SEU-Resistant Magnetic Flip Flops

The development of a practical magnetic tunneling junction (MTJ) ten years ago allowed the creation of a new class of non-volatile memories. This technology may offer superior resistance to total ionizing dose and virtually unlimited write endurance, making it more attractive than flash memories for space applications. Although a number of manufacturers are developing high-density bulk magnetic RAMs, or MRAMs, there has been little effort to incorporate an MTJ into a standard cell flip flop. Such a magnetic flip flop has a number of potential applications, such as the configuration memory in fieldprogrammable logic devices. However, using MTJs to hold state information in a flip flop cell requires radically different circuitry for storing and retrieving data. The storage element must be written with a magnetic field, while preventing this field from disturbing nearby storage elements and minimizing the power consumed. The very thin insulating layers in the MTJ, as well as the inherent idiosyncrasies of a tunneling junction, require new design concepts in the circuits used to retrieve the state of the MTJ. Finally, new techniques will be needed to insure that magnetic flip flops are robust in the radiation environment of space. We propose a new radiation-tolerant magnetic flip flop that uses the inherent resistance of the MTJ to increase its immunity to single event upset and employs a robust “Pac-man” magnetic element.