N.I. Morimoto

Characterization of an electrospinning process using different PAN/DMF concentrations

We performed an extensive characterization of an electrospinning process to evaluate how the process parameters and precursor solution characteristics affect the fibers morphology. The work was conducted using precursor solutions with different concentrations of polyacrylonitrile (PAN) diluted in a fixed amount of N,N/dimethylformamide (DMF). Fibers obtained with this process can find important applications in the field of nanosensors. The characteristics of the electrospun fibers were analyzed as a function of the solution viscosity, applied voltage and distance between the needle tip (positive electrode) and the collector plate (grounded electrode). The electrical current was monitored during the deposition process and its behavior was correlated with the characteristics of the fibers obtained. Our results demonstrate that the diameter of the fibers increases with increasing viscosity and applied voltage. The number of deposited fibers also increases with the applied voltage. Also, viscosity and applied voltage strongly affect the shape, length and morphology of the fibers. Of particular interest, we demonstrated that by monitoring the electrical current it is possible to control the fibers morphology and bead concentration. The distance between tip and collector plate determines the way the fibers arrive on the collector plate. A main contribution of this study was the definition of conditions to controllably obtain fibers that are smooth and that present diameters in the range between 140 and 300 nm.

Analysis of SiO2 Thin Films Deposited by PECVD Using an Oxygen-TEOS-Argon Mixture

This study analyses the influence of the argon flow on the Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon oxide thin films by using TEOS as silicon source. The argon flow increases the deposition rate, however it also can creates some defects in the deposited film. Several characterization techniques were used to analyze the deposited films. The presence of argon, in the gas phase, modifies the plasma composition, the surface roughness of silicon wafer, and the surface reaction. The optimum argon flow ranges between 65 and 80 sccm to obtain a silicon oxide thin film with high quality in terms of refractive index, smoothness, and uniformity.

Tetraethylorthosilicate SiO2 films deposited at a low temperature

Abstract In this work, we present the results obtained on the characterization of silicon oxide thin films deposited by plasma enhanced chemical vapor deposition using tetraethylorthosilicate (TEOS) as a silicon source. The influence of the reaction kinetics in the deposition process was analyzed. The RF power enhances the O* generation in the plasma increases the TEOS oxidation process in the gas phase. Also, the oxidation reaction and sub-products elimination, from the surface during solid phase reaction, are improved. The wafer holder temperature contributes to the volatile sub-products elimination from the substrate surface. There is no evidence of Si–OH and OH bonds in the Fourier transform infrared spectra from the films deposited above 300°C. The densification process improved the electrical characteristics of the film showing an elimination of the trapped charges promoted by the thermal treatment.

Sensing based on Mach-Zehnder interferometer and hydrophobic thin films used on volatile organic compounds detection

This paper presents the project, optimization, design details, and fabrication of an optical chemical sensor based on a Mach-Zehnder interferometer (MZI), fabricated with metal-oxide semiconductor compati- ble processes and materials. The sensing material is hexamethyldissila- zane (HMDS) plasma polymerized thin film, which exhibits hydrophobic characteristics, high resistance to acid or basic solution, and adsorption of polar and nonpolar organic compounds. Both reference and sensor arms of the fabricated MZIs are covered with HMDS thin film in order to keep the device balanced. Different substances, such as water, 2-propanol, and hexane vapors are investigated. The high sensitivity of the MZI structure, associated with refractive index variations of about 10 −4 , paves the way for a myriad of sensor applications, such as humidity, organic compounds, proteins, antibodies (antigens), enzymes, pesticides, and others. The minimum detectable measurements were 4.6 mg∕min for n-hexane and 0.2 mg∕min for 2-propanol.

pH meter based in Suspended Gate Field Effect Transistors to application in monitoring of water quality

The protocol to monitor the water pH variation during a long time using a full electronic pH-meter consisting of a SGFET (Suspended Gate Field Effect Transistor) is presented after the analysis of the transconductance and the drain current drifts under pH. The main advantages of using this device are its high sensitivity and the ability to integrate it with the electronic treatment into a miniaturized system.

Fabrication of Metal-Semiconductor-Metal Photodetectors Using Low Temperature Rapid Thermal Annealing

The electrical properties of Ti-Si-Ti Metal-Semiconductor-Metal (MSM) photodetector were studied as a function of annealing temperature, using Rapid Thermal Annealing (RTA) process. Low temperatures were used at the RTA (200-350°C) in order to avoid the formation of silicides. We observed a decrease in the dark current on samples annealed between 200 and 300°C. The lowest dark current was obtained in the sample annealed at 250°C (4.8 nA), which is one order of magnitude lower than as-deposited sample (53.5 nA). The sample annealed at 350°C had an increase in dark current (82.9 nA). This behavior of the dark current can be explained by the increase in the barrier height at 200-300°C annealing temperature range, due to increase of the thickness of the amorphous interdiffused Ti-Si interfacial layer, and decrease in the barrier value at sample annealed at 350°C, due to pre formation of C49 TiSi2.

Development of suspended gate field effect transistors array-based microsystem for pH measurements

This work presents the specifications of a microsystem which allows pH electrical measurements of solution especially for water monitoring applications. The architecture of this microsystem consists in SGFET (Suspended gate Field Effect Transistor) array-based, control and processing modules. The array is composed of 3 × 3 identical SGFET sensors. Each SGFET can be addressed independently to increase the accuracy and the reliability of the global measurements.

On the behavior of a novel miniaturized G-planar antenna in the presence of an infinity metal plane

A miniaturization of the printed monopole was made, resulting in a novel patch antenna, named G-planar antenna. The analysis of a prototype of this antenna on FR-4 was performed, presenting good agreement between measured and simulated results for the return loss. This antenna has good performance even in the vicinity of the metal walls.

Sensors based in suspended gate field effect transistors for pH measurements

This work presents a new pH sensor based on the architecture SGFET (Suspended Gate Field Effect Transistor). The pH variations are obtained using the threshold voltage and the transfer characteristics shift of the SGFET. To evaluate the accuracy and reliability of the pH sensor, pH variations were measured directly in the solution using both the SGFET and a commercial pH-meter.

Humidity Sensor Thanks Array of Suspended Gate Field Effect Transistor

This work deals with a sensor using array of Suspended Gate Field Effect Transistor (SGFET) to measure the relative humidity (%RH). Technics of microtechnology are used to fabricate a polysilicon bridge with a gap de 0,5 μm which acts as transistor gate. Electrical measures have been realized by sampling mode, involving a sensitivity of -5 μA/%. Also the SGFET humidity sensors are very interesting due to the simplicity to polarize and to analyze the output signal.