterning by nanoimprint technique allowing for reproduction of periodic structures, which may serve for example as grating couplers or DFB (distributed feedback) resonators.     

Comparative study of diamond films grown on silicon substrate using microwave plasma chemical vapor deposition and hot-filament chemical vapor deposition technique

Diamond films on the p-type Si(111) and p-type(100) substrates were prepared by microwave plasma chemical vapor deposition (MWCVD) and hot-filament chemical vapor deposition (HFCVD) by using a mixture of methane CH₄ and hydrogen H₂ as gas feed. The structure and composition of the films have been investigated by X-ray Diffraction, Raman Spectroscopy and Scanning Electron Microscopy methods. A high quality diamond crystalline structure of the obtained films by using HFCVD method was confirmed by clear XRD-pattern. SEM images show that the prepared films are poly crystalline diamond films consisting of diamond single crystallites (111)-orientation perpendicular to the substrate. Diamond films grown on silicon substrates by using HFCVD show good quality diamond and fewer non-diamond components.     

The influence of dark feature on optical and thermal property of DC Arc Plasma Jet CVD diamond films

Different grades of CVD diamond films were prepared by 100 kW DC Arc Plasma Jet system. The films were characterized using optical microscope (OM), high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), and Raman spectroscopy. The results show that dark feature mainly is inclusions in CVD diamond films, the concentration are amorphous carbon and nitrogen. As for transparent optical grade diamond film, it has very high IR transparency and high thermal conductivity. The appearance of dark feature degraded the quality of CVD diamond film, apparently influencing IR transparency and thermal conductivity. But even in optical grade diamond film, there are very strong absorption features in the 7–9 μm region, this will limit the practical applications of diamond films grown by Plasma Jet as IR windows for CO₂ lasers.     

半导体集成电路用表面钝化膜的研究

对高性能高可靠性集成电路来说，表面钝化已成为不可缺少的工艺措施之一。本文分析了目前应用最广泛的几种无机表面钝化膜（SiO2,Al2O3和Si3N4)的特点，并指出氮化硅薄膜是半导体集成电路中最具应用前景的表面钝化材料，发展低温的热化学气相沉积（CVD）工艺来沉积氮化硅表面钝化膜是集成电路发展的必然趋势，而开发新的能满足低温沉积氮化硅薄膜的硅源，氮源前驱体是解决这一难题的有效方法，并对这些前驱体物质的设计原则进行了阐述。     

Characterization of diamond fluorinated by glow discharge plasma treatment

The surface fluorination of diamond by treatment in glow discharge plasmas of CF₄ for different times has been investigated. High quality diamond films were deposited onto silicon substrates using hot filament chemical vapor deposition (HFCVD). Subsequently, the films were exposed to a radiofrequency glow discharge plasma of CF₄ for times ranging from 5 min to 1 h. The effects of the plasma treatment on the surface morphology, diamond quality and elemental composition were investigated using atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. Differences in film roughness caused by the plasma treatment were detected by AFM and confirmed by scanning electron microscopy (SEM). Raman spectroscopic analyses showed that the original diamond was of high quality and that the bulk of each film was unchanged by the plasma treatment. Analyses using XPS revealed increased surface fluorination of the films at longer treatment times. In addition, the density of free radicals in the films was probed using electron paramagnetic resonance spectroscopy (EPRS), revealing that untreated diamond possesses an appreciable density of free radicals (6×10¹² g⁻¹) which initially falls with treatment time in the CF₄ plasma but increases for long treatment times.