Susanna Martínez

Microinductive Signal Conditioning With Resonant Differential Filters: High-Sensitivity Biodetection Applications

Inductive-based devices integrated with Si technology for biodetection applications are characterized, using simple resonant differential filter configurations. This has allowed the corroboration of the viability of the proposed circuits, which are characterized by their very high simplicity, for microinductive signal conditioning in high-sensitivity sensor devices. The simulation of these simple circuits predicts sensitivities of the differential output voltage which can achieve values in the range of 0.1-1 V/nH, depending on the coil parameters. These very high-sensitivity values open the possibility for the experimental detection of extremely small inductance changes in the devices. For real microinductive devices, both series resistance and parasitic capacitive components contribute to the decrease of the differential circuit sensitivity. Nevertheless, measurements performed using micro-coils fabricated with relatively high series resistance and coupling parasitic effects have allowed detection of changes in the range of 2 nH. which are compatible with biodetection applications with estimated detection limits below the picomolarity range.

Electrochemical deposition of metal layers and structures for Si-based microsystems

This work reports the study of the electrochemical (EC) deposition of Ni metallic layers and Ni/Cu multilayer structures on Si based substrates. The structural analysis of the processed samples has been performed by X-ray diffraction (XRD) and these data have been correlated with the characterisation of their surface morphology by atomic force microscope (AFM) measurements. The results obtained show the strong dependence of the structural parameters of the deposited films on the substrate surface layer and growth current density, for Ni layers grown onto EC deposited Cu sacrifical ones a strong (2 2 0) preferred orientation evolves with deposition time. This is likely related to a textured structure of the Cu film. Direct deposition onto Au coated oxidised Si wafer allows to avoid this preferential orientation, but a strong decrease in the Ni growth rate is observed. Texturing of the Ni film can also be controlled by the current density during growth.

Growth and characterization of shape memory alloy thin films for Si microactuator technologies

NiTi thin film alloys have been grown on Si (1 0 0) substrates by sequential multilayer deposition of Ni and Ti layers followed by metal interdiffusion via annealing. Short-time (5 min) annealing of the deposited layers at 500 °C leads to alloying of Ni and Ti, provided that preferential oxidation of Ti is avoided. This has been achieved by capping the layers with AlN, which constitutes a very efficient barrier preventing oxygen contamination of the film. For uncapped films, annealing has to be performed under high vacuum conditions. The structure of the processed films strongly depends on the temperature and time of the thermal process, obtaining Ni- and Ti-rich phases when the films are annealed at higher temperatures and/or during longer times. As-grown and processed films are analyzed by X-ray diffraction, in-depth Auger electron spectroscopy and X-ray photoelectron spectroscopy techniques. Finally, resistivity measurements show the existence of a phase transition in the films annealed at 600 °C without the capping layers (vacuum furnace). This contrasts with the behavior observed for AlN capped films, where cracking of the film occurs during cooling, which has been attributed to generation of stress in the buried film during the phase transition.

Infrared analysis of buried insulator layers formed by ion implantation into silicon

Abstract In this work the strong influence of geometrical features on experimental transmission and reflection IR spectra on multilayer structures is reported. This dependence implies the need for a theoretical simulation of spectra in order to avoid misinterpretation of data. An experimental and theoretical procedure for the analysis of buried layers is proposed and discussed using experimental data from buried layers in Si formed by oxygen and nitrogen ion implantation. This procedure has allowed the structural analysis of the buried layers in Si to be made.

Buried oxide layers formed by oxygen implantation on screened oxide silicon wafers: structural analysis

Abstract In this work the structural analysis of the buried oxide layers formed by high dose oxygen ion implantation into Si through a screen oxide layer and annealing has been performed by infrared absorption, X-ray photoelectron spectroscopy and ellipsometry measurements. The correlation between the measurements from the different techniques points out the high structural quality of the buried oxide layers from the annealed structures. However, structural disorder is observed in the regions close to the Si/SiO 2 interfaces. This is strongly dependent on the screen oxide thickness. For the back Si/SiO 2 interface, this dependence can be correlated with the density of Si islands in the buried oxide layer.

Structural characterisation of nitrogen ion implantation into silicon for sensor technology

Abstract In this work buried etch-stop layers in silicon are formed by implantation of a substoichiometric dose of nitrogen and annealing at temperatures up to 1150°C. Transmission electron microscopy, secondary ion mass spectrometry, Raman spectroscopy and Fourier transform infrared spectroscopy are used to study the structure of the implanted material and its evolution with the thermal treatments. Results show that nitrogen is gettered around the implantation peak and that precipitation in the form of amorphous SiN and sometimes in α-Si3N4 occurs. Raman spectra suggest the presence of a remaining stress in the top Si layer, although the presence of a high density of amorphous SiN precipitates also contributes to the observed shifts.

Integrated inductances for Si-technology based high sensitivity biosensors

Inductive integrated devices for bio-sensing applications are simulated, designed and fabricated. These devices are based in the use of magnetic particles as markers of the biomolecule to be detected. The sensing principle of the device is related to the changes of the coil inductance determined by the presence of different densities of magnetic particles in the active device area. The devices are simulated assuming a continuous layer with an effective magnetic permeability /spl mu//sub ef/ which is given by the density of particles. This simulation has allowed analysing the influence of the different device parameters on the sensor response. Accordingly, a set of integrated coils with different dimensions (from 50 /spl mu/m up to 500 /spl mu/m) and number of turns has been fabricated using a two metal levels technology. Simulation of these devices gives inductance changes in the range 0.05-80 nH and sensitivities in the range 2-8% for /spl mu//sub ef/ = 10. The preliminary electrical characterisation of the devices agrees with their simulation, being the analysis of their sensor behaviour under progress.