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 ...

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In this research work, we prepared for the first time TiO 2 nanosheets and nanobowls assembled on an arrangement of TiO 2 nanocavities, and studied their morphological, optical, and structural properties. The assembled nanostructures were synthesized by a fast two-step electrochemical anodization using fluorides and ethylene glycol. By Field Emission Scanning Electron Microscopy, we showed that these nanostructures have a morphology well organized and ordered with a homogeneous distribution. Also, other characteristics such as photoluminescence, reflectance spectra, band gap energy, and Raman spectra were studied and compared with the optical and structural properties of TiO 2 nanotubes. We found that the time of anodization is a key parameter to control the final shape of the individual elements in the nanostructure. Our results show that when nanobowls or nanosheets are self-assembled on nanocavities the morphological, optical, and structural properties change significantly in comparison to TiO 2 nanotubes. Furthermore, the emission was improved considerably and the band gap energy was modified to higher energy values. Likewise, the interference fringes are generated in the reflectance spectra by the length of the nanocavities and by the thickness of the nanobowls and the nanosheets. Finally, a reduction on the displaced the E g(1) Raman mode was observed with decreasing of the length of the nanocavities.

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Heterojunctions with an n-type hydrogenated amorphous silicon germanium (a-SiGe:H) on p-type crystalline-silicon heterojunctions were fabricated and electrically characterized. The electrical characterization was made by current density-voltage (J -V ) and capacitance-voltage (C-V ) measurements. The C-V results confirm the existence of an abrupt heterojunction. The temperature dependence of the J -V curves shows that in the forward conduction at low bias voltage (V < 0.45 V) the current density is determined by the recombination on the n-type a-SiGe:H depletion region, while at higher voltages (V > 0.5 V), the space charge limited effect becomes the main transport mechanism. The conduction and valence band discontinuities of the heterojunction and the electron affinity of the n-type a-SiGe:H film were calculated using Anderson's model. Under reverse bias conditions the J -V curves suggest that the current density is limited by hopping through the localized states into the gap. One-dimensional (1D) simulations support the proposed transport mechanisms.

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We demonstrate Ge-on-Si metal-semiconductor-metal (MSM) photodetectors monolithically integrated with silicon oxynitride (SiOxNy) waveguides. The waveguide is placed on top of the photodetector and between the metal electrodes, evading the shading effect by metal electrodes, which is typical in surface-illuminated MSM photodetectors. The devices showed responsivity of about 0.45 A/W for 80 μm long devices at 1550 nm. The photodetector with 1.5 μm electrode spacing showed 3 dB bandwidth of 2.0 GHz at −2 V and 2 μA dark current. Further studies suggest that with a modified design the structure is capable of achieving 1 A/W responsivity and greater bandwidth.

Currently, researchers face new challenges in order to compensate or even reduce the noxious phenomenon known as bias-temperature instability (BTI) that is present in modern metal-oxide-semiconductor (MOS) technologies, which negatively impacts the performance of semiconductor devices. BTI remains a mystery in the way that it evolves in time, as well as the responsible mechanisms for its appearance and the further degradation it produces on MOS devices. The BTI phenomenon is usually associated with an increase of MOS transistor’s threshold voltage; however, this work also addresses BTI as a change in MOSFET’s drain current, transconductance, and the channel’s resistivity. In this way, we detail a physics-based model to get a better insight into the prediction of threshold voltage degradation for aging ranges going from days to years, in 180-nm MOS technology. We highlight that a physics-based BTI model improves accuracy in comparison to lookup table models. Finally, simulation results for the inclusion of such a physics-based BTI model into BSIM3v3 are shown in order to get a better understanding of how BTI impacts the performance of MOS devices.