Generating random bitstreams with magnetic tunnel junctions

Patent metadata

Field	Value
Publication number	US-10732933-B2
Application number	US-201815976384-A
Country	US
Kind code	B2
Filing date	May 10, 2018
Priority date	May 10, 2018
Publication date	Aug 4, 2020
Grant date	Aug 4, 2020

Abstract

True random number generation (TRNG) circuits are presented which employ magnetic tunnel junction (MTJ) elements that can change magnetization state probabilistically in response to application of electrical pulses. Some implementations include pulse generators which apply perturbation sequences to the MTJ elements. The MTJ elements responsively produce randomized outputs related to changes in magnetization states. Probability compensators are included which monitor for deviations in measured probabilities in the randomized outputs from a target probability. The probability compensators make adjustments to the perturbation sequences to influence probabilistic changes in the magnetization states of the MTJ elements and bring the measured probabilities to within a predetermined deviation from the target probability.

First claim

What is claimed is:

1. A circuit comprising:
a pulse generator having a pulse output terminal configured to produce perturbation pulses;
a random bitstream generator comprising:
a magnetic tunnel junction (MTJ) element coupled at a free layer terminal to the pulse output terminal of the pulse generator, and coupled at a pinned layer terminal to an adjustable reference node; and
an output node for the circuit coupled to the free layer terminal of the MTJ element; and

a probability compensator comprising:
a probability calculator coupled to the output node and configured to determine deviations from a target probability exhibited by the MTJ element responsive to the perturbation pulses;
a voltage offset generator coupled to a probability output terminal of the probability calculator; and
a reference buffer coupled to an output terminal of the voltage offset generator, wherein the reference buffer includes the adjustable reference node.

2. The circuit of claim 1 , wherein the MTJ element is configured to probabilistically change magnetization state responsive to the perturbation pulses applied between the pulse output terminal and the adjustable reference node.

3. The circuit of claim 1 , wherein the MTJ element comprises a memory bit in a magnetic random-access memory (MRAM) array selectable as either a memory storage element or a random bit generator element.

4. The circuit of claim 1 , wherein the pulse generator comprises a bidirectional pulse generation element to selectively apply reset pulses and read pulses through the MTJ element in a first direction via the pulse output terminal, and selectively apply perturbation pulses through the MTJ element in a second direction via the pulse output terminal.

5. The circuit of claim 1 , further comprising a random bit vector:
wherein the output node comprises a first bit of the random bit vector; and
wherein a second output node of a second random bitstream generator comprises a second bit of the random bit vector.

6. An apparatus comprising:
a plurality of random bit generators comprising magnetic tunnel junction (MTJ) elements configured to produce probabilistic changes in magnetization states responsive to applied perturbation sequences;
probability adjustment circuitry configured to monitor the probabilistic changes in the magnetization states for deviations in measured probabilities from a target probability, and initiate adjustments to the perturbation sequences to influence the probabilistic changes in the magnetization states of the MTJ elements and bring the measured probabilities to within a predetermined deviation from the target probability;
one or more pulse generators configured to apply the perturbation sequences to the plurality of random bit generators in accordance with at least the adjustments initiated by the probability adjustment circuitry; and
output circuitry configured to present a random bit vector comprised of the magnetization states of the plurality of random bit generators from at least one perturbation sequence.

7. The apparatus of claim 6 , wherein the perturbation sequences comprise:
reset phases which apply reset voltage pulses to the MTJ elements to place the MTJ elements into predetermined magnetization states before application of perturbation voltage pulses;
perturbation phases which apply the perturbation voltage pulses to the MTJ elements to produce the probabilistic changes in the magnetization states; and
read phases which apply read voltage pulses to the MTJ elements by the one or more pulse generators to determine the magnetization states among the MTJ elements due to application of the perturbation voltage pulses.

8. The apparatus of claim 6 , wherein the probability adjustment circuitry is configured to perform the adjustments to the perturbation sequences by altering one or more among pulse amplitudes, pulse widths, and reference voltages associated with application of perturbation voltage pulses by the one or more pulse generators that produce the probabilistic changes in the magnetization states.

9. The apparatus of claim 6 , wherein the probability adjustment circuitry monitors the magnetization states of the plurality of random bit generators across a predetermined quantity perturbation sequences to determine the deviations in the measured probabilities from the target probability.

10. The apparatus of claim 6 , wherein each of the MTJ elements have associated free layer terminals that generate and apply the perturbation sequences; and
wherein each of the MTJ elements have associated pinned layer terminals coupled to adjustable reference nodes that can vary in applied reference voltages according to the adjustments to the perturbation sequences.

11. The apparatus of claim 6 , wherein the target probability is selectable over a probability range by altering the adjustments to the perturbation sequences.

12. The apparatus of claim 6 , wherein the perturbation sequences are repeated in a cyclical manner to produce a series of random bit vector outputs; and
wherein the probability adjustment circuitry initiates the adjustments to the perturbation sequences after monitoring a predetermined quantity of random bit vectors.

13. A method of random number generation, comprising:
applying reset pulses to magnetic tunnel junction (MTJ) elements included in a plurality of random bitstream generators, the reset pulses placing the MTJ elements into predetermined magnetization states;
applying perturbation reset pulses to the MTJ elements;
applying read pulses to the MTJ elements to determine magnetization states among the MTJ elements after application of the perturbation pulses; and
producing random bit vector outputs comprised of each of the magnetization states of the plurality of random bitstream generators after application of at least one corresponding read pulse; and
monitoring for deviations in measured probabilities from a target probability among the magnetization states; and
making adjustments to the perturbation pulses to influence probabilistic changes in the magnetization states of the MTJ elements and bring the measured probabilities to within a predetermined deviation from the target probability.

14. The method of claim 13 , further comprising:
repeating application of the perturbation pulses alternated with the read pulses and corresponding reset pulses to produce a series of random bit vector outputs; and
making the adjustments to the perturbation pulses after monitoring a predetermined quantity of random bit vector outputs.

15. The method of claim 13 , wherein making the adjustments to the perturbation pulses comprises altering one or more among pulse amplitudes, pulse widths, and reference voltages associated with application of the perturbation pulses to the plurality of random bitstream generators.

16. The method of claim 13 , further comprising:
wherein the perturbation pulses are applied to free layer terminals of the MTJ elements as perturbation voltage pulses with first polarities;
wherein the read pulses are applied to the free layer terminals of the MTJ elements as read voltage pulses with the first polarities;
wherein the reset pulses are applied to the free layer terminals of the MTJ elements as reset voltage pulses with second polarities opposite of the first polarities; and
wherein pinned layer terminals of the MTJ elements are coupled to adjustable reference voltages used to make amplitude adjustments to the perturbation pulses to influence the probabilistic changes in the magnetization states of the MTJ elements.

17. The me

Assignees

• Sandisk Technologies Llc

Inventors

• Choi Won Ho

Classifications

• H10N50/10

  Magnetoresistive devices · CPC title

• H10B61/22

  of the field-effect transistor [FET] type · CPC title

• H10N50/80

  Constructional details · CPC title

• G11C11/1673

  Reading or sensing circuits or methods · CPC title

• G11C11/1675

  Writing or programming circuits or methods · CPC title