AIN Surface Research Articles

Study on high thermal conductivity insulation materials for wide temperature range applications

A new design method of highly reliable thermally conductive packaging material is proposed for the heat dissipation problem of high-density packaging of chips. The high reliability is obtained by high temperature condensation of AlN particles suspension of PAA. Focusing on the influence law of the content of AIN on the electronic packaging material, the experimental results show that the thermal conductivity reaches 3.8 W/(m⋅K) when the mass percentage of AIN reach more than 60%. The Td in N2 is 524°C. The surface of AIN is modified by the macromolecular coupling agent GBM to increase the compatibility of AIN with the Polymeric materials. The tensile strength of PI/AlN composite is 170 MPa, and the material has good insulation performance when the temperature rises to 200°C under 120 kV/mm electric field, which meets the application requirements of high-density chip packaging.

Enhancement-Mode AlN/GaN HFETs Using Cat-CVD SiN

High-performance enhancement-mode (E-mode) AIN (2.5 nm)/GaN heterostructure field-effect transistors (HFETs) were fabricated with a novel method using SiN passivation by catalytic chemical vapor deposition (Cat-CVD). We found that the formation of a 2-D electron gas (2DEG) in the AIN/GaN heterostructure can be controlled by the presence of the Cat-CVD SiN on the barrier layer. Before SiN deposition, the 2DEG at the AIN/GaN heterointerface was completely depleted because of the extremely thin barrier layer. On the other hand, after SiN deposition, the decrease in AIN surface barrier height induced a high-density 2DEG. The E-mode HFETs with gate lengths of 100-180 nm and threshold voltages from +0.14 to +0.55 V showed a maximum drain-current density of 0.70-0.92 A/mm and a maximum extrinsic transconductance of 362-400 mS/mm. A current-gain cutoff frequency of 87 GHz and maximum oscillation frequency of 149 GHz were obtained for the 100-nm-gate devices.

Ion Assisted Reaction In Polymer And Ceramics

AbstracrIon assisted reaction (IAR), which was firstly presented in 1995 MRS Fall meeting, has been reviewed for the surface modifications of polymer and ceramics. The reaction is assisted by energetic ions from 0.5 to 1.5 keV, doses 1014 to 1017 ions/cm2, and blowing rate of oxygen 0 ∼ 8 ml/min. Hydrophilic surfaces of polymers (wetting angle < 20° and surface energy 60 ∼ 70 erg/cm2) have been accomplished by the reaction, and an improvement of wettability and an increment of the surface energy are mainly due to the polar force and hydrophilic functional groups such as C=O, (C=O)-O, C-O, etc., without surface damage. The IAR was also applied on aluminum nitride in an O2 environment and AMON on AIN is formed by the Ar+ irradiation. The improvement of bond strength of Cu films on the AIN surface resulted from the interface bonds between Cu and the surface layers. Comparisons between the conventional surface treatments and the IAR are described in terms of physical bombardment, surface damage, functional group, and chain mobility in polymer.

Corrosion of aluminium nitride substrates in acid, alkaline solutions and water

Aluminium nitride substrates were immersed in acid, basic solutions and deionized water for 1–120 h at room temperature. The corrosion rates are higher in basic solutions (NaOH and KOH) than those in acid solutions (CH3COOH, HCOOH, HNO3, HCl and H2SO4) and deionized water. The weight loss of AIN corroded in alkali aqueous reaches 70% and results in an increase in surface roughness ranging from 10 nm to 7 μm after 3 days corrosion. However, the weight loss in acid solution is only 1/700 of the alkali case. Violent chemical reactions between AIN and basic solutions were observed. Na2O, or Na2Al2O4·6H2O, is the intermediate product, and NaOH is a catalytic agent of the reaction. The surface morphology of the AIN etched by alkaline solutions is coral-like in microscopic view and appears like hills. In contrast, only several atomic layers of AIN surface are etched off in acid solutions and in deionized water. The lightly etched surface is mirror-like and flat, and the shapes of the grains are visible under the microscope, as the corrosion rate of each AIN grain varies with different crystal orientations. Consequently, after etching in acid solutions, the resulting microscopic surface morphology looks like a map of a jigsaw puzzle.

Fourier-transform infrared characterization of an aluminium nitride surface

In order to identify the structure of the surface of AIN, an infrared study was conducted. AIN powder was thermally treated either under vacuum or under controlled atmospheres using probe molecules at different temperatures. The surface presented OH and NH groups originating from the hydrolysis of Al—N bonds as well as Al3+ Lewis-acid sites (Al3+ ions in both tetrahedral and octahedral coordination). Some Al—H bonds were also present.

Processability of Thin-Film, Fine-Line Pattern on Aluminum Nitride Substrates

Commercially available tape-case AIN substrates of > 99.5-percent purity were used in this study. Also, 99.5-percent pure alumina substrates were used as control samples. These substrates were tested for stability in water and in air, for laser scribability, and for thin film adhesion and pattern generation. In water, an AIN surface decomposes to a porous surface film of a hydrated alumina phase at 100°C. This decomposition film adversely affects the adhesion of thin films. In air, AIN oxidizes to a-alumina when heated above 1OOO”C. No obvious surface decomposition of AIN was observed in SEM micrographs of the samples aged at 8S4C/85-percent humidity for lo00 h. AIN is laser scribable and, unlike A1203, it does not undergo a phase transformation in the scribed region. Thin films of Ti, Pd, and Au with and without Ta,N were sequentially sputter-deposited on AIN. Adhesion of these films was adequate as confirmedl by a soldered lead pull test. Next, triple-track resistor pattern containing 300 A thick Ta2N resistors with 76-pm width, and spaced 76 pm apart with Ta2N, Ti, Pd, and Au contact pads were developed by photolithography. The adhesion of patterned thin film of sequentially deposited Ti, Pd, Au, and TazN on AIN substrates was good even after aging them for lo00 h at 8S0C/85-percent humidity. However, 53 percent of the thlin-film resistors on AIN had electrical “opens,” whereas no “opens” were observed on alumina substrates. This is attributed to poorer fine-line definition on AIN caused by its high surface roughness. The surface roughness of AIN substrates was fourfold higher than that of the alumina used in this study.

Study of the electronic structure of an AIN surface by electron spectroscopy

Study of the electronic structure of an AIN surface by electron spectroscopy

Study of the electronic structure of an AIN surface by electron spectroscopy

AlN is a wide band gap III–V semiconductor with piezoelectric properties. A thin AlN film was prepared in ultrahigh vacuum by nitrogen ion implantation in a pure AI(111) monocrystal. This procedure gives a stoichiometric and crystalline AIN film. A complete description of the electronic states of the compound is obtained by combining different spectroscopies, carried out in situ: (i) the density of electronic states in the valence band is given by photoemission experiments using different photon energies (corresponding to the He I, He II and AI K α lines). (ii) Excitation of a core level (AI 2p) and of secondary electrons, by an electron beam ( E p = 250 eV) provides information on the density of unoccupied states in the conduction band. (iii) Electron energy-loss spectroscopy allows one to study localized electronic levels in the band gap, due to the presence of structural defects.