Grain size dependent mechanical properties of nanocrystalline diamond films grown by hot-filament CVD

Nanocrystalline diamond (NCD) films with a thickness of ~ 6 µm and average grain sizes ranging from 60 to 9 nm were deposited on silicon wafers using a hot-filament chemical vapor deposition (HFCVD) process. These samples were then characterized in order to identify correlations between grain size, chemical composition and mechanical properties. The characterization reveals that our films are phase pure and exhibit a relatively smooth surface morphology. The levels of sp²-bonded carbon and hydrogen impurities are low, showing a systematic variation with the grain size. The hydrogen content increases with decreasing grain size, whereas the sp² carbon content decreases with decreasing grain size. The material is weaker than single crystalline diamond, since both stiffness and hardness decrease with the reduction in crystal size. These trends suggest gradual changes in the nature of the grain boundaries, from graphitic in case of 60 nm grain size material to hydrogen terminated sp³ carbon in 9 nm grain size material. The films exhibit low levels of internal stress and free-standing structures with a length of several centimeters could be fabricated without noticeable bending     

Fabrication of diamond micro tools for ultra precision machining

State of the art diamond tools for metal-cutting manufacturing are handcrafted by polishing and grinding of natural diamonds. Tools fabricated by these means are serially made unique copies with a limited variety of shapes. Furthermore, manual fabrication leads to deviation from ideal geometry. We present a novel technique for parallel fabrication of diamond micro tools with high contour accuracy by using lithographic methods followed by a modified ASE-process.     

Highly rectifying Au-contacts on diamond-on-silicon substrate

Au Schottky diodes have been fabricated on highly oriented diamond (HOD) films, grown on silicon using AC-bias nucleation and microwave plasma chemical vapor deposition. The active layers were selectively grown and doped by solid boron source. High rectification ratios were obtained up to 500°C in a bias voltage range up to ±15 V. A current density of more than 1 A/cm² and a breakdown field strength up to 2.0·10⁶ V/cm for point contacts has been demonstrated     

Very high temperature operation of diamond Schottky diode

For the first time, the operating temperature of a Schottky diode structure has been pushed to 1000°C. The diode structure consists of a Si-based Schottky material deposited onto a homoepitaxial boron doped diamond surface. At high temperatures, the forward I-V characteristics are dominated by the thermionic emission (n≈1.01) across a barrier of 1.9 eV height. The reverse characteristics are still dominated by thermally activated defects. The series resistance shows thermal activation associated with the boron doping     

High-temperature, high-voltage operation of pulse-doped diamondMESFET

The fabrication and operation of a pulse-doped diamond metal-semiconductor field-effect transistor (MESFET) is presented showing a usable source drain voltage of 70 V and no breakdown up to 100 V at 350°C operating temperature. A channel sheet concentration of 8.5×10¹² cm^-2 could be fully modulated leading to a maximum transconductance of 0.22 mS/mm, although full activation of the boron acceptor had not been reached. For an optimized device structure, with reduced gate length below 0.25 μm and full activation, more than 10 W/mm RF-power density can be predicted     

Diamond surface-channel FET structure with 200 V breakdown voltage

An enhancement mode diamond FET using a hydrogen-terminated surface as hole conductive channel has been fabricated with 200 V gate to drain breakdown voltage. At the 8.5-μm gate length the maximum drain current was 22 mA/mm. 90 mA/mm maximum drain current was obtained at a gate length of 3.0 μm. Scaling to below 1 μm gate length assuming undegraded breakdown conditions will result in a projected RF power handling capability above 6 W/mm     

Actuator – sensor technology on “electronic grade” diamond films

 Thermal microheaters as used for example in thermal ink print heads contain a variety of materials, the heater itself is commonly based on refractory metals. Here, a novel concept based on diamond as a multifunctional material is proposed and demonstrated. In this concept, diamond serves as an insulating substrate, a metal-like heater and as a temperature sensor. Superheating of water could be achieved after 7.5 μs heating of a 60×60 μm element. Bubble nucleation was visualized using a high speed stroboscopic technique. The influence of the diamond thermal properties and geometry on the thermal response were investigated by dynamic 3D-simulations. Received: 29 June 1997 / Accepted: 12 November 1997