Mingxing Piao

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.

Evaluation of power generated by thermoelectric modules comprising a p-type and n-type single walled carbon nanotube composite paper

We report on p-type and n-type thermoelectric (TE) materials made of single-walled carbon nanotube (SWCNT) networks incorporated into the cellulose fiber structure of a common packaging paper. This leads the paper to possess both mechanical flexibility from the cellulose fibers as a supporting matrix and the high electrical conductivity originating from the SWCNTs. Thermoelectric power of up to ±50 μV K−1 was successfully obtained as well, depending on their electronic type. Further, to demonstrate its thermoelectric voltage (VTEP) and generating power, a couple of thermoelectric modules composed of both p-type and n-type composite layers were assembled in series. The produced VTEP shows a quasi-linearity with respect to the number of p–n couples and the temperature difference ΔT. Our testing module enables the provision of VTEP and power generation as large as ≈16.8 mV and ≈75.5 nW upon inducing a 50 K temperature difference. The feasibility of commercial TE modules consisting of 10, 100 and 1000 p–n SWCNT couples was numerically calculated, taking into account our experimental results.

Effects of low-temperature (120 °C) annealing on the carrier concentration and trap density in amorphous indium gallium zinc oxide thin film transistors

We report an investigation of the effects of low-temperature annealing on the electrical properties of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). X-ray photoelectron spectroscopy was used to characterize the charge carrier concentration, which is related to the density of oxygen vacancies. The field-effect mobility was found to decrease as a function of the charge carrier concentration, owing to the presence of band-tail states. By employing the transmission line method, we show that the contact resistance did not significantly contribute to the changes in device performance after annealing. In addition, using low-frequency noise analyses, we found that the trap density decreased by a factor of 10 following annealing at 120 °C. The switching operation and on/off ratio of the a-IGZO TFTs improved considerably after low-temperature annealing.

Low frequency noise reduction in multilayer WSe2 field effect transistors

We report that noise level was reduced by passivating WSe2 field effect transistors (FETs) with high-k dielectric material. Low frequency noise and I-V characteristics of the device were measured from WSe2 FETs before and after the passivation with ZrO2 to confirm the effect of passivation by high-k dielectric material. As a result, there was no significant change in the I-V characteristics. In the low frequency noise analysis, our device showed 1/f noise behaviors, in agreement with the carrier number fluctuation (CNF) model. The passivation process contributed to the reduction of trap sites at the top surface, leading to the decrease of noise level at the low current regime. Extracted volume trap densities were reduced from 2.0 × 1020 cm-3eV-1 to 8.7 × 1019 cm-3eV-1.

Inductively coupled plasma etching of hafnium–indium–zinc oxide using chlorine based gas mixtures

Summary form only given. Amorphous Hafnium-Indium-Zinc Oxide(a-HIZO) semiconductor materials are used to replace amorphous Gallium-Indium-Zinc Oxide(a-GIZO) as channel layer of thin film transistors (TFTs) to improve the stability of the electrical characteristics. However, research activities of a-HIZO etching process for the fabrication of TFTs have not been reported. In this work, we present the etching characteristics of HIZO stacked with photoresist using Cl2/Ar chemistry. Etching behaviours of HIZO have been investigated as a function of source power, bias power and pressure. As the Cl2 concentration increased from pure Ar, the etch rate of HIZO film was slightly different from the trend of GIZO film. Atomic Force Microscopy(AFM), Depth profile of the HIZO film by Auger Electronspectroscopy(AES) and X-ray Photoelectron Spectroscopy(XPS) of the etched surface was carried to investigate the etching mechanism as Cl2 increased. Additionally we tried to compare the etching mechanism of HIZO film with GIZO film to confirm the difference of chemical bonds caused by the influence of hafnium doping, estimated that the low chemical reaction between hafnium and Cl2 based plasma suppress the reactive ion etching.