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Introduction
In the realm of space exploration and aerospace technology, the reliability and integrity of data are paramount. The extreme conditions of space, including high radiation levels and temperature variations, present significant challenges to electronic systems. To ensure the safe and accurate operation of critical systems in these harsh environments, the use of high-reliability and radiation-hardened memories has become indispensable. In this article, we will delve into the importance of high reliability and radiation-hardened memories in space and aerospace applications and explore how they safeguard crucial data.
The Challenges of Radiation:
Radiation can cause various types of damage to electronic devices, including single-event upsets (SEUs), single-event functional interrupts (SEFIs), and total ionizing dose (TID) effects. SEUs occur when a single ionizing particle strikes the sensitive nodes of a memory cell, altering its contents temporarily. SEFIs, on the other hand, result in the temporary or permanent disruption of the normal operation of a circuit due to radiation-induced faults. Lastly, TID effects accumulate over time and cause gradual degradation of the memory’s performance and reliability.
Over the past three years, SpaceX has deployed thousands of satellites into low-Earth orbit as part of its business to beam high-speed internet service from space. But the company’s latest deployment of 49 new satellites after a Feb. 2021 launch did not go as planned.
As a consequence of a geomagnetic storm triggered by a recent outburst of the sun, up to 40 of 49 newly launched Starlink satellites have been knocked out of commission. They are in the process of re-entering Earth’s atmosphere, where they will be incinerated.
Future small satellite systems for both Earth observation as well as deep-space exploration are greatly enabled by the technological advances in deep sub-micron microelectronics technologies. Ensuring the reliable operation of microcircuits in outer space is an important scientific and economic objective. For modern weather, communications and surveillance satellites to be cost-effective, they need to be operational for at least 10 to 15 years.
But with extended space missions comes the requirement for flawless performance by on-board equipment over a period of years, in a very harsh environment. On takeoff, electronic components endure violent beatings from extreme vibration, and once in orbit, every material needs to be able to endure wildly shifting thermal changes that can see a cycle through 260 degrees Fahrenheit (126.67 degrees Celsius) every hour of every day.
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. Aircraft flying at altitude, at about 30,000 feet and above, also are starting to experience radiation-induced effects. “There are 500 times more neutrons at 30,000 feet than there are on the ground,” points out Aitech’s Romaniuk. Long term exposure of astronauts to radiation is problematic and the effect that space radiation has on spacecraft electronics and software is equally challenging.
Future small satellite systems for both Earth observation as well as deep-space exploration are greatly enabled by the technological advances in deep sub-micron microelectronics technologies. For modern weather, communications and surveillance satellites to be cost-effective, they need to be operational for at least 10 to 15 years. Onboard electronic equipment failures are a common reason for early satellite failure. But with extended space missions comes the requirement for flawless performance by on-board equipment over a period of years, in a very harsh environment. Ensuring the reliable operation of microcircuits in outer space is an important scientific and economic objective.
The emerging earth observation (EO/IR/SAR) satellites all capture thousands upon thousands of terabytes of data every day, which equates to petabytes every year. And in the future, there will be even more data collected — NASA is planning two space missions called SWOT and NISAR that are expected to produce roughly 100 terabytes of data per day. Not all of this data can be sent back to earth in real time, nor should it, which means that effectively storing it in space is the only way of making this data useful and actionable.
To properly process and handle that data in space, to make that data useful, engineers have discovered acute requirements for data integrity to ensure that data retains the ability to be analyzed in space – or relayed back home for analysis. If data integrity is core to success in space, data storage is equally if not more important, for it’s the foundation on which data can be accessed, stored and analyzed.
Data storage in space needs to be able to endure the rigors of a space mission, from the challenges relating to launch, orbit, and return to earth, and the evolution in data storage reliability has led to an evolution of advanced data storage use cases around us.
Semiconductor memory devices used in outer space, for example, in a satellite, are subjected to severe environmental conditions that may compromise the integrity of the stored data, or cause the memory devices to fail. In many cases, the memory devices are part of a larger embedded system, where the memory device is just one of many devices sharing the same die.
The integrity of the memory devices used in outer space applications is critical because the information stored by the memory devices may be related to critical functions, such as guidance, positioning, and transmitting and receiving data from a ground base station. Furthermore, semiconductor memory devices for use in space applications should remain functional for the lifetime of the satellite, which may be as long as several years. Contrast this with applications where the memory devices are also subjected to harsh operating conditions, such as guidance systems in missiles, but only for a relatively short time period.
Memory technologies
Digital information can be stored in different types of device depending on the use and how frequently the data need to be accessed. Hard disk drives are magnetic devices that allow storing terabytes of data for long time, however speed of access to the data is relatively slow (a few milliseconds). On the other hand, data that are being used by a computer processor to perform an operation need to be accessed on a much faster timescale (nanoseconds). Silicon-based semiconductor memories are categorized into volatile and nonvolatile memories.
Volatile memories, such as static random-access memory (SRAM) and dynamic random-access memory (DRAM), need voltage supply to hold their information while nonvolatile memories, namely Flash memories, hold their information without one. Most devices like smartphones and notebooks currently use a combination of dynamic random-access memory (DRAM) and flash memory, with the former acting as active memory while devices are on, and the latter being used to store data long-term (off or on).
Flash memory is widely used in consumer electronic products such as cell phones and music players. NAND Flash-based solid-state disks (SSDs) are increasingly displacing hard disk drives as the primary storage device in laptops, desktops, and even data centers. However, Flash is slow and has low endurance. The integration limit of Flash memories is approaching; NAND cannot scale down past 10nm while DRAM and SRAM are costly.
New nonvolatile memory technologies are emerging such as magnetic random-access memory (MRAM), spin-transfer torque random-access memory (STT-RAM), ferroelectric random-access memory (FeRAM), phase-change memory (PCM), and resistive random-access memory (RRAM), that combine the speed of static random-access memory (SRAM), the density of dynamic random-access memory (DRAM), and the nonvolatility of Flash memory and becoming very attractive for future memory hierarchies. Western Digital, owner of the SanDisk brand, has unveiled what it calls the “world’s first” 1TB SD card. It’s only a prototype, but already the company is touting the card’s ability to adequately handle 4K, 8K, VR and 360-degree video when it officially becomes available
Radiation effects on memory
One cause of errors in semiconductor memory devices that are used in outer space applications is due to high-energy particles impinging on the memory device. There are several forms of high energy particles in outer space. For example, there are alpha particles and gamma rays, to name a couple. These high-energy particles strike the semiconductor material on which the memory devices are formed with enough energy to cause the generation of electron-hole pairs. The resulting charge carriers are often trapped in the various oxide layers of the memory devices.
In the case of metal oxide semiconductor (“MOS”) transistors, charges trapped in the gate oxide will shift the threshold voltage. Vt, of the transistor. As a result, leakage currents of the transistors, and consequently, of the memory devices may increase. Where the transistor is used as a transfer gate for a conventional memory cell, the increased leakage current may compromise the integrity of the data stored by the data storage node, such as a capacitor, by allowing the charge representing the data to dissipate.
The frequency or number of charges trapped in an oxide layer is proportional to the thickness of the oxide layer. Consequently, oxides having a greater thickness will, on the average, have a greater number of trapped charges.
Understanding High Reliability and Radiation-Hardened Memories:
High reliability and radiation-hardened memories are specialized electronic storage devices designed to withstand the demanding conditions encountered in space and aerospace applications. They are engineered to operate reliably in the presence of high levels of radiation, extreme temperatures, and other environmental stressors. These memories incorporate advanced technologies and protective measures to ensure data integrity and minimize the risk of radiation-induced errors or failures.
Radiation hardening is process of making electronic components such as momeory resistant to damage or malfunction caused by high levels of ionizing radiation (particle radiation and high-energy electromagnetic radiation), especially for environments in outer space and high-altitude flight, around nuclear reactors and particle accelerators, or during nuclear accidents or nuclear warfare.
Researchers have been working tirelessly to develop low-cost, high-density radiation-hardened non-volatile memory (NVM) solutions for space applications. Traditionally, the focus has been on employing redundancy and error-correcting codes, such as Hamming coding, to mitigate the effects of single event upsets. However, these solutions often come with a performance penalty and are not optimized for fabrication processes. Additionally, the use of moving parts, like those found in hard disk drives, is not feasible in many aerospace applications, highlighting the need for an ultra-high density storage solution.
Efforts made over the past two decades to develop practical NVM solutions for space have fallen short in terms of meeting density and performance requirements. The density and cost of commercial NVMs have significantly improved in recent years, creating a substantial gap of over six orders of magnitude between commercial and radiation-hardened devices. This underscores the urgency to bridge this gap and develop radiation-hardened NVMs that can achieve high density while maintaining reliability and affordability.
To address these challenges, researchers are exploring novel approaches to fabricate radiation-hardened NVMs. The focus is on integrating radiation-hardening techniques directly into the fabrication process, rather than relying on inefficient hardening techniques applied during layout or application architecture. By doing so, it is possible to achieve high-density NVMs that can withstand the harsh radiation environment of space.
The development of radiation-hardened NVMs is crucial for space applications as they play a vital role in storing critical data and ensuring the reliable operation of spacecraft and satellites. These memories are essential for tasks such as data storage, communication, navigation, and scientific research. By advancing radiation-hardened NVM technology, we can enhance the overall performance, reliability, and success of space missions.
For deeper understanding of memory technologies and applications please visit: Semiconductor Memory: Unleashing the Power of Data Storage and Retrieval
Importance of High Reliability and Radiation-Hardened Memories:
- Ensuring Data Integrity: In space and aerospace missions, accurate and reliable data is essential for critical operations, including navigation, communication, and scientific research. High reliability and radiation-hardened memories play a vital role in safeguarding data integrity, minimizing the risk of corruption or loss due to radiation-induced errors.
- Mission Success and Safety: The success and safety of space and aerospace missions rely heavily on the proper functioning of electronic systems. By utilizing high-reliability memories, engineers can mitigate the risks associated with radiation-induced failures and ensure the continuous operation of vital systems, such as propulsion, guidance, and life support.
- Extended Lifespan: Space missions often involve long durations and remote operations, making it challenging to repair or replace malfunctioning components. High-reliability memories are built to withstand the harsh conditions and have an extended lifespan, reducing the need for frequent maintenance or replacements and increasing mission reliability.
Design Considerations for High Reliability and Radiation-Hardened Memories:
- Radiation Hardening: Radiation-hardened memories employ specialized design techniques, such as redundancy and error correction codes, to detect and correct radiation-induced errors. These mechanisms enhance the resilience of the memory cells and protect against single-event upsets (SEUs) caused by ionizing radiation.
- Temperature Management: Extreme temperature variations in space and aerospace environments can affect the performance and reliability of electronic components. High-reliability memories incorporate thermal management strategies, including efficient heat dissipation and temperature monitoring, to ensure optimal operation across a wide temperature range.
- Packaging and Shielding: The physical packaging of high-reliability memories plays a crucial role in protecting against radiation and environmental hazards. Robust shielding materials, such as radiation-absorbing alloys and multilayer enclosures, are used to minimize radiation penetration and protect the sensitive memory components.
- Testing and Certification: High-reliability memories undergo rigorous testing and certification procedures to ensure their performance and reliability in extreme conditions. These tests simulate the harsh environments of space and aerospace missions, including radiation exposure, temperature cycling, and mechanical stress, to validate the memory’s ability to withstand such challenges.
Applications of High Reliability and Radiation-Hardened Memories:
- Satellites and Spacecraft: High-reliability and radiation-hardened memories are extensively used in satellites and spacecraft for tasks such as data storage, communication, attitude control, and guidance systems. These memories ensure accurate data retention and retrieval throughout the mission’s lifespan.
- Planetary Rovers and Probes: Robotic explorations on planets and moons require reliable data storage to support scientific investigations and maneuvering operations. High-reliability memories enable the storage of large volumes of data collected by planetary rovers and probes, ensuring the success of scientific missions.
- Avionics Systems: In aerospace applications, high-reliability memories are crucial components in avionics systems, including flight control, navigation, and communication systems. These memories ensure the reliability and real-time processing of critical flight data.
- Defense and Military Applications: High-reliability and radiation-hardened memories find extensive use in defense and military systems, such as missile guidance, radar systems, and surveillance equipment. These memories play a critical role in ensuring the accuracy and reliability of mission-critical data.
Advancements in Radiation hardened Memories
- Process technology enhancements: The use of advanced process technologies, such as silicon-on-insulator (SOI) and triple-well CMOS, has helped to improve the radiation hardness of memories. These technologies help to isolate the memory cells from the effects of radiation, making them less susceptible to damage.
- Specialized design techniques: Radiation hardened memories use a variety of specialized design techniques to improve their radiation hardness. These techniques include using redundant bits, error correcting codes, and special logic to detect and correct radiation-induced errors.
- Increased availability: In the past, RHM was only available from a limited number of specialized suppliers. However, in recent years, there has been an increase in the availability of RHM from commercial suppliers. This has made it easier for designers to incorporate RHM into their products.
Advancements in radiation-hardened memories for space and aerospace applications have made significant progress in recent years. Companies like Western Digital, Infineon Technologies, GSI Technology, Cobham Semiconductor Solutions, and Mercury Systems have developed innovative solutions to address the challenges of high radiation levels and extreme temperatures.
One notable advancement is the Design for Reliability (DFR) approach adopted by Western Digital, which focuses on incorporating reliability into product designs using state-of-the-art methods. This approach ensures high performance and low-voltage requirements, allowing electronic components to overcome various limitations. DFR has been widely adopted in the space technology sector and has contributed to the development of more reliable and resilient products.
Companies like Infineon Technologies and Cobham Semiconductor Solutions have introduced radiation-tolerant memory chips and non-volatile semiconductor memory products that are qualified for space applications. These memories offer high quality and reliability certifications, ensuring data integrity even in harsh radiation environments. Additionally, Mercury Systems has developed radiation-tolerant DDR4 memory components with high data transfer speeds, wide operating temperature ranges, and space-saving dimensions, making them ideal for data-intensive processing applications in space.
Overall, these advancements in radiation-hardened memories have significantly improved the reliability and performance of electronic systems used in space and aerospace applications. By ensuring data integrity and resilience in the face of extreme conditions, these memories play a critical role in the success of space missions and the safety of aerospace technologies.
Conclusion:
High reliability and radiation-hardened memories are instrumental in protecting crucial data in the challenging environments of space and aerospace applications. By employing advanced design techniques, robust packaging, and thorough testing, these memories enable the successful execution of missions, ensuring data integrity and system reliability. As space exploration and aerospace technology continue to advance, the development and implementation of high-reliability memories will remain indispensable for the progress and safety of these critical industries.
References and resources also include:
https://patents.google.com/patent/US6194276
https://venturebeat.com/2022/03/05/data-storage-from-space-to-earth-3-takeaways-for-the-real-world/
https://www.militaryaerospace.com/computers/article/14287964/radiationtolerant-ddr4-memory-space
