Geunbae Lim

Precise temperature control and rapid thermal cycling in a micromachined DNA polymerase chain reaction chip

We have fabricated Si-based micromachined DNA polymerase chain reaction (PCR) chips with different groove depths. The platinum thin-film micro heater and the temperature sensor have been integrated on the chip. The volume of the PCR chamber in the chip is about 3.6 ?l and the chip size is 17 ? 40 mm2. The effects of groove geometry, including width, depth and position, on the thermal characteristics of the PCR chip have been investigated by numerical analysis and experimental measurement. From the results, the power consumption required for the PCR chip is reduced with the increase of groove depth. Compared with results for the case of no groove, the power consumption of the chip with a groove of 280 ?m is reduced by 24.0%, 23.3% and 25.6% with annealing, extension and denaturation, respectively. The heating rate is increased rapidly with the increase of the groove depth. In particular, it is revealed that this effect is predominant for depths in the region above 280 ?m. For a more precise control of chip temperature, the nonlinear feedback proportional-integral control scheme is used. The obtained heating and cooling rates are about 36 ?C s?1 and 22 ?C s?1, respectively. The overshoot and the steady state error are less than 0.7 ?C and ?0.1 ?C, respectively. In the experiment, the effects of the PCR buffer and the bubbles in the chamber on the temperature uniformity have also been studied. From the temperature measurement, it is revealed that the temperature difference between the thin-film sensor (on the lower plate) and the PCR buffer can be neglected if there is no air bubble in the PCR buffer. With such a high performance control scheme, we could implement a remarkable thermal cycling of conducting 30 cycles for 3 min. Finally, the chip PCR of plasmid DNA was successfully performed with no additives using the temperature control system.

DNA hybridization electrochemical sensor using conducting polymer

We report the use of poly(thiophen-3-yl-acetic acid 1,3-dioxo-1,3-dihydro-isoindol-2-yl ester (PTAE) for application to electrochemical hybridization sensor. A synthetic route for the thiophen-3-yl-acetic acid 1,3-dioxo-1,3-dihydro-isoindol-2-yl ester (TAE) is described, which is used as a monomer of conducting polymer sensor. A direct chemical substitution of probe oligonucleotide to good leaving group site in the PTAE is carried out on the conducting polymer film. A biological recognition can be monitored by comparison with the electrochemical signal (cyclic voltammogram) of single and double strand state oligonucleotide. The sensitivity of the electrochemical sensor is 0.62 microA/nmole and the detection limit is 1 nmole. The oxidation current of double strand state oligonucleotide is a half of that of single strand, that is corresponding to the decrease of electrochemical activity of conducting polymer with increase of stiffness of side group of the polymer. The oxidation current decreasing ratios of perfect matched and single nucleotide mismatched samples are 52 and 25-30%, respectively. The more decreasing ratio is attributable to the more steric hindrance of single nucleotide mismatched sample.

Fabrication of a microchannel integrated with inner sensors and the analysis of its laminar flow characteristics

Abstract A rectangular straight microchannel was fabricated with dimensions of 57 μm (H)×200 μm (W)×48 ,050xa0μmxa0( L ), in which the resistance temperature detectors (RTDs) were integrated on the inner surface of the channel wall to measure the temperatures of the fluid more accurately. Platinum (Pt) was used as RTD material. The values of the temperature coefficient of resistance (TCR) of the fabricated Pt-RTDs without annealing ranged about 2800–2900xa0ppm/°C and the variation of the TCR values in the range of 0–110xa0°C was less than 2%. A micro-heater was also installed at the outlet/inlet of the channel to generate the heat flux. Effects of the temperature-dependent properties on the laminar flow characteristics in the microchannel were investigated experimentally using the fabricated microchannel device. DI water was used as the working fluid. The pressure drop was measured as the mass flow rate and the applied heating power were increased. The micro-particle image velocimetry (micro-PIV) was used to measure the detailed velocity fields along the microchannel having various wall temperatures. The pressure drop and micro-PIV measurements revealed that the variation of the fluid properties along the microchannel has a significant effect on the flow resistance but not a considerable effect on the velocity profile. Also, the measured flow resistance and velocity field showed a high degree of consistency with those estimated by the macro-laminar flow theory under our experimental conditions. The proposed microchannel device is expected to be useful in the field of microfluidics.

Field Effect Transistor-based Bimolecular Sensor Employing a Pt Reference Electrode for the Detection of Deoxyribonucleic Acid Sequence

We have fabricated field effect transistor (FET)-type biomolecular sensor for the detection of the deoxyribonucleic acid (DNA) sequence based on 0.5 µm standard complementary metal oxide semiconductor (CMOS) technology and investigated its electrical characteristics. A Pt reference electrode with improved performance was employed for the detection of the DNA sequence and Au, which has a chemical affinity with thiol by forming a self-assembled monolayer (SAM), was used as the gate metal in order to immobilize the DNA. It was fabricated as a p-channel metal oxide semiconductor (PMOS) FET-type because PMOSFET with positive surface potential could be very attractive for detecting negatively charged DNA from the view point of high sensitivity and fast response time. The FET-based biomolecular sensor can detect the DNA sequence by measuring the variation of drain current due to a biomolecular charge after DNA probe immobilization and variation of capacitance after DNA hybridization. The gate potential of the sensor was applied by the Pt reference electrode and DNA was detected by both in situ and ex situ measurements. The drain current increased when a single-stranded DNA (ss-DNA) with thiol was immobilized because the effect of DNA charge with thiol is dominant. The drain current decreased when the DNA was hybridized into a double-stranded DNA (ds-DNA) because of the decrease in capacitance due to DNA hybridization. In situ measurement showed good agreement with ex situ measurement.

Heat transfer enhancement using flow-induced vibration of a microfin array

Abstract Advanced computers are facing thermal engineering challenges from both high heat generation due to rapid performance improvement and the reduction of an available heat removal surface due to large packaging density. Efficient cooling technology is desired to provide reliable operation of microelectronic devices. This paper investigates the feasibility of heat transfer enhancement in laminar flow using the flow-induced vibration of a microfin array. The microfins are initially bent due to the residual stress difference. In order to characterize the dynamics of the microfin flow-induced vibration, a microfin sensor is fabricated. Increase in air velocity provides larger vibrating deflection, while the vibrating frequency of the microfin is independent of the air velocity. The thermal resistances are measured to evaluate the thermal performance of the microfin heat sink and compared with those of a plain-wall heat sink. For a fluid velocity of 4.4xa0m/s, the thermal resistance of the microfin array heat sink is measured to be 4.45°C/W and that of the plain-wall heat sink to be 4.69°C/W, which indicates a 5.5% cooling enhancement. At a flow velocity of 5.5xa0m/s, the thermal resistance of the microfin array heat sink is decreased by 11.5%. From the experimental investigations, it is concluded that the vibrating deflection plays a key role in enhancing the heat transfer rate.

Fabrication and Characteristics of a Field Effect Transistor-Type Charge Sensor for Detecting Deoxyribonucleic Acid Sequence

We have fabricated an field effect transistor (FET)-type deoxyribonucleic acid (DNA) charge sensor which can detect the DNA sequence by sensing the variation of drain current due to DNA hybridization and investigated its electrical characteristics. It is fabricated as a PMOSFET-type because the DNA probe has a negative charge. Au which has a chemical affinity with thiol was used as the gate metal in order to immobilize DNA. The operating principle is very similar to that of MOSFET. The gate potential is determined by the electric charge possessed by the DNA. The variation of the drain current with time was measured. The drain current increased when thiol DNA and target DNA were injected into the solution, because of the field effect due to the electrical charge of DNA molecules. Therefore it is confirmed that the DNA sequence can be detected by measuring the variation of the drain current due to the variation of DNA charge and it is concluded that the proposed FET-type DNA charge sensor might be useful for the implementation of the DNA chip.

Effects of mutual impedance on the radiation characteristics of transducer arrays

The mutual resistance of transducer arrays is investigated in order to design arrays with improved performance for high intensity sounds at a given frequency. This work proposes the theory that the mutual resistance is related to the loading effects of pressure waves propagated from a piston driver on the surface of another driver. Using this interpretation, the important characteristics of the mutual resistance of two piston drivers are explained and the conditions for local maxima in the mutual resistance are easily determined. On the basis of analyses of the interactions between a driver and acoustic pressure waves, we propose a method to determine the driver radius and the distance between two drivers that give maximum mutual radiation resistance. To evaluate the proposed method, the total resistance of a transducer array is calculated using the formulas for mutual and self-resistance established by Pritchard. The results of the calculations of the total resistances of arrays with many drivers show that a transducer array with drivers arranged sparsely can achieve a larger value of the radiation power per unit area as well as better radiation efficiency than an array in which the drivers are in a closely packed arrangement at a given frequency.

DNA Chip technologies

The genome sequencing project has generated and will continue to generate enormous amounts of sequence data. Since the first complete genome sequence of bacteriumHacmophilus influenzac was published in 1995, the complete genome sequences of 2 eukaryotic and about 22 prokaryotic organisms have been determined. Given this ever-increasing amounts of sequence information, new strategies are necessary to efficiently pursue the next phase of the genome project—the elucidation of gene expression patterns and gene product function on a whole genome scale. In order to assign functional information to the genome sequence, DNA chip technology was developed to efficiently identify the differential expression pattern of independent biological samples. DNA chip provides a new tool for genome expression analysis that may revolutionize many aspects of human life including new drug discovery and human disease diagnostics.

Formation and observation of ferroelectric domains in PbZr1-xTixO3(PZT) thin films using atomic force microscopy

Very small-sized ferroelectric domains were induced and observed using a modified atomic force microscopy (AFM). Bias voltage between a conductive AFM tip and a sol-gel processed PZT film caused the switching of small ferroelectric domains. ELectrostatic forces between the polarized area and the tip provide the imaging of the polarized small domains. Applying voltage with the opposite sign can depolarize the polarized area and the formation of a series of data dots was demonstrated. In addition, the retention phenomena of micron size domains in PZT films were investigated. The polarized images disappeared within a few days even without an application of voltage - often called the retention loss or failure. An empirical relationship between relaxation time, bit size and poling time is established and verified. Two operative processes for the retention loss are either the stray charge accumulation on the polarized surfaces or the stress relaxation of the piezoelectric films. An effective way of improving the retention characteristics is suggested. The experimental results obtained in this study provide substantial insight into the mechanism for the retention failure of the polarized domains as well as the polarization behavior in PZT films with a nanometer scale.

Reaction of Ozone and H2O2 in NH4OH Solutions and Their Reaction with Silicon Wafers

The main purpose of this study was to evaluate ozone chemistry in NH4OH solutions in terms of oxidizing power compared with H2O2-based NH4OH solutions. The solubility of ozone in the solutions tested was almost nil at room temperature when the solution pH was higher than 9. However, the decrease in solution temperature to 10°C resulted in a dissolved ozone concentration at the ppm level in NH4OH solutions. The slow decrease in pH and the increase in redox potential were measured as functions of ozone injection time in NH4OH solutions at 10°C. The half-life times of peroxide were 40 min and 4 h in 1:1:5 (volume ratio) NH4OH:H2O2:H2O (SC1, standard clean 1) solution at 80 and 50°C, respectively. However, the half-life of ozone at room temperature was less than 2~ 5 min at the concentrations investigated. The contact angles of bare silicon changed from 72° to less than 5° within 10 s in SC1 at 80°C. In ozonated solutions, change of contact angle to hydrophilic took longer than 3 min depending on the concentration of ozone in NH4OH solutions. The addition of peroxide and ozone significantly reduced the etch rate of silicon in NH4OH solutions. When Al2O3 particles were deposited on silicon wafers, ozonated NH4OH combined use with megasonic power at room temperature could remove more than over 90% of particles from the wafer surface.