Power Gain Cutoff Frequency Research Articles

GaAs-based metal-oxide-semiconductor field-effect transistor with aluminum oxide gate insulator prepared in situ by MOCVD

Preparation and properties of GaAs-based metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) are described. Aluminum oxide as a passivation and gate insulator was formed by room temperature oxidation of a thin Al layer deposited in situ on top of the InGaAs-channel/GaAs-substrate layer structure by metal-organic CVD (MOCVD). The devices yielded a maximum drain current of 480 mA mm−1 and a peak extrinsic transconductance of 147 mS mm−1. The devices exhibited negligible capacitance dispersion with frequency, which indicates low density of trap states in the structures prepared. From the microwave measurements, extracted current gain and unilateral power gain cutoff frequencies were 19 and 48 GHz, respectively, on devices with 1.5 µm gate length. Device modeling based on measured small signal S-parameters shows that the transconductance is predominantly responsible for an enhancement of the MOSHFET microwave performance.

High-frequency performance of scaled carbon nanotube array field-effect transistors

We report the radio-frequency performance of carbon nanotube array transistors that have been realized through the aligned assembly of highly separated, semiconducting carbon nanotubes on a fully scalable device platform. At a gate length of 100 nm, we observe output current saturation and obtain as-measured, extrinsic current gain and power gain cut-off frequencies, respectively, of 7 GHz and 15 GHz. While the extrinsic current gain is comparable to the state-of-the-art, the extrinsic power gain is improved. The de-embedded, intrinsic current gain and power gain cut-off frequencies of 153 GHz and 30 GHz are the highest values experimentally achieved to date. We analyze the consistency of DC and AC performance parameters and discuss the requirements for future applications of carbon nanotube array transistors in high-frequency electronics.

Device Characteristics of InGaSb/AlSb High-Hole-Mobility FETs

This letter reports the effect of growth temperature on carrier transport characteristics in In0.4Ga0.6Sb/AlSb heterostructure and demonstrates that hole mobility was enhanced by eliminating a parallel conducting channel in the buffer layers. Based on optimized growth conditions, hole mobility as high as 1220 cm2/V·s with carrier concentration of 1.3 ×1012 cm-2 was achieved. A 0.2- μm-gate-length In0.4Ga0.6Sb/AlSb p-channel device exhibited a maximum drain current of 102 mA/mm, a peak transconductance of 92 mS/mm, and an on-state breakdown voltage over 3 V. The pinchoff was observed for a gate bias of 0.6 V at drain current of 1 mA/mm. The current-gain and power-gain cutoff frequencies were 15 and 20 GHz, respectively.

AlGaN/GaN-based HEMT on SiC substrate for microwave characteristics using different passivation layers

In this paper, a new gate-recessed AlGaN/GaN-based high electron mobility transistor (HEMT) on SiC substrate is proposed and its DC as well as microwave characteristics are discussed for Si3N4 and SiO2 passivation layers using technology computer aided design (TCAD). The two-dimensional electron gas (2DEG) transport properties are discussed by solving Schrodinger and Poisson equations self-consistently resulting in various subbands having electron eigenvalues. From DC characteristics, the saturation drain currents are measured to be 600 mA/mm and 550 mA/mm for Si3N4 and SiO2 passivation layers respectively. Apart from DC, small-signal AC analysis has been done using two-port network for various microwave parameters. The extrinsic transconductance parameters are measured to be 131.7 mS/mm at a gate voltage of Vgs = −0.35 V and 114.6 mS/mm at a gate voltage of Vgs = −0.4 V for Si3N4 and SiO2 passivation layers respectively. The current gain cut-off frequencies (ft) are measured to be 27.1 GHz and 23.97 GHz in unit-gain-point method at a gate voltage of −0.4 V for Si3N4 and SiO2 passivation layers respectively. Similarly, the power gain cut-off frequencies (fmax) are measured to be 41 GHz and 38.5 GHz in unit-gain-point method at a gate voltage of −0.1 V for Si3N4 and SiO2 passivation layers respectively. Furthermore, the maximum frequency of oscillation or unit power gain (MUG = 1) cut-off frequencies for Si3N4 and SiO2 passivation layers are measured to be 32 GHz and 28 GHz respectively from MUG curves and the unit current gain, ∣ h21 ∣ = 1 cut-off frequencies are measured to be 140 GHz and 75 GHz for Si3N4 and SiO2 passivation layers respectively from the abs ∣ h21 ∣ curves. HEMT with Si3N4 passivation layer gives better results than HEMT with SiO2 passivation layer.

Design of High-Aspect-Ratio T-Gates on N-Polar GaN/AlGaN MIS-HEMTs for High $f_{\max}$

This letter discusses the design of high-aspect-ratio T-gates on molecular beam epitaxy (MBE)-grown nitrogen-polar (N-polar) GaN/AlGaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) for high power-gain cutoff frequency (fmax). A 351-GHz fmax is demonstrated, which is the highest published to date for an N-polar GaN HEMT. Novel 80-nm-long 1.1-m-tall T-gates with a 370-nm-tall stem were used to simultaneously minimize gate resistance (Rg) and parasitic gate-drain capacitance (Cgd). The device on -resistance (Ron) of 0.42 mm was obtained by employing n+ GaN MBE-regrown ohmic contacts and by scaling the lateral separation between regrown source-drain regions to 250 nm. Within the design space explored, this letter experimentally demonstrates that fmax is increased by reducing the gate width and the T-gate top length.

Flexible Gigahertz Transistors Derived from Solution-Based Single-Layer Graphene

Flexible electronics mostly relies on organic semiconductors but the limited carrier velocity in polymers and molecular films prevents their use at frequencies above a few megahertz. Conversely, the high potential of graphene for high-frequency electronics on rigid substrates was recently demonstrated. We conducted the first study of solution-based graphene transistors at gigahertz frequencies, and we show that solution-based single-layer graphene ideally combines the required properties to achieve high speed flexible electronics on plastic substrates. Our graphene flexible transistors have current gain cutoff frequencies of 2.2 GHz and power gain cutoff frequencies of 550 MHz. Radio frequency measurements directly performed on bent samples show remarkable mechanical stability of these devices and demonstrate the advantages of solution-based graphene field-effect transistors over other types of flexible transistors based on organic materials.

435mS/mm transconductance for AlGaN/GaN HEMTs on HR-Si substrate with optimised gate-source spacing

A report is presented on high transconductance Gm measured on AlGaN/GaN HEMTs with a 12.5 nm-thick AlGaN barrier layer, grown on high resistivity silicon substrate using the MOCVD growth technique. 105 nm T-gate transistors were successfully fabricated using Pt/Ti/Pt/Au Schottky contact. Maximum current density of 723 mA/mm, current gain cutoff frequency of 80 GHz and maximum power gain cutoff frequency of 153 GHz are achieved. The devices feature a record peak extrinsic transconductance of 435 mS/mm which to the authors' knowledge is the highest reported value for AlGaN/GaN HEMTs grown on Si (111). Different gate-source (Lgs) and drain-source (Lds) spacing were also designed to study their influence on the electrical device characteristics. The devices were fabricated in the framework of a tight collaborative project between OMMIC and IEMN.

InAlN/GaN HEMTs on Sapphire Substrate With 2.9-W/mm Output Power Density at 18 GHz

In this letter, small- and large-signal measurements of an In0.15Al0.82N/AlN/GaN high-electron-mobility transistor (HEMT) grown on a sapphire substrate with a 225-nm T-shaped gate are described. A maximum dc current density of 1.2 A/mm and a peak extrinsic transconductance of 460 mS/mm are obtained. The device exhibits a current gain cutoff frequency (FT) and a power gain cutoff frequency (FMAX) of 52 and 120 GHz, respectively. At VDS = 15 V, a continuous-wave output power density of 2.9 W/mm was achieved at 18 GHz with an associated power-added efficiency of 28% and a power gain of 15 dB. It is the best value ever reported from InAlN/GaN HEMTs grown on a sapphire substrate.

Ultimate RF Performance Potential of Carbon Electronics

Carbon electronics based on carbon nanotube array field-effect transistors (AFETs) and 2-dimensional graphene field-effect transistors (GFETs) have recently attracted significant attention for potential RF applications. Here, we explore the ultimate RF performance potential for these two unique devices using semi-classical ballistic transport simulations. It is shown that the intrinsic current-gain and power-gain cutoff frequencies (fT and fMAX) above 1 THz should be possible in both AFETs and GFETs. Thus, both devices could deliver higher cut-off frequencies than traditional semiconductors such as Si and III-V's. In the case of AFETs, we show that their RF operation is not sensitive to the diameter variation of semiconducting tubes and the presence of metallic tubes in the channel. The ultimate fT and fMAX values in AFETs are observed to be higher than that in GFETs. The optimum device biasing conditions for AFETs require smaller biasing currents, and thus, lower power dissipation compared to GFETs. The degradation in high-frequency performance in the presence of external parasitics is also seen to be lower in AFETs compared to GFETs.

High Frequency Performance of Graphene Transistors Grown by Chemical Vapor Deposition for Mixed Signal Applications

This paper demonstrates high frequency performance of graphene transistors grown by chemical vapor deposition on copper foils. Using Ti/Pd/Au-based ohmic contacts and a hybrid gate dielectric stack of 5 nm SiO2 and 15 nm Al2O3 grown by atomic layer deposition, graphene transistors with an extrinsic current-gain cut-off frequency (fT) of 2 GHz and power-gain cut-off frequency, fmax, of 5.6 GHz were obtained for a gate length of Lg = 1.6 µm. By applying a bias to the Si substrate the access resistances are reduced, which improved the fT and fmax in the devices to 3.5 and 6.5 GHz, respectively. Finally we demonstrate these devices in a real-application circuit for binary-phase shift keying.

Improved AlGaN/GaN HEMTs Grown on Si Substrates Using Stacked AlGaN/AlN Interlayer by MOCVD

AlGaN/GaN high electron mobility transistors (HEMTs) are grown on 2-inch Si (111) substrates by MOCVD. The stacked AlGaN/AlN interlayer with different AlGaN thickness and indium surfactant doped is designed and optimized to relieve the tensile stress during GaN epitaxial growth. The top 1.0μm GaN buffer layer grown on the optimized AlGaN/AlN interlayer shows a crack-free and shining surface. The XRD results show that GaN(002) FWHM is 480 arcsec and GaN(102) FWHM is 900 arcsec. The AGaN/GaN HEMTs with optimized and non-optimized AlGaN/AlN interlayer are grown and processed for comparison and the dc and rf characteristics are characterized. For the dc characteristics of the device with optimized AlGaN/AlN interlayer, maximum drain current density Idss of 737mA/mm, peak transconductance Gm of 185mS/mm, drain leakage current density Ids of 1.7μA/mm, gate leakage current density Igs of 24.8 μA/mm and off-state breakdown voltage VBR of 67 V are achieved with Lg/Wg/Lgs/Lgd = 1/10/1/1 μm. For the small signal rf characteristics of the device with optimized AlGaN/AlN interlayer, current gain cutoff frequency fT of 8.3 GHz and power gain cutoff frequency fmax of 19.9 GHz are achieved with Lg/Wg/Lgs/Lgd = 1/100/1/1 μm. Furthermore, the best rf performance with fT of 14.5 GHz and fmax of 37.3 GHz is achieved with a reduced gate length of 0.7μm.

Monolithic Integration of Enhancement- and Depletion-Mode AlN/GaN/AlGaN DHFETs by Selective MBE Regrowth

We have achieved the monolithic integration of two Ill-nitride device structures through the use of etching and re growth by molecular beam epitaxy (MBE). Using this regrowth technique, we integrated enhancement-mode (E-mode) and depletion-mode (D-mode) AIN/GaN/AlGaN double-heterojunction field-effect transistors (DHFETs) on a single SiC substrate, wherein the E-mode devices had a 2-nm-thick AlN barrier layer and the D-mode devices had a 3.5-nm-thick AlN barrier layer. The direct-current and radio-frequency (RF) performance of the resulting DHFETs was equivalent to devices fabricated using our baseline process with a normal MBE growth. D-mode devices with a gate length of 150 nm had a threshold voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of -0.10 V, a peak transconductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> value of 640 mS/mm, and current gain and power-gain cutoff frequencies f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 82 and 210 GHz, respectively. E-mode devices on the same wafer with the same dimensions had a V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> value of +0.24 V, a peak g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> value of 525 mS/mm, and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> values of 50 and 150 GHz, respectively. The application of this regrowth technique is not, in any way, limited to the integration of E- and D-mode devices, and this method greatly expands the design possibilities of RF and power switching circuits in the nitride material system.

ZnO NANOCRYSTALLINE HIGH PERFORMANCE THIN FILM TRANSISTORS

In this study, nc - ZnO films deposited in a Pulsed Laser Deposition (PLD) system at various temperatures were used to fabricate high performance transistors. As determined by Transmission Electron Microscope (TEM) images, nc - ZnO films deposited at a temperature range of 25°C to 400°C were made of closely packed nanocolums showing strong orientation. The influences of film growth temperature and post growth annealing on device performance were investigated. Various gate dielectric materials, including SiO 2, Al 2 O 3, and HfO 2 were shown to be suitable for high performance device applications. Bottom-gate FETs fabricated on high resistivity (&gt;2000 ohm-cm) Si substrates demonstrated record DC and high speed performance of any thin film transistors. Drain current on/off ratios better than 1012 and sub-threshold voltage swing values of less than 100mV/decade could be obtained. Devices with 2μm gate lengths produced exceptionally high current densities of &gt;750mA/mm. Shorter gate length devices (LG=1.2μm) had current and power gain cut-off frequencies, f T and f max , of 2.9GHz and 10GHz, respectively.

RF Performance of Deep-Recessed N-Polar GaN MIS-HEMTs Using a Selective Etch Technology Without Ex Situ Surface Passivation

We present a deep-recessed nitrogen-polar AlGaN/GaN MIS-HEMT employing a V-gate structure recessed through a thick GaN cap to prevent dc-to-RF dispersion. A process for selectively dry etching N-polar GaN over AlGaN has been established to achieve repeatable etch depth for the gate recess. Devices with a drawn gate length of 0.7- μm showed a current-gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fT</i> ) of 15 GHz and a power-gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fmax</i> ) of 42 GHz. A continuous-wave output power density of 5.5 W/mm was measured at 4 GHz, with a record associated power-added efficiency of 74% and a large-signal gain of 14.5 dB at a drain bias of 24 V.

RF performance of InAlN/AlN/GaN HEMTs on sapphire substrate

DC and RF performances of an In0.15Al0.85N/AlN/GaN high electron mobility transistor (HEMT) on sapphire substrate with 8.3 nm barrier layer thickness are reported. The device provides a maximum DC current density of 1 A/mm and a peak extrinsic transconductance of 325 mS/mm. A current gain cutoff frequency (FT) of 80 GHz and a power gain cutoff frequency (FMAX) of 130 GHz are obtained for a 110 nm gate length transistor corresponding to the highest reported values from InAlN/AlN/GaN HEMTs grown on sapphire substrate.

Microwave performance of ZnO/ZnMgO heterostructure field effect transistors

AbstractWe report the first microwave performance of single crystalline ZnO/ZnMgO heterostructure field‐effect transistors (HFETs). The structure consisted of a 15‐nm‐thick ZnO channel layer was grown by molecular beam epitaxy (MBE) on an a‐sapphire substrate. Two‐finger type HFETs with 1 or 2‐µm‐long gate were fabricated and measured for microwave performance. The transconductance of the HFETs are 28 and 23 mS/mm for 1 and 2‐µm‐gate devices, respectively. The microwave measurement of ZnO‐based TFTs revealed that the current gain cutoff frequency fT of 1.75 GHz and that of unilateral power gain fmax of 2.45 GHz for 1‐µm‐gate HFET. Electron velocity obtained by two‐terminal measurements implies that the structural design is crucial for further improvement of the high‐frequency performance of ZnO/ZnMgO HFETs.magnified image Small‐signal microwave characteristics of a 1‐µm‐gate ZnO/ZnMgO heterostructure FET. The current gain cutoff frequency of 1.75 GHz and the unilateral power gain cutoff frequency of 2.45 GHz were obtained.

Optoelectronic Mixer Based on Composite Transparent Gate InAlAs–InGaAs Metamorphic HEMTs

In this study, sputtered indium-tin-oxide (ITO) formed ITO/Au/ITO was used to form composite transparent gate InAlAs-InGaAs metamorphic HEMTs (CTG-MHEMT), with an optoelectronic mixer significantly markedly improved front-side optical coupling efficiency. The proposed CTG-MHEMT exhibits a high responsivity (λ = 1310 nm) of 1.71 A/W under optimal bias conditions. A -3 dB electrical bandwidth of 400 MHz is produced by the photovoltaic effect and dominated by the long lifetime of the excess holes. The -3 dB electrical bandwidth associated with the photoconductive effect is 2.3 GHz, and is determined mainly by the short electron life time. A power gain cut-off frequency (fmax) of CTG-MHEMT of 18.2 GHz was achieved. This value, is much larger than that of TG-MHEMT (14.6 GHz) because Au nano particles improved the gate resistance. The optoelectronic mixing efficiency was enhanced by tuning the gate bias conditions. The CTG-MHEMT optoelectronic mixer is a cost-effective device, and based on the optical and electrical characteristics, is a promising candidate for simplifying the system architecture in fiber-optic microwave transmission applications.

N-Polar InAlN/AlN/GaN MIS-HEMTs

N-polar metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were fabricated from a GaN/AlN/InAlN/GaN heterostructure grown by metalorganic chemical vapor deposition on a vicinal sapphire substrate, using Si3N4 as the gate insulator. Hall measurements in van der Pauw geometry on the heterostructure showed a sheet charge density and a mobility of 2.15 × 1013 cm-2 and 1135 cm2·V-1·s-1, respectively. Resistance measurements revealed anisotropic conductivity with respect to the surface steps induced by the substrate misorientation, and the sheet resistance of the 2-D electron gas was as low as 226 Ω/□ in the parallel direction. MIS-HEMTs with a gate length of 0.7 μm and a source-drain spacing of 2.2 μm had a peak drain current of 1.47 A/mm and an on-resistance of 1.45 Ω·mm. At a drain bias of 8 V, the current- and power-gain cutoff frequencies were 14 and 25 GHz, respectively.

120-nm gate-length In0.7Ga0.3As/In0.52Al0.48As InP-based HEMT

120 nm gate-length In0.7Ga0.3As/In0.52Al0.48As InP-based high electron mobility transitions (HEMTs) are fabricated by a new T-shaped gate electron beam lithograph (EBL) technology, which is achieved by the use of a PMMA/PMGI/ZEP520/PMGI four-layer photoresistor stack. These devices also demonstrate excellent DC and RF characteristics: the transconductance, maximum saturation drain-to-source current, threshold voltage, maximum current gain frequency, and maximum power-gain cutoff frequency of InGaAs/InAlAs HEMTs is 520 mS/mm, 446 mA/mm, −1.0 V, 141 GHz and 120 GHz, respectively. The material structure and all the device fabrication technology in this work were developed by our group.

High thermal stability AlGaAs/InGaAs enhancement-mode pHEMT using palladium-gate technology

The dc, flicker noise, power, and temperature dependence of AlGaAs/InGaAs enhancement-mode pseudomorphic high electron mobility transistors (E-pHEMTs) were investigated using palladium (Pd)-gate technology. Although the conventional platinum (Pt)-buried gate has a high metal work function, which is beneficial for increasing the Schottky barrier height of the E-pHEMT, the high rate of intermixing of the Pt–GaAs interface owing to the effect of the continuous production of PtAs 2 on the device influenced the threshold voltage ( V th ) and transconductance ( g m ) at high temperatures or over the long-term operation. Variations in these parameters make Pt-gate E-pHEMT-related circuits impractical. Furthermore, a PtAs 2 interlayer caused a serious gate leakage current and unstable Schottky barrier height. This study presents the Pd–GaAs Schottky contact because Pd, an inert material with high work function of 5.12 eV. Stable Pd inhibited the less diffusion at high temperatures and simultaneously suppressed device flicker noise. The V th of Pd/Ti/Au Schottky gate E-pHEMT was 0.183 V and this value shifted to 0.296 V after annealing at 200 °C. However, the V th shifted from 0.084 to 0.231 V after annealing of the Pt/Ti/Au Schottky gate E-pHEMT because the Pt sunk into a deeper channel. The slope of the curve of power gain cutoff frequency ( f max ) as a function of temperature was −5.76 × 10 −2 GHz/°C for a Pd/Ti/Au-gate E-pHEMT; it was −9.17 × 10 −2 GHz/°C for a Pt/Ti/Au-gate E-pHEMT. The slight variation in the dc and radio-frequency characteristics of the Pd/Ti/Au-gate E-pHEMT at temperatures from 0 to 100 °C revealed that the Pd–GaAs interface has great potential for high power transistors.