Breaking the computer memory speed record
The race is on to develop the next generation of computer technologies, and Europe is leading the pack. Recent experiments in magnetic memories have broken all past speed records and have reached the fastest possible speed that magnetic memories can reach. What this means for the average European is that new faster computers are just around the corner. While computers are getting smaller, consumer demands on them are increasing. More and more memory is required to run the latest computer programmes. More memory is also required to store the information now being collected, either by scientists or governments. To deal with these demands, larger and faster memory is required. Magnetic memory chips, or MRAM, are just what is needed to respond to this growing demand, and their development is revolutionising the computer industry. Europe is showing the way forward as recently indicated by an article published in the Physical Review Letters. The article highlights an experiment conducted by the Physikalisch-Technische Bundesanstalt (PTB) in Germany. In the experiment, the researchers realised spin torque switching of a nanomagnet that reached speeds as fast as the fundamental speed limit allows. This approach is called ballistic switching. Current memory systems in use include Dynamic and Static Random Access Memory (DRAM and SRAM). While they are faster than their predecessors, they do have some disadvantages. An interruption in the power supply would mean an immediate loss of information currently processed. Computers using these memory systems also take a long time to start up. Imagine turning on a computer and it being ready for use immediately, instead of having to wait for the computer programmes to be loaded. MRAM does away with that wait. With MRAM, the digital information is not stored by means of an electric charge but instead the orientation of the magnetization of a magnetic cell is used. Magnets can either be positively or negatively charged, each state corresponds to either a 0 or a 1. This is the binary system which is used on all computers. Spin torque is used by MRAM for programming the magnetic bits. Applying spin torque allows the memory state of a cell to be programmed through the application of a current pulse. A positive current switches the magnetisation to one direction (digital state 0) and a negative current to the other (digital state 1). To achieve this change in state, however, several current pulses, called precessions, are needed. At present MRAM needs several pulses lasting about 10 nanoseconds for the digital state to be altered; this causes severe drag on the speed. In this experiment, magnetisation was achieved in a single precessional turn thanks to the ballistic spin torque. This was achieved by precise tailoring of the current pulse parameters in combination with a small magnetic bias field. What this means for MRAM is that programming can be achieved using current pulses shorter than 1 nanosecond corresponding to write clock rates well above 1 GHz. It could thus enable a high-density and non-volatile memory operating at the clock rates of the fastest volatile memories.