“Electronics have dramatically changed the way we live, conduct business, communicate, and educate. Visions of the future foretell of ubiquitous computing and sensing. However, the environments in which electronics can reliably operate are limited. In consumer applications, typical operating temperatures range from -40° to 85°C. The “wider” military temperature range is only -55° to 125°C,” writes R. WAYNE JOHNSON, Ph.D., professor, at Auburn University.
However there are extreme environments include extreme temperatures, ion concentrations, humidities, stresses, transport rates, and radiation fields. Such environments exist during Hypersonic flights, re-entry, and propulsion vehicles, deep oil wells, nuclear reactors, and under extremes of load and pressure. Using electronics in corrosive chemical or high vibration environments places severe constraints on system complexity and reduces overall reliability. Extreme environments require development of new electronics and new materials that can function in such environments.
Deep-space and long-duration missions, where both crew members and spacecraft no longer benefit from the protection of Earth’s magnetic fields, are considered high risk for adverse radiation impacts. Long term exposure of astronauts to radiation is problematic and the effect that space radiation has on spacecraft electronics and software is equally challenging.
For example, single-event effects (SEE) caused by cosmic rays, which can produce either hard or soft errors, have been observed both on the Earth’s surface at levels that can measurably impact commercial microelectronics technologies, and in avionics at levels that would jeopardize the reliability of these systems if mitigation strategies are not employed.
Department of Defense platforms, weapons and their components also operate in harsh environments for which materials with superior strength, density and resiliency properties are required. Recent scientific advances have opened up new possibilities for material design in the ultrahigh pressure regime (up to three million times higher than atmospheric pressure), says DARPA.
Members of the Stanford XLab are creating nano-devices that can withstand the acid rains on Venus, radiation in space and the heat of car engines, improving research in these extreme environments.
Los Alamos is currently leading with NETL and the DOE Fossil Energy program, the development of a multi-lab initiative to further advance the development of materials in extreme environments. ExtremeMat would be a multi-lab consortium focused on developing cross-cutting “tool sets” to accelerate the discovery and scale-up of new, or enhanced materials that can tolerate extreme environments and be scaled up for manufacturing in a cost-effective manner.
Some Extreme Environments
Petroleum will still be the dominant source of energy 20 years from now, according to Department of Energy projections, despite advances in alternate energy sources. To increase oil and gas discovery and recovery, instrumentation is required that can withstand well temperatures varying from 150° to more than 300°C and pressures that can reach 25,000 psi. These wells also contain steam, corrosive gases, and naturally occurring radiation. During drilling, the drill and associated logging instrumentation are subjected to high levels of shock and vibration.
“Transportation is an important manufacturing segment in the world economy and a critical infrastructure for moving goods, services, and people. In the automotive industry, the system design trends are toward mechatronics (integration of electronics and mechanical systems) and X-by-wire (X = throttle, steer, shift, and brake). The goals are distributed electronic architectures, replacing mechanical and hydraulic systems with electromechanical systems to simplify assembly, improve fuel efficiency, and increase safety,” writes Dr Johnson.
Hybrid electric and future fuel cell vehicles will further increase the electronics content. The power and control electronics for these vehicles will require either elaborate cooling systems or electronics capable of reliable operation at high temperatures (Table 1). In addition to temperature, automotive electronics are exposed to extreme conditions such as wide thermal cycles, shock, vibration, fluids, and corrosive gases. Many next-generation mechatronics systems will use MEMS devices for miniature sensor applications. Packaging of these devices for extreme-environment applications will be critical to the success of these new systems.
Materials for successful hypersonic flights
There is global race to develop Hypersonic Missiles such as US HTV-2 and X-51, Chinese WU-14, Russian Yu-71, that travel at least five times the speed of sound (Mach 5or 6125 kilometers per hour) or more. This speed is faster than a bullet, which generally travels at Mach 2, or twice the speed of sound. These vehicles can fly along the edge of the space and can glide and maneuver to the targets.
Hypersonic flights, re-entry, and propulsion vehicles, regardless of their design, require maneuverability of materials against high temperature erosion in excess of 2400°C. “It’s all about the heat,” said hypersonics expert Brad Leland. At speeds of Mach 5 and higher, aerodynamic friction can heat an aircraft’s exterior enough to melt steel. Advanced materials, recently in development, are necessary.
For example, atmospheric re-entry vehicles, rockets and scramjet powered air-breathing hypersonic cruise vehicles primarily encounter high pressures and heat flux on the leading edges due to air stagnation and shock waves. Also the respective propulsion systems experience high temperature exothermic combustion reactions to produce thrust.
Extreme space Environments
“The environments for solar system in-situ exploration missions cover extremes of temperature, pressure, and radiation that far exceed the operational limits of conventional electronics, electronic packaging, thermal control, sensors, actuators, power sources and batteries,” writes NASA JPL. In these studies, environments are defined as “extreme” if they present extremes in pressure, temperature, radiation, and chemical or physical corrosion. In addition, certain proposed missions would experience extremes in heat flux and deceleration during their entry, descent and landing phases (EDL), leading to their inclusion as missions in need of technologies for extreme environments.
Only a handful of Soviet Venera and Vega landers and a Pioneer probe have successfully reached the surface of Venus. The robust landers only survived 23 to 127 minutes before the electronics failed in the hostile environment.
“At one extreme, Venus lander missions would need to survive at 460 °C (730 K) temperatures and 90-bar pressures, and must pass through corrosive sulfuric acid clouds during descent (the current technology limits the duration of Venus surface exploration to only one to two hours), writes NASA. At the other extreme, Titan, Europa, asteroids, comets, and Mars missions require operations in extremely cold temperatures in the range of -180 to -120 °C (~ 90-150 K). For missions to comets or close to the Sun, high-velocity impacts are a real concern, with impact velocities reaching greater than 500 km/second. Investments in technologies for developing these systems and for operations and survivability in extreme environments are continually emerging, and are crucial to the successful development of future NASA missions.
“Small-scale Mars rovers, such as Spirit and Discovery, use warm electronics boxes to maintain an earth-like temperature. This results in more than 2,000 point-to-point wires, increasing system complexity and weight. This centralized approach will be limiting as larger vehicles are needed. For intelligent, distributed sensors and actuators, electronics and sensors must operate in the ambient temperature,” writes Dr Johnson.
A space mission environment is considered “extreme” if one or more of the following criteria are met:
- Heat flux: at atmospheric entry exceeding 1 kW/cm2
- Hypervelocity impact: higher than 20 km/sec
- Low temperature: lower than -55°C
- High temperature: exceeding +125°C
- Thermal cycling: between temperature extremes outside of the military standard range of -55°C to +125°C
- High pressures: exceeding 20 bars
- High radiation: with total ionizing dose (TID) exceeding 300 krad (Si)
Additional extremes include:
- Deceleration:(g-loading) exceeding 100g
- Acidic environments: such as the sulfuric acid droplets in Venusian clouds
- Dusty environments: as experienced on Mars
SiGe Integrated Electronics for Extreme Environments
In 2010, a five-year project led by the Georgia Institute of Technology developed a novel approach to space electronics based on silicon-germanium (SiGe) technology, which can produce electronics that are highly resistant to both wide temperature variations and space radiation.
SiGe alloys combine silicon, the most common microchip material, with germanium at nanoscale dimensions. The result is a robust material that offers important gains in toughness, speed and flexibility. That robustness is crucial to silicon-germanium’s ability to function in space without bulky radiation shields or large, power-hungry temperature control devices. Compared to conventional approaches, SiGe electronics can provide major reductions in weight, size, complexity, power and cost, as well as increased reliability and adaptability.
“Our team used a mature silicon-germanium technology – IBM’s 0.5 micron SiGe technology – that was not intended to withstand deep-space conditions,” Cressler said. “Without changing the composition of the underlying silicon-germanium transistors, we leveraged SiGe’s natural merits to develop new circuit designs – as well as new approaches to packaging the final circuits – to produce an electronic system that could reliably withstand the extreme conditions of space.”
The silicon-germanium electronics developed by the extreme environments team has been shown to function reliably throughout that entire plus-120 to minus-180 Celsius range. It is also highly resistant or immune to various types of radiation.
Piezoelectric materials that can withstand extreme environment
EPSRC-sponsored research at the University of Leeds has resulted in development of piezoelectric materials that can withstand extreme environments of high-temperatures and high-pressures. A spin-out company, Ionix Advanced Technologies Ltd, has announced that it has received funding from IP Group plc. to accelerate the commercialization of a range of devices, based on the piezo materials developed by the university.
This technology is widely employed in SONAR to industrial sensors to ultrasound scans in pregnancy to convert physical forces of the environment into electricity and vice versa. This technology has potential market in aerospace, oil and gas and nuclear power industries, estimated at more than £500 million per annum.
EXtreme Environment Microsystems Laboratory (XLab) at Stanford University
The EXtreme Environment Microsystems Laboratory (XLab) is focused on the development of micro- and nano-systems for operation within extreme harsh environments. Researchers in the XLab are investigating the synthesis of temperature tolerant, chemically resistant and radiation-hardened wide bandgap semiconductor thin films and nanostructures.
These new material sets serve as a platform for the realization of sensor, actuator and electronic components that can operate and collect data under the most hostile conditions. More specifically, smart and adaptable structures for extreme environments are enabled through the technology developed in the XLab. “Our research efforts support a variety of applications including deep space systems, hypersonic aircrafts, combustion monitoring and subsurface monitoring,” write XLab.
One hurdle to studying extreme environments is the heat. Silicon-based semiconductors, which power our smartphones and laptops, stop working at about 300 degrees C. As they heat up, the metal parts begin to melt into neighboring semiconductor and don’t move electricity as efficiently. Ateeq Suria, graduate student in mechanical engineering, is one of the people at the XLab working to overcome this temperature barrier. To do that, he hopped into his bunny suit — overall lab apparel that prevents contamination — and made use of ultra-clean work spaces to create an atoms-thick, heat-resistant layer that can coat devices and allow them to work at up to 600 degrees C in air. “The diameter of human hair is about 70 micrometers,” said Suria. “These coatings are about a hundredth of that width.”
Suria and others at the XLab are working to improve these nano-devices, testing materials at temperatures of up to 900 C degrees. For space electronics, it’s a key step in understanding how they survive for long periods of time. Although a device might not be exposed to such temperature extremes in space, the test conditions rapidly age materials, indicating how long they could last.
The team at XLab tests materials and nano-devices they create either in-house in high-temperature probe stations or in a Venus simulator at the NASA Glenn Research Center in Cleveland, Ohio. That simulator mimics the pressure, chemistry and temperature of Venus. To mirror the effects of space radiation, they also test materials at Los Alamos National Laboratory and at NASA Ames Research Center.
Hot electronics at home
While space is an exciting frontier, Suria said that interest in understanding car engines initially fueled this research. Inside an engine, temperatures reach up to 1000 degrees C, and the outer surface of a piston is 600 degrees C. Current technology to monitor and optimize engine performance can’t handle this heat, introducing error because measuring devices have to be placed far away from the pistons.
Electronics designed to survive the intense conditions of space could be placed next to the engine’s pistons to directly monitor performance and improve efficiency. “You just put the sensor right in the engine and get much better information out,” said Suria. Other fiery, high pressure earth-bound environments that would benefit from these robust electronics include oil and gas wellbores, geothermal vents, aircraft engines, gas turbines and hypersonic structures.
More than just surviving on Venus, getting there is important, too. Objects in space are pounded by a flurry of gamma and proton radiation that knock atoms around and degrade materials. Preliminary work at the XLab demonstrates that sensors they’ve developed could survive up to 50 years of radiation bombardment while in Earth’s orbit.
Senesky said that if their fabrication process for nano-scale materials proves effective it could get incorporated into technologies being launched into space.
“I’m super excited about the possibility of NASA adopting our technology in the design of their probes and landers,” said Senesky.
Some of the research projects it is focusing are
Graphene-GaN UV Photodetector Arrays for Sun Sensing
GaN-based devices are studied for space environment applications. Metal semiconductor-metal (MSM) ultraviolet (UV) photodetectors, HEMTs and diodes integrating graphene and semi-transparent metals have been designed, fabricated and characterized under different irradiation sources (Cs-137, Co-60, protons) as well as UV light and dark conditions.
AlGaN/GaN Pressure Sensors for Venus Exploration
Micro-pressure sensors are being designed, microfabricated, and characterized from AlGaN/GaN heterostructures. Extreme environment testing is being completed in oxidizing environments temperatures up to 600°C and within Venus simulated environments (supercritical CO2, 480°C, 90bar).
Heat Flux Sensors for Thermal Protective Systems
Materials from the III-V Nitride family are utilized to make efficient thermoelectric structures using novel material combinations and in-house fabrication techniques. The end goal of this effort is to build a compact and reliable system (without the use of shielding) that can be used directly in aerospace and automobile thermal protective systems.
Stanford XLab Research Areas
AlGaN/GaN Sensors for Icy, Radiation-Rich Environments
There is rising interest in developing electronics for cold temperature environments. For example, NASA proposes sending a lander to the surface of Europa, the icy moon of Jupiter. This climate is extremely cold (-180°C) and highly radiative. The packaging required for electronics would add significant payloads, so an electronic system that can operate under harsh conditions is desired.
Reliability Analysis of GaN, SiC and Si under Thermal and Radiative Stress
The operational limits of GaN, SiC and Si devices are studied using accelerated life testing. In addition, the electrical characteristics and microstructure of the devices are examined after exposure to very high doses of proton and gamma irradiation.
4H-SiC Substrates Processed in Microgravity Environments
The effect of reduced gravity environments on 4H-SiC substrates at elevated temperatures is studied. Microstructural analysis through high resolution X-ray diffraction (HRXRD) is used to study crystal structure and stacking fault density. Further, the electrical responses and thermal properties of materials processed in the microgravity environments are characterized.
Deep Plasma Etching of SiC Microstructures
The bulk micromachining of 4H-SiC is being studied for improved high aspect ratio features. This is of interest for the development of micro-channels for microfluidic thermal cooling applications as well as complex “3D” MEMS structures.
High-Temperature Metal Contacts to GaN and SiC
The electrical and microstructural properties of Ti/Al/Pt/Au contacts to GaN at high temperatures (600°C) in air have been studied. Experimental results showed minimal change in contact resistance and surface roughness after 10 hours of thermal storage in air at 600°C. Our study supports the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.