About
131
Publications
21,422
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,634
Citations
Introduction
Additional affiliations
December 2005 - present
February 2003 - December 2005
Publications
Publications (131)
Al0.7Sc0.3N films are deposited on Si substrates
and SiO2/Mo-based acoustic mirrors in an Endeavor-MX
cluster tool equipped with a dual-cathode S-gun magnetron and
ring-shaped sputtering targets containing alternated Al and Sc
segments. The samples are subjected to one-hour thermal
treatments in vacuum at 600ºC to test the stability of the
crystall...
We prove the ability of a gravimetric sensor consisting in an AlN-based solidly mounted resonator (SMR) operating in the shear mode to decouple mass detection from temperature variations. This is achieved by simultaneously monitoring both the resonant and antiresonant frequency of the shear mode during a detection experiment subjected to temperatur...
Al0.7Sc0.3N films were reactively sputtered from Al-Sc segmented targets by ac powered dual-cathode S-gun magnetron. Films with homogeneous Sc concentration within 30 +/-0.5 at. % were grown at ambient temperature directly on 200-mm (100) silicon wafers and on 100-mm silicon substrates covered with SiO2/Mo-based acoustic reflectors terminated by hi...
We present the successful growth of few-layer graphene on top of AlN-based solidly mounted resonators (SMR) using a low-temperature chemical vapour deposition (CVD) process assisted by Ni catalysts, and its effective bio-functionalization with antibodies. The SMRs are manufactured on top of fully insulating AlN/SiO2 acoustic mirrors able to withsta...
In contrast to quartz crystal microbalances, the sensitivity of thin film bulk acoustic wave resonators (FBARs) is strongly dependent on all films comprising the multilayered structure. Previous studies proved that placing low acoustic impedance materials at the sensing surface of longitudinal-mode FBARs operating in air can enhance their mass sens...
We present the successful integration of graphene on top of AlN-based solidly mounted resonators (SMRs), using a low temperature CVD process and Ni layers as catalyst. We develop a protocol to functionalize the surface of the resonators that starts with a low damage O2 radical plasma treatment of the surface of the devices that introduces a control...
In this work, we grow different types of carbon nanotube (CNT) forests directly on AlN-based electroacoustic biosensors and study their functionalization efficiency. CNTs are used to increase the effective surface area of the sensor, pursuing a better sensitivity, without increasing the sensor capacitance. Here we use a general method for CNT bio-f...
Surface acoustic wave (SAW) devices are currently the most exploited acoustic wave devices for high temperature applications due to their straightforward fabrication (few photolithographic steps) and ability for wireless interrogation. However they have some drawbacks like the destructive agglomeration of their electrodes, leading to low power hand...
Carbon nanotubes (CNTs) have been typically employed as active layers in sensors, however their vertically-aligned (forest) morphology has not been fully explored yet. Here we directly integrate CNT forests on AlN-based solidly mounted resonators and study their influence on the performance of the longitudinal and shear mode of operation. Results s...
The first steps in the development of an aptasensor for bacterial meningitis diagnosis in real time are described: slow off-rate modified aptamers (SOMAmer) selection, gravimetric sensor fabrication and functionalization of its active surface. SOMAmers polyclonal populations were generated to surface specific proteins PavA (S. pneumoniae) and FHbp...
We analyse the performance of solidly mounted bulk acoustic wave resonators under induced mechanical stress to explore their viability as strain sensors. The resonators are made of polycrystalline AlN piezoelectric thin films containing uniformly tilted microcrystals to excite both longitudinal and shear modes. The resonators are grown on top of si...
In this communication we present the integration of graphene on the top electrode of solidly mounted resonators based on piezoelectric AlN thin films for gravimetric sensor applications. Because its particular chemical structure, graphene shows great potential as a bio-functionalization platform. However, in order to be commercially viable, direct...
Gravimetric sensors based on shear-mode resonators are suitable for in-liquid detection of biological species because their quality factors barely decrease during in-liquid operation. However, we have found that in the particular case of large ligands, such as bacteria, the transmission of the surface movement to them appears to be more efficient w...
We present the direct comparison of the performance of two gravimetric biosensors based on acoustic resonators, a quartz crystal microbalance and a high frequency AlN-based bulk acoustic wave film solidly mounted resonator (SMR). Both sensors are functionalized with streptavidin to detect the response to TBA29 aptamer biotin modified and different...
We investigate the performance of solidly mounted resonators based on Ir/tilted-AlN/Ir piezoelectric stacks as biosensors. These films are deposited by varying the pressure, the cathode power and the temperature of a two-step process based on depositing (00·2)-tilted AlN active layers over an (10·3)-oriented AlN seed layer. To minimize the influenc...
The frequency variation of solidly mounted resonators made with AlN thin films operating in longitudinal and shear acoustic modes with induced in plane mechanical strain is presented. The induced deformation range is in the hundreds of microstrains and the frequency variations in the hundreds of kHz, giving coefficients of resonant frequency with d...
Transparent electronic devices have interesting applications in a wide range of fields, such as wearables, intelligent windows, new concepts of smartphones and sensors. In this work we present fully transparent AlN-based thin film bulk acoustic wave solidly mounted resonators. We have used indium-tin oxide as the transparent material for the electr...
Electro-acoustic sensors proving an adequate operation in liquid media are appropriate candidates for biosensing or liquid monitoring applications. In this context, electro-acoustic devices based on Lamb waves have been widely used for such purpose during the last years. More particularly, S0 mode Lamb wave resonators (S0-LWRs) have shown promising...
ZnO films with a c-axis significantly inclined away from the surface normal were grown by a remote plasma sputtering technique at room temperature. The films were used to make solidly mounted resonators (SMRs) operating in shear mode at a resonant frequency of 1.35 GHz. Control of the ZnO microstructure was achieved using a polycrystalline AlN seed...
Gravimetric biosensors based on piezoelectric resonators have their active area just atop an electrical contact. Sometimes both contacts are located on the same surface (coplanar electrodes). The use of bio-buffers with high ionic content makes often electrical isolation of the electrodes from the liquid mandatory. This restricts the use of surface...
Owing to their outstanding electrical properties, carbon nanotubes (CNTs) are currently being considered as interconnects in microelectronic circuits and large area electrodes. For large area electrodes, CNT must grow as dense and vertically aligned forests, displaying sheet resistances as low as possible. Here we present two straightforward method...
Gravimetric sensors based on solidly mounted resonators require fully insulating acoustic reflectors to avoid parasitics when operating in liquid media. In this work we propose a new high acoustic impedance material, tungsten oxide (WO3), for acoustic reflectors. We have optimized the sputtering conditions of WO3 to obtain nonconductive layers with...
We grow carbon nanotube forests on piezoelectric AlN films and fabricate and characterize nanotube-based solidly mounted bulk acoustic wave
resonators employing the forests as the top electrode
material. The devices show values for quality factor at anti-resonance of ∼430, and at resonance of ∼100. The effective coupling coefficient is of ∼6%, and...
Abstract Biosensors based on AlN bulk acoustic wave resonators require shear mode operation to avoid acoustic losses upon analysing liquid samples. To generate shear modes, the microcrystals of the AlN thin film must be uniformly tilted with respect to the normal, yet keeping good piezoelectric properties. In this paper, we demonstrate AlN solidly...
Carbon nanotubes (CNTs) growth on piezoelectric AlN substrates has appeared to be important in sensing purposes using acoustic technology. CNT forests can act as sensing layers with high surface active area. We study such growth by using Fe as active catalyst and Ti, Cr and Al as catalyst underlayers. All underlayers enable CNT growth at temperatur...
Growing carbon nanotube (CNT) forests on metals for integrated circuits interconnections or active layers applications is currently a challenge. CNT forests easily develop on insulators but their growth on metallic substrates is subject to interdiffusion and wettability effects that hamper the formation of the catalyst nanoparticles. This paper rep...
Thin film acoustic resonators operating in the shear mode are being increasingly used for in-liquid sensing applications. A good design of such sensors requires accurate knowledge of the acoustic properties of the materials composing the whole device, which specifically includes their shear velocities. Here we present a method to assess the shear a...
In this work, we describe a sputter technique enabling deposition of AlScN thin films with homogeneous thickness and composition on production size wafers (150-200 mm) and present some preliminary results on the assessment of the structural and piezoelectric properties of the films with Sc content of about 6.5 at.%. The technique is based on the us...
This paper proposes several solutions to adapt AINbased acoustic resonators to sensors for in-liquid applications. The main requirements of these devices are addressed: the growth of AIN films with properly tilted grains for the excitation of shear modes, the isolation of the electrical connections from the microfluidic system that leads the liquid...
Owing to their outstanding electrical properties, carbon nanotubes (CNTs) are currently being considered as interconnects in microelectronic circuits and large area electrodes. For large area electrodes, CNT must grow as dense and vertically aligned forests, displaying sheet resistances as low as possible. Here we present two straightforward method...
Monitoring under harsh environments, particularly high temperatures (> 600°C), is on high demand nowadays. Applications such as gas control in propulsion systems or fire detection in early stages are good examples. During the last decades, materials and devices have been extensively investigated for these applications. Few have proven thermal and c...
High sensitive sensors are one of the goals of the
modern society due to an increasing necessity for real-time
monitoring. To achieve this, new devices and materials are being
developed nowadays. In particular, electroacoustic resonators
have gained importance in the chemical and biological sensors
field owing to their promising performances. Altho...
For many applications, compensation of the
temperature coefficient of the resonant frequency in solidly
mounted resonators is needed. The influence of the different
materials in such a complex structure upon this coefficient is not
easily understandable. The material characteristics of each layer
influence this coefficient but the relative position...
We have fabricated BAW resonators with a piezoelectric bilayer that combines ZnO and AlN films. These stacked devices show two resonances that could be used to simultaneously track temperature variations and another parameter, such as loaded mass or pressure. We have assessed the crystal quality of the stacked piezoelectric films using XRD and FT-I...
High frequency electroacoustic biosensors require the use of microfluidic systems to confine the liquid under test on the sensor surface. Owing to frequent conductive character of biochemical solutions, the contacting pads must be isolated from the active areas of the sensors by means of electrical extensions. At working frequencies in the GHz rang...
We present a method to assess the shear acoustic velocity in SiO2 and Mo sputtered films, which are materials commonly used as low and high acoustic impedance layers in the acoustic reflectors of solidly mounted resonators. The method consists in the analysis of the frequency response of AlN-based resonators operating in the shear mode using acoust...
We investigate different procedures for achieving ZnO films with the c-axis tilted with respect to the normal for their application in acoustic resonators operating in the shear modes. The approach consists in combining the use of textured surfaces of different nature with off-axis sputtering, which promotes the growth of ZnO with inclined microcry...
In this paper we analyze the effects of doping AlN films with vanadium and tantalum to concentrations up to 6% atomic. The structure and composition of the new compounds are assessed as a function of the dopant concentration by x-ray diffraction (XRD), IR reflectance and Rutherford backscattering spectrometry (RBS). Test devices consisting on bulk...
In this paper the acoustic characterization of a layer of carbon nanotubes (CNT) deposited on AlN solidly mounted resonators is described. The structure of the CNT layer is analyzed by scanning electron microscopy and Raman spectroscopy. The electrical sheet resistance is derived from 4 point probe measurements and from the fitting of the electrica...
Two methods currently used to induce surface roughness that promotes the growth of AlN tilted grains to fabricate shear mode resonators have been investigated. The first one involves the use of a rough substrate to provide tilted facets on which the AlN grains will grow with a certain angle. The second method is based on using a thin non-piezoelect...
In this paper we propose the use of infrared spectroscopy as an alternative technique to X-ray diffraction for the assessment of the crystal orientation of aluminum nitride thin films. Infrared scans of samples with different tilt angles of the c-axis are measured to accurately determine the structure of the longitudinal optical absorption band, wh...
We have investigated the crystal quality, the residual stress and the composition of AlN thin films with {00·2} preferred orientation sputtered on metallic surfaces (Al0.9Si0.1, Cr, Mo and Ti) and, for comparison, on oxidized Si wafers. The AlN films deposited on metallic surfaces showed values of strain and residual stress significantly lower than...
In this paper we describe the fabrication and frequency characterization of different structures intended for the lateral excitation of shear modes in AlN c-axis-oriented films, which are at the same time designed to minimize the excitation of longitudinal modes. Laterally excited resonators were built on partially metallic (SiO2, W) and insulating...
In this work we present the assessment of the structural and piezoelectric properties of Al(0.5-x)TixN0.5 compounds (titanium content <6% atomic), which are expected to possess improved properties than conventional AlN films, such as larger piezoelectric activity, thermal stability of frequency and temperature resistance. Al:Ti:N films were deposit...
The utilisation of thin film technology to develop film bulk acoustic resonators (FBARs) and solidly mounted resonators (SMRs), offers great potential to outperform the sensitivity and minimum detection limit of gravimetric sensors. Up to now, the choice between FBARs and SMRs depends primarily on the users' ability to design and fabricate Bragg re...
This work describes the assessment of the acoustic properties of sputtered tantalum oxide films intended for use as high-impedance films of acoustic reflectors for solidly mounted resonators operating in the gigahertz frequency range. The films are grown by sputtering a metallic tantalum target under different oxygen and argon gas mixtures, total p...
We investigate the sputter growth of very thin aluminium nitride (AlN) films on iridium electrodes for electroacoustic devices operating in the super high frequency range. Superior crystal quality and low stress films with thicknesses as low as 160nm are achieved after a radio frequency plasma treatment of the iridium electrode followed by a two-st...
We investigate the excitation and propagation of acoustic waves in polycrystalline aluminum nitride films along the directions parallel and normal to the c-axis. Longitudinal and transverse propagations are assessed through the frequency response of surface acoustic wave and bulk acoustic wave devices fabricated on films of different crystal qualit...
Solidly mounted resonators (SMRs) with a top carbon nanotubes (CNTs) surface coating that doubles as
an electrode and as a sensing layer have been fabricated. The influence of the CNTs on the frequency
response of the resonators was studied by direct comparison to identical devices with a top metallic
electrode. It was found that the CNTs introduce...
This work describes the performance of AlN-based bulk acoustic wave resonators built on top of insulating acoustic reflectors and operating at around 8 GHz. The acoustic reflectors are composed of alternate layers of amorphous Ta2O5 and SiO2 deposited at room temperature by pulsed-DC reactive sputtering in Ar/O2 atmospheres. SiO2 layers have a poro...
This work describes the structural and piezoelectric assessment of aluminum nitride (AlN) thin films deposited by pulsed-DC reactive sputtering on insulating substrates. We investigate the effect of different insulating seed layers on AlN properties (crystallinity, residual stress and piezoelectric activity). The seed layers investigated, silicon n...
The work reported here shows a direct experimental comparison of the sensitivities of AlN solidly mounted resonators (SMR)-based biosensors fabricated with standard metal electrodes and with carbon nanotube electrodes. SMRs resonating at frequencies around 1.75 GHz have been fabricated, some devices using a thin film of multi-wall carbon nanotubes...
This paper reports the simultaneous fabrication of Receive and Transmit Bulk Acoustic Wave filters for the WCDMA standard on the same die. Both filters are based on Solidly Mounted Resonators using a common Bragg mirror, but with each having a specific piezoelectric film thickness. Electrical measurements reveal that the process steps required to p...
This work describes the assessment of the acoustic properties of sputtered tantalum oxide films intended as high impedance films for the acoustic isolation of bulk acoustic wave devices operating in the GHz frequency range. The films are grown by sputtering a metallic tantalum target under different oxygen and argon gas mixtures, total pressures, p...
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, polycr...
We investigate the sputter growth of very thin aluminum nitride (AlN) films on iridium electrodes for high frequency filtering applications. The structure and piezoelectric activity of AlN films are assessed through XRD, FTIR, stress and frequency response measurements. A combination of a pre-deposition RF plasma treatment of the Ir bottom electrod...
The non-radiative exciton decay model recently developed to account for swift-ion-beam damage to LiNbO3 is, here, discussed within a general physical perspective, taking previous work on alkali halides as a reference. Some general rules for the validity of excitonic models have been put forward, allowing one to predict the irradiation behaviour of...
We investigate the influence of the structure of acoustic reflectors on the quality factors of solidly mounted bulk acoustic wave resonators made of aluminum nitride. We compare the quality factors of resonators built on conventional λ/4 Bragg reflectors with those of resonators fabricated on asymmetric acoustic reflectors composed of layers of thi...
The development of silicon oxide layers with high etch rates to be used as sacrificial layers in surface micromachining for microsystems fabrication poses a great technological challenge. In this work, we have investigated the possibility of obtaining easily removable silicon oxide layers by pulsed-direct current (DC) magnetron reactive sputtering....
In this paper we present the design, fabrication technology, and characterization of BAW filters for the Digital Cellular System (DCS) Tx-band at 1.75 GHz. The filters are fabricated with AlN-based solidly mounted resonators (SMR) using iridium electrodes, in an attempt to increase the effective electromechanical coupling factor of the BAW devices...
In this paper we describe the procedure to sputter low acoustic impedance SiO
<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>
films to be used as a low acoustic impedance layer in Bragg mirrors for BAW resonators. The composition and structure of the material are assessed through infrared absor...
We investigate the performance of Bragg mirrors containing iridium and porous silicon dioxide layers as acoustic reflectors for aluminum nitride solidly mounted resonators. The very large mismatch between the acoustic impedances of these materials allow to broaden the bandwidth of the mirrors to values larger than 2 GHz. Bragg mirrors consisting of...