JP2021179779A - Random number generator and random number generation method - Google Patents

Abstract

To provide a random number generator capable of speeding up and generating an extremely high-quality random number sequence.SOLUTION: A random number generator 10 includes: a voltage pulse supply unit 12 that supplies a voltage pulse to a magnetoresistive element 11; a discrimination unit 18 that discriminates whether the magnetoresistive element is in a parallel state or an antiparallel state from a resistance value each time a voltage pulse is supplied to the magnetoresistive element and outputs a bit of '0' or '1' according to a discrimination result; a voltage pulse amplitude adjustment unit 19 that adjusts a voltage amplitude of the voltage pulse so that appearance probability of a certain pattern in a bit string consisting of N consecutive bits (N is an even number of 2 or more) output by the discrimination unit is set to 1/2N; and a random number generation unit 20 that generates, based on the bit string consisting of N consecutive bits output by the discrimination unit according to the discriminant result of whether the magnetoresistive element is in a parallel state or an antiparallel state, a random number string, in which the voltage pulse whose voltage amplitude is adjusted by the voltage pulse amplitude adjustment unit is supplied to the magnetoresistive element.SELECTED DRAWING: Figure 1

Description

The present invention relates to a random number generation technique using a magnetoresistive element.

In recent years, the exchange of information via the Internet has increased explosively, and data encryption has become an indispensable technology. In cryptography, random numbers are used to generate keys and key pairs. Random numbers are required not only to have no statistical bias, but also to have the property that the next data cannot be predicted from the past random number sequence and the property that the same random number sequence cannot be reproduced. Random numbers having such properties use a physical phenomenon that cannot be reproduced as a random number source, and the generated random numbers are considered to have a uniform distribution, and are called true physical random numbers.

As a physical phenomenon used in a random number generator, it has been proposed to use a phenomenon in which magnetization reversal stochastically occurs in a magnetic resistance element due to an external field such as a magnetic field, current, or voltage. The magnetoresistive element is a device composed of three layers, a magnetization fixed layer, an intermediate layer, and a magnetization free layer. In the magnetoresistive element, the direction of magnetization of the magnetization free layer changes depending on the external field, and the resistance value changes according to the direction with respect to the direction of magnetization of the magnetization fixed layer.

In the current magnetization reversal method, a current pulse is passed through the magnetoresistive element to invert the direction of magnetization of the magnetization free layer. Specifically, in the current magnetization reversal, torque acts on the magnetization of the magnetization free layer when the angular momentum is passed from the current to the magnetization free layer, and the magnetization reversal is excited. In the current magnetization reversal method, the angular momentum passed from the current is proportional to the product of the current value of the current pulse and the pulse width (see, for example, Patent Document 1).

In the voltage magnetization reversal method, a voltage pulse is applied to the magnetoresistive element to reverse the direction of magnetization of the magnetization free layer (see, for example, Patent Document 2 and Non-Patent Document 1). Specifically, in the voltage magnetization reversal method, the magnetic anisotropy of the magnetization free layer is reduced by applying an electric field to the magnetization free layer by the voltage pulse applied to the magnetic resistance element, and the magnetization age difference of the magnetization free layer is reduced. The excitation of the motion excites the magnetization reversal.

Patent No. 4625936 International Publication No. 2015/0473228

Hochul Lee et al. “Design of high-throughput and low-power true random number generator utilizing orthogonally magnetized voltage controlled magnetic tunnel junction”, AIP Advances 7, 055934 (2017)

In the current magnetization reversal method, there is a problem that the shorter the pulse width of the current pulse, the larger the current value required for magnetization reversal. There is a problem that there is a limit to realizing a random number generator.

An object of the present invention is to solve the above-mentioned problems, and to provide a random number generator capable of increasing the speed and generating a highly high quality random number sequence.

According to one aspect of the present invention, a magnetization free layer, a magnetization fixing layer, and a tunnel barrier layer are formed between the magnetization free layer and the magnetization fixing layer, and the direction of magnetization of the magnetization free layer and the above. A magnetic resistance element whose resistance value changes depending on whether the direction of magnetization of the magnetization fixed layer is parallel or antiparallel, a means for supplying a voltage pulse to the magnetic resistance element, and the magnetic pulse. Each time it is supplied to the resistance element, the parallel state or the antiparallel state is discriminated from the resistance value, and a discriminant means for outputting a bit of "0" or "1" according to the discriminant state, and a continuous output by the discriminating means. An amplitude adjusting means for adjusting the voltage amplitude of the voltage pulse so that the appearance probability of a certain pattern in a bit string consisting of N bits (where N is an even number of 2 or more) is 1/2 ^{N, and the above.} The voltage pulse whose voltage amplitude has been adjusted by the amplitude adjusting means is supplied to the magnetic resistance element, and N consecutive pieces output by the discrimination means according to the parallel state or the antiparallel state of the magnetic resistance element. A randomizer generator comprising a generation means for generating a random number sequence based on a bit string consisting of bits is provided.

According to the above aspect, since the voltage magnetization reversal in the magnetic resistance element is used, the speed can be increased, and the appearance probability of a certain pattern in the bit string consisting of continuous N bits output by the discriminating means is halved. ^{The voltage amplitude of the voltage pulse is adjusted by the amplitude adjusting means so as to be N} and supplied to the magnetic resistance element, and the continuous N output by the discriminating means according to the parallel state or the antiparallel state of the magnetic resistance element. By generating a random number sequence by a generation means based on a bit string consisting of a number of bits, it is possible to provide a random number generator capable of generating a highly high quality random number sequence.

According to another aspect of the present invention, the magnetization free layer, the tunnel barrier layer, and the magnetization fixed layer are laminated, and the magnetization direction of the magnetization free layer and the magnetization direction of the magnetization fixed layer are parallel or antiparallel. The parallel state or the antiparallel state is discriminated from the step of supplying a voltage pulse to the magnetic resistance element whose resistance value changes depending on the state and the resistance value after supplying the voltage pulse, and correspondingly. The appearance probability of a pattern in which a bit string consisting of a discrimination step that outputs '0' or '1' bits and N consecutive bits (where N is an even number of 2 or more) output by the above discrimination step is a pattern. An amplitude adjusting step for adjusting the voltage amplitude of the voltage pulse so as to be 1/2 ^N , and the voltage pulse whose voltage amplitude is adjusted by the amplitude adjusting step are supplied to the magnetic resistance element, and the magnetic resistance element is supplied. Provided is a generation method including a generation step of generating a random number sequence based on a bit string consisting of N consecutive bits output by the discrimination step according to the parallel state or the antiparallel state of the above.

According to the above aspect, since the parallel state and the anti-parallel state of the magnetization are formed by using the voltage magnetization reversal of the magnetic resistance element, the speed can be increased, and the continuous N bits output by the discrimination step can be used. A voltage pulse whose voltage amplitude is adjusted by the amplitude adjustment step is supplied to the magnetic resistance element so that the appearance probability of a certain pattern in the bit string is 1/2 ^{N, and the parallel state of the magnetic resistance element or the opposite of the magnetic resistance element.} Provides a random number generation method that can generate a highly high quality random number sequence by generating a random number sequence by the generation step based on a bit string consisting of N consecutive bits output by the discrimination step according to the parallel state. can.

It is a schematic block diagram of the random number generator which concerns on one Embodiment of this invention. It is schematic cross-sectional view of the magnetic resistance element of the random number generator which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the reversal probability of the magnetization of the magnetization free layer, and the voltage pulse width. It is a figure which shows the relationship between the voltage amplitude of a voltage pulse and the frequency of the state change from the parallel state and the antiparallel state of the magnetization of a magnetic resistance element to the parallel state or the antiparallel state. It is a figure which shows the appearance probability of ‘01’ and ‘10’ with respect to the bit string used by the voltage pulse amplitude adjustment part for adjusting the voltage amplitude of a voltage pulse. It is a histogram which shows the average value for each packet of the appearance probability of '01' and'10' with respect to the bit string used by the voltage pulse amplitude adjustment part for adjustment of the voltage amplitude of a voltage pulse. When the random number generation unit generates a random number by allocating the bit strings '01' and '10' to '0' or '1' in which two consecutive bits input from the output unit of the discrimination unit alternate between 0 and 1. It is a histogram which shows the average value for each packet of the generation probability of '0' and '1'. It is a flowchart of the random number generation method which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to the elements common to the plurality of drawings, and the repetition of the detailed description of the elements will be omitted.

FIG. 1 is a schematic configuration diagram of a random number generator according to an embodiment of the present invention. Referring to FIG. 1, the random number generator 10 according to the embodiment has a magnetic resistance element 11, a voltage pulse supply unit 12 that generates and supplies a voltage pulse to the magnetic resistance element 11, and a DC to the magnetic resistance element 11. The DC voltage supply unit 13 and the resistor 14 to which the voltage bias is applied and the resistor 14 are connected to the DC terminal, the output unit of the voltage pulse supply unit 12 is connected to the AC terminal, and the DC voltage bias is applied to the magnetic resistance element 11. The bias tee 15 that applies and supplies a voltage pulse, _{the amplifier 16 that amplifies the voltage division V bp} according to the resistance value of the magnetic resistance element 11, and the resistance value of the magnetic resistance element 11 are detected from the amplified voltage value. Then, the discriminating unit 18 that discriminates between the parallel and antiparallel states of the magnetization of the magnetic resistance element 11 and allocates the bits of "0" or "1" accordingly, and the "0" or "1" output from the discriminating unit 18. Adjust the voltage amplitude of the voltage pulse so that the ^{appearance probability that N} consecutive bits of'(where N is an even number of 2 or more) becomes only '0' or only '1' is 1/2 N. The voltage pulse adjusted by the voltage pulse amplitude adjusting unit 19 and the voltage pulse amplitude adjusting unit 20 are supplied to the magnetic resistance element 11, and are output from the discriminating unit 18 according to the parallel state and the antiparallel state of the magnetization. It has a random number generation unit 20 that generates a random number sequence based on the bits of'or '1'.

FIG. 2 is a schematic cross-sectional view of the magnetoresistive element of the random number generator according to the embodiment of the present invention. Referring to FIG. 2 together with FIG. 1, the magnetoresistive element 11 has a magnetized free layer 23 and a magnetized fixed layer 24 between the lower electrode layer 21 and the upper electrode layer 22, and a tunnel barrier layer 25 between them. It is a laminated body in which and is formed.

The lower electrode layer 21 and the upper electrode layer 22 are made of a metal layer such as Cu (copper), Au (gold), and aluminum (Al).

The magnetization free layer 23 is composed of a ferromagnetic layer, for example, a CoFeB layer. The magnetization of the magnetization free layer 23 is shown so as to be inclined with respect to the laminating direction (shown in FIG. 2), but it may be oriented along the laminating direction, and is obliquely inclined by an external static magnetic field (for example, a magnet). It may be facing. For example, a Ta (tantalum) layer may be provided as a buffer layer under the magnetization free layer 23.

The tunnel barrier layer 25 is formed on the magnetization free layer 23 and is made of an insulating material such as aluminum oxide (Al—O) or MgO.

The magnetization fixing layer 24 has a ferromagnetic layer in which the direction of magnetization is fixed, or a ferromagnetic layer / intermediate layer / ferromagnetic layer having a laminated ferri (SAF) structure. In the SAF structure, two ferromagnetic layers are antiferromagnetically coupled, and their magnetizations are antiparallel. The intermediate layer is a thin conductive layer. The direction of magnetization of the magnetization fixing layer 24 is fixed in substantially the same direction. The magnetization fixing layer 24 is, for example, a CoPt laminated film / Ru layer / CoPt laminated film. A cap layer (not shown) made of a conductive material may be formed on the magnetization fixing layer 24. The cap layer is, for example, a Ta layer / Ru layer.

As will be described later, the direction of the magnetization of the magnetization free layer 23 is probabilistically reversed by the application of the voltage pulse by the voltage pulse supply unit 12 to the magnetoresistive element 11. That is, the magnetization of the magnetization free layer 23 may or may not be inverted by the application of the voltage pulse. The electrical resistance value of the magnetic resistance element 11 between the lower electrode layer 21 and the upper electrode layer 22 depending on whether the magnetization of the magnetization free layer 23 and the direction of the magnetization of the magnetization fixed layer 24 are parallel or antiparallel. Hereinafter, it is also referred to as “resistance value”). In FIG. 2, the directions of magnetization of the magnetization free layer 23 are shown to be diagonally upward and diagonally downward, but depending on whether the components along the stacking direction are upward or downward, they are parallel to the upward direction of the magnetization fixed layer 24 or are shown. An antiparallel state is formed.

Returning to FIG. 1, the DC voltage supply unit 13 is connected to, for example, a constant voltage power supply, and applies a DC bias voltage to the magnetoresistive element 11. _{Let the supply voltage V sp} of the DC voltage supply unit 13. Due to the resistance value R of the resistor 14 and the resistance value R _MR of the magnetic resistance element 11, the divided voltage V _BP (voltage at the point BP) of the supply voltage V _{sp is V BP} = R _MR / (R + R _MR ) × V _sp . (However, since the internal resistance value between the DC terminal 15a and the output terminal 15c of the bias tee 15 is _{extremely small with respect to R MR} and R, it is ignored.). _{The resistance value R MR} changes depending on whether the magnetization of the magnetization free layer 23 of the magnetoresistive element 11 is in a parallel state or an antiparallel state, and the partial pressure V _BP changes accordingly.

The voltage pulse supply unit 12 generates a voltage pulse and supplies it to the magnetoresistive element 11 via the AC terminal of the bias tee 15. By applying a voltage pulse to the magnetoresistive element 11, it is possible to reverse the direction of magnetization of the magnetization free layer 23 of the magnetoresistive element 11 at high speed.

FIG. 3 is a diagram showing the relationship between the magnetization reversal probability of the magnetization free layer and the voltage pulse width. P → AP (indicated by “●”) indicates the inversion probability that the magnetization of the magnetization free layer and the magnetization of the magnetization fixed layer change from a parallel state to an antiparallel state, and AP → P (indicated by “◯”). Shows the reversal probability when it changes in the opposite direction. The voltage amplitude of the voltage pulse was set to 1.05V. With reference to FIG. 3, the inversion probabilities of P → AP and AP → P are each 0.5, which is about 0.2 ns on the side where the voltage pulse width is narrow. On the other hand, in the method of injecting a current pulse into a magnetoresistive element to invert the magnetization, it is practical that the current pulse width is several tens of nanoseconds or more (see FIG. 10 of Patent Document 1). Therefore, the random number generator 10 of the present embodiment using the voltage pulse can generate random numbers at high speed. For the voltage pulse supply unit 12, for example, a pulse generation circuit can be used. It is preferable to set the voltage pulse width to 10 nanoseconds or less because the pulse width can be increased and is sufficient for magnetization reversal. The voltage pulse amplitude (voltage value) is determined by the voltage pulse amplitude adjusting unit 19.

Returning to FIG. 1, in the bias tee 15, the DC terminal 15a is connected to the input terminal of the resistor 14 and the amplifier 16, the AC terminal 15b is connected to the output unit of the voltage pulse supply unit 12, and the output terminal 15c is a magnetic resistance. It is connected to the element 11. The bias tee 15 superimposes a voltage pulse input to the AC terminal 15b on the DC voltage input to the DC terminal 15a and outputs the voltage pulse from the output terminal 15c to the magnetoresistive element 11.

In the magnetoresistive element 11, one electrode is connected to the output terminal 15c of the bias tee 15, and the other electrode is connected (grounded) to the ground.

The amplifier 16 has an input unit connected to the DC terminal 15a of the bias tee 15 and an output unit connected to the discrimination unit 18. _{As the amplifier 16, an amplifier capable of amplifying a change in the partial pressure VBP} due to a difference in resistance value between the parallel state and the antiparallel state of the magnetization of the magnetic resistance element 11, for example, a low noise amplifier can be used. For example, since the input in the parallel state of magnetization is about 100 millivolts and the input in the antiparallel state of magnetization is 120 millivolts, the amplifier 16 amplifies this input voltage by, for example, 10 times, and the discriminating unit 18 Output to.

The discriminating unit 18 discriminates between the parallel state and the antiparallel state of the magnetization of the magnetoresistive element 11 according to the input voltage value from the amplifier 16. For example, when the input voltage value from the amplifier 16 is lower than the predetermined threshold value, the discriminating unit 18 sets the bit '0' as a parallel state, and when the input voltage value is higher than the predetermined threshold value, the bit '1'is set as an antiparallel state. do. As the predetermined threshold value, a voltage value capable of discriminating between the parallel state and the antiparallel state of the magnetization of the magnetoresistive element 11 may be selected. The output unit of the discrimination unit 18 is connected to each input unit of the voltage pulse amplitude adjustment unit 19 and the random number generation unit 20, and the bit '0' or'corresponds to the parallel state and the antiparallel state of the magnetization of the magnetoresistive element 11. Output 1'. The discriminating unit 18 can use a circuit composed of a DC voltage measuring device, a comparator capable of comparing voltage values, and the like, and can also use a personal computer.

In the voltage pulse amplitude adjusting unit 19, a bit string including bits '0' and '1' is input from the output unit of the discriminating unit 18. The voltage pulse amplitude adjusting unit 19 sets the voltage of the voltage pulse so that the appearance probability of a certain pattern in the bit string consisting of N consecutive bits (where N is an even number of 2 or more) is 1/2 ^N. Adjust the amplitude. Here, N is the number of consecutive bits (that is, the number of bits in the bit string) that is the basis for the random number generation unit 20 described later to generate a random number.

Specifically, the voltage pulse amplitude adjusting unit 19 includes a counting circuit that counts the frequency of a bit string consisting of N consecutive bits for each pattern, and a predetermined number of bit strings (for example, every million). Obtaining the appearance probability of a certain pattern, and showing the relationship between the voltage amplitude of the voltage pulse acquired in advance and the appearance probability (or frequency) of the pattern. Voltage amplitude-A memory that stores appearance probability information and a voltage amplitude from that memory- An arithmetic circuit that reads out the appearance probability information and ^{determines the voltage amplitude of the voltage pulse so that the appearance probability of a certain pattern becomes 1/2 N} , and outputs the voltage amplitude of the determined voltage pulse to the voltage pulse supply unit 12. Has an output circuit. The counting circuit, the arithmetic circuit, and the output circuit are not shown. The counting circuit, the arithmetic circuit and the output circuit may be configured by hardware, or may be configured by using a personal computer and software.

Hereinafter, an example of N = 2 will be described. When the time between the voltage pulse applied to the magnetoresistive element 11 and the next voltage pulse is set sufficiently long (for example, 100 nsec or more), the present inventors make the event of magnetization reversal by each voltage pulse independent. I focused on what can be regarded. Assuming that the magnetization is '0' in the parallel state and '1' in the antiparallel state, the inversion probability from the parallel state to the antiparallel state is expressed by the ratio of the frequency of becoming '01' and the frequency of becoming '00'. NS. That is, the inversion probability from the parallel state is expressed by (frequency of '01') / (frequency of'01' + frequency of '00') × 100 (%). The inversion probability from the antiparallel state is expressed by (frequency of '10') / (frequency of '10' + frequency of '11') × 100 (%).

FIG. 4 is a diagram showing the relationship between the voltage amplitude of the voltage pulse and the frequency of state changes from the parallel state and the antiparallel state to the parallel state or the antiparallel state of the magnetization of the magnetic resistance element 11. Referring to FIG. 4, the frequencies of '00', '01', '10' and '11' are linear, respectively, with the voltage amplitude of the voltage pulse between 1.0325V (volts) and 1.081V, respectively. It can be seen that at 1.062V, the frequency of each event is almost the same. Therefore, in the voltage pulse amplitude adjusting unit 19, the appearance probability of the bit string of a certain pattern among the bit strings '00', '01', '10' and '11' is 1/2 ^N (N = 2), that is, 1. The voltage pulse amplitude adjusting unit 19 adjusts the voltage amplitude of the voltage pulse so as to be / 4. As a result, the probabilities that the patterns of '00', '01', '10' and '11' occur are likely to be equal, and high-quality random numbers can be generated.

Returning to FIG. 1, the random number generation unit 20 inputs a bit string including bits ‘0’ and ‘1’ from the output unit of the discrimination unit 18. This bit string is a bit string in which the voltage amplitude of the voltage pulse has been adjusted by the voltage pulse amplitude adjusting unit 19. When N = 2, the bit string patterns are '00', '01', '10' and '11'. The random number generation unit 20 generates a random number sequence based on a bit string composed of N consecutive bits. For example, out of a bit string consisting of N consecutive bits, a random number string is generated by assigning '0' to a bit string of a certain pattern and '1' to a bit string of another pattern. The random number generation unit 20 can be configured by hardware such as a logic circuit, a personal computer, software, or a combination thereof.

The voltage pulse amplitude adjusting unit 19 has a voltage amplitude of the voltage pulse so that the appearance probability that the pattern of the bit string consisting of N consecutive bits is only '0' or only '1' is 1/2 ^N. It is preferable to adjust. When N = 2, the appearance probability of the bit string of '00' or '11' among the bit strings '00', '01', '10' and '11' is 1/2 ^N (N = 2), that is, Adjust the voltage amplitude of the voltage pulse to 1/4 (25%). As a result, the appearance probabilities of '01' and '10' tend to be the same, so that the random number generation unit 20 can generate a higher quality random number sequence. This was obtained from the experimental results described below.

FIG. 5 is a diagram showing the appearance probabilities of '01' and '10' with respect to the bit string used by the voltage pulse amplitude adjusting unit for adjusting the voltage amplitude of the voltage pulse, and FIG. 5A shows the appearance probabilities of '10' 25. (B) is the case where the voltage amplitude of the voltage pulse is adjusted so that the probability of appearance of '00' is 25%, and one data point is 2 million trials (1 on the horizontal axis). It is the appearance probability of '01' (indicated by ●) and '10' (indicated by ○) obtained from (corresponding to a packet).

With reference to FIG. 5, in the case of adjusting the appearance probability of '00' in (b) to be 25%, the appearance probability of '10' in (a) is adjusted to be 25%. It can be seen that the appearance probability of '01' and the appearance probability of '10' are more uniform than in the case.

FIG. 6 is a histogram showing the average value of the appearance probabilities of '01' and '10' for each packet with respect to the bit string used by the voltage pulse amplitude adjusting unit for adjusting the voltage amplitude of the voltage pulse. FIG. 5A and FIG. It is a figure which showed the data of each about 800 points in the trial result shown in (b) by a histogram. FIG. 5A shows a case where the voltage amplitude of the voltage pulse is adjusted so that the appearance probability of '10' becomes 25%, and FIG. 5B shows a case where the appearance probability of '00' becomes 25%.

With reference to FIG. 6, (a) and (b) generally show a Gaussian distribution. When the appearance probability of '10' in (a) is adjusted, the half width of the distribution is 0.08, and when the appearance probability of '00' in (b) is adjusted, the half width of the distribution is 0. It is 04. Since one point of data was obtained from 2 million trials, and the histogram is an analysis with about 800 points of data and a large amount of data, there is a statistically significant difference between these two distributions. Can be judged. That is, it can be seen that the case where the appearance probability of '00' in (b) is adjusted is statistically narrower than the case where the appearance probability of '10' in (a) is adjusted, which is preferable. .. From these facts, adjusting the voltage amplitude of the voltage pulse so that the appearance probability of the bit string of '00' becomes 25% makes the appearance probability of the bit string of '10' 25%. It turns out that it is preferable to adjusting the voltage amplitude.

Here, from a physical point of view, there is a relationship that the sum of the probability that the direction of magnetization is reversed and the probability that the direction of magnetization is not reversed by the application of a voltage pulse is 1. Using the probability of generation of a bit string of '00' when the magnetization does not reverse is used to adjust the voltage amplitude of the voltage pulse, as well as the probability of generation of a bit string of '11' when the magnetization does not reverse is a voltage pulse. There is a 1: 1 correspondence with using the voltage amplitude of. Therefore, it can be seen that using the probability of generating the bit string of 11'for adjusting the voltage amplitude of the voltage pulse has the same effect as in the case of '00'. In the case of '01', the same effect as in the case of '10' can be obtained by the same logic. Therefore, it can be seen that it is preferable for the voltage pulse amplitude adjusting unit 19 to adjust the voltage amplitude of the voltage pulse by using the bit string of '00' or '11', as compared with the case of using '01' or '10'. This can be generalized by adjusting the voltage amplitude of the voltage pulse so that the probability of occurrence of a bit string consisting of only '0' or only '1' is 1/2 ^N. Is preferable.

In particular, the random number generation unit 20 generates random numbers by allocating '0' or '1' to a bit string in which N consecutive bits input from the output unit of the discrimination unit 18 alternate between 0 and 1. preferable. For example, the case where N = 2 will be described. The random number generation unit 20 allocates '0' when the input bit string is '01', which is a bit string in which '0' and '1' alternate, and the other 0 and 1 are alternating bit strings'. In the case of 10', a random number is generated by assigning '1'. The random number generation unit 20 does not allocate bits when the input bit strings are '00' and '11' in which '0' and '1' do not alternate.

Specifically, when the generation probability of '0' is 0.5 + δ, the generation probability of '1' is 0.5-δ. Here, δ represents a deviation from 0.5. In this case, the generation probabilities of '01' and '10', which are bit strings in which '0' and '1' are alternated, are both 0.25-δ ² and are equal to each other. Therefore, when N = 2, the random number generator 20 allocates '0' or '1' from '01' and '01', which are bit strings in which '0' and '1' alternate, to generate a random number. Is particularly preferable.

In FIG. 7, the random number generation unit assigns a random number from the bit strings '01' and '10' to '0' or '1' in which two consecutive bits input from the output unit of the discrimination unit alternate between 0 and 1. It is a histogram showing the average value for each packet of the generation probability of '0' and' 1'in the case of generating, and (b) is the figure which enlarged the horizontal axis of (a). Since 2 bits are read as 1 bit in 1 packet, the number of bits is 500,000.

With reference to FIGS. 7 (a) and 7 (b), the full width at half maximum of the distribution is 0.002, which is 1 / of 0.04 when the random number generator in FIG. 5 (b) does not use this allocation method. It turned out to be reduced to 20. When the curve of the binomial distribution (illustrated by BN) is applied to FIG. 6 (b), it can be seen that the histogram of the generated random numbers is in good agreement with the shape and half width of the binomial distribution. Statistically, true physical random numbers are said to have statistics similar to the binomial distribution. Therefore, it can be seen that the random number generation unit 20 was able to generate a higher quality and ideal binary random number.

The data of FIGS. 3 to 7 were obtained from experiments using a random number generator having the following configuration. The magnetoresistive element 11 includes a lower electrode layer 21: a Cu layer having a thickness of 100 nm, a buffer layer: a Ta layer having a thickness of 10 nm, a magnetization free layer 23: a CoFeB layer having a thickness of 1.1 nm, and a tunnel barrier layer 25: a thickness of 1. .4 nm MgO layer, magnetization fixed layer 24: CoPt laminated film with SAF structure and thickness 2.4 nm / Ru layer with thickness 0.9 nm / CoPt laminated film with thickness 1.3 nm, cap layer: thickness A Ta layer having a thickness of 5 nm / a Ru layer having a thickness of 7 nm and an upper electrode layer 22: a Cr layer having a thickness of 5 nm / an Au layer having a thickness of 200 nm. The magnetoresistive element 11 was formed into a film on a thermal silicon oxide substrate by a sputtering method, and processed into a cylinder having a diameter of 80 nm to 100 nm by a photolithography method and an electron beam lithography method.

A model M8195A manufactured by Keysight Co., Ltd. was used for the pulse generation circuit of the voltage pulse supply unit 12, and a model 5542 manufactured by Pico Second Pulse Lab Co., Ltd. was used as the bias tee 15. The DC voltage supply unit 13 was set to 200 mV, and the resistor 14 was set to 100 kΩ. For the amplifier 16, a low noise voltage preamplifier model SR560 manufactured by Stanford Research Systems, Inc. of the United States was used, and the amplification factor was set to 10 times. The discrimination unit 18 was composed of a digital multimeter 33465A manufactured by Keysight Technology, Inc. of the United States and a personal computer. The voltage value of the amplifier 16 is measured with a digital multimeter, the threshold value is set to 1.1V on a personal computer, the parallel state and antiparallel state of the magnetoresistive element 11 are discriminated, and the bits of '0' or '1' are determined by software. Was assigned. The voltage pulse amplitude adjusting unit 19 and the random number generation unit 20 are composed of a personal computer and software.

According to the random number generator 10 of the present embodiment, the appearance probability of a certain pattern in the bit string consisting of N consecutive bits (where N is an even number of 2 or more) output by the discriminating unit 18 is halved. ^The pulse amplitude adjusting unit 19 adjusts the voltage amplitude of the voltage pulse so that it becomes N, supplies it to the magnetic resistance element 11, and generates a random number based on a bit string consisting of N consecutive bits output by the discriminating unit 18. By generating a random number sequence by the unit 20, it is possible to generate a highly high quality random number sequence.

FIG. 8 is a flowchart of a random number generation method according to an embodiment of the present invention. A random number generation method will be described with reference to FIG. 8 together with FIGS. 1 and 2.

First, in step S100, a voltage pulse is supplied to the magnetoresistive element 11 by the voltage pulse supply unit 12. Specifically, a bias voltage (for example, 200 mV) is set by the DC voltage supply unit 13, and the voltage is divided into the magnetic resistance element 11 via the resistor 14 (for example, 100 kΩ) and the bias tee 15 (input by the DC terminal). While applying the pressure V _bp , one voltage pulse (pulse width is, for example, 0.1 ns (nanos) to several ns, voltage amplitude is, for example, 1.06 V) is applied by the voltage pulse supply unit 12. The application of the voltage pulse reverses or does not reverse the magnetization of the free magnetization layer 23, and as a result, whether the directions of the magnetization of the free magnetization layer 23 and the magnetization of the fixed magnetization layer 24 are parallel or antiparallel. The resistance value of the magnetic resistance element 11 is determined accordingly. The resistance values in the parallel state are lower than those in the antiparallel state, for example, 100 kΩ and 150 kΩ, respectively.

Next, in step S110, the resistance value of the magnetoresistive element after the voltage pulse is supplied by the discriminant unit 18 is detected to discriminate between the parallel state and the antiparallel state of the magnetoresistive element 11, and the state of '0' or '1' is determined. Allocate a bit. Specifically, the discriminant unit 18 detects the resistance value in the parallel state and the antiparallel state of the magnetoresistive element 11 from the _{voltage dividing Vbp applied to the magnetoresistive element 11.} The partial pressure V _bp is, for example, 100 mV and 120 mV, respectively, in the parallel state and the antiparallel state. The partial pressure V _bp is input to the amplifier 16, and the output amplified by the amplifier 16 is input to the discriminating unit 18. The discriminating unit 18 discriminates between the parallel state and the antiparallel state of the magnetoresistive element 11 based on the magnitude of the input voltage with respect to the predetermined threshold voltage, and assigns '0' to the parallel state and '1' to the antiparallel state, for example.

Next, in step S120, the voltage pulse amplitude adjusting unit 19 obtains the appearance probability of a certain pattern in the bit string consisting of N consecutive bits (where N is an even number of 2 or more). As a result, as shown in FIG. 3 above, the probability that each pattern of the bit string, for example, each pattern of '00', '01', '10' and '11' is equal when N = 2, is equal. It becomes easy to become, and it is possible to generate high-quality random numbers.

The pattern of the bit string can be appropriately selected, but it is preferably only '0' or only '1'. For example, when N = 2, the pattern of the bit string is preferred from the same point of view that '00' or '11' is better than '01' or '10' as described above in FIGS. 4 and 5.

Next, in step S130, the voltage pulse amplitude adjusting unit 19 reduces the appearance probability of a certain pattern of the bit string consisting of N consecutive bits obtained in step S120 to 1/2 ^N. To adjust. Specifically, the voltage pulse amplitude adjusting unit 19 acquires voltage amplitude-appearance probability information indicating the relationship between the voltage pulse amplitude Vpulse and the frequency (or appearance probability) as shown in FIG. 3 in advance, and then obtains the voltage pulse. It is stored in the amplitude adjusting unit 19, and the voltage amplitude of the voltage pulse is set so ^{that the appearance probability becomes 1/2 N} according to the voltage amplitude-appearance probability information and the appearance probability of a certain pattern obtained in step S120. Increase or decrease.

Next, returning to step S100, the voltage pulse adjusted by step S130 by the voltage pulse supply unit 12 is applied to the magnetoresistive element 11, and in S110, the magnetic resistance element 11 after supplying the voltage pulse by the discriminating unit 18 The resistance value is detected to determine the parallel state and the antiparallel state of the magnetoresistive element 11, and a bit of '0' or '1' is assigned.

Next, in step S140, the random number generation unit 20 generates a random number sequence based on the ‘0’ or ‘1’ bits output by the discrimination unit 18 in S110. Specifically, a random number string is generated by allocating "0" or "1" to a bit string consisting of N bits including "0" or "1" bits input from the discriminating unit 18. For example, the "0" and "1" bits input from the discriminating unit 18 may be assigned to 0'and" 1', respectively, and output as a random number.

In step S140, the random number generation unit 20 causes all of the N consecutive bits output by the determination unit 18 in S110 to generate '0' or '1' for a bit string in which '0' and '1' are alternated. It is particularly preferable to allocate and generate random numbers. For example, when N = 2, the random number generation unit 20 allocates '0' and '1' from the input '01' and '10', respectively, to generate a random number. As shown in FIG. 6 above, higher quality and ideal binary random numbers can be generated. When N = 4, the random number generation unit 20 allocates '0' and '1' from the input '0101' and '1010', respectively, to generate a random number. It should be noted that the bits are not assigned to the bit strings other than the bit strings in which all N bits of the input bit strings are alternated with "0" and "1".

According to the random number generation method of the present embodiment, the voltage pulse supplied to the magnetoresistive element 11 is output from the discriminating unit 18 among a bit string consisting of N consecutive bits (where N is an even number of 2 or more). The voltage amplitude of the voltage pulse is adjusted so that the appearance probability of the pattern is 1/2 ^N , and the voltage pulse is supplied to the magnetoresistive element 11 so that the magnetic resistance element 11 is in a parallel state or an antiparallel state in the direction of magnetization. By generating a random number sequence based on a bit string consisting of N consecutive bits output by the discriminating unit 18 accordingly, it is possible to generate a highly high quality random number sequence.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment, and various modifications and changes can be made within the scope of the present invention described in the claims. It is possible.

10 Random number generator 11 Magnetic resistance element 12 Voltage pulse supply unit 18 Discrimination unit 19 Voltage pulse amplitude adjustment unit 20 Random number generation unit 23 Magnetized free layer 24 Magnetized fixed layer 25 Tunnel barrier layer

Claims (10)

A free magnetization layer, a fixed magnetization layer, and a tunnel barrier layer are formed between the free magnetization layer and the fixed magnetization layer, and the direction of magnetization of the free magnetization layer and the direction of magnetization of the fixed magnetization layer are determined. A magnetic resistance element whose resistance value changes depending on whether it is in a parallel state or an antiparallel state, and
A means for supplying a voltage pulse to the magnetoresistive element and
Each time the voltage pulse is supplied to the magnetoresistive element, the parallel state or the antiparallel state is discriminated from the resistance value, and a bit of '0' or '1' is output according to the discriminating means.
The voltage amplitude of the voltage pulse such that the probability of occurrence of a pattern to 1/2 ^N of the bit sequence consisting of bits of N consecutive output by said determination means (where N is an even number of 2 or more.) Amplitude adjustment means to adjust and
The voltage pulse whose voltage amplitude is adjusted by the amplitude adjusting means is supplied to the magnetoresistive element, and N consecutive pieces output by the discriminating means according to the parallel state or the antiparallel state of the magnetoresistive element. A generation method that generates a random number sequence based on a bit string consisting of the bits of
Random number generator with. The amplitude adjusting means adjusts the voltage amplitude of the voltage pulse so that the appearance probability that the pattern of the bit string consisting of the continuous N bits is only '0' or only '1' is 1/2 ^N. The random number generator according to claim 1, which is adjusted. The generation means allocates '0' or '1' to the bit string in which all the bits of the bit string consisting of N consecutive bits output from the discrimination means alternate between '0' and '1'. The random number generator according to claim 1 or 2, which generates a random number. The N is 2,
The amplitude adjusting means adjusts the appearance probability in the case of '00' or '11' to 1/4, and adjusts the appearance probability to 1/4.
The random number generation according to claim 3, wherein the generation means assigns "0" to one of the bit strings of "01" or "10" output from the determination means and "1" to the other to generate a random number. vessel. The random number generator according to any one of claims 1 to 4, wherein the generation means does not allocate bits to a bit string other than the bit strings in which "0" and "1" alternate among the bit strings. The random number generator according to any one of claims 1 to 5, wherein the magnetoresistive element is made of an iron-cobalt boron alloy in the magnetization free layer and magnesium oxide in the tunnel barrier layer. The random number generator according to any one of claims 1 to 6, wherein the time width of the voltage pulse is 10 nanoseconds or less. The magnetization free layer, the tunnel barrier layer, and the magnetization fixed layer are laminated, and the resistance value is determined depending on whether the magnetization direction of the magnetization free layer and the magnetization direction of the magnetization fixed layer are in a parallel state or an antiparallel state. The step of supplying a voltage pulse to the changing magnetoresistive element,
A discrimination step of discriminating the parallel state or the antiparallel state from the resistance value after supplying the voltage pulse, and outputting a bit of "0" or "1" according to the discrimination step.
The voltage amplitude of the voltage pulse is adjusted so that the bit string consisting of N consecutive bits (where N is an even number of 2 or more) output by the discrimination step reduces the appearance probability of a certain pattern to 1/2 ^N. Amplitude adjustment step and
The voltage pulse whose voltage amplitude is adjusted by the amplitude adjustment step is supplied to the magnetoresistive element, and N consecutive elements output by the discrimination step according to the parallel state or the antiparallel state of the magnetoresistive element. A generation step that generates a random sequence based on a bit string consisting of the bits of
Random number generation method including. In the amplitude adjustment step, the voltage amplitude of the voltage pulse is adjusted so that the appearance probability that the pattern of the bit string consisting of the continuous N bits is only '0' or only '1' is 1/2 ^N. The random number generation method according to claim 8, which is adjusted. In the generation step, all the bits of the bit string consisting of N consecutive bits output from the discrimination step are allotted '0' or '1' to the bit string in which '0' and '1' are alternated. The random number generation method according to claim 8 or 9, wherein a random number is generated.

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