You might recall an earlier blog post – “MRAM’s Immunity to Radiation Makes It a Natural for Space”. In that post we talked about MRAM being superior to Flash, SRAM and DRAM in space. Exposure to charged particles affects memory technologies differently resulting in a Single Event Upset (SEU) or a Single Event Latch-up (SEL). SEU is defined as an induced error due radiation which changes the state of a memory element. Although there is no physical damage caused by an SEU, if multiple memory cells are affected, then the data may not be recoverable. The second issue, SEL, is a loss of device functionality due to an induced high current state that requires power cycling to recover normal operation. The concern is that an SEL condition may cause permanent damage to the device. Flash memory’s predominant failure mechanism in space applications is SEU while MRAM is immune to bit flips due to radiation. For DRAM and SRAM devices, the concern is not bit flips, but latch-up (SEL). Exposure to radiation can induce a condition where a low-impedance path between the power and ground rails is formed effectively producing a short circuit. In the testing, MRAM was proven to be latch-up resistant up to the maximum LET, 85.4 MeV•CM2/mg tested. This is more than twice the LET that DRAM and SRAM were exposed to before experiencing latch-up failure, thus providing significantly higher resistance. Table 1 compares SEU and SEL performance of different types of memories. In this blog post we focus on the advantages provided by Avalanche’s STT-MRAM based Space Grade P-SRAM over MRAM alternatives.
As of 2018, there are 2000+ satellites in orbit (accounting for both military and commercial satellites). Thousands more are being designed and manufactured for deployment in the Low Earth Orbit (LEO) by projects such as SpaceX’s Starlink which aims to provide internet to the entire planet using a fleet of 12,000 LEO satellites. LEO satellites face the same challenges related to radiation exposure as Geostationary (GEO) or Medium Earth Orbit (MEO) satellites. With every new mission, customers increasingly want more functionality, which requires larger satellite payloads, and that forces manufacturers to increase the size, weight and power (SWaP) of their satellite command and telemetry systems. Fortunately, there is a solution that solves these problems – MRAM. While all MRAM is immune to radiation, some MRAM technologies can be more advantageous than others, especially with regards to SWaP.
As previously discussed, all MRAMs use a Magnetic Tunnel Junction (MTJ) as the storage element. Toggle MRAM or the first generation MRAM, uses magnetic fields to write bit values into MTJ where as STT-MRAMs use a spin polarized current to write into the MTJ. This crucial difference enables major SWaP differences between Toggle and STT-MRAM products. Let’s look at these factors one by one.
Toggle MRAM based aerospace products are available from a couple of different vendors. These are packaged in custom packages that are very large in size – 50.8mmx24.4mm (1239.52mm2) and 34.925mmx35mm (1222.375mm2) respectively. In comparison, Avalanche Technology’s STT-MRAM based space grade P-SRAM is available in packages as small as 10mmx10mm (100mm2). The Toggle-MRAM based aerospace products require 12X the board space compared to Avalanche’s STT-MRAM based Space Grade P-SRAM products.
The Toggle-MRAM based aerospace products are much heavier than Avalanche’s STT-MRAM based Space Grade P-SRAM products because of their larger package size.
Toggle MRAM requires a lot more power compared to STT-MRAM. The Toggle MRAM based Aerospace products require 240mW to 360mW typical power during read operations. On the other hand the Avalache’s space grade P-SRAM products require a maximum of 99mW read power even when operating one speed grade faster (35ns performance vs 45ns performance)! The Toggle-MRAM based aerospace products require 4X (or higher) the power needed by Avalanche’s STT-MRAM based Space Grade P-SRAM products.
One more thing – COST. Avalanche’s STT-MRAM based Space Grade P-SRAM products cost 15x less compared to the Toggle MRAM based aerospace products. Designers face ever growing pressures to optimize SWaP profiles and cost, make the smart decision and opt for Avalanche’s STT-MRAM based Space Grade P-SRAM in your next design!