RF Power Performance Research Articles

Improved RF power performance via electrostatic shielding effect using AlGaN/GaN/graded-AlGaN/GaN double-channel structure

Improved RF power performance via electrostatic shielding effect using AlGaN/GaN/graded-AlGaN/GaN double-channel structure

(Invited) Gallium Oxides Devices for Grid-Scale Power Electronics and High Power Switched Mode RF Amplifiers

Within a decade of the first demonstration of a MESFET device, monoclinic β-Ga2O3 (Ga2O3) devices have made incredible progress in breakdown voltages, power device figure of merit and high-speed performance. It has emerged as a promising ultra-widebandgap semiconductor for next generation power, GHz switching and RF applications. In this talk, we will present an overview of our studies on fundamental transport properties, kilovolt class power MOSFETs and aggressively scaled RF devices. The large bandgap of Ga2O3 leads to a high critical field strength. This high field strength in combination with demonstrated room temperature mobility and calculated electron velocity leads to a higher Baliga’s Figure of Merit (BFoM) and Johnston Figure of Merit (JFoM) than current commercially available widebandgap technologies. Additionally, the large bandgap also enables high temperature operation and radiation hardness making it attractive for space applications such as Mars and Venus missions.In the first part, we will discuss the deep insights gained from the first-principles based transport calculations in Ga2O3. We will discuss the limits to low field mobility, saturation velocities and impact ionization coefficients. The impact of the plasmon-phonon coupling on the phonon limited transport will be discussed. We will present the experimental signatures of plasmon-phonon coupling and anti-screening behavior in ionic gated accumulation layers.Next, I will describe our work on the lateral MOSFETs with improved field plate design and beyond-kV breakdown. Temperature dependent analysis and device simulation suggest an extrinsic breakdown mechanism outside the channel. A simple and yet effective SU-8 polymer passivation technology was developed that results in significant improvement in breakdown voltages. The higher field strength of the SU-8 polymer enables a significant increase in breakdown voltage to 8 kVs in lateral MOSFETs. However, these devices show a high Ron, which is due to the depletion caused by RIE of the channel. We will present the use of ultra-high vacuum annealing techniques to improve the on-resistance of the devices still maintaining the multi-kilo-volt rating of the devices.Due to its high JFoM, Ga2O3 is a potential candidate for high power density RF amplifiers. We will also present the performance advancement that can be obtained in RF power performance using Ga2O3 technology. We will present the challenges in the technology and potential solutions. We will present the experimental DC and pulsed measurements on laterally scaled MOSFETs with 100 nm gate length. Severe DC-RF dispersion was observed which is attributed to the RIE damage and surface states on the oxide. Passivation of the devices shows reduced current collapse. Using aggressive gate lengths and gate-source spacing scaling, (AlxGa1-x)2O3/Ga2O3 heterostructure FETs were fabricated that show record high RF performance. The device transconductance was limited by the regrowth interface resistance. Ex-situ silicon nitride passivation was shown to be effective to reduce DC-RF dispersion. Recently, thin channel MOSFETs with deep-sub-micron gate lengths and source/drain regrowth have demonstrated devices with simultaneously low on resistance, high frequency, high voltages.

Efficacy of Π-Gate in RF Power Performance of Thin GaN Buffer AlGaN/GaN HEMTs

This brief investigates the influence of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Pi $</tex-math> </inline-formula> -shaped gate in extending the microwave performance of a thin GaN buffer AlGaN/GaN HEMT. A well-calibrated simulation deck based on the in-house fabricated thin GaN HEMT demonstrates better reliability when a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Pi $</tex-math> </inline-formula> -shaped gate is coupled with a thin GaN buffer. The sample has been investigated under different operating conditions with a specific focus on RF power performance. The modification in the gate architecture results in the enhancement of both the OFF-state breakdown characteristics and thermal reliability for continuous wave (CW) mode operation. The pulsed characteristics of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Pi $</tex-math> </inline-formula> -gate demonstrate a lower degree of current slump thereby improving the pulsed mode operation of the devices under test (DUT). This opens up the bottleneck for the GaN HEMT device to be operated at a higher voltage and exhibit higher power densities when benchmarked against their conventional counterparts all the while ensuring modest tradeoffs to the current and device gain metrics. The results presented point toward the possibility of further mitigating the dispersive trapping effects on the RF performance of a GaN HEMT by coupling a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Pi $</tex-math> </inline-formula> -shaped gate with a thin GaN buffer.

Modulator Demodulator In Phase Quadrature Dengan Pembawa Frekuensi 50 MHz Berbasis Komponen Diskrit

ABSTRACT&#x0D; &#x0D; One of the most important parts of a linear accelerator is the RF System. Two different input signals can produce distortion which can cause problems in intermodulation. Effect of RF power performance on noise as well as performance evaluation so as to produce a clear and strong signal without significant distortion or transmission loss.The Inphase quadrature analog modulator demodulator can achievec with 900 phase shit signal to I and Q inputs, the carrier signal using a variable oscillator or VCO with a single 50 MHz output. 16 Bit of ADC and DAC module optimized as input or output with I/Q analog modulator demodulator. In this paper, ADISIM RF simulation is used to display the results of the RF system design, with two parameters namely Spurios Free Dynamic Range) and IMD (Two Tone Intermodulation Distortion) for Transmitter and one parameter namely Noise Figure (NF) for Receiver.&#x0D; &#x0D; Keywords : I/Q Modulator Demoduator, ADISIM RF, SFDR, IMD, NF

Improved RF power performance of AlGaN/GaN HEMT on silicon with planar distributed channel

AlGaN/GaN HEMTs with planar distributed channel were fabricated on a silicon substrate. With a standard ion implantation isolation process, the area between the ohmic contacts was divided into conductive and non-conductive regions. Compared to a conventional HEMT, simulations and experimental results indicate the decreased channel temperature and improved RF power performance in the distributed channel device, while there is no significant degradation in small signal characteristics. The fabricated multi-finger distributed channel devices with 0.65-mm gate periphery demonstrated a decrease in channel temperature from 186 °C to 162 °C, accompanied by a 15.6 % increase (from 3.2 W/mm to 3.7 W/mm) in output power density, and an 8 % increase (from 42.0 % to 50.0 %) in drain efficiency at 3.5 GHz.

Passivation Schemes for ScAlN-Barrier mm-Wave High Electron Mobility Transistors

This article presents improvements of large-signal RF power performance at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band of gallium nitride high electron mobility transistors (HEMTs) utilizing a scandium aluminum nitride barrier. Three samples were fabricated and measured having different passivation schemes, including gallium nitride, silicon nitride, and aluminum gallium nitride. The pinning of the Fermi level against the valence band reduced the gain and output power density of the gallium nitride passivated device, resulting in 4.5 W/mm at a drain bias of 32 V. With silicon nitride alone as the passivation, dc/RF dispersion was reduced, and gain increased significantly, boosting the output power for this device to 8.0 W/mm at 28 V, though at the cost of a reduced breakdown voltage. Adding an epitaxial aluminum gallium nitride passivating layer increased the maximum bias voltage that the devices can operate at compared to devices with the silicon nitride passivation. When biased at 40 V, the output power of the devices reached 10.8 W/mm at 30 GHz. These devices show the importance of the passivation design to large-signal RF performance in scandium aluminum nitride-based HEMTs and will help guide further improvements.

AlN/GaN MISHEMTs on Si with in-situ SiN as a gate dielectric for power amplifiers in mobile SoCs

AlN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on silicon substrate using in situ SiN as gate dielectric were fabricated and their RF power performance at mobile system-on-chip (SoC) compatible voltages was measured. At a mobile SoC-compatible supply voltage of V d = 3.5 V/5 V, the 90 nm gate-length AlN/GaN MISHEMTs showed a maximum power-added efficiency of 62%/58%, a maximum output power density (P outmax) of 0.44 W mm−1/0.84 W mm−1 and a linear gain of 20 dB/19 dB at the frequency of 5 GHz. These results suggest that the in situ-SiN/AlN/GaN-on-Si MISHEMTs are promising for RF power amplifiers in 5G mobile SoC applications.

Improved RF Power Performance of AlGaN/GaN HEMT Using by Ti/Au/Al/Ni/Au Shallow Trench Etching Ohmic Contact

In this article, we report on the high dc and RF performance of AlGaN/GaN high electron mobility transistors that employ Ti/Au/Al/Ni/Au metallization stack with shallow trench etching ohmic contact (STEOC). An excellent ohmic contact performance including low contact resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{C}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.28~\Omega \cdot $ </tex-math></inline-formula> mm and smooth surface morphology have been achieved simultaneously. Atomic force microscope (AFM) reveals a highly smooth surface morphology with a root mean square (rms) roughness of 6.3 nm even after 810 °C high-temperature annealing (HTA), achieving an improvement of 79% as compared to the conventional Ti/Al/Ni/Au ohmic contact (COC). A high-resolution transmission electron microscope (HRTEM) showed a glossy morphology with a continuous and uniform TiN layer formed in the interface for the STEOC sample, while a bumpy morphology caused from the Ni-Al complexes balling up and TiN island penetrating into the AlGaN/GaN heterostructure were observed for the conventional sample. Consequently, the fabricated transistors with the STEOC process show a high output current of 1.52 A/mm and low ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{ \mathrm{ ON}}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.09~\Omega $ </tex-math></inline-formula> mm. In addition, a high current cutoff frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{T}$ </tex-math></inline-formula> ) of 60 GHz and maximum oscillation frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {max}}$ </tex-math></inline-formula> ) of 150 GHz were obtained for the STEOC HEMT with a gate length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {g}}$ </tex-math></inline-formula> ) of 150 nm. Sub-6 GHz continuous-wave mode power sweep measurements deliver a high power-added-efficiency (PAE) of 67%. These results show the significant potential of the STEOC process to facilitate the development of GaN-based power amplifier (PA) applied for 5G.

Noise characteristics of Ni/GaN Schottky barrier IMPATT diode based on polar- and nonpolar-oriented wurtzite GaN for terahertz application

Abstract This paper reports a study investigating the noise performance of Ni/GaN Schottky barrier impact-ionization-avalanche-transit-time (IMPATT) diodes based on the polar- and nonpolar-oriented wurtzite GaN by a numerical simulation. Results show that the nonpolar IMPATT diode exhibits a significant wider and higher frequency-band corresponding to the low noise measure (NM). The upper limit of the low-noise frequency-band of the IMPATT diode shifts from 159.2 GHz to 184.3 GHz, from 183.4 GHz to 245.7 GHz and from 212.2 GHz to 285.6 GHz when J0 = 1 kA/cm2, 10 kA/cm2 and 100 kA/cm2, respectively, comparing the polar with the nonpolar IMPATT diodes. Our analysis proves that the mechanism comes from excellent properties of the Negative Differential Mobility (NDM) characteristic in the nonpolar orientation wurtzite GaN. In particular, the nonpolar diode still demonstrates better unity between the noise and RF power performances and can significantly improve the stability of IMPATT diodes at terahertz frequency.

Simulation of the RF Power Performance of a GaN HFET and Comparison to Experiment

The large-signal RF power performance of an AlGaN/GaN heterostructure field-effect transistor (HFET) is simulated by technology computer-aided design (TCAD) software, and compared to measurement. A clear procedure for extraction of the simulation physical parameters is described. Trapping effects are included, but temperature effects are not. Good agreement between simulation and measurement is demonstrated, paving the way for efficiency optimization of GaN HFETs using TCAD.

Anisotropy effects on the performance of wurtzite GaN impact-ionization-avalanche-transit-time diodes

We demonstrate that a GaN impact-ionization-avalanche-transit-time (IMPATT) diode exhibits a higher frequency and a wider bandwidth in the basal plane (Γ–M direction) than along the c-axis (Γ–A direction). Because of the better efficiency, RF power, and negative resistance performance at a high frequency, the use of the diode in the Γ–M direction is more appropriate for high-frequency operation. In addition, the diodes are cut off when the specific contact resistances are ∼10−6 and ∼10−5 Ω·cm2. Thus, the very high specific contact resistance of p-type GaN of about ∼10−4 Ω·cm2 provides an important limitation to the fabrication of pn junction GaN IMPATT diodes.

(Invited) RF Power Performance of Nanocrystalline Diamond Coated InAlN/AlN/GaN HEMTs

While GaN high-electron-mobility transistors (HEMTs) provide the highest achievable RF power densities among all commercially available solid-state technologies, their rated output power densities are typically backed off substantially from the intrinsic limit of the device to ensure robust reliability. Power dissipation during RF operation is typically localized to an area near the drain-edge of the gate. The combination of this “hot spot” and the high electric fields that are present causes acceleration of known degradation mechanisms that limit device lifetime. In order to meet system reliability requirements, the rated output power is therefore constrained to keep the dissipated power, and thus the HEMT channel temperature, below a fixed limit. We previously showed that a high thermal conductivity nanocrystalline diamond (NCD) coating, 0.4 µm to 0.5 µm in thickness, on the top-side of the device nearest to the area of high power dissipation, can reduce channel temperature [1] while improving RF power performance [2] of AlGaN/GaN HEMTs compared to similar devices with SiNx passivation only. Here we continue this development with new designs that lead to further improvements in reduced junction temperature, RF output power, and operating frequency. The crucial design enhancements introduced here include a combination of thicker NCD coatings (>1 µm) and sub-micron gate lengths. Instead of a conventional AlGaN barrier, an InAlN barrier layer was used to reduce parasitic source/drain resistance, increase transconductance, and support gate lengths for millimeter wavelength operation (>30 GHz). In addition, the InAlN barrier is lattice-matched to GaN, which may provide reliability benefits by reducing the intrinsic strain in the layer compared to an AlGaN barrier. For devices with a 0.75 µm gate length and a 5 µm source-drain spacing, a maximum drain current of 1.8 A/mm, a peak fT of 29 GHz, and a peak fmax of 60 GHz was measured. Output power densities exceeded 5 W/mm and 3 W/mm with power-added efficiency of 52% and 42% for 4 GHz and 10 GHz operating frequencies, respectively. The effects of device design on electrical performance and the reduction in junction temperature will be discussed. Thermal simulations will be presented that verify the reduced channel temperature extracted through a calibrated pulsed I-V measurement technique [3] for NCD coated devices. [1] M.J. Tadjer et al., IEEE Electron Dev. Lett., vol. 33, no. 1, pp. 23-25 (2012). [2] D.J. Meyer et al., IEEE Electron Dev. Lett., vol. 35, no. 10, pp. 1013-1015 (2014). [3] J. Joh et al., IEEE T. Electron. Dev., vol. 56, no. 12, pp. 2895-2900 (2009).

(Invited) RF Power Performance of Nanocrystalline Diamond Coated InAlN/AlN/GaN HEMTs

We have previously demonstrated AlGaN/GaN high-electron-mobility transistors (HEMTs) that used a coating of high thermal conductivity nanocrystalline diamond (NCD) to reduce channel temperature for a given dissipated power and simultaneously improve electrical performance compared to devices with conventional silicon nitride (SiN) passivation only. Here we examine the effect of a protective SiN interlayer of varying thickness inserted between the semiconductor surface and NCD coating on large-signal output power density as well as the reduction in channel temperature. For an InAlN/AlN/GaN HEMT with a >1 µm NCD coating and SiN interlayer ranging from 5 to 50 nm in thickness, the output power density and power-added efficiency at 4 and 10 GHz are found to be maximized for the thickest SiN interlayer. At the same time, we find the reduction in channel temperature provided by the NCD coating is not strongly dependent on thickness, which is confirmed by numerical simulation.

Pulsed characterisation of GaN HEMTs on Si (1 1 1) substrate

The DC and RF power characteristics of GaN HEMTs under continuous wave (CW) and pulsed load-pull measurement are examined, in this article. The results give a comprehensive understanding of self-heating effects and allow improved heat dissipation, by pulsed measurement. The measured output power increases under the pulse load-pull measurement, due to the isothermal environment. The RF power performance for pulsed mode was measured at 3.5 GHz, with 18.4 dB power gain and a large 3.5 W/mm power output, under pulse load-pull, which is a 3.25 dB improvement, compared to CW operation. The relationship of output power and impedance is determined by load-pull measurement.

Discrete Event Simulation for Complex High-Power Medical Systems

This position paper describes research activities in the field of targeted lifetime extension of components which are used in medical devices and systems as well as in high-energy physics and industrial applications. The considered medical areas are mainly in the therapy field and imaging diagnostics. Industrial areas are cargo and container scanning as well as food treatment and nondestructive material testing. The analysis of medical machines and systems with high-power tubes focuses on the X-ray radiation or RF-power performance. The operational behavior of such tubes is of special interest. In this position paper, a multipurpose simulation tool and a method will be presented to examine the specific influence of lifetime-defining factors which cover the mentioned application areas but are focused on medical applications. For the implementation of the method, a discrete event simulation is constructed using the real-time design tool MLDesigner from MLDesign Technologies, Inc. Studies can be carried out with regard to the tube service life. The simulations show that the targeted impact on the service-lifetime-defining factors can prolong useful service life of a high-power tube.

Microwave Power Performance N-Polar GaN MISHEMTs Grown by MOCVD on SiC Substrates Using an $\hbox{Al}_{2}\hbox{O}_{3}$ Etch-Stop Technology

This letter presents the RF power performance of N-polar AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) grown by metal-organic chemical vapor deposition (MOCVD) on semi-insulating SiC substrates at 10 and 4 GHz. Additionally, an Al2 O3-based etch-stop technology was demonstrated for improving the manufacturability of N-polar GaN HEMTs with SixNy passivation. The reported output power densities of 16.7 W/mm at 10 GHz and 20.7 W/mm at 4 GHz represent the highest reported values so far for an N-polar device, at both of these frequencies. The improvements achieved in the RF output power density when compared with previously reported N-polar MISHEMTs can be attributed to high breakdown voltage of N-polar devices grown by MOCVD and high thermal conductivity of the SiC substrate.

Investigation of Loading Effect on Power Performance for Planar Gunn Diodes Using Load-Pull Measurement Technique

A one-port load-pull measurement has been carried out in order to investigate the effect of loading on the RF power performance of a planar Gunn diode operating in the transit-time mode at 102 GHz. A W-band manual E-H tuner was applied between a waveguide mixer and a wafer probe to vary the load impedance on the Gunn diode. It has been found that more than 25 dB variation of output power was obtained by systematically adjusting the tuner. By de-embedding the S-parameters of the probe, E-H tuner and mixer, the relationship between RF power and load impedance for the planar Gunn diode was derived. This method is extremely useful for assisting the design of matching networks to improve power output of one-port oscillator devices.

Thermal stability investigations of AlGaN/GaN HEMTs with various high work function gate metal designs

The operation of high power RF transistor generates a huge amount of heat and thermal effect is a major consideration for improving the efficiency of power transistors. AlGaN/GaN high electron mobility transistors (HEMTs) on silicon substrates have been studied extensively because of their high thermal conductivity. This study comprehensively investigates the DC, low frequency noise, microwave and RF power performance of Al 0.27Ga 0.73N/GaN HEMTs on silicon substrates at temperatures from room temperature to 100 °C using high work function metals such as palladium (Pd) and iridium (Ir) gate metals. Although the conventional Ni gate exhibited a good metal work function with AlGaN, which is beneficial for increasing the Schottky barrier height of HEMTs, the diffusion of Ni metal toward the AlGaN and GaN layers influences the DC and RF stability of the device at high temperatures or over long-term operation. Pd and Ir exhibited less diffusion at high temperature than Ni, resulting in less degradation of device characteristics after high temperature operation.

Enhanced prediction of GaN MISHEMT RF power performance using improved large-signal model

An empirical large-signal model for a high-power AlGaN/GaN metal–insulator–semiconductor HEMT (GaN MISHEMT) utilising improved drain current (I–V) and gate charge (Q–V) formulation is presented. The proposed modelling equations accurately model the asymmetric bell-shaped transconductance (Gm) and gate capacitance (C11) characteristics over a wide bias range of operation. The simulation results of RF large-signal harmonic power levels and two-tone intermodulation distortion products show excellent agreement with the measured data.

RF power performance evaluation of surface channel diamond MESFETs

We experimentally investigate the large-signal radio frequency performances of surface-channel p-type diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination have a coplanar layout with two gate fingers, total gate periphery of 100 μm; in DC they exhibit a hole accumulation behavior with threshold voltage V t ≈ 0–0.5 V and maximum drain current density of 120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency f T and oscillation frequency f max) were obtained close to the threshold and were of the order of 6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load impedance at a bias point V DS = −14 V, V GS = −1 V. To the best of our knowledge, these are the first large signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential of such technology for the development of microwave power devices.