RF Characteristics Research Articles

Reduction in Self-Heating Effect of SOI MOSFETs by Three Vertical 4H-SiC Layers in the BOX

In this paper a novel structure is proposed for silicon on insulator MOSFETs which improves DC and RF characteristics by three vertical layers of 4H-SiC. Vertical layers are in parallel and extended from silicon drift region toward the substrate through oxide region as heating passageways. These additional layers absorb the heat of active region and transfer to the substrate area. Thus, large value of temperature variation arising from high gate and drain biasing in SOI devices is reduced by applying the proposed structure. It reduced from ~690 K to ~353 K at VG = 10 V. The negative differential resistance is diminished and carriers mobility improved which result in higher and more stable saturation current in comparison with conventional structure. Also, the resultant device has lower delay time. Gate capacitances are approximately equal to the conventional structure but its higher transconductance results in more than 3-times higher cut-off frequency and about 75% improvement in maximum oscillation frequency, at VG = 10 V and VD = 3.5 V. Widespread simulations and comparisons demonstrate that this structure can be considered in high power and RF applications.

An Angelov Large-Signal FET Model Up To 67 GHz

A modified Angelov large-signal field effect transistor model is proposed in which dispersion branches are neglected. A systematic procedure is built up to directly extract all the key model parameters from hybrid measurements including dc and RF characteristics. Source-pull and load-pull iterations are conducted to verify the accuracy of large-signal performances. Owing to the effective parameter extraction and RF de-embedding, the modeled results show an excellent agreement with the measured ${I}$ – ${V}$ relations and multi-bias S-parameters up to 67 GHz. Output power and power added efficiency are sufficiently validated at 30 GHz.

Characterization of InP-based pseudomorphic HEMT with T-gate

This paper proposes two structures of InAlAs/InGaAs-based pseudomorphic high electron mobility transistor (PHEMT): one with rectangular-gate and another with T-gate. Both the proposed PHEMTs consist of an In0.52Al0.48As supply/barrier layer and In0.53Ga0.47As channel layer built on an InP substrate. The proposed InAlAs/InGaAs-based PHEMT with rectangular-gate exhibits 1.32 × increment in drain current and 0.55 × decrement in threshold voltage compared to those of AlGaAs/GaAs-based previously proposed HEMT on GaAs substrate. This is because of the role of indium in the new materials used for the proposed device layers. The proposed InAlAs/InGaAs-based PHEMT with T-gate exhibits further improvements in DC and RF characteristics. The PHEMT with T-gate shows 1.42 ×/1.14 ×/1.4 × increment in drain current/cut-off frequency/maximum oscillation frequency respectively compared to the PHEMT with rectangular-gate. It also exhibits 0.67 × decrement in noise figure compared to that of PHEMT with rectangular-gate. All the theoretical results are verified with the simulation results obtained while analyzing the structures considered in this work. The simulation results were recorded while simulating the devices using Silvaco Atlas.

Analysis of Passivation Techniques in InP HEMTs and Implementation of an Analytical Model of fT Based on the Small Signal Equivalent Circuit.

This paper analyses, the influence of Si₃N₄-PECVD and Al₂O₃-ALD surface passivation on the DC and RF characteristics of InP HEMTs with different gate lengths 0.08 μm, 0.1 μm, 0.12 μm, and 0.15 μm. A significant improvement in maximum drain current IDS, MAX, transconductance gm, MAX and oscillation frequency fmax, MAX is obtained by scaling the thickness of the passivation layers An increase in gm, MAX and fmax, MAX, fT, MAX is observed by reducing parasitic capacitance w.r.t. the decrease in gate length. In addition, an analytical model of fT based on a small-signal equivalent circuit is developed, which consist of extrinsic parameters Rs, Rd, Cgs_ext and Cgd_ext and intrinsic parameters Cgsi, Cgdi, gmi and goi. The carrier transport is improved by increasing gmi, thus the transit time τt , the parasitic charging delay τext and the τpar are reduced by lowering the extrinsic capacitances. An excellent fitting between measured and simulated fT is achieved, which inturn leads a realistic way for further improvement in fT.

Mid-plane PAM launcher study for KSTAR LHCD system

A prototype of a midplane passive active multijunction (PAM) antenna was fabricated for the lower hybrid current drive system of KSTAR. The antenna includes a PAM launcher, bidirectional couplers, power dividing components, and two RF windows. The RF characteristics of each component, such as the splitting ratio, phase shift, transmission, and reflection, were measured using a network analyzer. A taper adapter and matched load, which can be inserted into the active waveguide of the PAM mouth, were designed and fabricated for the phase shift and power coupling measurement. The maximum error and the standard deviation of measured phase shifts between adjacent active waveguides of the PAM were 6.5° and 2.28°, respectively. The design improvement of the mid-plane PAM launcher is suggested. Multiple round trips of the reflected field in a multijunction provides the advantage of lowering the reflection but, at the same time, it causes the deterioration of directivity and an increase of the electric field in the waveguide. Adding a hybrid splitter at the end of the multijunction structure reduces the reflection by redirecting the reflection to plasma as in multijunction, however, contrary to the multijunction, it does not switch the toroidal direction of phase progression and thus improves the antenna directivity. The directivity of the hybrid PAM increases by more than 10% and the reflection decreases to 1/3–1/100 in comparison with the prototype PAM.

Design and Analysis of MEMS Shunt Capacitive Switch with Si3N4 Dielectric and Au Beam Material to Improve Actuation Voltage and RF Performance in Consideration With and Without Circular Perforations

This paper presents the design of a MEMS shunt capacitive switch with fixed–fixed beam for high frequency RF applications. The switch dimensions were very carefully chosen to obtain the optimum performance of the switch when actuated with RF transmission line. The designed switch uses two different structures: beam without perforations and beam with circular perforations with same switch dimensions. Spring constant of the switch with perforations shows reduction in requirement of actuation voltage due to significant reduction in spring constant. Actuation voltage analysis was also done for two structures and the actuation voltage for switch with perforations found to be 6.80 V which is 35.23% less compare to switch without perforations (10.5 V). RF characteristics in terms of Insertion loss, return loss and isolation found to be − 0.05 dB, − 43 dB and − 12 dB without perforations and it was − 0.03 dB, − 48 dB and − 15.5 dB for the switch with perforations at 62 GHz frequency. The switch designed with circular perforations shows improvement in insertion loss, return loss and isolation by 20%, 15% and 24% respectively compare to switch without perforations. The switch can be used for V-band applications like satellite communications and RF applications.

Silicon Photonic IQ Modulators for 400 Gb/s and Beyond

Silicon photonics has enormous potential for ultrahigh-capacity coherent optical transceivers. We demonstrate an in-phase and quadrature (IQ) modulator using silicon photonic traveling-wave modulators optimized for higher order quadrature amplitude modulation (QAM). Its optical and RF characteristics are studied thoroughly in simulation and experiment. We propose a system-orientated approach to optimization of the silicon photonic IQ modulator, which minimizes modulator-induced power penalty in a QAM transmission link. We examine the tradeoff between modulation efficiency and bandwidth for the optimal combination of modulator length and bias voltage to maximize the clear distance between adjacent constellation points. This optimum depends on baud rate and modulation format, as well as achievable driving voltage swing. Measured results confirm our prediction using the proposed methodology. Without precompensating bandwidth limitation of the modulator, net data rates up to 232 Gb/s (70 Gbaud 16-QAM) on single polarization are captured, indicating great potential for 400+ Gb/s dual-polarization transmission.

Wafer Scale Mapping and Statistical Analysis of Radio Frequency Characteristics in Highly Uniform CVD Graphene Transistors

AbstractRadio frequency (RF) transistor based on graphene has attracted tremendous research efforts in the past few years. Despite the fact that such material is developed on a wafer‐scale level, the majority of reported high performance of individual transistors is limited to individual or a few devices. As a result, the electronic uniformity and stability study on a large number of transistors remain unexplored especially for RF performance, which are the most critical factors for any practical applications. In this work, a comprehensive statistical analysis of the uniformity of DC and RF characteristics simultaneously for hundreds of transistors fabricated from transferred large‐area CVD‐grown graphene in a 4‐inch HfSiO/Si wafer is carried out for the first time. For devices with the same gate length of 0.8 µm, the coefficient of variation (CV) for Dirac point voltage and extrinsic peak transconductance is only 0.07 and 0.03, respectively. In addition, the intrinsic f T*L g is high up to about 20 GHz · μm, which is among the best value for the graphene RF transistors. More importantly, the CV for the as‐measured f max/f T is as low as 0.11, indicating highly uniform RF characteristics across the 4‐inch wafer.

2D study of AlGaN/AlN/GaN/AlGaN HEMTs’ response to traps

In this work, the effects of GaN channel traps and temperature on the performance of AlGaN/AlN/GaN/AlGaN high electron mobility transistors (HEMTs) on Si (111) substrate, were investigated. 2D simulations carried out using the Silvaco TCAD simulator tool for different drain and gate voltages showed that acceptor-like traps in the channel have a significant influence on the DC and RF characteristics. It was found that deeper acceptors below the conduction band with larger concentration have a more pronounced effect on the transistor performance. Meanwhile, the donor-like traps show no influence. Pulsing the device with different pulse widths and bias conditions, as well as increasing temperature, showed that the traps are more ionized when the pulse is wider or the temperature is higher, which can degrade the drain current and thus the DC characteristics of the transistor. Passivation of the transistor has also a beneficial effect on performance.

A macro model of RF Schottky diode in 22-nm CMOS and its application

RF Schottky Barrier Diode (SBD) device can be compatible with deep submicron CMOS process, which is a research edge-cutting technology in the field of microelectronics. An accurate device model is highly required by the relevant circuit simulation work. In this paper, a macro device model of SBD in 22 nm CMOS node is developed based on the actual device structure. To increase its accuracy, a novel iterative algorithm is employed during the model parameter extraction. The simulation results are consistent with experimental data in frequency range from 10 MHz to 10 GHz, indicating that the developed SBD model can accurately reflect the DC and RF characteristics of the 22 nm device. Moreover, the application of the developed RF SBD device model is verified based on RF energy harvesting circuit in terms of the output voltage and efficiency, showing the feasibility of the developed SBD model in RF integrated circuit.

Design and analysis of 10 nm T-gate enhancement-mode MOS-HEMT for high power microwave applications

Abstract In this work, we propose a novel enhancement-mode GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with a 10 nm T-gate length and a high-k TiO2 gate dielectric. The DC and RF characteristics of the proposed GaN MOS-HEMT structure are analyzed by using a TCAD Software. The device features are heavily doped (n++ GaN) source/drain regions for reducing the contact resistances and gate capacitances, which uplift the microwave characteristics of the MOS-HEMT. The enhancement-mode GaN MOS-HEMTs showed an outstanding performance with a threshold voltage of 1.07 V, maximum extrinsic transconductance of 1438 mS/mm, saturation current at VGS = 2 V of 1.5 A/mm, maximum current of 2.55 A/mm, unity-gain cut-off frequency of 524 GHz, and with a record maximum oscillation frequency of 758 GHz. The power performance characterized at 10 GHz to give an output power of 29.6 dBm, a power gain of 24.2 dB, and a power-added efficiency of 43.1%. Undoubtedly, these results place the device at the forefront for high power and millimeter wave applications.

Analysis of nonlinear characteristics of a graphene based four-terminal ballistic rectifier using a drift-diffusion model.

In this study, rectification behavior and noise spectra of a graphene based four-terminal ballistic rectifier are reported utilizing semi-classical drift-diffusion 3D modeling. The room temperature DC and RF characteristics of the novel rectifier are demonstrated considering the traps in the material similar to a real device, reducing the rectification efficiency from 0.5% to 0.35%. The responsivity and noise equivalent power of about 89.21 mV mW−1 and 97.52 pW Hz−1/2, respectively, are obtained for different frequencies varying from 50 Hz to 1 THz. Furthermore, the noise spectral analysis of the device predicts a minimum low frequency noise, which depends upon the carrier concentration inside the device active region rather than mobility, and hence enables potential applications as THz detectors for imaging.

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

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

Analysis of AlGaN/GaN HEMT using discrete field plate technique for high power and high frequency applications

In this paper, the RF and DC characteristics of AlGaN/GaN High electron mobility transistor is analysed using discrete field plate technique. Surprisingly, it reduces the device parasitic capacitance exhibiting very low CGS and CGD of 5.8 × 10−13 F/mm and 4.2 × 10−13 F/mm respectively to improve the cut off frequency (fT) from 17.5 GHz to 20 GHz. The discrete field plate suppresses the maximum electric field between gate and drain region to achieve the high breakdown voltage of 330 V. The maximum transconductance (gm) achieved is 275 mS/mm, ensuring the better DC operation of the device. The simulated results clearly show that, the discrete field plate HEMTs are superior in performance over conventional GaN FP-HEMTs for future high frequency and high power applications.

RF Characteristics of Graphene for Reconfigurable Antennas

RF Characteristics of Graphene for Reconfigurable Antennas

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

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

DC and RF characteristics optimization of AlGaN/GaN/BGaN/GaN/Si HEMT for microwave-power and high temperature application

Abstract AlGaN/GaN/Si high electron mobility transistors (HEMTs) developed by molecular beam epitaxy (MBE) are studied with several methods for characterization, the most utilized are direct-current and radio-frequency measurements, to see power and microwave performance of components. The increase in these parameters is not based just with on improvement technological for example, decrease of length gate (Lg) and passivation. For sure, another very important point is to reduce the thickness of barrier while keeping the reduction in the length of gate, in order to reduce the transit time (τ), and consequently access to highest cut-off frequency (FT). For this situation, it’s appears a harmful phenomenon of type “punch-through”, because of the weak confinement of electrons in the channel. In this paper, the main objective is to show how to reduce this effect.

Broadband low‐loss power splitter based on ferrite cores

A broadband 3-dB power splitter based on ferrite cores is proposed for RF communication systems. This power splitter is developed from the transformer-type Wilkinson power splitter, where lumped components are detailed designed to achieve excellent input and output impedance match in an ultra-wide bandwidth (300 kHz–400 MHz). The power splitter demonstrates better RF characteristics in comparison with former designs. The voltage standing wave ratios of the input and output ports are 20 dB, the amplitude imbalance is <0.04 dB, and the insertion loss is <0.5 dB. Such power splitters have small dimensions and very low costs.

Analog and RF Characteristics of Power FinFET Transistors With Different Drain-Extension Designs

Analog and RF characteristics of power FinFET transistors with different drain-extension structures are investigated for microwave integrated circuit applications. The power FinFETs were designed based on the drain-extended MOSFET structure and fabricated using a standard low-voltage FinFET process. Three various drain-extension configurations are demonstrated and compared. With the low-doped drain extension, the breakdown voltage of power FinFETs is higher than 6.5 V for all samples. For standard power devices, where the drain extension is performed with narrow fins, a high drain resistance is inevitable, resulting in high on-resistance and poor analog and RF performances. For devices with wide drain-extension fins (wide drain FinFET) or a planar drain extension (hybrid FinFET), lower drain resistances are obtained owing to the larger extension width. Therefore, the on-resistances of the wide drain and hybrid devices are much lower than that of the standard counterpart. Moreover, these devices with modified drain extensions also exhibit better analog and RF behaviors. The cutoff frequency of power FinFETs is boosted from 30 to 53 GHz when the drain extension is changed from narrow fins to a planar layout. These experimental results indicate that RF power FinFETs with good performance would be realized with the modified drain-extension designs.

A fiber based diamond RF B-field sensor and characterization of a small helical antenna

We present a microwave B-field scanning imaging technique using a diamond micro-crystal containing a nitrogen vacancy center that is attached to a fiber tip. We propose a pulsed modulation technique, enabling the implementation of a variety of pulsed quantum algorithms for state manipulation and fast readout of the spin state. A detailed mapping of the magnetic B-field distribution of a helical antenna with sub-100 μm resolution is presented and compared with numerical simulations. This fiber based microwave B-field probe has the advantages of minimized invasiveness and small overall size and will boost broad interest in a variety of applications where near field distribution is essential to device characterization, to name a few, antenna radiation profiling, monolithic microwave integrated circuit failure diagnosis, electromagnetic compatibility test of microwave integrated circuits, and microwave cavity field mode mapping.