KR102056397B1 - Method for Reading PRAM to Improve Dispersion and Apparatus Therefor - Google Patents

Abstract

Disclosed are a phase change memory read method and apparatus for improving dispersion. A phase change memory read method according to an embodiment of the present invention includes applying a voltage that increases linearly based on a threshold voltage of a resistive switching element constituting a phase change memory for a read operation of the phase change memory; Increasing the current in the current path as the voltage increases using a pre-configured current path; And performing a read operation of the phase change memory using the linearly increasing voltage and the increasing current through the current path.

Description

Phase change memory reading method and device for improving dispersion {Method for Reading PRAM to Improve Dispersion and Apparatus Therefor}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reading a phase change memory, and more particularly, by improving a threshold voltage distribution of a resistive switching element constituting a phase change memory, thereby allowing a phase change to normally read data stored in the phase change memory. Memory read method and apparatus.

Multi-Level Cell (MLC) PRAMs are the most promising candidates for next-generation memory, offering a variety of benefits including high density, nonvolatile, high endurance, and low read / write latency.

Currently, Samsung Electronics and other competitors are conducting research and product development based on cross-bar array structure to commercialize and mass-produce PRAM. The cross-bar array PRAM has an Ovonic Threshold Switching (OTS) device and a Charcogenide material, a phase change material, between the upper bit line and the lower source line. contact) has a structure connected vertically by using a material.

 OTS has a characteristic that current flows when the bias exceeds the threshold voltage (Vth), and uses this characteristic to serve as a selection element of the PRAM.

However, the threshold voltage of the OTS has a variation of approximately ± 0.5 [V] from the reference threshold voltage, and this threshold voltage dispersion is a function of the accuracy of the data read by the PRAM read operation because it extends to the current and voltage sense margin in the operation of the PRAM. Problems may arise.

Therefore, there is a need for a read method and apparatus that can accurately read data stored in the PRAM by improving the threshold voltage distribution of the resistive switching element.

Embodiments of the present invention provide a phase change memory reading method and apparatus which can normally read data stored in a phase change memory by improving the threshold voltage distribution of the resistive switching element constituting the phase change memory.

A phase change memory read method according to an embodiment of the present invention includes applying a voltage that increases linearly based on a threshold voltage of a resistive switching element constituting a phase change memory for a read operation of the phase change memory; Increasing the current in the current path as the voltage increases using a pre-configured current path; And performing a read operation of the phase change memory using the linearly increasing voltage and the increasing current through the current path.

Increasing the current of the current path may increase the current of the current path by decreasing the resistance value of the current path as the voltage increases.

The current path may be formed in parallel with the resistive switching element and the cell of the phase change memory, between the bit line and the source line where the resistive switching element and the cell of the phase change memory are formed.

The current path may include at least one of a variable resistor and a variable resistance element.

The applying of the voltage may apply a read voltage that increases linearly to a voltage that is set larger than the maximum threshold voltage of the resistive switching element.

A phase change memory read device according to an embodiment of the present invention includes a voltage applying unit configured to apply a voltage that increases linearly based on a threshold voltage of a resistive switching element constituting a phase change memory for a read operation of the phase change memory. ; A current path unit for increasing a current of the current path as the voltage increases by using a current path provided in advance; And a controller configured to perform a read operation of the phase change memory using the linearly increasing voltage and the increasing current through the current path.

The current path part may increase the current of the current path by decreasing the resistance value of the current path as the voltage increases.

The current path part may be formed in parallel with the resistive switching element and the cell of the phase change memory between a bit line and a source line where the resistive switching element and the cell of the phase change memory are formed.

The current path part may include at least one of a variable resistor and a variable resistance element.

The voltage applying unit may apply a read voltage that increases linearly to a voltage set greater than a maximum threshold voltage of the resistive switching element.

According to embodiments of the present invention, by improving the threshold voltage distribution of the resistive switching element constituting the phase change memory, data stored in the phase change memory can be read normally.

According to embodiments of the present invention, in the process of sensing current to determine cell data, a linearly increasing read voltage is applied to improve the influence of threshold voltage distribution by a resistive switching device, eg, an OTS device. As the read voltage is increased, the resistance value of the current path is decreased to increase the current flowing in the current path, thereby maintaining a read operation that minimizes the influence of the threshold voltage distribution of the resistive switching element while maintaining the current flowing in the cell at a similar value. Can be done.

1 is a diagram illustrating a conventional read operation and a read operation of the present invention.
2 is a flowchart illustrating an operation of reading a phase change memory according to an embodiment of the present invention.
Figure 3 shows an exemplary view for explaining the operation according to the present invention.
4 shows a circuit structure for controlling the cell current.
5 illustrates a configuration of a phase change memory reading apparatus according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or limited by the embodiments. Also, like reference numerals in the drawings denote like elements.

Embodiments of the present invention provide a phase change memory by improving a threshold voltage distribution of a resistive switching device constituting a phase change memory by using a voltage that increases linearly and a current path capable of controlling current as the voltage increases. It is an object of the present invention to provide a method and a device capable of reading data normally stored in a storage device.

Here, the current path may be formed in parallel with a cell array formed of a resistive switch and a memory cell and formed between a bit line and a source line, and may include a variable resistance element having a variable resistance such as a variable resistor or a MOSFET. Can be.

1 is a diagram illustrating a conventional read operation and a read operation of the present invention. As shown in FIG. 1, a read operation for reading data from an existing PRAM applies a constant read voltage V _READ . At this time, the sensed current is sensed to output information of the cell stored in the memory cell. However, when the threshold voltage of the resistive switching device is large due to the threshold voltage distribution of the resistive switching device, for example, the OTS device, the OTS device is not turned on at the read voltage and thus the read operation cannot be performed. Will occur.

As shown in FIG. 1B, the present invention applies a saw-tooth-increasing read voltage, for example, a linearly increasing voltage, and sets the highest voltage to the turn-on voltage due to the threshold voltage distribution of the OTS element. By setting the voltage above, the OTS device can be normally turned on and the normal read operation can be performed in both the case where the threshold voltage distribution of the OTS device is large and small. This invention will be described in detail with reference to FIGS. 2 to 5 as follows.

2 is a flowchart illustrating an operation of reading a phase change memory according to an embodiment of the present invention.

Referring to FIG. 2, in order to perform a read operation of a phase change memory, a method according to an embodiment of the present invention applies a voltage that increases linearly, that is, a read voltage based on a threshold voltage of a resistive switching element ( S210).

Here, step S210 may be based on a threshold voltage range previously measured or set for resistive switching devices constituting the phase change memory, for example, OTS devices, that is, based on the threshold voltage distribution as shown in FIGS. 2B and 3A. A read voltage 310 may be applied that increases linearly to a voltage greater than the threshold voltage.

That is, when the resistance distribution of the PRAM is set to a value within a predetermined range, as shown in FIG. 3A, as the read voltage 310 increases, the magnitude of the current I _Cell flowing in the cell increases. This may cause a problem that a read error may occur in the process of sensing the current for determining the cell data.

Thus, the present invention can utilize a current path.

That is, the present invention increases the current flowing through the current path as the read voltage increases using the current path (S220).

Here, as shown in FIG. 3B, the resistance value R _path of the current path is increased as the read voltage is increased by using a current path including a variable resistor element that can be used as a variable resistor, such as a variable resistor or a MOSFET. By decreasing the (320), the current (I _path ) 330 flowing in the current _path increases, so that the current (I _Cell ) flowing in the cell is always maintained at a similar value even when the read voltage increases, so that the read operation can be performed accurately. have.

As shown in FIG. 4, the current path in the present invention is a resistive switching element (OTS) and a cell (PRAM) array formed between a bit line and a source line of a phase change memory. Connected in parallel with Of course, the resistance value of this current path can be controlled by control means capable of controlling the change in the resistance value as the read voltage is increased.

In this case, when performing a read operation using the structure shown in FIG. 4, in the generation of an array liquid such as a sneak leak that is raised in a cross-bar array, a non-selection is performed. Because there is always a current path with a low resistance value by the device, it is possible to eliminate the leakage current through the current path before the leakage occurs.

The linearly increasing read voltage is applied by steps S210 and S220, and when the current flowing through the current path increases with the increase of the read voltage, the linearly increasing read voltage and the current increasing through the current path are used. A read operation of the phase change memory is performed (S230).

As described above, the method according to the embodiment of the present invention distributes the threshold voltage of the resistive switching device constituting the phase change memory using a linearly increasing read voltage and a current path capable of controlling the current as the read voltage increases. As a result, the read operation may be performed to read data stored in the phase change memory normally.

In addition, the method according to the present invention utilizes a current path including a variable resistor element that can be used as a variable resistor, such as a variable resistor or a MOSFET, thereby decreasing the resistance value of the current path as the read voltage increases, thereby flowing into the current path. Even if the current increases and the read voltage increases, the current flowing through the cell is always maintained at a similar value, so that the read operation can be performed accurately.

FIG. 5 illustrates a configuration of a phase change memory read device according to an embodiment of the present invention, and illustrates a configuration of an apparatus for performing the phase change memory read method described with reference to FIGS. 1 to 4.

Referring to FIG. 5, the phase change memory reading apparatus 500 according to the present invention includes a voltage applying unit 510, a current path unit 520, and a controller 530.

The voltage applying unit 510 applies a voltage which increases linearly based on the threshold voltage of the resistive switching element of the phase change memory for the read operation of the phase change memory.

Here, the voltage applying unit 510 may apply a read voltage that increases linearly to a voltage set larger than the maximum threshold voltage of the resistive switching element.

The current path unit 520 increases the current of the current path as the read voltage increases by using the current path provided in advance.

Here, the current path unit 520 may increase the current of the current path by decreasing the resistance value of the current path, for example, linearly, as the read voltage increases.

In this case, the current path unit 520 may be formed in parallel between the resistive switching element and the phase change memory cell between the resistive switching element and the bit line and the source line where the cell of the phase change memory is formed, and the variable resistor. It may include at least one of a variable resistance element that can be used as a variable resistor, such as a MOSFET.

The controller 530 performs a read operation of the phase change memory using a linearly increasing read voltage and a current increasing through a current path.

Although the description thereof is omitted in the phase change memory reading apparatus of FIG. 5, it is apparent to those skilled in the art that all contents described in the phase change memory reading method of FIGS. 1 to 4 may be included.

The system or apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the systems, devices, and components described in the embodiments may include, for example, processors, controllers, arithmetic logic units (ALUs), digital signal processors, microcomputers, field programmable arrays (FPAs). ), A programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions, may be implemented using one or more general purpose or special purpose computers. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to the execution of the software. For ease of understanding, the processing device may be described as one used, but those skilled in the art will appreciate that the processing device includes a plurality of processing elements and / or a plurality of types of processing elements. It can be seen that it may include. For example, the processing device may include a plurality of processors or one processor and one controller. In addition, other processing configurations are possible, such as parallel processors.

The software may include a computer program, code, instructions, or a combination of one or more of the above, and configure the processing device to operate as desired, or process it independently or collectively. You can command the device. Software and / or data may be any type of machine, component, physical device, virtual equipment, computer storage medium or device in order to be interpreted by or to provide instructions or data to the processing device. Or may be permanently or temporarily embodied in a signal wave to be transmitted. The software may be distributed over networked computer systems so that they may be stored or executed in a distributed manner. Software and data may be stored on one or more computer readable recording media.

The method according to the embodiments may be embodied in the form of program instructions that may be executed by various computer means and recorded on a computer readable medium. The computer readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine code, such as produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

Although the embodiments have been described by the limited embodiments and the drawings as described above, various modifications and variations are possible to those skilled in the art from the above description. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different manner than the described method, or other components. Or even if replaced or replaced by equivalents, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the claims which follow.

Claims (10)

For the read operation of the phase change memory having the crossbar array structure in which the resistive switching element and the cell are vertically connected between the upper bit line and the lower source line, the threshold voltage of the resistive switching element constituting the phase change memory is applied. Applying a linearly increasing voltage on the basis;
Increasing the current in the current path as the voltage increases using a pre-configured current path; And
Performing a read operation of the phase change memory by maintaining a current flowing through a cell of the phase change memory at a constant value by using the linearly increasing voltage and a current increasing through the current path.
Including,
The current path is
When a specific cell is selected for a read operation, a specific cell and a resistive switching element of the specific cell are formed in parallel between a bit line and a source line connected to the selected specific cell,
The step of applying the voltage
Applying a read voltage that increases linearly to the voltage set larger than the maximum threshold voltage of the threshold voltage range measured in advance for the resistive switching elements constituting the phase change memory,
The performing of the read operation
And performing a read operation of the phase change memory by removing sneak leakage generated by an unselected element in the cross bar array structure through the current path.
The method of claim 1,
Increasing the current in the current path
And decreasing the resistance value of the current path as the voltage increases, thereby increasing the current of the current path.
delete The method of claim 1,
The current path is
A phase change memory read method comprising at least one of a variable resistor and a variable resistor element.
delete For the read operation of the phase change memory having the crossbar array structure in which the resistive switching element and the cell are vertically connected between the upper bit line and the lower source line, the threshold voltage of the resistive switching element constituting the phase change memory is applied. A voltage applying unit for applying a linearly increasing voltage based on the voltage;
A current path unit for increasing a current of the current path as the voltage increases by using a current path provided in advance; And
A controller for performing a read operation of the phase change memory by maintaining a current flowing through the cell of the phase change memory at a constant value by using the linearly increasing voltage and the current increasing through the current path.
Including,
The current path portion
When a specific cell is selected for a read operation, a specific cell and a resistive switching element of the specific cell are formed in parallel between a bit line and a source line connected to the selected specific cell,
The voltage applying unit
Applying a read voltage that increases linearly to the voltage set larger than the maximum threshold voltage of the threshold voltage range measured in advance for the resistive switching elements constituting the phase change memory,
The control unit
And a phase change memory read device performing a read operation of the phase change memory by removing a sneak leakage generated by an unselected element in the cross bar array structure through the current path.
The method of claim 6,
The current path portion
And decreasing the resistance value of the current path as the voltage increases, thereby increasing the current of the current path.
delete The method of claim 6,
The current path portion
A phase change memory read device comprising at least one of a variable resistor and a variable resistor element.
delete

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