RF Power Applications Research Articles

A Review of GaN Channel-Based MOSHEMTs for Next-Generation Medium/Low-Voltage Rating and High-Speed RF Power Applications

A Review of GaN Channel-Based MOSHEMTs for Next-Generation Medium/Low-Voltage Rating and High-Speed RF Power Applications

E-mode AlN/GaN HEMTs on Si with 80.4% PAE at 3.6 GHz for Low-Supply-Voltage RF Power Applications

E-mode AlN/GaN HEMTs on Si with 80.4% PAE at 3.6 GHz for Low-Supply-Voltage RF Power Applications

Investigation on effect of AlN barrier thickness and lateral scalability of Fe-doped recessed T-gate AlN/GaN/SiC HEMT with polarization-graded back barrier for future RF electronic applications

In this study, the influence of AlN barrier thickness (tb) on the RF & DC performances of 50 nm recessed T-gate Fe-doped AlN/GaN/SiC HEMT is investigated. The proposed HEMT incorporates a graded back-barrier (GBB) feature that raises the conduction band (CB) discontinuity at GaN/AlGaN junction to increase carrier confinement. With excellent electron confinement, the electrical characteristics for a 6 nm AlN barrier thickness show the highest transconductance of 468.9 mS/mm, a maximum ID of 1.546 A/mm, and a peak fT of 355 GHz at VDS = 2.5 V due to better epitaxial quality, and a reduction in parasitic channel generation due to GBB. When tb increases, the Vth decreases or becomes more negative i.e., moves left, which causes the ID to fall and degrades performance. This study also examines the influence of gate metals on the electrical performance of the proposed HEMT. According to the TCAD results, Pt-gate HEMTs had better RF performance. Furthermore, the simulation performed to examine the effects of scaling source-drain spacing (LSD) showed that the key to improving RF/DC performance is to reduce gate-to-drain and gate-to-source distances. It has been observed that the electron velocity of the HEMT is significantly influenced by the barrier thickness, LGS, and LGD. It comes as no surprise that this technology will be at the frontlines of future RF power applications.

High-directivity and compact microstrip coupler for RF power applications.

A microstrip coupler was designed, fabricated, and tested to monitor the power of the 500MHz kW-level amplifier modules currently installed in an 80-kW solid-state transmitter. The proposed coupler consists of multi-section coupled lines and employs a reverse-coupling scheme, achieving a very compact structure. The dual-side configuration with good termination enables the coupler to have high directivity and wide bandwidth without using any lump components for better temperature stability. Under a low-power test, the measured coupling is 37.69 dB with high directivity from 82 to 700MHz. The coupling is almost independent of the power at 499.65MHz, while the directivity slightly decreases to 33.85 dB at the input power of 1 kW. The maximal insertion loss of 0.08 dB was observed at 1-kW input power. The proposed directional coupler suits many high-power applications, especially in low-frequency regimes.

An intensive study on effects of lateral scaling and gate metals on the RF/DC performance of recessed T-gated Fe-doped AlN/GaN/SiC HEMTs for future RF and microwave power applications

In this simulation work, the effect of AlxGa1-xN and InxGa1-xN back barriers (BB) on the RF & DC performances of recessed T-gated Fe-doped AlN/GaN/SiC HEMT device is investigated. The novel HEMT achieved a peak GM of 435.9 mS/mm, the highest ID of 1.89 A/mm, and a maximum fT of 197.4 GHz with Al0.18Ga0.82N BB which can be attributed to enhanced mobility and carrier confinement in the quantum well (QW) due to the integration of BB, presence of Fe-doping in the GaN buffer in conjunction with recessed T-gate approach. On the other hand, the device with In0.20Ga0.80N BB recorded a peak GM of 434.9 mS/mm, a peak ID of 1.83 A/mm, and a maximum fT of 196.4 GHz. The flatness GM is attributable to the applied high drain bias of 5 V. The device performance deteriorated with an increase of Al and In mole fractions of the BB layers following an increased dislocation density which influenced the epitaxial quality of the heterostructures. This paper also investigates the impact of gate metals on the electrical performance of the Al0.18Ga0.82N and In0.20Ga0.80N BB devices. In both cases, the TCAD results revealed that the HEMT with lower ϕm (work function) gate metal i.e., Al-gate exhibited superior DC/RF performance. Owing to an uplift of the conduction band edge the performance degraded following the raise of the Schottky barrier that leads to the collection of the least number of carriers at the AlN/GaN interface hence resulting in poor sheet carrier density. Besides, the gate metal Pt with the highest work function of 5.65 eV is suitable to pursue E-Mode operation. In addition, the simulation to explore the impact of scaling source-drain spacing (LSD) revealed that limiting gate-to-drain distance (LGD) and gate-to-source distance (LGS) is the key to achieve enhance RF/DC performance. It is no surprise that this device is at the forefront of the future 5G/6G, military, defense, and RF power applications.

Investigation on impact of AlxGa1-xN and InGaN back barriers and source-drain spacing on the DC/RF performance of Fe-doped recessed T-gated AlN/GaN HEMT on SiC wafer for future RF power applications

The work function (φm) of gate metal is crucial to electrical characteristics in standard GaN-based high electron mobility transistors (HEMTs). In this simulation report, RF & DC performance of recessed T-gated Fe-doped AlN/GaN HEMT device with AlxGa1-xN back barrier (BB) and InGaN BB is explored by varying gate metal work functions which is a flexible approach to obtain wide modulation range of threshold voltage (Vth) with a positive shift. The simulations are carried out at an applied drain voltage of 1.4 V. As Al-content of AlxGa1-xN BB layer has an impact on surface roughness with GaN channel and effective mobility of electrons in the two-dimensional electron gas (2DEG), this work includes tuning the aluminum mole fraction. In comparison, the proposed device with Al0.15Ga0.85N BB layer exhibits high GM of 381.4 mS/mm with φm = 5.25 eV, highest ID of 0.702 A/mm with φm = 4.5 eV, and high fT/fmax of 173.1/247.4 GHz with φm = 5.25 eV which can be ascribed to enhanced mobility and carrier confinement in the quantum well due to integration of BB, presence of Fe-doping in the buffer in conjunction with recessed T-gate approach. Hence, optimized performance is achieved with Al0.15Ga0.85N BB layer at φm = 4.5 eV. In addition, we investigated the effect of scaling gate-to-source spacing (LGS) with constant gate-to-drain spacing (LGD) and vice-versa, on the device performance. The device with Al0.15Ga0.85N BB exhibited supreme performance at LGS = 300 nm with LGD = 800 nm, due to enhanced electric field component along the channel as a result of downscaling lateral device dimensions. No wonder, this device can be considered as most promising for future military, defence, and RF power applications.

A Π-shaped p-GaN HEMT for reliable enhancement mode operation

This paper presents a TCAD based investigation of virtually fabricated Π-shaped Gate p-GaN HEMT for reliable enhancement mode operation. A detailed comparison with the Conventional T-Gate counterpart, with a focus towards the trap related dispersive effect reveals the superiority of Π-shaped Gates P-GaN HEMT for suppressing both the vertical substrate and gate leakage currents, thereby enhancing the breakdown characteristics of the device. A modification of the electric fields, into a stepped profile, demonstrates effective suppression of the leakage through the surface defects, and spillover into GaN buffer, thereby mitigating the trap related dispersive effects. Dispersive effect of the two devices has also been compared using current Slump Ratio (SR) which is lower for Π-shaped Gate P-GaN HEMT. Further analysis into laterally scaled drain-access regions, demonstrates superiority of Π-shaped Gates in achieving a reliable thermal operation, and applicability of Π-shaped Gate P-GaN HEMT for future RF and High Power applications.

Electron mobility and velocity in Al0.45Ga0.55N-channel ultra-wide bandgap HEMTs at high temperatures for RF power applications

Ultra-wide bandgap AlGaN has attracted recent attention as a promising channel material for next-generation high electron mobility transistors (HEMTs) for RF power due to its high critical field, excellent transport properties, and potential for operation in extreme environments. However, the effects of temperature on the transport properties are not fully understood. Here, Al0.62Ga0.38N/Al0.45Ga0.55N HEMTs have been fabricated and characterized up to 150 °C at DC and RF to evaluate the effect of temperature on electron mobility and carrier velocity. Measured results indicate that both mobility and carrier velocity exhibit modest dependence on temperature, suggesting that AlGaN channel HEMTs are promising for future RF power applications.

From MHz to THz: Systems and Applications

This Special Issue is formed by collecting 46 regular papers on the topic of systems and applications, which reflects the latest progress in microwave systems and applications from MHz to THz. All those 46 papers are divided into six subtopics, namely, digital predistortion of RF power amplifiers (five articles), radar systems and applications (14 articles), wireless systems (nine articles), detectors and imaging (ten articles), microwave applications (five articles), and microwave power transfer technologies (three articles).

Multilayer SiNx passivated Al2O3 gate dielectric featuring a robust interface for ultralong-lifetime AlGaN/GaN HEMT

This paper presents a multilayer SiNx passivation-based robust and high-reliability interface for effective suppression of current collapse effect and reduction of leakage current at AlGaN/GaN heterostructure. The performance characterization of the fabricated HEMT reveals a high drain saturation current, peak extrinsic transconductance (up to 199.5 mS/mm), and dynamic RON/static RON of 1.067 even at a high drain voltage of 700 V. Moreover, an excellent mean time-to-failure of 2.204 × 108 h at an activation energy of 2.621 eV at TC = 150 °C is obtained, which indicates that the developed HEMT exhibits an ultralong operation lifetime for RF power applications.

A novel local impedance algorithm and contact force sensing to guide high power short duration radiofrequency ablation is efficient and safe for circumferential pulmonary vein isolation

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Local impedance (LI) drop can predict sufficient lesion formation during radiofrequency ablation (RF). Recently, a novel ablation catheter technology able to measure LI and contact force has been made available for clinical use. High power short duration (HPSD) RF ablation has been shown to be feasible for atrial fibrillation (AF) ablation with short procedure time. We used LI drop and plateau formation to guide duration of 50 Watt RF power applications for circumferential pulmonary vein isolation (PVI). Methods Consecutive patients with indication for de novo AF ablation (n = 32, age 65 ± 10 years) with paroxysmal (n = 16) or persistent (n = 16) AF underwent ultra high density 3D mapping of the left atrium and catheter ablation. Thereafter, ipsilateral PV encircling with 50 Watt RF-applications targeting an interlesion distance of ≤ 6mm and a contact force of 10-30g was performed. Duration of HPSD RF application between 7-15s was guided by impedance drop >20 Ohm and plateau formation of LI. Further ablation strategy was left to the investigator’s discretion. Esophageal temperature measurement was performed using a three thermistor catheter with temperature cut off 39.0°C. In case of temperature rise or very near esophageal contact to the circumferential line, RF application time was shortened to 7s. Patients underwent adenosine testing after PVI. Previously we performed all types of AF ablation using an LI guided HPSD ablation without contact force measurement capability in 80 patients. Results Complete PVI was achieved in all pts with only 13.5 ± 4.3 min cumulative RF application duration and an ablation procedure duration of 46.5 ± 10.4 min with the novel LI measuring catheter. First-pass isolation of ipsilateral veins was achieved in 75% of circles. Recurrence of PV conduction during waiting period (20min) and adenosine testing occured in 25% of circles, and was reablated in most patients with a single spot of HPSD application. Using 94 ± 36 RF application per patient, mean maximum LI drop was 23.6 ± 4.0 Ohm. Reconnected fibers were associated with low LI drop due to instability of contact in most cases due to breathing in case of difficult sedation of the patients. No serious complications occurred in all 32 pts using HPSD with the novel contact force catheter design. Conclusion Guiding of HPSD RF ablation by LI is highly efficient and safe. A novel local impedance algorithm in combination with contact force sensing enable short PVI times with low early recurrence of PV conduction. Prediction of permanent lesions seems possible and the only limitation seems to be unstable RF catheter contact due patients breathing. Follow up have to be waited.

AlInGaN/GaN double-channel FinFET with high on-current and negligible current collapse

In this work, we fabricated AlInGaN/GaN FinFETs and compare electrical performances with those of AlGaN/GaN FinFETs in different channel structures, such as single and double channel. The double-channel structure is promising to compensate for the degradation of the drain current density caused by the fin structure, as well as the FinFET structure is suitable to control the double-channel structure. The fabricated AlInGaN/GaN double channel FinFETs exhibit considerably higher maximum drain current of 290 mA/mm than those of AlGaN/GaN FinFETs such as 245 mA/mm and 165 mA/mm of double- and single-channel FinFETs, respectively. This is because of the high electron density caused by the strong polarization charge of AlInGaN/GaN heterostructure and double channel structure. Moreover, the double-channel FinFETs effectively suppress the current collapse. In conclusion, the AlInGaN/GaN double-channel fin structure is a very promising candidate for the GaN-based RF power applications.

CLOSE-guided Pulmonary Vein Isolation Using High Power and Stable RF Applications: a Randomized Study

CLOSE-guided Pulmonary Vein Isolation Using High Power and Stable RF Applications: a Randomized Study

Analysis of Deep Level and Oxide Interface Defects Using 100V HF Schottky Diodes and MOS CV for Silicon and 4H SiC HV MOSFETs, Advanced Power Electronics, and RF ASIC

AbstractIn this paper we report high voltage MOS and Schottky Diode CV techniques for silicon and SiC power devices. 4H Silicon carbide is a wide bandgap semiconductor suitable for high voltage power electronics and RF applications due to high avalanche breakdown critical electric field, and thermal conductivity. The performance of various power devices, which may include MOSFET and Static Induction Transistor (SIT), can be affected by the deep level traps in the substrate and the oxide interfacial defects. We have characterized deep level trap (High Voltage Schottky Diode HF CV) and oxide interface trap densities (High Voltage HF MOS CV), measured the device channel doping profile for both 4H SiC and silicon, gate metal workfunction, and simulated the effects on DC/AC performance.

High RF Performance AlGaN/GaN HEMT Fabricated by Recess-Arrayed Ohmic Contact Technology

In this letter, a high-performance gate-recessed AlGaN/GaN high electron mobility transistor (HEMT) fabricated by the recess-arrayed ohmic contact technology is presented. An array of square columns was etched in the ohmic region, using Ti/Al/Ni/Au metal deposition and rapid annealing to fabricate a low-resistance ohmic contact. By using the transmission line method measurement, an ohmic contact resistance ( ${R}_{c}$ ) of 0.12 $\Omega$ • mm is measured, which is 70% lower than that of the reference device. The patterned ohmic contact HEMT (POC HEMT) exhibits the saturation current of 1130 mA/mm at ${V}_{ds}=10$ V and ${V}_{gs}=1$ V, with a shift of the knee voltage from 6 V to 3 V. The RF measurement shows the power-added efficiency (PAE) of 71.6% at 5 GHz. After the third harmonic tuning, the PAE of 85.2% and the corresponding power density of 11.2 W/mm and power gain of 16.9 dB are obtained. According to the achieved results, the recess-arrayed ohmic contact processed GaN HEMT has a great potential for high RF efficiency and power applications.

Evaluation of AlGaN/GaN metal–oxide–semicondutor high-electron mobility transistors with plasma-enhanced atomic layer deposition HfO2/AlN date dielectric for RF power applications

A plasma enhanced atomic layer deposition (PEALD) HfO2/AlN dielectric stack was used as the gate dielectric for AlGaN/GaN metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) for high-frequency power device applications. The capacitance–voltage (C–V) curves of the HfO2/AlN/GaN MOS capacitor (MOSCAP) showed a small frequency dispersion along with a very small hysteresis (∼50 mV). Moreover, the interface trap density (Dit) was calculated to be 2.7 × 1011 cm−2 V−1 s−1 at 150 °C. Using PEALD-AlN as the interfacial passivation layer (IPL), the drain current of the HfO2/AlN MOS-HEMTs increased by about 46% and the gate leakage current decreased by six orders of magnitude as compared with those of the conventional Schottky gate AlGaN/GaN HEMTs processed using the same epitaxial wafer. The 0.3-µm-gate-length HfO2/AlN/AlGaN/GaN MOS-HEMTs demonstrated a 2.88 W/mm output power, a 23 dB power gain, a 30.2% power-added efficiency at 2.4 GHz, and an improved device linearity as compared with the conventional AlGaN/GaN HEMTs. The third-order intercept point at the output (OIP3) of the MOS-HEMTs was 28.4 as compared with that of 26.5 for the conventional GaN HEMTs. Overall, the MOS-HEMTs with a HfO2/AlN gate stack showed good potential for high-linearity RF power device applications.

RF power FinFET transistors with a wide drain-extended fin

Drain-extended FinFET transistors for RF power applications have been fabricated and is presented in this paper. Power FinFETs with a wide drain extension are proposed to reduce the drain resistance. Compared with conventional drain-extended FinFETs, our proposed new devices exhibit lower on-resistances and better high-frequency performances while keeping a similar breakdown voltage. The enhancements of the on-resistance and peak cutoff frequency are 16 and 56%, respectively, under an optimal drain-extension layout. These experimental results suggest that FinFET transistors with a wide drain extension could be used for RF power applications, increasing the possibility of integrating RF power parts into future FinFET system-on-a-chip technologies.

(Invited) Strain Engineered Crack-Free GaN on Si for Integrated Vertical High Power GaN Devices with Si CMOS

We demonstrated beyond 10 µm thick crack-free GaN growth on Si substrate using selective area growth technique. Systematic characterization by scanning electron and optical microscopy on the grown samples revealed that cracks nucleate and propagate on {1-1 00} planes in <1-2 10> directions. By developing {1 -101} facet planes in selective area growth, thermal mismatch strain relief at facet surfaces eliminate cracking and enable growth over 10 µm thick crack-free GaN on Si. These grown structures exhibited high crystalline quality throughout the thickness of the structure as validated by selective area diffraction in high resolution transmission electron microscopy, with a dislocation density of 2-3 x 108 cm-2 at the GaN surface. On the same Si substrate, we were able to fabricate enhancement mode CMOS devices. The overall progress reported here paves the way for monolithically integrated GaN technologies for RF and high power applications on Si CMOS devices.

Abstract 303: Optical Tissue Interrogation Technology Incorporated in Irrigated Radiofrequency Ablation Provides Real Time Monitoring of Ablation Lesion Depth

Background: Radiofrequency ablation (RFA) is an effective therapy to treat cardiac arrhythmias. The success rate depends on the location and size of ablation lesions. Electroanatomic Mapping and Contact force-sensing catheters have been shown to enhance the success rates of RFA. We used real-time optical tissue interrogation within the NADH fluorescence (fNADH) range to assess the progression of ablation lesion depth in real time during RF delivery (LuxCath catheter). Methods: Multiple RFA lesions (n=20) were made on an intubated and mechanically ventilated canine (Mongrel) thigh muscles using 7 Fr quadripolar RFA catheter with a 3.5 mm tip open 3.5 mm irrigated electrode incorporating imaging optic. Light was delivered at (360+/-25nm), and fluorescence acquired through fiberoptic bundle at (370-660 nm) by a spectrometer and analyzed in real time. Two types of plots were created for each lesion: intensity (in counts) vs. wavelength (nm), and 465nm peak amplitude (normalized) vs. time (sec). The lesions were made at room temperature with fixed power (15W) and four different durations (10, 20,30,40 sec). After ablation the muscle was stained with 2,3,4-triphenyl-2H-tetrazolium chloride (TTC), bisected at the center and measured the with and depth of the lesion using imageJ software. Results: We performed a total of twenty lesions that were divided into four groups based on the duration of the ablation (10, 20, 30, 40 seconds). The mean lesion depth for those groups was 4.05+/-1.28, 4.99+/-0.9, 6.9+/-1.06 and 7.14+/-1.41 mm, respectively. Lesion depth was correlated with the duration of ablation and fNADH signal intensity with a correlation coefficient of 0.93 and 0.99, respectively. Finally, there was a significant correlation between lesion size and fNADH signal intensity with a correlation coefficient of 0.96. Conclusion: Real-time optical tissue characterization can provide an excellent assessment of lesion progression during RF delivery. Lesion depth was directly correlated to the decrease in fNADH signal intensity. This information may be used to optimize the selection of RF power and RF application time to maximize RF lesion formation and improve the success of ablation procedures.

High-frequency performances of superjunction laterally diffused metal–oxide–semiconductor transistors for RF power applications

This paper presents the dc and high-frequency performances of laterally diffused metal–oxide–semiconductor (LDMOS) transistors with superjunction (SJ) structures. The SJ-LDMOS transistors were fabricated using a 0.5-µm CMOS process. By utilizing a modified SJ/RESURF layout (Type I) or a tapered SJ layout (Type II) in our devices, better high-frequency performances and higher breakdown voltages are achieved compared with conventional SJ counterpart, owing to the suppression of the substrate-assisted depletion effect and the reduction of the drain resistance. For Type I device with an optimal SJ layout dimension, the cutoff frequency and the breakdown voltage are 3.7 GHz and 68 V, respectively. For Type II device with a smallest p-pillar width near the drain, they can be enhanced further and reach to 4.9 GHz and 83 V. These experimental results suggest that the SJ-LDMOS can be used in the RF power amplifiers.