introduction to graphene, nano electronics

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    CONTENTS

    1. Introduction

    1.1.Graphene.

    1.2.

    Frequency Doubler.

    2. Objectives.

    3. Literature survey

    3.1.Graphene Field Effect Transistor (GFET) & Its Operation at Radio Frequency.

    3.2.Equivalent circuit model - SPICE Implementation.

    3.3.Operation of GFET as a Frequency Doubler.

    4.

    Work done till now.5. References.

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    1. Introduction:

    1.1 Graphene

    Graphene is a two-dimensional (2D) material with great potential for electronics. It is thethinnest material in the universe and the strongest ever measured. Its charge carriers exhibit

    giant intrinsic mobility, have the smallest effective mass (it is zero) and can travel

    micrometer-long distances without scattering at room temperature. Graphene can sustain

    current densities 6 orders higher than copper, shows record thermal conductivity and

    stiffness, is impermeable to gases and reconciles such conflicting qualities as brittleness and

    ductility [1]. Graphene is an exciting material. It has a large theoretical specific surface area

    (2630 m 2 g 1), high intrinsic mobility (200 000 cm 2 v 1 s 1), high Youngs modulus

    (1.0 TPa) and thermal conductivity (5000 Wm 1 K 1), and its optical transmittance

    (97.7%) and good electrical conductivity [2].

    With essentially the same lattice structure as an unwrapped carbon nanotube, graphene shares

    many of the advantages of nanotubes, such as the highest intrinsic carrier mobility at room

    temperature of any known materials. This makes these carbon-based electronic materials

    particularly promising for high-frequency circuits. However, due to the high impedance of a

    single carbon nanotube transistor, high-frequency properties of nanotubes were investigated

    indirectly using various mixing techniques, and direct ac measurements of these devices at

    GHz frequencies were realized only recently, enabled by the larger device current in

    nanotube arrays[1]. One distinct advantage of graphene lies in its 2D nature, so that the drive

    current of a graphene device, in principle, can be easily scaled up by increasing the device

    channel width. This width scaling capability of graphene is of great significance for realizing

    high-frequency graphene devices with sufficient drive current for large circuits and

    associated measurements. Recently, it was shown that graphene devices can exhibit currentgain in the microwave frequency range [3].

    1.2 Frequency Doubler

    The output frequency of a frequency doubler is doubled purely via the simple GFET, and the

    deviation from the ideal parabolic relation leads to more even-order harmonics. Odd-order

    harmonics will also be introduced to the system once the IDS-VGS relation deviates to an

    asymmetric shape. An input single period of sinusoidal wave leads to double period at the

    output port. Wang et al. [5] reported ambipolar frequency doubler based on exfoliated

    graphene for the first time in 2009, which showed a frequency response up to 10 kHz and

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    output second-order harmonic wave purity of more than 90%. A single transistor is enough

    for frequency doubling while filters or rectification units are not necessary. However, the

    signal gain of the back-gate setup is very low (less than 1/200) due to its small trans-

    conductance for typical back-gate GFETs. Afterwards, Y2O3 top-gate was introduced and

    utilized to graphene based frequency doubler. Benefited by the high-efficiency gate oxide, the

    signal gain is increased by 10 times (as high as 1/20) compared to that of the back-gate

    geometry and the working [3].

    2. Objectives:

    1. To study characteristics of Graphene field effect transistor.

    2. Modeling and simulation of GFET and Circuit based on it.

    3.

    Analysis of characteristics of the circuit simulated.

    4.

    Performance evaluation with contemporary silicon based circuit.

    3. Literature Survey:

    3.1 Graphene Field Effect Transistor (GFET) & Its Operation at Radio Frequency

    The band less graphene leads to a low or almost zero on/off ratios in graphene closing all its

    options for the digital circuits. Digital circuits can only be realized if there is switching action

    present in the graphene which is only possible by inducing the band-gap in graphene.

    However, graphene could still be very useful in analog and radio-frequency (RF) applications

    where high ON/OFF current ratios are not required [4]. In small signal amplifiers, for

    instance, the transistor is operated in the ON-state and small RF signals that are to be

    amplified are superimposed onto the DC gatesource voltage. Instead, what is needed to

    push the limits of many analog/RF figures of merit (FoM), for instance, the cutoff frequency

    or the intrinsic gain, is an operation region where high trans-conductance, together with a

    small output conductance, is accomplished [2]. These conditions are realized for state-of-the-

    art graphene field-effect transistors (GFETs). Specifically, for large-area GFETs, the output

    characteristic shows a weak saturation that could be exploited for analog/RF applications.

    Using this technology, cutoff frequencies in the terahertz range are envisioned. Cutoff

    frequencies in the range of hundreds of gigahertz have been demonstrated using non-

    optimized technologies [5].Graphene is considered as a promising material to construct field-

    effect transistors (FETs) for high frequency electronic applications due to its unique structure

    and properties, mainly including extremely high carrier mobility and saturation velocity, theultimate thinnest body and stability. Through continuously scaling down the gate length and

    optimizing the structure, the cut-off frequency of graphene FET (GFET) was rapidly

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    increased and up to about 300 GHz, and further improvements are also expected. Because of

    the lack of an intrinsic band gap, the GFETs present typical ambipolar transfer characteristic

    without off state, which means GFETs are suitable for analog electronics rather than digital

    applications [6]. Taking advantage of the ambipolar characteristic, GFET is demonstrated as

    an excellent building block for ambipolar electronic circuits, and has been used in

    applications such as high performance frequency doublers, radio frequency mixers, digital

    modulators, and phase detectors [7]. The use of ambipolar-transport properties of graphene

    for the fabrication of a new kind of RF mixer device is in air now-a- days. Due to the

    symmetrical ambipolar conduction in graphene, graphene-based mixers can effectively

    suppress odd order inter modulations and lead to lower spurious emissions in the circuit. The

    mixer operation was demonstrated at a frequency of 10 MHz using graphene grown by

    chemical vapor deposition [4].

    3.2 Equivalent circuit model - SPICE Implementation

    Device models can be divided into two major groups [8], viz:

    1. Physical models

    2. Empirical models

    Physical models are important in the early stages of device development, and they provide

    better understanding of the device behavior based on its carrier transport parameters. Several

    physical models for G-FETs have been demonstrated. However, since the physical models

    are based on device physics, they are usually too intricate for circuit-level modeling. They are

    neither fast nor easily implemented for use in circuit design tools. Empirical (semi-empirical)

    models can provide acceptable accuracy with less calculation time, and they can be

    implemented in standard electronic design automation (EDA) tools. Recently, several models

    for G-FETs have been proposed. These models can describe the currentvoltage

    characteristics. However, they utilize the same carrier mobility for electrons and holes and

    the same contact resistance independent of the carrier type in the channel. Due to the

    substrate effect, the carrier mobility differs for electrons and holes [9]. The evaluation of the

    circuit performances can be carried out using appropriate electrical compact models. The

    electrical compact model must be able to represent properly the electrical behavior for dc, ac,

    and transient simulation [10].

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    The equivalent circuits can be implemented in electronic design automation tools such as

    cadence PSPICE etc. the circuits simulated with these models give results that are at only 5-

    10% variance from the compared results as shown in [11]

    In order to validate the model and to demonstrate its capability to model some GFETs using

    different graphene material and insulator, they have modeled three technologies: the first one

    is from HRL Laboratories, the second one is from MIT, and the last one is from Columbia

    University. The transistor described in is a top gated device using HfO2 insulator for the gate

    oxide. The graphene is grown by chemical vapor deposition on Ni substrate and is composed

    of about four monolayers [10].

    3.3 Operation of GFET as a Frequency Doubler:

    Graphene ambipolar frequency multiplier is presented that can operate at gigahertz

    frequencies. The contributions of this multiplier are three-fold. First, RF performance of

    graphene field effect transistors (GFET) grown by chemical vapor deposition (CVD) is

    presented for the first time. Second, this device demonstrates ambipolar frequency

    multiplication at 1.4 GHz. This improves frequency performance of graphene frequency

    multipliers by more than 4 orders of magnitude from previous work, making it suitable for a

    much wider range of applications in communication systems[12]. Low loss bias tees are used

    both at the input and the output to combine DC and RF signals, and provide isolation betweenthem. Tuners are used at the input to provide adequate impedance matching. Under the test

    conditions, the gate of the GFET is biased at its minimum conduction point. As a sinusoidal

    RF signal is superimposed to the gate DC bias, the GFET will operate in alternating half

    cycles of electron and hole conduction due to the V-shape transfer characteristics of the

    GFET. The sinusoidal input signal is, hence, full-wave rectified by the GFET, giving an

    output signal that has a fundamental frequency twice of the input frequency [11].

    4.

    Work done (till now):

    1. Implemented the large signal model of graphene equivalent circuit in PSPICE.

    2. Implemented the Graphene field effect transistor based frequency doubler in PSPICE.

    3. Implemented the drain current vs gate voltage characteristics in Matlab so as to study

    the behavior of GFET.

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    5. References:

    1.

    A. K. Geim, GRAPHENE: STATUS AND PROSPECTS, Manchester Centre for Meso

    science and Nanotechnology, University of Manchester, Oxford Road M13 9PL,

    Manchester, UK.2.

    Yanwu Zhu , Shanthi Murali , Weiwei Cai , Xuesong Li , Ji Won Suk , Jeffrey R. Potts

    ,and Rodney S. Ruoff Graphene and Graphene Oxide: Synthesis, Properties, and

    Applications.

    3.

    M. Baus, T.J. Echtermeyer, B.N. Szafranek, M.C. Lemme, Senior Member, IEEE, and H.

    Kurz Device Architectures based on Graphene Channels.

    4. WANG Zhen Xing, ZHANG Zhi Yong & PENG Lian Mao Graphene-based ambipolar

    electronics for radio frequency Applications Key Laboratory for the Physics and

    Chemistry of Nano devices and Department of Electronics, Peking University, Beijing

    100871, China.

    5.

    David Jimnez and Oana Moldovan Explicit Drain-Current Model of Graphene Field-

    Effect Transistors Targeting Analog and Radio-Frequency Applications IEEE

    TRANSACTIONS ON ELECTRON DEVICES, VOL. 58, NO. 11, NOVEMBER 2011.

    6.

    Wang H, Nezich D, Kong J, et al. Graphene frequency multipliers. IEEE Electron

    Device lett, 2009, 30: 547549 IEEE ELECTRON DEVICE LETTERS, VOL. 30, NO.

    5, MAY 2009

    7. Han Wang, Student Member, IEEE, Allen Hsu, Justin Wu, Jing Kong, Member, IEEE,

    and Tomas Palacios, Member, IEEE, Graphene-Based Ambipolar RF Mixers, IEEE

    ELECTRON DEVICE LETTERS, VOL. 31, NO. 9, SEPTEMBER 2010

    8. Omid Habibpour, Student Member, IEEE, Josip Vukusic, and Jan Stake, Senior Member,

    IEEE , A Large-Signal Graphene FET Model. IEEE TRANSACTIONS ON

    ELECTRON DEVICES, VOL. 59, NO. 4, APRIL 2012.

    9.

    Sebastien regon`ese, Maura Magallo, Cristell Maneux, Henri Happy, and Thomas

    Zimmer, Senior Member, IEEE , Scalable Electrical Compact Modeling for Graphene

    FET Transistors , IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 12, NO.

    4, JULY 2013.

    10. Han Wang, Allen Hsu, Ki Kang Kim, Jing Kong, and Toms Palacios Gigahertz

    Ambipolar Frequency Multiplier based on CVD Graphene Department of Electrical

    Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge

    MA 02139, USA.

    11.Shu-Jen Han, Keith A. Jenkins, Alberto Valdes Garcia, Aaron D. Franklin, Ageeth A.

    Bol, and Wilfried Haensch High-Frequency Graphene Voltage Amplifier IBM T. J.

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    Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598,

    United States.

    12.

    J. S. Moon, D. Curtis, D. Zehnder, S. Kim, D. K. Gaskill, G. G. Jernigan, R. L. Myers-

    Ward, C. R. Eddy, Jr., P. M. Campbell, K.-M. Lee, and P. Asbeck, Low-Phase-Noise

    Graphene FETs in Ambipolar RF ApplicationsIEEE ELECTRON DEVICE LETTERS,

    VOL. 32, NO. 3, MARCH 2011.