|
Descripción
|
|
|---|---|
| Early diagnosis and detection of diseases are essential for reducing mortality rate and preventing long-term hospitalization and waste of resources. These requirements have boosted the efforts and funding on the research of accurate and reliable means for detection and quantification of biological species, also known as biosensors. The work presented in this thesis describes the development and fabrication of gravimetric biosensors based on piezoelectric AlN bulk acoustic wave (BAW) solidly mounted resonators (SMRs) for detection of biological species in liquid media. These type of devices base their sensing principles in the variation that their resonant frequency suffers when a mass is attached to their surface. They need to operate in the shear mode to maintain a strong resonance in liquid and an adequate functionalisation of the sensing area guarantees that only the targeted molecules cause the shift. The challenges that need to be overcome to achieve piezoelectric BAW resonators for high sensitivity detection in fluids require a multidisciplinary approach, that include the study of the materials involved, the design of the device and the fluidic system, the biochemical functionalisation of the active area, the experimental proof-of-concept with different target species and the design of an electronic readout circuit. All this tasks have been tackled at different stages of the thesis and the relevant contributions are described in the document. In the field of materials, a two-stage sputtering deposition process has been developed to obtain good-quality AlN films with uniformly tilted grains. This is necessary to fabricate transducers capable of operating in the shear mode. The shear acoustic velocities of the materials composing the acoustic reflector have been accurately studied to ensure an optimum design of the stack. WO3, a novel material with high acoustic impedance for insulating acoustic reflector has been presented. It displays several technological advantages for the processing of the resonators. Regarding the design, a study of the influence of the electrical extensions on the performance of the devices has been performed. These extensions are necessary to fit a fluidic system that holds the liquid during the measurements. The results indicate that high resistivity Si wafers and insulating reflectors are necessary to avoid the hindering of the resonance due to the parasitic effects induced by the extensions. The influence of the different layers of the stack on the resultant TCF of the SMR has also been investigated. The two layers of the reflector closer to the piezoelectric layer have a significant influence on the TCF, and it can be reduced by modifying their thicknesses accordingly. The data provided by these studies has led to the final design of the devices, which operate at 1.3 GHz in the shear mode and display an active area of 65000 µm2 and electrical extensions of 1.7 mm while keeping a Qshear=150 in liquid. The extensions enable to fit a custom-made fluidic system made of methacrylate. To perform the biosensing experiments, an experimental setup with a liquid closed circuit and a constant flow has been presented. Buffers with different ionic characteristics have been tested on devices without isolation layer, discovering that the high frequency of operation avoids the risk of short circuit. An ad-hoc functionalisation protocol based on the standard APTES ? Glutaraldehyde process has been developed. It includes two main variations that simplify the fabrication of the transducers: the use of IrO2 as oxidation layer and the replacement of the Piranha Attack by an O2 plasma treatment that does not damage the resonators. Both antibodies and aptamers are used as receptors. In-liquid sensing proof-of-concept experiments with thrombin, IgG mouse monoclonal antibody and sonicated bacteria have been displayed. A preliminary calibration of the devices using SiO2 layers reveals a sensitivity of 1800 kHz/pg?cm2 an | |
|
Internacional
|
Si |
|
ISBN
|
|
|
Tipo de Tesis
|
Doctoral |
|
Calificación
|
Apto cum laude |
|
Fecha
|
29/01/2016 |