Papers by Keyword: Aluminum Nitride (AlN)

Abstract: A medium-carbon V-microalloyed steel (38MnSiVS5) with three different Al levels (0.006, 0.020, and 0.031 wt pct) was used to examine the interaction of V, Al, and N after hot deformation. A complete thermomechanical cycle was simulated in the laboratory using a Gleeble® 1500. Specimens were heated to a soaking temperature that varied from 1100 to 1250 °C for 5 or 45 min and control cooled to 1000 °C in 6 min, where they were compressed to 40 pct reduction at a strain rate of 1.0 s^-1. After compression, the specimens were control cooled to 500 °C at 0.25 °C·s^-1 and die quenched to room temperature. Additional specimens were processed without the compression step for comparison. The thermal and thermomechanically processed specimens were characterized by quantitative metallography and microhardness testing. The thermomechanically processed specimens with 0.006 wt pct Al maintained their hardness while reducing pearlite fraction by approximately 10 pct. The thermomechanical processed specimens with 0.020 and 0.031 wt pct Al showed a significant drop in microhardness and pearlite fractions, as compared to the thermal only processed specimens. The decrease in microhardness and pearlite fraction for the two higher-Al–containing alloys in both the thermal and thermomechanically processed specimens appears to follow the same linear trend, suggesting that AlN precipitation reduces the amount of N in solid solution, lowers the temperature at which V(C,N) precipitation occurs, and effectively reduces such strain-induced precipitation.

Abstract: A study of depositing high quality c-axis oriented polycrystalline aluminum nitride thin film at room temperature was presented. Aluminum nitride films were grown by mid-frequency (MF) reactive sputtering. Metallic aluminum target was used to deposit AlN films in Ar/N₂ gas mixture. A 50nm thick of N-rich AlN buffer layer was deposited at the initial stage of sputtering process to improve the film quality. The composition, preferred orientation and residual stress of the films were analyzed by EDS, XRD and Raman microscope, respectively. The results showed that the N-rich AlN buffer layer improved the textured degree and reduced the residual stress significantly of the AlN thin films. The near stoichiometric AlN thin film with highly textured degree was obtained. The FWHM value of the rocking curve for (0002) diffraction peak was about 1.6°, and the residual tensile stress was about 500MPa. The piezoelectric d₃₃ coefficient increased with the decreasing of FWHM value, and the highest d₃₃ coefficient of 3.6 pF/C was obtained.

Abstract: Highly dense AlN/CNT composite ceramics with 1-10% volume fractions of CNT were fabricated by spark plasma sintered (SPS) at 1400°C-1700°C. The results indicated that origination diameter of AlN had a great effect on microstructure and thermal conductivity. In details, for the system with AlN origination diameter of nanosized, the tubular structure of CNT has not been destructed, but when micro-sized AlN powder was adopted, the structure of CNT showed unstable at high temperature. Even though the degradation with incorporation of CNT into AlN, thermal conductivity of sintered AlN/CNT composites ceramics was evidently improved by adjusting content of additive Y₂O₃ and the sintering process. Both the real part and imaginary part of the composites of Ka-Band (26.540.0 GHz) increase with the increase of CNT content, in which the increase of imaginary part is more than that of real part, resulting in an increase of loss factor. The AlN/ CNT thermal conductivity composites with appropriate CNT content and sintering temperature possess good dielectric dissipation and thermal conductivity.

Abstract: In this paper, the aluminum nitride (AlN) was fabricated by pressureless sintering with YF3 and various silicon compounds as the sintering aids. The phase, microstructure, density and thermal conductivity were characterized by XRD, SEM and laser thermal diffusivity method. The sample densities were detected varied from 3.17 to 3.30g/cm3 and room-temperature thermal conductivity varied from 196 to 233 W/m·K. Samples sintered with YF3 additives have the highest thermal conductivity. The sintering aids with SiO2, Si3N4 and SiC would decrease the density and the thermal conductivity obviously, and also change the fracture mode from the intergranular to transgranular , which is a key for the toughness of the AlN substrate.

Abstract: The aim of this work was to determine the effect of composite additives on the thermal and mechanical properties of aluminum nitride (AlN) in detail. The composite system has not been studied in depth before. The hot-pressed AlN was prepared with Y₂O₃-Dy₂O₃-YF₃ and Y₂O₃-Dy₂O₃-CaO as the composite sintering additives. As the result, the thermal conductivities for the sintered body with two composite additives were 171 W/m.K and 152 W/m.K, respectively. The fracture toughness values calculated by the Evans & Clarkes’s equation for both of the samples were 2.34±0.09 MPa.m^1/2and 2.63±0.13 MPa.m^1/2 at 10 kg load. The toughness difference is the result of comprehensive effect of the grain size, the properties of the boundary phase, its distribution, and also the interactions between different phases.

Abstract: Polycrystalline aluminum nitride (AlN) films were deposited on Si (111) substrates by radio frequency (RF) magnetron sputtering method in an nitrogen (N₂) + argon (Ar) gas mixture. The effect of the preparation conditions- sputtering pressure (p), sputtering power (w), gas mixture (Ar/N₂) and post-deposition annealing treatment -on the properties of AlN films were investigated by means of X-ray diffraction (XRD). Highly c-axis oriented AlN films were obtained with optimized growth parameters: p=0.3Pa, w=400w and Ar/N₂=2.

Abstract: We have formed a SiC interfacial buffer layer on AlN/Si substrates at a low temperature by low-pressure chemical vapor deposition (LPCVD) using monomethylsilane (CH₃SiH₃; MMS), and grew 3C-SiC films on the low-temperature buffer layer by LPCVD using MMS. We investigated the surface morphology and crystallinity of the grown SiC films. It was found that the formation of the SiC buffer layer suppressed the outdiffusion of Al and N atoms from the AlN intermediate layer to the SiC films and further improved the surface morphology and crystallinity of the films.

Abstract: Aluminium alloys is widely applied in heat sink but its application of heat absorption is still unsatisfied. While, Aluminum Nitride (AIN) was discovered as another option for heat sink application because of its great thermal conductivity and it also has high electrical conductivity at high temperature. Thus, the mechanical and chemical properties of a sintered mixed powder of Alumina and AIN are investigated experimentally. There are five different compositions of mixed powder of Alumina-AIN and sintered at three different sintering temperatures which are 1400°C, 1500°C and 1600°C. As applying a high sintering temperature on samples inducted great flexural strength and increase it modulus of rupture. High sintering temperature (1600°C) also affected the materials microstructure as the particle was arranged closely between each other and reduces the amount of porosity. The application of high temperature in the mixture of AIN with Alumina reduces the occurrence of flaws like cracking and accordingly improves the strength. These combination of Alumina-AIN brought acceptable result in thermal conductivity value analysis and as well enhancing the thermal conductivity.

Abstract: In the present study, we have successfully grown Si-doped AlN developed by solution growth technique using Ga-Al melt as a solvent under nitrogen atmosphere at 1300 °C. Si doping was introduced to the Ga-Al melt by adding pure Si metal. To allow homoepitaxial growth during solution growth experiment, sapphire substrate were nitrided with precise control to produce hiqh quality single crystalline AlN films with low dislocation density. With the help of AlN film template from above methods, we have successfully grown Si-doped AlN single crystalline layer with a flat surface and almost free from cracks. The full width at half maximum (FWHM) of x-ray rocking curve values for (0002) and (10-12) diffraction from the Si-doped AlN film were 43,2 and 594 arcsec, respectively.

Abstract: The growth of AlN buffer layer at extremely high temperature (1100-1150oC) in ammonia MBE STE3N2 system is shown to be the key step to obtain high quality GaN layers for DHFET channels. The buffer layer sequence from c-sapphire substrate involved AlN, AlGaN/AlN superlattice and AlGaN transition layers. TEM study showed gradual decrease of threading dislocation density from (2-4)×10¹⁰ cm^-2 in AlN to (9-10)×10⁸ cm^-2 in the top GaN active layer. The improvement of structural quality resulted in substantial increase in electron mobility up to 600-650 сm²/Vs in a 1.5-μm-thick GaN top layer lightly doped with silicon up to n=(3-5)×10¹⁶ cm^-3. These results correspond to a good quality MOCVD GaN grown on sapphire and several times better than in conventional MBE. Employing such a GaN layer in a double heterostructure (DH) with the cap Al_xGa_1-xN barrier layer (x=0.25-0.4) allows to change the electron sheet density, mobility and sheet resistance in a two dimensional electron gas in the range of 1300-1700 cm²/V^.s, (1.0-1.8)×10¹³ cm^-2 and 230-400 Ω/, respectively. Application of this technology and DH design for growing on SiC substrates enabled one to manufacture a DHFET with a gate length of 0.5 μm for 0.03-4.0 GHz extra-broadband power amplifiers having P_out=2.5 W, gain 17-25 dB and efficiency 30%.