Emerging memories

In an MTJ, how do the resistances compare when the magnetizations of the two magnetic layers are parallel versus antiparallel?

  1. AThe resistance is the same in both cases
  2. BThe resistance is higher when parallel
  3. CThe resistance is lower when parallel
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Answer: C. The resistance is lower when parallel

When the magnetizations are parallel, electrons with matching spin tunnel through the insulator easily, so the resistance is low. When antiparallel, tunneling is harder and the resistance is high. This resistance difference distinguishes 0 from 1.

Two states of a magnetic tunnel junction (MTJ) Free layer (switchable) Tunnel barrier (MgO) Reference layer (fixed) Parallel Low resistance Antiparallel High resistance
  • A. If the resistances were equal, the information could not be read.
  • B. The resistance is higher in the antiparallel state.
  • C. Correct. The resistance is lower when parallel.
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More Emerging memories questions

  1. Which correctly describes the roles of the two magnetic layers in an MTJ?
  2. In phase-change memory (PCM), how is a cell heated to put it into the low-resistance crystalline state (set)?
  3. On the hysteresis loop (polarization versus electric field) of a ferroelectric, what is the polarization that remains when the field returns to zero called?
  4. Which external environmental factor requires care when using MRAM?
  5. Why are MRAM and FeRAM sometimes used in high-radiation environments such as space equipment?