Polycrystalline Diamond Substrates Research Articles

Synthesis and Surface Acoustic Wave Property of Aluminum Nitride Thin Films Fabricated on Silicon and Diamond Substrates Using the Sputtering Method

C-axis oriented aluminum nitride (AlN) thin films with a thickness of 1 µm were prepared by reactive DC magnetron sputtering on polycrystalline diamond substrates at a substrate temperature of 623 K. The average surface roughness (Ra) of the AlN thin films was less than 2 nm obtained by locating the diamond substrates at a position of 100 mm from the aluminum target. The full width at half maximum (FWHM) of the rocking curve for the AlN(002) peak determined by X-ray diffraction analysis was about 0.2°. The surface acoustic wave (SAW) structures were completed by the deposition of aluminum electrodes on the as-deposited AlN surfaces. The SAW characteristics of an interdigital transducer (IDT)/AlN/diamond structure were investigated. The phase velocity and coupling coefficient were 10,120 m/s and 0.3%, respectively.

Chemical-Vapor-Deposited Diamond Overgrowth on Platinum Thin Films Deposited on Diamond Substrates

Overgrowth characteristics of B-doped diamond chemical-vapor-deposited on thin Pt films (with thicknesses of 100–200 nm) that were sputter-deposited on polycrystalline and single-crystalline diamond substrates have been studied by scanning electron microscopy with X-ray emission analysis, Raman scattering spectroscopy and a conventional X-ray diffraction method. The main feature observed is that a complex three-dimensional structure of polycrystalline Pt is formed in the overgrown diamond layer for both types of diamond substrates used. This suggests that significant agglomeration and recrystallization of the thin Pt film occurred at ∼900°C, well below the Pt melting point of 1772°C, during the diamond overgrowth process. A considerable amount of B segregation was also observed after the overgrowth. It is concluded that a sputter-deposited Pt thin film with a thickness of 100–200 nm is not suitable as a mask usable in fabrication processes of multilayered diamond structures.

Electronic properties of diamond/nondiamond carbon heterostructures

In this paper the properties of diamond/amorphous carbon heterostructures are studied using photoelectron spectroscopy in the ultraviolet (UPS) and x-ray (XPS) regime. The nondiamond carbon films are deposited on a p-doped polycrystalline diamond substrate, and produced by first, electron beam evaporation of graphite forming hydrogen-free amorphous carbon $(a\ensuremath{-}\mathrm{C}:\mathrm{H})$ films. The overlayer formation is monitored step-by-step, and the changes in band bending in the diamond substrate and the valence band discontinuities are deduced from the UPS and XPS spectra. In the $\mathrm{diamond}/a$-C structure a downward band bending in diamond evolves continuously with overlayer thickness and a final value of about 1.1 eV is obtained, resulting in a band offset of $1.5\ifmmode\pm\else\textpm\fi{}0.1\mathrm{eV}.$ In the $\mathrm{diamond}/a\ensuremath{-}\mathrm{C}:\mathrm{H}$ structure a downward band bending of 1.4 eV is observed after only a brief deposition time, when the estimated overlayer thickness is still less than a monolayer. The ion energies employed for the film deposition were 200 and 600 eV and although the resulting overlayers exhibit characteristic structural differences, the band bending and band offset $(1.4\ifmmode\pm\else\textpm\fi{}0.15\mathrm{eV})$ are not noticeably influenced. It appears likely that in this case the defects formed in the diamond lattice through the energetic ions used for the overlayer deposition, are responsible for a pinning of the Fermi level at the surface. In an additional experiment the diamond substrate was irradiated with ${\mathrm{Ar}}^{+}$ ions (3 keV) and the resulting band bending, induced through the creation of a defect-rich surface layer, amounts to about 1.3 eV. The introduction of dangling bonds and/or \ensuremath{\pi}-bonded regions, which are energetically located in the gap of diamond, leads to the observed increase in downward band bending in the p-doped diamond.

Growth Rate of Diamond on Polycrystalline 〈110〉 Diamond Substrates from Carbon Disulfide in Hydrogen by Hot‐Filament‐Assisted Chemical Vapor Deposition

The growth rates for the deposition of diamond by hot‐filament‐assisted chemical vapor deposition using carbon disulfide (CS2) in hydrogen and methane (CH4) in hydrogen were investigated on polished, 〈110〉 textured, polycrystalline diamond substrates. The carbon concentration in each system was varied from 1% to 2.5%. The deposition rate increased proportionately with carbon concentration for both systems. The CH4‐H2 system gave higher growth rates with an essentially constant difference in rate between CS2 and CH4. Possible explanations for this are discussed with the most likely either a catalytic effect of sulfur or sulfur‐containing species on gas‐phase homogeneous atomic hydrogen recombination, or the surface chemisorption of relatively less labile sulfur‐containing species at the diamond surface.

The characterization of single structure diamond heater and temperature sensor

Abstract Heat generation and temperature sensing, essential for most heater applications, were achieved by using a single diamond resistor. Chemical vapor-deposited p-type diamond resistors were fabricated on polycrystalline diamond substrates and oxidized Si wafers using diamond film technology compatible with integrated circuit processing. The resistivity-temperature relationship of diamond thermistors was characterized in the temperature range of 300–1000 K. The maximum heating temperature and power density of 950 K and 93 W cm −2 , respectively, were achieved for heating application. The average difference between the temperatures determined by self-sensing of diamond thin film heaters and the temperatures measured by thermocouples was in the range of 1.05–3.6%. Due to its high thermal conductivity, the substrate temperature was isothermal, as indicated by two-dimensional optical thermometry.

Piezoresistive property of CVD diamond films

Abstract Electrical and piezoresistive properties of chemical vapor-deposited boron-doped p-type polycrystalline diamond films were investigated. The p-type polycrystalline diamond films of about 2 μm thickness were grown on a flat insulating polycrystalline diamond substrate using a conventional microwave plasma CVD system. The optimized p-type polycrystalline CVD film exhibited similar quality to homoepitaxial single crystalline diamond film with activation energy of 0.31–0.33 eV and small effects of grain boundaries. Piezoresistors (500 μm long and 50 μm wide) constituted from the optimized p-type polycrystalline diamond films were fabricated on diaphragm structure using photolithography and reactive-ion etching in an oxygen plasma. Relative change of the electrical resistance (ΔR/R0) of the p-type diamond piezoresistor was almost proportional to the applied strain. Gauge factor K for the p-type diamond piezoresistor was derived to be ∼ 1000 at room temperature and > 700 even at 200°C.

(001)-textured growth of diamond films on polycrystalline diamond substrates by bias-assisted chemical vapor deposition

(001)-textured diamond films were deposited on as-grown polycrystalline and polished polycrystalline diamond substrates by means of bias-assisted chemical vapor deposition (CVD). Scanning electron microscopy (SEM) and Raman scattering were carried out to investigate the morphology and phase purity before and after the growth process. It is observed that an in-plane oriented diamond domain can be formed on a diamond face with undefined crystal direction. The roughness of the substrate will affect the morphology of the top layer. The mechanism for (001)-textured growth during bias-assisted process is discussed.

Reactions between tungsten and molybdenum thin films and polycrystalline diamond substrates

Reactions between thin sputtered tungsten and molybdenum films and polycrystalline diamond substrates were studied in the temperature range 675–1120 °C. The mass transport effects and carbides that formed were characterized by Rutherford backscattering (RBS), X-ray diffraction and transmission electron microscopy (TEM) methods. It was found that for tungsten films, W 2C formed at low annealing temperatures (800 °C), whereas at higher temperatures only WC was observed. For molybdenum films only Mo 2C formed. The formation of W 2C at the vacuum surface was favored relative to the metal-diamond interface. The reverse was true for Mo 2C where, in addition, a surface layer of graphite formed at temperatures of 1020 °C. No similar graphite formation occurred in WC films below 1100 °C. From both the RBS spectral profiles and TEM observations a model for interstitial and/or grain boundary diffusion assisted carbide formation is suggested. These results for tungsten are consistent with the Bene' rule for the sequence of compound phase formation in metal-metal couples.

Selective Copper Cvd on Diamond Surfaces Using Self-Assembled Monolayers

ABSTRACTSelective chemical vapor deposition (CVD) of conductive, adherent copper films was achieved on single-crystal and polycrystalline diamond substrates modified with a ligating aminosilane and a Pd-based catalyst. Only isolated copper particles deposited on hydrogenated or aminosilane-coated diamond substrates without Pd. The Pd catalyst enhanced selectivity by a factor of 103 to 104. Copper CVD was performed in a cold-walled chamber at 446-456 K and 8x10-3 Pa using hexafluoroacetylacetonate-Cu-trimethylvinylsilane in H2 (1:1). Surfaces were characterized with x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Patterned Cu features were formed by exposing the aminosilane films to patterned ultraviolet (193 nm) radiation prior to Pd-catalyst addition and Cu CVD.

Diamond Field-Effect Transistors

ABSTRACTMetal-oxide-semiconductor field-effect transistors (FETs) have been fabricated using B-doped diamond thin films deposited on polycrystalline, (100) highly-oriented, and single crystal diamond insulating substrates. Diamond films were grown using a microwave plasma chemical vapor deposition technique. Various electrical and materials characterization techniques were employed to confirm that the films exhibited properties suitable for FET fabrication. Devices with gate lengths and widths of 2 μm and 314 μm respectively, were processed using standard photolithography. Silicon dioxide was used as the gate dielectric. Current-voltage characteristics of these devices have been measured during variable temperature cycling in air. Devices fabricated on the randomly oriented polycrystalline diamond substrates have been operated to 285°C. Field-effect transistors fabricated using the highly-oriented diamond substrates have been characterized to 400°C. Single crystal diamond devices exhibited saturation and pinch-off of the channel current at temperatures up to 500°C. These devices have been biased in amplifier circuit configurations that have been characterized from 20 Hz to 1 MHz. Single crystal FETs exhibited voltage gain over an extended temperature range. Transconductances as large as 1.7 mS/mm have been observed. The electronic properties, fabrication technologies, and performance of devices fabricated on the three diamond substrate materials will be discussed and compared.

Small signal equivalent circuit of an isotype heterojunction dominated by traps : M. J. Hampshire and R. D. Tomlinson, Solid-St. Electron. 13 (1970), p. 41

DC and RF performance of submicron gate-length metal–semiconductor field effect transistors (MESFETs) fabricated on hydrogen-terminated polycrystalline diamond is investigated in detail for different material electronic quality (grain size in the range 100–200 µm) and device geometry (drain-source channel length in the range 1–3 µm). DC characteristics appear almost independent of both properties, giving maximum drain-source current values in the range 120–140 mA/mm in MESFETs having same gate length (0.2 µm) and gate width (25 µm). The layer properties underneath the hydrogenated surface seem then to affect the DC behaviour to a lesser extent when the same hydrogenation procedure is used. At variance, the electronic quality of diamond layers employed for MESFETs realization largely affects the RF performance, resulting into a low oscillation frequency fmax for a MESFET realized by a self-aligned process (1 µm drain-source channel length) onto low quality diamond polycrystalline film. Such a performance improves to fmax = 35 GHz for devices realized onto large grain polycrystalline diamond, although fabricated without self-aligned gate procedure (3 µm drain-source channel length). These findings are discussed in terms of different roles played by surface hydrogenation, device geometry detail and electronic quality of the polycrystalline diamond substrate for MESFET realization.