Papers by Keyword: High Temperature

Abstract: Experimental analysis of 4H-SiC lateral MOSFETs characteristics up to 773K is shown. The reduction of threshold voltage, V_TH, and the increase of the field effect channel mobility, µ_CH, with temperature cause an increase of MOSFET current up to 623K. However, when scattering with lattice vibration starts to be predominant, µ_CH decreases with an abrupt drop at 773K, reducing MOSFET current. Channel resistance, R_CH, decreases with the temperature up to the range between 523 K and 573 K, implying possible thermal instability effects. However, when the temperature increases over this range, the thermal scattering predominates and R_CH again increases, ensuring thermal stability of MOSFETs.

Abstract: In this study, we systematically evaluated the fluid loss reduction effect of four nanomaterials in high-temperature water-based drilling fluids. Compared to the natural polymer PAC, the synthetic acrylamide-based polymer-maintained integrity and reduced fluid loss from 36.25 mL to 14 mL after aging at 180 °C, while forming a thinner and less permeable filter cake. Among the nanomaterials tested, 0.5 wt.% TiO₂ showed the most significant fluid loss reduction after aging at 180 °C, significantly optimizing the particle size distribution and reducing the fluid loss. When the polymer was used in combination with TiO₂, a significant synergistic enhancement was observed, which reduced the fluid loss to a minimum value of 11.6 mL at 180 °C. Zeta potential, particle size analysis, and SEM images showed that the effect resulted from the improved colloidal stability, closer packing of the particles, and the formation of a dense filter cake structure. The results show that the nanomaterial-polymer composite system can significantly improve the high-temperature fluid loss reduction performance of drilling fluids through the dual mechanism of physical blocking and chemical interaction, which provides an effective strategy for the design of high-performance fluid loss reduction agents.

Abstract: The degradation behavior of adhesion between cycloaliphatic epoxy resin and copper under high temperature and high humidity conditions was investigated. The Cu/resin joints were aged at 175°C and at 85°C in 85% R. H. The degradation behavior of the joint interface was analyzed by tensile tests and Fourier infrared transform spectroscopy (FT-IR). As a result, it was confirmed that the adhesion strength was retained after aging at 175°C for 1000 h, while it decreased with an increase in the aging time by aging at 85°C in 85% R. H. Furthermore, the interfacial fracture mode increased with aging at 175°C. In contrast, cohesive fracture was the main fracture mode and hardly changed by aging at 85°C in 85% R. H. The FT-IR analysis results showed that the peak intensity of the carbonyl group increases and that of the methylene group decreases by aging at 175°C. The result indicates that the resin was oxidized. Moreover, the peak intensities of carboxy and hydroxyl groups increased and that of ester groups decreased by aging at 85°C in 85% R. H. The results suggest that ester groups may be hydrolyzed due to aging and thus the adhesion is degraded.

Abstract: Silicon Carbide (SiC) is renowned for its exceptional thermal stability, making it a crucial material for high-temperature power devices in extreme environments. While optically detected magnetic resonance (ODMR) in SiC has been widely studied for magnetometry, it requires complex setups involving optical and microwave sources. Similarly, electrically detected magnetic resonance (EDMR) in SiC, which relies on an electrical readout of spin resonance, has also been explored for magnetometry. However, both techniques require microwave excitation, which limits their scalability. In contrast, SiC’s spin-dependent recombination (SDR) currents enable a purely electrical approach to magnetometry through the near-zero field magnetoresistance (NZFMR) effect, where the device resistance changes in response to small magnetic fields. Despite its potential, NZFMR remains underexplored for high-temperature applications. In this work, we demonstrate the use of NZFMR in SiC diodes for high-temperature relative magnetometry and achieve sensitive detection of weak magnetic fields at temperatures up to 500°C. Our technology provides a simple and cost-effective alternative to other magnetometry architectures, eliminating the need for a microwave source or complex setup. The NZFMR signal is modulated by an external magnetic field, which alters the singlet-triplet pair ratio controlled by hyperfine interactions between nuclear and electron/hole spins, as well as dipole-dipole/exchange interactions between electron and hole spins, providing a novel mechanism for relative magnetometry sensing at elevated temperatures. A critical advantage of our approach is the sensor head's low power consumption, which is less than 0.5 W at 500°C for magnetic fields below 5 Gauss. This approach provides a sensitive, reliable, and scalable solution with promising applications in space exploration, automotive systems, and industrial sectors, where high performance in extreme conditions is essential.

Abstract: This work compares design layouts and circuit simulations of the next two prototype NASA Glenn SiC JFET-R IC fabrication runs designated “IC Gen. 12” and “IC Gen. 13”. Even though both generations employ the same physical JFET gate length and chip size, SPICE simulations predict drastic improvements to IC capabilities and performance metrics for Gen. 13 over Gen. 12. The main factors behind simulated performance differences are thinner n-channel layer leading to reduced operating voltages and switch to stepper-based photolithography that enables roughly 4-fold layout area reductions for functionally identical circuit blocks.

Abstract: In proton exchange membrane fuel cells, the substitution of hydrated Nafion^® for lower cost materials is compulsory. In this work, a material based on a two commercial polyarylenes blend, with chemical modification, has been developed. The dynamic properties of the material were evaluated, and correlated to microscopic morphology and physico-chemical properties. The material showed thermal resistance above 200 °C, and featured conductivities in the order of 10^-2 S cm^-1, measured at up to 90 °C. In order to obtain better microscopic phase separation, between the conducting polymer (sPEEK) and the structural polymer (PES), certain solvent mixtures were evaluated, based on polarity character. The NMP/DMSO (0,3/0,7 %(v/v)) solvent mixture formed the film with the best properties, under hydrated conditions. Microscopic phase separation was approached by theoretical calculation of solubility parameters as compared to experimental data. This is an unusual and promising approach, as well as modification of materials structure through solvent manipulation, which is a more practical and unexpensive procedure than synthesis of new polymer structures.

Abstract: This paper presents results from metal contact processing experiments towards the implementation of durable 500 °C high-frequency 4H-SiC bipolar junction transistors (BJTs). Specifically, p-type ohmic contacts have been demonstrated on a 0.25 μm-thick p-type homoepitaxial layer of doping 8 × 10¹⁸ ± 4 × 10¹⁸ cm^-3. Finally, preliminary current-voltage characteristics of fabricated BJTs are presented.

Abstract: With the rising need for power devices suitable for harsh environment conditions like high temperature applications, contact materials and packaging of the devices have become critical factors in device fabrication [1, 2]. Therefore, a contact metal stack containing silver and titanium nitride which can be used at elevated temperatures under oxygen atmosphere was investigated. For patterning of the approx. 2 µm thick sputter-deposited metal stack on the wafer front side, a lift-off process using a negative photoresist was established. Characterization of the photoresist sidewall shape was performed by cross-sectional views prepared with SEM and top view images taken on a microscope. It was found that for a successful lift-off, a distinct undercut is needed so no metal is deposited at the downside of the undercut, ensuring a metal-free surface for the solvent to reach the photoresist. To obtain this, most influencing factors are exposure dose and development time, which were optimized considering the undercut shape as well as pattern fidelity. Lift-off with acetone proved to be good for the fabricated 4H-SiC MOSFET devices.

Abstract: Silicon carbide (SiC) is intrinsically more suitable for high temperature operation than silicon. However, for devices and circuits based on metal-oxide-semiconductor, high temperature behavior of gate oxides is still under investigation. This work aims to provide insights on how temperatures from room temperature up to 500 °C affect gate oxide properties of metal-oxide-semiconductor structures. Characterization is performed by current-voltage (I-V) and capacitance-voltage (C-V) measurements with different SiC and polysilicon gate electrode doping types. Increasing breakdown voltages were observed with higher temperatures for n-type SiC doping, while p-type ones break down at lower voltages. Polysilicon doping type only has minor impact on the breakdown voltage but influences the I-V behavior. High temperatures increase the probability of strong inversion being observable in C-V investigation. Regarding the I-V results, it can be stated that the 55 nm gate oxide used in the utilized HT CMOS technology has breakdown voltages above absolute values of around 55 V, independent of any doping types, and no significant current could be observed within the intended 20 V operation range of the technology.

Abstract: This paper describes a first attempt to build and operate a multi-chip prototype lander control and sensor signal digitization electronics circuit board comprised of ten NASA Glenn IC Generation 11 SiC JFET-R IC chips in 460 °C, 9.4 MPa harsh Venus surface conditions. The lander circuit ceased electrical operation prematurely at 107 °C as the Venus chamber heated up. Microscopic post-test inspections indicate that only one of the ten SiC chips on the board failed. Most of circuit-damaging cracks observed on the failed chip corresponded to micron-scale irregularly-shaped dielectric film hillock defects. The study of these defects suggests minor processing changes to eliminate this suspected root failure cause.