Intrinsic Current Gain Cutoff Frequency Research Articles

High-Frequency Graphene Base Hot-Electron Transistor.

The integration of graphene and other two-dimensional (2D) materials with existing silicon semiconductor technology is highly desirable. This is due to the diverse advantages and potential applications brought about by the consequent miniaturization of the resulting electronic devices. Nevertheless, such devices that can operate at very high frequencies for high-speed applications are eminently preferred. In this work, we demonstrate a vertical graphene base hot-electron transistor that performs in the radio frequency regime. Our device exhibits a relatively high current density (∼200 A/cm2), high common base current gain (α* ∼ 99.2%), and moderate common emitter current gain (β* ∼ 2.7) at room temperature with an intrinsic current gain cutoff frequency of around 65 GHz. Furthermore, cutoff frequency can be tuned from 54 to 65 GHz by varying the collector-base bias. We anticipate that this proposed transistor design, built by the integrated 2D material and silicon semiconductor technology, can be a potential candidate to realize extra fast radio frequency tunneling hot-carrier electronics.

Large-Velocity Saturation in Thin-Film Black Phosphorus Transistors.

A high saturation velocity semiconductor is appealing for applications in electronics and optoelectronics. Thin-film black phosphorus (BP), an emerging layered semiconductor, shows a high carrier mobility and strong mid-infrared photoresponse at room temperature. Here, we report the observation of high intrinsic saturation velocity in 7 to 11 nm thick BP for both electrons and holes as a function of charge-carrier density, temperature, and crystalline direction. We distinguish a drift velocity transition point due to the competition between the electron-impurity and electron-phonon scatterings. We further achieve a room-temperature saturation velocity of 1.2 (1.0) × 107 cm s-1 for hole (electron) carriers at a critical electric field of 14 (13) kV cm-1, indicating an intrinsic current-gain cutoff frequency ∼20 GHz·μm for radio frequency applications. Moreover, the current density is as high as 580 μA μm-1 at a low electric field of 10 kV cm-1. Our studies demonstrate that thin-film BP outperforms silicon in terms of saturation velocity and critical field, revealing its great potential in radio-frequency electronics, high-speed mid-infrared photodetectors, and optical modulators.

Analysis of MOCVD SiNx Passivated N-Polar GaN MIS-HEMTs on Sapphire With High $f_{max}\cdot V_{DS,Q}$

This letter presents an analysis of N-polar metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a 40 nm MOCVD SiNx passivation and a trench-gate design. A device with a 50 nm gate-length ( L g ) demonstrates a 313 GHz power gain cutoff frequency ( f max ) at a quiescent drain bias ( V $_{{DS,Q}}$ ) of 26 V. The high $f_{max}\cdot V_{DS,Q}$ of 8.1 THz $\cdot$ V exhibits great potential of the device in high-frequency power applications. Investigation on small-signal parameters shows that f max improves with V $_{{DS,Q}}$ due to a reduction of gate-drain capacitance ( c gd ) and an increase of output resistance ( rds ). When comparing with the previously reported planar HEMT design, the shorter L g enabled by the trench-gate design enhances the intrinsic current gain cutoff frequency ( f $_{{T,int}}$ ) leading to a higher peak f max at a higher V $_{{DS,Q}}$ .

Enhancement-Mode AlGaN/GaN Nanowire Channel High Electron Mobility Transistor With Fluorine Plasma Treatment by ICP

This letter reports on a novel enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) that combines nanowire channel and fluorine plasma treatment using inductively coupled plasma (ICP). Compared with the conventional HEMTs, the threshold voltage of E-mode HEMT shifts from −2.8 to +0.7 V, and the Schottky reverse leakage current is reduced by one order of magnitude. The device exhibits a superior performance with a drain current of 460 mA/mm at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{{{\text {GS}}}}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{{{\text {TH}}}} = 2$ </tex-math></inline-formula> V. High <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{{ \mathrm{\scriptscriptstyle ON}}}/\text{I}_{{ \mathrm{OFF}}}$ </tex-math></inline-formula> ratio of approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{\mathbf {9}}}$ </tex-math></inline-formula> and high breakdown voltage of 138 V with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{L}_{{{\text {DS}}}}=4~\mu \text{m}$ </tex-math></inline-formula> are obtained, i.e., the breakdown voltage of E-mode HEMT is improved by 25% than that in conventional HEMTs. The drain induced barrier lowering (DIBL) is as low as 4 mV/V, and the subthreshold swing (SS) of 70 mV/decade is achieved. The device exhibits an intrinsic current gain cutoff frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{{\text T}}$ </tex-math></inline-formula> of 22 GHz and a maximum oscillation frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{{\text {max}}}$ </tex-math></inline-formula> of 60 GHz.

Investigation of enhancement-mode AlGaN/GaN nanowire channel high-electron-mobility transistor with oxygen-containing plasma treatment

A novel enhancement-mode (E-mode) AlGaN/GaN high-electron-mobility transistor (HEMT) has been fabricated, by combining nanowire channel (NC) structure fabrication and N2O (or O2) plasma treatment. A comparison of two NC-HEMTs with different plasma treatments has been made. The NC-HEMT with N2O plasma treatment shows an output current of 610 mA/mm and a peak transconductance of 450 mS/mm. The DIBL of the NC-HEMT with N2O plasma treatment is as low as 2 mV/V, and an SS of 70 mV/decade is achieved. The device exhibits an intrinsic current gain cutoff frequency fT of 19 GHz and a maximum oscillation frequency fmax of 58 GHz.

First Power Performance Demonstration of Flexible AlGaN/GaN High Electron Mobility Transistor

This letter reports on the first demonstration of microwave power performance at 10 GHz on flexible AlGaN/GaN high-electron-mobility transistor (HEMT). A maximum dc current density of 620 mA/mm at $\text{V}_{\mathrm {GS}} = 0$ V and a peak extrinsic transconductance of 293 mS/mm are obtained for a $2\times 50 \times 0.1~\mu \text{m}^{2}$ flexible device. At $\text{V}_{\mathrm {DS}} = 5$ V, a continuous-wave saturation output power density of 0.42 W/mm is achieved at 10 GHz, and associated with a maximum power-added efficiency of 29.8% and a linear power gain of 15.8 dB. The device exhibits an intrinsic current gain cutoff frequency $F_{T}$ of 38 GHz and a maximum oscillation frequency $\text{F}_{\mathrm {MAX}}$ of 75 GHz. This result demonstrates the capability of flexible GaN-based HEMT for the development of applications requiring mechanical flexibility, high frequency operation, as well as high power performance.

Quasi-free-standing bilayer epitaxial graphene field-effect transistors on 4H-SiC (0001) substrates

Quasi-free-standing epitaxial graphene grown on wide band gap semiconductor SiC demonstrates high carrier mobility and good material uniformity, which make it promising for graphene-based electronic devices. In this work, quasi-free-standing bilayer epitaxial graphene is prepared and its transistors with gate lengths of 100 nm and 200 nm are fabricated and characterized. The 100 nm gate length graphene transistor shows improved DC and RF performances including a maximum current density Ids of 4.2 A/mm, and a peak transconductance gm of 2880 mS/mm. Intrinsic current-gain cutoff frequency fT of 407 GHz is obtained. The exciting DC and RF performances obtained in the quasi-free-standing bilayer epitaxial graphene transistor show the great application potential of this material system.

Graphene FETs With Aluminum Bottom-Gate Electrodes and Its Natural Oxide as Dielectrics

In this paper, we present a fabrication process of graphene field effect transistors (GFETs) using natural oxidation of aluminum as dielectrics, which provide an alternative fabrication choice for future flexible electronics with the large scale and arbitrary substrates. The high-quality monolayer graphene is preserved by our process, and the mobility up to 3250 cm2/Vs is measured after whole device fabrication. GFETs with double bottom-gate structure varying from 300 to 100 nm in gate length have been characterized by both static and dynamic measurements. The total gate capacitances of our device structure are evaluated based on the measurement results of scattering parameters. We report an intrinsic current gain cutoff frequency $(f_{t{\hbox{-}}\text {int}})$ of 11 GHz and a maximum oscillation frequency $(f_{\max })$ of 8 GHz in devices with 100 nm gate length. Moreover, both the values of $f_{t{\hbox{-}}\text {int}}$ and $f_{\max }$ for different gate lengths are also discussed. Our results indicate that the full process exhibits great potential, especially for graphene-based flexible electronics.

Power Performance at 40 GHz of AlGaN/GaN High-Electron Mobility Transistors Grown by Molecular Beam Epitaxy on Si(111) Substrate

This letter reports on the demonstration of microwave power performance at 40 GHz on AlGaN/GaN high-electron mobility transistor grown on silicon (111) substrate by molecular beam epitaxy. A maximum dc current density of 1.1 $\text{A}\cdot $ mm $^{-1}$ and a peak extrinsic transconductance of 374 mS $\cdot $ mm $^{-1}$ are obtained for 75-nm gate length device. At $V_{\rm DS} = 25$ V, continuous-wave output power density of 2.7 $\text{W}\cdot $ mm $^{-1}$ is achieved at 40 GHz associated with 12.5% power-added efficiency and a linear power gain ( $G_{p})$ of 6.5 dB. The device exhibits an intrinsic current gain cutoff frequency $F_{T}$ of 116 GHz and a maximum oscillation frequency $F_{\rm MAX}$ of 150 GHz. This performance demonstrates the capability of low cost microwave power devices up to Ka-band.

T-Gate Aligned Nanotube Radio Frequency Transistors and Circuits with Superior Performance

In this paper, we applied self-aligned T-gate design to aligned carbon nanotube array transistors and achieved an extrinsic current-gain cutoff frequency (ft) of 25 GHz, which is the best on-chip performance for nanotube radio frequency (RF) transistors reported to date. Meanwhile, an intrinsic current-gain cutoff frequency up to 102 GHz is obtained, comparable to the best value reported for nanotube RF transistors. Armed with the excellent extrinsic RF performance, we performed both single-tone and two-tone measurements for aligned nanotube transistors at a frequency up to 8 GHz. Furthermore, we utilized T-gate aligned nanotube transistors to construct mixing and frequency doubling analog circuits operated in gigahertz frequency regime. Our results confirm the great potential of nanotube-based circuit applications and indicate that nanotube transistors are promising building blocks in high-frequency electronics.

Fabrication and Characterization of an Epitaxial Graphene Nanoribbon-Based Field-Effect Transistor

The static and dynamic characteristics of top-gated graphene nanoribbon-based field-effect transistors were investigated. Multilayer graphene was synthesized by thermal decomposition of Si-face silicon carbide. The impact of the number of graphene layers on device performance was explored. It was found that, with the reduction of the layer number from ten to five, a significant improvement of direct-current characteristics and high-frequency performance can be observed. A high intrinsic current-gain cutoff frequency of 60 GHz and a maximum oscillation frequency of 28 GHz are reported.

Modeling of a 6H-SiC MESFET for High-power and High-gain Applications

A Monte Carlo simulation has been used to model steady state and transient electron transport in 6H-SiC field effect transistor. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible and the predicted I-V and transfer characteristics for the intrinsic devices show fair agreement with the available experimental data. Simulations of the effect of modulating the gate bias have also been carried out to test the device response and derived the frequency bandwidth. Value of 90±10 GHz has been derived for the intrinsic current gain cut-off frequency of the 6H-SiC MESFETs.

60 GHz current gain cut-off frequency graphene nanoribbon FET

We report investigations on the fabrication and characterization of graphene nanoribbon (GNR) field-effect transistors. Graphene layers are obtained from the thermal decomposition of a Si-face 4H-SiC substrate. To achieve high dynamic performance, a structure with an array of GNR connected in parallel was fabricated by e-beam lithography. The best intrinsic current gain cut-off frequency of 60 GHz and maximum oscillation frequency of 28 GHz were achieved. This study demonstrates the exciting potential of GNR in high-frequency electronics.

12 GHz $F_{\rm MAX}$GaN/AlN/AlGaN Nanowire MISFET

GaN/AlN/AlGaN/GaN nanowire metal-insulator-semiconductor field-effect transistors (MISFETs) have been fabricated for the first time with submicrometer gate lengths. Their microwave performances were investigated. An intrinsic current-gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 5 GHz as well as an intrinsic maximum available gain ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> ) cutoff frequency of 12 GHz have been obtained for the first time and associated with a gate length of 0.5 mum. These results show the great potentiality of GaN-based nanowire FETs for microwave applications.

COMPUTER SIMULATION OF ZnO FIELD-EFFECT TRANSISTOR FOR HIGH-POWER AND HIGH-TEMPERATURE APPLICATIONS USING THE MONTE CARLO METHOD

The steady-state and transient electron transport in ZnO field effect transistor have been studied using an ensemble Monte Carlo simulation which takes into account the hot-electron transport phenomena. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible, and the predicted I–V and transfer charateristics for the intrinsic devices show fair agreement with the available experimental data. Simulations of the effect of modulating the gate bias have also been carried out to test the device response and derived the frequency bandwidth. The value of 80 ± 5 GHz has been derived for the intrinsic current gain cut-off frequency of the ZnO MESFETs.

Intrinsic current gain cutoff frequency of 30GHz with carbon nanotube transistors

High frequency capabilities of carbon nanotube field-effect transistors (CNTFETs) are investigated. Structures with a large number of single-walled carbon nanotubes were fabricated using dielecrophoresis to increase the density of nanotubes in the device channel. The authors obtained an intrinsic current gain cutoff frequency of 30GHz establishing state-of-the-art high frequency (hf) potentialities of CNTFETs. The device also showed a maximum stable gain above 10dB at 20GHz. Finally, the parameters of an equivalent circuit model of multitube CNTFET at 20GHz are determined, which open the route to the modeling of nanotubes-based hf electronics.

DC and high frequency performance of 0.1 µ m n -type Si/Si 0.6 Ge 0.4 MODFET with f MAX =188 GHz at 300K and f MAX =230 GHz at 50K

Maximum oscillation frequency fMAX as high as 188 GHz at 300K and 227 GHz at 50K are reported for a 0.1×30 µm2n-type strained Si/Si0.6Ge0.4 modulation doped field-effect transistor (n-MODFET) together with high quality DC characteristics. These fMAX are the highest values reported so far for Si-based hetero-FETs. The frequency performances are discussed using analytical expressions of fMAX and fTi (intrinsic current gain cutoff frequency) together with the main equivalent circuit elements extracted.

1510 mS/mm 0.1 µm gate length pseudomorphicHEMTswith intrinsic current gain cutoff frequency of 220 GHz

The state of the art for a planar doped pseudomorphic Al0.2Ga0.8As/In0.2Ga0.8As HEMT with a gate length of 0.1 µm is presented. The devices exhibit an extrinsic and intrinsic transconductance of 1070 and 1510 mS/mm, respectively, a maximum current density of 550 mA/mm and a peak current gain cutoff frequency of 220 GHz. These results are the highest ever reported for HEMTs fabricated on GaAs substrates.

Cryogenic behavior of Ultrashort gate AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs HEMT's

High performance ?-doped double recess 0.1-0.4?m AlGaAs-GaAs S-HEMTs[1] and ?-doped single-recess 0.1-0.7?m AlGaAs/GaInAs/GaAs PM-HEMTs [2-3] are studied from 300K down to 60K. DC and 0.1-40GHz HF measurements followed by electric parameter extractions give extensive evolutions of HEMT electric parameters versus temperature T, gatelength 1 g . The results are interpreted in terms of the transition regime from diffusive to strong overshoot/near ballistic carrier transport under the gate. In the longer devices (1 g =0.4-0.7?m), the latter effects become important at low temperatures and bring frequency intrinsic performance improvement mainly in terms of an increase of maximum intrinsic transconductance g mo . The shorter devices (0.1-0.2?m) appear to be already well in the overshoot regime at 300K due to the high quality epitaxial layers, and their frequency performance improvement upon cooling comes mainly from a reduction of intrinsic capacitance C gsint . The relative increase of intrinsic unity current gain cut-off frequency f tint upon cooling rates at a similar value of 30-40% for all investigated gatelengths(0.1-0.7?m).

GaAs microwave MOSFET's

GaAs microwave metal-oxide-semiconductor field-effect transistors (MOSFET's) with plasma-grown native oxides as gate insulator have been fabricated using a low-temperature magnetically controlled plasma-oxidation technique. A small-signal enhancement device with the gate length of 2.0 µm has demonstrated useful unilateral power gains in the 2-8-GHz frequency range. A maximum frequency of oscillation in the enhancement device is 13 GHz. This is the highest in all enhancement-mode GaAs devices reported up to this time. A medium-power depletion device with the gate length of 1.8 µm has the maximum frequency of oscillation of 22 GHz. This value is 10 percent larger than that of the best analogous metal-semiconductor field-effect transistor (MESFET). The intrinsic current-gain cutoff frequency for the depletion MOSFET is 4.5 GHz which is 22 percent higher than that of the MESFET. The superiority of the depletion MOSFET in the small-signal microwave performance over the MESFET results from the smaller gate parasitic capacitance in the MOSFET as compared to the MESFET. The depletion MOSFET has produced 0.4-W output power at 6.5 GHz as a Class A amplifier. Quite a large frequency dispersion of transconductance is observed in the enhancement MOSFET at a frequency range between 10 and 100 kHz and attributed to interface states. The effect of the interface states does not severely restrict the microwave-frequency capabilities of the enhancement MOSFET as well as the depletion MOSFET since the interface states are unable to follow the input-signal variations at high frequencies.