Minju Shin

Low-frequency noise in multilayer MoS2 field-effect transistors: the effect of high-k passivation

Diagnosing of the interface quality and the interactions between insulators and semiconductors is significant to achieve the high performance of nanodevices. Herein, low-frequency noise (LFN) in mechanically exfoliated multilayer molybdenum disulfide (MoS2) (~11.3 nm-thick) field-effect transistors with back-gate control was characterized with and without an Al2O3 high-k passivation layer. The carrier number fluctuation (CNF) model associated with trapping/detrapping the charge carriers at the interface nicely described the noise behavior in the strong accumulation regime both with and without the Al2O3 passivation layer. The interface trap density at the MoS2-SiO2 interface was extracted from the LFN analysis, and estimated to be Nit ~ 10(10) eV(-1) cm(-2) without and with the passivation layer. This suggested that the accumulation channel induced by the back-gate was not significantly influenced by the passivation layer. The Hooge mobility fluctuation (HMF) model implying the bulk conduction was found to describe the drain current fluctuations in the subthreshold regime, which is rarely observed in other nanodevices, attributed to those extremely thin channel sizes. In the case of the thick-MoS2 (~40 nm-thick) without the passivation, the HMF model was clearly observed all over the operation regime, ensuring the existence of the bulk conduction in multilayer MoS2. With the Al2O3 passivation layer, the change in the noise behavior was explained from the point of formation of the additional top channel in the MoS2 because of the fixed charges in the Al2O3. The interface trap density from the additional CNF model was Nit = 1.8 × 10(12) eV(-1) cm(-2) at the MoS2-Al2O3 interface.

Experimental and Theoretical Investigation of Magnetoresistance From Linear Regime to Saturation in 14-nm FD-SOI MOS Devices

The feasibility of geometric magnetoresistance (MR) measurement from linear to saturation operation regime is demonstrated in ultrathin body and BOX fully depleted silicon-on-insulator devices from 14-nm technology node. Besides, we propose a new physical compact model for MOSFET drain current under high field transport, which reproduces experimental MR mobility from linear to saturation operation region and serves as the basis for a new extraction method of carrier saturation velocity. A benchmarking with state-of-the-art saturation velocity extraction methodologies is also conducted. Our saturation velocity results indicate that, for this technology, nonstationary transport prevails as manifested by an overshoot velocity behavior, still far from the ballistic limit.

The Influence of Cu Lattices on the Structure and Electrical Properties of Graphene Domains during Low‐Pressure Chemical Vapor Deposition

The influence of various Cu lattices on the texturing of graphene domains during low-pressure chemical vapor deposition was investigated in a large area. The results show that the sizes and shapes of graphene domains grown on Cu(111) substrates match well with those of the underlying Cu(111) domains, which seem to be quasi-single-crystalline. In contrast, on other Cu substrates such as (100) and more intermediate domains, graphene islands with poly-domains (ca. 85 %) are significantly nucleated, eventually merging into polycrystalline graphene. Within the overall channel-length range, graphene from a Cu foil shows a higher resistance compared to graphene from a Cu(111) domain, with the extracted average channel resistances being 34.51 Ω μm(-1) for Cu(111) and 66.17 Ω μm(-1) for the Cu foil.

Current fluctuation of electron and hole carriers in multilayer WSe2 field effect transistors

Two-dimensional materials have outstanding scalability due to their structural and electrical properties for the logic devices. Here, we report the current fluctuation in multilayer WSe2 field effect transistors (FETs). In order to demonstrate the impact on carrier types, n-type and p-type WSe2 FETs are fabricated with different work function metals. Each device has similar electrical characteristics except for the threshold voltage. In the low frequency noise analysis, drain current power spectral density (SI) is inversely proportional to frequency, indicating typical 1/f noise behaviors. The curves of the normalized drain current power spectral density (NSI) as a function of drain current at the 10 Hz of frequency indicate that our devices follow the carrier number fluctuation with correlated mobility fluctuation model. This means that current fluctuation depends on the trapping-detrapping motion of the charge carriers near the channel interface. No significant difference is observed in the current fluc...

Nanoscale Friction Characteristics of a Contact Junction with a Field-Induced Water Meniscus

The effect of the field-induced water meniscus on the friction level and oscillation was studied using an atomic force microscopy tip sliding on a highly ordered pyrolytic graphite (HOPG) surface. The results showed that the friction characteristics were significantly affected by the bias voltage, humidity, and sliding velocity. The friction level increased when the bias voltage increased beyond a threshold value (Vth). The stick–slip-type friction oscillation was observed at low velocity and periodicity, and intensity of the friction oscillation was diminished at high velocity. The velocity dependence of the friction oscillation indicated that the mechanical properties of the field-induced water meniscus were comparable to the solid state due to field-induced ordering of water molecules in the meniscus. The static friction and amplitude of the friction oscillation during scanning were inversely proportional to the scan velocity, suggesting that the hydrophobic HOPG surface turned hydrophilic due to the electrical field at the meniscus and demonstrating the possibility of manipulating the friction using an electrical bias, which can be useful for functionalizing nanoscale devices.

The Wear Mechanism of a Polyphenylene Sulfide (PPS) Composite Mixed with Ethylene Butyl Acrylate (EBA)

Friction and wear of polyphenylene sulfide (PPS) mixed with ethylene butyl acrylate (EBA) were studied using a block-on-ring tribotester. Results showed that the friction coefficient decreases with an increase in the EBA content due to the reduced surface contact area occupied by the PPS. The PPS/EBA composite showed higher threshold temperatures for viscoelastic behavior and the wear rate was significantly decreased after mixing with EBA due to a radical reduction in transfer films. The wear mechanism of the composite changed from an adhesive wear mode to an abrasive wear mode upon the addition of EBA, which supports the wear debris morphology and the wear map suggested by Lancaster (Proc Inst Mech Eng 183:98–106, 1968).