Charndet Hruanun

Surface modification of silicon dioxide, silicon nitride and titanium oxynitride for lactate dehydrogenase immobilization

Three different types of surface, silicon dioxide (SiO2), silicon nitride (Si3N4), and titanium oxynitride (TiON) were modified for lactate dehydrogenase (LDH) immobilization using (3-aminopropyl)triethoxysilane (APTES) to obtain an amino layer on each surface. The APTES modified surfaces can directly react with LDH via physical attachment. LDH can be chemically immobilized on those surfaces after incorporation with glutaraldehyde (GA) to obtain aldehyde layers of APTES-GA modified surfaces. The wetting properties, chemical bonding composition, and morphology of the modified surface were determined by contact angle (CA) measurement, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), respectively. In this experiment, the immobilized protein content and LDH activity on each modified surface was used as an indicator of surface modification achievement. The results revealed that both the APTES and APTES-GA treatments successfully link the LDH molecule to those surfaces while retaining its activity. All types of tested surfaces modified with APTES-GA gave better LDH immobilizing efficiency than APTES, especially the SiO2 surface. In addition, the SiO2 surface offered the highest LDH immobilization among tested surfaces, with both APTES and APTES-GA modification. However, TiON and Si3N4 surfaces could be used as alternative candidate materials in the preparation of ion-sensitive field-effect transistor (ISFET) based biosensors, including lactate sensors using immobilized LDH on the ISFET surface.

Magnetotransistor Based on the Carrier Recombination—Deflection Effect

This paper presents the three-terminal magnetotransistor based on the carrier recombination-deflection effect. Three-terminal magnetotransistor can detect vertical and lateral magnetic field direction. The structure of magnetotransistor consists of one emitter, one collector and one base contact. The devices can detect magnetic field by relying on the difference between base current and collector current (¿ICB). The result from experiments closely matched the simulated 3-D modeling with base width of 20 ¿m at substrate thickness of 600 ¿m . From the experiment, the magnetotransistor had the highest sensitivity of 10.25%/T when emitter current was at 10 mA. This research on the three-terminal magnetotransistor can achieve magnetic sensors with small size, high performance and wide range of applications.

Fabrication of a micro-direct methanol fuel cell using microfluidics

A direct-methanol fuel cell containing three parts: microchannels, electrodes, and a proton exchange membrane (PEM), was investigated. Nafion resin (NR) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PS) were used as PEMs. Preparation of PEMs, including compositing with other polymers and their solubility, was performed and their proton conductivity was measured by a four point probe. The results showed that the 5 % Nafion resin has lower conductivity than the 5 % PS solution. The micro-fuel cell contained two acrylic channels, PEM, and two platinum catalyst electrodes on a silicon wafer. The assembled micro-fuel cells used 2 M methanol at the flow rate of 1.5 mL min−1 in the anode channel and 5 × 10−3 M KMnO4 at the flow rate of 1.5 mL min−1 in the cathode channel. The micro-fuel cell with the electrode distance of 300 μm provided the power density of 59.16 μW cm−2 and the current density of 125.60 μA cm−2 at 0.47 V.

UV-enhanced photodetector with nanocrystalline-TiO 2 thin film via CMOS compatible process

This research presents nanocrystal titaniumdioxide (nanocrystal-TiO2) film deposition technique with CMOS compatible process [1] to extend the optical response bandwidth of silicon based photodetecting devices toward ultraviolet range [2]. The thin films were initially deposited as Titanium Nitride (TiN) using DC magnetron reactive sputtering system. It was then annealed under nitrogen atmosphere at 800°C. After analyzing crystal structures and surface morphology with X-ray diffraction and FE-SEM systems, it was found that the deposited thin films showed the crystal phase of TiO2 oriented along (200) plane of Rutile crystal structure with 50 nm grain size and increasing with film thickness. Using electroreflectance (ER) spectroscopy measurement [3], the bandgap of nanocrystal-TiO2 was revealed to be 3.16 eV. PN-heterojunction photodiodes were fabricated with Nanocrystal-TiO2/SiO2/p-Si structures. Interdigitated aluminum structures were used as electrodes. By varying the thickness of nanocrystal-TiO2 film, i.e. 30, 60, and 90 nm, the devices could response further into the UV range. The absorption edge wavelength investigated by photoresponse measurement was at 275 nm and shifting to the shorter wavelength as a function of the nanocrystal-TiO2 grain size due to quantum confinement phenomenon [4]. The nanocrystal-TiO2/SiO2/p-Si photodetector had dark current = 5.31nA (2V), photocurrent = 0.9 uA, rise time = 58 us, fall time = 47 us at 30 nm thickness of TiO2.

Merged three-terminal magnetotransistor based on the carrier recombination - deflection effect

This article presents a merged three terminals magnetotransistor based on the carrier recombination - deflection effect. This particular magnetotransistor structure relies on the combination of difference of base current and collector current in +x and -x directions. As a result, the output voltage and absolute sensitivity to magnetic field will be double. The structure of magnetotransistor consists of one emitter, two collector and two base contacts. The devices can detect magnetic field in vertical direction (BZ) by relying on the difference between base current and collector current (DeltaICB). From the experiment, with emitter current at 5, 8, and 10 mA, the magnetotransistor had the highest sensitivity of 1.125 mV/mT when emitter current was at 10 mA.

The low power 3D-magnetotransistor based on CMOS technology

This article presents a 3D magnetotransistor for detecting magnetic field in three dimensions (BX, BY, and BZ) by relying on the difference between base and collector currents (ΔICB). This device used low biasing current. It was designed and fabricated using CMOS fabrication technology. The device structure consisted of one emitter, 4 collectors and 4 bases. LOCOS oxide was grown to surround the emitter area to limit lateral carrier loss, and therefore reducing the overall biasing current. The experiment showed that, at 0.2 mA of biasing current, the BX, BY and BZ direction sensitivity to magnetic field within the range of 0 – 400 mT are 0.05, 0.07 and 0.145 mV/mT, respectively.

A Micrograting Sensor for DNA Hybridization and Antibody Human Serum Albumin–Antigen Human Serum Albumin Interaction Experiments

A biosensor structure comprising silicon nitride (Si3N4) micrograting arrays coated with a spin-on-glass (SOG) material was investigated. This grating structure was located on a silicon groove, which was etched by a deep reactive ion etching (DRIE) process. The biosensor was used as a specific detector of DNA molecules and antibody–antigen interactions. In our DNA sensing experiments, the first step was the activation of the grating surface with amine functional groups, followed by attachment of a 23-base oligonucleotide probe layer for hybridization with a complementary target DNA. The sensing device was tested for detecting specific antigen/antibody interactions for human serum albumin (HSA) and antigen bovine serum albumin (BSA). The readout system consisted of a white light lamp that illuminated a small spot on the grating surface at normal incidence through a fiber optic probe with a spectrometer used to collect the reflected light through a second fiber. We show that these sensing devices have the capability to detect DNA as well as antigen–antibody binding for HSA. The detection sensitivity for HSA was better than that for DNA mainly owing to the larger size and concomitant refractive index changes upon binding to the sensor. We show that it is possible to quantify the amount of biomolecules bound to the grating surface by measuring the wavelength shift of the reflectance spectra upon exposure to the samples.

Optimization of Fabrication Process for MEMS Based Microneedles Using ICP Etching Technology

In this paper, optimization of fabrication process for microneedles has been presented. Using inductively coupled plasma (ICP) etching technology, fabrication of out-of-plane hollow silicon microneedles for blood extraction has been carried out. Sharp tip microneedles with length 1100 µm were designed for fabrication. The fabrication of microneedles was not successful because the lumen section was fabricated first and then hole was created for fluid flow. Previously, using same fabrication method successful fabrication of microneedles was done for drug delivery with length 200 µm. This fabrication method is not suitable for long structure. Thus, the alternative microneedle fabrication steps using ICP etching have been developed and presented in this paper. These steps can be more optimized and suitable for sharp tip, long and hollow structure.

Effect of temperature to characteristics of polysilicon based surface micromachining piezoresistive pressure sensor

This paper presents the effect of temperature to strain gauge resistance, sensitivity, and hysteresis of surface micromachining pressure sensor with polysilicon membrane and polysilicon resistor as piezoresistive strain gauge. The resistance value is nominally 2.7 k Omega, under normal atmospheric pressure and room temperature. The experiments measured the relationship between resistance of strain gauge and pressure under different temperatures setting. The pressure range was from 1 to 10 bar, whereas the temperature range was from -20 to 125degC. The resulting curves were used to calculate sensitivity, temperature hysteresis, pressure hysteresis, and temperature coefficient of resistivity (TCR). Increasing temperature resulted in higher resistance with TCR of 0.04%/degC. However, the sensitivity reduced at the rate of 0.165 and 0.144%/degC at pressure ranges of 1 -7 bars and 7 - 10 bars, respectively. Furthermore, pressure hysteresis also increased but stay within 5%, similar to temperature hysteresis value of 4.8%.

Characteristics of silicon thin film thermistors

This paper presents the characteristics of silicon thin film thermistors. The polycrystalline silicon and amorphous silicon films were deposited by low pressure chemical vapor deposition (LPCVD) to serve as thermistors. We have studied the effects of temperature on thermistor with various boron implantation doses from 1.0times1016 to 2.0times1016 cm-2. The thermistors were characterized by temperature control system from -50 to +150degC. In the case of poly-Si thermistors, the results show the U-shaped polynomial relationship between resistance and temperature. Negative slope occurred in the low temperature range, whilst positive slope appeared in the high temperature range. The critical point was found where the slope was zero. The position of the critical point shifted depend on implanted doses. Furthermore, the characteristics of the poly-Si thermistor can be determined by implantation doses. In the case of the resistance of amorphous thermistor, it changed with temperature in linear function, resistance increased when temperature was increased. In addition, doses of implantation are independent of the effects of resistance-temperature relationship. Finally, doses of implantation are the main parameter used to describe characteristics of thermistors. The results data are useful for simulation, selection and integration of thin films thermistor as temperature devices in integration circuit(IC).