Radio Frequency Field-effect Transistors Research Articles

Improving Carbon Nanotube-Based Radiofrequency Field-Effect Transistors by the Device Architecture and Doping Process.

The semiconducting carbon nanotube (CNT) has been considered a promising candidate for future radiofrequency (RF) electronics due to its excellent electrical properties of high mobility and small capacitance. After decades of development, great progress has been achieved on CNT-based RF field-effect transistors (FETs). However, almost all elevations are owing to advancement of the CNT materials and fabrication process, while the study of device architecture is seldom considered and reported. In this work, we innovatively combined device architecture and related doping processes to further optimize CNT-based RF FETs by guiding process or materials with collaborative optimization for the first time and explore their effect on device performance carefully and statistically. Based on more mature random-oriented CNT materials, we fabricated CNT-based RF FETs having three different gate positions of device architecture variation accompanied by suitable doping schemes. The optimized FETs obtained 2-3 times of current density (transconductance) and 1.3 times the cutoff frequency and maximum oscillation frequency compared with unoptimized devices at the same channel length. After transistor-level verification of effect, we further built a CNT RF amplifier and demonstrated almost 10 dB of transducer gain improvement operating at 8 GHz for X-band application. The achieved results from this work would help further improve CNT RF performance beyond the materials and process point of view.

Carbon Nanotube Based Radio Frequency Transistors for K-Band Amplifiers.

Owing to the combination of high carrier mobility and saturation velocity, low intrinsic capacitance, and excellent stability, the carbon nanotube (CNT) has been considered as a perfect semiconductor to construct radio frequency (RF) field-effect transistors (FETs) and circuits with an ultrahigh frequency band. However, the reported CNT RF FETs usually exhibited poor real performance indicated by the as-measured maximum oscillation frequency (fmax), and then the amplifiers, which are the most important and fundamental RF circuits, suffered from a low power gain and a low frequency band. In this work, we build RF transistors on solution-derived randomly orientated CNT films with improved quality and uniformity. The randomly orientated CNT film FETs exhibit the record as-measured maximum fmax of 90 GHz, demonstrating the potential for over 28 GHz (at least one-third of 90 GHz) 5G mmWave (frequency range 2) applications. Benefiting from the large-scale uniformity of CNT films, FETs are designed and fabricated with a large channel width to present low internal resistance for the standard 50 Ω impedance matching guide line, which is critical to construct an RF amplifier. Furthermore, we first demonstrate amplifiers with a maximum power gain up to 11 dB and output third-order intercept point (OIP3) of 15 dBm, both at the K-band, which represents the record of a CNT amplifier and is even comparable with a commercial amplifier based on III-V RF transistors.

Pulsed techniques for the characterization of low-frequency dispersive effects in RF power FETs using a flexible measurement set-up

This work describes an on-wafer measurement architecture tailored to the broadband pulsed characterization of radio-frequency (RF) power field-effect transistors (FETs). Based on a 50-Ω environment and corresponding wave-variable domain representation, the set-up exploits the impedance matching and the broadband feature of its components, together with a full-bandwidth calibration, for the synthesis and measurement of pulsed waveforms with short pulse rise/fall times in the order of a few ns, while guaranteeing a reduced risk of oscillations.These measurement capabilities are particularly suited for experimentally assessing the FET performance reduction due to low-frequency dispersive effects caused by thermal and charge trapping phenomena. The flexibility of the set-up is showcased by discussing experimental examples of different measurement techniques in the kHz-to-GHz range, including single- and double-pulsed I–V characteristics and S-parameters, as well as pulsed continuous-wave (CW) measurements, performed on state-of-the-art gallium nitride (GaN) RF FETs for microwave and millimeter-wave applications.

Radiofrequency Switches Based on Emerging Resistive Memory Technologies - A Survey

High-performance radio frequency (RF) switches play a critical role in allowing radio transceivers to provide access to shared resources such as antennas. They are important, especially in reconfigurable radios, where the connections within and between the different blocks (e.g., filters, amplifiers, and mixers) can be changed to customize and compose RF functions for distinct frequency bands. To realize this potential, new concepts for RF switch devices that can be integrated with standard transistor process, while providing better transmission performance, lower power consumption, smaller area, and lower actuation voltage than current RF switch technologies [e.g., field-effect transistors (FETs) and microelectromechanical systems (MEMSs)] are needed. Recently, RF switches based on emerging memory technologies, such as conductive-bridge RAM (CBRAM), resistive RAM (ReRAM), and phase-change memory (PCM), have been proposed. These nanoscale switches present major advantages, for example, high cutoff frequency, nonvolatility, fast and low-energy switching, small footprint, and compatibility with back-end-of-line (BEOL) of the standard CMOS process, thus placing them as possible contenders for high-performance RF switches. This article surveys high-performance RF switches based on resistive memories, comparing them with mature RF switching technologies like RF MEMS, p-i-n diodes, and FETs. We discuss the physical mechanisms, device structure, performance characteristics, and applications of these novel RF switches. Furthermore, we examine the prospects and future research directions of these technologies that could lead to their adoption at the industrial level.

Carbon Nanotube Film-Based Radio Frequency Transistors with Maximum Oscillation Frequency above 100 GHz.

Carbon nanotubes (CNTs) have been considered a preferred channel material for constructing high-performance radio frequency (RF) transistors with outstanding current gain cutoff frequency (fT) and power gain cutoff frequency (fmax) but the highest reported fmax is only 70 GHz. Here, we explore how good RF transistors based on solution-derived randomly oriented semiconducting CNT films, which are the most mature CNT materials for scalable fabrication of transistors and integrated circuits, can be achieved. Owing to the significantly reduced number of CNT/CNT junctions obtained by scaling the channel length down to below 100 nm, we realized RF field-effect transistors (FETs) with maximum transconductance Gm up to 0.38 mS/μm, which is the record among CNT-based RF FETs. After de-embedding the pad-induced capacitances and resistances, the CNT FETs with different gate lengths (Lg) exhibit fT as high as 103 GHz (intrinsically 281 GHz) or fmax up to 107 GHz (intrinsically 190 GHz), which are the records among CNT-based RF FETs. In particular, the CNT FETs with an Lg of 50 nm present pad de-embedding fT of 86 GHz and fmax of 85 GHz, and represent the best CNT RF transistor in terms of comprehensive performance to date. To demonstrate the actual high-speed and scalable fabrication of our CNT RF FETs, we fabricated CNT FET-based five-stage ring oscillators with oscillation frequencies above 5 GHz.

Gigahertz Field-Effect Transistors with CMOS-Compatible Transfer-Free Graphene.

High-quality graphene grown on metal-free substrates represents a vital milestone that provides an atomic clean interface and a complementary metal-oxide-semiconductor-compatible manufacturing process for electronic applications. We report a scalable approach to fabricate radio frequency field-effect transistors with a graphene channel grown directly on the sapphire substrate using the technique of remote-catalyzed chemical vapor deposition (CVD). A mushroom-shaped AlO x top gate is used to allow the self-aligned drain/source contacts, yielding remarkable increase of device transconductance and reduction of the associated parasitic resistance. The quality of thus-grown graphene is reflected in the high extrinsic cutoff frequency and maximum oscillation frequency of 10.1 and 5.6 GHz for the graphene channel of length 200 nm and width 80 μm, respectively, potentially comparable with those of transferred CVD graphene at the same channel length and holding promise for applications in high-speed wireless communications.

Embedded gate CVD MoS2 microwave FETs

Recent studies have increased the cut off frequencies achievable by exfoliated MoS2 by employing a combination of channel length scaling and geometry modification. However, for industrial scale applications, the mechanical cleavage process is not scalable but, thus far, the same device improvements have not been realized on chemical vapor deposited MoS2. Here we use a gate-first process flow with an embedded gate geometry to fabricate short channel chemical vapor deposited MoS2 radio frequency transistors with a notable fT of 20 GHz and fmax of 11.4 GHz, and the largest high-field saturation velocity, vsat = 1.88 × 106 cm/s, in MoS2 reported so far. The gate-first approach, facilitated by cm-scale chemical vapor deposited MoS2, offers enhancement mode operation, ION/IOFF ratio of 108, and a transconductance (gm) of 70 μS/μm. The intrinsic fT (fmax) obtained here is 3X (2X) greater than previously reported top-gated chemical vapor deposited MoS2 radio frequency field-effect transistors. With as-measured S-parameters, we demonstrate the design of a GHz MoS2-based radio frequency amplifier. This amplifier has gain greater then 15 dB at 1.2 GHz, input return loss > 10 dB, bandwidth > 200 MHz, and DC power consumption of ~10 mW.

Radio Frequency Transistors and Circuits Based on CVD MoS2.

We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations of fabricated MoS2 FETs yielded current densities exceeding 200 μA/μm and maximum transconductance of 38 μS/μm. A contact resistance corrected low-field mobility of 55 cm(2)/(V s) was achieved. Radio frequency FETs were fabricated in the ground-signal-ground (GSG) layout, and standard de-embedding techniques were applied. Operating at the peak transconductance, we obtain short-circuit current-gain intrinsic cutoff frequency, fT, of 6.7 GHz and maximum intrinsic oscillation frequency, fmax, of 5.3 GHz for a device with a gate length of 250 nm. The MoS2 device afforded an extrinsic voltage gain Av of 6 dB at 100 MHz with voltage amplification until 3 GHz. With the as-measured frequency performance of CVD MoS2, we provide the first demonstration of a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

Radio-frequency transistors from millimeter-scale graphene domains

Graphene is a new promising candidate for application in radio-frequency (RF) electronics due to its excellent electronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors (RF-FETs). Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum oscillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits.

Step-by-step implementation of an amplifier circuit with a graphene field-effect transistor on a printed-circuit board

Power amplifier circuits are implemented with graphene field-effect transistors (FETs), capacitors and inductors, and their gain is improved step-by-step by adjusting the passive components. The transistors are fabricated on a 150-mm wafer using conventional complementary-metal-oxide semiconductor processing along with graphene transferring processes. The completed circuit is implemented on a printed circuit board, which allows for adjustment of the external capacitance and inductance to study the performance of graphene RF FETs. A maximum signal gain of 1.3 dB is achieved at 380 MHz. The device parameters of the transistors are then extracted and the gain is analyzed, and the results show that lowering the source–drain conductance and gate resistance is the key in realizing high performance circuits.

Chemical Vapour Deposition Graphene Radio-Frequency Field-Effect Transistors

We report the dc and rf performance of graphene rf field-effect transistors, where the graphene films are grown on copper by using the chemical vapour deposition (CVD) method and transferred to SiO2/Si substrates. Composite materials, benzocyclobutene and atomic layer deposition Al2O3 are used as the gate dielectrics. The observation of n- and p-type transitions verifies the ambipolar characteristics in the graphene layers. While the intrinsic carrier mobility of CVD graphene is extracted to be 1200 cm2/V·s, the parasitic series resistances are demonstrated to have a serious impact on device performance. With a gate length of 1 μm and an extrinsic transconductance of 72 mS/mm, a cutoff frequency of 6.6 GHz and a maximum oscillation frequency of 8.8 GHz are measured for the transistors, illustrating the potential of the CVD graphene for rf applications.

Wafer-scale epitaxial graphene growth on the Si-face of hexagonal SiC (0001) for high frequency transistors

Up to two layers of epitaxial graphene have been grown on the Si-face of 2 in. SiC wafers exhibiting room-temperature Hall mobilities up to 2750 cm2 V−1 s−1, measured from ungated, large, 160×200 μm2 Hall bars, and up to 4000 cm2 V−1 s−1, from top-gated, small, 1×1.5 μm2 Hall bars. The growth process involved a combination of a cleaning step of the SiC in a Si-containing gas, followed by an annealing step in argon for epitaxial graphene formation. The structure and morphology of this graphene has been characterized using atomic force microscopy, high resolution transmission electron microscopy, and Raman spectroscopy. Furthermore, top-gated radio frequency field-effect transistors (rf-FETs) with a peak cutoff frequency fT of 100 GHz for a gate length of 240 nm were fabricated using epitaxial graphene grown on the Si-face of SiC that exhibited Hall mobilities up to 1450 cm2 V−1 s−1 from ungated Hall bars and 1575 cm2 V−1 s−1 from top-gated ones. This is by far the highest cutoff frequency measured from any kind of graphene.

Epitaxial-Graphene RF Field-Effect Transistors on Si-Face 6H-SiC Substrates

We report dc and the first-ever measured small-signal radio-frequency (RF) performance of epitaxial-graphene RF field-effect transistors (FETs), where the epitaxial-graphene layer is formed by graphitization of 2-in-diameter Si-face semi-insulating 6H-SiC (0001) substrates. The gate is processed with a metal gate on top of a high-k Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gate dielectric deposited via an atomic-layer-deposition method. With a gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of 2 mum and an extrinsic transconductance of 148 mS/mm, the extrinsic current-gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) is measured as 4.4 GHz, yielding an extrinsic f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ldr L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> of 8.8 GHz middot mum. This is comparable to that of Si NMOS. With graphene FETs fabricated in a layout similar to those of Si n-MOSFETs, on-state current density increases dramatically to as high as 1.18 A/mm at Vds = 1 V and 3 A/mm at Vds = 5 V. The current drive level is the highest ever observed in any semiconductor FETs.

Development of Scalable Graphene RF Field-Effect Transistors

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Improving FET Switch Linearity

RF field-effect transistors, especially pseudomorphic high-electron mobility transistors (pHEMTs), are commonly used as switches in communication applications. These small high-speed devices are vital for routing and conveying signals in such uses. The important characteristics of pHEMTs, besides their small size, are their high-frequency capability, insertion loss, isolation, power handling, switching speed, and linearity. A topology using a pair of simple but modified series and shunt elements was designed to improve upon the linearity of an RF switch. Each element of the switch was composed of a single, unbiased, but relatively long pHEMT, which was designed for the test. By shifting the position of the gate asymmetrically toward the source terminal in these transistors, it was found that the linearity was improved without cost to other performance parameters