Levent Trabzon

Microfluidic device on a nonwoven fabric: A potential biosensor for lactate detection

In the present study, a novel, wearable textile based microfluidic device was developed that provides a non-invasive, rapid, semi-quantitative detection of the lactate level in simulated sweat solution. The potential application was envisioned to be a biosensor that can monitor an athlete’s physical status during exercise. A photolithography technique was used for the fabrication of hydrophilic micro channels and reservoirs surrounded by hydrophobic barriers made from SU-8 negative photoresist. The reservoirs were functionalized by co-immobilization of lactate oxidase (LOX) and horseradish peroxidase (POX) enzymes. LOX uses L-(+)-Lactic acid as substrate and produces H2O2 which is a POX substrate. Then, POX oxidases H2O2 in the presence of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) and results in color formation. The studies showed that excess amount of analyte presence resulted in analyte inhibition. It was also shown that analyte pH and temperature were effective on the color formation. For effective results, analyte pH and temperature should be ≥5℃ and 25–30℃, respectively. Lower pH and higher temperature values resulted in a decrease in the enzyme activity. The textile based biosensor system could make a semi-quantitative visual detection to differentiate between the normal (<5 mM) and high (≥5 mM) lactate level: while a high lactate level led to a denser purple color formation, normal levels led to a light purple formation and a green color started to be observed.

Damage to sub-half-micron metal-oxide-silicon field-effect transistors from plasma processing of low- k polymer interlayer dielectrics

We report on the effects of via plasma etching of low-dielectric-constant (low-k ) polymers, used as interlayer dielectrics (ILDs), on the characteristics of sub-half-micron n-channel metal-oxide-silicon field-effect transistors (MOSFETs). The low-k polymers investigated are benzocylobutene and fluorinated poly-arylene-ether. The MOSFETs employed are made sensitive to via etching by incorporating an array of either 58 × 58 or 183 × 213 via holes to the gate electrode. We have found that the via etching of the polymer ILD damages the MOSFET as witnessed by the observed degradation in the transistors parameter. The damage incurred by the MOSFET is of a charging type and is caused by plasma-induced stress current flowing into the gate oxide and oxide-Si interface through regions in the polymer ILD that are rendered leaky by the via etching plasma. We have observed that the inclusion of an insulating layer, such as Si3 N4 , can significantly inhibit the damaging effects of the via etch. Annealing at ~350 °C is found to eliminate the via-etch-induced damage and to improve the MOSFETs parameters.

The impact of trench geometry and processing on the performance and reliability of low voltage power UMOSFETs

We report on the performance and reliability of n-channel U-shaped trench-gate metal-oxide-Si field-effect transistors (n-UMOSFETs). Damage induced on the trench sidewalls from the reactive ion etching of the trench is concealed by post-etch cleaning as witnessed by the independence of the effective electron mobility in the channel of the trench geometry. However, charge pumping measurements coupled with electrical stressing of the gate oxide in the Fowler-Nordheim (FN) regime, have shown that the oxide edge adjacent to the drain and the oxide/silicon interface therein are the most susceptible regions to damage in the n-UMOSFET. Using scanning electron microscopy, this is shown to result from gate-oxide growth nonuniformity that is more pronounced at the trench bottom corners where the oxide tends to be thinnest. We also report on n-UMOSFET performance and hot electron stress reliability as functions of the p-well doping.

The dependence of UMOSFET characteristics and reliability on geometry and processing

We have examined the impact of trench processing and trench and device cell geometries on the characteristics of a single n-channel U-shaped trench metal-oxide-silicon field-effect transistor (n-UMOSFET) and a device cell comprising several n-UMOSFETs. The geometrical parameters investigated included the trench depth and width, the trench cross-section and the device cell pitch. We have found out that the geometry does not affect the electron mobility in the channel; however, the effects of the geometry on the characteristics of the isolated device or device cell are manifested on the spreading resistance of the drain end. Trench processing, in the form of trench etching, trench cleaning and subsequent gate-oxide growth, is observed to primarily influence the n-UMOSFETs immunity to electrical stress, which is studied using charge pumping current and gate-oxide breakdown measurements. It is shown that the gate-oxide edge adjacent to the drain and the oxide/silicon interface overlapping the drain are the regions most susceptible to degradation by Fowler-Nordheim stress. These observations coupled with results from scanning electron microscopy suggest that the gate-oxide growth non-uniformity as well as its condition at the trench corners are the key factors in determining the n-UMOSFETs reliability.

Comparison between direct current and sinusoidal current stressing of gate oxides and oxide/silicon interfaces in metal–oxide–silicon field-effect transistors

It was recently reported that plasma process-induced damage to metal–oxide–silicon field-effect transistors (MOSFETs) comprises a damage mechanism that involves alternating-current (ac) stressing of the oxide and the oxide/silicon interface. The study reported herein is aimed at establishing signatures of MOSFET damage induced by ac stressing applied at conditions that emulate plasma processing environment. We apply sinusoidal ac voltage stress signals to 0.5 μm n-channel or p-channel MOSFETs with 90-A-thick gate oxides. We assess damage on MOSFETs by measuring transconductance, threshold voltage, and subthreshold swing. We find that the onset of damage to devices subjected to ac stressing occurs at voltage amplitudes as low as 4 V, whereas in dc stressing, applied for the same time, damage becomes significant only at dc voltages larger than 10 V. We also show that damage from ac stressing attains a maximum at frequencies in the range 1–100 kHz and decreases at frequencies above 5 MHz. It is proposed that...

Sinusoidal AC stressing of thin-gate oxides and oxide/silicon interfaces in 0.5-μm n-MOSFETs

Sinusoidal ac signals are applied to 90-/spl Aring/ thick gate-oxide in 0.5-/spl mu/m n-MOSFETs. The objective is to emulate ac stressing to devices, recently reported to occur during plasma processes. AC stressing is found to be more damaging to the oxide and oxide/silicon interface when compared to dc stressing. The damage induced by the ac stress is observed to depend on the signals frequency and amplitude. It is proposed that carrier hopping is primarily responsible for oxide current and device damage observed following the ac stress. This hopping current is insignificant during high-field dc stress when Fowler-Nordheim tunneling becomes the dominant conduction mechanism.

A review of recent research on materials used in polymer–matrix composites for body armor application:

The development of personal protection systems with improved ballistic performance and reduced weight has received a great interest in the last decade with the unfortunate ever-increasing threats and conflicts. In this review, the ordinarily polymeric fibers used in body armors manufacturing were first reported, then some nanomaterials, such as carbon nanotubes and graphene with advanced structural and mechanical properties, as well as their potential reinforcement of armor composites were investigated through some recent studies available in the literature. Additionally, natural fibers integrated into multilayered armor systems, and ballistic tests which endorse their future importance were also cited. This short review which sheds light on novel materials used in personal armor systems, a specific and an important topic that was not previously reviewed, aims to provide to the new researchers, engineers and manufactures in this field some guidelines about what are the promising materials that can be used in order to construct the ultimate body armors of the future.

Microfluidic Nonwoven-Based Device as a Potential Biosensor for Sweat Analysis

Monitoring body fluids such as sweat composition can provide useful information about the physiological status. Physiological monitoring of body fluids such as sweat with a textile-based system has the advantage of being non-invasive and easily accessible and such monitoring is beneficial to indicate information about bodys physiological status. In the present study, it is aimed to design a textile-based system with non-invasive methods which can be used to monitor a sportsmans performance. A novel, disposable and wearable biochemical analytical device was designed and fabricated by patterning micro channels and reservoirs using SU-8 photoresist through photolithography technique on an absorbant bicomponent Evolon® nonwoven substrate. It was obtained that hydrophilic reservoirs were well defined and demarcated by hydrophobic barriers. Therefore, no liquid leakage was observed around the reservoirs which was crucial for achieving a proper enzyme immobilization and the successful detection of the color change after the simulated sweat was deposited on the hydrophilic reservoir areas. Analyte optimization studies revealed that color change became more evident with the increasing analyte concentration until 20 mM and started to decrease with further increase due to analyte inhibition. Also, on textile fabrics, color densities started to decrease after 40 mM analyte concentration.

Fabrication and Characterization of Si Nano-Columns by Femtosecond Laser

We fabricated Si Nano-columns by a femtosecond laser with various wavelengths and process parameters, whilst the specimen was submerged in water. The experiments were carried out by three types of wavelengths i.e. 1030 nm, 515nm, 343nm, with 500 fs laser pulses. The scales of these spikes are much smaller than micro spikes that are constructed by laser irradiation of silicon surface in vacuum or gases like SF6, Cl2. The Si nano-columns of 300 nm or less in width were characterized by SEM measurements. The formation of these Si Nano-columns that were revealed by SEM observation, indicates chemical etching with laser ablation occurred when surface exposed by laser beam. We observed 200 nm spikes height at the center of laser beam profile and the ones uniform in height at lateral incident area.

Electrical-stress simulation of plasma-damage to submicron metal–oxide–silicon field-effect transistors: Comparison between direct current and alternating current stresses

The study reported herein is aimed at establishing signatures of metal–oxide–silicon field-effect transistors (MOSFETs) damage induced by alternating current (ac) stressing applied at conditions that simulate plasma processing environment and the comparison of the ac stress induced damage to damage from an equivalent direct current (dc) stress. We also examine the response of stress induced damage to annealing that emulates postmetallization annealing in complementary metal–oxide–silicon processing. We apply sinusoidal and dc voltage stress signals to 0.5 μm n- or p-MOSFETs with 90-A-thick gate oxides and anneal the stressed transistors in forming gas ambient (6% H2 and 94% N2) at 400 °C for 30 min. We assess damage on MOSFETs by measuring transconductance, threshold voltage, and subthreshold swing. We find out that the onset of damage to devices subjected to ac stressing occurs at voltage amplitudes as low as 6 V, whereas in dc stressing damage becomes significant only at voltages larger than 10 V. We al...