Trap-assisted space charge limited transport in short channel MoS2 transistor

We present temperature dependent $I-V$ measurements of short channel MoS$_2$ field effect devices at high source-drain bias. We find that although the $I-V$ characteristics are Ohmic at low bias, the conduction becomes space charge limited at high $V_{DS}$ and existence of an exponential distribution of trap states was observed. The temperature independent critical drain-source voltage ($V_c$) was also determined. The density of trap states was quantitatively calculated from $V_c$. The possible origin of exponential trap distribution in these devices is also discussed.Comment: 5 pages, 3 figure

Percolative switching in transition metal dichalcogenide field-effect transistors at room temperature

We have addressed the microscopic transport mechanism at the switching or on-off transition in transition metal dichalcogenide (TMDC) field-effect transistors (FET), which has been a controversial topic in TMDC electronics, especially at room temperature. With simultaneous measurement of channel conductivity and its slow time-dependent fluctuation (or noise) in ultra-thin WSe2 and MoS2 FETs on insulating SiO2 substrates, where noise arises from McWhorter-type carrier number fluctuations, we establish that the switching in conventional backgated TMDC FETs is a classical percolation transition in a medium of inhomogeneous carrier density distribution. From the experimentally observed exponents in the scaling of noise magnitude with conductivity, we observe unambiguous signatures of percolation in random resistor network, particularly in WSe2 FETs close to switching, which crosses over to continuum percolation at a higher doping level. We demonstrate a powerful experimental probe to the microscopic nature of near-threshold electrical transport in TMDC FETs, irrespective of the material detail, device geometry or carrier mobility, which can be extended to other classes of 2D material-based devices as well

Microscopic origin of low frequency noise in MoS₂ field-effect transistors

We report measurement of low frequency 1/f noise in molybdenum di-sulphide (MoS2) field-effect transistors in multiple device configurations including MoS2 on silicon dioxide as well as MoS2-hexagonal Boron Nitride (hBN) heterostructures. All as-fabricated devices show similar magnitude of noise with number fluctuation as the dominant mechanism at high temperatures and density, although the calculated density of traps is two orders of magnitude higher than that at the SiO2 interface. Measurements on the heterostructure devices with vacuum annealing and dual gated configuration reveals that along with the channel, metal-MoS2 contacts also play a significant role in determining noisemagnitude in these devices

The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors

We present low temperature electrical transport experiments in five field effect transistor devices consisting of monolayer, bilayer and trilayer MoS2 films, mechanically exfoliated onto Si/SiO2 substrate. Our experiments reveal that the electronic states in all films are localized well up to the room temperature over the experimentally accessible range of gate voltage. This manifests in two dimensional (2D) variable range hopping (VRH) at high temperatures, while below \sim 30 K the conductivity displays oscillatory structures in gate voltage arising from resonant tunneling at the localized sites. From the correlation energy (T0) of VRH and gate voltage dependence of conductivity, we suggest that Coulomb potential from trapped charges in the substrate are the dominant source of disorder in MoS2 field effect devices, which leads to carrier localization as well.Comment: 10 pages, 5 figures; ACS Nano (2011

An approach to seamlessly cloudify user-generated content from mobile devices

Current users own and use many network-connected devices viz. laptop, smartphone, or tablet. The user creates content using the default applications in these devices. One approach is to share and ubiquitously access the contents through a social media or content community. Such an approach will however make the users dependent on these communities or social media; moreover the user may also lose privacy of her content and even ownership of her data depending on the licensing policy of each community. We argue that the contents residing in mobile devices viz. smartphones or tablets should be available from anywhere, without any explicit user activity. That is, a user's content should get cloudified, while still remaining operable with the existing applications. In this thesis we propose to cloudify a user's content in all her mobile devices. We present as a proof of concept, a middleware that allows a user to use the existing applications uniformly, on local as well as remote content, and to also share the contents in a controlled way. The middleware hides all network activity from the user; it also makes the applications almost unaware while operating on a content residing in a remote location. To evaluate our approach in a mobile device context, we also present the efficiency measures of the middleware in terms of latency in content-retrieval, as well as in terms of resource usage viz. power consumption

Boosting Algorithms based Cuff-less Blood Pressure Estimation from Clinically Relevant ECG and PPG Morphological Features

Blood Pressure (BP) is often coined as a critical physiological marker for cardiovascular health. Multiple studies have explored either Photoplethysmogram (PPG) or ECG-PPG derived features for continuous BP estimation using machine learning (ML); deep learning (DL) techniques. Majority of those derived features often lack a stringent biological explanation and are not significantly correlated with BP. In this paper, we identified several clinically relevant (bio-inspired) ECG and PPG features; and exploited them to estimate Systolic (SBP), and Diastolic Blood Pressure (DBP) values using CatBoost, and AdaBoost algorithms. The estimation performance was then compared against popular ML algorithms. SBP and DBP achieved a Pearson’s correlation coefficient of 0.90 and 0.83 between estimated and target BP values. The estimated mean absolute error (MAE) values are 3.81 and 2.22 mmHg with a Standard Deviation of 6.24 and 3.51 mmHg, respectively, for SBP and DBP using CatBoost. The results surpassed the Advancement of Medical Instrumentation (AAMI) standards. For the British Hypertension Society (BHS) protocol, the results achieved for all the BP categories resided in Grade A. Further investigation reveals that bio-inspired features along with tuned ML models can produce comparable results w.r.t parameter-intensive DL networks. ln(HR × mNPV), HR, BMI index, ageing index, and PPG-K point were identified as the top five key features for estimating BP. The group-based analysis further concludes that a trade-off lies between the number of features and MAE. Increasing the no. of features beyond a certain threshold saturates the reduction in MAE

Chemosensitization of IκBα-overexpressing glioblastoma towards anti-cancer agents

Burgeoning research on gene-directed therapeutics has significant translational scope to combat multidrug resistant glioblastoma when conventional anticancer drugs cease to work alone or in combination. In the present work, a novel strategy to sensitize drug resistant glioblastoma cells (U87MG) has been proposed by overexpressing the IκBα gene, which is a cellular inhibitor of NFκB signaling pathways. The IκBα overexpressing U87MG cell line (U87-IκBα) was established by the G418 selection of IκBα transfected U87MG cells. The expression of IκBα was studied by semi-quantitative RT PCR, real time PCR and Western blot analysis. The stable cells were found to be easily sensitized by the anticancer drug 5-fluorouracil (5-FU) and an unconventional therapeutic agent curcumin nanoparticles. Cell viability assays and flow cytometry-based cell cycle studies showed dose dependent differential effects of 5-FU on U87-IκBα and U87MG cells. The expression status of various cell cycle genes was examined by real time PCR analysis. Furthermore, water soluble curcumin nanoparticles (NPs) were synthesized in the presence of poly-L-lysine and BSA to sensitize U87-IκBα cells. Results demonstrated the augmentation of the therapeutic potential of 5-FU and curcumin nanoparticles on IκBα overexpressed cells. Thus, this simple strategy offers the scope of using combination modules as a potential cancer therapeutic