# Patent

## Title
Techniques for refreshing a semiconductor memory device

## Abstract

Techniques for refreshing a semiconductor memory device are disclosed. In one particular exemplary embodiment, the techniques may be realized as a method for refreshing a semiconductor memory device may include applying a plurality of voltage potentials to a memory cell in an array of memory cells. Applying a plurality of voltage potentials to the memory cell may include applying a first voltage potential to a first region of the memory cell via a respective source line of the array. Applying a plurality of voltage potentials to the memory cells may also include applying a second voltage potential to a second region of the memory cell via a respective local bit line and a respective selection transistor of the array. Applying a plurality of voltage potentials to the memory cells may further include applying a third voltage potential to a respective word line of the array, wherein the word line may be spaced apart from and capacitively to a body region of the memory cell that may be electrically floating and disposed between the first region and the second region. Applying a plurality of voltage potentials to the memory cells may further include applying a fourth voltage potential to a third region of the memory cell via a respective carrier injection line of the array.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This patent application claims priority to U.S. Provisional Patent Application No. 61/332,037, filed May 6, 2010, which is hereby incorporated by reference herein in its entirety.


FIELD OF THE DISCLOSURE
The present disclosure relates generally to semiconductor memory devices and, more particularly, to techniques for refreshing a semiconductor memory device.
BACKGROUND OF THE DISCLOSURE
The semiconductor industry has experienced technological advances that have permitted increases in density and/or complexity of semiconductor memory devices. Also, the technological advances have allowed decreases in power consumption and package sizes of various types of semiconductor memory devices. There is a continuing trend to employ and/or fabricate advanced semiconductor memory devices using techniques, materials, and devices that improve performance, reduce leakage current, and enhance overall scaling. Silicon-on-insulator (SOI) and bulk substrates are examples of materials that may be used to fabricate such semiconductor memory devices. Such semiconductor memory devices may include, for example, partially depleted (PD) devices, fully depleted (FD) devices, multiple gate devices (e.g., double, triple gate, or surrounding gate), and Fin-FET devices.
A semiconductor memory device may include a memory cell having a memory transistor with an electrically floating body region wherein electrical charge may be stored. When excess majority electrical charges carriers are stored in the electrically floating body region, the memory cell may store a logic high (e.g., binary “1” data state). When the electrical floating body region is depleted of majority electrical charge carriers, the memory cell may store a logic low (e.g., binary “0” data state). Also, a semiconductor memory device may be fabricated on silicon-on-insulator (SOI) substrates or bulk substrates (e.g., enabling body isolation). For example, a semiconductor memory device may be fabricated as a three-dimensional (3-D) device (e.g., a multiple gate device, a Fin-FET device, and a vertical pillar device).
In one conventional technique, the memory cell of the semiconductor memory device may be read by applying bias signals to a source/drain region and a gate of the memory transistor. As such, a conventional reading technique may involve sensing an amount of current provided/generated by/in the electrically floating body region of the memory cell in response to the application of the source/drain region and gate bias signals to determine a data state of the memory cell. For example, the memory cell may have two or more different current states corresponding to two or more different logical states (e.g., two different current conditions/states corresponding to two different logic states: a binary “0” data state and a binary “1” data state).
In another conventional technique, the memory cell of the semiconductor memory device may be written to by applying bias signals to the source/drain region(s) and the gate of the memory transistor. As such, a conventional writing technique may result in an increase/decrease of majority charge carriers in the electrically floating body region of the memory cell which, in turn, determines the data state of the memory cell. Such an excess of majority charge carriers may result from channel impact ionization, band-to-band tunneling (gate-induced drain leakage “GIDL”), or direct injection. Majority charge carriers may be removed via drain region hole removal, source region hole removal, or drain and source region hole removal, for example, using back gate pulsing.
Often, conventional reading and/or writing operations may lead to relatively large power consumption and large voltage potential swings which may cause disturbance to unselected memory cells in the semiconductor memory device. Also, pulsing between positive and negative gate biases during read and write operations may reduce a net quantity of majority charge carriers in the electrically floating body region of the memory cell, which, in turn, may result in an inaccurate determination of the data state of the memory cell. Furthermore, in the event that a bias signal having a voltage potential that is below a threshold voltage potential of the memory transistor is applied to the gate of the memory transistor, a channel of minority charge carriers beneath the gate may be eliminated. However, some of the minority charge carriers may remain “trapped” in interface defects. Some of the trapped minority charge carriers may combine with majority charge carriers, which may be attracted to the gate as a result of the applied bias signal. As a result, the net quantity of majority charge carriers in the electrically floating body region may be reduced. This phenomenon, which is typically characterized as charge pumping, is problematic because the net quantity of majority charge carriers may be reduced in the electrically floating body region of the memory cell, which, in turn, may result in an inaccurate determination of the data state of the memory cell.
In view of the foregoing, it may be understood that there may be significant problems and shortcomings associated with conventional techniques for operating a semiconductor memory device.
SUMMARY OF THE DISCLOSURE
Techniques for refreshing a semiconductor memory device are disclosed. In one particular exemplary embodiment, the techniques may be realized as a method for refreshing a semiconductor memory device may comprise applying a plurality of voltage potentials to a memory cell in an array of memory cells. Applying a plurality of voltage potentials to the memory cell may comprise applying a first voltage potential to a first region of the memory cell via a respective source line of the array. Applying a plurality of voltage potentials to the memory cells may comprise applying a second voltage potential to a second region of the memory cell via a respective local bit line and a respective selection transistor of the array. Applying a plurality of voltage potentials to the memory cells may further comprise applying a third voltage potential to a respective word line of the array, wherein the word line may be spaced apart from and capacitively to a body region of the memory cell that may be electrically floating and disposed between the first region and the second region. Applying a plurality of voltage potentials to the memory cells may further comprise applying a fourth voltage potential to a third region of the memory cell via a respective carrier injection line of the array.
In accordance with other aspects of this particular exemplary embodiment, the respective local bit line may be coupled to a multiplexer.
In accordance with further aspects of this particular exemplary embodiment, the multiplexer may be coupled to a global bit line.
In accordance with additional aspects of this particular exemplary embodiment, the multiplexer may comprise at least one masking transistor coupled to the respective local bit line.
In accordance with yet another aspect of this particular exemplary embodiment, the multiplexer may further comprise at least one hold transistor coupled to the respective local bit line.
In accordance with other aspects of this particular exemplary embodiment, the respective selection transistor may be coupled to the at least one mask transistor and the at least one hold transistor.
In accordance with further aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise maintaining the first voltage potential applied to the first region at a constant level via the respective source line during the refresh of the semiconductor memory device.
In accordance with additional aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise applying a selection control signal to the respective selection transistor to activate the respective selection transistor.
In accordance with yet another aspect of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise increasing the second voltage potential applied to the respective source line from the second voltage potential applied to the respective source line during a hold operation via the activated respective selection transistor.
In accordance with other aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise increasing the fourth voltage potential applied to the respective carrier injection line from the fourth voltage potential applied to the respective carrier injection line during a hold operation.
In accordance with further aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise applying decoupling control signals to the respective selection transistor to deactivate the respective selection transistor.
In accordance with additional aspects of this particular exemplary embodiment, the respective local bit line may be electrically floating after the respective selection transistor is deactivated.
In accordance with yet another aspect of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise increasing the third voltage potential applied to the respective word line from the third voltage potential applied to the respective word line during a hold operation in order to perform a read operation.
In accordance with other aspects of this particular exemplary embodiment, the increase in the third voltage potential may activate the memory cell to decrease the second voltage potential applied to the respective local bit line.
In accordance with further aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise decreasing the third voltage potential applied to the respective word line from the third voltage potential applied to the respective word line during a write logic low operation to perform a write logic high operation.
In accordance with additional aspects of this particular exemplary embodiment, the third voltage potential applied to the respective word line during the write logic high operation may be higher than the third voltage potential applied to the respective word line during a hold operation.
In accordance with yet another aspect of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise applying a coupling control signals to the respective selection transistor to activate the respective selection transistor in order to perform an end to a write logic high operation.
In accordance with other aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise discharging the second voltage potential applied to the respective local bit line to forward bias a junction between the second region and the third region.
In accordance with further aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise decreasing the fourth voltage potential applied to the respective carrier injection line from the fourth voltage potential applied to the respective carrier injection line during a write logic high operation to perform a hold operation.
In accordance with additional aspects of this particular exemplary embodiment, applying a plurality of voltage potentials to the memory cells may further comprise decreasing the second voltage potential applied to the respective local bit line from the second voltage potential applied to the respective local bit line during a write logic high operation to perform a hold operation.
The present disclosure will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility.



BRIEF DESCRIPTION OF THE DRAWINGS
In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only.
FIG. 1 shows a block diagram of a semiconductor memory device including a memory cell array, data write and sense circuitry, and memory cell selection and control circuitry in accordance with an embodiment of the present disclosure.
FIG. 2 shows a schematic diagram of at least a portion of a memory cell array having a plurality of memory cells in accordance with an embodiment of the present disclosure.
FIG. 3 shows a cross-sectional view of the memory cell array shown in FIG. 2 in accordance with an embodiment of the present disclosure.
FIG. 4 shows a schematic diagram of at least a portion of a memory cell array having a plurality of memory cells coupled to a plurality of sense amplifier circuits via a hierarchical bit line configuration in accordance with another embodiment of the present disclosure.
FIG. 5 shows a schematic diagram of a multiplexer for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure.
FIG. 6 shows a schematic diagram of a source line driver for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure.
FIG. 7 shows control signal voltage waveforms for performing a refresh operation in accordance with an embodiment of the present disclosure.



DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Referring to FIG. 1, there is shown a block diagram of a semiconductor memory device 10 comprising a memory cell array 20, data write and sense circuitry 36, and memory cell selection and control circuitry 38 in accordance with an embodiment of the present disclosure. The memory cell array 20 may comprise a plurality of memory cells 12 each coupled to the memory cell selection and control circuitry 38 via a word line (WL) 28 and a carrier injection line (EP) 34, and to the data write and sense circuitry 36 via a bit line (CN) 30 and a source line (EN) 32. It may be appreciated that the bit line (CN) 30 and the source line (EN) 32 are designations used to distinguish between two signal lines and they may be used interchangeably.
The data write and sense circuitry 36 may read data from and may write data to selected memory cells 12. In an exemplary embodiment, the data write and sense circuitry 36 may include a plurality of data sense amplifier circuits. Each data sense amplifier circuit may receive at least one bit line (CN) 30 and a current or voltage reference signal. For example, each data sense amplifier circuit may be a cross-coupled type sense amplifier to sense a data state stored in a memory cell 12. The data write and sense circuitry 36 may include at least one multiplexer that may couple to a data sense amplifier circuit to at least one bit line (CN) 30. In an exemplary embodiment, the multiplexer may couple a plurality of bit lines (CN) 30 to a data sense amplifier circuit.
Each data sense amplifier circuit may employ voltage and/or current sensing circuitry and/or techniques. In an exemplary embodiment, each data sense amplifier circuit may employ current sensing circuitry and/or techniques. For example, a current sense amplifier may compare current from a selected memory cell 12 to a reference current (e.g., the current of one or more reference cells). From that comparison, it may be determined whether the selected memory cell 12 stores a logic high (e.g., binary “1” data state) or a logic low (e.g., binary “0” data state). It may be appreciated by one having ordinary skill in the art that various types or forms of the data write and sense circuitry 36 (including one or more sense amplifiers, using voltage or current sensing techniques, to sense a data state stored in a memory cell 12) may be employed to read data stored in the memory cells 12.
The memory cell selection and control circuitry 38 may select and/or enable one or more predetermined memory cells 12 to facilitate reading data therefrom by applying control signals on one or more word lines (WL) 28 and/or carrier injection lines (EP) 34. The memory cell selection and control circuitry 38 may generate such control signals from address signals, for example, row address signals. Moreover, the memory cell selection and control circuitry 38 may include a word line decoder and/or driver. For example, the memory cell selection and control circuitry 38 may include one or more different control/selection techniques (and circuitry thereof) to select and/or enable one or more predetermined memory cells 12. Notably, all such control/selection techniques, and circuitry thereof, whether now known or later developed, are intended to fall within the scope of the present disclosure.
In an exemplary embodiment, the semiconductor memory device 10 may implement a two step write operation whereby all the memory cells 12 in a row of memory cells 12 may be written to a predetermined data state by first executing a “clear” or a logic low (e.g., binary “0” data state) write operation, whereby all of the memory cells 12 in the row of memory cells 12 are written to logic low (e.g., binary “0” data state). Thereafter, selected memory cells 12 in the row of memory cells 12 may be selectively written to the predetermined data state logic high (binary “1” data state)). The semiconductor memory device 10 may also implement a one step write operation whereby selected memory cells 12 in a row of memory cells 12 may be selectively written to either a logic high (e.g., binary “1” data state) or a logic low (e.g., binary “0” data state) without first implementing a “clear” operation. The semiconductor memory device 10 may employ any of the exemplary writing, preparation, holding, refresh, and/or reading techniques described herein.
The memory cells 12 may comprise N-type, P-type and/or both types of transistors. Circuitry that is peripheral to the memory cell array 20 (for example, sense amplifiers or comparators, row and column address decoders, as well as line drivers (not illustrated herein)) may also include P-type and/or N-type transistors. Regardless of whether P-type or N-type transistors are employed in memory cells 12 in the memory cell array 20, suitable voltage potentials (for example, positive or negative voltage potentials) for reading from the memory cells 12 will be described further herein.
Referring to FIG. 2, there is shown a memory cell array 20 having a plurality of memory cells 12 in accordance with an embodiment of the present disclosure. Each of the memory cells may comprise a first bipolar transistor 14a and a second bipolar transistor 14b coupled to each other. For example, the first bipolar transistor 14a and/or the second bipolar transistor 14b may be an NPN bipolar transistor or a PNP bipolar transistor. As illustrated in FIG. 2, the first bipolar transistor 14a may be an NPN bipolar transistor and the second bipolar transistor 14b may be a PNP bipolar transistor. In another exemplary embodiment, the first memory transistor 14a may be a PNP bipolar transistor and the second memory transistor 14b may be an NPN bipolar transistor. In another exemplary embodiment, each of the memory cells 12 may comprise a first field effect transistor (FET) 14a and a second bipolar transistor 14b. For example, the first field effect transistor (FET) 14a may be a metal-oxide semiconductor field effect transistor (MOSFET) or junction field effect transistor (JFET). The memory cells 12 may be coupled to a respective word line (WL) 28, a respective bit line (CN) 30, a respective source line (EN) 32, and/or a respective carrier injection line (EP) 34. Data may be written to or read from a selected memory cell 12 by applying suitable control signals to a selected word line (WL) 28, a selected bit line (CN) 30, a selected source line (EN) 32, and/or a selected carrier injection line (EP) 34. In an exemplary embodiment, the word line (WL) 28 may extend horizontally parallel to the carrier injection line (EP) 34. In another exemplary embodiment, the bit line (CN) 30 may extend vertically parallel to the source line (EN) 32.
In an exemplary embodiment, one or more respective bit line (CN) 30 may be coupled to a data sense amplifier circuit of the data write and sense circuitry 36. For example, one or more control signals may be applied to one or more selected memory cells 12 via a selected word line (WL) 28, a selected bit line (CN) 30, a selected source line (EN) 32, and/or a selected carrier injection line (EP) 34. A voltage potential and/or a current may be generated by the one or more selected memory cells 12 and outputted to the data sense amplifier circuit of the data write and sense circuitry 36 via a corresponding bit line (CN) 30.
Also, a data state may be written to one or more selected memory cells 12 by applying one or more control signals via one or more corresponding bit lines (CN) 30. The one or more control signals applied via the corresponding bit lines (CN) 30 may control the second bipolar transistor 14b of the memory cell 12 in order to write a desired data state to the memory cell 12. In the event that a data state is read from and/or written to the memory cell 12 via the bit line (CN) 30, then the bit line (CN) 30 may be coupled to the data sense amplifier circuit of the data write and sense circuitry 36 while the source line (EN) 32 may be separately controlled via a voltage/current source (e.g., a voltage/current driver) of the data write and sense circuitry 36. In an exemplary embodiment, the data sense amplifier circuit of the data write and sense circuitry 36 and the voltage/current source of the data write and sense circuitry 36 may be configured on opposite sides of the memory cell array 20. In another exemplary embodiment, the data write and sense circuitry 36 may include a plurality of data sense amplifier circuits configured on opposite sides of the memory cell array 20.
In the event that the source line (EN) 32 is coupled to the data sense amplifier circuit of the data write and sense circuitry 36, a voltage potential and/or current generated by the one or more selected memory cells 12 may be outputted to the data sense amplifier circuit of the data write and sense circuitry 36 via the corresponding source line (EN) 32. Also, a data state may be written to one or more selected memory cells 12 by applying one or more control signals via one or more corresponding bit lines (CN) 30. The one or more control signals applied via the corresponding bit lines (CN) 30 may control the second bipolar transistor 14b of the memory cell 12 in order to write a desired data state to the memory cell 12. For example, the bit line (CN) 30 and the source line (EN) 32 may be coupled to disparate subcircuits (e.g., drivers and/or sense amplifiers) of the data write and sense circuitry 36 configured on opposite sides of the memory cell array 20. In an exemplary embodiment, the bit line (CN) 30 may be coupled to a driver and/or a sense amplifier circuit of the data write and sense circuitry 36, while the source line (EN) 32 may be coupled to a driver and/or a sense amplifier circuit of the data write and sense circuitry 36. Also, the driver and/or the data sense amplifier circuit coupled to the bit line (CN) 30 and the driver and/or the data sense amplifier circuit coupled to the source line (EN) 32 may be configured on opposite sides of the memory cell array 20. By reading a data state via the source line (EN) 32 and writing a data state via the bit line (CN) 30, the resistance to the memory cell 12 may be reduced because the source line (EN) 32 and the bit line (CN) 30 are driven from opposite sides of the memory cell array 20.
Referring to FIG. 3, there is shown a cross-sectional view of the memory cell 12 shown in FIG. 1 in accordance with an embodiment of the present disclosure. As discussed above, the memory cell 12 may comprise two bipolar transistors. In an exemplary embodiment, the first bipolar transistor 14a may be a NPN bipolar transistor and the second bipolar transistor 14b may be a PNP bipolar transistor. In an exemplary embodiment, the first bipolar transistor 14a and the second bipolar transistor 14b may share one or more common regions. The first NPN bipolar transistor 14a may comprise an N+ emitter region 120, a P− base region 122, and an N+ collector region 124. The second PNP bipolar transistor 14b may comprise a P− collector region 122, an N+ base region 124, and a P+ emitter region 126. The N+ region 120, the P− region 122, the N+ region 124, and/or the P+ region 126 may be disposed in sequential contiguous relationship within a pillar or fin configuration that may extend vertically or perpendicularly to a plane defined by an N-well region 128 and/or a P− substrate 130. In an exemplary embodiment, the P− region 122 may be an electrically floating body region of the memory cell 12 configured to accumulate/store charges that may be spaced apart from and capacitively coupled to the word line (WL) 28.
The N+ emitter region 120 of the first bipolar transistor 14a may be coupled to the source line (EN) 32 formed of a metal layer. Also, the P− base region 122 of the first bipolar transistor 14a and/or the P− collector region 122 of the second bipolar transistor 14b may be capacitively coupled to the word line (WL) 28 formed of a metal layer. In another exemplary embodiment, the N+ region 124 of the memory cell 12 may be coupled to a bit line (CN) 30 formed of a metal layer. The bit line (CN) 30 may circumferentially surround the N+ region 124 of the memory cell 12. In another exemplary embodiment, the bit line (CN) 30 may be coupled to the N+ region 124 on one or more side regions (e.g., one side region or two side regions) of the N+ region 124. The bit line (CN) 30 may reduce a disturbance to the memory cell 12. In particular, the bit line (CN) 30 may be formed of a metal layer and therefore may reduce a hole disturbance to the memory cell 12. The bit line (CN) 30 may extend horizontally in parallel to the source line (EN) 32 coupling to a plurality of memory cells 12 (e.g., a column of memory cells 12). For example, the bit line (CN) 30 and the source line (EN) 32 may be arranged in different planes and configured to be parallel to each other. The source line (EN) 32 may provide an alternative means for addressing or accessing the memory cell 12. The memory cell 12 may be addressed or accessed via either the bit line (CN) 30 or the source line (EN) 32, or the combination of the bit line (CN) 30 and the source line (EN) 32.
Referring to FIG. 4, there is shown a schematic diagram of at least a portion of a memory cell array 20 having a plurality of memory cells 12 coupled to a plurality of sense amplifier circuits 402 via a hierarchical bit line configuration in accordance with another embodiment of the present disclosure. Each of the memory cells 12 of the memory cell array 20 may be coupled to a data sense amplifier circuit 402 via the hierarchical bit line configuration. The hierarchical bit line configuration may include a local bit line (LCN) 404 (e.g., the bit line (CN) 30) coupled directly to a respective memory cell 12. Each local bit line (LCN) 404 may be coupled to a global bit line (GCN) 406 via a multiplexer (MUX) 408. The hierarchical bit line configuration may reduce bit line capacitance and resistance and may result in less attenuation of signals during various operations on the memory cell 12. Also, the reduction of the bit line capacitance may result in lower power consumption on a selected column of memory cells 12. Further, the hierarchical bit line configuration may reduce an amount of disturbance on unselected memory cells 12 because only unselected local bit lines (LCN) 404 adjacent to a selected local bit line (LCN) 404 may experience disturbance. Additionally, power consumption may be reduced by applying masking control signals only to unselected local bit lines (LCNs) 404 that are adjacent to a selected local bit line (LCN) 404.
The hierarchical bit line configuration may include a plurality of local bit lines (LCNs) 404 coupled to a respective multiplexer (MUX) 408. In an exemplary embodiment, four local bit lines (LCNs) 404 may be coupled to a respective multiplexer (MUX) 408. It may be appreciated by one skilled in the art that the number of local bit lines (LCNs) 404 coupled to a respective multiplexer (MUX) 408 may vary. For example, eight local bit lines (LCNs) 404, sixteen local bit lines (LCNs) 404, thirty-two local bit lines (LCNs) 404, sixty-four local bit lines (LCNs) 404 etc., may be coupled to a respective multiplexer (MUX) 408.
The hierarchical bit line configuration may include a global bit line (GCN) 406 coupled to a plurality of multiplexers (MUXs) 408. In an exemplary embodiment, a global bit line (GCN) 406 may be coupled to four multiplexers (MUXs) 408. It may be appreciated by one skilled in the art that the number of multiplexers (MUXs) 408 coupled to a global bit line (GCN) 406 may vary. For example, eight multiplexers (MUXs) 408, sixteen multiplexers (MUXs) 408, thirty-two multiplexers (MUXs) 408, sixty-four multiplexers (MUXs) 408 etc., may be coupled to the global bit line (GCN) 406. Each global bit line (GCN) 406 may be coupled to a plurality of local bit lines (LCNs) 404 via a plurality of multiplexers (MUXs) 408. In an exemplary embodiment, each global bit line (GCN) 406 may be coupled to sixteen local bit lines (LCNs) 404 via four multiplexers (MUXs) 408.
Each memory cell 12 may be biased by a respective source line driver 412. Each source line driver 412 may be coupled to a plurality of memory cells 12 via a plurality of local source lines (LEN) 410. In an exemplary embodiment, each source line driver 412 may be coupled to four memory cells 12. It may be appreciated by one skilled in the art that the number of memory cells 12 coupled to a source line driver 412 may vary. For example, eight local source lines (LENS) 410, sixteen local source lines (LENs) 410, thirty-two local source lines (LENs) 410, sixty-four local source lines (LENs) 410 etc., may be coupled to a source line driver 412. In an exemplary embodiment, the number of memory cells 12 coupled to a source line driver 412 may be equal to the number of memory cells 12 coupled to a multiplexer (MUX) 408.
Referring to FIG. 5, there is shown a schematic diagram of a multiplexer 508 for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure. As shown in FIG. 5, a global bit line (GCN) 506 may be coupled to a plurality of local bit lines (LCNs) 504 via the multiplexer 508. In an exemplary embodiment, the multiplexer 508 may include a plurality of selection transistors (SELs) 514 coupled to the plurality of local bit lines (LCN) 504 and the global bit line (GCN) 506. Each selection transistor 514 may be, for example, an N-type or a P-type bipolar junction transistor or an N-Channel or a P-Channel metal-oxide semiconductor field effect transistor (MOSFET). Each of the plurality of selection transistors (SELs) 514 may be biased to selectively couple a local bit line (LCN) 504 to the global bit line (GCN) 506. In an exemplary embodiment, selection transistor (SEL<0>) 504 may be biased to couple the local bit line (LCN<0>) 504 to the global bit line (GCN) 506, while the selection transistors (SEL<1>, SEL<2>, and SEL<3>) may be biased to decouple the local bit lines (LCN<1>, LCN<2>, and LCN<3>) 504 from the global bit line (GCN) 506.
The multiplexer 508 may also include a plurality of biasing transistor pairs 516. Each biasing transistor pair 516 may include, for example, an N-type or a P-type bipolar junction transistor and/or an N-Channel or a P-Channel metal-oxide semiconductor field effect transistor (MOSFET). Each biasing transistor pair 516 may be coupled to a global hold line (GHL) 510 and/or a global mask line (GML) 512. Each biasing transistor pair 516 may include a hold transistor (HD) 518 and a mask transistor (MSK) 520. In an exemplary embodiment, each hold transistor (HD) 518 may be coupled to the global hold line (GHL) 510 and each mask transistor (MSK) 520 may be coupled to the global mask line (GML) 512. Control signals may be applied to the gates of the hold transistors (HD) 518 to bias the hold transistors (HD) 518 in order to apply a holding voltage potential to a memory cell 12 during a hold operation via the local bit line (LCN) 504. For example, when control signals are applied to the gates of the hold transistors (HD) 518, the control signals may cause the plurality of hold transistors (HD<0>, HD<1>, HD<2>, and HD<3>) 518 to assume an “ON” state. Subsequently, the plurality of hold transistors (HD<0>, HD<1>, HD<2>, and HD<3>) 518 may output a holding voltage potential to a corresponding plurality of memory cells 12 via the local bit lines (LCN<0>, LCN<1>, LCN<2>, and LCN<3>) 504.
Also, control signals may be applied to the gates of the mask transistors (MSK) 520 to bias the mask transistors (MSK) 520 in order to apply a masking voltage potential to a memory cell 12 during a read and/or write operation via the local bit line (LCN) 504. For example, when control signals are applied to the gates of the mask transistors (MSK) 520, the control signals may cause the plurality of mask transistors (MSK<0>, MSK<1>, MSK<2>, and/or MSK<3>) 520 associated with unselected memory cells 12 to assume an “ON” state. Subsequently, the plurality of mask transistors (MSK<0>, MSK<1>, MSK<2>, and/or MSK<3>) 518 may output a masking voltage potential to a corresponding plurality of unselected memory cells 12 via the local bit lines (LCN<0>, LCN<1>, LCN<2>, and/or LCN<3>) 504 associated with the unselected memory cells 12.
Referring to FIG. 6, there is shown a schematic diagram of a source line driver 608 for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure. The source line driver 608 may include a plurality of biasing transistor pairs 616. Each biasing transistor pair 616 may include, for example, an N-type or a P-type bipolar junction transistor and/or an N-Channel or a P-Channel metal-oxide semiconductor field effect transistor (MOSFET). Each biasing transistor pair 616 may be coupled to a global hold line (GHL) 610 and/or a global mask line (GML) 612. Each biasing transistor pair 616 may include a hold transistor (HD) 618 and a mask transistor (MSK) 620. In an exemplary embodiment, each hold transistor (HD) 618 may be coupled to the global hold line (GHL) 610 and each mask transistor (MSK) 620 may be coupled to the global mask line (GML) 612. Control signals may be applied to the gates of the hold transistors (HD) 618 to bias the hold transistors (HD) 618 in order to apply a holding voltage potential to memory cells 12 during a hold operation via local source lines (LEN) 604. For example, when control signals are applied to the gates of the hold transistors (HD) 618, the control signals may cause the plurality of hold transistors (HD<0>, HD<1>, HD<2>, and HD<3>) 618 to assume an “ON” state. Subsequently, the plurality of hold transistors (HD<0>, HD<1>, HD<2>, and HD<3>) 618 may output a holding voltage potential to a corresponding plurality of memory cells 12 via the local source lines (LEN<0>, LEN<1>, LEN<2>, and LEN<3>) 604.
Also, control signals may be applied to the gates of the mask transistors (MSK) 620 to bias the mask transistors (MSK) 620 in order to apply a masking voltage potential to memory cells 12 during a read and/or write operation via local source lines (LEN) 604. For example, when control signals are applied to the gates of the mask transistors (MSK) 620, the control signals may cause the plurality of mask transistors (MSK<0>, MSK<1>, MSK<2>, and/or MSK<3>) 620 associated with unselected memory cells 12 to assume an “ON” state. Subsequently, the plurality of mask transistors (MSK<0>, MSK<1>, MSK<2>, and/or MSK<3>) 618 may output a masking voltage potential to a corresponding plurality of unselected memory cells 12 via the local source lines (LEN<0>, LEN<1>, LEN<2>, and/or LEN<3>) 604 associated with the unselected memory cells 12.
Referring to FIG. 7, there are shown control signal voltage waveforms for performing refresh operation in accordance with an embodiment of the present disclosure. For example, the refresh operation may include one or more steps. The refresh operation may reduce an amount of power consumption because a read operation may not be performed (e.g., not activating data sense amplifier circuitry). Also, the refresh operation may reduce an amount of power consumption by simultaneously refreshing all memory cells 12 that are coupled to selected local bit lines (LCNs) 30 and that are coupled to a selected word line (WL) 28. Further, the refresh operation may reduce an amount of power consumption because the voltage potential applied to the source line (EN) 32 may remain constant during the entire refresh operation. Furthermore, by maintaining the voltage potential applied to the source lines (EN) 32 constant during the entire refresh operation, an amount of disturbance on the memory cells 12 may be reduced.
The refresh operation may include control signals configured to perform the one or more steps. Prior to performing a refresh operation, the control signals may be configured to perform a hold operation in order to maintain a data state (e.g., a logic high (binary “1” data state) or a logic low (binary “0” data state)) stored in the memory cell 12. In particular, the control signals may be configured to perform a hold operation in order to maximize a retention time of a data state (e.g., a logic low (binary “0” data state) and/or a logic high (binary “1” data state)) stored in the memory cell 12. Also, the control signals for the hold operation may be configured to eliminate or reduce activities or field (e.g., electrical fields between junctions which may lead to leakage of charges) within the memory cell 12. In an exemplary embodiment, during a hold operation, a negative voltage potential may be applied to the word line (WL) 28 that may be capacitively coupled to the P− region 122 of the memory cell 12, while the voltage potential applied to other regions (e.g., the N+ region 120, the N+ region 124, and/or the P+ region 126) may be maintained at 0V. For example, the negative voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122 of the memory cell 12) may be −1.8V. During the hold operation, the junction between the N+ region 124 and the P− region 122 and the junction between the N+ region 120 and the P− region 122 may be reverse biased in order to retain a data state (e.g., a logic high (binary “1” data state) or a logic low (binary “0” data state)) stored in the memory cell 12.
In an exemplary embodiment, a first step of a refresh operation may include control signals to perform a preparation to start operation where the control signals may be applied to a memory cell 12 in order to prepare the memory cell 12 for one or more subsequent steps. For example, precharge controls signals may be applied to one or more selected local bit lines (LCNs) 30 to a predetermined voltage potential. The precharge control signals may be applied to the one or more selected local bit lines (LCNs) 30 via the multiplexer (MUX) 408. Selection control signals may be applied to one or more selection transistors (SELs) 514 to activate the one or more selection transistors (SELs) 514. The selection control signals may turn the one or more selection transistors (SELs) 514 to an “ON” state in order to couple the precharge control signal to the one or more corresponding local bit lines (LCNs) 30. In an exemplary embodiment, the precharge control signal may precharge the one or more local bit lines (LCNs) 30 to 0.7V.
The second step of the refresh operation may include control signals to apply to one or more memory cells 12 to perform a preparation to start operation where the control signals may be applied to a memory cell 12. The control signals may be applied to the P+ region 126 of the memory cell 12 via the carrier injection line (EP) 34. The control signals may apply a predetermined voltage potential to the P+ region 126 of the memory cell 12 via the carrier injection line (EP) 34. In an exemplary embodiment, the control signals may apply approximately 1.0V to 1.2V to the P+ region 126 of the memory cell 12 via the carrier injection line (EP) 34. The control signals applied to the P+ region 126 of the memory cell 12 will not cause the second bipolar transistor 14b to turn to an “ON” state. In an exemplary embodiment, the second step of the refresh operation may be performed simultaneously as the first step of the refresh operation. In another exemplary embodiment, the second step of the refresh operation may be performed after the first step of the refresh operation.
The third step of the refresh operation may include control signals to perform a preparation to start operation where the control signals may be applied to a memory cell 12. For example, after precharging the one or more local bit lines (LCNs) 30 to a predetermined voltage potential, decoupling control signals may be applied to the one or more selection transistors (SELs) 514 and turn the one or more selection transistors (SELs) 514 to an “OFF” state. In another exemplary embodiment, after precharging the one or more local bit lines (LCNs) 30 to a predetermined voltage potential, the selection control signals may be withdrawn from the one or more selection transistors (SELs) 514 in order to turn the one or more selection transistors (SELs) 514 to an “OFF” state. The one or more turned “OFF” selection transistors (SELs) 514 may decouple the one or more local bit lines (LCNs) 30 from the precharge control signals. In an exemplary embodiment, the one or more local bit lines (LCNs) 30 may be electrically floating.
The fourth step of the refresh operation may include control signals configured to perform a read operation. The read operation may include control signals configured to perform one or more write operations to one or more selected memory cells 12 of one or more selected rows of the memory cell array 20. For example, the read operation may be performed on one or more selected memory cells 12 and one or more selected rows of the memory cell array 20. For example, an increase in the voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) may be higher than a voltage potential applied to the local bit line (LCN) 30 and/or the source line (EN) 32 by a predetermined voltage potential. The predetermined voltage potential may be a threshold voltage potential or forward bias voltage potential of the first bipolar transistor 14a and/or the second bipolar transistor 14b. For example, the predetermined voltage potential may be approximately 0.7V.
In an exemplary embodiment, a voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) may be raised to 0V from −1.8V. In the event that a logic high (e.g., binary “1” data state) is stored in the memory cell 12, the first bipolar transistor 14a may be turned to an “ON” state. For example, the junction between the N+ region 120 and the P− region 122 may be forward biased and the junction between the P− region 122 and the N+ region 124 may be reverse biased and the first bipolar transistor 14a may be turned to an “ON” state. When the first bipolar transistor 14a is turned to an “ON” state, the N+ region 124 (e.g., electrically floating) may be discharged to approximately 0.2V in order to turn the second bipolar transistor 14b to an “ON” state. By turning the second bipolar transistor 14b to an “ON” state, majority charge carriers may be injected into the P− region 122 in order to refresh a logic high (e.g., binary “1” data state) stored in the memory cell 12.
In the event that a logic low (e.g., binary “0” data state) is stored in the memory cell 12, the first bipolar transistor 14a may remain in an “OFF” state. For example, the junction between the N+ region 120 and the P− region 122 may not be forward biased or may be weakly forward biased and the junction between the P− region 122 and the N+ region 124 may or may not be forward biased or may be weakly forward biased so that the first bipolar transistor 14a may remain in an “OFF” state. When the first bipolar transistor 14a remains in an “OFF” state, the N+ region 124 (e.g., electrically floating) may not be discharged and may remain at a predetermined voltage potential (e.g., a precharge voltage potential). The second bipolar transistor 14b may remain in an “OFF” state when the N+ region is not discharged. When the second bipolar transistor 14b remains in an “OFF” state, majority charge carriers may not be injected into the P− region 122 in order to refresh a logic low (e.g., binary “0” data state) stored in the memory cell 12.
In an exemplary embodiment, when no charges or a small amount of charges are accumulated in the P− region 122 to indicate a logic low (e.g., binary “0” data state), the junction between the P− region 122 and the N+ region 124 is not forward biased and the N+ region 124 may not be discharged (e.g., maintaining a precharged voltage potential). The second bipolar transistor 14b may remain in an “OFF” state when the N+ region 124 is not discharged and the logic low (e.g., binary “0” data state) may be maintained in the memory cell 12. However, when a larger amount of charges are accumulated in the P− region 122 to indicate a logic low (e.g., binary “0” data state) is stored in the memory cell 12, the junction between the P− region 122 and the N+ region 124 may be weakly forward biased to deplete or discharge excessive charges stored in the P− region 122 to maintain a logic low (e.g., binary “0” data state) in the memory cell 12.
The fifth step of the refresh operation may include control signals configured to perform a write logic high (e.g., binary “1” data state) operation to memory cells 12 that may have voltage potential at the N+ region 124 discharged (e.g., to approximately 0.2V). The write logic high operation may include control signals configured to write a logic high (e.g., binary “1” data state) to the one or more selected memory cells 12. For example, a predetermined voltage potential may be applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122). In an exemplary embodiment, a voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) may be lowered to −1.0V from 0V.
Under such biasing, the majority charge carriers may continue to inject into the P− region 122 because the second bipolar transistor 14b which may be turned to an “ON” state in step four. The majority charge carriers may continue to inject into the P− region 122 even as the voltage potential applied by the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) switches from 0V to −1.0V. For example, the junction between the N+ region 124 and the P+ region 126 may become forward biased and majority charge carriers (e.g., holes) may be injected into the P− region 122. The P− region 122 may accumulate/store an amount of charge carriers that may represent a predetermined voltage potential above the voltage potential at the N+ region 120. In an exemplary embodiment, the predetermined voltage potential may be 0.7V above the voltage potential at the N+ region 120. In the event that a logic low (e.g., binary “0” data state) is stored in the memory cell 12, the second bipolar transistor 14b may remain in an “OFF” state and the majority charge carriers may not be injected into the P− region 122. When the voltage potential applied by the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) switches from 0V to −1.0V, the second bipolar transistor 14b may remain in the “OFF” state and the majority charge carriers may not be injected into the P− region 122. When majority charge carriers are not injected into the P− region 122, a logic low (e.g., binary “0” data state) may be maintained in the memory cell 12.
The sixth step of the refresh operation may include control signals to terminate the write logic high (e.g., binary “1” data state) operation. For example, coupling control signals may be applied to the one or more selection transistors (SELs) 514 and turn the one or more selection transistors (SELs) 514 to an “ON” state. The one or more turned “ON” selection transistors (SELs) 514 may couple a predetermined voltage potential to the one or more local bit lines (LCNs) 30 in order to turn the second bipolar transistor 14b to an “OFF” state and end the write logic high (e.g., binary “1” data state) in the selected memory cells 12. The predetermined voltage potential applied to the one or more local bit lines (LCNs) 30 to end the write logic high (e.g., binary “1” data state) operation may be determined based at least in part on the threshold voltage potential below which the majority charge carriers injected through the junction between the N+ region 124 and the P+ region 126 may be insignificant. For example, a predetermined voltage potential applied to the one or more local bit lines (LCNs) 30 may be approximately 0.7V.
As discussed above, the voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) may be lowered to −1.0V from 0V and the voltage potential applied to the local bit lines (LCNs) 30 may be discharged to approximately 0.2V, while the voltage potential applied to the P+ region 126 via the carrier injection line (EP) 34 may be maintained at 1.0V. Under such biasing, the junction between the P− region 122 and the N+ region 124 may become forward biased so that a logic high (e.g., binary “1” data state) may be written to the P− region 122 (e.g., charge injection into the P− region 122 from the P+ region 126).
The seventh step of the refresh operation may also include control signals configured to perform a preparation to end operation. During the seventh step of the refresh operation, the voltage potentials applied to the memory cells 12 may adjust the amount of charge (e.g., an indication of data state) stored in the memory cells 12. In an exemplary embodiment, a voltage potential applied to the P+ region 126 via the carrier injection line (EP) 34 may be lowered to 0V. The P− region 122 which may be charged to approximately 0.7V above the voltage potential at the N+ region 124 during the write logic high (e.g., binary “1” data state) operation may be coupled low to approximately 0V by the voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122). The voltage potential applied to the word line (WL) 28 (e.g., capacitively coupled to the P− region 122) may be lowered to −1.8V and may determine an amount of charge (e.g., an indication of data state) stored in the P− region 122 of the memory cells 12. Also, a voltage potential applied to the N+ region 124 via the bit line (CN) 30 may be lowered to 0V to return to the hold operation in order to retain a data state (e.g., logic low (binary “0” data state) or logic high (binary “1” data state)).
At this point it should be noted that providing techniques for refreshing a semiconductor memory device in accordance with the present disclosure as described above typically involves the processing of input data and the generation of output data to some extent. This input data processing and output data generation may be implemented in hardware or software. For example, specific electronic components may be employed in a semiconductor memory device or similar or related circuitry for implementing the functions associated with refreshing a semiconductor memory device in accordance with the present disclosure as described above. Alternatively, one or more processors operating in accordance with instructions may implement the functions associated with refreshing a semiconductor memory device in accordance with the present disclosure as described above. If such is the case, it is within the scope of the present disclosure that such instructions may be stored on one or more processor readable media (e.g., a magnetic disk or other storage medium), or transmitted to one or more processors via one or more signals embodied in one or more carrier waves.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

## Claims

1. A method for refreshing a semiconductor memory device comprising the steps of:
applying a plurality of voltage potentials to a memory cell in an array of memory cells, wherein applying a plurality of voltage potentials to the memory cell comprises:
applying a first voltage potential to a first region of the memory cell via a respective source line of the array;
applying a second voltage potential to a second region of the memory cell via a respective local bit line and a respective selection transistor of the array;
applying a third voltage potential to a respective word line of the array, wherein the word line is spaced apart from and capacitively to a body region of the memory cell that is electrically floating and disposed between the first region and the second region;
applying a fourth voltage potential to a third region of the memory cell via a respective carrier injection line of the array; and
maintaining the first voltage potential applied to the first region at a constant level via the respective source line during the refresh of the semiconductor memory device.

2. The method according to claim 1, wherein the respective local bit line is coupled to a multiplexer.

3. The method according to claim 2, wherein the multiplexer is coupled to a global bit line.

4. The method according to claim 2, wherein the multiplexer comprises at least one masking transistor coupled to the respective local bit line.

5. The method according to claim 4, wherein the multiplexer further comprises at least one hold transistor coupled to the respective local bit line.

6. The method according to claim 5, wherein the respective selection transistor is coupled to the at least one mask transistor and the at least one hold transistor.

7. The method according to claim 1, further comprising applying a selection control signal to the respective selection transistor to activate the respective selection transistor.

8. The method according to claim 7, further comprising increasing the second voltage potential applied to the respective local bit line from the second voltage potential applied to the respective local bit line during a hold operation via the activated respective selection transistor.

9. The method according to claim 1, further comprising increasing the fourth voltage potential applied to the respective carrier injection line from the fourth voltage potential applied to the respective carrier injection line during a hold operation.

10. The method according to claim 1, further comprising applying decoupling control signals to the respective selection transistor to deactivate the respective selection transistor.

11. The method according to claim 10, the respective local bit line is electrically floating after the respective selection transistor is deactivated.

12. The method according to claim 1, further comprising increasing the third voltage potential applied to the respective word line from the third voltage potential applied to the respective word line during a hold operation in order to perform a read operation.

13. The method according to claim 12, wherein the increase in the third voltage potential activates the memory cell to decrease the second voltage potential applied to the respective local bit line.

14. The method according to claim 1, further comprising decreasing the third voltage potential applied to the respective word line from the third voltage potential applied to the respective word line during a write logic low operation to perform a write logic high operation.

15. The method according to claim 14, wherein the third voltage potential applied to the respective word line during the write logic high operation is higher than the third voltage potential applied to the respective word line during a hold operation.

16. The method according to claim 1, further comprising applying a coupling control signals to the respective selection transistor to activate the respective selection transistor in order to perform an end to a write logic high operation.

17. The method according to claim 16, further comprising discharging the second voltage potential applied to the respective local bit line to forward bias a junction between the second region and the third region.

18. The method according to claim 1, further comprising decreasing the fourth voltage potential applied to the respective carrier injection line from the fourth voltage potential applied to the respective carrier injection line during a write logic high operation to perform a hold operation.

19. The method according to claim 1, further comprising decreasing the second voltage potential applied to the respective local bit line from the second voltage potential applied to the respective local bit line during a write logic high operation to perform a hold operation.