High Junction Temperature Research Articles

A High Temperature Linear Wideband Power Amplifier for a Downhole Communication System

Abstract In order to reach previously untapped wells, the oil and gas industry continues to drill deeper, resulting in extreme operating temperatures for electronic systems. It is essential for electronic circuits and systems to be able to withstand extreme temperatures. The proposed power amplifier (PA) intends for a downhole communication system operating at an ambient temperature of 230 °C. The proposed PA is designed with Qorvo T2G6003028-FL GaN on SiC HEMT, which offers a high junction temperature. The proposed PA can operate reliably up to an ambient temperature of 230 °C with the operation frequency from 228 MHz to 263 MHz. At 230 °C, it achieves maximum output power of 1.66 W, the peak gain of 24 dB, peak PAE (power added efficiency) of 25%, OP1dB (output 1-db compression point) of 32 dBm, and OIP3 (output third intercept point) of 37.9 dBm..

Design of 2N-diode power-combined frequency tripler with coupled suspended striplines

A novel scheme for power-combined frequency tripler adopting 2N diodes is proposed in this work. Even mode coupled suspended substrate stripline is used to divide and recombine the input and output power. The circuits of the tripler are printed on both sides of the substrate, with N diodes on the front side and the other N diodes on the back side. The front diodes and back diodes are in anti-parallel connection, and DC biased separately to increase the bandwidth and power capacity. Three Q-band prototypes with two, four, and six diodes are fabricated and tested. The output compression powers at output frequency of 43.5 GHz for two/four/six-diode tripler are 9.2, 11, and 12 dBm, respectively. Power capacity is improved with the proposed tripler. Optimum DC bias is also discussed in this work, and it is found that it first increases with drive power, and then drops when large drive power applied because of the increased series resistance of the diode due to high junction temperature.

Experimental investigation of high-power light-emitting diodes’ thermal management by ionic wind

It is urgently necessary to find an effective way to solve the problem of thermal management in high-power light-emitting diodes (HPLED) because most of the input power is converted into heat, which leads to a high junction temperature. Novel ionic wind generators have been developed in the present work for effective cooling of high-power LEDs. The working performance of the ionic wind using ‘wire-to-net’ and ‘needle-to-net’ electrodes were investigated experimentally. The electric field intensity distribution of ‘needle-to-net’ ionic wind generator was described mathematically. The results indicate that better cooling performance could be obtained when thin wire or pointed needle were used at smaller discharge gap with reasonable electrode spacing under negative corona discharge. The maximum electric field intensity could be obtained at the tip of needles. Finally, the advantages of using ionic wind for cooling the LEDs were confirmed to be higher in efficiency, lower in energy consumption and mechanical noise.

Optical, spectral, and thermal analyses of InGaN/GaN near‐ultraviolet flip‐chip light‐emitting diodes with different package structures

We analyzed and compared the optical, spectral, and thermal characteristics of InGaN/GaN near‐ultraviolet (NUV) flip‐chip (FC) light‐emitting diodes (LEDs) packaged on the board with dielectric/metal layers (DMB package), board with ceramic/metal layers (CMB package), and board with ceramic/metal layers and thermal tape (CMBT package) in the injection current range of 0–800 mA at 298 and 358 K. For the DMB packaged LED, the relatively high junction temperature was observed due to the inefficient heat dissipation, leading to the more optical output power drop and spectral shift. For the CMBT packaged device, it further dissipated heat at high currents where the performance of CMB packaged device was degraded. In comparison with the experimental results, the theoretically calculated temperature and stress distributions of the NUV FC LEDs with the DMB and CMB packages were also investigated by finite element method‐based simulations.

Investigation of the Dynamic On-State Resistance of 600 V Normally-Off and Normally-On GaN HEMTs

In this paper, current collapse phenomena and thermal effects in normally-off and normally-on GaN HEMTs are investigated. The experimental results show that a high-off-state voltage and high-switched drain current at high junction temperature cause an increase of the on-state resistance ${{\rm{R}}_{{\rm{DSON}}}}$ . Varying the switching frequency from 50 to 400 kHz, an increase of the on-state resistance is further observed for both types of GaN devices. It is evident from these experiments that the number of switching transients significantly influences the increase of the RDSON, suggesting that this increase is due to a current collapse in GaN HEMTs. A detailed comparison of the evaluated R DSON between GaN transistors and the high-speed CoolMOS-C7 transistor is presented.

Design and implementation of a rigid-flex RF front-end system-in-package

This paper presents a kind of 3D stacked system-in-package (SiP) for the minimization of the RF front-end system used in a micro base station. The RF SiP, based on a rigid-flex substrate, retains a small volume of 5 cm × 5.25 cm × 0.8 cm, which is almost 95 % reduced from the prototype board. The detail design process is presented including system-in-package design, substrate design and thermal management evaluation. Simulation is performed for the electrical characterization of the substrate and the thermal management evaluation of the package. The simulation results reveal that the insertion loss of the RF signal going through the rigid-flex substrate is controlled under 0.38 dB and the eye diagrams of the differential clock signals meet the requirements. Power distribution network is also well designed since the biggest DC voltage drop is less than 6 mV and the highest current density is 3370 A/cm2, which is much lower than the maximum current-carrying capacity of the conductors with 20 °C temperature rise according to the IPC standard. Also, thermal simulation demonstrates the reliability of this RF SiP because the highest junction temperature reaches 79.3 °C for the normal air convection environment (20 °C) and 91.1 °C for the extreme condition (60 °C) with the forced air cooling method. Junction temperatures of both conditions are below 95 °C, which indicates the proper functioning of active chips in this RF SiP.

(Invited) InGaN/GaN Nanowire LEDs and Lasers on Nonconventional Substrates

Conventional planar group-III nitride epitaxy for light-emitting diode (LED) is typically grown on sapphire, which results in high threading dislocation densities in the order of 106-108 cm-2 because of thermal- and lattice-mismatch. The challenge in realizing efficient InGaN QWs in the green gap and beyond stems from the spontaneous and piezoelectric polarization fields induced electron-hole wave functions separation as the indium composition increased to 25% and above.1 SiC and GaN bulk substrates, and nonpolar nitride materials have been used to address the lattice-mismatch, efficiency-droop, polarization field, and green gap issues, at the expense of high development and material costs.2 Nanowire LEDs on silicon has numerous advantages over planar epitaxial LEDs, such as a reduced polarization field, wavelength tunability by increasing indium composition and light extraction.3, 4 The blue, green, red and infrared LEDs grown using molecular beam epitaxy (MBE) demonstrated the potential of nanowires emitters for practical applications.5, 6 However, the large specific surface, and therefore a high density of surface states was found to limit the quantum efficiency and output power of nanowire devices.7 The phonon and carrier confinement in nanowires also led to junction heating and reduced heat dissipation. In this talk, we will present our investigations on nanowires LEDs and lasers emitting at green-to-infrared wavelength range. The approach in surface states passivation in InGaN/GaN quantum-disk-in-nanowires LEDs, as well as enhancing heat dissipation by growing nanowires-crystal on metal substrates will also be presented. Ammonium sulfide was used to passivate the nanowires in the laser fabrication process to reduce the p-contact resistance of GaN:Mg.5 We also developed octadecylthiol (ODT) passivation process for LEDs, which led to a ~4 times increase in photoluminescence peak intensity, and 50% increase in relative peak external-quantum-efficiency in passivated LEDs.8 The passivation changed the surface dynamic charge and recovered the band-edge emission. The faster-increasing trend in quantum efficiency is due to the reduced Shockley–Read–Hall (SRH) non-radiative recombination on the nanowires surface, which was confirmed using 4D scanning ultrafast electron microscopy technique, and the associated rate-equations simulations.9 Current high-power planar LEDs have to be transferred to a heat sink, such as Cu or CuMo, via laser liftoff or wafer bonding because of the high junction temperature during operation. It is more severe for nanowire LEDs on Si because of the small diameter, and the formation of SiN layer before nanowires growth. We developed the first high-power red InGaN/GaN Qdisks-in-nanowire LEDs on bulk polycrystalline Mo; the platform simultaneously implements buffer layer, reflector, n-metal contact, and heat-sink, thus greatly simplifies the fabrication process for high-power devices.10 The LEDs showed a low turn-on voltage of ∼2 V without droop, much lower junction temperature compared to LEDs on Si, and longer lifetime, thus is promising for high-power device operation. In conclusion, the InGaN/GaN nanowire edge-emitting lasers at green-to-infrared wavelength range on Si were demonstrated. We showed the first organic chemical passivation treatment on nitride nanowires, to increase external quantum efficiency and reduce SRH non-radiative recombination. We also reported the first nanowires device growth process on metal substrates. The fabricated device from the high-crystal-quality nanowires shows low turn-on voltage, high-power, droop-free, and stable operation.

Aging characteristics of blue InGaN micro-light emitting diodes at an extremely high current density of 3.5 kA cm−2

The aging characteristics of blue InGaN micro-light emitting diodes (micro-LEDs) with different sizes have been studied at an extremely high current density 3.5 kA cm−2 for emerging micro-LED applications including visible light communication (VLC), micro-LED pumped organic lasers and optogenetics. The light output power of micro-LEDs first increases and then decreases due to the competition of Mg activation in p-GaN layer and defect generation in the active region. The smaller micro-LEDs show less light output power degradation compared with larger micro-LEDs, which is attributed to the lower junction temperature of smaller micro-LEDs. It is found that the high current density without additional junction temperature cannot induce significant micro-LED degradation at room temperature but the combination of the high current density and high junction temperature leads to strong degradation. Furthermore, the cluster LEDs, composed of a micro-LED array, have been developed with both high light output power and less light output degradation for micro-LED applications in solid state lighting and VLC.

Superlattice-based thin-film thermoelectric modules with high cooling fluxes.

In present-day high-performance electronic components, the generated heat loads result in unacceptably high junction temperatures and reduced component lifetimes. Thermoelectric modules can, in principle, enhance heat removal and reduce the temperatures of such electronic devices. However, state-of-the-art bulk thermoelectric modules have a maximum cooling flux qmax of only about 10 W cm−2, while state-of-the art commercial thin-film modules have a qmax <100 W cm−2. Such flux values are insufficient for thermal management of modern high-power devices. Here we show that cooling fluxes of 258 W cm−2 can be achieved in thin-film Bi2Te3-based superlattice thermoelectric modules. These devices utilize a p-type Sb2Te3/Bi2Te3 superlattice and n-type δ-doped Bi2Te3−xSex, both of which are grown heteroepitaxially using metalorganic chemical vapour deposition. We anticipate that the demonstration of these high-cooling-flux modules will have far-reaching impacts in diverse applications, such as advanced computer processors, radio-frequency power devices, quantum cascade lasers and DNA micro-arrays.

Effect of Sintering Cycle on Physical and Mechanical Properties of Open Pore Cell Copper Foam

Poor thermal management leads to high LED junction temperature and give negative impacts to its life and performance. High temperature of LED junction has proven to produce less light and accelerate chip degeneration. Open pore cell copper foam provide good solution to the poor thermal management problem since it has higher surface area, thus increase surface emissivity and enhance thermal conductivity. In this study, copper foams were fabricated using metal injection moulding using potassium carbonate as space holder. The effect of sintering cycle on physical and mechanical properties were studied using two different sintering cycle which are 450-850°C and 450-850-950°C. It is found that sintered copper foams using 450°C-850-950°C sintering cycle has better mechanical properties in term of hardness and transverse rupture strength. It also exhibited higher porosity which is up to 33.9% compared to 33.1%, thus has higher surface area. This is proven by higher thermal conductivity exhibit by the specimen sintered using 450°C-850-950°C.

Experimental study of high power LEDs heat dissipation based on corona discharge

High power light-emitting diodes (LEDs) consume most of the applied power as heat, which leads to a high junction temperature; thus, an efficient cooling device is needed. Most of the developed cooling systems face constraints such as cost, consumption, and noise, leading to low work efficiency. In this study, a needle-to-net type ionic wind generator based on corona discharge is suggested for high power LED cooling. The LEDs' junction temperature was calculated by measuring the case temperature, which is called the pin-temperature measurement method. The characteristics of ionic wind in various electrode arrangements or electrical parameters were analyzed, and the case temperature changes induced by ionic wind were measured under various conditions for analysis. The experimental results indicate that the designed ionic wind generator had good cooling performance close to cooling fan, coupled with lower energy consumption and less mechanically induced noise. The maximum ionic wind velocity was measured to be 2.97m/s at a 15 mm discharge distance and 17 kV applied voltage.

Thermal Characteristics Analysis of Die Attach Layer Based on Time-Constant Spectrum for High-Power LED

The performance and reliability of the high-power light-emitting diodes (HP LEDs) are closely related to the quality of the die attach adhesive (DAA) layer, because voids or delaminations in the layer may cause higher junction temperature, and even result in the break of the chip. In this paper, a dynamic compact thermal model is constructed for an independent HP LED without being attached on a cold plate. The time-constant spectrum method based on the thermal model is applied to characterize the transient thermal behavior of the DAA layer and other layers along the heat flow path. Thermal transient experiments are carried on HP LED samples with different DAA dosages. The theoretical and experimental results demonstrate that the time-constant spectrum for LEDs tested without cold plate can reflect the thermal characteristics of the DAA layer as well as that with cold plate. Differences in the HP LED samples with different DAA layers can be obviously distinguished in the time-constant spectrums as well. Compared with the traditional testing method with cold plate, direct test in air for HP LEDs has the advantages of easy operation, time saving, and no pollution to samples.

Metal Salt Solution-Nanoprecipitation Method for Improvement in Reliability of Sintered Ag Nanoparticle Bonding

Interest in die-attach materials with high thermostability has been stimulated by the high junction temperature of power semiconductors. Sintered Ag nanoparticle bonding is the most attractive candidate for use as solder because of its high melting point (1253 K) and low process temperature (~573 K). Recent studies have assumed that this bonding exhibits high thermostability above 573 K. However, in fact, it is difficult to preserve the bonding strength after high-temperature storage at 523 K for 1000 h. Thus, we first clarified that the sintered Ag nanoparticle bonding was degraded by micropore coalescence caused by the Ag grain growth. We then developed the metal salt solution-nanoprecipitation (MS2NP) method for improving the reliability of the sintered Ag nanoparticle bonding. We found that the bonding used by the MS2NP method can maintain a high die-shear strength (~40 MPa) even after high-temperature storage at 573 K for 1000 h.

Thermally enhanced blue light-emitting diode

We investigate thermoelectric pumping in wide-bandgap GaN based light-emitting diodes (LEDs) to take advantage of high junction temperature rather than avoiding the problem of temperature-induced efficiency droop through external cooling. We experimentally demonstrate a thermally enhanced 450 nm GaN LED, in which nearly fourfold light output power is achieved at 615 K (compared to 295 K room temperature operation), with nearly no reduction in the wall-plug efficiency (i.e., electrical-optical energy conversion efficiency) at bias V&amp;lt;ℏω/q. The LED is shown to work in a mode similar to a thermodynamic heat engine operating with charged carriers pumped into the active region by a combination of electrical work and Peltier heat (phonons) drawn from the lattice. In this optimal operating regime at 615 K, the LED injection current (3.26 A/cm2) is of similar magnitude to the operating point of common high power GaN based LEDs (5–35 A/cm2). This result suggests the possibility of removing bulky heat sinks in current high power LED products thus realizing a significant cost reduction for solid-state lighting.

Investigation on Some Parameters Affecting Optical Degradation of LED Packages During High-Temperature Aging

The mechanism of optical degradation for the light emitting diode (LED) packages in the light bars under the high-temperature aging condition, one of the accelerated life tests, is studied experimentally and numerically. Some parameters, including junction temperature, encapsulant materials, delamination, leadframe surface degradation, and encapsulation, are closely investigated. It is found that the encapsulants (with or without phosphors) and interface delamination have no effect on the optical degradation during the high-temperature aging. On the contrary, junction temperature, leadframe surface degradation, and encapsulation play important roles on this degradation. Optical degradation of the LED packages is found to be mainly caused by silver chloride, which is generated on the leadframe surfaces with an exposure of silver finish in light and heating conditions after interface delamination happening during the high-temperature aging. The high junction temperature could speed up the generation of silver chloride. Moreover, the blue LED package with an encapsulant (silicone) surprisingly give a lower lumen maintenance than one without encapsulant during the high-temperature aging, because of more light absorption on the darkening leadframe surface by total light reflection from silicone encapsulant. Some important parameters affecting the thermal reliability of the LED packages have been identified and the corresponding optical degradation mechanism has been clarified.

Thermal Engineering of GaN Semiconductor Devices

The development of gallium nitride (GaN) on a variety of substrates from Si to diamond has been used to create a variety of devices for both RF and power electronics technologies. In general, GaN devices can accommodate faster switching speeds, higher junction temperatures, and high voltages, allowing for devices operating at higher power with increased efficiency in smaller form factors. However, the lattice mismatch between c-axis hexagonal GaN and other non-native substrates requires the use of buffer layers in order to grow high quality, relaxed GaN required for advanced devices. Such layers can add to the thermal resistance which impacts to overall device thermal performance and thus, device reliability. In addition, these interfacial layers impact the growth and residual stress in the GaN epitaxial layers that can limit the overall voltage limits of lateral HEMT devices. In this work we use a variety of experimental techniques to measure the thermal boundary resistance (TBR) for GaN on Si, SiC, and diamond substrates. The impact of the structure of the interface on the overall TBR and thermal conductivity of the GaN layers grown by MOCVD will be discussed. In addition to the TBR, the overall stress in the devices caused by growth on the differing substrates, measured by Raman spectroscopy, will be presented. A unique superlattice structure used to reduce the stress in GaN layers on Si will also be highlighted. Finally, the electro-thermomechanical performance of GaN devices under DC and pulsed operation will be presented where the temperature of the devices was measured using Raman Spectroscopy while the mechanical deformation was measured by Scanning Joule Expansion Microscopy. Data will show that rapid heating and high tensile stresses near the drain side edge of the gate during pulsed operation is dependent on the bias conditions, the TBR, substrate material, and the mechanical properties of the device. Overall, challenges associated with the structure of GaN devices that must be overcome for effective thermally management will be presented.

Influence of Relative Humidity on the Temperature Increase of a Power Converter

As a vital part of renewable energy and electrical traction, power converters are supposed to have high reliability and good performance. However, power semiconductors produce considerable heat when the power converter works, which results in high junction temperatures that lower the reliability and performance of the power semiconductors. Many studies show that ambient humidity has a significant effect on power devices, but the influence of high humidity on junction temperatures has yet to be studied. Therefore, this paper presents a thermal model for power converters in moist air to obtain the junction temperature increase, which is utilized for the power converter used in a Switched Reluctance Motor System. Simulation results show that the law of converter temperature distribution is independent of the relative humidity in the case of fixed ambient temperature, whereas the temperature in the power converter decreases as the ambient relative humidity increases. These simulation results are validated with the experimental results.

Thermal Analysis of High-Power Multichip COB Light-Emitting Diodes With Different Chip Sizes

This paper demonstrates the thermal analysis of high-power light-emitting diodes (LEDs) with various chip sizes, in the same chip-on-board (COB) package and with the same total chip size and input power. The 4-, 9-, 25-, and 100-chip multichip COB LEDs with chip-side lengths of 1500, 1000, 600, and 300 $\mu $ m were used. The simulation results indicate that the maximal junction temperature of the multichip COB LEDs increased as the number of chips in the multichip COB LED decreased. In addition, with the same input power, the difference between the maximal and minimal junction temperatures of the multichip COB LED increased as the number of chips in multichip COB LEDs increased. That is, if the multichip COB LED contains a few number of large chips, the output power of each chip will drop but uniform owing to the high junction temperature and low temperature difference. Oppositely, if the multichip COB LED contains a lot of small chips, the output power of the chips at the corners will be higher than other chips, but the output power of each chip will be nonuniform owing to the nonuniform junction temperature distribution.

High Junction Temperature and Low Parasitic Inductance Power Module Technology for Compact Power Conversion Systems

Advanced power module technology capable of taking advantage of the superior features of next-generation power devices, such as those fabricated with SiC and GaN, must be developed to create much more compact and cost-effective power conversion systems. New power modules based on such technology are especially required to allow fast switching of power devices in the extended junction temperature range. This paper describes the major technical challenges involved in sufficiently improving the thermal stress reliability of the critical package systems in SiC power modules and in markedly reducing internal parasitic inductance. Thermal stress reliabilities of the die attachment system, wire bonding system, and encapsulant system are successfully improved, all of which are shown to be able to achieve common life targets: 1) 3000 h for a storage test at 250 °C and 2) 3000 cycles for thermal cycling between −40 °C and 250 °C. A novel phase-leg power module capable of substantially reducing the loop inductance along the principal current tracks is proposed and fabricated by applying SiC-JFETs, SiC-Schottky barrier diodes, and the abovementioned reliable thermal stress package systems. Double pulse switching testing of the module reveals smaller drain-source voltage spikes and ringing even in turn-ON and turn-OFF transients at very high slew rates of current and voltage. Finally, a 0.34 L forced-air-cooled dc 600 V input ac 50 Hz 400 V 25 kW output three-phase SiC inverter is fabricated using three-phase leg modules and its operation is demonstrated at high-power levels.

Improvements on high voltage capacity and high temperature performances of Si-based Schottky potential barrier diode

In order to improve the reverse voltage capacity and low junction temperature characteristics of the traditional silicon-based Schottky diode, a Schottky diode with high reverse voltage capacity and high junction temperature was fabricated using ion implantation, NiPt60 sputtering, silicide-forming and other major technologies on an N-type silicon epitaxial layer of 10.6–11.4 μm and (2.2–2.4) × 1015 cm−3 doping concentration. The measurement results show that the junction temperature of the Schottky diode fabricated can reach 175 °C, that is 50 °C higher than that of the traditional one; the reverse voltage capacity VR can reach 112 V, that is 80 V higher than that of the traditional one; the leakage current is only 2 μA and the forward conduction voltage drop is VF = 0.71 V at forward current IF = 3 A.