Simulated Venus Research Articles

Device and material investigations of GaN enhancement-mode transistors for Venus and harsh environments

This Letter reports the device and material investigations of enhancement-mode p-GaN-gate AlGaN/GaN high electron mobility transistors (HEMTs) for Venus exploration and other harsh environment applications. The GaN transistor in this work was subjected to prolonged exposure (11 days) in a simulated Venus environment (460 °C, 94 bar, complete chemical environment including CO2/N2/SO2). The mechanisms affecting the transistor performance and structural integrity in harsh environment were analyzed using a variety of experimental, simulation, and modeling techniques, including in situ electrical measurement (e.g., burn-in) and advanced microscopy (e.g., structural deformation). Through transistor, Transmission Line Method (TLM), and Hall-effect measurements vs temperature, it is revealed that the mobility decrease is the primary cause of reduction of on-state performance of this GaN transistor at high temperature. Material analysis of the device under test (DUT) confirmed the absence of foreign elements from the Venus atmosphere. No inter-diffusion of the elements (including the gate metal) was observed. The insights of this work are broadly applicable to the future design, fabrication, and deployment of robust III-N devices for harsh environment operation.

Investigation of vertical GaN-on-GaN p–n diode with regrown p-GaN for operation in Venus and other extreme environments

This Letter reports the performance of vertical GaN-on-GaN p–n diodes with etch-then-regrown p-GaN after exposure to a simulated Venus environment (460 °C, ∼94 bar, containing CO2/N2/SO2 etc., atmosphere) for over 10 days, and compared them to the performance of GaN p–n diodes without the etch-then-regrow process. After the above-mentioned Venus test, temperature-dependent I–V and microscopy investigation were conducted to study the robustness of etch-then-regrow p-GaN and vertical GaN p–n diodes under harsh environments and operation up to 500 °C. p-electrode degradation is found to be the main issue of the device's performance. This is the highest temperature at which such characterization has been conducted for vertical GaN p–n diodes, therefore establishing a critical reference for the development of p-GaN regrown and vertical GaN-based electronics for extreme environments.

Enhancement-Mode GaN Transistor Technology for Harsh Environment Operation

This letter reports an enhancement-mode (E-mode) GaN transistor technology which has been demonstrated to operate in a simulated Venus environment (460 °C, ~ 92 atm., containing CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> etc.) for 10 days. The robustness of the W/p-GaN-gate AlGaN/GaN high electron mobility transistor (HEMT) was evaluated by two complementary approaches, (1) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> electrical characterization, which revealed proper transistor operation (including E-mode <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_TH</i> with < 0.09 V variation) in extreme environments; and (2) advanced microscopy investigation of the device after test, which highlighted the effect of the stress conditions on the epitaxial and device structures. To the best of the authors’ knowledge, this is the first demonstration and comprehensive analysis of E-mode GaN transistors in such harsh environments, therefore establishing the proposed GaN technology as a strong contender for harsh environment mixed-signal electronics.

Experimental Study of Structural Materials for Prolonged Venus Surface Exploration Missions

Materials used in the fabrication of landers for Venus exploration need to be carefully selected to assure functional durability throughout anticipated prolonged future mission durations in the harsh conditions that include 460°C and 9.2 MPa pressure with supercritical and trace corrosive gases. Previous work has shown the adverse effects that trace quantities of the atmospheric sulfide and halogen Venus gas constituents have on some materials used in sensor and electronic component fabrication. In this study, a limited, systematic evaluation of several pure elemental metals as well as Ti-6Al-4 V is conducted to determine on an elemental level the constituents of structural materials that could survive prolonged Venus exploration. The metals are characterized before and after exposure to a simulated Venus surface atmosphere using X-ray photoelectron spectroscopy, Auger electron spectroscopy, energy-dispersive spectroscopy, and field-emission-scanning electron microscopy. Ti-6Al-4 V, titanium, and molybdenum all demonstrate stability when exposed to the simulated Venus surface environment. In contrast, cobalt, palladium, and to some extent chromium have adverse reactions to the sulfur constituents. The 96% supercritical leads to the complete oxidation of niobium and zirconium, as well as spalling oxide layers on tantalum and formation of a thick oxide layer on tungsten.

Stability of pyrrhotite under experimentally simulated Venus conditions

The stability of pyrrhotite (Fe1-xS; Fe7S8) was tested under simulated Venus conditions in two different temperature/pressure regimes and three different gas mixtures. The two regimes correlate to the average conditions in the lowlands (460 ​°C/92 ​bar) and the conditions found at the top of Maxwell Montes, 11 ​km above the planetary radius (380 ​°C/42 ​bar). The three gas mixtures consisted of 99.999% CO2, 100 ​ppm SO2 in CO2, and 100 ​ppm of COS in CO2. All experiments lasted between 24 and 96 ​h. Analysis using X-ray Diffraction (XRD) and Laser Induced Breakdown Spectroscopy (LIBS) revealed that pyrrhotite was stable at all tested temperature/pressures and gases. Our results further expand on our knowledge of the chemical reactions that may take place on Venus and highlights the need for in situ measurements of the near surface geology and atmosphere.

High-Temperature Electronics Packaging for Simulated Venus Condition

Abstract An electronic packaging technology that survives the simulated Venusian surface temperature of 465°C and 96 bar pressure in carbon dioxide (CO2) and nitrogen environments, without the corrosive trace gases, was developed. Alumina ceramic substrates and gold conductors on alumina were evaluated for electrical and mechanical performance. The most promising die-attach materials are thick-film gold and alumina-based ceramic pastes. Alumina, sapphire, silicon, and silicon carbide dies were attached to the alumina substrates using these die-attach materials and exposed to 96 bar pressure in a CO2 environment at 465°C for 244 h. The ceramic die-attach material showed consistent shear strengths before and after the test. An alumina ceramic encapsulation material was also evaluated for thermomechanical stability. The devices on the packaging substrates were encapsulated by a ceramic encapsulation with no significant increase in cracks and voids after the Venusian simulator test. Wire pull strength tests were conducted on the gold bond wire to evaluate mechanical durability before and after the Venusian simulator exposure. The average gold bond wire pull strengths before and after exposure were 5.78 g-F and 4 g-F for 1-mil gold bond wires, respectively, meeting the minimum MIL-STD-885 2011.9 standard. The overall wire bond daisy chain resistance change was .47% after the Venus simulator test, indicating a promising wire bond integrity. A titanium package was fabricated to house the ceramic packaging substrate and a two-level metalized feedthrough was fabricated to provide electrical interfaces to the package.

Response of QIT-MS to Noble Gas Isotopic Ratios in a Simulated Venus Flyby

The primary objective of the present study is to investigate the science return of future Venus atmosphere probe mission concepts using the Quadrupole Ion Trap (QIT) Mass Spectrometer (MS) Instrument (QIT-MS-I). We demonstrate the use of Monte-Carlo simulations in determining the optimal ion trapping conditions and focus the analysis on retrieving isotope ratios of noble gases in the model sample of the Venus atmosphere. Sampling takes place at a constant velocity of ~10 km/s between 112–110 km altitude and involves the use of getter pumps to remove all chemically-active species, retaining inert noble gases. The enriched sample is leaked into passively pumped vacuum chamber where it is analyzed by the QIT-MS sensor (QIT-MS-S) for 40 minutes. The simulated mass spectrum, as recorded by the QIT-MS-S, is deconvoluted using random walk algorithm to reveal relative abundances of noble gas isotopes. The required precision and accuracy of the deconvolution method is benchmarked against the a priori known model composition of the atmospheric sample.

Sixty Earth-Day Test of a Prototype Pt/HTCC Alumina Package in a Simulated Venus Environment

Abstract This article presents experimental results of a prototype high-temperature cofired ceramic (HTCC) package with Au/Pt metallization in a three-phase harsh environment test that culminated with a 60-d demonstration in a simulated Venus surface environment consisting of a 465°C corrosive atmosphere at 90 bar pressure. The prototype package is based on a previously developed and reported HTCC package successfully tested with multiple analog and digital silicon carbide high-temperature semiconductor integrated circuits in 500°C Earth air ambient for more than 10,000 hours, and short-term tested at temperatures above 800°C. The three-phase harsh environment test started with 48 h in 465°C Earth air, followed by 48 h in 465°C nitrogen at 90 bar pressure and 1,400 h in a simulated Venus surface environment of 465°C corrosive atmosphere at 90 bar. In addition to in situ electrical tests in a three-phase harsh environment and posttest electrical diagnosis, initial posttest analysis of the package materials and surfaces was performed to assess the stability of the packaging materials in the testing environments, as well as the surface conditions after the test. The test in the simulated Venus environment was implemented in the NASA Glenn Extreme Environment Rig. The results of this study suggest that an effective encapsulation of areas of surface metallization and vicinities may help improve the long-term electrical performance of an HTCC alumina packaging system in a Venus environment.

The millimeter-wavelength absorption of sulfuric acid vapor measured under simulated Venus conditions

Laboratory measurements of the 2–4 millimeter-wavelength rotational absorption spectrum of H2SO4 vapor pressure-broadened by CO2 have been made under simulated Venus conditions using a semi-confocal microwave open resonator. Results of the measurements are used to derive an absorption model based on the JPL Millimeter Spectral Line Catalog using a Van Vleck-Weisskopf lineshape. The millimeter-wavelength H2SO4 vapor absorption predicted by this derived model contrasts with extrapolation of the absorption model of Kolodner and Steffes (1998), which is based on the results of centimeter-wavelength measurements made under similar conditions. The results of the measurements presented here and other laboratory measurements under Venus conditions have been used to develop a Venus microwave radiative transfer model. This model can be used to predict the wavelength-dependent brightness temperature observed by remote sensing platforms and Earth-based radio telescopes. Based on the results of the new model for H2SO4 vapor absorption, previously measured brightness temperature variations >10 K in the 3 millimeter wavelength range are unlikely directly due to variations in the abundance of gaseous H2SO4.

Chemical Analysis of Materials Exposed to Venus Temperature and Surface Atmosphere

AbstractPlanetary exploration in the harsh Venus surface environment faces a myriad of technical challenges related to material survivability, durability, and overall reliable systems operation. An understanding of material reactions in Venus relevant atmospheric conditions is core to enabling future successful Venus science missions. This work investigated various candidate materials used in fabricating electronics, sensors, and packaging after exposure to simulated Venus surface atmosphere. The NASA Glenn Extreme Environments Rig is capable of reproducing Venusian temperature, pressure, and atmospheric composition of the Venus surface consisting mostly of CO2 and N2 as well as traces of SO2, H2O, CO, OCS, HCl, HF, and H2S. The exposed materials were characterized using Auger electron spectroscopy, X‐ray photoelectron spectroscopy, energy dispersive spectroscopy, field emission‐scanning electron microscopy, X‐ray diffraction, and optical imaging. The reactivity of the sulfur gas constituents with several of the exposed materials were found to have adverse effects on the materials, particularly those composed of transition metals. Alloys, brazes, and cladded materials all exhibited extensive reactions. In contrast, compounds of SiC, SiO2, Al2O3, and elemental Au and Ir were found to be chemically inert. The fundamental experimental understanding of material interactions with the simulated Venusian environment gained in this study enables improved selection of materials and hardware designs that would increase the success margin of future long duration science mission on Venus.

Sixty Earth-Days Test of a Prototype Pt/HTCC Alumina Package in Simulated Venus Environment

Abstract This paper presents experimental results of a prototype high temperature co-fired ceramic (HTCC) package with Au/Pt metallization in a three-phase harsh environment test that culminated with 60-day demonstration in simulated Venus surface environment of 465 °C with corrosive atmosphere at 90 bar pressure. The prototype package is based on previously developed and reported HTCC package successfully tested with multiple analog and digital silicon carbide (SiC) high temperatures semiconductor integrated circuits (ICs) at NASA Glenn Research Center in 500 °C Earth air ambient for over ten thousands hours, and short-term tested at temperatures above 800 °C. The three-phase harsh environment test started with 48 hours in 465 °C Earth air, followed by 48 hours in 465 °C nitrogen at 90 bar pressure and 1400 hours in simulated Venus surface environment of 465 °C with corrosive atmosphere at 90 bar. Initial analytical results of the package materials and surfaces after exposure to Venus environment are discussed to assess the stability of the packaging materials in the tested environments. The test in simulated Venus environment was implemented in the NASA Glenn Extreme Environment Rig (GEER). The results of this study suggest that an effective encapsulation of areas of surface metallization and vicinities may help to improve electrical performance of a HTCC alumina packaging system in Venus environment.

The millimeter-wavelength sulfur dioxide absorption spectra measured under simulated Venus conditions

Over 130 laboratory measurements of the 2–4mm wavelength opacity of sulfur dioxide in a carbon dioxide atmosphere under simulated conditions for the upper Venus troposphere (temperatures between 308 and 343K and pressures between 0.03 and 2bar) have been made. These measurements along with the centimeter wavelength measurements by Steffes et al. (Steffes, P.G. et al. [2015]. Icarus 245, 153–161) have been used to empirically assess existing formalisms for sulfur dioxide opacity in a carbon dioxide atmosphere (Fahd, A.K., Steffes, P.G. [1992]. Icarus 97(2), 200–210; Suleiman, S.H. et al. [1996]. J. Geophys. Res.: Planets 101(E2), 4623–4635). The Van Vleck and Weisskopf Model (VVW) used by Fahd and Steffes with the JPL rotational line catalog (Pickett, H. et al. [1998]. J. Quant. Spectrosc. Radiat. Transfer 60(5), 499–890) was found to fit 85.88% of all 500 measurements within the 2-sigma uncertainty. This work will improve the confidence in retrievals of the atmospheric abundance of sulfur dioxide from millimeter-wavelength observations of the Venus atmosphere.

Dynamics of Venus' superrotation: The eddy momentum transport processes newly found in a GCM

A 4‐day superrotation 60‐times faster than the planetary rotation (243 days) is observed in Venus' atmosphere. Although it has been difficult to reproduce the extraordinary phenomenon in GCMs, the superrotation is reproduced by meridional circulation and planetary‐scale waves with phase velocities slower than 50 m s−1 in our improved GCM. Thermally induced waves produce equatorward momentum fluxes in the middle atmosphere, while the planetary‐scale pattern of two different gravity and Rossby waves with the same frequency is found to produce the equatorward momentum flux in the lower atmosphere. These processes play crucial roles in dynamics of the simulated Venus superrotation.

Production of nitric oxide by lightning on Venus

The first measurements of the production of nitric oxide (NO) by a laboratory discharge in a simulated Venus atmosphere (CO2 ‐ 96% and N2 ‐ 4%) are presented. The average NO yield over a range of energies was found to be 3.7 ± 0.7 × 1015 molecules joule−1. Simultaneous measurements of carbon monoxide (CO) resulting from the lightning‐induced dissociation of carbon dioxide (CO2) indicated a CO yield of about 4 × 1017 molecules joule−1 (presumably with a comparable yield of atomic oxygen). These measurements suggest that at and below cloud level, a region where solar ultraviolet radiation cannot penetrate, the dissociation of CO2 by lightning may be a significant source of oxygen atoms. Depending on the assumed value for the total energy dissipated by lightning on Venus (which is not known), the production of NO by lightning may be a significant sink of atmospheric nitrogen (in the absence of recycling) over the history of Venus.

N2O and CO production by electric discharge: Atmospheric implications

Enhanced levels of N2O and CO were measured in tropospheric air samples exposed to a 17.5 × 10³ joule laboratory discharge. These enhanced levels correspond to an N2O production rate of about 4 × 1012 molecules joule−1 and a CO production rate of about 1 × 1014 molecules joule−1. The CO measurements suggest that the primary region of chemical production in the discharge is the shocked air surrounding the lightning channel, as opposed to the slower‐cooling inner core. Additional experiments in a simulated Venus atmosphere (CO2 ‐ 95%, N2 ‐ 5%, at one atmosphere) indicate an enhancement of CO from less than 0.1 ppm prior to the laboratory discharge to more than 2000 ppm after the discharge. Comparison with theoretical calculations appears to confirm the ability of a shock wave/thermochemical model to predict the rate of production of trace species by an electrical discharge.

Ice Nucleation in a Venus Atmosphere

Abstract The possible phase of Venus cloud particles has been experimentally studied. Carbon dioxide gas of 0.83 atm held in a uniform temperature mixing cloud chamber was used as a simulated Venus atmosphere at the condensation level. The ice nucleating behavior of some artificial and natural ice nuclei were tested. The heterogenous and homogeneous ice nucleation temperatures in the CO2 atmosphere were found to be 0.5–1.0C lower than those in air. The formed ice crystals showed no appreciable difference in comparison with those found in air. The results indicated that at temperatures < −38.5C the condensate in Venus atmosphere is likely to be ice crystals and above that temperature it can be either supercooled aqueous CO2 solution or ice crystals, depending on the availability of natural ice nuclei.