Study of effect of deposition temperature of Surface Acoustic Wave devices on Aluminum
Nitride thin films obtained by Pulsed Laser Deposition
J.A. Pérez1,2*, J. C. Caicedo3, H. H. Caicedo4,5, L. Yate6, H. Riascos3
1,2Synchrotron
Radiation and Particle Accelerators, Universidad Autónoma Barcelona, Spain
de Física, Universidad Tecnológica de Pereira, Colombia
1Grupo Películas Delgadas, Universidad del Valle, Cali – Colombia
4Department of Bioengineering University of Illinois at Chicago, IL 60612, USA
5 Department of Anatomy and Cell Biology, University of Illinois at Chicago, USA
6Department de Física Aplicada i Óptica, Universitat de Barcelona, Catalunya, Spain
3Departamento
jaimeandres@ingenieros.com
Abstract
This document describes the relationship between surface acoustic wave (SAW) designed on thin films
of aluminum nitride (AlN) grown on Si3N4 substrates by using a Pulsed Laser Deposition and optical
properties. Moreover the dependency of both properties with temperature of deposition. The thickness
measured by profilometer was 150 nm for all films. Moreover Surface Acoustic Wave (SAW) devices
with a Mo/AlN/Si3N4 configuration have been fabricated, employing AlN-buffer and Mo Channel. The
morphology and composition of the films were studied using Atomic Force Microscopy (AFM), Scanning
Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy analysis (XPS), respectively. The
value of binding energy obtained for the Al2p peak was 73.9 eV and the higher value for Al2p was 75.6
eV, respectively. According to the literature [1-3] for the Al2p peak, the first one (73.9 eV) and the
second one (75.6 eV) can be assigned to Al–N and Al O bonds. The appearance of the peak at 73.9 eV
clearly shows that Al has reacted with N; therefore, it can be assigned to Al N. In Fig. 1, N1s peak is
composed of spin doublets, each separated by 2.9 eV. The XPS spectrum of N1s, well fitted by two
Gaussian functions, depicts the N1s spectrum with values at 397.3 eV and 400.2 eV characteristic for
N-N and Al-N bonds, respectively [4]. The magnification image showed in Fig. 2 exhibits that Mo lines
are continuous, without any interruption or short circuit. After electrical measurements, it was possible to
deduce an insulator behavior for our AlN structures, a good prerequisite for using them as surface
acoustic wave (Mo/AlN/SAW) devices. The optical reflectance spectra and color coordinates of the films
were obtained by optical spectral reflectometry technique in the range of 400 – 900 cm-1 by an Ocean
Optics 2000 spectrophotometer. In this work, a clear dependence in morphological properties,
reflectance, dominant wavelength color purity, frequency response and acoustic wave velocity in terms
of the applied temperature to the substrate was found. It was observed a reduction in reflectance of
about 10% and the increase of acoustic wave velocity of about 1.2 % when the temperature was
increased from 200 to 630°C. Therefore, the AlN films deposited around 450 ºC offer the best synergy
for optical and acoustic properties with good reflectance and an acceptable acoustic wave velocity.
Furthermore, the nanometric grain size and in thickness of such thin films AlN/Si 3N4 a low surface
roughness (≤120 nm), the nucleation side is characterized by a relatively small grain size (≤70 nm),
which can be decreased with increased substrate temperature improving processes nucleation, hence
enhancing the propagation of elastic waves.
References
[1]
C. Zhuang, J. Zhao, F. Jia, C. Guan, Z. Wu, Y. Bai. Surf. Coat. Technol. 204 (2009) 713–717
[2]
P.W. Wang, S. Sui, W. Wang, W. Durrer, Thin Solid Films 295 (1997) 142-146
[3]
V. Brien, P. Pigeat. J. CrystGrowth. 299 (2007) 189
[4]
J.A. Pérez, H. Riascos, J. C. Caicedo, G. Cabrera, L. Yate, (2011) J. Phys.: Conf. Ser. 274
Figures
1800
1600
1800
(a)
1600
1400
N-AL
397.3 eV
N1s
(b)
Intensity (c/s)
1400
1200
1000
800
600
Al-O
75.6 eV
400
1200
1000
800
600
N-N
400.2 eV
400
200
200
0
82
80
78
76
74
72
70
68
66
0
64
408 406 404 402 400
Binding energy (eV)
398 396 394 392 390
Binding energy (eV)
Figure 1. High-resolution XPS spectrum of: (a) Al2p and (b) N1s of Al-N film is around 300 °C
Figure 2. SEM micrographs showing the interdigital structure of Mo coating on AlN
films obtained by PLD: (a) general interdigital structure, (b) magnification images
where it is possible to observe the width and distribution of lines that conform the
interdigital device.
36
Re(%)
V(m/s)
34
25050
140
Velocity
Roughness
25000
(b)
25000
130
30
24900
28
24850
26
24800
24
24750
24950
Roughness (nm)
24950
Velocity (m/s)
32
120
24900
110
24850
24800
100
Velocity (m/s)
Reflectance (%)
Intensity (c/s)
Al-N
73.9 eV
Al2p
24750
22
20
24700
90
24650
200 250 300 350 400 450 500 550 600 650 700
80
Wavelength 760 - 800 (nm)
Mo/AlN/Si SAW
Deposition temperature (°C)
24700
200
300
400
500
600
700
o
Deposition Temperature ( C)
Figure 3. Correlation between optical properties (Reflectance) and acoustic wave velocity in Mo/AlN
SAW devices. In Figure 14b. There is a correlation between roughness and Rayleigh velocity as a
function of temperature deposit AlN thin films.