Olle Axelsson

Application Relevant Evaluation of Trapping Effects in AlGaN/GaN HEMTs With Fe-Doped Buffer

This paper investigates the impact of different iron (Fe) buffer doping profiles on trapping effects in microwave AlGaN/gallium nitride (GaN) high electron mobility transistors (HEMTs). We characterize not only the current collapse due to trapping in the buffer, but also the recovery process, which is important in the analysis of suitable linearization schemes for amplitude modulated signals. It is shown that the simple pulsed dc measurements of current transients can be used to investigate transient effects in the RF power. Specifically, it is revealed that the design of the Fe-doping profile in the buffer greatly influences the recovery time, with the samples with lower Fe concentration showing slower recovery. In contrast, traditional indicators, such as S-parameters and dc as well as pulsed I-V characteristics, show very small differences. An analysis of the recovery shows that this effect is due to the presence of two different detrapping processes with the same activation energy (0.6 eV) but different time constants. For highly doped buffers, the faster process dominates, whereas the slower process is enhanced for less doped buffers.

Impact of Trapping Effects on the Recovery Time of GaN Based Low Noise Amplifiers

This study investigates recovery time of the gain of AlGaN/GaN HEMT based low noise amplifiers (LNA) after an input overdrive pulse. Three LNAs, fabricated in two commercial MMIC processes and a Chalmers in-house process, are evaluated. The Chalmers process has an unintentionally doped buffer instead of the intentional Fe doping of the buffer which is standard in commercial GaN HEMT technologies. It is shown that the LNAs from the two commercial processes experience a severe drop in gain after input overdrive pulses higher than 28 dBm, recovering over a duration of around 20 ms. In contrast the LNA fabricated in-house at Chalmers experienced no visible effects up to an input power of 33 dBm. These results have impact for radar and electronic warfare receivers, which need to be operational immediately after an overdrive pulse. The long time constants suggest that these effects are due to trapping in the transistors with the Fe doped buffer playing an important role.

Highly Linear Gallium Nitride MMIC LNAs

In this paper, two Low Noise Amplifiers designed in Gallium Nitride HEMT MMIC technology are presented. The focus of the designs is to achieve good linearity at low power consumption and acceptable noise figure. The first design achieves an OIP3/PDC of 12 using traditional LNA design techniques. In a second design, the OIP3 is improved by 2 dB, raising OIP3/PDC to 19, among the highest figures reported for GaN LNAs. This is achieved by using both inductive source feedback and drain-gate RC feedback.

Fabrication and Characterization of Thin-Barrier Al05Ga05N/AlN/GaN HEMTs

The growth, fabrication, and performance of Al0.5Ga0.5 N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic dc transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.The growth, fabrication, and performance of Al0.5Ga0.5N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an Ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic DC transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.

Fabrication and Characterization of Thin-Barrier HEMTs

The growth, fabrication, and performance of Al0.5Ga0.5 N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic dc transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.The growth, fabrication, and performance of Al0.5Ga0.5N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an Ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic DC transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.

Low-Pressure-Chemical-Vapor-Deposition SiNx passivated AlGaN/GaN HEMTs for power amplifier application

A Low-Pressure-Chemical-Vapor-Deposition (LPCVD) bilayer SiNx passivation scheme has been investigated and developed, which effectively suppress the current collapse in AlGaN/GaN HEMTs. Low current slump is very helpful for microwave power amplifier application. Compared to in-situ SiNx passivations by metal-organic-chemical-vapor-deposition (MOCVD) and ex-situ SiNx passivations by plasma-enhanced-chemical-vapor-deposition (PECVD), the LPCVD SiNx exhibits the quickest recovery time from double-sweep IV curves. From pulsed IV and load-pull measurements, LPCVD SiNx is also confirmed to deliver superior large signal performance. The bilayer LPCVD SiNx passivated device shows negligible current slump (<;6%). These characteristics are directly reflected in the large signal operation, where HEMTs with bilayer LPCVD SiNx have highest output power (2.9 W/mm at 3 GHz).

Fabrication and Characterization of Thin-Barrier

The growth, fabrication, and performance of Al0.5Ga0.5 N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic dc transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.The growth, fabrication, and performance of Al0.5Ga0.5N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an Ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic DC transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.

\hbox{Al}_{0.5}\hbox{Ga}_{0.5}\hbox{N/AlN/GaN}

Three transistors with different AlGaN/GaN interface designs (sharp interface, standard interface, and an extra AlN interlayer) were studied in-depth under conditions mimicking low-noise amplifiers (LNAs) operation. A new measurement setup, analog to LNAs operation condition, is established to measure recovery time on device level. For the first time, a direct relationship between the recovery time and the design of AlGaN/GaN interface is revealed in devices with Carbon doping buffer in this letter. An extremely low-recovery time is demonstrated in the transistor with an AlN interlayer. Both transistors without an AlN interlayer exhibit severe gain and drain current degradation after pulsed input stress. The transistor with a sharp interface shows a recovery time around 10 ms, whereas the transistorwith a standard interface shows even much longer recovery time. These results imply that AlN interlayer, which can effectively block the injection of hot electrons to AlGaN bulk or surface traps, is highly preferred in systems where LNAs need to function promptly after an input overdrive.

HEMTs

In this paper, the noise temperature of an electronic tuner is determined and its significance for the suitability of such tuners in noise parameter measurement systems discussed. The noise temperature of the tuner was found to be higher than the ambient room temperature in the laboratory and vary significantly between tuner states. For impedance states with small input reflections coefficients, the excess noise temperature is around 25 K. For some of the states with higher reflection coefficients, this figure increases, reaching around 45 K at |Γ| = 0.75. Unless accounted for, this leads to errors in noise parameter extraction when using an electronic tuner in noise parameter measurements.

Achieving Low-Recovery Time in AlGaN/GaN HEMTs With AlN Interlayer Under Low- Noise Amplifiers Operation

In this paper a highly linear amplifier using an in-house gallium nitride (GaN) high electron mobility transistor (HEMT) technology is presented. A 3 dB bandwidth of 2.7–3.6 GHz with a maximum gain of 18 dB was measured. The output third-order intercept point (OIP3) was measured to 39 dBm with a maximum power consumption of 2.1 W. With a reduction of power consumption to 1 W the noise figure was improved by 0.6 dB while the OIP3 was degraded 3 dB.