Nanomagnetic Logic

Abstract

Diverting away from the monotony of charge-based paradigms, nanoelectronics looks towardnanomagnetics for help. CMOS logic is likely to become unacceptably energy inefficient below 10 nm gate length. QDCA-based logic too is confronted with the problem of allowing operation only at temperatures close to 0 K at the present technological competence. Nanomagnetics comes to rescue with a technology offering orders of magnitude lower heat dissipation than CMOS and capable of providing room-temperature operation. Nanomagnetic logic in the form of magnetic quantum cellular automata could serve as the holy grail of IC industry after CMOS has reached the end of the roadmap. This chapter highlights the limitations of CMOS and QDCA paradigms. Single-spin logic is introduced as a probable option. But the necessity of very cold environments for its deployment discourages us to tread this path. Then ferromagnetic dot-based logic is discussed and the actualization of magnetic quantum cellular automata (MQCA) through reconfigurable array of magnetic automata (RAMA) is treated.

Review Exercises

• 20.1 How is the performance of charge-based MOSFET nanoelectronics depending on flow of current limited by power dissipation as heat? How does quantum dot coupled automata model based on electrostatic coupling and requiring no current flow overcome this limitation? If it succeeds in doing so, what is preventing its widespread adoption?

• 20.2 Elaborate the statement, “Single-spin logic is highly energy-efficient.” Put your arguments in favor of and against the proposal of single-spin logic.

• 20.3 What is a ferromagnetic material? Give some examples of such a material. What is the special property of this material?

• 20.4 A ferromagnetic dot may contain as high as 10⁴ electron spins working cooperatively. Why is the flipping energy required to switch the dot from spin up to spin down state not 10⁴ times the energy required to flip a single electron spin?

• 20.5 How is the proposal of room-temperature operation for nanomagnetic logic based on ferromagnetic dots justified from: (i) power dissipation viewpoint; (ii) thermal energy considerations?

• 20.6 Why is the anisotropy of shapes of nanomagnets desirable for MQCA logic?

• 20.7 Compare QDCA and MQCA in terms of the thermal environments required for their operations. Give reasons for your answer.

• 20.8 Compare MQCA with CMOS, pointing out their relative advantages and disadvantages.

• 20.9 How is MQCA obtained from the reconfigurable array of magnetic nanopillars ? How is the gate operation initiated in MQCA? Explain the clocking of MQCA? How is the output signal obtained from MQCA?

• 20.10 Can RAMA be used as a memory array? If so, how can this be done?

• 20.11 Mention one important shortcoming of MQCA with respect to CMOS.