Sandia National Labs FY20 LDRD Annual Report

FY20 ANNUAL REPORT

Radiation-hard nonvolatile memory and logic based on magnetic tunnel junctions. State- of-the-art computer processors using electric-charge-based devices have drawbacks including fundamental limits on energy efficiency and sensitivity to radiation. Changing the state variable from charge to magnetization can overcome these limitations. Magnetic memory, which represents the stored memory state by two parallel ferromagnetic layers, is now commercialized. In addition, ferromagnetic layers were recently extended to form logic devices using magnetic domain walls (MDW), replicating complementary metal oxide semiconductor (CMOS) logic. In these devices, logic states are delineated using the separation of magnetic domains that are polarized in different directions (see figure). For the first time, Sandia and the University of Texas at Austin demonstrated MDW logic gates using the efficient spin orbit torque (SOT) effect, that are cascadable, electrically controlled, and demonstrate a record 164% separation between logic states. Furthermore, a device- circuit codesign model predicts power efficiency beyond CMOS limits using SOT MDW logic. Finally, initial radiation measurements on SOT devices confirm resilience to these effects. These results

pave the way for low-power, radiation-resilient magnetic computing. (PI: Matthew Marinella) Traditional CMOS cascaded buffer circuit (left) next to the equivalent magnetic domain wall buffer circuit (center) representing the device demonstrated by the Sandia-UT Austin LDRD project. (Right) A scanning electron image of the device is shown.

GaN vacuum nanoelectronics: A new platform for radiation-hard devices and beyond. Sandia developed a new type of on-chip, nanoscale vacuum electronic device that combines the advantages of modern, solid-state devices with “old-school” vacuum tubes. Vacuum tubes are still prized for applications requiring very high frequency and power as well as operation in harsh environments, where even modern silicon-based solid-state electronics are lacking. However, traditional vacuum tubes are large, power hungry, and require a vacuum

environment to operate, greatly limiting their use. The new, solid-state “nano-vacuum tubes” were fabricated from gallium nitride (GaN), due to its optimal properties for this technology. Recent GaN devices demonstrated ultra-low turn-on voltages that are an order of magnitude lower than competing silicon- or silicon carbide-based devices. Additionally, due to the nanoscale dimensions of the vacuum channel, the GaN devices achieve this performance in air, without the need for vacuum packaging. Future devices that can be enabled by this novel technology include radiation- and EMP-resistant electronics and photonics that can operate at high speeds and with low power consumption. (PI: George Wang)

Schematic (top) and electron micrograph (bottom) images of an on-chip, integrated GaN nanoscale vacuum “tube” (diode) with gap size below 30 nm and operable in air.

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LABORATORY DIRECTED RESEARCH & DEVELOPMENT