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 ...

The chemical and morphological characteristics of ALD Al2O3 and HfO2 layers after the immersion in no-buffer pH solutions have been obtained. These films are usually used as sensing layers in chemical sensors applications, and the morphology and chemical characteristics are of great importance to the chemicall sensitivity which they can provide. Hence, morphological changes has been recorded by atomic force microscopy (AFM), while the chemical characteristics has been obtained by Fourirer Transform Infrared Spectroscopy (FTIR). Also, the electrical characteristics, which need to be of high quality in ion-sensing applications, has been determined by High-Frequency Capacitance Voltage (C-V) measurements in Metal-Insulator-Metal capacitors (MIM). The results suggest that the changes experienced by the films under immersion are highly time and ionstrenght dependent, and this might be the main cause of drift in ionsensitive solid state sensors. Moreover, the data shows that HfO2 and Al2O3 exihibit different chemical characteristics after immersion than Si3N4, nonetheless, due to their high chemical sensitivity and higher dielecric constant these materials are well suited for applications in ion-sensing devices.

The design, fabrication and characterization of Ion-Sensitive Capacitive Sensors (ISCAPs) is presented. These sensors were fabricated with a single metal level CMOS process, and they incorporate special capacitive arrangements which help to improve the sensor's response (sensitivity). Specifically, the main advantage of this kind of sensor is that the measurements can be recorded by flat-band voltage shift and maximum capacitance (Cox) changes. Additionally, an integrated quasi-reference electrode has been included in the design, which provides the possibility of making measurements with both: an external or the integrated electrode. Based on previous results of the chemical and morphological characterization of materials after immersion in buffer solutions, ALD aluminum oxide (Al2O3) has been selected as the sensing material, providing both, high sensitivity and stability for measurements in the short term. It is shown that these sensors operate with both sensing mechanisms and with stability when measuring with the included quasi-reference electrode.

This work reports the surface chemical characterization of thin aluminum oxide (Al 2 O 3 ) layers after immersion in pH buffer and no-buffer solutions, and the fabrication of Ion-Sensitive Capacitors (ISCAP) employing these layers as the sensitive gate dielectric. We relate Al 2 O 3 chemical changes with the ISCAP's sensing characteristics, i.e. the density of surface/bulk chemical bonds present in these films with the sensitivity of ISCAPs to pH. In our fabricated chip, different ISCAP geometries are proposed for these sensors and these are integrated along with quasi-reference electrodes (using a thin metal layer directly exposed to the electrolytic solution), thus providing different pH sensitivities and flexibility with measurements in aqueous solutions.