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A W-band MMIC Resistive Mixer Based on Epitaxial Graphene FET
Abstract
This letter presents the design, fabrication and characterization of the first graphene based monolithic microwave integrated circuit (MMIC) in microstrip technology operating in W-band. The circuit is a resistive mixer in a 250 nm graphene field effect transistor (G-FET) technology on a SiC substrate. A conversion loss of 18 dB is achieved which is limited by the available local oscillator (LO) power. The mixer exhibits a flat response over radio frequency (RF) range of 90-100 GHz. The RF bandwidth is also limited by the measurement setup.
... One of the best properties of a GFET is its ambipolar characteristics, and it is best used in RF components [10]- [13]. To date, several GFET-based RF components have been demonstrated, such as oscillators [14]- [20], phase shifters [21], [22], amplifiers [23]- [26], mixers [27]- [31], and frequency multipliers [32], [33]. A GFET in RF was first demonstrated in 2008 [34], and since then, its performance has gradually improved. ...
... As opposed to the conventional subharmonic mixers, the design of their mixer realized a more compact structure as it is implemented using only one transistor. Thus, with this success, more GFET-based mixers have been investigated by fabricating the mixers with GFETs using monolayer [27]- [29] or bilayer graphene [30], [31]. ...
... In order to optimize the CL, different ways to enhance it have been discussed in several published articles. For example, a study done in [30] stated that a low CL can be achieved by reducing the on-state channel resistance, and a study done in [31] suggested increasing the off-state resistance. Both can be achieved by using graphene with high mobility or high charge density, obtained, for example, in a pure bilayer graphene. ...
Graphene has been extensively investigated in the context of electronic components due to its attractive properties, such as high carrier mobility and saturation velocity. In the past decade, the graphene field-effect transistor (GFET) has been considered one of the potential devices to be used in future radio frequency (RF) applications and can help usher in the Internet of Things and the 5G communication network. This review presents recent developments of GFETs in RF applications with a focus on components such as amplifiers, frequency multipliers, phase shifters, mixers, and oscillators. Initially, the figures of merit (FoMs) for the GFET are briefly described to understand how they affect these RF components. Subsequently, the FoMs of GFET-based RF components are compared with other non-GFET-based RF components. It is found that, due to its zero-band gap and ambipolar characteristics, GFETs are more suitable for use in frequency multiplier and phase shifter applications, outperforming non-GFET-based RF components. Finally, future research on GFETs themselves as well as GFET-based RF components is recommended. This review provides valuable insights into such components that could give rise to innovative applications in industry.
... In case of the GFET and because they cannot be switched off, the on-off resistance ratio is always low because of a high on-resistance and a low off-resistance. The reported CL values of GFET-based mixers consequently varies from 45 dB [35] to 18 dB [36]. The latter work is the minimum reported CL so far for any graphene-based mixer, as indicated in Table 2.1 which compares the key performance parameters of the reported GFET-based mixers. ...
... To the best knowledge of the author, no graphene-based transmitter has been reported so far. However, the W -band mixer which has been reported in [36] was measured as an upconverter modulator for an 8 Gbit/s OFDM signal [67]. Although these measurement results suggest a promising potential of the GFET mixers for high data-rate communications, they are still beyond other competing technologies. ...
... In case of GFETs which have a high R min and a low R max , no hard switching can be achieved and, consequently, the conversion loss is always high. The reported values vary from 45 dB [35] to 18 dB [36]. The latter one is the minimum conversion loss reported so far for a GFET-resistive mixer. ...
Graphene is one of the first two-dimensional (2D) materials to be isolated in nature. It has the thinnest crystal-structure known, with a thickness of one carbon atom. Since more than seventy years, properties of graphene have been theoretically studied as a thermodynamically-unstable material, which can not exist in a free state. Therefore, it was considered for a long time as academic material. In 2004, thermodynamically-stable single-layer graphene (SLG) was successfully isolated from a graphite surface. This breakthrough stimulated intense theoretical and experimental studies, exploring the outstanding mechanical strength, chemical stability, optical transparency, and the excellent electronic properties of graphene. This includes the extraordinary high mobility and saturation-velocity of the charge carriers in graphene, promising a great potential in high-frequency electronics. However, the research in graphene-based circuits and systems shows a significantly slower pace for two main reasons. First, the fabrication technology of the graphene field-effect transistors (GFETs) results in poor current-saturation and relatively low cut-off frequency, fT, and maximum oscillation frequency, fmax. The second reason is that most of the graphene-based circuits have been presented as the extension to the study of the transistor itself. Accordingly, they are limited to single-transistor designs and not adapted to large-scale integration. These two reasons raise some doubts about the true feasibility of using graphene in microelectronics. The goal of this thesis is to establish the mandatory foundation from the design and technology perspectives to push forward the activities in graphene electronics towards the applied research. In this way, useful applications can be demonstrated exploiting the excellent properties of graphene and competing with conventional semiconductor technologies. As a first step, a graphene-compatible Monolithic Microwave Integrated Circuit (MMIC) process has been developed and optimised to enable the fabrication of high-quality passive components. In addition, graphene-based diodes are introduced as Metal-Insulator-Graphene (MIG) junctions, integrated alongside with the developed MMIC process. MIG diodes exhibit superior performance, in terms of high current-density, low series-resistance, large current-asymmetry, adequate nonlinearity, and high voltage-responsivity. In addition, the proposed fabrication technology, using graphene grown by chemical vapour deposition (CVD), ensures the reproducibility of the MIG diode and the repeatability of its electrical properties. These performance metrics boost the realisation of high-frequency graphene-based circuits, overcoming the limited speed of state-of-the-art GFETs. Moreover, small-signal and nonlinear models for the MIG diodes have been extracted and verified in order to facilitate the circuit design process. The study of the MIG diode as a high-frequency mixing and frequency multiplying device reveals a promising performance in terms of conversion-loss (CL). Accordingly, several microwave circuits have been proposed employing MIG diodes and the developed MMIC process. This includes a single-diode mixer at 2.4 GHz and fully-integrated balanced fundamental and subharmonic microwave mixers for X-band applications, i.e., 8-12 GHz. The measured performance of the fabricated mixers sets a new record compared to state-of-the-art GFET-based counterparts and competes with the commercial Schottky-diode mixers. Moreover, fully-integrated and wideband resistive frequency multiplier circuits have been demonstrated in frequency doubler and tripler configurations. The theoretical analysis, together with the measurement results, proves a low-loss performance which, in turn, opens the opportunity to realise higher-order graphene-based frequency multipliers circuits. Moreover, using GFETs as power detectors enables operation beyond their fT and fmax. This concept has been utilised to realise a fully-integrated millimetre-wave receiver frontend in a six-port configuration. Successful demodulation of an On-Off Keying digitally modulated signal has been demonstrated at 90 GHz. The proposed graphene technology and design concepts in this thesis represent the basis for future demonstrations of graphene-based micro- and millimetre-wave integrated circuits. This endorses the potential of graphene as the material for future microelectronics, such as wearable and flexible devices for biomedical and sensing applications.
... Although the integration level of the down-conversion chip in [11] and the receiver chip in [12] is improved, their image rejection ratio (IRR) is 10~15 dB. In addition, according to the single-ended mixer mixer structure similar to [13], the isolation between LO and RF is approximately The above-mentioned MMICs perform well in radar or communication fields, bu low image rejection will deteriorate the noise characteristics of small signals in th ometer and fail to meet the requirements of PMMI systems. In addition, in order to ment a highly integrated MMIC, the inevitable coupling problems in the circuit als to be analyzed and solved. ...
... It provides a virtual ground by adding a balun to each port, so that all ports are mutually isolated. Furthermore, by using resistive FETs to realize DBM [13], the demand for LO power can be effectively reduced [15,16], which is also important for large-scale array applications to reduce power consumption. But relatively speaking, the design difficulty is increased, requiring additional bias on the gate of each FET. ...
This paper presents the coupling effects analysis and suppression of a highly integrated receiver front-end MMIC for a passive millimeter-wave imager system. The receiver MMIC consists of a low-noise amplifier, double-balanced image-reject mixer, frequency quadrupler, and analog phase shifter. In order to integrate these devices into a compact single chip without affecting the core performance, coupling problems need to be solved. We analyze the influence of coupling effects on the image rejection ratio, and propose corresponding solutions for three different coupling paths. (1) The coupling in the LO-RF path of the mixer is solved by designing a double-balanced mixer with high isolation characteristics. (2) The coupling between the LO chain and the LNA from space and dielectric is suppressed by optimizing the two main transmission lines spacing and adding isolation vias. (3) The coupling caused by the line crossing is restrained by designing a differential line crossover structure. The design and implementation of the MMIC are based on 0.15 µm GaAs pHEMT process. The receiver chip has 6.1~8.7 dB conversion gain in 32~36 GHz, less than 3.5 dB of noise figure, and more than 35 dB of image rejection ratio. The measurement results show that the receiver MMIC is especially suitable for high-sensitivity passive millimeter-wave imaging systems.
... In the particular realm of mixers, the low transconductance of GFETs still hinders the deployment of active architectures with comparable performance to conventional technologies [1,16]. The scenario is more favorable with subharmonic resistive mixers (taking advantage from the frequency doubling phenomenon enabled by graphene quadratic I DS -V GS response, see Fig. 1), which have demonstrated to be on par with state-of-the-art mixing performance [18][19][20][21]. Subharmonic mixers are especially convenient at high frequencies since they relax the frequency requirement of the high-power local oscillator (LO) source [22]. ...
Ambipolar conductance in graphene field-effect transistors (GFETs), and in particular their quasi-quadratic I–V transfer characteristic, makes these devices excellent candidates for exploiting subharmonic mixing at high frequencies. Several realizations have already demonstrated the ability of GFETs to compete with, or even improve, state-of-the-art mixers based on traditional technologies. Nonetheless, a systematic analysis of the influence on performance of both circuit design and technological aspects has not been conducted yet. In this work, we present a comprehensive assessment of the conversion losses by means of applying radio-frequency circuit design techniques in terms of filtering and matching, along with the impact stemming from physical and geometric variations of a fabricated graphene technology.
... Due the properties of graphene, in graphene plasmons exhibit low losses 1 , tunable optical properties 2 , strong optical field confinement 3,4 , and environmental sensitivity [5][6][7] . This makes graphene an attractive material for next generation technologies 8 in sensing 5,9 , photonics, electronics 10,11 , and communication 12 . To improve device design and performance, it is crucial to extend the microscopic theory of plasmons to include nonlocal effects [13][14][15] together with the impact of defects and impurities 16 in the sample as well as chemical compounds deposited on the surface 17,18 . ...
This work analyses how impurities and vacancies on the surface of a graphene sample affect its optical conductivity and plasmon excitations. The disorder is analysed in the self-consistent Green's function formulation and nonlocal effects are fully taken into account. It is shown that impurities modify the linear spectrum and give rise to an impurity band whose position and width depend on the two parameters of our model, the density and the strength of impurities. The presence of the impurity band strongly influences the electromagnetic response and the plasmon losses. Furthermore, we discuss how the impurity-band position can be obtained experimentally from the plasmon dispersion relation and discuss this in the context of sensing.
... Transfer-free p-type hydrogen-intercalated [1][2][3][4][5] quasi-free-standing (QFS) graphene grown on semi-insulating (SI), nominally on-axis, hexagonal SiC(0001) in the process of epitaxial Chemical Vapor Deposition (CVD) in argon flow [6], has been appreciated for its reproducible hole density [7,8], thermal stability of transport properties [9,10], scalable growth technology [11], and verified as the optimum graphene platform for monolithic microwave integrated circuits (MMICs) [12][13][14] and high-temperature Hall effect sensors [9,10,15]. ...
In this report, we present transfer-free p-type hydrogen-intercalated quasi-free-standing epitaxial Chemical
Vapor Deposition graphene on 15-mm × 15-mm semi-insulating vanadium-compensated on-axis 6H–SiC(0001),
characterized in that its room-temperature direct-current Hall-effect-derived hole mobility 𝜇p = 5019 cm2/Vs,
and its statistical number of layers (N), as indicated by the relative intensity of the SiC-related Raman-active
longitudinal optical A1 mode at 964 cm−1, equals N = 1.05. The distribution of the ellipsometric angle 𝛹
measured at an angle of incidence of 50◦ and 𝜆 = 490 nm points out to N = 0.97. The close-to-unity value of
N implies that the material under study is a close-to-perfect quasi-free-standing monolayer, which is further
confirmed by High-Resolution Transmission Electron Microscopy. Therefore, its spectroscopic properties, which
include the Si–H peak at 2131 cm−1, the histograms of 𝛹 and 𝛥, and the Raman G and 2D band positions,
widths, and the 2D-to-G band intensity ratios, constitute a valuable reference for this class of materials.
... Graphene FETs can achieve an impedance of below 200 Ω due to their ultra-high-mobility. [27][28][29] But there exists a big challenge to grow wafer-scale, uniform, and high-mobility material. It is possible to effectively reduce the impedance by a channel's large width-to-length ratio (WLR) of beyond 100. ...
In this paper, a 330 GHz terahertz heterodyne detector based on bowtie-antenna-coupled AlGaN/GaN high-electron-mobility transistor (HEMT) is designed and demonstrated. The bowtie antenna and a silicon lens couple the terahertz wave into a transmission line, in which the HEMT’s channel generates both self-mixing and heterodyne signals. Compared to field-effect detectors without front low-noise amplifier and output impedance matching, this detector boosts the intermediate-frequency (IF) bandwidth to 2.9 GHz due to a low output impedance of 505 Ω while maintaining a comparable sensitivity. With further sensitivity enhancement, such detector would develop to be room-temperature, high-sensitivity and high-IF-bandwidth heterodyne arrays.
... However, non-hydrogen-intercalated graphene on SiC(0001) is rarely the choice for device-oriented technology. Numerous authors report on the application of hydrogen-intercalated p-type epitaxial graphene on SiC(0001) [14][15][16][17][18], widely appreciated for the high mobility of charge carriers and their well-defined sheet density [19,20]. ...
In this report, we introduce a novel method based on low-frequency noise analysis for the assessment of quality and pattern of inhomogeneity in intentionally-aged Hall effect sensors featuring hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene mesa on semi-insulating high-purity on-axis 4H-SiC(0001), all passivated with a 100-nm-thick atomic-layer-deposited Al2O3 layer. Inferring from the comparison of the measured noise and one calculated for a homogeneous sensor, we hypothesize about possible unintentional contamination of the sensors’ active regions. Following in-depth structural characterization based on Nomarski interference contrast optical imaging, confocal micro-Raman spectroscopy, high-resolution Transmission Electron Microscopy and Secondary Ion Mass Spectrometry, we find out that the graphene’s quasi-free-standing character and p-type conductance make the Al2O3/graphene interface exceptionally vulnerable to uncontrolled contamination and its unrestrained lateral migration throughout the entire graphene mesa, eventually leading to the blistering of Al2O3. Thus, we prove the method’s suitability for the detection of these contaminants’ presence and location, and infer on its applicability to the investigation of any contamination-induced inhomogeneity in two-dimensional systems. https://authors.elsevier.com/a/1eyP64xMlkIhhc
... Although further improvement of the RF device performance is expected [15], the already proven GFET figures of merit (FoMs) allow the design of applications operating at millimeter wave (mmWave) frequencies. Those encompass applications where the GFET leverages either its remarkable high transconductance, e.g., low noise amplifiers (LNAs) [16]; or the graphene ambipolarity such as resistive mixers [17][18][19][20][21]; frequency multipliers [21,22]; and power detectors [23], all of them demonstrated to properly operate in the gigahertz band. ...
The Dirac voltage of a graphene field-effect transistor (GFET) stands for the gate bias that sets the charge neutrality condition in the channel, thus resulting in a minimum conductivity. Controlling its dependence on the terminal biases is crucial for the design and optimization of radio-frequency applications based on multiple GFETs. However, the previous analysis of such dependence carried out for single devices is uncomplete and if not properly understood could result in circuit designs with poor performance. The control of the Dirac point shift (DPS) is particularly important for the deployment of graphene-based differential circuit topologies where keeping a strict symmetry between the electrically balanced branches is essential for exploiting the advantages of such topologies. This note sheds light on the impact of terminal biases on the DPS in a real device and sets a rigorous methodology to control it so to eventually optimize and exploit the performance of radio-frequency applications based on GFETs.
... With the growing interest in epitaxial Chemical Vapor Deposition (CVD) of graphene on semiinsulating (SI) silicon carbide and noticeable progress in applied activities [1][2][3][4][5][6], it has become crucial to reliably quantify, compare and categorize graphene's properties. ...
In this report we demonstrate a method for direct determination of the number of layers of hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene on semiinsulating vanadium-compensated on-axis 6H-SiC(0001). The method anticipates that the intensity of the substrate’s Raman-active longitudinal optical A1 mode at 964 cm^(−1) is attenuated by 2.3 % each time the light passes through a single graphene layer. Normalized to its value in a graphene-free region, the A1 mode relative intensity provides a greatly enhanced topographic image of graphene and points out to the number of its layers within the terraces and step edges, making the technique a reliable diagnostic tool for applied research.
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... Although further improvement of the RF device performance is expected [15], the already proven GFET figures of merit (FoMs) allow the design of applications operating at millimeter wave (mmWave) frequencies. Those encompass applications where the GFET leverages either its remarkable high transconductance, e.g., low noise amplifiers (LNAs) [16]; or the graphene ambipolarity such as resistive mixers [17][18][19][20][21]; frequency multipliers [21,22]; and power detectors [23], all of them demonstrated to properly operate in the gigahertz band. ...
The Dirac voltage of a graphene field-effect transistor (GFET) stands for the gate bias that sets the charge neutrality condition in the channel, thus resulting in a minimum conductivity. Controlling its dependence on the terminal biases is crucial for the design and optimization of radio-frequency applications based on multiple GFETs. However, the previous analysis of such dependence carried out for a single device can lead to confusion and if not properly understood could result in circuit designs with poor performance. The control of the Dirac point shift (DPS) is particularly important for the deployment of graphene-based differential circuit topologies where keeping a strict symmetry between the electrical balanced branches is crucial for exploiting the advantages of such topologies. This note sheds light on the impact of terminal biases on the DPS in a real device and sets a rigorous methodology to control it so to eventually optimize and exploit the performance of radio-frequency applications based on GFETs.
... The technology of graphene epitaxy through Chemical Vapor Deposition (CVD) from decomposed propane [1] on semiinsulating (SI) on-axis SiC(0001) has already been verified in a number of potential applications, including broad-temperature magnetic field sensing [2,3] and monolithic microwave integrated circuits (MMICs) [4][5][6]. Historically, first to synthesize on SiC was n-type monolayer graphene in the form of a covalently bonded to the substrate carbon buffer layer [7][8][9][10] topped with a single graphene layer. The technology's potential was further improved with the introduction of hydrogen atom intercalation [11][12][13][14][15][16] that converts the electrically inactive buffer [10] into quasi-free-standing (QFS) monolayer graphene [17] and monolayer graphene into QFS-bilayer graphene [11,18]. ...
In this report we investigate structural and electrical properties of epitaxial Chemical Vapor Deposition quasi-free-standing graphene on an unintentionally-doped homoepitaxial layer grown on a conducting 4H-SiC substrate 4° off-axis from the basal [0001] direction towards [11-20]. Due to high density of SiC vicinal surfaces the deposited graphene is densely stepped and gains unique characteristics. Its morphology is studied with atomic force and scanning electron microscopy. Its few-layer character and p-type conductance are deduced from a Raman map and its layers structure determined from a high-resolution X-ray diffraction pattern. Transport properties of the graphene are estimated through Hall effect measurements between 100 and 350 K. The results reveal an unusually low sheet resistance below 100 Ω/sq and high hole concentration of the order of 10¹⁵ cm⁻². We find that the material’s electrical properties resemble those of an epitaxially-grown SiC PIN diode, making it an attractive platform for the semiconductor devices technology.
https://authors.elsevier.com/a/1cvqR5aLOStCsP
... It has many fascinating properties, such as high thermal conductivity (2000-4000 W m -1 K -1 ) [1][2][3], high carrier mobility (10 3 -10 5 cm 2 V −1 s −1 ) [4][5][6], high mechanical strength (Young's modulus of ∼1000 GPa) [7], high fracture strength (∼125 GPa) [8], chemical inertness [9][10][11], and lubricity [12][13][14]. A lot of research has implemented graphene as transparent electrodes [15][16][17], field-effect devices [18][19][20], corrosion barriers [21], and micro-and nanoelectromechanical systems [22] with the focus of electrical, thermal, and chemical applications of graphene. The mechanical properties of graphene have not much explored, such as using graphene to reduce friction between dynamic interfaces of metal surface for specific industrial applications discussed as follows. ...
Multi-layer graphene, serving as a conductive solid lubricant, is coated on the metal surface of electrical terminals. This graphene layer reduces the wear and the friction between two sliding metal surfaces while maintaining the same level of electrical conduction when a pair of terminals engage. The friction between the metal surfaces was tested under dry sliding in a cyclical insertion process with and without the graphene coating. Comprehensive characterizations were performed on the terminals to examine the insertion effects on graphene using scanning electron microscopy, four-probe resistance characterization, lateral force microscopy, and Raman spectroscopy. With the thin graphene layers grown by plasma enhanced chemical vapor deposition on gold (Au) and silver (Ag) terminals, the insertional forces can be reduced by 74 % and 34 % after the first cycle and 79 % and 32 % after the 10th cycle of terminal engagement compared with pristine Au and Ag terminals. The resistance of engaged terminals remains almost unchanged with the graphene coating. Graphene stays on the terminals to prevent wear-out during the cyclic insertional process and survives the industrial standardized reliability test through high humidity and thermal cycling with almost no change.
... Consequently, the CL is always high. The integrated GFET-resistive mixer reported in [42] and shown in Fig. 3(a) utilizes a single GFET device fabricated using epitaxial graphene on top an SiC substrate. In this design, the channel resistance ratio equals to 160/50, as shown in Fig. 3(b), which theoretically corresponds to 15.5 dB of CL according to (2). ...
This article presents the recent development of frequency-conversion mixer circuits employing graphene-based electron devices targeting microwave and millimeter-wave applications. Mixer circuits that have been reported using graphene field-effect transistors and graphene diodes are investigated. The concept of operation of these circuits utilizing the unique properties of graphene as well as their performance metrics are discussed in comparison with their counterparts realized based on conventional semiconductor technologies. In addition, the demanded improvement in the properties of the graphene electron devices for better circuit performance is highlighted.
... References [32]- [34] describe MMIC circuits based on GFETs. Although they reported good conversion gain values, VOLUME 4, 2016 LO signals with frequency around 100 [33], [34] and 200 GHz [32], and power level between 8 and 16 dBm are used, requiring external high-performance frequency multipliers. ...
In this work, a graphene-based single-stage high-order subharmonic mixer is presented. The device is able to up-and downconvert a signal in the 330 – 500 GHz frequency range, using a local oscillator signal with frequency located in the 26 – 40 GHz band. It exploits the strong nonlinear electromagnetic behavior exhibited by macroscopic graphene sheets when they are exposed to an incident electromagnetic wave to generate the output signal as a mixing product between the input signal and a high-order harmonic component of the local oscillator, which is internally generated without requiring additional circuitry. A prototype was implemented and its performance was experimentally characterized considering several different local oscillator multiplication orders. The maximum measured downconversion gain is around –50 dB, whereas the maximum output signal reached when working as upconverter is –43 dBm at 340 GHz and –63 dBm at 480 GHz. These values are good enough to be used in practical short-range applications. Furthermore, the measurement results are in good agreement with the theoretical predictions about graphene behavior.
... There are several literatures of the mixer devices with compact sizes, such as a monolithic microwave integrated circuit (MMIC) technique and CMOS fabrication. [8][9][10][11][12][13] To reduce the size of the mixers, a high relative permittivity substrate can be used; however, the cost is high. 14,15 In this article, the proposed compact size of the Wilkinson power divider is presented and it is applied to mixer. ...
In the modern day, wireless communications systems are widely used for medical services and medical information security. A wireless communication device for medical services is required for a high performance and small size technique. In this article, a proposed compact size of the single‐ended mixer using small size of the Wilkinson power divider with T‐shaped transmission line is presented. The compact size of the mixer used for small size is based on Wilkinson power divider using T‐shaped transmission line which is connected to amplifier circuit part. The electrical length of the transmission line for the conventional Wilkinson power divider was 90°. However, the electrical length of the T‐shaped transmission line was 30°. Therefore, the physical length was reduced by 1/2 times. The size of a proposed mixer was 22.21 × 18.32 mm² at a center frequency of 2.165 GHz. It will be applied to a transceiver for wireless communication system of medical services.
... Conventionally, depending on its drain bias, a mixing transistor can be classified exclusively as active (V ds ≠ 0) or passive (V ds = 0). While active mixing comes from the LO-induced transconductance (G m ) modulation, passive mixing relies on channel-conductance (G ds ) modulation [21][22][23][24]. In the more advanced silicon processes such as 65-or 40-nm CMOS where the early effect cannot be neglect (because of their short channel length), a strict separation of active and passive mixing becomes impossible, as both G m and G ds will be affected whenever V ds ≠ 0. A dual-modulation mixing theory is then needed to clarify their impact on mixer's performance under different drain biases and IF loading impedances. ...
This manuscript presents the design of a W‐band receiver in which an radio frequency‐low noise amplifier (RF‐LNA), a wideband mixer, intermediate frequency (IF) amplification, a local oscillator frequency (LO) tripler and a driving amplifier are all integrated into one single chip of 1050 × 820 μm². To effectively extend the mixer's IF bandwidth while retaining its conversion gain, impacts of the mixing transistor's drain bias and output loading impedance are explored using a dual‐modulation conversion‐matrix method, which allows both the LO‐induced transconductance modulation and channel‐conductance modulation to be considered simultaneously. It is shown that, by merging the input capacitance of the IF amplifier into a high‐impedance artificial transmission line, an actively biased mixer can have constant conversion gain over broad bandwidth. A 77–110 GHz 65 nm‐complementary metal‐oxide‐semiconductor (CMOS) receiver with 33 GHz IF bandwidth is then designed and measured. Its conversion gain and noise figure are 10 and 20 dB, respectively, and the input‐referred P1 dB is −15 dBm; the overall power consumption is 330 mW under 1.3 V drain bias.
... In case of the GFET and because of its ambipolar behaviour, the on-off resistance-ratio is always low with high on-resistance and low off-resistance. Therefore, the reported CL varies from 45 dB [3] to 18 dB [4] which is the minimum reported CL so far for graphene-based mixers to the best of our knowledge. ...
In this paper we present the design, fabrication and characterisation of a fully-integrated, wideband double-balanced mixer based on graphene diodes. The circuit is implemented on glass substrate utilising an in-house monolithic microwave integrated circuits (MMIC) process and provides 10 dB conversion loss at 10 GHz with a 3-dB bandwidth of 6 GHz. The measured LO-to-RF isolation is better than 25 dB in the entire band with better than 12 dB return loss at both LO and RF ports in 50 Ω measurement system. To the best knowledge of the authors, the mixer conversion-loss performance outperforms the state-of-the-art graphene-transistor-based mixer circuits.
... Hence, most of the reported GFET-based circuits exploit the change in channel resistance (R ds ) with gate-source voltage rather than its transconductance (g m ). Examples are reported FET-resistive mixers in [4]- [7], frequency multiplier in [8], and power detectors in [9] and [10]. A graphene radio frequency (RF) receiver has been reported [11] at 4.3 GHz employing a three-stage GFET-based amplifier by using the last stage as a down-conversion mixer. ...
We demonstrate a full-fledged millimeter-wave graphene-based six-port receiver frontend at 90 GHz employing graphene power detectors. Exploiting the high responsivity and wide dynamic range reported for the state-of-the-art graphene field-effect transistors (GFETs), graphene power detectors are demonstrated beyond the maximum oscillation frequency, fmax, of the graphene transistor. The proposed circuit is fabricated on thinned SiC substrate and its functionality is verified by demodulation of 10-Mbps ON-OFF keying (OOK) digitally modulated signal.
... the intrinsic nonlinearity provided by GFETs. This includes frequency multipliers 4 , power detectors up to THz frequencies 5,6 , and mixers [7][8][9][10] , which are demonstrated at frequencies up to 200 GHz 11 . On the contrary, few amplifiers have been reported either with moderate power gain of 7 dB up to 4 GHz 12 , or with higher gain at lower frequency; 10 dB at 1 GHz 13 . ...
This work demonstrates a design approach which enables the fabrication of fully integrated radio frequency (RF) and millimetre-wave frequency, direct-conversion graphene receivers by adapting the frontend architecture to exploit the state-of-the-art performance of recently reported waferscale CVD metal-insulator-graphene (MIG) diodes. As a proof-of-concept, we built a fully integrated microwave receiver in the frequency range 2:12:7 GHz employing the strong nonlinearity and the high responsivity of MIG diodes to successfully receive and demodulate complex, digitally modulated communication signals at 2:45 GHz. In addition, the fabricated receiver uses zero biased MIG diodes and consumes zero dc power. With the flexibility to be fabricated on different substrates, the prototype receiver frontend is fabricated on a low-cost, glass substrate utilising a custom-developed MMIC process backend which enables high performance passive components. The measured performance of the prototype makes it suitable for Internet-of-Things (IoT), Radio Frequency Identification (RFID) systems for medical and communications applications.
... Due the properties of graphene, in graphene plasmons exhibit low losses 1 , tunable optical properties 2 , strong optical field confinement 3,4 , and environmental sensitivity [5][6][7] . This makes graphene an attractive material for next generation technologies 8 in sensing 5,9 , photonics, electronics 10,11 , and communication 12 . To improve device design and performance, it is crucial to extend the microscopic theory of plasmons to include nonlocal effects [13][14][15] together with the impact of defects and impurities 16 in the sample as well as chemical compounds deposited on the surface 17,18 . ...
This work analyses how impurities and vacancies on the surface of a graphene sample affect its optical conductivity and plasmon excitations. The disorder is analysed in the self-consistent Green's function formulation and nonlocal effects are fully taken into account. It is shown that impurities modify the linear spectrum and give rise to an impurity band whose position and width depend on the two parameters of our model, the density and the strength of impurities. The presence of the impurity band strongly influences the electromagnetic response and the plasmon losses. Furthermore, we discuss how the impurity-band position can be obtained experimentally from the plasmon dispersion relation and discuss this in the context of sensing.
... This work demonstrates, for the first time, OFDM signal transmission through a resistive mixer implemented in Graphene FET (G-FET) monolithic microwave integrated circuit (MMIC) [10]. The mixer promises a highly linear behavior, and is therefore suitable for the high PAPR requirement. ...
This letter reports a crossbar mixer based on the substrate-integrated suspended line (SISL) platform, with two contributions below. First, multistage stepped double-ridge waveguides are designed for the radio frequency (RF) signal coupling to the Schottky diode pair directly, with low-RF path loss as well as easier wideband matching. Furthermore, the surface roughness of the waveguide sidewall plating layer is measured to analyze the additional metal loss. Measurements show that the results are in reliable agreement with the simulation after considering the practical factors, including surface roughness and dielectric frequency properties. The conversion loss of this mixer is 6.16–9.84 dB within the RF range of 104–118.5 GHz, which is competitive with those in the similar frequency band that adopt advanced processing technology, yielding a good balance between the cost, weight, and performance of the circuits.
Graphene field-effect transistors (GFETs) exhibit negligible transconductance under two scenarios: for any gate-to-source voltage when the drain-to-source voltage is set to zero and for an arbitrary drain-to-source voltage provided that the gate-to-source voltage equals the Dirac voltage. Hence, extracting the channel and the parasitic series resistances from
S
-parameters under these conditions enables analyzing their dependence on the gate and drain biases. This is fundamental to assess the portion of the output resistance that is controlled by the gate. Besides, the drain bias dependence of the drain and source resistances is also evidenced. Within the proposal, resistive components accounting for the lossy nature of the gate capacitance are incorporated into the model, which exhibits a broadband correlation with experimental data. This avoids the series resistances to be considered as frequency dependent in the model.
Exploiting ambipolar electrical conductivity based on graphene field‐effect transistors has raised enormous interest for high‐frequency (HF) analog electronics. Controlling the device polarity, by biasing the graphene transistor around the vertex of the V‐shaped transfer curve, enables to redesign and highly simplify conventional analog circuits, and simultaneously to seek for multifunctionalities, especially in the HF domain. This study presents new insights for the design of different HF applications such as power amplifiers, mixers, frequency multipliers, phase shifters, and modulators that specifically leverage the inherent ambipolarity of graphene‐based transistors.
En este trabajo, se implementan un conjunto de modelos que resuelven la física de los transistores basados en grafeno, capturando la conducción ambipolar y proporcionando las peculiares curvas de corriente frente a voltaje de puerta con forma de “V”. Estas herramientas pueden ser potencialmente utilizadas por estudiantes de ingeniería para explorar la electrónica ambipolar, abriendo la posibilidad de 1) rediseñar y simplificar aplicaciones de microondas convencionales; y 2) buscar nuevas funcionalidades en el ámbito analógico y de alta frecuencia. A este respecto, como ejemplo, presentamos nuevos enfoques para el diseño de multiplicadores de frecuencia, amplificadores de potencia, mezcladores y desfasadores en radiofrecuencia que específicamente aprovechan la ambipolaridad
Over the past two decades, the research on two-dimensional materials has received much interest. Graphene is the most promising candidate regarding high frequency applications thus far due to is high carrier mobility. This review discusses the research about the employment of graphene in micro- and millimetre-wave circuits. The review starts with the different methodologies to grow and transfer graphene before discussing the way graphene-based field-effect-transistors (GFETs) and diodes are built. A review on different approaches for realising these devices is provided before discussing the employment of both GFETs and graphene diodes in different micro- and millimetre-wave circuits, showing the possibilities but also the limitations of this 2D-material for high frequency applications.
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In this article, the bias dependence of intrinsic channel thermal noise of single-layer (SL) graphene field-effect transistors (GFETs) is thoroughly investigated by experimental observations and compact modeling. The findings indicate an increase of the specific noise as drain current increases, whereas a saturation trend is observed at very high carrier density regime. Besides, short-channel effects, such as velocity saturation (VS) also result in an increment of noise at higher electric fields. The main goal of this work is to propose a physics-based compact model that accounts for and accurately predicts the above experimental observations in short-channel GFETs. In contrast to long-channel MOSFET-based models adopted previously to describe thermal noise in graphene devices without considering the degenerate nature of graphene, in this work, a model for short-channel GFETs embracing the 2-D material's underlying physics and including a bias dependence is presented. The implemented model is validated with deembedded high-frequency data from two short-channel devices at quasi-static (QS) region of operation. The model precisely describes the experimental data for a wide range of low-to-high drain current values without the need of any fitting parameter. Moreover, the consideration of the degenerate nature of graphene reveals a significant decrease of noise in comparison with the nondegenerate case and the model accurately captures this behavior. This work can also be of utmost significance from the circuit designers' aspect since noise excess factor, a very important figure of merit for RF circuits implementation, is defined and characterized for the first time in graphene transistors.
In this article, the bias-dependence of intrinsic channel thermal noise of single-layer graphene field-effect transistors (GFETs) is thoroughly investigated by experimental observations and compact modeling. The findings indicate an increase of the specific noise as drain current increases whereas a saturation trend is observed at very high carrier density regime. Besides, short-channel effects like velocity saturation also result in an increment of noise at higher electric fields. The main goal of this work is to propose a physics-based compact model that accounts for and accurately predicts the above experimental observations in short-channel GFETs. In contrast to long-channel MOSFET based models adopted previously to describe thermal noise in graphene devices without considering the degenerate nature of graphene, in this work a model for short-channel GFETs embracing the 2D materials underlying physics and including a bias dependency is presented. The implemented model is validated with de-embedded high frequency data from two short-channel devices at Quasi-Static region of operation. The model precisely describes the experimental data for a wide range of low to high drain current values without the need of any fitting parameter. Moreover, the consideration of the degenerate nature of graphene reveals a significant decrease of noise in comparison with the non degenerate case and the model accurately captures this behavior. This work can also be of outmost significance from circuit designers aspect, since noise excess factor, a very important figure of merit for RF circuits implementation, is defined and characterized for the first time in graphene transistors.
Diodes made of heterostructures of the 2D material graphene and conventional 3D materials are reviewed in this manuscript. Several applications in high frequency electronics and optoelectronics are highlighted. In particular, advantages of metal–insulator–graphene (MIG) diodes over conventional metal–insulator–metal diodes are discussed with respect to relevant figures‐of‐merit. The MIG concept is extended to 1D diodes. Several experimentally implemented radio frequency circuit applications with MIG diodes as active elements are presented. Furthermore, graphene‐silicon Schottky diodes as well as MIG diodes are reviewed in terms of their potential for photodetection. Here, graphene‐based diodes have the potential to outperform conventional photodetectors in several key figures‐of‐merit, such as overall responsivity or dark current levels. Obviously, advantages in some areas may come at the cost of disadvantages in others, so that 2D/3D diodes need to be tailored in application‐specific ways. Diodes made of heterostructures of the 2D material graphene and conventional 3D materials are reviewed in this article. In particular, metal–insulator–graphene diodes and graphene‐silicon Schottky diodes are discussed with relevant figures‐of‐merit. Several applications in high frequency electronics and optoelectronics are highlighted, such as power detectors, mixers, frequency doublers, receivers, and photodetectors.
This article presents the small-signal and noise characterization of different technologies based on chemical vapor deposition (CVD) and silicon-carbide (SiC) graphene field-effect transistors (GFETs). The noise model, built on noise figure measurements under
using the F
50
method, was verified by additional source-pull measurements, with special care for the GFET stability. The four noise parameters were then extracted by using the validated F
50
model up to 18 GHz, and the correlations between noise and small-signal parameters were shown for two different configurations: top-gated and back-gated GFETs.
In this report, we demonstrate a novel high-temperature Hall effect sensor that is based on quasi-free-standing monolayer graphene epitaxially grown on high-purity semiinsulating (SI) on-axis 4H-SiC(0001) substrate in a chemical vapor deposition process. To ensure statistical perspective, characteristics of 23 elements are determined as a function of temperature ranging from 300 to 770 K. Passivated with a 100-nm-thick atomic-layer-deposited aluminum oxide, the sensor offers current-mode sensitivity of 80 V/AT with thermal stability of -0.02%/K within the range between 300 and 573 K, and -0.06%/K between 573 and 770 K. The sensor's room-temperature output voltage is monitored in the magnetic field from -300 to +300 mT and its offset voltage at 0 T is assessed. Its high-temperature electrical properties are explained through a double-carrier transport involving spontaneous-polarization-induced holes in the graphene layer and thermally activated electrons emitted from a deep acceptor level related to silicon vacancy VSi^1-/2- occupying the k site of the 4H-SiC lattice. The sensor is compared with a previously reported one on vanadium-compensated SI on-axis 6H-SiC(0001). The new sensor's applicability to magnetic field detection at high temperatures is verified.
In this letter, we present dual-gate Bernal-stacked bilayer graphene FETs which are used for gate-pumped resistive mixers. The results show that conversion loss improves when the device on/off ratio increases. At 2 GHz, a record conversion loss of 12.7 dB has been obtained from 160 nm device among graphene resistive mixers. Furthermore, more than 10 dB change of conversion loss has been obtained by adjusting the electric displacement field by dual-gate voltage. Finally, high-temperature characteristics of this type of graphene mixer exhibit excellent thermal stability with only 2 dB degradation in conversion loss from 300 to 380 K. This result shows the Bernal-stacked bilayer graphene mixer is promising for low-loss and high-temperature radio frequency circuit applications.
The design approach of a W‐band single diode fundamental mixer is presented here. This mixer features planar structure easy for integrating and high intermediate frequency (IF). The mixer consists of a diplexer formed by a hammer‐head lowpass filter and a coupled line with open stubs, a broadband bandpass filter (BPF) using short stubs, a series diode, and the matching networks. This mixer covers IF signal up to 18 GHz by optimizing the frequency response of the diplexer, the radio frequency (RF) BPF, and the matching networks. Two open stubs are attached to both ends of the RF BPF, in order to add a transmission zero at local oscillator (LO) frequency. By this way, the required out‐of‐band rejection is fulfilled with lower order BPF, thus reducing the in‐band insertion loss. In addition, the coupled line with open stubs has low insertion loss at LO frequency, while having a transmission zero at RF frequency. All of the techniques above lead to a low loss high IF mixer. The measured conversion loss is 6.7–10 dB with 8–19 GHz IF and 82 GHz LO.
In this letter we present for the first time a mixer circuit based on Metal-Insulator-Graphene (MIG) diodes, fabricated with large scale monolayer graphene grown by chemical vapor deposition. A small-signal model extracted from the diode physical structure is used together with a large-signal model extracted from the DC characteristics of the MIG diode to build a down-conversion mixer. The measured conversion loss (CL) at a local oscillator power (PLO) of 5 dBm is lower than 15 dB, while RF-to-IF isolation is 36 dB with an input return loss (RL) and RF-to-LO isolation better than 10 dB over the frequency band from 1.7 – 6 GHz. Promising mixer results in combination with the CVD-based process promote the MIG diode-based mixer to be used in low-power, low-cost, microwave and millimetre-wave circuit applications.
We are developing millimeter wave (mm-wave) components and circuits based on hydrogen-intercalated graphene. The development covers epitaxial graphene growth, device fabrication, modelling, integrated circuit design and fabrication, and circuit characterizations. The focus of our work is to utilize the distinctive graphene properties and realize new components that can overcome some of the main challenges of existing mm-wave technologies in term of linearity.
We discuss the residual carrier density (n*) near the Dirac point (DP) in
graphene estimated by quantum capacitance (CQ) and conductivity measurements.
The CQ at the DP has a finite value and is independent of the temperature. A
similar behavior is also observed for the conductivity at the DP, because their
origin is residual carriers induced externally by charged impurities. The n*
extracted from CQ, however, is often smaller than that from the conductivity,
suggesting that the mobility in the puddle region is lower than that in the
linear region. The CQ measurement should be employed for estimating n*
quantitatively.
Graphene, a monoatomic layer of graphite hosts a two-dimensional electron gas system with large electron mobilities which makes it a prospective candidate for future carbon nanodevices. Grown epitaxially on silicon carbide (SiC) wafers, large area graphene samples appear feasible and integration in existing device technology can be envisioned. This article reviews the controlled growth of epitaxial graphene layers on SiC(0001) and the manipulation of their electronic structure. We show that epitaxial graphene on SiC grows on top of a carbon interface layer that – although it has a graphite-like atomic structure – does not display the linear π-bands typical for graphene due to a strong covalent bonding to the substrate. Only the second carbon layer on top of this interface acts like monolayer graphene. With a further carbon layer, a graphene bilayer system develops. During the growth of epitaxial graphene on SiC(0001) the number of graphene layers can be precisely controlled by monitoring the π-band structure. Experimental fingerprints for in-situ growth control could be established. However, due to the influence of the interface layer, epitaxial graphene on SiC(0001) is intrinsically n-doped and the layers have a long-range corrugation in their density of states. As a result, the Dirac point energy where the π-bands cross is shifted away from the Fermi energy, so that the ambipolar properties of graphene cannot be exploited. We demonstrate methods to compensate and eliminate this structural and electronic influence of the interface. We show that the band structure of epitaxial graphene on SiC(0001) can be precisely tailored by functionalizing the graphene surface with tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) molecules. Charge neutrality can be achieved for mono-and bilayer graphene. On epitaxial bilayer graphene, where a band gap opens due to the asymmetric electric field across the layers imposed by the interface, the magnitude of this band gap can be increased up to more than double of its initial value. The hole doping allows the Fermi level to shift into the energy band gap. The impact of the interface layer can be completely eliminated by decoupling the graphene from the SiC substrate by a hydrogen intercalation technique. We demonstrate that hydrogen can migrate under the interface layer and passivate the underlying SiC substrate. The interface layer alone transforms into a quasi-free standing monolayer. Epitaxial monolayer graphene turns into a decoupled bilayer. In combination with atmospheric pressure graphitization, the intercalation process allows to produce quasi-free standing epitaxial graphene on large SiC wafers and represents a highly promising route towards epitaxial graphene based nanoelectronics.
Low-noise amplifier is one of the most attractive applications of graphene transistors in the RF area. In this letter, a graphene amplifier MMIC is fabricated on the quasi-free-standing bilayer epitaxial graphene grown on SiC (0001) substrate. In order to realize both the high gain and low return loss, Au matching lines are designed as the input and output impedance match networks. The fabricated graphene amplifier MMIC shows a small-signal power gain of 3.4 dB at 14.3 GHz and a minimum noise figure of 6.2 dB. This letter is a significant step forward for graphene electronics in low-noise amplifier and demonstrates graphene's potential in RF applications for future high-speed electronics.
We demonstrate the demodulation of a multi-Gb/s ON-OFF keying (OOK) signal on a 96 GHz carrier by utilizing a 250-nm graphene field-effect transistor as a zero bias power detector. From the eye diagram, we can conclude that the devices can demodulate the OOK signals up to 4 Gb/s.
A monolithic double-balanced graphene mixer integrated circuit (IC) has been successfully designed and fabricated. The IC adopted the cross-coupled resistive mixer topology, integrating four 500-nm-gate-length graphene field-effect transistors (GFETs), four on-chip inductors and four on-chip capacitors. Passive-first-active-last fabrication flow was developed on 200-mm CMOS wafers. CMOS back-end-of-line processes were utilized to realize most fabrication steps followed by GFET-customized processes. Test results shows excellent output spectrum purity with suppressed radio frequency (RF) and local oscillation (LO) signals feedthroughs, and third-order input intercept (IIP3) reaches as high as 21 dBm. The results are compared with a fabricated single-GEFT mixer, which generates IIP3 of 16.5 dBm. Stand-alone 500-nm-gate-length GFETs feature cut-off frequency 22 GHz and maximum oscillation frequency 20.7 GHz RF performance. The double-balanced mixer IC operated with off-chip baluns realizing a print-circuit-board level electronic system. It demonstrates graphene's potential to compete with other semiconductor technologies in RF front-end applications.
Owing to its ultra high carrier mobility, graphene transistor shows great application potential as high-frequency electronics. Intrinsic cutoff frequency (fT) of 427 GHz has been reported. But the maximum oscillation frequency (fmax) remains low, limiting its use in practical radio-frequency (RF) circuits. Here, we report an ultra clean self-aligned graphene transistors fabrication by pre-deposition of gold film on graphene as protection layer. This improved self-aligned fabrication keeps graphene away from any possible contamination, which makes our graphene transistors show good gate coupling and less parasitics, thus good dc and RF performances. The 100 nm gate-length graphene transistor exhibits a fmax of 105 GHz. Our study shows a pathway to fabrication of high-performance graphene transistors for future application in RF circuits.
Reported is the realisation of a graphene FET microwave amplifier operating at 1 GHz, exhibiting a small-signal power gain of 10 dB and a noise figure of 6.4 dB. The amplifier utilises a matching inductor on the gate yielding a return loss of 20 dB. The design is optimised for maximum gain and the optimum noise figure is extracted by noise modelling and predicted to be close to 1 dB for the intrinsic graphene FET at this frequency. The presented results complement existing graphene FET applications and are promising for future graphene microwave circuits.
A 30-GHz integrated subharmonic mixer based on a single graphene field-effect transistor (G-FET) has been designed, fabricated, and characterized. The mixer is realized in microstrip technology on a 250- μm-high-resistivity silicon substrate. In order to enhance the current on-off ratio, the G-FET utilizes a channel consisting of an array of bow-tie structured graphene, yielding a current on-off ratio of 7. A conversion loss (CL) of 19 ± 1 dB over the frequency range of 24-31 GHz is obtained with a local oscillator (LO) to RF isolation better than 20 dB at an LO power of 10 dBm. The overall minimum CL is 18 dB at 27 GHz. The mixer has a 3 GHz ± 1-dB IF bandwidth, which is achieved with a fixed LO signal of 15 GHz. The mixer linearity is characterized and the highest third-order intercept point is measured to be 12.8 dBm.
Graphene has attracted much interest as a future channel material in radio frequency electronics because of its superior electrical properties. Fabrication of a graphene integrated circuit without significantly degrading transistor performance has proven to be challenging, posing one of the major bottlenecks to compete with existing technologies. Here we present a fabrication method fully preserving graphene transistor quality, demonstrated with the implementation of a high-performance three-stage graphene integrated circuit. The circuit operates as a radio frequency receiver performing signal amplification, filtering and downconversion mixing. All circuit components are integrated into 0.6 mm(2) area and fabricated on 200 mm silicon wafers, showing the unprecedented graphene circuit complexity and silicon complementary metal-oxide-semiconductor process compatibility. The demonstrated circuit performance allow us to use graphene integrated circuit to perform practical wireless communication functions, receiving and restoring digital text transmitted on a 4.3-GHz carrier signal.
In this letter, we present the first graphene FET operation for zero-bias resistive FET mixers, utilizing modulation of graphene channel resistance rather than ambipolar mixer operations, up to 20 GHz. The graphene FETs with a gate length of 0.25 μm have an extrinsic cutoff frequency fT of 40 GHz and a maximum oscillation frequency fMAX of 37 GHz. At 2 GHz, the graphene FETs show a conversion loss of 14 dB with gate-pumped resistive FET mixing, with at least > 10-dB improvement over reported graphene mixers. The input third-order intercept points (IIP3s) of 27 dBm are demonstrated at a local oscillator (LO) power of 2.6 dBm. The excellent linearity demonstrated by graphene FETs at low LO power offers the potential for high-quality linear mixers.
A tantalum nitride (TaN) thin-film resistor (TFR) lift-off process was developed by reactively sputtering TaN from a pure Ta metal target. The films were deposited at a rate of approximately 3 angstrom/s using a N-2/Ar ratio of 0.22 at 5 mTorr and 100 W of dc power. TFRs were fabricated on silicon and semi-insulating InP with reproducible resistances of 80-85 Omega/square at thicknesses of 550-700 angstrom using a lift-off technique. Resistors fabricated on semi-insulating InP utilizing microstrip technology were characterized by S-parameter measurements up to 67 GHz. A model, based on a lossy transmission line, described the TFRs with good accuracy. (C) 2004 The Electrochemical Society.
We demonstrate the growth of high quality graphene layers by chemical vapor deposition (CVD) on insulating and conductive SiC substrates. This method provides key advantages over the well-developed epitaxial graphene growth by Si sublimation that has been known for decades. (1) CVD growth is much less sensitive to SiC surface defects resulting in high electron mobilities of ∼1800 cm(2)/(V s) and enables the controlled synthesis of a determined number of graphene layers with a defined doping level. The high quality of graphene is evidenced by a unique combination of angle-resolved photoemission spectroscopy, Raman spectroscopy, transport measurements, scanning tunneling microscopy and ellipsometry. Our measurements indicate that CVD grown graphene is under less compressive strain than its epitaxial counterpart and confirms the existence of an electronic energy band gap. These features are essential for future applications of graphene electronics based on wafer scale graphene growth.
A MMIC process in AlGaN/GaN technology for advanced transceiver design has been developed. The process is based on microstrip technology with a complete model library of passive elements and AlGaN/GaN HEMTs. The transistor technology in this process is suitable for both power and low noise design, demonstrated with a power density of 5 W/mm, and an NFmin of 1.4 dB at X-band. Process stability of subcircuits, complementary to power amplifiers and LNAs, in a transceiver system have been investigated. The results indicate that an all AlGaN/GaN MMIC transceiver is realizable using this technology.
Closed-form expressions are derived for the transfer
characteristic of a low-power monolithic RF peak detector. These are
compared with computer simulation and experimental measurements
A subharmonic graphene FET mixer
- O Habibpour
- S Cherednichenko
- J Vukusic
- J Stake