Current Gain Cutoff Frequency Research Articles

High-performance InAlN/GaN HEMTs on silicon substrate with high fT × Lg

We report an 80 nm gate-length In0.17Al0.83N/GaN high-electron mobility transistor (HEMT) on silicon substrate with a record low gate leakage current of 7.12 × 10−7 A mm−1, a record high on/off current ratio of 1.58 × 106, and a steep subthreshold swing of 65 mV dec−1, which are excellent features among the reported InAlN/GaN HEMTs on Si. Due to the excellent DC performance, a current gain cutoff frequency fT of 200 GHz is achieved, resulting in fT × Lg = 16 GHz μm for GaN HEMTs on Si which to the best of our knowledge is a new record.

High performance dual-gate SiGe MOSFET for radio-frequency applications

In this paper, we propose a new Si0.6Ge0.4 n-channel dual-gate metal-oxide-semiconductor field-effect transistor (DGMOS) structure for high frequency small signal applications. The gate length of the device is 60 nm and gate-oxide (SiO2) thickness is 2 nm with n+ poly-silicon as gate material. Both the gates of DGMOS are placed in the oxide-filled trenches leading to formation of dual conduction channels which enhances the drive current, gain and frequency response. Two-dimensional simulation tool (ATLAS) is used to analyse and compare the performance of the proposed structure with conventional device. The DGMOS provides 5.35 times higher current drivability, 306% improvement in peak transconductance, 114% enhancement in unity current gain cut-off frequency and 3.75 times higher oscillation frequency with good control of short channel effects in comparison to the conventional MOSFET.

Effect of Electron Irradiation Fluence on InP-Based High Electron Mobility Transistors.

In this paper, the effect of electron irradiation fluence on direct current (DC) and radio frequency (RF) of InP-based high electron mobility transistors (HEMTs) was investigated comprehensively. The devices were exposed to a 1 MeV electron beam with varied irradiation fluences from 1 × 1014 cm−2, 1 × 1015 cm−2, to 1 × 1016 cm−2. Both the channel current and transconductance dramatically decreased as the irradiation fluence rose up to 1 × 1016 cm−2, whereas the specific channel on-resistance (Ron) exhibited an apparent increasing trend. These changes could be responsible for the reduction of mobility in the channel by the irradiation-induced trap charges. However, the kink effect became weaker with the increase of the electron fluence. Additionally, the current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) demonstrated a slightly downward trend as the irradiation fluence rose up to 1 × 1016 cm−2. The degradation of frequency properties was mainly due to the increase of gate-drain capacitance (CGD) and the ratio of gate-drain capacitance and gate-source capacitance (CGD/CGS). Moreover, the increase of Ron may be another important factor for fmax reduction.

$\beta$ -Ga2O3 Delta-Doped Field-Effect Transistors With Current Gain Cutoff Frequency of 27 GHz

As an ultra-wide bandgap semiconductor, $\beta $ -Ga2O3 has attracted great attention for high-power, high-voltage, and optoelectronic applications. However, until now, high-frequency performance of gallium oxide devices has been limited to relatively low current gain cutoff frequencies below 5 GHz. Here, we show that highly localized delta-doping designs can enable high-sheet-charge density to enable devices with short gate lengths that allow high-frequency operation. Field-effect transistors with a gate length of 120 nm on such delta-doped $\beta $ -Ga2O3 are reported here with extrinsic unity current gain frequency of 27 GHz. The device has a peak drain current of 260 mA/mm, transconductance (gm) of 44 mS/mm, and three-terminal off-state breakdown voltage of 150 V. These results demonstrate that the potential of $\beta $ -Ga2O3 for future RF and millimeter-wave device applications.

Improved RF and DC performance in AlGaN/GaN HEMT by P-type doping in GaN buffer for millimetre-wave applications

In this paper, the RF and DC performance of AlGaN/GaN HEMT having p-type doping in GaN buffer layer was analysed. Novelty of this work lies in the inclusion of P-type doping in GaN buffer of proposed GaN-HEMT. The result shows the significance of p-type doping at GaN buffer layer for enhancing the RF characteristics of the AlGaN/GaN HEMT. The use of p-type doping in GaN buffer layer increase the conduction band minima in the channel and thereby improving the transconductance of the device. The proposed HEMT achieves a peak transconductance of 330 mS/mm at VGS = −2 V and a maximum drain current of 850 mA/mm. The unity-gain cut-off frequency, small signal capacitance and conductance were also extracted to demonstrate its influence on RF performance. The proposed GaN HEMT has exhibited a unity current gain cut-off frequency of 45 GHz, which is 40% higher than that of conventional HEMT. The improved RF and DC performance of proposed HEMT makes it suitable for millimetre-wave applications.

28 nm FDSOI analog and RF Figures of Merit at N2 cryogenic temperatures

This work presents a detailed characterization of 28 nm FDSOI CMOS process at cryogenic temperatures. Electrostatic, Analog and RF Figures of Merit (FoM) are studied. At liquid nitrogen temperatures, 30% to 200% enhancement of drain current, Id, and maximum transconductance, gm_max, values are demonstrated. Current gain cutoff frequency, fT, increase by about 85 GHz is shown. Temperature behavior of analog and RF FoMs is discussed in terms of mobility and series resistance effect. This study suggests 28 nm FDSOI as a good contender for future read-out electronics operated at cryogenic temperatures (as e.g. around qubits or in space).

Evaluation of Low-Temperature Saturation Velocity in <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-(AlxGa1–x)2O3/Ga2O3 Modulation-Doped Field-Effect Transistors

We report on the high-field transport characteristics and saturation velocity in a modulation-doped β-(Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> ) <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> /Ga <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> heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s at room temperature to 1520 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s at 50 K. The high electron mobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current-voltage measurements and smallsignal radio frequency (RF) measurements. The measured velocity-field profile suggested a saturation velocity above 1.1 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The 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> ) and maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) showed significant increases from 4.0/11.8GHz at room temperature to 17.4/40.8GHz at 50 K for the device with gate length of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> = 0.61 μm. The analysis of the low temperature f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> based on device simulations indicated a peak velocity of 1.2 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in β-Ga <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> make it a promising candidate for high-power and high-frequency device applications.

Ultra-Wide Bandgap AlxGa1-xN Channel Transistors

High Al-composition AlxGa1-xN, an emerging class of materials, is gaining significant traction due to its high critical breakdown electric field exceeding that of GaN and high electron saturation velocity that is comparable to GaN. High Al-composition AlxGa1-xN holds promise for applications such as highly scaled next generation RF devices and power devices. However, significant strides remain to be made before AlxGa1-xN can take a share of the limelight. Encouraging progress has been made in recent years, including multiple reports of RF operation of AlxGa1-xN channel transistors with reported unity current gain cutoff frequency as high as 40 GHz, high current density devices with the maximum reported current density exceeding 600 mA/mm and reports of breakdown fields in lateral transistors that are almost 3× the reported breakdown field for GaN channel devices of similar dimensions. This paper focuses on the lateral devices demonstrated thus far and discusses breakthrough performance results achieved for AlxGa1-xN channel transistors together with the key challenges that are yet to be properly addressed. The paper starts with a discussion of contact formation to AlxGa1-xN films – the key difficulty of fabricating AlxGa1-xN transistors. This is followed by a discussion of the types of devices that are typically used. This is followed up with a discussion of the approach required to make high quality devices with AlxGa1-xN as a template together with some recent result highlights.

Investigation of the UTB-InAs-MOSFETs structure

An Ultra-Thin-Body (UTB) InP/InAs/InGaAs MOSFETs is investigated. Computer Aided Design(CAD) tools are used to extract the electrical properties of this structure.Our simulation work gives us the possibility to extract the output characteristics, transfer characteristics and RF performances. With the small-signal equivalent circuit models, intrinsic elements are calculated from the Y-parameters matrix using AC analysis. To further improve the accuracy of the simulation, the effect of doping in the channel and source-drain regions, the Indium content in different layers are discussed and optimized. The results are validated with device characteristics of the fabricated 150 nm InP/InAs/InGaAs MOSFET. A high drain current of 665 mA/mm and extrinsic peak transconductance of 440 mS/mm are obtained at Vds = 0.7 V. A current gain cutoff frequency fT of 41.69 GHz and a simultaneous maximum oscillation frequency fmax of 94 GHz are estimated at Vds = 0.7 V and Vgs = 0.2 V.

28-nm FDSOI nMOSFET RF Figures of Merits and Parasitic Elements Extraction at Cryogenic Temperature Down to 77 K

This paper presents detailed RF characterization of 28-nm FDSOI nMOSFETs at cryogenic temperatures down to 77 K. Two main RF figures of merit (FoM), i.e., current gain cutoff frequency ( $f_{T}$ ) and maximum oscillation frequency ( $f_{\max }$ ), as well as elements of small-signal equivalent circuit are extracted from the measured S-parameters. Increases of $f_{\textit T}$ and $f_{\max }$ by about 85 GHz and about 30 GHz, respectively, are demonstrated at 77 K. The observed behavior of RF FoMs versus temperature is discussed in terms of small-signal equivalent circuit elements, both intrinsic and extrinsic (parasitics). This paper suggests 28-nm FDSOI as a good candidate for future cryogenic applications.

Impact of the Source-to-Drain Spacing on the DC and RF Characteristics of InGaAs/InAlAs High-Electron Mobility Transistors

In this letter, we investigated the impact of the source-to-drain spacing ( ${L}_{\textsf {SD}}$ ) on the dc and high-frequency characteristics of indium-rich In0.8Ga0.2As/In0.52Al0.48As high-electron mobility transistors (HEMTs) on a 3-in InP substrate. ${L}_{g} = \textsf {87}$ nm HEMTs with different values of ${L}_{\textsf {SD}}$ were fabricated ranging from 1.55 to $0.8~\mu \text{m}$ , and their dc and RF responses were measured and analyzed in detail. In order to suppress the increase of the parasitic gate capacitance, we maintained the gate stem height as high as 200 nm in our device fabrication. Both the maximum transconductance (gm_max) and on-resistance ( ${R}_{\textsf {ON}}$ ) improved as ${L}_{\textsf {SD}}$ scaled down to $0.8~\mu \text{m}$ . At the same time, the high-frequency figures of the merit, such as current-gain cutoff frequency ( ${f}_{T}$ ) and maximum oscillation frequency ( ${f}_{\textsf {max}}$ ), increased with the reduction of ${L}_{\textsf {SD}}$ . These improvements are attributed to the reduction of series resistances. In particular, the ${L}_{g} =87$ nm device with an ${L}_{\textsf {SD}} = \textsf {0.8} \mu \text{m}$ exhibited an excellent combination of dc and RF characteristics, such as gm_max = 2.7 mS/ $\mu \text{m}$ , ${R}_{\textsf {ON}} = \textsf {318}\,\,\Omega \cdot \mu \text{m}$ , ${f}_{T} = \textsf {519}$ GHz, and ${f}_{\textsf {max}} = \textsf {645}$ GHz, respectively. The results obtained in this letter indicate that the reduction of ${L}_{\textsf {SD}}$ down to $0.8~\mu \text{m}$ continues to improve both the dc and RF characteristics of the InGaAs/InAlAs HEMTs, and a possible increase in parasitic capacitance components, associated with a T-shaped, is still negligible in our device architecture.

Stability of radio-frequency graphene field-effect transistors in ambient

While many studies on radio-frequency (RF) graphene field-effect transistor (GFET) aimed to study its high performances, explorations of the long-term stability of RF GFETs in atmosphere may be required as well. In this paper, we investigated the stability of the RF GFETs stored in ambient for four years. Both the RF and direct current characteristics are measured and compared with the initial properties. Changes of current-gain cut-off frequency and field-effect mobility, reductions of maximum oscillation frequency, peak transconductance and gate capacitance are observed butthe extracted contact resistance remains unchanged. The permeation of water vapor and oxygen into the thin Al2O3 dielectric, the diffusion of Pd atoms from contact onto the graphene channel and the rougher Al2O3 surface may challenge the stability of RF GFETs. This work may pave the way for the fabrication of more stable RF GFETs, which further serve steady graphene-based RF circuits.

Effect of gate structures on the DC and RF performance of AlGaN/GaN HEMTs

This work analyzes the effect of various gate structures on the DC and radio frequency (RF) performance of AlGaN/GaN high-electron mobility transistors (HEMTs). AlGaN/GaN HEMT devices with a 3 μm drain-to-source spacing, 125 μm gate width and 0.3 μm gate length in various gate structures were fabricated to achieve the desired frequency response with a robust, high yield, and repeatable process. The maximum drain current (IDS,max), maximum DC transconductance (gm), pinch-off voltage (Vth), current-gain cutoff frequency (fT), maximum oscillation frequency (fmax), and RF characteristics of the devices in terms of the small-signal gain and RF output power (Pout) at 8 GHz were investigated. The results showed that the output power is increased by 1 dB when the gate structure is changed from field plate to gamma gate. The Vth, gm, fT and fmax values are maximized when the thickness of the passivation layer between the gate foot and the gate head is minimized. It is shown that the IDS,max is decreased and Pout is increased when the gate recess etching process is performed.

&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${L}_{{g}} = {87}$ &lt;/tex-math&gt; &lt;/inline-formula&gt;nm InAlAs/InGaAs High-Electron- Mobility Transistors With a &lt;italic&gt;g&lt;/italic&gt; m_max of 3 S/mm and &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$f_{{T}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; of 559 GHz

We present our latest results on L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 87 nm InAlAs/InGaAs high-electron-mobility transistors with an excellent combination of dc and high-frequency characteristics. We obtained a maximum transconductance of 3 S/mm at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = 0.9 V, an ON-resistance of 273 Ω-μm, a current gain cutoff frequency of 559 GHz, and a maximum oscillation frequency of 671 GHz. According to small-signal modeling, these outstanding device metrics are a consequence of the indium-rich InGaAs channel with very high Hall mobility, compact device design with L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD</sub> = 1 μm, and an optimized gate process that yields well-tempered behavior.

A High Frequency Hydrogen-Terminated Diamond MISFET With ${f}_{{\text{T}}}/{f}_{\max}$ of 70/80 GHz

A high frequency hydrogen-terminated diamond metal-insulator-semiconductor field-effect transistor (MISFET) with extremely small source-drain distance of about 350 nm was realized by self-aligned process on (001)-oriented single crystal diamond substrate. To suppress the gate leakage current, a low temperature Al2O3 film was deposited as the gate insulator by inductance coupled plasma enhanced atomic layer deposition. A low ohmic contact resistance of $1.84~\Omega \cdot $ mm was measured by using transmission line method. The fabricated 100 nm gate length MISFET shows a high current density of 585 mA/mm and a high transconductance of 206 mS/mm. By minimizing the parasitic parameters of the device, a high current gain cut-off frequency ${f} _{\textsf {T}}$ of 70 GHz and maximum frequency of oscillation ${f} _{\textsf {max}}$ of 80 GHz have been realized.

Comparison of reliability of 100 nm AlGaN/GaN HEMTs with T-gate and SAG-gate technology

The effect of gate technology and semiconductor passivation on the switching speed and device reliability has been investigated. By reducing the parasitic capacitances and reducing the passivation induced surface charge density a median lifetime of around 106 h at a channel temperature of 125 °C and a current-gain cut-off frequency of 74 GHz for a T-gate technology has been achieved. By electroluminescence and TEM cross-sectioning of a stressed device a local inhomogeneous pit formation process was found as the major degradation mechanism for the decrease of the saturation current.

Prediction of RF performances of advanced MOS transistors from DC and low frequency measurements

AbstractThis work presents a new method to easily and rapidly extract RF figures of merit of MOSFET transistors. Using DC and low frequency measurements, the extrinsic resistances (Rg, Rs, Rd), the intrinsic conductances (gm, gd), and the input capacitance Cgg have been extracted. The evaluation of these parameters has enabled to compute 2 RF figures of merit (FoM), namely, the current gain cutoff frequency fT and the maximum oscillation frequency fmax. It has been shown that both the proposed method and the conventional RF extraction technique give quite close values.

Transferred-Substrate InP/GaAsSb Heterojunction Bipolar Transistor Technology With &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${f}_{\text{max}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; ~ 0.53 THz

We report on the realization mymargin of transferred-substrate InP/GaAsSb double heterostructure bipolar transistors in a terahertz monolithic integrated circuit process. Transistors with 0.4- $\mu \text{m}$ -wide single emitters reached unilateral gain cutoff frequencies of around 530 GHz with simultaneous current gain cutoff frequencies above 350 GHz. Extrinsic collector capacitance is effectively reduced in the transfer-substrate process. In combination with the high collector breakdown voltage in the InP/GaAsSb heterobipolar transistor structure of 5 V, this process is amenable to analog power applications at millimeter (mm-wave) and sub-mm-wave frequencies. We demonstrate reliable extraction procedures for unilateral gain and current gain cutoff frequencies.

Stepper-based Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As PHEMTs on a 3-inch InP substrate with record product of fT and Lg

We have fabricated and characterized Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As pseudomorphic high-electron-mobility-transistors (PHEMTs) on a 3-inch InP substrate. Stepper-based photo-lithography was used in all the process steps for device fabrication, aiming to miniaturize key device geometries, such as gate-to-source and gate-to-drain spacing. The fabricated device with Lg = 0.5 μm exhibits an excellent maximum transconductance (gm_max) of 1.9 S/mm at VDS = 1.5 V and an ON-resistance (RON) of below 0.4 Ω-mm. A high value of gm in our device leads to a fantastic combination of current-gain cut-off frequency (fT) of 120 GHz and maximum oscillation frequency (fmax) of 366 GHz at VDS = 0.8 V. These remarkable characteristics stem from the compact geometry design of the In0.52Al0.48As/In0.7Ga0.3As PHEMTs with LGS = LGD = 0.4 μm, coupled with an optimized gate recess process that yields tight control of side-recess spacing (Lside). More importantly, the product of fT and Lg in this work yields 60 GHz-μm which is the highest in any field-effect-transistor (FET) technology on any material system.

A Pulse-Biasing Small-Signal Measurement Technique Enabling 40\u2009MHz Operation of Vertical Organic Transistors

Organic/polymer transistors can enable the fabrication of large-area flexible circuits. However, these devices are inherently temperature sensitive due to the strong temperature dependence of charge carrier mobility, suffer from low thermal conductivity of plastic substrates, and are slow due to the low mobility and long channel length (L). Here we report a new, advanced characterization circuit that within around ten microseconds simultaneously applies an accurate large-signal pulse bias and a small-signal sinusoidal excitation to the transistor and measures many high-frequency parameters. This significantly reduces the self-heating and therefore provides data at a known junction temperature more accurate for fitting model parameters to the results, enables small-signal characterization over >10 times wider bias I–V range, with ~105 times less bias-stress effects. Fully thermally-evaporated vertical permeable-base transistors with physical L = 200 nm fabricated using C60 fullerene semiconductor are characterized. Intrinsic gain up to 35 dB, and record transit frequency (unity current-gain cutoff frequency, fT) of 40 MHz at 8.6 V are achieved. Interestingly, no saturation in fT − I and transconductance (gm − I) is observed at high currents. This paves the way for the integration of high-frequency functionalities into organic circuits, such as long-distance wireless communication and switching power converters.