Power reduction in nanomagnetic logic clocking through high permeability dielectrics

Nanomagnetic logic (NML) has emerged as a novel paradigm to realize non-volatile, nanometer scale, ultra-low energy digital logic [1]. Since there are large energy differences between magnetization states, an external stimulus is required for circuit re-evaluation. In our first experiments we applied an off-chip magnetic field along the hard (i.e., short) axis of a group of nanomagnets. Later, structures that generate fields on-chip were demonstrated [2]. These current-carrying copper wires clad with ferromagnetic material (Supermalloy, Ni79Fe16Mo5), can provide local magnetic fields for NML circuits. However, the required current densities could be as high as ∼107 A/cm2 [2]. The ratio of flux density to magnetic field strength (μ = B/H) can be increased by surrounding the magnets with a material of high permeability. While we will need to ensure that the binary state of a magnet is not adversely affected, candidate materials do exist. Freescale demonstrated enhanced permeability dielectrics (EPDs) with embedded magnetic nano-particles to increase the field from a word or bit line in field MRAM without increasing current [3]. That EPD particle sizes are below the superparamagnetic limit helps to ensure that a magnet's state is not unduly influenced. With similar considerations, we have proposed a clocking structure where EPD films surround the nanomagnets, as shown in Fig. 1. With this new design, the magnetic flux can be confined within the EPD film area instead of leaking to the air. As such, the field intensity for switching the nanomagnets can be increased, and the required current density and power for clocking can be reduced (potenitially by μr2 in the case of power). This work shows our efforts of integrating EPD films with nanomagnets for NML clocking.