Simulation and Optimization of Gate Temperatures in GaN-on-SiC Monolithic Microwave Integrated Circuits

This paper presents 3-D thermal simulation studies of GaN-on-SiC monolithic microwave integrated circuits (MMICs) containing multifinger micrometer-scale high electron mobility transistors (HEMTs). The heat spreading effect of HEMT source, gate, and drain metallizations on peak structure temperatures is examined. The impacts of a realistic die attach material and rear-of-die heat transfer coefficient on structure temperatures, and in particular on temperature nonuniformity, are examined. Variable gate finger spacing, in which the gate spatial positions are described by polynomials as a function of gate number, is investigated as a means for optimizing the temperature uniformity from gate-to-gate. A thermal simulation code with a parametric MMIC geometry-based mesh generator and a deformable mesh consistent with sequential movement of gate finger positions during optimization is employed for all of the studies. The code is multiscale with a sufficient resolution range to handle a multifinger HEMT structure while also including the MMIC die, die attach metallization, and a realistic heat transfer coefficient associated with microchannel coolers. A variable gate pitch geometry based on an optimized cubic polynomial demonstrates considerable advantage in temperature uniformity.      

Low-conductance drain (LCD) design of InAlAs/InGaAs/InP HEMT's

The concepts of the low-conductance drain (LCD) design approach for lattice-matched InAlAs/InGaAs/InP HEMTs are demonstrated for improved device performance. The tradeoff for LCD HEMT characteristics is a tapered current gain cutoff frequency f_t under high drain-to-source bias. This behavior is, in principle, due to the fact that the LCD approach increases the effective gate length of the HEMTs in exchange for reduced peak channel electric field. Two-dimensional PISCES simulation was used to optimize the improvements while simultaneously minimizing this undesirable effect for an LCD HEMT structure     

Self-heating effects in a BiCMOS on SOI technology for RFIC applications

Self-heating in a 0.25 /spl mu/m BiCMOS technology with different isolation structures, including shallow and deep trenches on bulk and silicon-on-insulator (SOI) substrates, is characterized experimentally. Thermal resistance values for single- and multifinger emitter devices are extracted and compared to results obtained from two-dimensional, fully coupled electrothermal simulations. The difference in thermal resistance between the investigated isolation structures becomes more important for transistors with a small aspect ratio, i.e., short emitter length. The influence of thermal boundary conditions, including the substrate thermal resistance, the thermal resistance of the first metallization/via layer, and the simulation structure width is investigated. In the device with full dielectric isolation-deep polysilicon-filled trenches on an SOI substrate-accurate modeling of the heat flow in the metallization is found to be crucial. Furthermore, the simulated structure must be made wide enough to account for the large heat flow in the lateral direction.     

一种紧凑的GaN高电子迁移率晶体管大信号模型拓扑

GaN高电子迁移率晶体管（HEMT）以其复杂的器件特性使其大信号建模变得十分困难,尽管EEHEMT、Angelov等模型结构曾经成功应用于GaAs HEMT/MESFET的大信号模型,但当它们被用于GaN HEMT建模时却不再准确和完备.面向GaN HEMT器件的大信号模型,本文提出了一种紧凑的模型拓扑,此模型拓扑综合了GaN HEMT器件的直流电压-电流（I-V）特性、非线性电容、寄生参数、栅延迟漏延迟与电流崩塌、自热效应以及噪声等特性.经验证此模型拓扑在仿真中具有很好的收敛性,适用于GaN HEMT器件的大信号模型的建立,满足GaN基微波电路设计对器件模型的需求.     

Monte Carlo simulation of electronic characteristics in short channel δ-doped AlInAs/GaInAs HEMTs

We present a microscopic analysis of electronic noise in short channel δ-doped AlInAs/GaInAs HEMTs. A classical Monte Carlo device simulation, appropriately modified to locally introduce the effects of electron degeneracy and nonequilibrium screening, is used for the calculations. Even if the energy quantization in the channel is not taken into account in the Monte Carlo model, its validity has been checked by means of the comparison with experimental results of static characteristics, small signal behavior and noise performance in a recessed 0.1 μm T-gate δ-doped HEMT (InP based). The geometry and layer structure of the simulated HEMT is completely realistic, including recessed gate and δ-doping configuration and also the T-shape of the gate and the dielectric disposition has been included in the simulation     

Time-dependent thermal crosstalk in multifinger AlGaN/GaN HEMTs and implications on their electrical performance

The thermal dynamics of multifinger AlGaN/GaN high electron mobility transistors (HEMTs) with varying gate pitch was investigated using time-resolved Raman thermography. An identical temperature rise was measured in all gate fingers within the first ∼500 ns duration of electrical pulses. Gate finger temperature differences only emerge after 500 ns, due to the onset of thermal crosstalk. This thermal crosstalk onset delay is attributed to the finite rate of heat diffusion between gate fingers. Reducing the device gate pitch was found to increase the magnitude of transient thermal crosstalk. Implications of each gate finger within a multifinger HEMT having a different transient temperature are discussed in the context of device characteristics. The experimental results are compared to time-domain three-dimensional finite difference heat diffusion simulations.     

Electrostatic capacitances in standard and pseudomorphic ultrashort gate length HEMTs

HEMT electrostatic capacitances are determined with a 2D finite element solver according to the device geometry. The calculation is compared with measurements on recessed ultrasubmicrometre rectangular gate and T-gate pseudomorphic and standard HEMTs on GaAs.<>     

Experimental analysis of HEMT behavior under low-temperatureconditions

An experimental analysis of high-electron-mobility transistor (HEMT) behavior under low-temperature conditions is presented. Specific measurements have been performed to investigate the deep-level trapping effects on basic device characteristics such as carrier concentration, electron mobility in the structure, and access resistances. The influence of the collapse phenomenon on the microwave device parameters completes the knowledge of these parasitic effects. Explanation of mechanisms responsible for the anomalous phenomena and means to suppress them are reported. Microwave parameters measurements demonstrate that HEMTs showing no parasitic collapse effects exhibit improved performance at 77 K. Large improvements of current gain cutoff frequency and noise figure are presented     

Low-/spl kappa/ BCB passivation on AlGaN-GaN HEMT fabrication

Due to the stress-induced polarization effect on the GaN HEMTs, the surface passivation of the device is critical and is deserved to conduct a detailed study. It has been proven that the GaN HEMTs demonstrate nondispersive pulsed current-voltage (I-V) characteristics and better microwave power performances after passivating the Si/sub 3/N/sub 4/ film on the GaN surface. In this letter, we proposed to use the BCB material, a negative photoresist with a low-/spl kappa/ characteristic, as the surface passivation layer on GaN HEMTs fabrication. After comparing the dc I-V, pulsed I-V, RF small-signal, microwave power characteristics, and device reliability, this BCB-passivated GaN HEMT achieved better performance than the Si/sub 3/N/sub 4/ passivated device.     

14W X波段AlGaN/GaN HEMT功率MMIC

报道了研制的SiC衬底AIGaN/GaN HEMT微带结构微波功率MMIC,芯片工艺采用凹槽栅场板结构提高AlGaN/GaNHEMTs的微波功率特性.S参数测试结果表明AlGaN/GaN HEMTs的频率特性随器件的工作电压变化显著.研制的该2级功率MMIC在9～11GHz带内30V工作,输出功率大于10W,功率增益大于12dB,带内峰值输出功率达到14.7W,功率增益为13.7dB,功率附加效率为23%,该芯片尺寸仅为2.0mm×1.1mm.与已发表的X波段AlGaN/GaN HEMT功率MMIC研制结果相比,本项工作在单位毫米栅宽输出功率和芯片单位面积输出功率方面具有优势.     

Characteristics of a coplanar waveguide HEMT mount on GaAssubstrate

In a special integrated coplanar waveguide HEMT mount, designed for a wide band (1-60 GHz) on-wafer measurement of the characteristics of HEMTs on GaAs, significant power loss as high as 30% of the input power over a range of frequencies is observed. This power loss is mainly attributed to the radiation through two via holes connecting the coplanar waveguide ground planes to the backside metallization in the mount. Based on this assumption, an approximate theoretical model is developed to substantiate the experimental observations     

Smart 3-D Finite-Element Modeling for the Design of Ultra-Low On-Resistance MOSFET

A 3-D electrical finite-element model (FEM) for the design of an ultra-low on-state resistance power MOSFET device is presented. Model building and layer conductivity are discussed to take into account microscopic, technological, and electrical effects, such as metal step coverage and MOS behavior of each elementary cell of the transistor. Model simplifications are also presented to ensure time-efficient simulations. FEM gauging is then achieved, by comparing simulation results to electrical measurements, on devices subjected to top metallization debiasing effects. Simulations show a good agreement with measurements for result errors at less than 2%. The aim of this paper is to provide an accurate estimation of the contribution of parasitic elements such as the shape and number of power bonding wires or top metallization thickness to power device on-state resistance (R_ON). The 3-D electrical FEM is a mandatory first step towards an accurate electrothermal FEM for the design of efficient power products.     

High-power V-band AlInAs/GaInAs on InP HEMTs

The DC and RF performance of δ-doped channel AlInAs/GaInAs on InP power high-electron-mobility transistors (HEMTs) are reported. A 450-μm-wide device with a gate-length of 0.22 μm has achieved an output power of 150 mW (at the 1-dB gain compression point) with power-added efficiency of 20% at 57 GHz. The device has a saturated output power of 200 mW with power-added efficiency of 17%. This is the highest output power measured from a single InP-based HEMT at this frequency, and demonstrates the feasibility of these HEMTs for high-power applications in addition to low-noise applications at V -band     

Electrothermal Monte Carlo Simulation of Submicrometer Si/SiGe MODFETs

In this paper, we present results from the simulation of submicrometer Si/SiGe modulation-doped field-effect transistors (MODFETs) using an electrothermal Monte Carlo method. The relationships between the thermal droop effect observed in the electrothermal I_d -V_ds characteristics of the devices and the microscopic properties of electron transport and the temperature profiles are studied. The effects of varying the effective semiconductor die dimensions and the thickness of the SiGe buffers on the electrothermal behavior of the devices are also investigated. A comparison of the electrothermal performance of the simulated Si/SiGe MODFET with that of a GaAs-based HEMT is also carried out     

14W X波段AlGaN/GaN HEMT功率MMIC

报道了研制的SiC衬底AIGaN/GaN HEMT微带结构微波功率MMIC,芯片工艺采用凹槽栅场板结构提高AlGaN/GaNHEMTs的微波功率特性.S参数测试结果表明AlGaN/GaN HEMTs的频率特性随器件的工作电压变化显著.研制的该2级功率MMIC在9～11GHz带内30V工作,输出功率大于10W,功率增益大于12dB,带内峰值输出功率达到14.7W,功率增益为13.7dB,功率附加效率为23%,该芯片尺寸仅为2.0mm×1.1mm.与已发表的X波段AlGaN/GaN HEMT功率MMIC研制结果相比,本项工作在单位毫米栅宽输出功率和芯片单位面积输出功率方面具有优势.     

High breakdown Voltage undoped AlGaN-GaN power HEMT on sapphire substrate and its demonstration for DC-DC converter application

Undoped AlGaN-GaN power high electron mobility transistors (HEMTs) on sapphire substrate with 470-V breakdown voltage were fabricated and demonstrated as a main switching device for a high-voltage dc-dc converter. The fabricated power HEMT realized a high breakdown voltage with a field plate structure and a low on-state resistance of 3.9 m/spl Omega//spl middot/cm/sup 2/, which is 10 /spl times/ lower than that of conventional Si MOSFETs. The dc-dc converter operation of a down chopper circuit was demonstrated using the fabricated device at the input voltage of 300 V. These results show the promising possibilities of the AlGaN-GaN power HEMTs on sapphire substrate for future switching power devices.     

Investigation of Self-Heating Effects in Submicrometer GaN/AlGaN HEMTs Using an Electrothermal Monte Carlo Method

An electrothermal Monte Carlo (MC) method is applied in this paper to investigate electron transport in submicrometer wurtzite GaN/AlGaN high-electron mobility transistors (HEMTs) grown on various substrate materials including SiC, Si, GaN, and sapphire. The simulation method is an iterative technique that alternately runs an MC electronic simulation and solves the heat diffusion equation using an analytical thermal resistance matrix method. Results demonstrate how the extent of the thermal droop in the I_d-V_ds characteristics and the device peak temperature depend upon both the biasing conditions and the substrate material type. Polarization effects are considered in the simulations, as they greatly influence electron transport in GaN/AlGaN HEMTs by creating a highly concentrated two-dimensional electron gas (2DEG) at the GaN/AlGaN interface. It is shown that a higher 2DEG density provides the devices with a better current handling capability but also increases the importance of the thermal effects     

MOCVD-Grown AlGaN Buffer GaN HEMTs With V-Gates for Microwave Power Applications

We report the performance of AlGaN buffer GaN high-electron mobility transistors (HEMTs) grown by metal–organic chemical vapor deposition. GaN HEMTs on high-quality AlGaN buffer were grown on SiC substrates. The incorporation of an AlGaN buffer into the GaN HEMT significantly improves channel confinement and suppresses the short-channel effect. Advanced deep-recess V-gate structures were employed to optimize the device for better microwave power performance. With a 10-nm GaN channel layer sandwiched between the AlGaN barrier and buffer, excellent power performance was achieved. The output power density is 13.1 W/mm, and the associated power-added efficiency is 72% at 4-GHz frequency and 48-V drain bias. This power performance is comparable to the state-of-the-art GaN HEMTs grown on GaN buffers, indicating that the AlGaN buffer in our optimized device structure does not introduce any noticeable trapping.      

Analysis of delta-doped and uniformly doped AlGaAs/GaAs HEMT's byensemble Monte Carlo simulations

Transport properties and device performance of delta-doped and uniformly doped AlGaAs/GaAs high electron mobility transistors (HEMTs) with identical threshold voltages and gate capacitors are investigated using two-dimensional self-consistent ensemble Monte Carlo simulations. The model includes the effects of real-space transfer and carrier degeneracy, as well as the influence of DX centers and surface states. A one-to-one comparison of simulation results for the two devices demonstrates superior performance for the delta-doped HEMT and provides a physical basis for the observed improvements. In particular, the delta-doped HEMT maintains its superior device performance as gate bias is increased. Reasons for these improvements are reported     

SiN钝化前的NF3等离子体处理对AlGaN/GaN HEMT性能的影响

研究了SiN钝化前利用感应耦合等离子体（ICP）对AlGaN/GaN HEMT表面进行NF3等离子体处理对器件性能的影响. 结果表明,运用低能量的NF3等离子体处理钝化前的AlGaN/GaN HEMT表面能有效抑制器件电流崩塌,而器件直流及微波小信号特性则未受影响. 微波功率测试表明,经过6min NF3等离子体处理的AlGaN/GaN HEMT在2GHz, 30V工作电压下达到6.15W/mm的输出功率密度,而未经过处理的器件只达到1.82W/mm的输出功率密度.