AlN Passivation Research Articles

Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures

Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures were investigated by X-ray diffraction and Hall effect measurements. AlN passivation induced an additional compressive stress in an AlGaN barrier layer instead of an additional tensile stress induced by Si3N4 passivation. The change of strain after passivation contributes in a relatively small proportion to the variation of the carrier concentration in AlGaN/GaN heterostructures compared with the contribution from passivation of surface traps. The results from Hall effect measurements show that the AlN passivation layer has a better effect on passivation of deep levels than the Si3N4 film and also results in a remarkable increase in mobility of the two-dimensional electron gas.

Stress-Assisted Atomic Migration in Thin Copper Films

Stress-assisted atomic migration occurs in thin films due to thermal stress development, followed by hillock and void formation on a film surface. Relation between thermal stresses and hillock formation was investigated on copper films with and without passivation layer. Copper films with a thickness of 10, 50 and 100 nm on oxidized silicon wafer were prepared for investigating thermal stress and hillock formation. In-situ thermal stress observation by X-ray measurement revealed that compressive stresses develop in an early stage of heating followed by a sudden decrease in the temperature region between 100 and 200 deg. In a cooling stage, stresses in a film linearly changed with decreasing temperature to form a tensile residual stress state. Surface morphology is observed by optical microscope and SEM after the heat cycle as well as at elevated temperatures in a vacuum chamber. Dome-like swells were formed on an AlN passivation layer. Almost of all of the swells on 100 nm thick film collapsed after the heat treatment up to 350 deg whereas the swells on 10 nm thick film had no collapse excepting a few case. Comparing with the film without passivation, the swell is considered to be the result of atomic migration of copper film to form hillocks in the interface between copper film and AlN passivation film during heating. Atoms are considered to migrate reversibly into the copper film in the cooling stage, resulting to make vacant hall in the swell of AlN film and then collapse due to tensile stress development.

Improved transport properties of the two-dimensional electron gas in AlGaN∕GaN heterostructures by AlN surface passivation layer

The transport properties of the two dimensional electron gas (2DEG) in AlGaN∕GaN heterostructures with AlN, Si3N4, and SiO2 passivation layers and without passivation layer were investigated using Hall effect measurements over a temperature range of 30–550°C. Compared to the Si3N4 and SiO2 passivation dielectrics, the AlN film led to an obvious increase not only in carrier concentration but also in mobility of the 2DEG. The variation of the carrier concentration with temperature in the AlN passivated sample is also smaller in comparison with the Si3N4 passivated sample. These indicate that the AlN film is a promising passivation dielectric. In addition, the results from Hall and high-resolution x-ray diffraction measurements show that the change of strain after passivation contributes only in a relatively small proportion to the variation of the carrier concentration in AlGaN∕GaN heterostructures.

Surface Passivation of AlGaN/GaN HFETs Using AlN Layer Deposited by Reactive Magnetron Sputtering

In this paper we show the characteristics of an AlGaN/GaN metal–insulator–semiconductor heterostructure field effect transistor (MISFET) which uses an AlN film as the gate insulator, a passivated MISFET with another layer of AlN over the gate, a regular AlGaN/GaN heterostructure field effect transistor (HFET) and an AlN passivated regular HFET. The AlN insulating layer was deposited by Reactive Magnetron Sputtering. The thickness of each AlN passivation layer is about 50 nm. The gate leakage currents for the MISFET, passivated MISFET, and passivated HFET were much smaller than that for the regular HFET. We observed the current collapse for the regular HFET and the passivated MISFET, unstable DC characteristics for the MISFET, and the suppression of the current collapse for the passivated HFET.

High Performance HFET Devices on Sapphire and SiC: Passivation with AlN

ABSTRACTAlGaN/GaN two dimensional electron gas (2DEG) heterostructures were grown by ammonia-MBE on sapphire and SiC substrates. Devices fabricated from these optimized HFET layers, with optically defined gates showed excellent characteristics, e.g. a maximum drain current density of 1.3 A/mm, maximum transconductance of 220 mS/mm, fT of 15.6 GHz and fMAX of 58.1 GHz was measured for devices with 0.9 μm gate length and 40 μm gate width. Shorter gate length devices exhibited higher frequency responses: fT of 68 GHz and fMAX of 125 GHz for 0.25 μm gate length and fT of 103 GHz and fMAX of 170 GHz for 0.15 μm gate length. However, these devices showed “current collapse” when subjected to load pull measurements. Current collapse was also observed in sequentially repeated DC measurements in the dark, both on sapphire and SiC substrates, although the degree of collapse varied greatly from one wafer to another. One method of reducing the current collapse was to apply a thin (100 - 6000 Å) magnetron sputtered AlN passivation layer (over the gates) or a 500 Å layer under the gates so that MISFET devices were obtained. The electrical characteristics of the passivated and unpassivated devices are discussed.

AlN thin films deposited by pulsed laser ablation, sputtering and filtered arc techniques

The present work describes the growth and characterization of AlN thin films deposited by pulsed laser deposition (PLD), DC magnetron sputtering and filtered arc techniques. The focus of this paper is not only on the optimization of process parameters for the production of device quality thin AlN films, but also to investigate deposition techniques that could provide stable and reliable dielectric films wide band-gap power device. We investigated the working gas pressure dependence of the deposition of AlN on the vertical walls of the etched/patterned silicon for device passivation studies. Under high-pressure (13.334–93.343 Pa) conditions, high-density plasma was achieved which produced AlN passivation of a vertically etched Si wall. The films were characterized by X-ray diffraction (XRD), Rutherford backscattering and ion channeling spectrometry, atomic force microscopy (AFM), UV-visible spectroscopy, scanning electron microscopy (SEM).

Measurements of the temperature and spatial variations of coercivity in magneto-optic recording media using a scanning laser microscope

A scanning laser microscope was used to obtain images of the spatial variation, on a micron scale, of coercivity in TbFeCo thin film samples with compositions close to the room-temperature compensation composition, which are to be used in magnetooptic recording applications. These images reveal local reductions in coercivity of about 30% in regions surrounding surface defects which are believed to be pinholes in the AlN passivation layer. The dependence of coercivity on the incident laser power, and hence sample temperature, was also observed, the coercivity being seen to reduce by an order of magnitude for a doubling of incident laser power density.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>