Abstract
A true random number generator based on perpendicularly magnetized voltage-controlled magnetic tunnel junction devices (MRNG) is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA). This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA) effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps) by implementing a 64×64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit) due to the high energy efficiency of the voltage-controlled MTJ switching.
Highlights
In the era of internet based information, the use of electronic financial transactions, on-line communications, and digital signature applications have exponentially increased over the last few decades
We propose a voltage-controlled MTJ based true random number generator (MRNG) where the electric field is used to induce switching instead of substantial current flow in the MTJ device, drastically reducing Ohmic loss
It has been experimentally observed that the voltage controlled magnetic anisotropy (VCMA) effect can change the perpendicular magnetic anisotropy (PMA) of the free layer under electric bias condition, which in turn leads to a coercivity modulation.[6]
Summary
In the era of internet based information, the use of electronic financial transactions, on-line communications, and digital signature applications have exponentially increased over the last few decades. A spin transfer torque (STT) MTJ based random number generators have been proposed by many research groups.[7,8,9] the STT-MTJ based random number generators require a precise write pulse width at given amplitude to achieve high-quality randomness (e.g. 50% switching probability), which in turn necessitates a dedicated control circuit and a calibration process.[10] a current driven STT-MTJ intrinsically requires a significant amount of charge current to switch, resulting in high Ohmic dissipations. Unlike STT driven switching, generating a random bit is not sensitive to the write pulse width because the magnetic moment converges to an in-plane (meta-stable) direction under the long enough electric bias condition. The non-volatile characteristic of MTJs makes it possible for the circuit to be in sleep mode, realizing zero leakage
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