Sanghyun Park

Study on the resistive switching time of TiO2 thin films

The required time for voltage-pulse-induced resistive switching of 40-nm-thick TiO2 thin films integrated in a contact-type structure (Pt top and TiN bottom contact, contact area ∼0.07μm2) was studied as a function of pulse voltage. For off→on switching at least 2V was necessary and the minimum switching times were ∼20ns at 2V and ∼10ns at 3V. For on→off switching, a minimum switching time of 5μs was obtained at 2.5V. The resistance of the on-state device was also dependent on the switching voltage and time.

Material-Independent Nanotransfer onto a Flexible Substrate Using Mechanical-Interlocking Structure

Nanowire-transfer technology has received much attention thanks to its capability to fabricate high-performance flexible nanodevices with high simplicity and throughput. However, it is still challenging to extend the conventional nanowire-transfer method to the fabrication of a wide range of devices since a chemical-adhesion-based nanowire-transfer mechanism is complex and time-consuming, hindering successful transfer of diverse nanowires made of various materials. Here, we introduce a material-independent mechanical-interlocking-based nanowire-transfer (MINT) method, fabricating ultralong and fully aligned nanowires on a large flexible substrate (2.5 × 2 cm2) in a highly robust manner. For the material-independent nanotransfer, we developed a mechanics-based nanotransfer method, which employs a dry-removable amorphous carbon (a-C) sacrificial layer between a vacuum-deposited nanowire and the underlying master mold. The controlled etching of the sacrificial layer enables the formation of a mechanical-interlocking structure under the nanowire, facilitating peeling off of the nanowire from the master mold robustly and reliably. Using the developed MINT method, we successfully fabricated various metallic and semiconductor nanowire arrays on flexible substrates. We further demonstrated that the developed method is well suited to the reliable fabrication of highly flexible and high-performance nanoelectronic devices. As examples, a fully aligned gold (Au) microheater array exhibited high bending stability (106 cycling) and ultrafast (∼220 ms) heating operation up to ∼100 °C. An ultralong Au heater-embedded cuprous-oxide (Cu2O) nanowire chemical gas sensor showed significantly improved reversible reaction kinetics toward NO2 with 10-fold enhancement in sensitivity at 100 °C.

The Study on In-situ Diagnosis of Chemical Vapor Deposition Processes

The diagnosis studies of the process of chemical vapor deposition were carried out by using in-situ particle monitor (ISPM) and self-plasma optical emission spectroscopy (SPOES). We used the two kinds of equipments such as the silicon plasma enhanced chemical vapor deposition system with silane gas and the borophosphosilicate glass depositon system for monitoring. Using two sensors, we tried to verify the diagnostic and in-situ sensing ability of by-product gases and contaminant particles at the deposition and cleaning steps. The processes were controlled as a function of precess temperature, operating pressure, plasma power, etc. and two sensors were installed at the exhaust line and contiguous with each other. the correlation of data (by-product species and particles) measured by sensors were also investigated.

Chemical Vapor Deposition of Silica Nanowires using Heteroleptic Bis(ethylmethylamino)silane Precursor

One-dimentional nanomaterials have attracted great attention due to their exceptional properties since the discovery of carbon nanotubes by S. Iijima in 1991 [1]. Among 1D nanomaterials, silica nanowires have been a subject of intense study in view of their unique properties like blue light emission and easy surface functionalization [2, 3]. In the present study, silica nanowires were synthesized by employing inherent directionality of chemical vapor reaction between heteroleptic bis(ethylmethylamino)silane ((H2Si[N(C2H5)(CH3)]2) precursor and water without a metal catalyst at room temperature. Figs. 1A and 1B show the molecular structures of precursors, bis(ethylmethylamino)silane and tetrakis(ethylmethylamino)silane respectively. The conceptual scheme used here is that the difference in the oxidation reactivities between Si-H and Si-N groups with water leads the formation of linear shaped products. Fig. 1C shows the cross-section SEM image of representative silica nanowires produced using bis(ethylmethylamino)silane precursor. When tetrakis(ethylmethylamino)silane was used instead of bis(ethylmethylamino)silane, as shown in Fig. 1D, twodimensional film growth with limited nucleation is observed. Figs. 2A, 2B, and 2C show crystallinity and composition of synthesized silica nanowires, including that they are in an amorphous state with Si:O elements of a ratio of ~1:2. Fig. 2D presents the FTIR spectrum of the as-grown silica nanowires on the Si substrates. An absorption band was detected between 837 and 885 cm, which is assigned to the bending modes of H-SiO. The existence of this H-SiO peak and the absence of the Si-N peak indicate that water preferentially replaces the amine groups bonded with Si.

ELECTRICAL PROPERTIES OF Pb(Zr,Ti)O3 FERROELECTRIC CAPACITOR ON TiN/W PLUG STRUCTURE

ABSTRACT We investigated the electrical properties of ferroelectric Pb(Zr,Ti)O3(PZT) capacitor on TiN/W storage node contact plug that is capacitor over bitline(COB) cell structure for a high density ferroelectric memory. In order to protecting TiN/W contact plug from oxidation failure during furnace annealing of PZT capacitor, the oxidation barrier of Ti1 − x Al x N (x∼ 0.25) film was interposed at between Pt/IrO2/Ir bottom electrode and TiN/W plug of the COB cell, resulting in the robust contact resistance property of 27 ohm per contact plug after furnace annealing performed at 600°C in O2 ambient for 90 min. The remanent polarization value and leakage current density of the fully integrated PZT capacitor with a top electrode area of 1.8 × 1.8 um2 on TiN/W contact plug showed 32 μ C/cm2 and 2.5 × 10− 6A/cm2, respectively.