Current Gain Cutoff Frequency Research Articles

Investigation on Fe-Doped AlGaN/GaN HEMT at 148 GHz Using E-FPL Technology for High-Frequency Communication Systems

In this research work, design of the Extended Field Plate Length (E-FPL) T-gate with Fe doped AlGaN buffer structure on the graded Aluminum Gallium nitride (AlGaN)/ Gallium nitride (GaN) high electron mobility transistor (HEMT) is proposed. The gate length of 60 nm with an ExFPL up to 50 nm towards the drain shows remarkable improvement in breakdown voltage. Meanwhile, the drain current (IDS) and transconductance (GM) is further improved by the Fe doped AlGaN Buffer design. In radio frequency (RF) small signal analysis this device exhibits a peak current-gain cutoff frequency fT of 148 GHz. This device has improved transconductance of 24% with high frequency has compared with conventional GaN HEMT device. It is highly compatible with military applications such as Radio Frequency (RF) upstream transmitters, ship and aircraft communication transmitters and High-frequency Radars (HFRs).

Aligned Carbon Nanotube Arrays with Germanium Protective Layers for Improving the Performance of Radio Frequency Transistors

Aligned carbon nanotube arrays with high semiconducting purity and high density have been regarded as an ideal channel material for constructing high-frequency field effect transistors and high-speed integrated circuits. However, contaminants (mainly resist residues) that leave the surface of carbon nanotubes during the fabrication process seriously deteriorate the interface contact quality, which will trigger large contact resistance and thus inhibit the ultimate performance of the carbon nanotube-based transistors. Here, we demonstrate a germanium protective layer technique that can keep a clean surface of carbon nanotube films from the contaminants during device fabrication and thus boost the quality of ohmic contact between carbon nanotubes (CNTs) and metal. The transfer length method (TLM) is used to evaluate the effect of the germanium protective layer technique on the ohmic contact resistance. The contact resistance from metal–CNTs extracted using the TLM was reduced by 93%, from 1.66 to 0.123 KΩ μm before and after the germanium process treatment. Owing to the great improvement of contact between metal and CNTs by introducing the germanium protective layer technique, the fabricated aligned CNT array-based radio-frequency field-effect transistors with a gate length of 110 nm on the quartz substrate present excellent DC performance, with an on-state current of 1.28 mA/μm and maximum transconductance of up to 1.05 mS/μm at a bias of −1.2 V. Meanwhile, the as-measured current gain cut-off frequency (fT,EXT) and power gain frequency (fMAX,EXT) increase from 12 to 110 GHz and 13 to 105 GHz, respectively. This approach provides a simple and reproducible means of improving the interface quality and reducing contact resistance in CNT-based devices to enhance performance.

Study of GaN/AlGaN air structure gate HEMTs with high linearity for RF applications

The effect of a novel float gate HEMT with Gan cap under the gate is studied, its DC and RF characteristics have been shown by using SILVACO TCAD tool, as contrast, the simulation of the conventional T shape gate hemt, which fitting well with the experimental result, is also demonstrated. The proposed structure offers approximately 5 times improvement in power gain cutoff frequency (fmax) and current gain Cut-off frequency(fT) (from 5.68 and 3.7 GHz to 30.1 and 20.1 GHz, respectively.) and it greatly enhances the linearity of the Gan based HEMT, a much flatter curve for fT/fmax versus gate voltage are also shown, and 1 V positive threshold voltage shift is gained, meanwhile the off-state drain leakage current is also improved to a certain extend, therefor the hemt obtains a much higher Ion/Ioff ratio, without sacrificing the saturate current. Besides, the degradation of drain current due to the self-heating effect is also ameliorated by applying the novel structure. Finally, the corresponding electrical characteristic changes are systematically analyzed according to the energy band and other schematic diagrams, the physical insight is given in explaining the mechanism inside.

Impact of Output Conductance on Current-Gain Cut-Off Frequency in InxGa1-xAs/In0.52Al0.48As Quantum-Well High-Electron-Mobility Transistors on InP Substrate

In this study, we investigated the impact of intrinsic output conductance (goi) on the short-circuit current-gain cut-off frequency (fT) in InxGa1-xAs/In0.52Al0.48As quantum-well (QW) high-electron-mobility transistors. At its core, we attempted to extract values of fT using a simplified small-signal model (SSM) of the HEMTs and to derive an analytical formula for fT in terms of extrinsic model parameters that are related with intrinsic model parameters of a general SSM. We projected how fT was influenced by goi in HEMTs, emphasizing that the improvement in electrostatic integrity would also be of critical importance to fully benefit from scaling down Lg.

Novel Stacked Passivation Structure for AlGaN/GaN HEMTs on Silicon With High Johnson’s Figures of Merit

We present a high-performance AlGaN/GaN high electron mobility transistors (HEMTs) on silicon substrate with novel stacked passivation layer (HfO2/SiO2). The stacked passivation structure can effectively modulate the electric field and reduce the electric field peak on the gate side, thus improving the breakdown voltage of the device. The prepared device with a gate length of 450 nm has a unit current gain cutoff frequency (fT) of 31.5 GHz, a maximum oscillation frequency (fMAX) of 46.3 GHz, and a three-terminal OFF-state breakdown voltage (BVgd) of 140 V at the gate-drain distance of 2.3 μm. The estimated Johnsonfs figure of merit (J-FOM=BVgd×fT) is 4.4 THz∙V, which is three and five times higher than that of the device with single HfO2 passivation layer and single SiO2 passivation layer, respectively. Furthermore, a significant suppression of the current collapse ( 5.7%) is observed due to the electric field redistribution near the drain region. The results show that the AlGaN/GaN HEMTs with stacked passivation layer proved to be a promising candidate for high-performance radio frequency (RF) power device applications.

Research on self-supporting T-shaped gate structure of GaN-based HEMT devices

A self-supporting T-shaped gate (SST-gate) GaN device and process method using electron beam lithography are proposed. An AlGaN/GaN high-electron-mobility transistor (HEMT) device with a gate length of 100 nm is fabricated by this method. The current gain cutoff frequency (f T) is 60 GHz, and the maximum oscillation frequency (f max) is 104 GHz. The current collapse has improved by 13% at static bias of (V GSQ, V DSQ) = (–8 V, 10 V), and gate manufacturing yield has improved by 17% compared with the traditional floating T-shaped gate (FT-gate) device.

Effect of the Indium Compositions in Tri-Gate InxGa1−xAs HEMTs for High-Frequency Low Noise Application

In this paper, we investigated the tri-gate InxGa1−xAs high electron mobility transistors (HEMTs) with different indium compositions for low noise applications. The tri-gate configuration in this work exhibits better device performances of the transconductance (gm), the current gain cutoff frequency (fT), the maximum oscillation frequency (fmax), and the minimum noise figure compared with the conventional planar structure due to the improved gate controllability. The indium contents of 20%, 40%, and 100% tri-gate devices were also fabricated for comparison. The resistances and leakage current were measured to investigate the effect between the indium compositions and the noise figure. Experimental results exhibited that the tri-gate In0.4Ga0.6As mHEMT with neither the highest transconductance nor the lowest gate leakage current exhibited the lowest minimum noise figure (NFmin) of 2 dB when operating at 50 GHz. The study reveals that device architecture and indium composition are important factors in the determination of noise performance.

Heterogeneous and Monolithic 3D Integration Technology for Mixed-Signal ICs

For next-generation system-on-chips (SoCs) in diverse applications (RF, sensor, display, etc.) which require high-performance, small form factors, and low power consumption, heterogeneous and monolithic 3D (M3D) integration employing advanced Si CMOS technology has been intriguing. To realize the M3D-based systems, it is important to take into account the relationship between the top and bottom devices in terms of thermal budget, electrical coupling, and operability when using different materials and various processes during integration and sequential fabrication. In this paper, from this perspective, we present our recent progress of III-V devices on Si bottom devices/circuits for providing informative guidelines in RF and imaging devices. Successful fabrication of the high-performance InGaAs high electron mobility transistors (HEMTs) on the bottom ICs, with a high unity current gain cutoff frequency (fT) and unity power gain cutoff frequency (fMAX) was accomplished without substrate noise. Furthermore, the insertion of an intermediate metal plate between the top and bottom devices reduced the thermal interaction. Furthermore, the InGaAs photodetectors (PDs) were monolithically integrated on Si bottom devices without thermal damage due to low process temperature. Based on the integrated devices, we successfully evaluated the device scalability using sequential fabrication and basic readout functions of integrated circuits.

Improvement of DC and f T performances of graded-channel HEMTs by polarization engineering

The graded-channel high-electron-mobility transistors with graded AlGaN buffer are investigated in this paper by Atlas drift-diffusion simulation. The short-channel effects are suppressed in a manner by employing the graded AlGaN buffer instead of the fixed Al-content AlGaN buffer. Then, the Al-content of the graded AlGaN channel is also optimized. The flatter and wider transconductance and current gain cutoff frequency (f T) curves are garnered by utilizing the graded AlGaN channel whose top Al-content is the same as the AlGaN barrier. At the gate length (L G) of 50 nm, the saturated drain current of the proposed device is 0.98 A mm−1, which is 34% higher than the reference device. Simultaneously, the f T and f T × L G are also analyzed with the gate length from 50 nm to 250 nm. The f T of the proposed architecture is 181 GHz at L G = 50 nm and V GS = 1 V which is 12% higher than the reference device under the same conditions. The f T × L G is up to 19.2 GHz · μm at the gate length of 250 nm, and it obtains a 12% improvement over the reference device.

20.2 GHz‐µm fT–LG in InAlN/GaN‐on‐Si High Electron Mobility Transistors

Herein, InAlN/GaN‐on‐Si high‐electron‐mobility transistors (HEMTs) with an fT–LG product of 20.2 GHz–μm are demonstrated. The device with a gate length of 200 nm and a source–drain spacing of 900 nm exhibits a peak transconductance of 543 mS mm−1, an ION/IOFF ratio of ≈107, a maximum on‐current of 2.4 A mm−1, and an on‐resistance of 1.07 Ω mm. Small‐signal characteristics show a unity current gain cutoff frequency of 101 GHz. Delay time analysis is performed to evaluate various delay components and their contribution to the small‐signal performance of the device. An effective electron velocity of 1.56 × 107 cm s−1 is estimated in these devices, which minimizes the intrinsic delay of the transistor. The factors limiting the fT–LG product in deeply scaled devices are discussed using the delay analysis.

RF performance enhancement in sub-μm scaled β-Ga2O3 tri-gate FinFETs

In this Letter, we report on the enhanced radio frequency (RF) performance in sub-micrometer scaled β-Ga2O3 tri-gate FinFETs. With a 200-nm-thick β-Ga2O3 bulk channel and a 0.35 μm gate length, the FinFETs exhibit an improved current-gain cutoff frequency of 5.4 GHz and a maximum oscillation frequency of 11.4 GHz, which are 20% and 58% improved with respect to the planar counterpart, respectively. The improved RF performance results from the enhanced gate control capability and the suppressed short-channel effects, as evidenced by the improved pinch-off characteristics, the improved transconductance, and the suppressed output conductance. It suggests that the tri-gate multi-fin architecture is a promising strategy to break the scaling limitation of the gate-channel aspect ratio toward high-performance β-Ga2O3 RF MOSFETs.

Enhanced drain current and cut off frequency in AlGaN/GaN HEMT with BGaN back barrier

The DC and RF capability of GaN high electron mobility transistor (HEMT) was enhanced by incoorporating BGaN back barrier (BB). Different types of back barriers like AlGaN, BGaN, AlN, AlInN, InGaN and p-diamond was used and the small and large signal RF characteristics were simulated and compared at gate length of 0.8 µm. The AlGaN/GaN HEMT with BGaN back barrier exhibited the highest drain current density of 1.45 A/mm at drain voltage of VD = 10 V. Also, the device with BGaN back barrier had a transconductance of 275 mS/mm at drain voltage of VD = 10 V. The highest value of current gain cutoff frequency (fT) of 27 GHz was attained for HEMT with BGaN back barrier. At 100 nm gate length, the device with BGaN back barrier exhibited the highest fT of 118 GHz. The voltage gain of the devices is also simulated, BGaN back barrier device exhibited better performance above 12 GHz. The BGaN back barrier device exhibited better performance in terms of drain current, transconductance, current gain cut off frequency, voltage gain and linearity. Thus, the device with BGaN back barrier has a good potential for high frequency and high gain power applications that require highly linear devices.

High-Frequency Operation of Vertical Organic Field-Effect Transistors.

The high‐frequency and low‐voltage operation of organic thin‐film transistors (OTFTs) is a key requirement for the commercial success of flexible electronics. Significant progress has been achieved in this regard by several research groups highlighting the potential of OTFTs to operate at several tens or even above 100 MHz. However, technology maturity, including scalability, integrability, and device reliability, is another crucial point for the semiconductor industry to bring OTFT‐based flexible electronics into mass production. These requirements are often not met by high‐frequency OTFTs reported in the literature as unconventional processes, such as shadow‐mask patterning or alignment with unrealistic tolerances for production, are used. Here, ultra‐short channel vertical organic field‐effect transistors (VOFETs) with a unity current gain cut‐off frequency (f T) up to 43.2 MHz (or 4.4 MHz V−1) operating below 10 V are shown. Using state‐of‐the‐art manufacturing techniques such as photolithography with reliable fabrication procedures, the integration of such devices down to the size of only 12 × 6 µm2 is shown, which is important for the adaption of this technology in high‐density circuits (e.g., display driving). The intrinsic channel transconductance is analyzed and demonstrates that the frequencies up to 430 MHz can be reached if the parasitic electrode overlap is minimized.

Effect of InGaN Channel on Radio‐Frequency Performance in High‐Electron‐Mobility Transistors with an InAlGaN Barrier

The effect of the InGaN channel on the performance of high‐electron‐mobility transistors (HEMTs) through the Silvaco Atlas simulator is investigated in detail. It is shown that the 2D electron gas (2DEG) density and carrier confinement of the device can be enhanced by replacing the GaN channel with the InGaN channel. The higher 2DEG density significantly increases the saturation drain current density, thus improving the current drive capability of the device. Meanwhile, better carrier confinement alleviates the short channel effects (SCEs) and traps state‐related current collapse in the GaN buffer, effectively improving the reliability of the device. Better carrier confinement also increases the current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) to 133 and 226 GHz, while the fT and fmax of conventional GaN channel HEMTs are 104 and 167 GHz, respectively. These results indicate that AlInGaN/InGaN HEMTs achieve better performance in direct current (DC) and radio frequency (RF).

Heterogeneous and Monolithic 3D Integration of III-V-Based Radio Frequency Devices on Si CMOS Circuits.

Next-generation wireless communication such as sixth-generation (6G) and beyond is expected to require high-frequency, multifunctionality, and power-efficiency systems. A III-V compound semiconductor is a promising technology for high-frequency applications, and a Si complementary metal-oxide-semiconductor (CMOS) is the never-beaten technology for highly integrated digital circuits. To harness the advantages of these two technologies, monolithic integration of III-V and Si electronics is beneficial, so that there have been everlasting efforts to accomplish the monolithic integration. Considering that the on horizon 6G wireless communication requires faster and more energy-efficient system-on-chip technologies, it is imperative to realize a radio frequency (RF) system in which III-V technology and Si CMOS technology are integrated at a device level. Here we report heterogeneous and monolithic three-dimensional (3D) analog/RF-digital mixed-signal integrated circuits that contain two types of InGaAs high-electron-mobility transistors (HEMTs) designed for high fT and fMAX in the top and Si CMOS mixed-signal circuits consisting of an analog-to-digital converter and digital-to-analog converter in the bottom. A high unity current gain cutoff frequency of 448 GHz and unity power gain cutoff frequency of 742 GHz have been achieved by the fT oriented and fMAX oriented InGaAs HEMTs, respectively, without being affected by mixed-signal interference. At the same time, the bottom Si CMOS circuits provide valid signals without any performance degradation by the integration process.

In0.3Ga0.7As heterojunction bipolar transistor grown on GeSi substrate for high-frequency application

We report an In0.3Ga0.7As HBT device grown on a 200 mm Si wafer using GeSi as virtual starting substrate and InAlAs as the compositionally graded buffer layer from GaAs to In0.3Ga0.7As lattice constant. A DC gain, emitter-base, and base-collector ideality factors of 10, 1.43, and 1.56, respectively, are obtained for a device with an emitter area of 40 × 50 μm2. Small-signal simulation of an In0.3Ga0.7As HBT device with 2 × 8 μm2 emitter area shows that current gain cutoff frequency (fT) and maximum cut-off frequency (fMax), of 50 GHz and 220 GHz, respectively, can be achieved with base doping and layer thickness of 2 × 1018cm−3 and 30 nm, respectively.

Effect of GaN cap layer on the performance of AlInN/GaN-based HEMTs

The effect of the GaN cap layer on the performance of AlInN/GaN-based HEMTs has been studied. Detailed analysis of the DC characteristics reveals that the addition of the GaN cap layer reduces the gate leakage current and increases the saturation drain current of HEMT. We have observed a slight increase in the two-dimensional electron gas density on the addition of the GaN cap layer. The addition of the GaN cap layer shifts the threshold voltage towards the negative direction, reduces the off-state drain leakage current, improves subthreshold swing, and enhances the ION/IOFF ratio of HEMT. The TCAD simulation shows that the addition of the GaN cap layer reduces the peak electric field at the drain side edge of the gate and improves the breakdown voltage. From the double pulsed ID-VDS measurement, we have found that the presence of the GaN cap layer reduces the current collapse due to gate-lag and drain-lag by passivating the surface traps of the access regions. Although there is a slight reduction in transconductance, the current gain cut-off frequency (fT) of the HEMT with GaN cap is higher than the HEMT without GaN cap.

A Dielectrically Modulated AlGaN/InN/GaN Nanoelectronic High Electron Mobility Transistor based Biosensor for Protein Detection

In this work, a high electron mobility transistor (HEMT) based biosensor is designed to detect the virus-protein. Conduction band engineering of the biosensor is studied. DC and RF properties of the designed biosensor are studied. Sensitivity of the biosensor is studied corresponding to electric field, surface potential, drain current, transconductance, and current gain cut-off frequency. Sufficient sensitivity is obtained corresponding to each electrical parameter to detect the virus-protein. This work may be helpful to design and experimentally fabricate the HEMT based biosensor.

8.7 W/mm output power density and 42% power-added-efficiency at 30 GHz for AlGaN/GaN HEMTs using Si-rich SiN passivation interlayer

In this work, high-performance millimeter-wave AlGaN/GaN structures for high-electron-mobility transistors (HEMTs) are presented using a Si-rich SiN passivation layer. The analysis of transient and x-ray photoelectron spectroscopy measurements revealed that the presence of the Si-rich SiN layer leads to a decrease in the deep-level surface traps by mitigating the formation of Ga–O bonds. This results in a suppressed current collapse from 11% to 5% as well as a decreased knee voltage (Vknee). The current gain cutoff frequency and the maximum oscillation frequency of the devices with the Si-rich SiN layer exhibit the values of 74 and 140 GHz, respectively. Moreover, load-pull measurements at 30 GHz show that the devices containing the Si-rich SiN deliver excellent output power density of 8.7 W/mm at Vds = 28 V and high power-added efficiency up to 48% at Vds = 10 V. The enhanced power performance of HEMTs using Si-rich SiN interlayer passivation is attributed to the reduced Vknee, the suppressed current collapse, and the improved drain current.

Investigation on the Influence of Ohmic Structure on Channel-to-Channel Coupling Effect in InAlN/GaN Double Channel HEMTs

In this paper, the impact of ohmic structure on channel-to-channel (C2C) coupling effect in InAlN/GaN double channel (DC) HEMTs is systematically analyzed and studied. For the un-recessed ohmic structure, the electrons in the upper channel can easily inject into the bottom channel due to the ultra-thin InAlN back barrier layer. Therefore, the maximum drain current and transconductance peak of the bottom channel significantly increase. For recessed ohmic structure, the reduced vertical electric field strength of the upper channel can effectively weaken the coupling effect between the two GaN channels. Benefiting from the suppressed vertical transport of electrons in the upper channel, higher drain current and transconductance of the upper channel are obtained in the recessed ohmic structure. In addition, the transmission electron microscope (TEM) microstructural analysis of the DC HEMTs with recessed ohmic structure was also performed. This shows that the recessed ohmic structure can modulate the electron transport mode in the InAlN/GaN DC HEMTs. The coupling effect of the two channels will play a major role in influencing the characteristics of current gain cutoff frequency (fT) / maximum power gain cutoff frequency (fmax) versus VGS and have a significant effect on large-signal characteristics, which is quite attractive for the fabrication of power microwave GaN-based HEMTs with wide gate swing.