In this work, we study the modes of vibration for various aluminium nitride-actuated square microplates. We combine electrical and optical techniques to fully characterize the modes of vibration in different media, with special attention to the modes with the highest quality factor. An electronic speckle pattern interferometry technique is used for a full 3D detection of the movement of the microplates, allowing a precise identification of the modal shape, even under liquid immersion. The electrical characterization was carried out with an impedance analyser. Quality factors as high as 6700 were obtained in vacuum, and as high as 155 in isopropanol, for a high order out-of-plane mode. The effective excitation of these modes is made possible by a proper design of the electrode layout.
In-situ monitoring of the physical properties of liquids is of great interest in the automotive industry. For example,
lubricants are subject to dilution with diesel fuel as a consequence of late-injection processes, which are necessary for
regenerating diesel particulate filters. This dilution can be determined by tracking the viscosity and the density of the
lubricant. Here we report the test of two in-plane movement based resonators to explore their capability to monitor oil
dilution with diesel and biodiesel. One of the resonators is the commercially available millimeter-sized quartz tuning
fork, working at 32.7 kHz. The second resonator is a state-of-the-art micron-sized AlN-based rectangular plate, actuated
in the first extensional mode in the MHz range. Electrical impedance measurements were carried out to characterize the
performance of the structures in various liquid media in a wide range of viscosities. These measurements were completed
with the development of low-cost electronic circuits to track the resonance frequency and the quality factor
automatically, these two parameters allow to obtain the viscosity of various fluids under investigation, as in the case of
dilution of lubricant SAE 15W40 and biodiesel.
In this work, we study the modes of vibration for two different families of aluminium nitride-actuated piezoelectric
microstructures: contour modes and flexure-actuated modes. For the contour modes, the structure vibrates at frequencies
determined by its edge dimensions whereas for the flexure-actuated modes a suspended structure is displaced by the
lateral bending of the flexures. We combine electrical and optical techniques to fully characterize the vibrating modes of
these types of in-plane MEMS structures. An electronic speckle pattern interferometry technique is used for a full 3D
detection of the movement of the structures. Quality factors as high as 5000 and motional resistance as low as 4 KOhm
were obtained for in-plane modes in air and a quality factor as high as 300 was obtained for an in-plane structure with
water on the top surface. This work shows the great flexibility in the selection of resonant modes in piezoelectric
resonators and actuators, implemented by a proper design of the electrode layout geometry.
In this paper we report on the high temperature compatibility of various adhesion layers for plat inum (Pt ) thin films. We
investigated different adhesion layers, such as titanium (Ti), tantalum (Ta), aluminium nitride (AlN), aluminium oxide
(Al<sub>2</sub>O<sub>3</sub>) and titanium oxide (TiO<sub>2</sub>). All films were deposited on SiO<sub>2</sub>/Si substrate by using the sputter technique. After
deposition the films were annealed in air at 800°C for different time lengths up to 16 h ours. After annealing, Al<sub>2</sub>O<sub>3</sub> and
TiO<sub>2</sub> showed a dense oxide layer between Pt and SiO<sub>2</sub>/Si and they seem to be suitable as adhesion layers for Pt at high
temperatures. AlN is not suitable as adhesion layer for Pt at high temperatures. Ti and Ta are also not suitable for high
temperatures, diffusing strongly into Pt layers and leading to the format ion of oxide precipitates (TiO<sub>x</sub> or TaO<sub>x</sub>) in the Pt
grain boundaries. In addition, the format ion of Pt-crystallites (hillocks) on the surface was common in all the films.
In this work, the fabrication process of piezoelectric AlN cantilevers is presented. The cantilevers were electrically
characterized in a vacuum chamber offering the possibility to close-loop control the back pressure from atmospheric
conditions down to 5x10<sup>-3</sup> mbar. The quality factor (Q factor) is an important figure of merit to evaluate the performance
of micro-resonators. In particular, two different modes were detected and analyzed. The first bending mode detected at
19.5 kHz has a quality factor of 470 at atmospheric pressure which increases continuously to 985 at 1x10<sup>-1</sup> mbar. The
corresponding resonant frequency shifted from 19.500 kHz at atmospheric pressure to 19.573 kHz at 5 mbar. Below this
pressure level, the resonance frequency stays unaffected within the measurement accuracy.
The second bending mode detected at 117.264 kHz exhibits a quality factor of about 570 at atmospheric pressure
increasing continuously to 1275 at 1x10<sup>-1</sup> mbar. In agreement with the other resonant frequency under investigation the
corresponding resonant frequency decreased from 117.264 kHz at atmospheric pressure to 117.630 kHz at 5 mbar.
In this work, we present a detailed study of the first vibration modes of a micro-tuning fork electrically actuated by
means of a differential electrode lying on a piezoelectric AlN layer. The actuation through a differential electrode allows
the optimal excitation of the modes of interest, including in-plane modes. Lateral and perpendicular displacements have
been measured for a complete characterization of the resonator. Promising results have been obtained, including high
values of the quality factor, which reach values above 4300 in air for the anti-phase in-plane modes.
Resonant microcantilevers are widely spread for different applications, such as atomic force microscopy or biosensor
devices. The use of piezoelectric films on top of the cantilevers is a very promising technology due to the possibility of
implementing an all electrical actuation/detection scheme. Among the different piezoelectric materials, polycrystalline
aluminium nitride (AlN) is a very attractive material as, in contrast to typical alternatives such as lead zirconate titanate
or zinc oxide, it is fully compatible with standard silicon technology, what facilitates its integration in silicon-based
In this study, our objective is to use sputter-deposited polycrystalline AlN as the actuation material for cantilever-based
biosensors and to study the performance of high frequency modes for bio-detection in liquid media. Our results
demonstrate a limit of mass detection of 0.07 ng for a 300x200 μm<sup>2</sup> cantilever in liquid media, which represents a value
below the mass of a monolayer of IgG on a 300x200 μm<sup>2</sup> area.
The characterization of the first in-plane mode of AlN-actuated piezoelectric microcantilevers was done using different
techniques. The top electrode of the cantilever was designed to allow for an efficient electrical actuation of these in-plane
modes. The detection of the electrically induced in-plane movement was performed optically with the help of a
stroboscopic microscope and electrically by means of an impedance analyzer. The quality factor and the resonant
frequencies of the in-plane modes were estimated from the above techniques. Our results show quality factor values as
high as 3000 for the first in-plane mode in air.
Aluminium nitride (AlN) reactively sputter deposited from an aluminium target is an interesting compound material due
to its CMOS compatible fabrication process and its piezoelectric properties. The crystal structure obtained during
sputtering is a very importance criterion to obtain a good piezoelectric performance. To demonstrate this, we focused our
investigations on two types of films. The first type shows a good c- axis orientation with round grain geometry. The
second type is (101) oriented having a triangular grain shape. For measuring the out-of-plane displacements for dij
determination, a MSV 400 Polytec scanning laser Doppler vibrometer was used. To obtain the piezoelectric constants d33
and d31 a fitting procedure between experimental and theoretical predicted results is used. Effective values for d33 and d31
in c-axis oriented films are about 3.0 pm/V and -1.0 pm/V, respectively. By contrast, films with (101) orientation show a
lower effective longitudinal piezoelectric coefficients, consistent with this different orientation.
Finally, both types of AlN layers were deposited on 640 μm long micro-cantilevers. The average displacement of the
first mode on the vertical axis was about 12 nm for the film with good c -axis orientation and 0.3 nm for that with (101)-
orientation when applying the same excitation.
The behaviour of AlN self-actuated beams for potential applications in the field of resonant sensors is analyzed focusing
on the characterization of the quality factor. This study is extended to high-order modes up to 7 MHz. Laser Doppler
vibrometry and impedance analysis were the measurement techniques used. For the former, the quality factor (Q factor)
is deduced from both, the frequency response and the transient response. The impedance measurement is not possible for
all the modes due to the symmetry in the modal shape, but when it can be measured, the Q factor may be deduced either
from the characteristic frequencies of the resonance or from the equivalent resonant circuit. All the four methods yielded
comparable magnitudes for the Q factor in air. In order to validate the quality of the devices, and for comparison
purposes, calculations based on finite element method were utilized, and a good agreement was found with measured
data, regarding modal shapes and resonance frequencies of each mode.
Here we present a comparison between polycrystalline AlN and (100) silicon as a support for the development of an
immunosensor. A covalent approach was followed for the modification of the initially oxidized surfaces. First a layer of
epoxy-based silane organic molecules was deposited. Next, protein A was immobilized with the purpose of taking
advantage of its ability to properly orient the antigen binding sites of IgG antibody molecules. Finally the antibodyantigen
reaction was accomplished using rabbit IgG and a corresponding antigen, such as anti-rabbit goat IgG. The antirabbit
goat IgG was labelled with HRP. This allowed us to quantify the quantity of immobilized antigen. Our results
demonstrate the reliability of polycrystalline AlN as a platform for immunosensing, with results comparable to those of
Micro-cantilevers and micro-bridges actuated by sputter-deposited aluminium nitride (AlN) thin films were measured
with a scanning laser Doppler vibrometer up to 6 MHz, covering more than 10 resonance modes of different nature. A
finite element model (FEM) was used to simulate the modal response of the micromachined structures. The comparison
between experiment and simulation, regarding modal shapes and frequencies, resulted in an excellent agreement, what
confirmed the quality of the structures. Finally, we point out, and illustrate with the help of micro-bridges, the
importance for a locally tailored distribution of electrical excitation on the top surface of the device, in order to either
optimize or cancel out the displacement of a given mode.
To ensure an enhanced life-time of micromachined devices, passivation layers are commonly applied to protect functionalized components against environmental stress. For flow sensitive elements on a flexible polyimide foil the use of reactively sputter-deposited aluminium oxide is investigated. Due to a high defect density located at the interface between the passivation layer and the organic substrate, the adhesion of the pure aluminium oxide thin films on the organic substrate was found to be poor when applying a combination of mechanical and thermal treatment as an accelerated ageing procedure. A bi-layer consisting of aluminium nitride and aluminium oxide is proposed to enhance the low adhesion capability being strongly disadvantageous for any technical application.
Aluminium nitride (AlN) reactively sputter deposited from an aluminium target is an interesting
compound material due to its CMOS compatible fabrication process and its piezoelectric properties. For the
implementation in micromachined sensors and actuators an appropriate patterning technique is needed to
form AlN-based elements. Therefore, the influence of different sputtering conditions on the vertical etch rate
of AlN thin films with a typical thickness of 600 nm in phosphoric acid (H<sub>3</sub>PO<sub>4</sub>) is investigated. Under
comparable conditions, such as temperature and concentration of the etchant, thin films with a high c-axis
orientation are etched substantially slower compared to films with a low degree of orientation. When a high
c-axis orientation is present detailed analyses of the etched topologies reveal surface characteristics with a
low porosity and hence, low roughness values. From temperature dependant etching experiments an
activation energy of 800 (± 30) meV is determined showing a reaction-controlled etching regime independent
of sputter deposition conditions.