• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.420-424
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• 1999

In this paper, an optical switching circuit and several types of all-optical transmitter/receiver circuits which are configured with photodiodes, multiple quantum-well(MQW) optical modulators, and field-effect transistors(FETs) were simulated using PSPICE and their results of these are examined and discussed. 20 $\mu\textrm{m}$ ${\times}$ 20 $\mu\textrm{m}$ of window size was used for the optical modulators and 100 $\mu\textrm{m}$ wide FETs with the transconductance value of 55 mS/mm were used for the simulations. Simulation results clearly show that in order for the high speed operation of the all-optical circuits, the size of each device should be minimized to reduce the parasitic capacitance, the circuits should be designed to operate at the wavelength where the resposivity of photodiodes becomes the maximum peak, and the use of short, high-intensity input optical signal beams is very advantageous.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.491-491
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• 2011

Transparent and flexible electronic devices that are light-weight, unbreakable, low power consumption, optically transparent, and mechanical flexible possibly have great potential in new applications of digital gadgets. Potential applications include transparent displays, heads-up display, sensor, and artificial skin. Recent reports on transparent and flexible field-effect transistors (tf-FETs) have focused on improving mechanical properties, optical transmittance, and performances. Most of tf-FET devices were fabricated with transparent oxide semiconductors which mechanical flexibility is limited. And, there have been no reports of transparent and flexible all-organic tf-FETs fabricated with organic semiconductor channel, gate dielectric, gate electrode, source/drain electrode, and encapsulation for sensor applications. We present the first demonstration of transparent, flexible all-organic sensor based on multifunctional organic FETs with organic semiconductor channel, gate dielectric, and electrodes having a capability of sensing infrared (IR) radiation and mechanical strain. The key component of our device design is to integrate the poly(vinylidene fluoride-triflouroethylene) (P(VDF-TrFE) co-polymer directly into transparent and flexible OFETs as a multi-functional dielectric layer, which has both piezoelectric and pyroelectric properties. The P(VDF-TrFE) co-polumer gate dielectric has a high sensitivity to the wavelength regime over 800 nm. In particular, wavelength variations of P(VDF-TrFE) molecules coincide with wavelength range of IR radiation from human body (7000 nm ~14000 nm) so that the devices are highly sensitive with IR radiation of human body. Devices were examined by measuring IR light response at different powers. After that, we continued to measure IR response under various bending radius. AC (alternating current) gate biasing method was used to separate the response of direct pyroelectric gate dielectric and other electrical parameters such as mobility, capacitance, and contact resistance. Experiment results demonstrate that the tf-OTFT with high sensitivity to IR radiation can be applied for IR sensors.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.199-203
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• 2008

The effects of surface treatment by $O_2$ plasma on the Bio-FETs were investigated by using the pseudo-MOSFETs on the SOI substrates. After a surface treatment by $O_2$ plasma with different RF powers, the current-voltage and field effect mobility of pseudo-MOSFETs were measured by applying back gate bias. The subthreshold characteristics of pseudo-MOSFETs were significantly degraded with increase of RF power. Additionally, a forming gas anneal process in 2 % diluted $H_2/N_2$ ambient was developed to recover the plasma process induced surface damages. A considerable improvement of the subthreshold characteristics was achieved by the forming gas anneal. Therefore, it is concluded that the pseudo-MOSFETs are a powerful tool for monitoring the surface treatment of Bio-FETs and the forming gas anneal process is effective for improving the electrical characteristics of Bio-FETs.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.549-549
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• 2012

Early detection of cancer biomarkers in the blood is of vital importance for reducing the mortality and morbidity in a number of cancers. From this point of view, immunosensors based on nanowire (NW) and carbon nanotube (CNT) field-effect transistors (FETs) that allow the ultra-sensitive, highly specific, and label-free electrical detection of biomarkers received much attention. Nevertheless 1D nano-FET biosensors showed high performance, several challenges remain to be resolved for the uncomplicated, reproducible, low-cost and high-throughput nanofabrication. Recently, two-dimensional (2D) graphene and reduced GO (RGO) nanosheets or films find widespread applications such as clean energy storage and conversion devices, optical detector, field-effect transistors, electromechanical resonators, and chemical & biological sensors. In particular, the graphene- and RGO-FETs devices are very promising for sensing applications because of advantages including large detection area, low noise level in solution, ease of fabrication, and the high sensitivity to ions and biomolecules comparable to 1D nano-FETs. Even though a limited number of biosensor applications including chemical vapor deposition (CVD) grown graphene film for DNA detection, single-layer graphene for protein detection and single-layer graphene or solution-processed RGO film for cell monitoring have been reported, development of facile fabrication methods and full understanding of sensing mechanism are still lacking. Furthermore, there have been no reports on demonstration of ultrasensitive electrical detection of a cancer biomarker using the graphene- or RGO-FET. Here we describe scalable and facile fabrication of reduced graphene oxide FET (RGO-FET) with the capability of label-free, ultrasensitive electrical detection of a cancer biomarker, prostate specific antigen/${\alpha}$ 1-antichymotrypsin (PSA-ACT) complex, in which the ultrathin RGO channel was formed by a uniform self-assembly of two-dimensional RGO nanosheets, and also we will discuss about the immunosensing mechanism.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.152-158
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• 2016

We investigated the effect of capacitively coupled Ar plasma treatment on contact resistance ($R_c$) and channel sheet resistance ($R_{sh}$) of graphene field effect transistors (FETs), by varying their channel length in the wide range from 200 nm to $50{\mu}m$ which formed the transfer length method (TLM) patterns. When the Ar plasma treatment was performed on the long channel ($10{\sim}50{\mu}m$) graphene FETs for 20 s, $R_c$ decreased from 2.4 to $1.15k{\Omega}{\cdot}{\mu}m$. It is understood that this improvement in $R_c$ is attributed to the formation of $sp^3$ bonds and dangling bonds by the plasma. However, when the channel length of the FETs decreased down to 200 nm, the drain current ($I_d$) decreased upon the plasma treatment because of the significant increase of channel $R_{sh}$ which was attributed to the atomic structural disorder induced by the plasma across the transfer length at the edge of the channel region. This study suggests a practical guideline to reduce $R_c$ using various plasma treatments for the $R_c$ sensitive graphene and other 2D material devices, where $R_c$ is traded off with $R_{sh}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.20-20
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• 2007

Nanowire-based field-effect transistors (FETs) decorated with nanoparticles have been greatly paid attention as nonvolatile memory devices of next generation due to their excellent transportation ability of charge carriers in the channel and outstanding capability of charge trapping in the floating gate. In this work, top-gate single ZnO nanowire-based FETs with and without Au nanoparticles were fabricated and their memory effects were characterized. Using thermal evaporation and rapid thermal annealing processes, Au nanoparticles were formed on an $Al_2O_3$ layer which was semi cylindrically coated on a single ZnO nanowire. The family of $I_{DS}-V_{GS}$ curves for the double sweep of the gate voltage at $V_{DS}$ = 1 V was obtained. The device decorated with nanoparticles shows giant hysterisis loops with ${\Delta}V_{th}$ = 2 V, indicating a significant charge storage effect. Note that the hysterisis loops are clockwise which result from the tunneling of the charge carriers from the nanowire into the nanoparticles. On the other hand, the device without nanoparticles shows a negligible countclockwise hysterisis loop which reveals that the influence of oxide trap charges or mobile ions is negligible. Therefore, the charge storage effect mainly comes from the nanoparticles decorated on the nanowire, which obviously demonstrates that the top-gate single ZnO nanowire-based FETs decorated with Au nanoparticles are the good candidate for the application in the nonvolatile memory devices of next generation.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.17.2-17.2
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• 2007

• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.3
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• pp.175-181
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• 2006

Wide band-gap semiconductor electron devices have made great progresses to produce very high power amplifiers for various wireless standards. The advantages of wide band-gap electronic devices and their progresses are summarized in this paper.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.213.1-213.1
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• 2015

Field effect transistors (FETs)를 기반으로 한 바이오센서는 빠른 응답속도, 저비용, label-free 등을 이유로 각광받고 있다. 그러나 3D 구조를 기반으로 한 FETs 바이오센서의 낮은 sensitivity의 한계점을 지니며, 이를 극복하기 위해 1D 구조의 나노튜브 등을 활용하였으나 여전히 높은 sensitivity의 확보는 힘들다. 최근에는 이러한 문제점을 극복하기 위해 이차원 반도체 물질 중 하나인 Transition metal dichalcogenide (TMD)를 이용하여, 700 이상의 sensitivity를 지니는 pH센서 및 100 이상의 sensitivity를 지니는 바이오센서가 보고되었다. 하지만 이보다 더 높은 정확성 및 반응성을 높이기 위한 연구는 부족한 실정이다. 우리는 DNA 템플릿을 이용하여, TMD FET 기반 pH 및 바이오센서의 반응성을 극대화시키는 연구를 선보인다. DNA는 7~8정도의 유전상수 (K)를 가지는 물질로 기존 $SiO_2$(K=3.9)보다 높은 유전상수를 가지며 두께를 0.7 nm로 매우 얇게 형성할 수 있는 장점이 있다. 이는 FET 기반 바이오센서의 표면 캐패시턴스를 높여 sensitivity를 극대화할 수 있으며, 기존에 사용된 high-k 기반 바이오센서와 비교하여도 약 10배 이상의 sensitivity 향상을 노릴 수 있다. 또한, TMD 물질로 우리는 $WSe_2$를 선택하였으며, pH 용액의 receptor로써 우리는 3-Aminopropyltriethoxysilane (APTES)를 활용하였고, 템플릿으로 사용된 DNA는 DX tile 및 Ring type의 두 가지를 사용하였다. 추가로, DNA의 phosphate backbone을 중성화시키고 DNA의 base pairing의 charge 안정화를 위해 구리 이온($Cu^{2+}$) 및 란타넘족($Tb^{3+}$)을 추가하였다. 완성된 바이오센서의 pH 센싱을 위해 우리는 pH 6,7,8의 표준 용액을 사용하였으며, 재현성 및 반복성의 확인하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.413-413
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• 2009

Silicon nanowires (Si NWs)-based top-gate field-effect transistors (FETs) are constructed by using Si NWs transferred onto flexible plastic substrates. Si NWs are obtained from the silicon wafers using photolithography and anisotropic etching process, and transferred onto flexible plastic substrates. To evaluate the electrical performance of the silicon nanowires, we examined the output and transfer characteristics of a top-gate field-effect transistor with a channel composed of a silicon nanowire selected from the nanowires on the plastic substrate. From these FETs, a field-effect mobility and transconductance are evaluated to be $47\;cm^2/Vs$ and 272 nS, respectively.