Pros and Cons of Space-based Flash—Microchip Takes Flash Off to Space
Microchip has recently extended its commercial-off-the-shelf (COTS) radiation-tolerant technology to flash memory. However, what pros and cons exist for flash memory in space?
Designing electronics is challenging enough, but the challenges get even greater when designing electronics for space. Requirements for radiation tolerance often limit the selection of components for these designs, resulting in less advanced space-qualified components than their terrestrial counterparts.
In an attempt to push the state of space electronics, Microchip announced a new family of radiation-tolerant flash memory devices for space applications.
Microchip's latest flash memory devices for space applications. Image used courtesy of Microchip
In this article, we’ll take a look at the place of flash memory in space devices, the challenges facing the technology, and what Microchip is bringing to the table.
Benefits of Flash Memory for Space
One technology that has recently gained popularity in electronic space applications is flash memory.
The reason this technology is seen as beneficial for space applications is that flash memory is non-volatile. Non-volatile memory can be beneficial, in the context of space applications, because non-volatile memory does not require a battery backup to maintain its state.
In an application like a satellite or spaceship, every gram counts, and the less hardware needed the better.
A high-level application diagram of flash memory. Image used courtesy of Caramia et al
Unlike other non-volatile memories, flash has the added benefit of being a high-density device. This means that, by using flash memory in space applications, designers can ensure a high memory capacity in a small volume.
Finally, compared to hard drive memory, flash is also much more power-efficient. Again, this attribute is vital in space as power availability is limited, and designers ideally want the smallest battery possible for a given device.
Challenges of Flash Memory for Space
Despite its many advantages in space applications, flash memory faces several severe limitations that prevent widespread adoption.
One of the significant challenges facing flash memory in space is its inherent susceptibility to the effects of radiation. In particular, NAND-based flash memory is known to be particularly susceptible to single-event effects (SEE) and total ionizing dose (TID) degradation, which cause corruption and loss of stored data.
According to researchers at NASA, this can be attributed to the structure of a traditional NAND flash cell, which stacks many transistors in series, making it inherently more sensitive to gate-threshold shifts caused by total dose irradiation.
An example NAND cell structure of Samsung KM29N16000. Image used courtesy of Nguyen et al
One way to correct this is by having many flash devices utilize tools such as error correction code (ECC) algorithms that can detect and correct memory errors. Sophisticated ECC is required for space-grade flash, necessitating larger areas and computational overheads. Some even believe that in order to improve flash’s tolerance to radiation, it is necessary to reconsider the device architecture altogether.
Microchip’s SuperFlash Technology
Recently, Microchip announced that it had extended its family of radiation-tolerant, commercial-off-the-shelf devices to include its SuperFlash technology.
The new product called the SST26LF064RT is a radiation tolerant serial quad I/O flash device designed for harsh space applications. The device, using a new, proprietary split-gate cell architecture, is said to improve performance, data retention, and reliability compared to the traditional stacked-gate architecture.
Functional block diagram of the SST26LF064RT. Image used courtesy of Microchip
An important result of the new architecture is that the SST26LF064RT can withstand a total TID of 50 kilorad along with a single event upset rate of < 3.33E-14 upsets/bit-day. Together, these improvements in intolerance have allowed the device to be space-qualified.
According to the datasheet, the device itself can operate at a maximum frequency of 80 MHz while enduring up to 10,000 cycles and a 20-year data retention estimate.
Microchip claims that the device is "ideal" for systems operating in harsh radiation environments such as Low Earth Orbit (LEO), where the protection of digital memory is of the utmost importance.
All in all, this new device appears to be a useful step in keeping space-rated technology advancing.