Aluminum Nitride Film Thickness Research Articles

Optical and Structural Properties of Aluminum Nitride Epi-Films at Room and High Temperature

The high-quality aluminum nitride (AlN) epilayer is the key factor that directly affects the performance of semiconductor deep-ultraviolet (DUV) photoelectronic devices. In this work, to investigate the influence of thickness on the quality of the AlN epilayer, two AlN-thick epi-film samples were grown on c-plane sapphire substrates. The optical and structural characteristics of AlN films are meticulously examined by using high-resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), a dual-beam ultraviolet-visible spectrophotometer, and spectroscopic ellipsometry (SE). It has been found that the quality of AlN can be controlled by adjusting the AlN film thickness. The phenomenon, in which the thicker AlNn film exhibits lower dislocations than the thinner one, demonstrates that thick AlN epitaxial samples can work as a strain relief layer and, in the meantime, help significantly bend the dislocations and decrease total dislocation density with the thicker epi-film. The Urbach’s binding energy and optical bandgap (Eg) derived by optical transmission (OT) and SE depend on crystallite size, crystalline alignment, and film thickness, which are in good agreement with XRD and SEM results. It is concluded that under the treatment of thickening film, the essence of crystal quality is improved. The bandgap energies of AlN samples obtained from SE possess larger values and higher accuracy than those extracted from OT. The Bose–Einstein relation is used to demonstrate the bandgap variation with temperature, and it is indicated that the thermal stability of bandgap energy can be improved with an increase in film thickness. It is revealed that when the thickness increases to micrometer order, the thickness has little effect on the change of Eg with temperature.

Atomic Layer Deposition of Aluminum Nitride and Oxynitride on Silicon Using Tris(dimethylamido)aluminum, Ammonia, and Water

Thin films of aluminum nitride and oxynitride were deposited by atomic layer deposition (ALD) in the temperature range from 170 to 290°C (optimal deposition temperature 200–230°C). Tris(dimethylamido) aluminum and ammonia were used as precursors for the atomic layer deposition of aluminum nitride (AlN). The average AlN film thickness per ALD cycle (deposition rate) at 200°C was ~0.8 A. Films were deposited on a silicon substracte with a native oxide layer. The N/Al atomic concentration ratio in the obtained films was ~1.3. Aluminum oxynitride films obtained by periodical dose of water vapor in the course of atomic layer deposition of AlN at 200°C. The composition of the deposited oxynitride films was Al0.5O0.43N0.07.

Microstructure of epitaxial AlN layers on sapphire substrates deposited by physical vapor deposition

ABSTRACTAsymmetric (10L) XRD peaks have been employed as a measure of epitaxial quality for aluminum nitride (AlN) nucleation layers (NL) deposited on sapphire substrate. Epitaxial AlN films have been deposited on 2-6” sapphire substrate by reactive sputtering. FWHM of AlN (103) and (105) were found to be an excellent indicator of quality of AlN films for GaN growth. AlN films produced nucleation layers with highly reproducible microstructure and GaN film growth. NLs had in-plane and out-of-plane texture as evident by the pole-figure results and selected area diffraction pattern. Based on electron microscopy results, AlN film thickness for complete atomic ordering was estimated to be 6-7 nm and most of the edge dislocations were seen in the first 20 nm of the film. Excellent thickness and texture uniformity were seen on planar and patterned sapphire substrates. A compressive stress of 2.9±0.2 GPa was seen in our BKM films. The maximum screw and edge dislocation densities of films were found to be ∼3 x 108 cm−2 and ∼9 x 109 cm−2 respectively. The root mean square roughnesses of A-polar films were found to be < 0.3 nm.

Thermally compensated aluminum nitride Lamb wave resonators for high temperature applications

In this letter, temperature compensation for aluminum nitride (AlN) Lamb wave resonators operating at high temperature is presented. By adding a compensating layer of silicon dioxide (SiO2), the turnover temperature can be designed for high temperature operation by varying the normalized AlN film thickness (hAlN/λ) and the normalized SiO2 film thickness (hSiO2/λ). With different designs of hAlN/λ and hSiO2/λ, the Lamb wave resonators were well temperature-compensated at 214 °C, 430 °C, and 542 °C, respectively. The experimental results demonstrate that the thermally compensated AlN Lamb wave resonators are promising for frequency control and sensing applications at high temperature.

Microscale inverse acoustic band gap structure in aluminum nitride

This work presents the design and demonstration of a microscale inverse acoustic band gap (IABG) structure in aluminum nitride (AlN) with a frequency stop band for bulk acoustic waves in the very high frequency range. Conversely to conventional microscale acoustic band gaps, the IABG is formed by a two-dimensional periodic array of unit cells consisting of a high acoustic velocity material cylinder surrounded by a low acoustic velocity medium. The periodic arrangement of the IABG array induces scattering of incident acoustic waves and generates a stop band, whose center frequency is primarily determined by the lattice constant of the unit cell and whose bandwidth depends on the cylinder radius, the film thickness, and the size of the tethers that support the cylinder. A wide band gap (>13% of the center frequency) is formed by the IABG even when thin AlN films are used. The experimental response of an IABG structure having a unit cell of 8.6 μm and an AlN film thickness of 2 μm confirms the existence of a...

Fabrication of piezoelectric AlN thin film for FBARs

This paper focuses on the fabrication of film bulk acoustic-wave resonator (FBAR) comprising an aluminum nitride (AlN) piezoelectric thin film sandwiched between two metal electrodes and located on a silicon substrate with a low-stress silicon nitride (Si3N4) support membrane for high frequency wireless applications, and analyzes the optimization of the thin AlN film deposition parameters on Mo electrodes using the reactive RF magnetron sputter system. Several critical parameters of the sputtering process such as RF power and Ar/N2 flow rate ratio were studied to clarify their effects on different electrodes characteristics of the AlN films. The experiment indicated that the process for Mo electrode was easier compared with that of the Pt/Ti or Au/Cr bi-layer electrode as it entailed only one photo resist and metal deposition step. Besides, Pt/Ti or Au/Cr electrodes reduced the resonance frequency due to their high mass density and low bulk acoustic velocity. Compared with the case of the Al bottom electrode, there is no evident amorphous layer between the Mo bottom electrode and the deposited AlN film. The characteristics of the FBAR devices depend not only upon the thickness and quality of the AlN film, but also upon the thickness of the top electrode and the materials used. The results indicate that decreasing the thickness of either the AlN film or the top electrode increases the resonance frequency. This suggests the potential of tuning the performance of the FBAR device by carefully controlling AlN film thickness. Besides, increasing either the thickness of the AlN film or higher RF power has improved a stronger c-axis orientation and tended to promote a narrower rocking curve full-width at half-maximum (FWHM), but increased both the grain size and the surface roughness. An FBAR device fabricated under optimal AlN deposition parameters has demonstrated the effective electromechanical coupling coefficient (k eff 2 ) and the quality factor (Q f x ) are about 1.5% and 332, respectively.

Shear mode coupling and properties dispersion in 8 GHz range AlN thin film bulk acoustic wave (BAW) resonator

8 GHz range solidly mounted resonator (SMR) based on high quality direct current pulsed sputtered aluminum nitride (AlN) thin films have been fabricated on 100 mm diameter silicon wafer. Dispersion in AlN film thickness has been measured and on-wafer distribution of operating frequency, mechanical coupling and quality factor of the SMR has been investigated. Data is presented showing efficient coupling of a shear mode resonating in the 4 GHz range. This coupling was found to increase with wafer radius and related to the increasing tilt of crystalline c-planes of AlN thin film.

Highly c-axis oriented thin AlN films deposited on gold seed layer for FBAR devices

In this study, highly c-axis oriented aluminum nitride (AlN) films are deposited on gold (Au) seed layer using a rf reactive sputtering method under various rf power and sputtering pressures. The evolution of preferred orientation and surface morphologies of the deposited films was studied by x-ray diffraction, scanning electron microscope, and atomic force microscope. It was found that the AlN films prepared using the higher rf power of 400 W and sputtering pressure of 7 mTorr were shown to have the stronger c-axis orientation and exhibit smoother morphologies. The fabricated film bulk acoustic-wave resonator (FBAR) devices considered here with AlN film thickness are 2.25μm, Au and Al are used as bottom electrode and top electrode with the thickness of 0.1 and 0.18μm, respectively. The effective electromechanical coupling coefficient (keff2), quality factor (Qfx) and resonant frequency of the fabricated FBAR device were about 1.47%, 535 and 2.172 GHz, respectively. Moreover, the effect of the top electrode materials, AlN and Al top electrode film thickness on the frequency response characteristics of FBAR devices is also investigated.

Effect of AlN Film Thickness and Top Electrode Materials on Characteristics of Thin-Film Bulk Acoustic-Wave Resonator Devices

Highly c-axis-oriented aluminum nitride (AlN) thin films were deposited on Mo electrodes by reactive RF magnetron sputtering and their thickness effects on thin-film bulk acoustic-wave resonator (FBAR) characteristics are presented. The results obtained in this study show that thick AlN films have a strong c-axis orientation and tend to promote a small rocking curve full-width at half-maximum (FWHM), but a high grain size and a high surface roughness, hence degrading the characteristics of FBARs. The characteristics of FBARs depend not only the thickness and quality of AlN films, but also the thickness of the top electrode and the type of material used. Specifically, an increase in either AlN film or top electrode thickness increases parallel resonant quality factor (QP), but reduces effective electromechanical coupling coefficient (keff2). However, the resonance provides a maximum keff2 when AlN film thickness approaches the fundamental one-half-wavelength. The effects of the type of top-electrode material and AlN film thickness on the keff2 and quality factor of the fabricated FBARs are also discussed.

The dispersion properties of surface acoustic wave devices on AlN/LiNbO 3 film/substrate structure

Highly c-axis oriented aluminum nitride (AlN) films were deposited on z-cut LiNbO 3 substrates by reactive rf magnetron sputtering. The crystalline properties investigated by X-ray diffraction (XRD) revealed that AlN film with (0 0 2) preferred orientation was improved by an increase of the deposition time within the experimental range. However, the surface morphology of AlN film measured by scanning probe microscopy (SPM) showed that the roughness was getting worse with increase of deposition time. Surface acoustic wave (SAW) properties, measured by a network analyzer in the structure consisting of highly c-axis AlN films on z-cut LiNbO 3 substrates, were investigated. The phase velocity (V P) was significantly increased by the increase of h/ λ, where h is the thickness of AlN film and λ is the wavelength. However, the insertion loss (IL) of SAW filters was also increased by the increase of h/ λ. Experimental results on the temperature characteristics of SAW devices are also presented.

Synthesis of C-Axis-Oriented Aluminum Nitride Films by Reactive RF Magnetron Sputtering for Surface Acoustic Wave

C-axis-oriented aluminum nitride (AlN) films were deposited on SiO2-coated Si substrates by reactive rf magnetron sputtering. The crystallization of the AlN films, identified by X-ray diffraction (XRD) , was dependent on the deposition conditions. Highly c-axis-oriented AlN films, for fabricating AlN/SiO2/Si-based surface acoustic wave (SAW) devices, were obtained under an rf power of 300 W, substrate temperature of 350°C, sputtering pressure of 7.5 mTorr and N2 concentration of 75%. A dense pebblelike surface texture of the c-axis-oriented AlN films with an average grain size of about 100 nm was observed by scanning electron microscopy (SEM). The phase velocity showed a tendency to decrease with increasing kh, where k=2π/λ is the wavenumber and h is the AlN film thickness. In partucular, the phase velocity and the electromechanical coupling coefficient of the sample at kh=0.4 were calculated to be about 6080 m/s and 1.1%, respectively.