= 아 래 =
1. 일 시 : 2014. 3. 27 (목), 16:00 ~
2. 장 소 : 신소재공학과 2425호 강의실
3. 연 사 : 남성욱 박사 (IBM T.J. Watson Research Center, Research Scientist)
4. 제 목 : Real-Time Visualizations of Electrical Phenomena in Nano- and Bio-Devices
In nano- and bio-functional materials, real-time observation of electrical events provides us valuable information about transient behaviors in which we can study the fundamental mechanisms underlying the physical properties. In the first part of my talk, I will present in-situ transmission electron microscope (TEM) observations of electrical switching behaviors in nanowire phase-change memory (PCM) devices. We visualized structural evolutions in nanowire PCM devices, including vacancy condensation, dislocation generation, transport, and amorphization process. By correlating electrical properties with the dynamics of structural defects, we discovered that “dislocations” serve as precursors of amorphization process in PCM devices. In particular, electrical voltage-pulse creates dislocations by vacancy condensation in single-crystalline Ge2Sb2Te5 (phase-change material). And electrical wind force moves the dislocations along with hole-carrier wind force in a unidirectional way, thus causing jamming of dislocations, which eventually induces amorphization process. One-dimensional traffic model was adopted to interpret the unidirectional motions (of dislocations) followed by jamming behavior. We claim that the transition from crystalline to amorphous states in a phase-change material may not require a melting process, which upsets commonly-known knowledge that the amorphization in PCM occurs as melt-quench process. In the second part, I will talk about nanofluidic device platform to visualize the motions of DNA with single-molecule resolution. We developed sub-20 nm nanopore/nanochannel fabrication methods in a manufacturable wafers-scale approach. For nanopore device (vertical-type channels), we fabricated ion-transistor devices in which the transport of liquid electrolyte (such as KCl) was regulated by gate voltage bias. We have tested the ion transistor performance in different pH solutions, exhibiting a pronounced contrast in device-properties depending on pH state. We are going to discuss about applications of the ion-transistor devices potentially for a single-molecule DNA sequencer: By hybridizing the nanopore device platform with pH-sensing capabilities, we will examine polymerization reactions of single-stranded DNA molecules. For nanochannel device (lateral-type channels), we developed a fabrication method of sub-20 nm nanochannels by utilizing silicon (Si) as sacrificial material. Given a well-established Si nanopatterning technology, we converted sub-20 nm Si patterns into nanochannel structure through XeF2 gas-phase etching process. Through state-of-the-art triple-level (e-beam, DUV and MUV) lithography method, the gradient pillar structure was defined, by making the fluidic structure suitable for stretching coiled-DNA single molecules. Linearizing DNA single molecule was visualized by fluorescent optical microscope. This method offers on-chip nanofluidic devices free from any kinds of extra wafer-bonding (sealing) procedures, thus enabling us to couple CMOS-based circuits with sub-20 nm nanofluidics.