Receiver components and systems

AlGaN/GaN high electron mobility transistors (HEMTs) are promising candidates for high power and high current applications with its high mobility and high breakdown field. Epitaxial films for device substrate are typically grown on sapphire or silicon carbide, SiC, with dislocation densities in the order of 108 - 1010cm-2 due to their thermal coefficient and lattice mismatches. The thinner GaN buffer layers on SiC have been reported to have higher threading dislocation density in the GaN, but lead to higher off-state breakdown voltages. However, thick GaN buffer layers on sapphire and their impact on dc performance have not been widely studied. In this study, the impact of GaN buffer layer quality on dc and gate-lag pulse performance of AlGaN/GaN HEMTs was studied. Transmission electron microscopy (TEM) was used to measure the dislocation density in the GaN buffer layer of the HEMT samples. Dc characteristics, including drain I-Vs, transfer characteristics, and gate pulsed drain I-V characteristics of the HEMTs, were measured to establish a correlation between the AlGaN/GaN HEMTs’ dc and gate-pulsed performance and GaN buffer layer quality. AlGaN/GaN HEMT structures grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates were acquired from two different vendors. Both types of wafers had 24% Al concentration in the AlGaN barrier layer. One type of wafer had a 5 µm GaN buffer and the other had a 2 µm GaN buffer layer. HEMT fabrication was started with mesa patterning by conventional optical lithography. The mesa-etching was achieved using a unaxis shuttle-lock reactive ion etcher with inductively coupled plasma module (ICP) for device isolation with a Cl2/Ar plasma. Ohmic metallization of electron-beam evaporated Ti/Al/Ni/Au (25 nm/125 nm/45 nm/100 nm) was patterned by lift-off and subsequently rapid thermally annealed at 850⁰C in a flowing N2 ambient for 45 seconds. Schottky gates of e-beam evaporated Ni/Au (20 nm/80 nm) with 100 μm width and 1 μm length were obtained by standard lift-off patterning. DC current–voltage (I-V) characteristics were measured using an HP4156 parameter analyzer, and gate-lag pulse measurements were measured using an Agilent 8114A pulse generator. Figure 1 shows the bright field cross-sectional transmission electron microscopy (BF-XTEM) pictures of AlGaN/GaN surface for the top layers of (a) HEMT structure with 2 µm GaN buffer layer, (b) HEMT structure with 5 μm GaN buffer layer as well as the GaN/sapphire interface for the (c) HEMT structure with 2 μm GaN buffer layer, and (d) HEMT structure with 5 μm GaN buffer layer. Dislocations are seen to originate near the GaN/sapphire interface and propagate up through the AlGaN/GaN interface to the surface of both HEMT wafers. However, it is clear that the HEMT structure with 2 μm GaN buffer layer exhibited a much higher defect density. The calculated defect density for 2 μm GaN buffer layer substrate had an order of magnitude higher defect density. However, 5μm GaN buffer layer wafer showed that it was under high strain with larger height difference across the 2 inch with lower radius of curvature. There was no major difference in HEMTs’ dc performance was observed. In the other hand, Figure 2 (a) and (b) shows that gate lag measurement on fabricated HEMTs on 5 μm GaN buffer layer wafer showed no degradation and on 2 μm GaN buffer layer wafer showed the otherwise. The effects of defect density on HEMT dc and radio frequency performance were studied. HEMTs were fabricated on 2 and 5 μm of GaN buffer layers with the same composition of active layers. Despite there was no significant difference was seen in dc characteristics, significant reduction in pulse measurements was observed on thinner GaN layer HEMTs. These results suggest that the defects created in GaN buffer layer do not largely influence device dc performance but are closely related to high frequency performance. Figure 1

Fifth generation communication networks promise extremely high data throughputs, low latencies, and ultra-high reliability by employing small cells in high density networks. This will increase the use of highly inefficient microwave power amplifiers, that exhibit efficiencies sometimes as low as 10% for advanced multi-carrier waveforms. To overcome these inefficiencies and enable next generation technology development, the internal distributed behaviour of the packaged microwave power transistor has to be fully characterised, which is impossible using conventional port-based measurements. In this dissertation, the development of a set of multiphysics measurement techniques that capture the distributed electrical, electromagnetic, and thermal device behaviour is described. These new multiphysics measurement techniques enable the characterisation and direct visualisation of the inefficient device performance, providing a basis for future design optimisation. The techniques combine a non-linear vector network analyser, electro-optic, load-pull and thermoreflectance measurement systems that enable large signal time-domain electrical, distributed multi-harmonic vector electric field (E-field), and transient and steady-state thermal measurements. The multiphysics measurement set-up was used to characterise various transistors and PAs including 260 W silicon (Si) laterally diffused metal oxide semiconductor (LDMOS) field effect transistors in both air-cavity ceramic and plastic packages, 25 W gallium nitride (GaN) on silicon carbide high electron mobility transistors (HEMTs), 250 W GaN HEMT and 360 W Si LDMOS Doherty power amplifiers. The E-field measurements enabled the first ever imaging of parametric odd-mode oscillations within multi-die packaged high-power microwave transistors. Additionally, the measurement system was used to verify the effectiveness of in-package oscillation suppression circuits. As high-resolution E-field measurements can be slow, a surrogate modelling-based measurement algorithm was implemented to accelerate measurements 10-fold. Transient thermal measurements helped to identify abnormal transistor finger-to-finger heating in GaN HEMTs and revealed thermal differences along the gate width in GaN-based asymmetric transistors for Doherty power amplifier applications.

The fabrication, characterization, and statistical analysis of the performance and yield of AlInAs-GaInAs on InP low-noise high electron mobility transistors (HEMTs) with subquarter-micron T-gates fabricated with electron beam lithography are reported. This was undertaken to establish the manufacturability of submicron AlInAs-GaInAs HEMT technology for various low-noise microwave receiver applications. Excellent DC device yield (up to 90%) was obtained from devices to gate widths 300 mu m and 1000 mu m. A range of minimum noise figures between 0.026 to 0.5 dB at 2 GHz and 0.39 to 0.8 dB at 12 GHz were obtained for 0.15- mu m and 0.20- mu m gate length devices. The results establish the correlation between the noise figure and yield for this new class of microwave devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaN-based high electron mobility transistors (HEMTs) are expected to be used in battery charger inverters in an electric vehicle because of their low on-resistance and high switching speed. Currently, AlGaN/GaN HEMTs fabricated on Si substrates are rapidly becoming more widespread in compact AC adapters. However, in order to achieve high-voltage devices for in-vehicle applications, etc., thicker epitaxial films are required, and various problems arise, such as an increase in the growth time of the epitaxial film and an increase in the warping of the wafer due to the stress of the epitaxial film, making it difficult to manufacture epitaxial wafers suitable for high-voltage AlGaN/GaN HEMTs. Therefore, we have focused on GaN substrates that can be grown by homoepitaxy and have been developing high-breakdown-voltage AlGaN/GaN HEMTs.Kuzuhara et al. fabricated AlGaN/GaN HEMTs using iron-doped GaN freestanding substrates and demonstrated a breakdown voltage of over 5000 V. They also showed that the higher the resistivity of the semi-insulating layer, the higher the breakdown voltage [1].Iso et al. used the HVPE method to dope high-resistivity freestanding GaN substrates with iron and carbon, and showed that the resistivity of the carbon-doped substrates was higher than that of the iron-doped substrates [2].In this report, we used two types of dual-layer semi-insulating GaN substrates purchased from Mitsubishi chemical corporation. Thick semi-insulating layers containing carbon of a 2E18 cm-3 and iron of a 1E18 cm-3 were grown on conductive GaN substrates. The resistivity of the carbon-doped layer and the iron-doped layer was 1E12ohm⋅cm and 1E8ohm⋅cm, respectively, according to the specification sheet. And AlGaN/GaN HEMTs were fabricated on each substrate and evaluated their three-terminal breakdown voltage. The epitaxial structure consisted of a 3-nm-thick GaN cap layer, a 17-nm-thick AlGaN barrier layer with an Al composition of 22%, a 200-nm-undoped GaN channel layer, and a 300-nm-thick GaN buffer layer doped with carbon of a 1E17 cm-3. Ion implantation was used to isolate the devices. The gate length (Lg), gate width (Wg), and gate-to-source distance (Lgs) were fixed at 2, 100 and 2 µm, respectively, while the gate-to-drain distance (Lgd) was varied between 10 µm, 15 µm and 20 µm. The gate-field-plate length and source-field-plates were also fixed at 2, 4 µm, respectively. The curve tracer (IWATSU CS3200) was used to measure the electrical characteristics of AlGaN/GaN HEMTs. Since the top surface of the device does not have a passivation film, to prevent dielectric breakdown on the device surface, the off-state breakdown voltage of the GaN HEMTs were measured while soaked in Solvay's Garten solution. In both GaN HEMTs on the different semi-insulating substrates, the off-state breakdown voltage increased linearly with the gate-to-drain distance and was successfully confirmed to exceed 1400 V at Lgd of 20 μm. The breakdown electric field in the AlGaN/GaN HEMTs are about 0.7 MV/cm, no resistivity dependence on the breakdown electric field was observed. Kuzuhara et al. reported that, in addition to the resistivity of the semi-insulating GaN layer, isolation technology is also important for achieving high breakdown voltage [1]. When the breakdown voltage of the isolation regions formed by ion-implantation was examined, the breakdown electric field of the carbon-doped and iron-doped insulating substrate was 0.75 MV/cm, 0.86 MV/cm, respectively. These breakdown electric fields are close to the off-state breakdown field of AlGaN/GaN HEMTs, which suggests that the isolation process for AlGaN/GaN HEMTs has not been yet optimized. In order to further improve the breakdown voltage of AlGaN/GaN HEMTs on semi-insulating GaN substrates, it is necessary to further evaluate their electrical characteristics and investigate the cause of decrease in breakdown field strength compared to the physical properties of GaN. This research was performed using C-TEFs (Center for Integrated Research of Future Electronics, Transformative Electronics Facilities), Nagoya university, Japan. This research was conducted with the support of the Ministry of the Environment “Carbon Neutral Technology Research and Development Program”.Reference[1] M. Kuzuhara, J. T. Asubar, and H. Tokuda, ”AlGaN/GaN high-electron-mobility transistor technology for high-voltage and low-on-resistance operation,” Jpn. J. Appl. Phys, 55, 070101, (2016).[2] K. Iso, H. Ikeda, T. Mochizuki, T. Odai, and S. Izumikawa, ”Dual-Layer Semi-insulating GaN Substrates Doped with Fe, C, and Mn,” Phys. Status. Solidi, B, 260, 2200489 (2023).

AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising features in high power and high frequency applications such as inverter units in hybrid electric vehicles, advanced radar systems, and satellite-based communication networks with its high density of sheet carrier concentration, high electron mobility, and radiation hardness. In order to lower the cost of HEMTs, larger diameters substrates are needed. Currently, the HEMT structures are grown on non-native sapphire, SiC and Si substrates or on native substrate of vapor phase epitaxy (VPE) GaN wafers. HEMTs grown on sapphire substrate suffer from poor heat dissipation and higher defect density due to the relative larger lattice mismatch to GaN. SiC has a very good thermal conductivity and is less lattice mismatch to GaN, but high quality semi-insulating SiC substrates are quite expensive. Although, Si substrates are fair low cost and available for larger diameter substrates, due to larger lattice mismatch to GaN, it requires to grow thick complex AlGaN buffers prior to the growth of GaN layer to reduce the threading dislocation density. These thick AlGaN layers are very defective and thermal resistive, which will hinder device heat dissipation. VPE grown GaN wafers are limited to 2-3” diameter and very expensive. Recently, it was reported that high quality GaN layers were grown by RF plasma-assisted molecular beam epitaxy (PA-MBE) or metal organic chemical vapor deposition (MOCVD) on high-quality, single crystal ZrTi refractory metal alloys deposited by plasma sputtering on c-plane sapphire and Si substrates. These ZrTi refractory metal alloys are not only lattice match to GaN, but have a similar coefficient of thermal expansion (CTE) as the CTE of GaN [1]. By employing these ZrTi alloys, there is no need to grow thick AlGaN buffer, both photonic and electronic GaN based device structure can be grown on large area Si substrates to achieve low cost GaN based device fabrication. In this work, we have demonstrated AlGaN/GaN HEMTs grown on ZrTi refractory metal alloys, which were deposited on both Si and sapphire substrates. HEMTs with a gate dimension of 1 µm × 100 um were fabricated and characterized. Both dc and rf performance of AlGaN/GaN HEMTs fabricated on the ZrTi metal alloys will be presented. 1. “Epitaxial Growth of High Quality GaN Films on Lattice Matched Metallic Layers”, A.M. Dabiran, F. Machuca, I. De, and R. Weiss, ECS Trans. 66, 113-117 (2015).

The purpose of this paper is to design a microwave monolithic integrated circuit (MMIC) for low noise amplifier (LNA) X-band (7-12 GHz) based on technology of gallium nitride (GaN) high electron mobility transistor (HEMT) with a T-gate, which has 100 nm width, on a silicon (Si) semi-insulating substrate of the OMMIC company. The amplifier is based on common-source transistors with series feedback, which was formed by high-impedance transmission line, and with parallel feedback to match noise figure and power gain. The key characteristics of an LNA are noise figure and gain. However, in this paper, it was decided to design the LNA, which should have a good margin in terms of input and output power. As a result, GaN technology was chosen, which has a higher noise figure compared to other technologies, but eliminates the need for an input power limiter, which in turn significantly increases the overall noise figure. As a result LNA MMIC was developed with the following characteristics: noise figure less than 1.6 dB, small-signal gain more than 20 dB, return loss better than -13 dB and output power more than 19 dBm with 1 dB compression in the range from 7 to 12 GHz in dimensions 2x1.5 mm², which has a supply voltage of 8 V and a current consumption of less than 70 mA. However, it should be said that LNA was only modeled in the AWR DE.

Field effect transistors: FETs and HEMTs

Background and Objectives: High electron mobility transistors (HEMTs) are designed so that they are able to work at higher frequencies than conventional transistors and this has made them an attractive topic of research.Methods: Two developed designs of InGaAs/InAlAs high electron mobility transistors have been studied. The proposed laterally contacted HEMTs satisfy the desired high frequency characteristics and are good candidates for high frequency applications. Two kinds of HEMTs have been designed and simulated: single-gate laterally contacted HEMT (SGLC-HEMT) and doublegate laterally contacted HEMT (DGLC-HEMT).Results: The proposed SGLC-HEMT exhibits 111 GHz current-gain cut-off frequency. By using double-gate design, the current-gain cut-off frequency has been increased to 256 GHz. The simulation results show that the maximum oscillation frequency for the proposed SGLC and DGLC HEMTs, are 410 GHz and 768 GHz, respectively. The maximum value of transconductance (gm) for SGLC-HEMT is obtained 620 mS/mm while it is 1130 mS/mm for DGLC-HEMT.Conclusion: In order to increase the fT and fmax, instead of decreasing the gate length which is a restricted solution because of short channel effects, a very efficient structure was proposed. The designed HEMT benefits from laterally source and drain contacts. The results showed superior performance of the laterally contacted HEMTs compared to top contacted ones. The best frequency response was obtained for DGLC-HEMT. The proposed DG-HEMT design could improve the current-gain cut-off frequency and maximum oscillation frequency to 256 GHz and 768 GHz, respectively. The comparison of the performance of the DGLC-HEMT with SGLC-HEMT and with previously reported double gate HEMTs, verified the significant improvements in DC and AC characteristics of the HEMTs caused by the proposed design.

With the wide band-gap of Gallium Nitride (GaN) and high mobility of 2 dimensional electron gas(2DEG), AlGaN/GaN high electron mobility transistors (HEMTs) are considered ideal candidates for high speed and power applications ranging from hybrid vehicles to space communication. Developments in the fabrication of GaN-based blue LEDs have been incorporated into the processing of AlGaN/GaN HEMT structures leading to improvements in amount of defects and dislocations resulting from heteroepitaxial growth. But evident degradation of dynamic performance of such devices due to the presence of as-grown defects still remains a subject of major concern. Using FLorida Object Oriented Device Simulator (FLOODS) TCAD, this work looks to analyze the impact of variation of defect properties as well as their spatial distribution and concentration on the steady-state and dynamic behavior of AlGaN/GaN HEMTs. FLOODS TCAD’s defect modeling capability will be applied to examine how multiple defect levels, of both donor and acceptor-like nature, can influence device performance. Particular emphasis will be on transient switching, such as gate-lag and drain-lag experiments, in consideration of the slow nature observed frequently in literature. While comprehensive investigation of the role of charged defects at the AlGaN/passivation layer interface on performance degradation has already been performed, contribution by as-grown defects, expected to be in significant quantity in the GaN buffer layer, is yet to be investigated. Building on experimental results, which suggest the presence of multiple acceptor-like defects, impact on steady-state current-voltage characteristics will be observed followed by an examination of how such defects will affect dynamic performance by isolating their contribution to transient and switching behavior. Figure: (a) Drain current against gate voltage at VDS=0.5V for HEMT A with 1 acceptor-like level (nT=1014 cm-3, Et=Ec-0.7eV) and HEMT B with 2 acceptor levels(Level 1: nT=1014 cm-3, Et=Ec-0.7eV; Level 2: nT=1015 cm-3, Et=Ec-0.5eV) (b) Optical pumping like detrapping of electrons, biasing at VDS=1V and VGS=0V. HEMT A(Level 1: nT=1013 cm-3, Ec-0.2eV, τ=1s; Level 2: nT=4x1013 cm-3, Ec-0.5eV, τ=1ms), HEMT B(Level 1: nT=1013 cm-3, Ec-0.2eV, τ=1s; Level 2: nT=1013 cm-3, Ec-0.5eV, τ=1ms) Figure 1

AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising performance in high power and high frequency, which can be used for applications such as satellite-based communication networks, inverter units in hybrid electric vehicles and advanced radar systems. However, intrinsic defects and defects generated during the device fabrication degraded HEMT performance, such as drain current collapse, high gate leakage, and lower rf power density and power add efficiency. Furthermore, subsequent electrical stressing of the HEMTs during operation leads to creation of more traps and further device degradation through various mechanisms, including gate contact sinking, shallow trap formations, and the inverse piezoelectric effect. It is highly desirable to have non-destructive methods available to identify the activation energies of the defects and spatial location of trap states in HEMT. A sub-bandgap optical pumping technique was developed to identify trap locations in AlGaN/GaN HEMTs. By varying photon fluxes, the traps with different activation energies appeared at different photon flux levels. This implies that the defects originate at different physical locations in the HEMT. The locations of the traps identified with the sub-bandgap optical pumping methods confirmed by gate pulse measurements under optical pumping.

The effects of proton irradiation doses on dc characteristics of reference, electrically stressed under off-state conditions and stressed/annealed AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. The HEMTs were irradiated with protons at a fixed energy of 5 MeV and doses ranging from 1013 to 1015 cm−2. As expected, in all three types of HEMTs, more degradation of the device dc characteristics was observed for higher doses due to the larger displacement damage in two-dimensional electron gas channel of the HEMTs. The electrically stressed HEMTs after proton irradiation showed more degradation compared with reference and stressed/annealed HEMTs. After proton irradiation at a dose of 1015 cm−2, the drain saturation current and maximum transconductance of stressed HEMTs were decreased by 28.5% and 15%, respectively, compared to 24% and 11.5%–12%, respectively, for reference and stressed/annealed devices. The dc characteristics of stressed/annealed HEMTs after proton irradiation showed similar degradation trends compared with those of reference HEMTs, confirming that annealing is effective in removing defects created by the off-state stressing. In some cases, the authors also annealed stressed/irradiated HEMTs after the proton irradiation step. The drain current and transconductance of stressed/irradiated HEMTs were slightly increased after subsequent thermal annealing at 450 °C for 10 min, while reverse gate leakage current after annealing was decreased more than an order of magnitude. The interface trap density of stressed HEMTs after proton irradiation at a dose of 1015 cm−2 increased from 3.05 × 1012 to 1.37 × 1013/cm2 V and were reduced to 6.01 × 1012/cm2 V following thermal annealing. Our results are consistent with the notion that off-state stressing creates defects that have a common origin with those created by proton irradiation, and thus, irradiation of off-state stressed devices leads to more defects than in unstressed devices that are subsequently irradiated. Annealing the stressed devices prior to irradiation makes them behave the same as unstressed HEMTs when both are irradiated with protons.

As one key building block for mixed-signal IC applications, AlGaN/GaN high electron mobility transistor (HEMT) voltage comparator shows obvious advantages. This paper aims to study on the dc and dynamic characterization of AlGaN/GaN HEMT voltage comparator by simulation under different conditions. In this paper three characteristics of the AlGaN/GaN HEMT comparator are simulated by Advanced Design System (ADS) software: the DC characteristics of discrete E and D mode AlGaN/GaN HEMTs, the voltage transfer characteristics of the HEMTs voltage comparator and the propagation delay time. These results show that the AlGaN/GaN HEMT comparator has the features of a good voltage transfer characteristics and a small propagation delay time.

AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires modified gate exhibit significant changes in channel conductance upon expose to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition (CVD), with perfect crystal quality will attach CO molecule and release electrons, which will lead to a change of su rface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasin g the piezoinduced charge density in the HEMTs channel. These electrons create an image positive char ge on the gate region for the required neutrality, thus increasing the drain current of the HEMT s. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm and 3200ppm in the open cavity with continuous gas flow using a 50 ™ 50 P m 2 gate sensing area for polar and nonpolar ZnO nanowire gated HEMTs sensor.

With Gallium Nitride (GaN) device technology for power electronics applications being ramped up for volume production, an increasing amount of research is now focused on the performance of GaN power devices in circuits. In this study, an enhancement mode GaN high electron mobility transistor (HEMT) is switched in a clamped inductive switching configuration with the aim of investigating the source of oscillatory effects observed. These arise as a result of the increased switching speed capability of GaN devices compared to their silicon counterparts. The study identifies the two major mechanisms (Miller capacitance charge and parasitic common source inductance) that can lead to ringing behaviour during turn-off and considers the effect of temperature on the latter. Furthermore, the experimental results are backed by SPICE modelling to evaluate the contribution of different circuit components to oscillations. The study concludes with good design techniques that can suppress the effects discussed.

This paper describes a novel low-noise input-termination-less cascode distributed amplifier (DA) monolithic microwave integrated circuit (MMIC) design. The design was implemented with a 0.15 μm gate gallium nitride on silicon carbide GaN-SiC high electron mobility transistor (HEMT) 6 inch wafer process technology. The GaN MMIC achieves a bandwidth from 100 MHz-45 GHz with greater than 10 dB gain and previously benchmarked the first published mm-wave MMIC results produced on a 6 inch GaN on SiC wafer process technology. The unique input-gate-termination-less DA topology reduces the low-frequency noise figure (NF) of the conventional resistive-terminated DA without compromising the third order intercept point (IP3) linearity. The new design achieves 1.6 dB NF at 250 MHz and a NF improvement of at least 1 dB and as much as 4 dB or greater for frequencies below 5 GHz compared to the conventional DA approach. The GaN MMIC also achieves an average mid-band NF of 2.5-3 dB, a saturated output power (Psat) of 1 Watt, and a mid-band output IP3 of 38 dBm. The new design architecture combined with the inherent device characteristics of GaN-SiC technology can provide performance benefits for next-generation coherent fiber optic, instrumentation and advanced broadband radio architecture applications.