Israel Mejia

This work presents an analysis and modeling of the electrical stress effects caused by different voltages on a logic inverter device circuit based on thin-film transistor (TFT) technology. The study includes the characterization of single indium-gallium-zinc oxide (IGZO) TFTs and inverters with an active load configuration to investigate the behavior of their threshold voltage ( $\textit{V}_{\text{TH}}\text{)}$ under various bias voltages. Additionally, an analytical model is used to quantify the impact of electrical stress on the trapping parameters of the dielectric–semiconductor interface. The model demonstrates that the charged trapped concentration increases exponentially with the applied voltage bias, resulting in a significant initial shift in $\textit{V}_{\text{TH}}$ . Importantly, this analytical model allows the assessment of the electrical stress effect on TFT-based circuits. The findings can inform the determination of a maximum applied voltage bias based on the desired threshold voltage. Furthermore, the model facilitates the estimation of circuit reliability and lifetime by considering the polarization time under different applied voltage bias conditions.

It is by reported the effect of natural reducing agents such as plant extracts ( Equisetum myriochaetum leaves, Cymbopogon citratus , Camellia sinensis , Syzygium aromaticum ), fruits (orange, apple), and biopolymers (arabic gum, and chitosan) on the size distribution of silver nanoparticles, obtained by green synthesis, to be incorporated in a MCM‐41@Ag nanocomposite. The aim is to determine the influence of temperature, agitation time, concentration, atmosphere, and nature of the reducing agent on the MCM‐41@Ag particle size. According to the DLS analysis, the extract of Syzygium aromaticum produced silver nanoparticles in the range of 8–80 nm. Further structural, morphological, optical, and surface characterization confirmed the obtention of the desired MCM‐41@Ag nanocomposite. Our results show the potential of MCM‐41@Ag to be incorporated in Metal‐insulator‐semiconductor capacitors for detection purposes.

In this study, thin films of zinc oxide doped with fluorine ZnO: F were deposited via ultrasonic spray pyrolysis (USP) with an atomic ratio of [F/Zn] in a starting solution of 15 at.% on borosilicate glass coverslips and SiO₂/Si substrates. The structure, electrical resistivity, and thickness were obtained via X-ray diffraction, the four-point technique, and profilometry, respectively. A ZnO: F piezoresistor was modeled at the fixed end of the cantilever through lithography and chemical etching. A SiO₂/Si cantilever structure was used to evaluate the piezoresistivity of a ZnO: F thin film, and temperature coefficient of resistance (TCR) measurements were performed in an electric furnace. The strain on the ZnO: F piezoresistor caused by the application of masses at the free end of the cantilever was determined using a theoretical equation, in addition to a simulation in the COMSOL Multiphysics 5.3a FEM (finite element method) software considering the dimensions and materials of the manufactured device. The ZnO: F thin films were hexagonal wurtzite (phase 002), with thicknesses in the range from 234 nm to 295 nm and with resistivities of the order of 10⁻² Ω.cm. The ZnO: F thin-film piezoresistor showed a gauge factor (GF) of 12.7 and a TCR of −3.78 × 10⁻³ %/K up to 525 K, which are suitable properties for sensor development.

This article documents the design, manufacture, and testing of a silicon inertial optical sensor for low-frequency (lower than 2 kHz) applications. Three accelerometer designs optimized by parameterization using Finite Element Analysis were considered. The accelerometers were manufactured and the one with the highest performance at low frequency was chosen for testing, which was attached to a steel package. The feasibility of using probes, based on micro-machined sensing elements, to measure mechanical vibrations with high resolution was also studied. The detection is performed with an air interferometer, eliminating the need for electric signals that are susceptible to electromagnetic interference and large temperature variations. From the fabrication technology using only a silicon wafer with both sides etched, the frequency response of the sensor, temperature operation (higher than 85 °C) and with a resolution of 17.5 nm, it was concluded that is achievable and feasible to design and manufacture an optical vibration sensor for potential harsh environments with a low cost.

The development of silicon-based sensor devices has enabled the possibility to pursue novel integrated smart sensor technologies. Under this scenario, capacitive sensor devices are one viable option for implementing different kinds of applications. In this paper, an interdigitated coplanar capacitive device fabricated over a silicon substrate is presented and its potential use as liquid sensor is demonstrated. Additionally, a detailed capacitance model, which includes the parasitic capacitances introduced by the silicon substrate, was developed. The capacitance model has been theoretically validated through finite-element simulations as well as experimentally by comparison with fabricated devices. A polydimethylsiloxane mold has been fabricated and bonded to the sensor device with the aim of defining a cavity to collect the liquid sample into the device’s active region. The active capacitance component correlates to the electric field coupling between adjacent metal lines. Therefore, any change to the dielectric constant of the medium above the coplanar metal lines will produce a change to the device capacitance. Finally, the main guidelines for device performance improvement are depicted.

This brief presents a methodology to design RF energy harvesting rectifiers that produce a system with higher efficiency when compared to traditionally optimized circuits. The proposed methodology uses a dual-perspective approach, exploiting the designer’s knowledge of the rectifier’s operation, as a qualitative evaluation, and the precise results obtained by SPICE simulation as quantitative computation of the system’s response. The compromises considered by the mathematical steady state models in the existing literature limit their practical use for manual calculations. Instead, nonlinear steady state simulation methods, such as harmonic balance, provide a much better design tool. The proposed method improves the efficiency of rectifiers by up to 27% with respect to arbitrary initial conditions.

This paper presents the structural, optical and electrical characterization of ZnO thin films obtained by ultrasonic spray pyrolysis (USP). Based on these characterizations, the deposition conditions that provide films with higher crystallinity and greater absorption were determined. The resistivity of the films was reduced by annealing in nitrogen environment and was measured with a 4-point probe. The annealed films were characterized by AFM, SEM and XPS. Two photoconductive detectors were fabricated, with high and low resistivity films, and the responsivity was obtained for both. The two detectors showed a high UV response, but the photodetector developed from the annealed film demonstrated a maximum responsivity of 3000 A/W at 369 nm with a 2 V bias voltage. This result is higher than results obtained with low-cost techniques such as sol-gel, pneumatic spray pyrolysis, and even some results reported by sputtering.

Performance and reliability comparison of oxide-based thin-film transistors fabricated at a maximum process temperature of 115 °C is presented. A fully patterned and passivated process was successfully evaluated and implemented using polycrystalline ZnO and amorphous indium–gallium–zinc–oxide (IGZO) as an active layer in glass substrates. Saturation mobilities of 14.2 and 9.0 cm $^{{2}}\cdot \text{V}^{-{1}}\cdot \text{s}^{-{1}}$ were obtained for ZnO and IGZO, respectively, with threshold voltages of 2.2 and 2.0 V, an ON/ OFF ratio $> {1} \times 10^{{8}}$ , and an ${I}_{{\text {off}}}< {1} \times 10^{-{12}}$ A. The small mobility change in IGZO with gate voltage is due to its amorphous character. Longer variation is observed in polycrystalline ZnO due to its grain boundaries. Reliability studies show a threshold voltage shifting of 0.4 and 1.8 V for ZnO and IGZO devices, testing after 1200-s stress. Devices were successfully implemented in ZnO- and IGZO-based inverters using saturation and zero-drive structures, showing a maximum dc gain of 2.4- and 25-V/V, respectively.