Current Gain Cutoff Frequency Research Articles

Influence of back barrier layer thickness on device performance of AlGaN/GaN MOS-HEMT

In this work, we have performed the influence of back barrier layer thickness variation on AlGaN/GaN Metal Oxide Semiconductor High Electron Mobility Transistor (MOS-HEMT) device with 0.5 µm Schottky gate length. The AlGaN back barrier layer presented increases the conduction band with respect to GaN channel layer so that more no of electron confinement into the GaN channel layer and improve the high-frequency performance. The effect of the back-barrier layer thickness is performed by using 2-D TCAD Atlas Silvaco numerical simulation tool by taking Hydrodynamic mobility model. Due to a large amount of two-dimensional electron gas (2-DEG) density at the AlGaN/GaN heterointerface of the MOS-HEMT device higher drain current density is obtained. The 2-D simulation is carried out with a variation of back barrier layer thickness for various device parameter such as transfer characteristics (Id-Vg), drain current with a drain voltage (Id-Vd), transconductance (gm), drain induced barrier lowering (DIBL), conduction band energy and electron concentration into the channel. In this simulation, we have also performed the RF performance like a gate to source capacitance (Cgs) and current gain cut-off frequency of AlGaN/GaN MOS-HEMT device. The results obtained by variation of AlGaN back barrier layer thickness can be a better solution in future analog and RF device application. Copyright © 2018 VBRI Press.

Strain-engineering in AlGaN/GaN HEMTs: impact of silicon nitride passivation layer on electrical performance

In this work, we present a physics-based analysis of two-dimensional electron gas (2DEG) sheet carrier density and other microwave characteristics such as transconductance and cutoff frequency of AlxGa1−xN/GaN high electron mobility transistors (HEMT). An accurate polarization-dependent charge control-based analysis is performed for microwave performance assessment in terms of current, transconductance, gate capacitances, and cutoff frequency of lattice-mismatched AlGaN/GaN HEMTs. The influence of stress on spontaneous and piezoelectric polarization is included in the simulation of an AlGaN/GaN HEMT. We have shown the change in threshold voltage (Vt) due to tensile and compressive strain with different gate lengths. Also, the influence of stress due to the change in nitride thickness is presented. Our simulation results for drain current, transconductance, and current-gain cutoff frequency for various gate length devices are calibrated and verified with experimental data over a wide range of gate and drain applied voltages, which are expected to be useful for microwave circuit design. The predicted transconductance, drain conductance, and operation frequency are quite close to the experimental data. The AlGaN/GaN heterostructure HEMTs with nitride passivation layers show great promise as a candidate in future high speed and high power applications.

Electrical properties of 90-nm InAlN/GaN HEMT on silicon substrate

GaN high-electron-mobility transistors (HEMTs) on silicon substrate have attracted much attention owing to the low-cost and the large area availability of the Si substrate. In this paper, the 90-nm-gate-length InAlN/GaN HEMT on silicon was fabricated and the device electrical properties were studied. The device presents a low drain-induced barrier lowing (DIBL) of 43 mV/V, a parasitic source resistance ( R S ) of 0.91 Ω⸱mm, and a peak of the intrinsic transconductance ( g m0 ) of 553 mS/mm. To the best of our knowledge, this is the lowest DIBL value among the reported GaN HMET on Si with gate length ( L g ) below 100 nm. The low-filed two-dimensional electron gas (2DEG) electron mobility ( μ n ) was extracted and the dominated polarization Coulomb field scattering contributed to the increased μ n with the increased of two-dimensional electron gas electron density ( n 2D ). A current gain cutoff frequency ( f T ) of 175 GHz was achieved on InAlN/GaN HEMTs with a gate length of 90-nm.

Investigation to Enhance the DC and RF Performances of Nitride-Based Nanoelectronic HEMTs

In this work, a structural optimisation is performed on the basis of DC and RF performances of high electron mobility transistors (HEMTs) in nano-scale regime by simulation results obtained from SILVACO-ATLAS physical simulator. The formation of quantum well is demonstrated at unbiased condition in each type of these HEMT structures. In DC analysis of each structure, the variations in drain current are studied with respect to drain voltage, gate voltage and doping concentration. Also, the variations in transconductance are studied with gate voltage and doping concentration corresponding to each structure. In RF analysis, the variations in current gain cut-off frequency and power gain cut-off frequency are studied with gate voltage and doping concentration corresponding to each structure. The DC and RF performances are observed to be the highest for modified HEMT structure with inserted InN atomic layer (0.36 nm thick) having AlGaN doping concentration of 4×1018 cm-3 among all designed structures in this work. To investigate the effect of doping concentration on DC and RF performances in nano-scale regime is one novelty in this work. Our work may be helpful in the applications related to biomedical sensors. Also, our work may be suitable for high frequency applications.

Novel gate air cavity GaN HEMTs design for improved RF and DC performance

Studies are performed to develop physical insights into the RF and DC behavior of GaN HEMTs. In purpose of improving the current gain cutoff frequency (fT) and power gain cutoff frequency (fmax), an air cavity structure was proposed, which efficiently decreases the gate–drain capacitance and gate–source capacitance. As a result, the proposed HEMTs with air cavity offers over 2× improvements in cutoff frequency comparing with the design without, which increases the fT and fmax to 14.9 GHz and 33.1 GHz, respectively. It breaks through the performance bottleneck limited by the length of gate, realizing a relatively high scaling factor that Lg × fT = 20.86 GHz μm when compared with previous reports. Besides, in order to realize both DC and RF performance improvement we proposed another kind of air cavity design, the fT and fmax can be increased by 82% and 37.6% respectively. The maximum saturation drain current approximately increased by 50%, maximum transconductance (gm, max) raise from 209 to 237 mS/mm and the gate current leakage performance is improved to a certain extent. Furthermore, forth bias sweep C–V (capacitance–voltage) curves and current density are also extracted to discuss the mechanism accompany with the reported physical model, based on which 2 simplified capacitive networks are proposed.

Investigation of β-Ga2O3-based HEMTs using 2D Simulations for low noise amplification and RF applications

Here we demonstrate a two-dimensional β-gallium oxide-based high electron mobility transistor (HEMT) comprising of a finite gap—access region gap in Ohmic-contact access regions with record transconductance linearity. Apart from limiting two-dimensional electron gas (2-DEG) density dependency on gate voltage, higher saturation current is estimated for the proposed design. Since access regions length directly affects the Capacitance of the device and resultant switching applications. In this work, the effect of the gate-source and gate-drain length on device linearity is performed using Atlas-2D simulations. characteristics of the proposed device are explained based on the physical explanation and validated using appropriate models. The higher values of transconductance and current gain cut-off frequency on a large span of operating voltages ensure improved transistors’ performance and are reported for the first time.

Electron irradiation effects on InP-based HEMTs with different gate widths

In this paper, the influence of electron irradiation on DC and RF characteristics of InP-based HEMTs with different gate widths were studied by irradiation experiment. The results show that the value of channel current (IDS) and transconductance (gm) are decreased for device with different gate width after electron irradiation, which is mainly due to the reduction of mobility in the channel by the irradiation-induced defects. However, the carrier concentration in the channel has a little change. Compared with the device with 100 μm gate width, IDS and gm of the device with 40 μm gate width were decreased by 1.5% and 3%. Meanwhile, the forward gate current decreased due to the increase of series resistance of gate contact caused by electron irradiation. The interface defects induced by electron irradiation induced the increase of the reverse gate current. Additionally, the current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) were reduced by 19.8% and 10.9% for device with 40 μm gate width, and the fT and fmax were only reduced by 7.1% and 8.2% for device with 100 μm gate width. The experimental results indicate that designing a reasonable structure is an effective method to enhance the radiation resistance in InP-based HEMTs, and this method can also be utilized in other semiconductor devices.

The lattice-matched AlInN/GaN high electron mobility transistor with BGaN buffer

This work studies the lattice-matched AlInN/GaN high-electron mobility transistor (HEMT) with BGaN buffer in drain-current (DC) and radio-frequency (RF) characteristics in theory. The results demonstrate that the BGaN buffer can effectively confine two-dimensional electron gas (2DEG) in the channel area and significantly improve the pinch-off velocity of devices. Compared with the standard GaN buffer HEMT as a reference, the BGaN buffer HEMT with only 1.5% B-component significantly suppressed the short-channel effects (SCEs). And the subthreshold swing (SS) and drain-induced barrier lower (DIBL) are reduced to 124 mV/dec and 77 mV/V, respectively. The threshold voltage of the proposed HEMT is about −3.61 eV, which positive shifts about 2.45 eV compared with the reference HEMT, and this mainly due to the reduction of 2DEG density. In addition, the peak current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) of the proposed HEMT are 155 GHz and 174 GHz, respectively. And this is slightly lower than that of the reference device, which mainly results from the lower transconductance and 2DEG density.

Improved On/Off Current Ratio and Linearity of InAlN/GaN HEMTs with N2O Surface Treatment for Radio Frequency Application

Due to the strong spontaneous polarization, InAlN/GaN high-electron-mobility transistors (HEMTs) offer advantages over conventional AlGaN/GaN HEMTs with a thinner barrier. However, a thin InAlN barrier layer inevitably leads to a high gate leakage current and thus degrades the device performance. Here, we demonstrate a reduced gate leakage current (I g) and an improved on/off current ratio (I ON/I OFF) on a 60-nm-gate-length InAlN/GaN HEMTs on Si by using N2O treatment. The device presents that I g decreases from ∼1 × 10−4 A mm−1 (without N2O) to 5 × 10−6 A mm−1 (with N2O), and I ON/I OFF increases from ∼1 × 105 (without N2O) to ∼1 × 108 (with N2O). The short-channel effects (SCEs) are also suppressed and the drain-induced barrier lowering (DIBL) decreases from more than 120 mV V−1 (without N2O) to 90 mV V−1 (with N2O). In addition, the InAlN/GaN HEMT with N2O treatment shows a flatter trend of transconductance (g m) with gate-source voltage (V gs) and three folds of the gate voltage swing(GVS) increase from 1.6 V (without N2O) to 4.8 V (with N2O), an indication of the improved device linearity. RF performance shows that a current gain cutoff frequency (f T) of 185 GHz is obtained on a 60-nm-gate-length InAlN/GaN HEMTs with N2O treatment. It presents the great potential of N2O surface treatment for the InAlN/GaN HEMTs for radio frequency application.

High frequency hydrogen-terminated diamond MESFET with an fmax of 103GHz

High-quality polycrystalline diamond substrate was used to fabricate diamond MESFETs by a self-aligned process. The fabricated diamond MESFETs with a gate length of 130 nm show good direct current and radio frequency performances, with the maximum saturation source-drain current IDS of 560 mA/mm, the Ion/Ioff ratio of 107, the transconductance of 225 mS/mm, and the current gain cut-off frequency fT of 40.7 GHz and the maximum oscillation frequency fmax of 103 GHz. These results show that the high-quality polycrystalline freestanding diamond is a promising candidate for the investigation of high frequency electronic devices.

Heterogeneous integration of InP HEMTs on quartz wafer using BCB bonding technology

Heterogeneous integrated InP high electron mobility transistors (HEMTs) on quartz wafers are fabricated successfully by using a reverse-grown InP epitaxial structure and benzocyclobutene (BCB) bonding technology. The channel of the new device is In0.7Ga0.3As, and the gate length is 100 nm. A maximum extrinsic transconductance g m,max of 855.5 mS/mm and a maximum drain current of 536.5 mA/mm are obtained. The current gain cutoff frequency is as high as 262 GHz and the maximum oscillation frequency reaches 288 GHz. In addition, a small signal equivalent circuit model of heterogeneous integration of InP HEMTs on quartz wafer is built to characterize device performance.

High-frequency enhancement-mode millimeterwave AlGaN/GaN HEMT with an f T/f max over 100 GHz/200 GHz* *Project supported by the National Key Research and Development Program of China (Grant No. 2020YFB1804902), the National Natural Science Foundation of China (Grant No. 61904135), the China Postdoctoral Science Foundation (Grant Nos. 2018M640957 and BX20200262), and the Natural Science Foundation of Shaanxi Province, China (Grant No.

Ultra-thin barrier (UTB) 4-nm-AlGaN/GaN normally-off high electron mobility transistors (HEMTs) having a high current gain cut-off frequency (f T) are demonstrated by the stress-engineered compressive SiN trench technology. The compressive in-situ SiN guarantees the UTB-AlGaN/GaN heterostructure can operate a high electron density of 1.27 × 1013 cm−2, a high uniform sheet resistance of 312.8 Ω/□, but a negative threshold for the short-gate devices fabricated on it. With the lateral stress-engineering by full removing in-situ SiN in the 600-nm SiN trench, the short-gated (70 nm) devices obtain a threshold of 0.2 V, achieving the devices operating at enhancement-mode (E-mode). Meanwhile, the novel device also can operate a large current of 610 mA/mm and a high transconductance of 394 mS/mm for the E-mode devices. Most of all, a high f T/f max of 128 GHz/255 GHz is obtained, which is the highest value among the reported E-mode AlGaN/GaN HEMTs. Besides, being together with the 211 GHz/346 GHz of f T/f max for the D-mode HEMTs fabricated on the same materials, this design of E/D-mode with the realization of f max over 200 GHz in this work is the first one that can be used in Q-band mixed-signal application with further optimization. And the minimized processing difference between the E- and D-mode designs the addition of the SiN trench, will promise an enormous competitive advantage in the fabricating costs.

Stackable InGaAs-on-Insulator HEMTs for Monolithic 3-D Integration

In this article, we have demonstrated 125-nm-gate InGaAs-on-insulator (InGaAs-OI) high-electron-mobility transistors (HEMTs) on Si substrates via wafer bonding. The highlights of this device were the i-In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/i-InAs/i-In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As quantum-well channel for high RF performance by improving electron transport properties and the low processing temperature of 250 °C or less for monolithic 3-D integration. As a result, we obtained a 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 227 GHz and a 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 187 GHz. These results are the highest ever reported in monolithic 3-D RF transistors above L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> = 100 nm. In addition, through the small-signal modeling, we have found that the impact of the back-gate (BG) on RF performances of top devices is a critical issue in M3D RF systems.

Highly scaled graded channel GaN HEMT with peak drain current of 2.48 A/mm

The dc and high frequency performances of Al composition Graded Channel AlGaN/GaN high electron mobility transistor on GaN substrate was investigated and compared with Conventional AlGaN/GaN HEMT. The high frequency characteristics were measured on both the AlGaN/GaN HEMTs scaling the gate length from 800 nm to 50 nm. The 50 nm gate length Graded Channel AlGaN/GaN HEMT exhibited the highest drain current of 2.48 A/mm and transconductance of 0.32 S/mm respectively at a drain voltage of VD = 10 V. Also the transconductance curve of the Graded Channel HEMT is flatter than that of conventional GaN HEMT. The flatter transconductance curve reduces the power gain roll off in Graded Channel HEMT and thus gives improved performance in terms of device linearity. The current gain cutoff frequency fT = 126.5 GHz was obtained for the Graded Channel HEMT at a gate length of 50 nm. This accounts to 61.6% increase in fT when compared to conventional GaN HEMT at the same gate length of 50 nm.

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.

High‐Current‐Density Enhancement‐Mode Ultrawide‐Bandgap AlGaN Channel Metal–Insulator–Semiconductor Heterojunction Field‐Effect Transistors with a Threshold Voltage of 5 V

Enhancement‐mode ultrawide‐bandgap Al0.65Ga0.35N/Al0.4Ga0.6N metal–insulator–semiconductor heterojunction field‐effect transistors are demonstrated using fluorine‐plasma treatment for threshold voltage control and Al2O3 as gate dielectric. The device exhibits a threshold voltage of 5 V, a maximum drain current density of 105 mA mm−1, and a transconductance of 19 mS mm−1. In addition, the capability to achieve low off‐state current density at 3–4 × 10−9 mA mm−1, an exceptionally low gate leakage current density of 1.4 × 10−8 mA mm−1 even at a high forward gate bias of VGS = 12 V, and a current on/off ratio &gt;1010 is shown. Small signal measurement shows that the device has a unity current gain cutoff frequency fT of 3.8 GHz and power gain cutoff frequency fmax of 4.5 GHz.

Comparative studies on the DC and RF performances of conventional HEMT and double quantum well heterostructure

In this work, we propose a novel double quantum well (QW) high electron mobility transistor (HEMT) structure. The DC and RF performances of this proposed structure are compared with those of conventional single QW HEMT. According to this work, the peak drain current of 651 mA/mm is achieved in conventional single QW HEMT, and the peak drain current of 758 mA/mm is achieved in proposed double QW HEMT. Also, the peak transconductances related to the proposed HEMT and conventional HEMT are compared. The peak current gain cut-off frequencies of two structures are compared. Also, the peak power gain cut-off frequencies of two structures are compared. According to these comparisons by simulation studies, the proposed double QW HEMT is more electrically efficient than the conventional single QW HEMT. Therefore, this present work may be a suitable prediction for the experimental fabrication of proposed double QW HEMT in future. This work may be suitable in sensor related applications and high frequency applications.

The Characteristics of 6-Inch GaN on Si RF HEMT with High Isolation Composited Buffer Layer Design

In this study, a 50-nm Al0.05Ga0.95N back barrier (BB) layer was used in an AlGaN/GaN high-electron-mobility transistor between the two-dimensional electron gas channel and Fe-doped/C-doped buffer layers. This BB layer can reduce the channel layer. The BB layer is affected by doped carriers in the buffer layer and the conduction energy band between the channel and the buffer layers. The Ion/Ioff ratio of the BB device was 4.66 × 105, and the ratio for the device without BB was 1.91 × 103. Lower leakage currents were obtained in the BB device because of the higher conduction energy band. The 0.25-μm gate length device with the BB exhibited a high current gain cutoff frequency of 24.4 GHz, and power gain cutoff frequency of 73 GHz.

AlInGaN/GaN HEMTs With High Johnson’s Figure-of-Merit on Low Resistivity Silicon Substrate

This work demonstrates high-performance AlInGaN/AlN/GaN high electron mobility transistors grown on 150 mm p-type low resistivity (resistivity~ 20-100 Ω-cm) silicon substrate with state-of-the-art Johnson's figure-of-merit (JFOM). Current gain cut-off frequency (fT) of 83 GHz and 63 GHz and power gain cut-off frequency (fmax) of 95 GHz and 77 GHz with a three-terminal off-state breakdown voltage of 69 V and 127 V, resulting in a high JFOM of 5.7 THz-V and 8.1 THz-V are achieved on the devices with a gate length of 0.16 μm and gate to drain distance of 2 μm and 4 μm, respectively. The fT and J-FOM are comparable or better than the reported values obtained on high resistivity silicon and SiC substrates for devices with similar gate length. On the other hand, GaN-on-Si HEMT structure on the LR-Si substrate exhibits lower power gain and power added efficiency due to strong capacitive coupling effects. TCAD large signal output power simulation indicates significant improvements in output power by minimizing the defects and free charge carriers in the GaN buffer even in the presence of the parasitic channel conduction and conductive silicon substrate. We further propose a modified equivalent circuit model of the parasitic conduction to take into account the conductivity of the GaN and AlGaN buffer.

Small signal analysis of ultra-wide bandgap Al0.7Ga0.3N channel MESFETs

We report RF small signal analysis of ultra-wide bandgap AlGaN channel MESFETs with Al composition of 70%. Ohmic contacts are achieved using a linearly-graded and heavily-doped AlGaN layer grown by metal organic chemical vapor deposition. The device with a gate length of 250 nm shows a drain current density (IDSS) of 370 mA/mm when the gate is shorted to source, unity current gain cutoff frequency (fT) of 8.8 GHz, and maximum oscillating frequency (fMAX) of 15 GHz. Bias-dependent device parameters are extracted from measured S-parameters based on a small-signal equivalent circuit model. The peak effective electron velocity of 2.9 × 106 cm/s is obtained at VGS = − 7 V. We show that the average electron velocity (ve) under the gate limits the device intrinsic RF performance while the high source access resistance (Rs) and drain access resistance (Rd) limits the device extrinsic RF performance.