High Temperature Electronics Research Articles

Polyimide-Based High-Temperature Plastic Electronics

All-plastic transistor devices with thermal stability up to 220 °C are demonstrated. We employ polyimide substrates, polyimide dielectrics, and a polyimide-based semiconducting blend to achieve fle...

Shear strength of off-eutectic Au[sbnd]Ge joints at high-temperature

High-temperature compatible devices of SiC have been demonstrated in recent years. Together with a high-temperature compatible die-attach, they can form a basis for future reliable high-temperature electronics. This article presents shear strength capacity of Au-rich off-eutectic AuGe die-attach at temperatures above the eutectic melting point. Metallized (Ni/Au) SiC dice were joined to metallized (Cu/Ni/Au) Si3N4 substrates with eutectic AuGe preforms. The joints demonstrated a significant shear strength capacity up to 410 °C (50 °C above the eutectic melting point). High-quality Au-rich off-eutectic AuGe joints, comprising a AuGe mixture with 8 ± 4 at.% Ge, were formed with a low bond line pressure (240 kPa). At room temperature the shear strength was measured to be approximately 140 MPa, falling to approximately 40 MPa at 410 °C. This demonstrates that off-eutectic joints might be considered for use at temperatures above the eutectic melting point. The fracture mode was mainly cohesive in the off-eutectic AuGe layer when tested at a temperature below the eutectic melting point. Above the eutectic melting point, the fracture mode was complex with signs of a partially melted off-eutectic AuGe compound. Within this compound, columnar structures of the primary α phase (Au) was surrounded by an apparently melted and solidified phase. In other regions, an adhesive fracture at the interface between a slightly off-eutectic compound and a GeNi layer was discovered. The microstructure was found to be inhomogeneous with large regional variations within joints. From almost pure Au, primary α phase with up to 2–3 at.% Ge, up to near eutectic AuGe regions with an overall composition of 20–30 at.% Ge. In general, Ge was segregated into explicit domains within a primary α phase.

Wide band gap semiconductor technology: State-of-the-art

Applications of the wide band gap (WBG) semiconductors, such as GaN, AlGaN, and InGaN, range from lighting and ultraviolet (UV) technology to high power, radiation hard, high temperature, terahertz (THz) and sub-THz electronics and pyroelectronics. Wurtzite (hexagonal) symmetry makes these materials to be quite different from conventional cubic semiconductors. Spontaneous and piezoelectric polarization associated with the wurtzite crystal structure induces two-dimensional electron gases at AlGaN/GaN, AlInN/GaN, and AlGaN/InGaN interfaces with sheet concentrations 10–20 times higher than those in Si CMOS. A high current carrying capability and a high breakdown field make these materials perfect for high power applications. Adjusting the energy gaps of AlxGa1−xN and of InxGa1−xN by varying the molar fraction changes the wavelength of light they emit or absorb and enables light and UV emitters, solar cells, and photodetectors operating from THz and infrared to deep UV range. Blue, green, and white LEDs using InGaN revolutionized smart solid-state lighting. AlGaN UV LEDs are used for water purification, fighting antibiotic resistant bacteria and viruses, and dramatically increasing produce storage time. InN, ZnO, and BN have potential to compete with the AlN/GaN family. Diamond has re-emerged not only as a substrate for a record heat removal but also as a viable THz detector material. The WBG technology has many difficult problems to solve. High dislocation density in the WBG materials leads to a low efficiency of deep AlGaN UV LEDs and reliability problems of high power devices. Non-uniformities of the electric field distribution cause a premature breakdown. Using ultrathin WBG quantum well layers and nanowires and exploring radically new physics-based device designs might alleviate or even solve these problems.

Electronic Structure Tunability of Diamonds by Surface Functionalization

Wide-bandgap semiconductors are exploited in several technological fields such as electron emission devices, energy conversion, high-power high-temperature electronics, and electrocatalysis. Their electronic properties vary significantly depending on the functionalization of the surface. Here, we investigated as a proof-of-concept the modulation of the electronic properties of one of the most common wide-bandgap semiconductors, that is, diamonds, to show the tunability of their properties by modifying the surface termination. Photoelectron spectroscopy was used to demonstrate the availability of a wide window of band bending, work function, and electron affinity. The band bending and work function were found to change by up to 360 meV and 2 eV, respectively, by varying the surface from hydrogen- to oxygen-terminated. Because of the negative electron affinity of diamonds, we were able to experimentally show the rigid shift of the whole band structure.

Thermal Degradation of Monolayer MoS2 on SrTiO3 Supports

Monolayer MoS2 is a wide-bandgap semiconductor suitable for use in high-temperature electronics. It is therefore important to understand its thermal stability. We report the results of a study on t...

Vibrational and electron-phonon coupling properties of β-Ga2O3 from first-principles calculations: Impact on the mobility and breakdown field

The wide band gap semiconductor β-Ga2O3 shows promise for applications in high-power and high-temperature electronics. The phonons of β-Ga2O3 play a crucial role in determining its important material characteristics for these applications such as its thermal transport, carrier mobility, and breakdown voltage. In this work, we apply predictive calculations based on density functional theory and density functional perturbation theory to understand the vibrational properties, phonon-phonon interactions, and electron-phonon coupling of β-Ga2O3. We calculate the directionally dependent phonon dispersion, including the effects of LO-TO splitting and isotope substitution, and quantify the frequencies of the infrared and Raman-active modes, the sound velocities, and the heat capacity of the material. Our calculated optical-mode Grüneisen parameters reflect the anharmonicity of the monoclinic crystal structure of β-Ga2O3 and help explain its low thermal conductivity. We also evaluate the electron-phonon coupling matrix elements for the lowest conduction band to determine the phonon mode that limits the mobility at room temperature, which we identified as a polar-optical mode with a phonon energy of 29 meV. We further apply these matrix elements to estimate the breakdown field of β-Ga2O3. Our theoretical characterization of the vibrational properties of β-Ga2O3 highlights its viability for high-power electronic applications and provides a path for experimental development of materials for improved performance in devices.

Pressureless die attach by transient liquid phase sintering of Cu nanoparticles and Sn-58Bi particles assisted by polyvinylpyrrolidone dispersant

Highly reliable bonding materials have attracted tremendous interest due to a growing demand for high-temperature electronics. We developed a fluxless and binder-free paste comprising Cu nanoparticles (NPs), Sn-58Bi (SnBi) particles, and polyvinylpyrrolidone (PVP) dispersing agent, which enables pressureless, low-temperature (190–250 °C) formation of robust joints (over 7 MPa) by means of transient liquid phase sintering (TLPS). Microstructural evolution of the joint was investigated under variations in PVP molecular weight (MW; 10,000, 55,000, 360,000, or 1,300,000) and bonding conditions including temperature and time. In a die-shear test, the joint formed with PVP MW 360,000 was the strongest due to its proper particle dispersion and the formation of intermetallic compounds (IMCs). Conditions of excessive PVP MW, bonding temperature, and time impeded the bonding characteristics of the TLPS joint, with formation of voids and increasing brittleness. TLPS bonding with the optimal dispersing agent enabled pressureless die attach without chip damage, demonstrating applicability as a simple, robust interconnection for high-temperature electronics.

Simulation study of a 4H-SiC lateral BJT for monolithic power integration * * Project supported by the National Natural Science Foundation of China (No. 51577054).

Power integration based on 4H-SiC is a very promising technology for high-frequency and high-temperature power electronics applications. However, the fabrication processes used in Si BiCMOS technology is not applicable in 4H-SiC at present, and few studies on the monolithic power integration of the SiC signal devices and power devices have been reported. In this paper, we propose a novel lateral BJT structure, which is suitable for monolithically integrating with the vertical power BJT on the same epitaxial wafer at the cost of one additional mask. The signal BJT’s static and dynamic characteristics are comprehensively investigated by TCAD simulation. Simulation results show that the common-emitter current gains of the 4H-SiC signal BJT are 133 and 52 at room temperature and 300 °C, respectively. Its implementation in an inverter shows that its switching time is about 200 ns.

Flexible ceramic film capacitors for high-temperature power electronics

Flexible ceramic film capacitors with high dielectric constant and high breakdown strength hold special promise for applications in power electronics. We deposited lanthanum-doped lead zirconate titanate (PLZT) films on aluminum-metallized polyimide films at room temperature by an aerosol deposition (AD) process and examined the electrical and dielectric properties of the PLZT films over a wide temperature range between −55 and 175 °C. The PLZT film capacitors fabricated by high deposition rate AD process not only satisfy X8R temperature rating but also exhibit superior volumetric and gravimetric specific capacitance. At room temperature, we measured a dielectric constant of ≈85, dielectric loss of ≈0.012, energy density of ≈13.2 J/cm3 with an applied voltage of ≈1000 V. A mean dielectric breakdown field strength (EB) of ≈1.25 MV/cm was determined by Weibull analysis for the ≈8-μm-thick PLZT film capacitors fabricated on flexible aluminum-metallized polyimide substrates. These results revealed that the PLZT-based ceramic film capacitors meet the requirements for advanced high-temperature power inverters. Our results demonstrated that AD process offers the greatest potential for producing low-cost, robust, compact and light-weight ceramic film capacitors with enhanced reliability for power inverters of electrical drive vehicles and various power electronic devices that are critical for high-efficiency energy conversion and renewable energy systems.

Arresting high-temperature microstructural evolution inside sintered silver

The surface oxidation of internal pore surfaces of nano-scale sintered silver has increased stability for high temperature applications. Operating temperatures of up to 400 °C have resulted in no or minimal changes in microstructure. By contrast, it is known that the microstructure of untreated pressure-less sintered silver continuously evolves at temperatures above 200 °C, grain and pore growth resulting in microstructure coarsening and increased susceptibility to fatigue. Oxidation of the internal pore surfaces has been shown to freeze the microstructure when the contact metallization is also silver or chemically inert. Samples exhibited no change in microstructure either through continuous observation through glass, or after cross sectioning. The tested specimens under high temperature storage resisted grain growth for more than 1000 h at 300 °C. The oxidising treatment can be performed via many different routes. For example, exposure to steam, or even by dipping in water for 10 min followed by immediate high temperature exposure and the effectiveness of these varying treatments is assessed. In this work we explore the mechanism that causes stabilization and explore the hypothesis that oxidation prevents grain boundary movements by arresting the fast migration of atoms along the internal pore surfaces. Analysis of the surface structure of the sintered silver by X-ray photoelectron spectroscopy shows presence of silver oxide (Ag2O) and computer simulation of grain boundary movements confirm the presence of a barrier to atomic movement on the internal silver surfaces. These findings are very promising for potential applications of sintered silver as a die attach material for High Temperature electronics packaging.

Assembly of β‐SiC Nanowires film and humidity sensing performance

Abstractβ‐SiC materials have been seen as the third‐generation semiconductor widely used in kinds of photoelectric device, high temperature electronics, and other fields. Compared with ordinary semiconductors, β‐SiC materials have huge potential application in replacing monocrystalline silicon in extreme environments because of their numerals extraordinary chemical and physical properties. Based on this, β‐SiC nanowires obviously are more desirable in any way. Here, we present a modified chemical vapor deposition (CVD) method to synthesis β‐SiC nanowires, which needs no protect gas, and transfer it to Si/SiO2 substrates equipped with Au electrodes. The microstructure of the as‐prepared samples is tested by field emission scanning electron microscopy (FESEM). The humidity sensing performance of electronic device is measured by electrochemical workstation test equipment. It shows that the resistance of β‐SiC nanowires increases with increasing environment humidity within very short response/recovery time‐0.5 seconds/0.5 seconds and also performs excellent cycling stability. Such advantage superiorities make it highly possible to apply β‐SiC nanowires into various environments.

Initial interfacial reactions of Ag/In/Ag and Au/In/Au joints during transient liquid phase bonding

A comparative study of initial interfacial reactions and kinetics of AgIn and AuIn as die-attach materials for high-temperature power electronics applications was performed in this study. Sequential interfacial reactions and transformations of the In solder to intermetallic compound (IMC) phases of the Ag/In/Ag and Au/In/Au joints were investigated and compared for transient liquid phase (TLP) bonding at 190 °C for 1 min under different bonding pressures. The interfacial reaction of the Ag/In/Ag joint was faster than that of the Au/In/Au joint under same bonding conditions. In the Ag/In/Ag joints, the TLP joint was fully converted into the Ag-rich Ag2In IMC. On the other hand, the Au/In/Au TLP joint was composed of three AuIn IMCs of Au7In3, AuIn, and AuIn2.

A Brief Review on High-Temperature, Pb-Free Die-Attach Materials

High-Pb solders have been used as die-attach and interconnect materials for decades in discrete power components. Because of the known harmful effects of Pb to human health and the environment, as well as the demand of the wide-band-gap SiC/GaN power devices serving under high power density and high junction temperature, alternative Pb-free solders/materials and solutions have been studied intensively. Pb-free alternatives to replace high-Pb solders are still in their infancy. The exemption of using high-Pb solders has been extended to 2021, although it may be terminated anytime if a new technology or material were to be accepted industry-wide. The potential high-temperature Pb-free materials, including solders (AuSn/AuSi/AuGe, ZnAl and BiAgX®), Ag-sintering material, and transient liquid-phase bonding (TLPB) material, are reviewed in this paper with an emphasis on BiAgX® solders. The extremely high cost of Au-based solders limits their applications, although they have been used in high-temperature electronics. Zn-Al has a high melting temperature, good mechanical properties, and good thermal performance. However, the high reactivity makes Zn-Al solders only available in wire and preform. BiAgX® solder (available in paste, wire and preform) has been developed to replace the high-Pb solders for use in low-power discrete components, with relatively low cost and better reliability than the high-lead counterpart. Ag-sintering material and TLPB material form joints by atomic diffusion (either solid diffusion for sintering or solid–liquid interdiffusion for TLPB). The challenges in mass-production and the cost have restricted their success to be widely used in industry. Although it is likely that none of these materials/technologies are ideal to satisfy all the requirements of the variety of high temperature Pb-free die attach applications in terms of processing/reliability/cost, each solution has the potential to satisfy a niche within this broader categorization.

Process Development of Al-alloy Wire Bonding for High-Temperature Power Electronics

Abstract In this work, process parameters are developed for an Al-alloy wire for high-temperature power electronics. Shear and pull forces of the bonds on IGBT devices reach 2200 g and 1100 g respectively, without causing any die cratering. Comparison of the Al-alloy wire and standard Al wire bonded on battery cells shows that both the pull and shear forces of the bonds with the Al-alloy wire are improved by ~20%. This indicates that this Al-alloy wire potentially could be used for bonding on the power electronics and batteries in automotive industry, where better mechanical strength and wider bond window are required.

Growth kinetics of bismuth nickel intermetallics

Bismuth (Bi)-based systems are of great interest as it is considered to potentially replace high lead (Pb)-content solders used in high temperature electronics. In particular, molten Bi strongly reacts with Ni to form higher melting point intermetallic compounds (IMCs) via transient liquid phase (TLP), which can offer a joining method alternative to the traditional solder approach. A fundamental understanding of nucleation and growth of intermetallic phases is crucial to create a reliable joint. Two intermetallic phases form between Bi and Ni (Bi3Ni, BiNi). In this study, growth kinetics for Bi3Ni and BiNi was investigated, both of which show a parabolic growth behavior. Bi3Ni exhibits rapid growth and apparent activation energy of 65.5 kJ/mol at lower temperatures (from 160 to 240 °C) and of 132.9 kJ/mol at higher temperatures (> 240 °C), where the transition is likely due to a viscous-flow nature near melting temperature of Bi. On the other hand, BiNi grows at a later stage with a slower rate with the apparent activation energy of 125.6 kJ/mol (from 260 to 340 °C). In addition, based on the formation sequence and growth direction of these IMCs, interdiffusion coefficients for each of these IMCs were determined. Micro-hardness tests show that Bi3Ni is softer and more brittle than BiNi.

High-quality indium gallium nitride baskets revealed by their differential indium content

Clusters of lattice dislocations cause relative changes in the indium content in defect-free regions of gallium indium nitride needed in high-quality devices for high-temperature electronics.

Thermal reliability investigation of Ag-Sn TLP bonds for high-temperature power electronics application

Transient liquid phase (TLP) bonding is a potential joining technology for high-temperature power electronics packaging. In this study, the thermal reliability of Ag-Sn TLP bond was investigated through high-temperature storage test, in which the relationship between microstructure evolution and mechanical property was developed during 350 °C aging. After aging for 120 h, the Ag3Sn or ζ phase within the joint evolved totally into Ag(Sn) solid solution, which fractured with a ductile characteristic during shear test. The Ag-Sn TLP bond was confirmed to operate at ambient temperature of 350 °C for nearly 1000 h without serious failure, still possessing high shear strength of about 40 MPa. During thermal aging, a great amount of irregular Ni-Sn intermetallic particles were precipitated and dispersed adjacent to the interface between the Cu substrate and the Ag-Sn phases once the Ag metallization layer was consumed entirely. Moreover, a relatively thick Ni buffer layer should be carefully considered to prevent continuous cracks propagating along the Cu/Ag(Sn) interface, which was induced by the significant outflow of Cu flux from the interfacial zone, like a Kirkendall voiding process.

High-Temperature BSE and EBAC Electronics for ESEM

High-Temperature BSE and EBAC Electronics for ESEM

Direct Wafer Bonding of GaN for Power Devices Applications

Gallium nitride is a semiconductor material with a high potential for diverse applications as optoelectronic devices (high brightness LEDs, lasers, displays), wireless communication (microwave amplifiers, RF filters), high power and high temperature electronics, power devices or space applications requiring radiation-hard components working over wide temperature range. The economical advantages of GaN-based applications imposed the development of new manufacturing technologies. Wafer bonding was already adopted by semiconductor industry for consumer electronics, automotive or space applications so existing process solutions could be further developed for the new applications. One of the most significant benefits of using wafer bonding for GaN-based applications is the possibility to combine GaN with various substrate materials offering a high flexibility by imposing strict quality requirements only to the surfaces to be joined together by bonding and not to their crystal structure. The diversity of the new devices imposes different design criteria for the wafer bonding process. In order to provide a good platform for manufacturing the European research project AGATE aimed to create a substrate manufacturing pilot line to provide high quality substrates to device manufacturers. As main target, high quality substrates were produced by transferring GaN layers to different engineered substrates by a wafer bonding and layer transfer process. The process flow was: - The GaN layers on Sapphire substrates were coated with silicon dioxide layers and planarized by CMP - The Molibdenum substrates/ Poly-AlN substrates were coated with silicon dioxide layers and planarized by CMP - Both wafers were plasma activated using nitrogen plasma - The wafers were bonded at room temperature and further thermally annealed at low temperatures - The Sapphire substrate was removed. In order to further expand the application field of the pilot line the oxide-free direct bonding of GaN on Si was performed. In this approach, the process flow used was as below: - The GaN layers on Sapphire substrates were surface activated using ion beam sputtering for removing native oxides and contaminants from the surface. - The Si wafers were surface activated using same principle and native oxide was removed. - The GaN-Si direct bonding was performed in situ under high vacuum at room temperature, then thermal annealing was performed at low temperature. This work presents experimental details on the two process flows described. The incoming substrates were inspected by measuring the surface microroughness by Atomic Force Microscopy (AFM), their geometry (bow measurement using white light interferometry) and the presence of oxides on their surfaces was investigated by elipsometry. The bonded substrates were characterized in terms of bow and the bonding quality was inspected using visual inspection and Scanning Acoustic Microscopy (SAM). The oxide free bonds were characterized by cross-section TEM and EDAX and their thermal and electrical performance were measured. Figure 1

Surface hole gas enabled transparent deep ultraviolet light-emitting diode

The inherent deep-level nature of acceptors in wide-band-gap semiconductors makes p-ohmic contact formation and hole supply difficult, impeding progress for short-wavelength optoelectronics and high-power high-temperature bipolar electronics. We provide a general solution by demonstrating an ultrathin rather than a bulk wide-band-gap semiconductor to be a successful hole supplier and ohmic contact layer. Free holes in this ultrathin semiconductor are assisted to activate from deep acceptors and swept to surface to form hole gases by a large electric field, which can be provided by engineered spontaneous and piezoelectric polarizations. Experimentally, a 6 nm thick AlN layer with surface hole gas had formed p-ohmic contact to metals and provided sufficient hole injection to a 280 nm light-emitting diode, demonstrating a record electrical-optical conversion efficiency exceeding 8.5% at 20 mA (55 A cm−2). Our approach of forming p-type wide-band-gap semiconductor ohmic contact is critical to realizing high-efficiency ultraviolet optoelectronic devices.