KR20080053567A - Flash memory device and method for sensing channel boosting level - Google Patents

Abstract

A flash memory device for measuring a channel boosting voltage and a method thereof are provided to measure the channel boosting voltage in a floating node state accurately, in case of global self boosting and local boosting. A cell string(102) includes a plurality of cells. A channel selection part(106) performs a function of selecting at least one channel among channels of the cell string. A sensing current measurement part(108) performs a function of measuring a current in the program operation condition of the channel selected by the channel selection part, among the channels of the cell string. A reference voltage/current measurement part(104) performs a function of measuring a voltage or a current in the reference condition of the channel selected by the channel selection part, among the channels of the cell string.

Description

Flash memory device and method for sensing channel boosting level

1 is a block diagram illustrating a configuration of a flash memory device for measuring a channel boosting voltage according to an embodiment of the present invention.

FIG. 2 is a graph illustrating a relationship between a reference voltage / current and a sensing voltage / current for measuring a channel boosting voltage in the flash memory device of FIG. 1 of the present invention.

3 is a schematic diagram of a NAND flash memory device for measuring a channel boosting voltage according to an embodiment of the present invention.

4 is a schematic diagram of a NAND flash memory device for measuring a channel boosting voltage according to another embodiment of the present invention.

The present invention relates to a channel boosting voltage measurement of a flash memory device, and more particularly, to a flash memory device and a method capable of accurately measuring the channel boosting voltage not only for global self boosting but also for local boosting. will be.

Recently, there is an increasing demand for a nonvolatile semiconductor memory device that can be electrically programmed and erased and that data can be stored without being erased even when power is not supplied. In order to develop a large-capacity memory device capable of storing a large number of data, a high integration technology of memory cells has been developed. To this end, a NAND type flash memory device in which a plurality of memory cells are connected in series and configured as one string, and the plurality of strings form one memory cell array has been proposed.

NAND flash memory devices perform program or erase by injecting or releasing electrons into a floating gate of a cell by using a Fowler-Nordheim Tunneling (FN) tunneling. Done. In order to program the NAND flash memory device, a high voltage of about 18V is applied to the word line of the selected cell and a pass voltage (Vpass) lower than the program voltage is applied to the unselected word lines, and 0V is applied to the bit line connected to the programmed cell. Is authorized. In addition, by applying a voltage higher than 0V, for example, a power supply voltage Vcc to a bit line connected to a cell where the program is prohibited, the channel is boosted at a voltage ratio due to the coupling ratio, thereby preventing FN tunneling of unselected cells. Prevent it.

However, if the channel boosting voltage is reduced due to leakage current or the like, and there is a cell that is not channel boosted, the cells to be erased may be programmed, and these cells are represented as fail bits and are NAND type. It is the most decisive factor in reducing the yield of flash memory devices.

Since the program disturb occurs due to the boosting voltage level, the boosting voltage of the floating channel must be measured and reflected in the accurate cell design, but it is difficult to accurately measure the boosting voltage. This is because when the probe is performed to measure the floating state of the channel, the channel changes from the floating state to the ground state, and thus the boosting voltage changes. In other words, if the probe tip is connected to measure the channel boosting voltage, the boosting voltage is discharged through the probe, so that voltage cannot be measured, and if a fail bit is found in the product, the boosting voltage is caused by any leakage current. It was confirmed that this reduced cell existed, and timely and accurate process optimization could not be performed.

Thus, current methods rely on simulating the boosting voltage, and it is not easy to predict the boosting voltage that is changed by the leakage current of the channel.

In addition, although a technique for measuring channel boosting voltage in a floating node state has been proposed, it is also a structure capable of measuring only a rough global self-boosting voltage, and has a hot carrier or a GIDL (Gate) which has an important effect on cell characteristics. In consideration of the induced drain leakage phenomenon, there is a problem in that it is impossible to measure a more accurate boosting voltage caused by a specific word line in the local boosting dimension.

An object of the present invention to solve the above problems is to compare the current flowing through the sensing transistors connected to all the cells of the cell string with the current flowing through the reference transistor, it is possible to measure the channel boosting voltage in the floating node state The present invention provides a flash memory device and method capable of accurately measuring not only global self boosting but also local boosting.

In addition, another object of the present invention is to place an unselected cell string on both sides of a selected bit line, thereby freeing space between lines that may occur when a contact is defined, thereby reducing memory size and improving process margins. To provide a flash memory device and method that can be.

According to an embodiment of the present invention for achieving the above object, a cell string including a plurality of cells; A channel selector configured to select at least one channel among channels of the cell string; A sensing current measuring unit configured to measure a current in a program operating condition of a channel selected by the channel selecting unit among the channels of the cell string; And a reference voltage / current measuring unit configured to measure a voltage or current at a reference condition of the channel selected by the channel selector among the channels of the cell string. A flash memory device is provided.

According to another embodiment of the present invention for achieving the above object, selecting at least one channel of the channel of the cell string including a plurality of cells; Measuring a voltage or current at a reference condition of a selected channel among the channels of the cell string; Measuring a current at a program operating condition of a selected channel among the channels of the cell string; And measuring a channel boosting voltage by comparing the current in the measured program operating condition with a voltage or current in the measured reference condition. .

According to another embodiment of the present invention for achieving the above object, the first and second unselected cell string disposed on both sides of the selected cell string; A channel selector configured to select at least one channel among channels of the first and second unselected cell strings; A sensing current measuring unit configured to measure a current in a program operating condition of a channel selected by the channel selecting unit among the channels of the first and second unselected cell strings; And a reference voltage / current measuring unit which performs a function of measuring a voltage or a current under reference conditions of a channel selected by the channel selecting unit among the channels of the first and second non-selected cell strings. A flash memory device for measuring channel boosting voltage is provided.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even if displayed on different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is a block diagram illustrating a configuration of a flash memory device for measuring a channel boosting voltage according to an embodiment of the present invention.

Referring to FIG. 1, a flash memory device 100 for measuring a channel boosting voltage according to an exemplary embodiment of the present invention may include a memory cell array 102, a reference voltage / current measurer 104, and a channel selector 106. And a sensing current measuring unit 108.

A cell array of a typical NAND flash memory device includes a plurality of cell strings in which a plurality of cells are connected in series, for example, 3 to 64 cell strings, a plurality of word lines WL and bit lines BL for selecting cells in the cell string. ), A drain select transistor connected between the drain terminal of the cell string and the bit line BL, and a source select transistor connected between the source terminal of the cell string and the common source line CSL. In order to program the selected cell of the cell block, a program voltage of about 18V is applied to the word line of the selected cell and a pass voltage of about 10V is applied to the word line of the unselected cell, and a voltage of 0V is applied to the bit line connected to the programmed cell. Is applied. Then, a voltage higher than 0V, for example, a power supply voltage Vcc is applied to the bit line connected to the cell where the program is prohibited.

The channel selector 106 selects a specific channel among the channels of the memory cell array 102. That is, in order to measure the channel boosting voltage by a specific word line in order to measure the individual local boosting voltage rather than the global self boosting, the cell to be measured among the cells of the unselected cell strings (which share the word line with the selected cell). Allows you to select channels that are not selected.

The reference voltage / current measuring unit 104 performs a function of detecting a reference current according to the reference voltage applied to the channel selected by the channel selector 106. In addition, a reference voltage according to the applied reference current may be detected.

The sensing current measuring unit 108 performs a function of detecting a sensing current of a channel selected by the channel selecting unit 106 while applying a bias of a program operating condition to the memory cell array 102.

A method of measuring a channel boosting voltage of a specific channel by using the detected reference voltage / current and sensing current will be described with reference to FIG. 2.

FIG. 2 is a graph illustrating a relationship between a reference voltage / current and a sensing voltage / current for measuring a channel boosting voltage in the flash memory device of FIG. 1 of the present invention.

Referring to FIG. 2, first, a reference voltage / current graph indicating a relationship with a reference current according to a reference voltage measured by the reference voltage / current measuring unit 104 may be prepared. When the sensing current is measured by the sensing current measuring unit 108, the channel boosting voltage may be obtained by matching the measured sensing current with the generated reference voltage / current graph. That is, the voltage value corresponding to the sensing current value in the reference voltage / current graph becomes the channel boosting voltage of the channel to be obtained.

In this way, by selecting a specific channel through the channel selector 106 and comparing the sensing current detected by the sensing current measuring unit 108 with the reference current detected by the reference voltage / current measuring unit 104, the flash memory The channel boosting voltage can be accurately measured at the local boost level when the cell is programmed.

3 is a schematic diagram of a NAND flash memory device for measuring a channel boosting voltage according to an embodiment of the present invention.

Referring to FIG. 3, a NAND flash memory device 300 for measuring a channel boosting voltage according to an exemplary embodiment of the present invention may include a sensing transistor 304, a sensing pass transistor 306, a reference pass transistor 308, and a reference. And a transistor 310.

Here, the sensing transistor 304 corresponds to the sensing current measuring unit 108 in FIG. 1, the reference transistor 310 corresponds to the reference voltage / current measuring unit 104 in FIG. 1, and a plurality of sensing passes. The transistor 306 and the reference pass transistor 308 correspond to the channel selector 106 in FIG. 1.

The sensing transistors Sen_0 to Sen_32 are connected to have a one-to-one correspondence with all the source-drain nodes N0 to N32 of the unselected cell string 302 to be subjected to the channel boosting voltage measurement. That is, each of the gates of the sensing transistors Sen_0 to Sen_32 is connected to nodes N0 to N32 between all source-drains of the cell string 302. Here, the gate and the node of the sensing transistor may be connected by a process such as a poly plug.

In addition, the sensing transistors Sen_0 to Sen_32 are connected such that each source terminal is shared with the source terminal of the reference transistor 310.

The sensing pass transistor 306 and the reference pass transistor 308 select specific channels of the unselected cell string 302, that is, the nodes N0 to N32 and the sensing transistors Sen_0 to Sen_32 corresponding to each node. Perform the function of selecting.

That is, the sensing pass transistors 306 are connected to correspond to the drains of the sensing transistors Sen_0 to Sen_32 in one-to-one correspondence, and the reference pass transistor 308 is connected to the drain of the reference transistor 310, thereby providing a sensing pass transistor ( By turning on and off the 306 one by one, a specific node and a sensing transistor can be selected.

For example, to select the first node N0 and the sensing transistor Sen_0, only the first sensing pass transistor is turned on and the other sensing pass transistors are turned off.

Here, the reference pass transistor 308 is turned on regardless of the turning off of the sensing pass transistors 306 to be symmetrical with the sensing pass transistors 306 so that the current flowing through the sensing transistor 304 is sensed current. This is for adjusting to accurately reflect as (Id_sen).

In the sensing transistor 304, a drain sensing voltage Vd_sen is applied to a drain terminal, and a source voltage Vss is applied to a source terminal. In addition, the reference transistor 310 has a gate reference voltage Vg_ref applied to a gate terminal, a drain reference voltage Vd_ref applied to a drain terminal, and a source terminal shared with the source terminal of the sensing transistor 304 so as to share the source voltage. (Vss) is applied.

Here, the sensing transistor 304 and the reference transistor 310 may have the same device characteristics. For example, they may have the same size, i.e., the same or equal device conditions (doping, Tox, Xj, etc.). In addition, the sensing pass transistors 306 and the reference pass transistor 308 may also have the same material characteristics. Meanwhile, the sensing transistor 304 and the reference transistor 310 may be configured as high voltage transistors.

After designing the circuit as described above, the sensing transistor 304 is extracted while extracting the drain current Id_ref according to the reference gate voltage Vg_ref of the reference transistor 310 and applying a bias of a program operating condition to the NAND flash memory cell array. Is monitored to compare the sensing current Id_sen and the reference current Id_ref. In this way, the channel boosting voltage of the NAND type flash memory cell may be measured more accurately in the local boosting dimension by comparing the reference current of the reference transistor 310 and the sensing current of the sensing transistor 304.

4 is a schematic diagram of a NAND flash memory device for measuring a channel boosting voltage according to another embodiment of the present invention.

Referring to FIG. 4, a NAND flash memory device 400 for measuring a channel boosting voltage according to an exemplary embodiment of the present invention may include sensing transistors 404 and 414, sensing pass transistors 406 and 416, and a reference pass transistor ( 408 and 418 and reference transistors 410 and 420.

Basically, the function and configuration of each component is similar to that of the NAND flash memory device 300 in FIG. 3. However, there is a difference in that the unselected cell string 302 in FIG. 3 is disposed on both sides of the selected cell string.

That is, as shown in FIG. 4, unselected first and second cell strings 402 and 412 are disposed on both sides of the selected cell string, so that source-drain is not available for the unselected first cell string 402. The sensing transistors Sen_0 and Sen_2 ... Sen_32 are connected to the nodes N0, N2 ... N32 between the nodes, and for the unselected second cell string 412, the nodes N1, The sensing transistors Sen_1, Sen_3 ... Sen_31 are connected to N3 ... N31 so that one-to-one correspondence is provided to nodes N0 to N32 of all source-drain nodes of the unselected cell string as shown in FIG. 3. The sensing transistors Sen_0 to Sen_32 are connected.

A description of the interconnections and functions of the remaining sensing transistors 404 and 414, the sensing pass transistors 406 and 416, the reference pass transistors 408 and 418, and the reference transistors 410 and 420 is described with reference to FIG. 3. It is redundant, so please omit it.

By placing the unselected cell strings on both sides of the selected cell strings as shown in FIG. 4, a space that may occur when a contact is defined, rather than a sensing transistor, a reference transistor, etc., disposed only on one side as shown in FIG. 3. Line-to-Line Spacing can be secured to reduce size and improve process margins.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

According to the structure and method of measuring the channel boosting voltage of the flash memory device, the channel boosting voltage is measured in the floating node state by comparing the current flowing through the sensing transistors connected to the cells of the cell string with the current flowing through the reference transistor. And accurate measurement of local self-boosting as well as global self-boosting, which has the effect of accurately understanding cell characteristics and facilitating yield analysis and defect analysis.

In addition, by placing the unselected cell strings on both sides of the selected bit line, the space between the lines that can occur when a contact is defined can be secured to reduce memory size and improve process margins.

Claims (12)

A cell string comprising a plurality of cells; A channel selector configured to select at least one channel among channels of the cell string; A sensing current measuring unit configured to measure a current in a program operating condition of a channel selected by the channel selecting unit among the channels of the cell string; And A flash for measuring a channel boosting voltage, comprising: a reference voltage / current measuring unit configured to measure a voltage or a current at a reference condition of a channel selected by the channel selector among the channels of the cell string; Memory device. The method of claim 1, The sensing current measuring unit includes a plurality of sensing transistors connected one-to-one with a plurality of source-drain nodes included in the cell string, and the reference voltage / current measuring unit includes a reference transistor connected to the plurality of sensing transistors. Flash memory device for measuring the channel boosting voltage. The method of claim 2, Each of the plurality of sensing transistors is connected to the source-drain node corresponding to a gate thereof, and a source is connected to a source of the reference transistor. The method of claim 3, wherein The channel selector includes a plurality of sensing pass transistors one-to-one connected to the drain of each of the plurality of sensing transistors, and a reference pass transistor connected to the drain of the reference transistor. Device. The method of claim 3, wherein The sensing transistors have a drain sensing voltage applied to each drain terminal, and the reference transistor has a gate reference voltage applied to a gate terminal and a drain reference voltage applied to a drain terminal. Flash memory device. The method of claim 4, wherein The plurality of sensing transistors and the reference transistor have the same device characteristics, and the plurality of sensing pass transistors and the reference pass transistor have the same device characteristics, the flash memory device for measuring the channel boosting voltage . Selecting at least one channel of channels of a cell string comprising a plurality of cells; Measuring a voltage or current at a reference condition of a selected channel among the channels of the cell string; Measuring a current at a program operating condition of a selected channel among the channels of the cell string; And And measuring a channel boosting voltage by comparing the current in the measured program operating condition with a voltage or current in the measured reference condition. The method of claim 7, wherein The flash memory device includes a plurality of sensing transistors connected one-to-one with a plurality of source-drain nodes included in the cell string and a reference transistor connected with the plurality of sensing transistors, Each of the plurality of sensing transistors is connected to a source-drain node to which a gate corresponds, a source is connected to a source of the reference transistor, The sensing is performed when a gate reference voltage is applied to a gate terminal of the reference transistor and a drain reference voltage is applied to a drain terminal to measure a reference drain current according to the gate reference voltage, and a bias of a program operating condition is applied to the cell string. And measuring a channel boosting voltage during programming by comparing the sensing current flowing through the transistor with the reference drain current of the reference transistor. First and second unselected cell strings disposed on both sides of the selected cell string; A channel selector configured to select at least one channel among channels of the first and second unselected cell strings; A sensing current measuring unit configured to measure a current in a program operating condition of a channel selected by the channel selecting unit among the channels of the first and second unselected cell strings; And And a reference voltage / current measuring unit configured to measure a voltage or a current under reference conditions of a channel selected by the channel selecting unit among the channels of the first and second unselected cell strings. Flash memory device for channel boosting voltage measurement. The method of claim 9, The sensing current measuring unit includes a plurality of sensing transistors connected one-to-one with a plurality of source-drain nodes included in the first and second unselected cell strings, and the reference voltage / current measuring unit includes the plurality of sensing transistors. And a reference transistor coupled to the flash memory device for measuring a channel boosting voltage. The method of claim 10, Each of the plurality of sensing transistors is connected to the source-drain node corresponding to a gate thereof, and a source is connected to a source of the reference transistor. The method of claim 11, The channel selector includes a plurality of sensing pass transistors connected one-to-one to a drain of each of the plurality of sensing transistors and a reference pass transistor connected to a drain of the reference transistor. Device.

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