The chemical and morphological properties of thin aluminum oxide film surfaces (Al 2 O 3 having 10 nm in thickness) in the asdeposited (dry) and after immersion (in pH buffer solutions) conditions were studied. Careful measurement conditions have been followed in order to determine any possible physical and/or chemical change on the surface of these films (after immersion in pH), so that proper correlation to their high and stable sensitivity to pH is possible. After deposition of thin Al 2 O 3 films (by Atomic Layer Deposition, ALD) on chemically oxidized p-type silicon wafers, the resulting Al 2 O 3 /SiO X /Si stacked structures were characterized by Fourier-Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM) before and after immersion in pH buffer solutions. Also, the Capacitance-Voltage (C-V) and Current-Voltage (I-V) characteristics were obtained after fabrication of Metal-Insulator-Semiconductor (MIS) devices in order to correlate the good chemical and morphological characteristics of thin Al 2 O 3 to its electrical properties. Based on the characterization results, low surface oxidation/dissolution mechanisms are found in ALD aluminum oxide films when immersed in pH buffer solutions during short immersion times (immersion time ≤ 10 minutes); therefore, leading to the characteristic slow degradation of the sensitivity to pH for this dielectric material.Ion-Sensitive Field-Effect Transistor (ISFET) devices, which are able to sense the activity of diverse chemical and biological species by transducing an electrochemical reaction into an electronic current, have a widespread use in these areas due to their micron-sized geometries (high integration density), fast speed of response and relatively low cost. Although they have many advantages, there are also various drawbacks to overcome. For instance, there is a considerable drift and hysteresis of ISFET response when it is operated in the long term under continuous conditions. These instabilities are usually related to the degradation of the chemical composition of the sensing layer (typically silicon nitride, Si 3 N 4 ); i.e., oxidation degrades the commonly stable chemical response of the nitride layer to the unstable SiO 2 ; 1 also, hydration of the Si 3 N 4 film could modify its dielectric properties in such a way that a more conductive surface layer is formed 2 and finally, saturation of the film's surface could occur from continuous adsorption of the chemical species of interest. 1 On the other hand, for integration into useful electronic devices, these sensing materials must comply with a fully compatible Complementary Metal-Oxide-Semiconductor (CMOS) fabrication process, so that a low manufacturing cost of the final sensor can be obtained; 3-5 as a result, world research efforts are being focused into using novel dielectric materials as sensitive gates for ISFETs like stoichiometric Al 2 O 3 . Although aluminum oxide presents a high sensitivity to pH (close to the ideal Nernstian response), 2,6 neither the degradation mechanisms for ...

An analysis of the effect of distance and alignment between two magnetically coupled coils for wireless power transfer in intraocular pressure measurement is presented. For measurement purposes, a system was fabricated consisting of an external device, which is a Maxwell-Wien bridge circuit variation, in charge of transferring energy to a biomedical implant and reading data from it. The biomedical implant is an RLC tank circuit, encapsulated by a polyimide coating. Power transfer was done by magnetic induction coupling method, by placing one of the inductors of the Maxwell-Wien bridge circuit and the inductor of the implant in close proximity. The Maxwell-Wien bridge circuit was biased with a 10 MHz sinusoidal signal. The analysis presented in this paper proves that wireless transmission of power for intraocular pressure measurement is feasible with the measurement system proposed. In order to have a proper inductive coupling link, special care must be taken when placing the two coils in proximity to avoid misalignment between them.

This paper reports the novel design of a touch mode capacitive pressure sensor (TMCPS) system with a wireless approach for a full-range continuous monitoring of ventricular pressure. The system consists of two modules: an implantable set and an external reading device. The implantable set, restricted to a 2 × 2 cm2 area, consists of a TMCPS array connected with a dual-layer coil, for making a reliable resonant circuit for communication with the external device. The capacitive array is modelled considering the small deflection regime for achieving a dynamic and full 5–300 mmHg pressure range. In this design, the two inductive-coupled modules are calculated considering proper electromagnetic alignment, based on two planar coils and considering the following: 13.56 MHz frequency to avoid tissue damage and three types of biological tissue as core (skin, fat and muscle). The system was validated with the Comsol Multiphysics and CoventorWare softwares; showing a 90% power transmission efficiency at a 3.5 cm distance between coils. The implantable module includes aluminum- and polyimide-based devices, which allows ergonomic, robust, reproducible, and technologically feasible integrated sensors. In addition, the module shows a simplified and low cost design approach based on PolyMEMS INAOE® technology, featured by low-temperature processing.

We studied the surface morphology and biocompatibility of hydrogenated amorphous silicon-germanium (a-Si1-xGex:H) thin films prepared by Low Frequency Plasma Enhanced Chemical Vapor Deposition (LF-PECVD). These films were deposited on a Corning 2947 glass substrate having a thickness of 3 μm, the electrical performance showed a decreased electrical resistance for low regime voltage. The root mean square (RMS) surface roughness of the films was measured by atomic force microscopy (AFM) in a non-contact mode. A biocompatibility tests was carried out using primary cultures of dorsal root ganglion (DRG) of Wistar rats. The DRG neurons were incubated for 18 hours on a-Si1-xGex:H thin films, and subsequent electrophysiological recording was performed. These neurons displayed typical ionic currents, including a fast-inward current at the beginning of voltage clamp pulse (Na+ current) and ensuing outward currents (K+ current). In current clamp experiments, depolarizing current pulse injection caused typical action potential discharge of the neurons. These results confirmed the feasibility of using a-Si1-xGex:H thin films as a biocompatible material.

In this research work, we present the synthesis and characterization of four different TiO2 structures, such as nanotubes, nanocavities, nanosheets assembled on nanocavities and nanobowls assembled on nanocavities, prepared by electrochemical anodization using organic electrolytes. After synthesis, the structures were thermally annealed to pass from the amorphous phase to the anatase phase, which is one of the most important crystalline structures of TiO2 due to its high photocatalytic activity and stability. The unique morphology and topography were studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental composition was determined by energy-dispersive X-ray spectroscopy (EDS). The anatase phase was verified by Raman microscopy and X-ray diffraction (XRD), the band gap energy was calculated by the Kubelka–Munk function, and the main defect states that generate the emission, as well as their lifetime, were determined by photoluminescence spectroscopy and time response photoluminescence (TRPL), respectively. The TiO2 nanomaterials were tested as catalysts in the photodegradation of a solution of methylene blue using a UV lamp at room temperature. The results showed complex morphologies and different surface roughness areas of these nanomaterials. Furthermore, a relationship between defect states, band gap energy, and photocatalytic activity was established. We found that the catalytic activity was improved as an effect of geometric parameters and oxygen vacancies.