Current Gain Cutoff Frequency Research Articles

Record-low contact resistance for InAlN/AlN/GaN high electron mobility transistors on Si with non-gold metal

We have demonstrated 0.17-µm gate-length In0.17Al0.83N/GaN high-electron-mobility transistors (HEMTs) on Si(111) substrates using a non-gold metal stack (Ta/Si/Ti/Al/Ni/Ta) with a record-low ohmic contact resistance (Rc) of 0.36 Ω mm. This contact resistance is comparable to the conventional gold-based (Ti/Al/Ni/Au) ohmic contact resistance (Rc = 0.33 Ω mm). A non-gold ohmic contact exhibited a smooth surface morphology with a root mean square surface roughness of ∼2.1 nm (scan area of 5 × 5 µm2). The HEMTs exhibited a maximum drain current density of 1110 mA/mm, a maximum extrinsic transconductance of 353 mS/mm, a unity current gain cutoff frequency of 48 GHz, and a maximum oscillation frequency of 66 GHz. These devices exhibited a very small (<8%) drain current collapse for the quiescent biases (Vgs0 = −5 V, Vds0 = 10 V) with a pulse width/period of 200 ns/1 ms. These results demonstrate the feasibility of using a non-gold metal stack as a low Rc ohmic contact for the realization of high-frequency operating InAlN/AlN/GaN HEMTs on Si substrates without using recess etching and regrowth processes.

Impact of the silicon-nitride passivation film thickness on the characteristics of InAlAs/InGaAs InP-based HEMTs

In this research, the DC and RF characteristics for our own InAlAs/InGaAs InP-based high-electron-mobility transistors (HEMTs) with 0-nm, 50-nm, and 200-nm silicon-nitride (Si3N4) passivation films have been investigated comprehensively and systematically. With increasing Si3N4 passivation film thickness, the device exhibits an apparent improvement in the output conductance and a distinct drift of the pinch-off voltage toward a positive value. Especially, the device passivated by using a 50-nm Si3N4 film demonstrates the highest extrinsic transconductance and channel current. The appeared changes of the DC properties can be interpreted as due to the passivationinduced positively-charged surface state increasing the sheet carrier density with the carrier mobility and parasitic resistance of device being deteriorated by long-time high-stress-intensity ion bombardment. Additionally, the degradations of the current-gain cutoff frequency (f T) and maximum oscillation frequency (f max) can be attributed to the drastically-increased parasitic capacitance and resistance induced by the passivation process. This work will be of great importance in fabricating InP HEMTs with high performances.

Impact of the spacer dielectric constant on parasitic RC and design guidelines to optimize DC/AC performance in 10-nm-node Si-nanowire FETs

In this paper, we propose an optimized design for Si-nanowire FETs in terms of spacer dielectric constant (κsp), extension length (LEXT), nanowire diameter (Dnw), and operation voltage (VDD) for the sub-10 nm technology node. Using well-calibrated TCAD simulations and analytic RC models, we have quantitatively evaluated geometry-dependent parasitic series resistances (RSD) and capacitances (Cpara). Compared with low-κ spacers, high-κ spacers exhibit a higher on/off-current ratio with a lower RSD, but show severe degradation in their AC performance owing to a higher Cpara. Considering the trade-off between RSD and Cpara, optimal geometry-dependent κsp values at various supply voltages (VDD) are determined using gate delay (CV/I) and current-gain cutoff frequency (fT). We found that as LEXT and VDD decrease and Dnw increases, the optimal κsp value shifts from the high-κ to low-κ regime.

On the AlGaInP-bulk and AlGaInP/GaAs-superlattice confinement effects for heterostructure-emitter bipolar transistors

The confinement effect and electrical characteristics of heterostructure-emitter bipolar transistors with an AlGaInP bulk-confinement layer and an AlGaInP/GaAs superlattice-confinement layer are first demonstrated and compared by experimentally results. In the two devices, the relatively large valence band discontinuity at AlGaInP/GaAs heterojunction provides excellent confinement effect for holes to enhance current gain. As to the AlGaInP/GaAs superlattice-confinement device, part of thermionic-emission electrons will be trapped in the GaAs quantum wells of the superlattice. This will result in lower collector current and current gain as compared with the bulk-confinement device. Nevertheless, the superlattice-confinement device exhibits a larger current-gain cutoff frequency, which can be attributed that the tunneling behavior is included in the carrier transportation and transporting time across the emitter region could be substantially reduced.

Design of InAlAs/InGaAs PHEMTs and small-signal modeling from 0.5 to 110 GHz

90-nm T-shaped gate InP-based In0.52Al0.48As/In0.6Ga0.4As pseudomorphic high electron mobility transistors were designed and fabricated with a gate-width of 2 × 30 μm, a source—drain space of 2.5 μm, and a source—gate space of 0.75 μm. DC, RF and small-signal model characterizations were demonstrated. The maximum saturation current density was measured to be 755 mA/mm biased at Vgs = 0.6 V and Vds = 1.5 V. The maximum extrinsic transconductance was measured to be 1006 mS/mm biased at Vgs = −0.1 V and Vds = 1.5 V. The extrapolated current gain cutoff frequency and maximum oscillation frequency based on S-parameters measured from 0.5 to 110 GHz were 180 and 264 GHz, respectively. The inflection point (the stability factor k = 1) where the slope from −10 dB/decade (MSG) to −20 dB/decade (MAG) was measured to be 83 GHz. The small-signal model of this device was also established, and the S-parameters of the model are consistent with those measured from 0.5–110 GHz.

Growth and characterization of AlGaN/GaN/AlGaN double-heterojunction high-electron-mobility transistors on 100-mm Si(111) using ammonia-molecular beam epitaxy

To improve the confinement of two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistor (HEMT) heterostructures, AlGaN/GaN/AlGaN double heterojunction HEMT (DH-HEMT) heterostructures were grown using ammonia-MBE on 100-mm Si substrate. Prior to the growth, single heterojunction HEMT (SH-HEMT) and DH-HEMT heterostructures were simulated using Poisson-Schrödinger equations. From simulations, an AlGaN buffer with “Al” mole fraction of 10% in the DH-HEMT was identified to result in both higher 2DEG concentration (∼1013 cm−2) and improved 2DEG confinement in the channel. Hence, this composition was considered for the growth of the buffer in the DH-HEMT heterostructure. Hall measurements showed a room temperature 2DEG mobility of 1510 cm2/V.s and a sheet carrier concentration (ns) of 0.97 × 1013 cm−2 for the DH-HEMT structure, while they are 1310 cm2/V.s and 1.09 × 1013 cm−2, respectively, for the SH-HEMT. Capacitance-voltage measurements confirmed the improvement in the confinement of 2DEG in the DH-HEMT heterostructure, which helped in the enhancement of its room temperature mobility. DH-HEMT showed 3 times higher buffer break-down voltage compared to SH-HEMT, while both devices showed almost similar drain current density. Small signal RF measurements on the DH-HEMT showed a unity current-gain cut-off frequency (fT) and maximum oscillation frequency (fmax) of 22 and 25 GHz, respectively. Thus, overall, DH-HEMT heterostructure was found to be advantageous due to its higher buffer break-down voltages compared to SH-HEMT heterostructure.

Microwave and power characteristics of AlGaN/GaN/Si high-electron mobility transistors with HfO2 and TiO2 passivation

This work presents AlGaN/GaN high-electron mobility transistors (HEMTs) that are grown on silicon. Various passivation layers are deposited on AlGaN/GaN HEMTs. AlGaN/GaN HEMTs were fabricated with TiO2 dielectrics, and their performance was compared with that of unpassivated and that of HfO2-passivated HEMTs. The TiO2-passivated HEMT with a gate length of 1 μm exhibits a maximum extrinsic transconductance of 134.4 mS mm−1, a current-gain cutoff frequency of 10.62 GHz, and a maximum frequency of oscillation of 16.37 GHz. Capping with any of the dielectric materials used herein improves the device performance over that of the unpassivated HEMTs. Additionally, experimental data demonstrate that the use of TiO2 is a favorable alternative to HfO2 passivation. This work is the first to present the microwave power of TiO2-passivated AlGaN/GaN HEMTs.

Design and analysis of Si-based arch-shaped gate-all-around (GAA) tunneling field-effect transistor (TFET)

In this work, a Si-based arch-shaped gate-all-around (GAA) tunneling field-effect transistor (TFET) has been designed and analyzed. Various studies on III–V compound semiconductor materials for applications in TFET devices have been made and we adopt one of them to perform a physical design for boosting the tunneling probability. The GAA structure has a partially open region for extending the tunneling area and the channel is under the GAA region, which makes it an arch-shaped GAA structure. We have performed the design optimization with variables of epitaxy channel thickness (tepi) and height of source region (Hsource) in the Si-based TFET. The designed arch-shaped GAA TFET based on Si platform demonstrates excellent performances for low-power (LP) applications including on-state current (Ion) of 694 μA/μm, subthreshold swing (S) of 7.8mV/dec, threshold voltage (Vt) of 0.1 V, current gain cut-off frequency (fT) of 12 GHz, and maximum oscillation frequency (fmax) of 283 GHz.

GaAsSb-Based DHBTs With a Reduced Base Access Distance and $f_{\mathrm {T}}/f_{\mathrm {MAX}}=$ 503/780 GHz

We report InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with simultaneous current and power gain cutoff frequencies of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> /f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> = 503/780 GHz. Devices with a 0.2 × 4.4 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> emitter area feature a peak DC current gain β = 17 and a common-emitter breakdown voltage BVCEO = 4.1 V. To the best of our knowledge, the present transistors are the first GaAsSb-based DHBTs to feature f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> > 750 GHz. The progress in RF performance is enabled by a reduction of the base access resistance and base-collector capacitance achieved via an improved self-aligned emitter etching procedure.

Demonstration of radio-frequency response of amorphous IGZO thin film transistors on the glass substrate

The relatively high-mobility metal-oxide thin-film transistors (TFTs) have the potential to realize radio-frequency (RF) circuits operating in the megahertz regime. Here, we investigate the RF performance of amorphous indium gallium zinc oxide (a-IGZO) TFTs on the glass substrate with the sputtered channel layer. The device exhibits a high current density of 22.6mA/mm by employing thin bi-layer Al2O3/SiO2 gate dielectrics. The 1.5μm gate length device achieves a current gain cutoff frequency fT of 384MHz and a maximum frequency of oscillation fmax of 1.06GHz. The record high RF response among the amorphous oxide channels makes it possible to explore new large-area electronics applications, such as low-cost radio frequency identification (RFID) tags. Furthermore, the corresponding small signal parameters were extracted and the voltage dependences of RF response were studied.

Black phosphorus radio-frequency transistors.

Few-layer and thin film forms of layered black phosphorus (BP) have recently emerged as a promising material for applications in high performance nanoelectronics and infrared optoelectronics. Layered BP thin films offer a moderate bandgap of around 0.3 eV and high carrier mobility, which lead to transistors with decent on-off ratios and high on-state current densities. Here, we demonstrate the gigahertz frequency operation of BP field-effect transistors for the first time. The BP transistors demonstrated here show respectable current saturation with an on-off ratio that exceeds 2 × 10(3). We achieved a current density in excess of 270 mA/mm and DC transconductance above 180 mS/mm for hole conduction. Using standard high frequency characterization techniques, we measured a short-circuit current-gain cutoff frequency fT of 12 GHz and a maximum oscillation frequency fmax of 20 GHz in 300 nm channel length devices. BP devices may offer advantages over graphene transistors for high frequency electronics in terms of voltage and power gain due to the good current saturation properties arising from their finite bandgap, thus can be considered as a promising candidate for the future high performance thin film electronics technology for operation in the multi-GHz frequency range and beyond.

A simple method for forming compositionally graded InxGa1−xAs1−ySby base of double-heterojunction bipolar transistors modulating CBr4-doping-precursor flow in metalorganic chemical vapor deposition

We studied a CBr4-flow-modulation method as a way of simplifying the formation of a compositionally graded InxGa1−xAs1−ySby base of InP-based heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition. An investigation of C-doping in InxGa1−xAs1−ySby revealed that In and Sb contents decrease as the supply ratio of CBr4 to group-III (RC) increases. We fabricated 0.25-µm-emitter HBTs with a compositionally graded InxGa1−xAs1−ySby base formed by varying RC at constant group-III, group-V, and V/III ratios. By this method, we obtained higher current-gain cut-off frequency (504 GHz) and maximum-oscillation frequency (328 GHz) than those of uniform-InxGa1−xAs1−ySby-base HBTs with the same base/collector thicknesses.

Performance Optimization Study of FinFETs Considering Parasitic Capacitance and Resistance

Recently, the first generation of mass production of FinFET-based microprocessors has begun, and scaling of FinFET transistors is ongoing. Traditional capacitance and resistance models cannot be applied to nonplanar-gate transistors like FinFETs. Although scaling of nanoscale FinFETs may alleviate electrostatic limitations, parasitic capacitances and resistances increase owing to the increasing proximity of the source/drain (S/D) region and metal contact. In this paper, we develop analytical models of parasitic components of FinFETs that employ the raised source/drain structure and metal contact. The accuracy of the proposed model is verified with the results of a 3-D field solver, Raphael. We also investigate the effects of layout changes on the parasitic components and the current-gain cutoff frequency (fT). The optimal FinFET layout design for RF performance is predicted using the proposed analytical models. The proposed analytical model can be implemented as a compact model for accurate circuit simulations.

Lg = 100 nm T-shaped gate AlGaN/GaN HEMTs on Si substrates with non-planar source/drain regrowth of highly-doped n+-GaN layer by MOCVD

High-performance AlGaN/GaN high electron mobility transistors (HEMTs) grown on silicon substrates by metal—organic chemical-vapor deposition (MOCVD) with a selective non-planar n-type GaN source/drain (S/D) regrowth are reported. A device exhibited a non-alloyed Ohmic contact resistance of 0.209 Ω·mm and a comprehensive transconductance (gm) of 247 mS/mm. The current gain cutoff frequency fT and maximum oscillation frequency fMAX of 100-nm HEMT with S/D regrowth were measured to be 65 GHz and 69 GHz. Compared with those of the standard GaN HEMT on silicon substrate, the fT and fMAX is 50% and 52% higher, respectively.

High-Frequency Microwave Noise Characteristics of InAlN/GaN High-Electron Mobility Transistors on Si (111) Substrate

We report for the first time high-frequency microwave noise performance on 0.17-μm T-gate In 0.17 Al 0.83 N/GaN high-electron mobility transistors (HEMTs) fabricated on Si(111). The HEMTs exhibited a maximum drain current density of 1320 mA/mm, a maximum extrinsic transconductance of 363 mS/mm, an unity current gain cutoff frequency (f T ) of 64 GHz and, a maximum oscillation frequency [fmax (U)/ f max (MSG)] of 72/106 GHz. The product f max (U) × L g =12.24 GHz· μm is the highest value ever reported for InAlN/GaN HEMTs on Si substrate. At V d =4 V and V g =-2.25 V, the device exhibited a minimum noise figure (NF min ) of 1.16 dB for 10 GHz and 1.76 dB for 18 GHz. Small variation of NF min (<;0.5 dB) from 8% to 48% with I Dmax (100-636 mA/mm) was observed.

RF Performance and Avalanche Breakdown Analysis of InN Tunnel FETs

This paper reports radio frequency (RF) performance and channel breakdown analysis in an n-type tunneling field-effect transistor based on InN. The tunneling current is evaluated from the fundamental principles of quantum mechanical tunneling. We investigate the RF performance of the device. High transconductance of 2.18 mS/μm and current gain cutoff frequency of 460 GHz makes the device suitable for terahertz applications. A significant reduction in gate-to-drain capacitance is observed under a relatively higher drain bias (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> = 1 V). Impact ionization coefficient in the channel is evaluated quantitatively considering semiclassical carrier transport and avalanche breakdown is found to be unlikely at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> = 1.0 V.

High-performance AlGaInP tunneling heterostructure-emitter bipolar transistor

In this paper, a high-performance heterostructure-emitter bipolar transistor employing an AlGaInP quaternary compound tunneling layer is fabricated and demonstrated. In the studied device, a 50Å n-AlGaInP tunneling emitter layer together with a 200Å n-GaAs layer forms the heterostructure emitter to decrease the collector–emitter offset voltage. On the other hand, due to the relatively large valence band discontinuity (∼0.4eV) at AlGaInP/GaAs heterojunction and the small hole transmission coefficient across the AlGaInP tunneling layer, most of holes injecting from base to emitter will be blocked at AlGaInP/GaAs heterojunction and then high collector current and current gain are achieved. The experimental results exhibit a large collector current of 92mA, a large current gain of 446, and a relatively low offset voltage of only 45mV, respectively. Furthermore, a large current-gain cutoff frequency ft up to 63.7GHz is obtained for the device with a thin tunneling layer.

MOCVD-grown compressively strained C-doped InxGa1−xAs1−ySby with high-In/Sb content for very low turn-on-voltage InP-based DHBTs

We investigated metalorganic chemical vapor deposition of C-doped high-In-and-Sb-content compressively strained InxGa1−xAs1−ySby and examined InP-based heterojunction bipolar transistors (HBTs) with low base-emitter turn-on voltage. By lowering the growth temperature to 530°C, the etching effect of CBr4 is suppressed, which is consistent with the results of thermodynamic calculations. We obtained high hole concentration of mid-1019cm−3 with the In content of over 0.20. The base-emitter voltage (VBE) at collector current density (JC) of 10nA/μm2 of large-area HBTs with the high-In-and-Sb-content compressively strained InxGa1−xAs1−ySby base is lower than those of the HBTs with a tensile strained InxGa1−xAs1−ySby or GaAs1−ySby base, owing to the reduction of the band gap of the base layer. We fabricated InP/In0.20Ga0.80As0.55Sb0.45/InP HBTs with a 0.25-μm-wide emitter and obtained the VBE of 0.66V at JC of 1mA/μm2. At JC=13mA/μm2, the device exhibits peak current-gain cut-off frequency of over 400GHz, which is comparable to the value for GaAs1−ySby-base HBTs with the same base and collector thicknesses.

&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;${\rm SiN}_{x}$ &lt;/tex-math&gt;&lt;/inline-formula&gt;/InAlN/AlN/GaN MIS-HEMTs With 10.8 &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;${\rm THz}\cdot{\rm V}$ &lt;/tex-math&gt;&lt;/inline-formula&gt; Johnson Figure of Merit

A high combination of three-terminal breakdown voltage (VBK) and current gain cutoff frequency (fT) was achieved with SiNx/InAlN/AlN/GaN metal-insulator- semiconductor high-electron mobility transistors (MIS-HEMTs). A 1-nm SiNx gate dielectric was deposited ex situ in a molecular beam epitaxy system and used to increase the carrier density of the 2-D electron gas under an ultrathin InAlN/AlN (2.3 nm/1 nm) barrier. Passivated MIS-HEMTs with a gate length of 80 nm exhibited a drain current density greater than 1.1 A/mm, a peak intrinsic transconductance gm,max of 800 mS/mm, and a maximum frequency of oscillation fmax of 230 GHz. The combination of f T of 114 GHz and VBK of 95 V provides a Johnson figure of merit of 10.8 THz · V, which is among the highest reported values for fully passivated GaN HEMTs. A peak power-added efficiency of 37.5% with an output power of 1.25 W/mm and an associated gain of 9.7 dB was obtained by load-pull measurements at 40 GHz.

T-Shaped Gate GaN HFETs on Si With Improved Breakdown Voltage and &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$f_{\rm MAX}$ &lt;/tex-math&gt;&lt;/inline-formula&gt;

In this letter, we have fabricated GaN heterostructure field-effect transistors (HFETs) with submicrometer T-shaped gate on Si substrate to realize compact solid-state power amplifiers used in Ku-band and higher. An AlGaN buffer layer was incorporated under the GaN channel layer, which was expected to enhance the breakdown voltage without decreasing the gain. The fabricated GaN HFETs 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 0.16 μm showed a three-terminal breakdown voltage (BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) of 98 V and a peak maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> ) of 226 GHz, with a simultaneous 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> ) of 63 GHz at VDS = 15 V. In addition, a minimum noise figure (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Fmin</sub> ) of 1.01 dB with an associated gain of 16 dB at 14 GHz was obtained at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = 5 V. A 0.1-mm-wide GaN HFETs exhibited a saturated power density of 3.82 W/mm at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = 30 V, indicating the successful reduction of current collapse. To the best of our knowledge, this is the first demonstration of a GaN HFETs on Si, which combines high BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> , high power density, and low NF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> at the Ku-band.