Pyung Choi

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.

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.

A Low Power Fully CMOS Integrated RF Transceiver IC for Wireless Sensor Networks

A fully CMOS integrated RF transceiver for ubiquitous sensor networks in sub-gigahertz industrial, scientific, and medical (ISM)-band applications is implemented and measured. The integrated circuit is fabricated in 0.18-mum CMOS technology and packaged in leadless plastic chip carrier (LPCC) package. The fully monolithic transceiver consists of a receiver, a transmitter, and an RF synthesizer with on-chip voltage-controlled oscillator. The chip fully complies with the IEEE 802.15.4 wireless personal area network in sub-gigahertz mode. The cascaded noise figure of the overall receiver is 9.5 dB and the overall transmitter achieves less than 6.3% error vector magnitude for 40 kb/s mode. The chip uses 1.8-V power supply and the power consumption is 25 mW for reception mode and 29 mW for transmission mode

Relationship between ADC performance and requirements of digital-IF receiver for WCDMA base-station

The recent rapid development of digital wireless systems has led to the need for multistandard, multichannel radiofrequency (RF) transceivers. The paper presents the relationship between the performance of a bandpass-sampling analog-to-digital converter (ADC) and the requirements of a digital intermediate-frequency receiver for a wideband code-division multiple-access (WCDMA) base-station. As such, the ADC signal-to-noise ratio (SNR), the derivation of the receiver sensitivity using the SNR/spurious free dynamic range (SFDR) of the ADC, the effect of the ADC clock jitter and receiver linearity, plus the relationship between the receiver IF and the ADC sampling frequency are all analyzed. As a result, when a WCDMA base-station receiver has a data rate of 12.2 kbps, bit error rate (BER) of 0.001, and channel index, k, of 5 (sampling frequency of 122.88 MHz and IF of 92.16 MHz), the performance of a bandpass-sampling ADC was analytically determined to require a resolution of 14 bits or more, SNR of 66.6 dB or more, SFDR of 86.5 dBc or more, and total jitter of 0.2 ps or less, including internal ADC jitters and clock jitters.

Low cost implementation of filterless class D audio amplifier with constant switching frequency

A new and simple configuration of filterless class D audio amplifier is proposed in this paper. The proposed filterless class D audio amplifier provides the advantages of both low total system cost and generation of synchronized 3-level pulse-width modulated (PWM) output. Moreover, as a result of hysteresis window variation, a close to constant switching frequency of PWM output is obtained. The proposed filterless class D audio amplifier is verified by the PSpice simulation and prototype circuit experiment

Highly and Variably Sensitive Complementary Metal Oxide Semiconductor Active Pixel Sensor Using P-Channel Metal Oxide Semiconductor Field Effect Transistor-Type Photodetector with Transfer Gate

In this paper, a new sensor using a p-channel metal oxide semiconductor field effect transistor (PMOSFET)-type photodetector with a transfer gate has been designed and fabricated by a 0.35 µm standard complementary metal oxide semiconductor (CMOS) process. The photodetector is composed of a floating gate connected to an n-well and a transfer gate. The transfer gate controls photocurrent flow by controlling the barrier for holes in the PMOSFET-type photodetector. The designed photodetector has similar IDS–VDS characteristics to a conventional PMOSFET when the incident light power instead of the gate voltage is varied. A unit pixel that uses this photodetector consists of a PMOSFET-type photodetector with a transfer gate and four n-channel metal oxide semiconductor field effect transistors (NMOSFETs). Its area is 7.2 ×8.1 µm2. It is confirmed that this photodetector, with a high and variable level of sensitivity, could be applied to an image acquisition system at a low illumination level.

Detection of streptavidin-biotin protein complexes using a 3-dimensional MOSFET in the Si micro-fluidic channel

Biotechnology is being revolutionized by the availability of information about many different genome sequences. Particularly, semiconductor microsensor technology has been applied to various parts of biosensors and chemical sensors[l]. In general, conventional methods for protein analysis include optical measurements, electrochemistry measurements, mass spectrometry. These methods have disadvantages in terms of time-consuming, expensive equipment and portable diagnostic application: Above all, it was difficult to apply in the Si micro-fluidic channel. To overcome these problems, The introduction of a 3-dimensional metal oxide semiconductor field effect transistor(3-D MOSFET) in silicon micro-fluidic channel is needed in the integrated biochemical detection system[2]. A 3-D MOSFET for the application in the micro-fluidic channel provides many advantages such as miniaturization, standardization, mass production and highly suitable configuration for smart sensors in which both the sensor and measurement circuit are integrated. In this study, we have fabricated a p-channel 3-D MOSFET-type biosensor in order to detect a protein biomolecule. Its electrical characteristics have been investigated. Furthermore, a surface piasmon resonance(SPR) experiment was performed under the same condition to verify interactions among self-assembled monolayer(SAM), streptavidin and biotin[3].

Active Pixel Sensor Using a 1?16 Nano-Wire Photodetector Array for Complementary Metal Oxide Semiconductor Imagers

In this paper, a novel photodetector using an N-channel metal oxide semiconductor field effect transistor (NMOSFET) with a 30 nm-wide silicon nano-wire is described. The photodetector was fabricated on silicon-on-insulator (SOI) substrate and its wire was patterned by optical lithography, electron beam lithography and thermal oxidation. At room temperature, the device has similar IDS-VDS characteristics to a general NMOSFET when incident light is supplied instead of the gate voltage. A maximum responsivity of higher than 1×102 A/W and optical transient time of 80 µs have been obtained. Additionally, for the purpose of demonstrating the feasibility of the new device application, a 1×16 complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) connected with the novel photodetector array was also designed and fabricated using 1-poly and 2-metal 1.5 µm CMOS technology. It is confirmed that this photodetector with high sensitivity as well as nano-scaled area could be applied to an image acquisition system for low illumination level.

Characteristics of piezoresistive mass flow sensor fabricated by porous silicon micromachining

Piezoresistive flow sensors with four different types of microcantilever structures were fabricated using [100], n/n+/n three-layer silicon wafer and their characteristics were investigated.

The formation and characterization of electrical contacts (Schottky and Ohmic) on gallium nitride nanowires

We report on the fabrication and characterization of Ti/Au Ohmic contacts to unintentionally doped gallium nitride (n-GaN) nanowires. The specific contact resistance and resistivity were determined to be ~1.1 × 10−5 ± 5 × 10−6 Ω cm2 and ~6.9 × 10−3 ± 3 × 10−4 Ω cm, respectively, with a diameter of ~140 nm using a transmission line model (TLM). We also present the electrical characterizations of metal/GaN nano-Schottky diodes with four Schottky metals (Al, Ti, Cr and Au) on unintentionally doped GaN nanowires using current–voltage (I–V) characteristics at room temperature. We observed the abnormal electrical characteristics of GaN nano-Schottky diodes for each Schottky metal.