Rf linearity in low dimensional nanowire mosfets

Ever decreasing cost of electronics due to unique scaling potential of today's VLSI processes such as CMOS technology along with innovations in RF devices, circuits and architectures make wireless communication an un-detachable part of everyday's life. This rapid transition of communication systems toward wireless technologies over last couple of decades resulted in operation of numerous standards within a small frequency window. More traffic in adjacent frequency ranges imposes more constraints on the linearity of RF front-end stages, and increases the need for more effective linearization techniques. Long-established ways to improve linearity in DSM CMOS technology are focused on system level methods which require complex circuit design techniques due to challenges such as nonlinear output conductance, and mobility degradation especially when low supply voltage is a key factor. These constrains have turned more focus toward improvement of linearity at the device level in order to simplify the existing linearization techniques. This dissertation discusses the possibility of employing nanostructures particularly nanowires in order to achieve and improve RF linearity at the device level by making a connection between the electronic transport properties of nanowires and their circuit level RF characteristics (RF linearity). Focus of this work is mainly on transconductance (gm) linearity because of the following reasons: 1) due to good electrostatics, nanowire transistors show fine current saturation at very small supply voltages. Good current saturation minimizes the output conductance nonlinearities. 2) non-linearity due to the gate to source capacitances (Cgs) can also be ignored in today's operating frequencies due to small gate capacitance values. If three criteria: i) operation in the quantum capacitance limit (QCL), ii) one-dimensional (1-D) transport, and iii) operation in the ballistic transport regime are met at the same time, a MOSFET will exhibit an ideal linear Id-Vgs characteristics with a constant gm of which is independent of the choice of channel material when operated under high enough drain voltages. Unique scaling potential of nanowires in terms of body thickness, channel length, and oxide thickness makes nanowire transistors an excellent device structure of choice to operate in 1-D ballistic transport regime in the QCL. A set of guidelines is provided for material parameters and device dimensions for nanowire FETs, which meet the three criteria of i) 1-D transport ii) operation in the QCL iii) ballistic transport, and challenges and limitations of fulfilling any of the above transport conditions from materials point of view are discussed. This work also elaborates how a non-ideal device, one that approaches but does not perfectly fulfill criteria i) through iii), can be analyzed in terms of its linearity performance. In particular the potential of silicon based devices will be discussed in this context, through mixture of experiment and simulation. 1-D transport is successfully achieved in the lab. QCL is simulated through back calculation of the band movement of the transistors in on-state. Quasi-ballistic transport conditions can be achieved by cooling down the samples to 77K. Since, ballistic transport is challenging to achieve for practical channel lengths in today's leading semiconductor device technologies the effect of carrier back-scattering on RF linearity is explored through third order intercept point (IIP3) analysis. These findings show that for the devices which operate in the QCL, while 1-D sub-bands are involved in carrier transport, current linearity is directly related to the nature of the dominant scattering mechanism in the channel, and can be improved by proper choice of channel material in order to enforce a specific scattering mechanism to prevail in the channel. Usually, in semiconductors, the dominant scattering mechanism in the channel is the superposition of different mechanisms. Suitable choice of channel material and bias conditions can magnify the effect of a particular scattering mechanism to achieve higher linearity levels. The closing section of this thesis focuses on InAS due to its potential for high linearity since it has small effective mass and large mean-free-path

Worldwide wind energy status and the characteristics of wind energy in Iran, case study: the province of Sistan and Baluchestan

In this paper, the recent trend of the worldwide wind energy utilisation is reviewed and the recent activities in using renewable energy sources in Iran are explained. As a case study, the wind characteristics of the province of Sistan and Baluchestan are statistically analysed. The wind characteristics such as the monthly mean wind speed and the wind power density of each station are presented. The monthly variation of the wind direction is presented and also the dominant wind direction is shown in a wind rose diagram. The values of turbulence intensity at different heights are calculated. The results show that the stations of Khash and Nosratabad are more suitable for limited off-grid utility applications. Lootak with the average annual wind power density of 388 W m−2 at the height of 40 m and constant wind direction is recommended for large-scale grid-connected wind turbines

Transconductance Linearity Analysis of 1-D, Nanowire FETs in the Quantum Capacitance Limit

The impact of channel material and dimensionality on the linearity of nanowire transistors is studied theoretically. This paper also evaluates various scattering mechanisms in this context. While operating under 1-D transport conditions in the quantum capacitance limit, the achievable device linearity strongly depends on the details of the scattering mechanisms limiting the transport. Interestingly, it is not only the scattering length that determines the third-order intercept point but also the particular energy dependence of the dominant-scattering mechanism that needs to be considered. Our results provide critical insights for the choice of material to obtain the desired device linearity

Inhibitory Effect of Ruta graveolensL. Extract on Guinea PigLiverand Bovine Milk Xanthine Oxidase: Inhibitory effect of Ruta graveolenson xanthine oxidase

Flavonoids could serve as potent inhibitors of xanthine oxidase (XO). In the present study, the effects of Ruta graveolensL. extract and its major isolated flavonoids,quercetin and rutin, on guinea pig liver XO have been investigated. The inhibitory effects of R. graveolens, quercetin and its glycoside form, rutin, were assayed spectrophotometrically. R. graveolensextract showed moderate inhibition on XO activity. Interestingly, bovine milk and guinea pig liver XO were inhibited significantly at different ranges by either the extract or its flavonoids, whereas allopurinol acted with almost the same potency on both enzymes. Rutin inhibited the enzymes in a competitive manner, while quercetin was found to be a competitive and mixed inhibitor of guinea pig liver and bovine milk XO, respectively. In conclusion, R.graveolensextract can act as a good inhibitor of XO. Interestingly, it was shown that the inhibitory effects of flavonoids on XO could be species dependent

Inhibitory Effect of Ruta graveolens L. Extract on Guinea Pig Liver and Bovine Milk Xanthine Oxidase

Abstract Flavonoids could serve as potent inhibitors of xanthine oxidase (XO). In the present study, the effects of Ruta graveolens L. extract and its major isolated flavonoids, quercetin and rutin, on guinea pig liver XO have been investigated. The inhibitory effects of R. graveolens, quercetin and its glycoside form, rutin, were assayed spectrophotometrically. R. graveolens extract showed moderate inhibition on XO activity. Interestingly, bovine milk and guinea pig liver XO were inhibited significantly at different ranges by either the extract or its flavonoids, whereas allopurinol acted with almost the same potency on both enzymes. Rutin inhibited the enzymes in a competitive manner, while quercetin was found to be a competitive and mixed inhibitor of guinea pig liver and bovine milk XO, respectively. In conclusion, R. graveolens extract can act as a good inhibitor of XO. Interestingly, it was shown that the inhibitory effects of flavonoids on XO could be species dependent

Utilizing the Unique Properties of Nanowire MOSFETs for RF Applications

Nanostructures have attracted a great deal of attention because of their potential usefulness for high density applications. More importantly, they offer excellent avenues for improved scaling beyond conventional approaches. Less attention has been paid to their intrinsic potential for distinct circuit applications. Here we discuss how a combination of 1-D transport, operation in the quantum capacitance limit, and ballistic transport can be utilized for certain RF applications. In particular this work explores how the above transport properties can provide a high degree of transconductance linearity at the device level. The article also discusses how device characteristics can be interpreted and analyzed in terms of device linearity if the above conditions are not ideally fulfilled. Using aggressively scaled silicon nanowire field-effect transistors as an example device in this work provides new insights toward the proper choice of channel material to improve linearity through the above-mentioned transport conditions. According to this study, a high degree of linearity occurs feasible while operating at low supply voltages making low-dimensional systems, and here in particular nanowires, an interesting candidate for portable RF applications