# Patent

## Title
Techniques for providing a semiconductor memory device having hierarchical bit lines

## Abstract

Techniques for providing a semiconductor memory device having hierarchical bit lines are disclosed. In one particular exemplary embodiment, the techniques may be realized as a semiconductor memory device including a plurality of memory cells and a plurality of local bit lines coupled directly to the plurality of memory cells. The semiconductor memory device may also include a multiplexer coupled to the plurality of local bit lines and a global bit line coupled to the multiplexer.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This patent application claims priority to U.S. Provisional Patent Application No. 61/310,573, filed Mar. 4, 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 providing a semiconductor memory device having hierarchical bit lines.
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/or 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 or gate bias signals to determine a data state stored in 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).
Often, conventional reading and/or writing operations may lead to relatively large power consumption and large voltage potential swings which may cause disturbances 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 in the semiconductor memory device, which, in turn, may result in an inaccurate determination of the state of the memory cell. Furthermore, the semiconductor memory device may have bit lines that are spaced close together and may cause bit line cross-talk due to capacitive coupling between adjacent bit lines. Additionally, the semiconductor memory device may have a small bit line pitch leading to a high bit line resistance and thus a high power consumption when performing various operations.
In view of the foregoing, it may be understood that there may be significant problems and shortcomings associated with conventional techniques for fabricating and/or operating semiconductor memory devices.
SUMMARY OF THE DISCLOSURE
Techniques for providing a semiconductor memory device having hierarchical bit lines are disclosed. In one particular exemplary embodiment, the techniques may be realized as a semiconductor memory device comprising a plurality of memory cells and a plurality of local bit lines coupled directly to the plurality of memory cells. The semiconductor memory device may also comprise a multiplexer coupled to the plurality of local bit lines and a global bit line coupled to the multiplexer.
In accordance with other aspects of this particular exemplary embodiment, four local bit lines may be coupled directly to the multiplexer.
In accordance with further aspects of this particular exemplary embodiment, the multiplexer may be coupled to a global hold line.
In accordance with additional aspects of this particular exemplary embodiment, the multiplexer may be coupled to a global mask line.
In accordance with yet another aspect of this particular exemplary embodiment, the multiplexer may comprise a plurality of selection transistors.
In accordance with other aspects of this particular exemplary embodiment, the plurality of selection transistors may be coupled to the plurality of memory cells via the plurality of local bit lines.
In accordance with further aspects of this particular exemplary embodiment, the plurality of selection transistors may be coupled to the global bit line.
In accordance with additional aspects of this particular exemplary embodiment, each of the plurality of selection transistors may be coupled to a respective one of the plurality of memory cells.
In accordance with yet another aspect of this particular exemplary embodiment, the multiplexer may comprise a plurality of hold transistors.
In accordance with other aspects of this particular exemplary embodiment, the plurality of hold transistors may be coupled to the plurality of local bit lines.
In accordance with further aspects of this particular exemplary embodiment, each of the plurality of hold transistors may be coupled to a respective one of the plurality of local bit lines.
In accordance with additional aspects of this particular exemplary embodiment, the plurality of hold transistors may be coupled to a global hold line.
In accordance with yet another aspect of this particular exemplary embodiment, the multiplexer may comprise a plurality of mask transistors.
In accordance with other aspects of this particular exemplary embodiment, each of the plurality of mask transistors may be coupled to a respective one of the plurality of local bit lines.
In accordance with further aspects of this particular exemplary embodiment, the plurality of mask transistors may be coupled to a global mask line.
In accordance with additional aspects of this particular exemplary embodiment, the multiplexer may comprise a plurality of selection transistors, a plurality of mask transistors, and a plurality of hold transistors.
In accordance with yet another aspect of this particular exemplary embodiment, each of the plurality of selection transistors, each of the plurality of mask transistors, and each of the plurality of hold transistors may be directly coupled to a respective one of the plurality of local bit lines.
In accordance with other aspects of this particular exemplary embodiment, the plurality of mask transistors may be coupled to a global mask line and the plurality of hold transistors may be coupled to a global hold line.
In accordance with further aspects of this particular exemplary embodiment, the global mask line may be configured between adjacent global bit lines.
In accordance with additional aspects of this particular exemplary embodiment, the global hold line may be configured between adjacent global bit lines.
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 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 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 12 coupled to a plurality of sense amplifier circuits via a hierarchical bit line configuration in accordance with another embodiment of the present disclosure.
FIG. 4A shows a three-dimensional 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 an embodiment of the present disclosure shown in FIG. 4.
FIG. 5 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. 6 shows a schematic diagram of a multiplexer for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure.
FIG. 7 shows a schematic diagram of a source line driver for a hierarchical bit line configuration 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 source line (EN) 32 and a bit line (CN) 30. It may be appreciated that the source line (EN) 32 and the bit line (CN) 30 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 (ON) 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 (ON) 30. In an exemplary embodiment, the multiplexer may couple a plurality of bit lines (ON) 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 therefor) to select and/or enable one or more predetermined memory cells 12. Notably, all such control/selection techniques, and circuitry therefor, 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 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 (e.g., a 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. 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) 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 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) 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 separately.
Referring to FIG. 3, 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 302 via a hierarchical bit line configuration in accordance with an 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 302 via a hierarchical bit line configuration. The hierarchical bit line configuration may include a local bit line (LCN) 304 (e.g., the bit line (CN) 30) coupled directly to each of the memory cells 12. The local bit line (LCN) 304 may be coupled to a global bit line (GCN) 306 via a multiplexer (MUX) 308. 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) 304 adjacent to a selected local bit line (LCN) 304 may experience disturbance. Additionally, power consumption may be reduced by applying masking control signals only to unselected local bit lines (LCNs) 304 that are adjacent to a selected local bit line (LCN) 304.
The hierarchical bit line configuration may include a plurality of local bit lines (LCNs) 304 coupled to the multiplexer (MUX) 308. In an exemplary embodiment, four local bit lines (LCNs) 304 may be coupled to the multiplexer (MUX) 308. It may be appreciated by one skilled in the art that the number of local bit lines (LCNs) 304 coupled to the multiplexer (MUX) 308 may vary. For example, eight local bit lines (LCNs) 304, sixteen local bit lines (LCNs) 304, thirty-two local bit lines (LCNs) 304, sixty-four local bit lines (LCNs) 304 etc., may be coupled to the multiplexer (MUX) 308.
The hierarchical bit line configurations may include a global bit line (GCN) 306 coupled to a plurality of multiplexers (MUXs) 308. In an exemplary embodiment, the global bit line (GCN) 306 may be coupled to four multiplexers (MUXs) 308. It may be appreciated by one skilled in the art that the number of multiplexers (MUXs) 308 coupled to the global bit line (GCN) 306 may vary. For example, eight multiplexers (MUXs) 308, sixteen multiplexers (MUXs) 308, thirty-two multiplexers (MUXs) 308, sixty-four multiplexers (MUXs) 308 etc., may be coupled to the global bit line (GCN) 306. The global bit line (GCN) 306 may be coupled to a plurality of local bit lines (LCNs) 304 via a plurality of multiplexers (MUXs) 308. In an exemplary embodiment, the global bit line (GCN) 306 may be coupled to sixteen local bit lines (LCNs) 304 via four multiplexers (MUXs) 308.
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. The memory cell array 20 illustrated in FIG. 4 may be similar to the memory cell array 20 illustrated in FIG. 3, except that the hierarchical bit line configuration may include a plurality of global hold lines (GHLs) 410 and a plurality of global mask lines (GMLs) 412. Each of the memory cells 12 of the memory cell array 20 may be coupled to a data sense amplifier circuit 402 via a 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 the memory cell 12. The local bit line (LCN) 404 may be coupled to a global bit line (GCN) 406, a global hold line (GHL) 410, and a global mask line (GML) 412 via a multiplexer (MUX) 408.
The global hold line (GHL) 410 may be coupled to a plurality of multiplexers (MUXs) 408. The global hold line (GHL) 410 may be configured between contiguous global bit lines (GCN) 406 in order to reduce and/or eliminate the cross-talk of the bit line capacitance due to cross-talks between contiguous global bit lines (GCNs) 406. In an exemplary embodiment, the global hold line (GHL) 410 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 the global hold line (GHL) 410 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 hold line (GHL) 410. In an exemplary embodiment, the number of multiplexer (MUX) 408 coupled to the global hold line (GHL) 410 may be equal to the number of multiplexer (MUX) 408 coupled to the global bit line (GCN) 406. The global hold line (GHL) 410 may be coupled to a plurality of local bit lines (LCNs) 404 via a plurality of multiplexers (MUXs) 408. In an exemplary embodiment, the global hold line (GHL) 410 may be coupled to sixteen local bit lines (LCNs) 404 via four multiplexers (MUXs) 408.
The global mask line (GML) 412 may be coupled to plurality of multiplexers (MUXs) 408. The global mask line (GML) 412 may be configured between contiguous global bit lines (GCN) 406 in order to reduce and/or eliminate the cross-talk of the bit line capacitance due to cross-talks between contiguous global bit lines (GCNs) 406. In an exemplary embodiment, the global mask line (GML) 412 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 the global mask line (GML) 412 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 mask line (GML) 412. In an exemplary embodiment, the number of multiplexer (MUX) 408 coupled to the global mask line (GML) 412 may be equal to the number of multiplexer (MUX) 408 coupled to the global bit line (GCN) 406. The global mask line (GML) 412 may be coupled to a plurality of local bit lines (LCNs) 404 via a plurality of multiplexers (MUXs) 408. In an exemplary embodiment, the global mask line (GML) 412 may be coupled to sixteen local bit lines (LCNs) 404 via four multiplexers (MUXs) 408.
Referring to FIG. 4A, there is shown a three-dimensional 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 an embodiment of the present disclosure shown in FIG. 4. As discussed in FIG. 4, a plurality of memory cells 12 of the memory cell array 20 may be coupled to a data sense amplifier circuit 402 via a 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 the memory cell 12. The local bit line (LCN) 404 may be coupled to a global bit line (GCN) 406, a global hold line (GHL) 410, and a global mask line (GML) 412 via a multiplexer (MUX) 408.
The multiplexer (MUX) 408 may be configured in a plurality of planes. For example, the multiplexer (MUX) 408 may include a metal layer configured in a plane above a plane containing the plurality of memory cells 12. Also, the multiplexer (MUX) 408 may include a switch transistor configured in a plane containing the plurality of memory cells 12. The global hold line (GHL) 410 and the global mask line (GML) 412 may be configured in the same plane. In an exemplary embodiment, the metal layer of the multiplexer (MUX) 408, the global hold line (GHL) 410, and the global mask line (GML) 412 may be configured in the same plane. The multiplexer (MUX) 408 may be coupled to a global bit line (GCN) 406 via a global bit line contact 414. In an exemplary embodiment, the global bit line (GCN) 406 may be configured in a plane above a plane containing the memory cells 12. In another exemplary embodiment, the global bit line (GCN) 406 may be configured in a plane above the plane containing the memory cells 12 and the plane containing the global hold line (GHL) 410 and the global mask line (GML) 412.
Referring to FIG. 5, 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 502 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 502 via a hierarchical bit line configuration. The hierarchical bit line configuration may include a local bit line (LCN) 504 (e.g., the bit line (CN) 30) coupled directly to the memory cell 12. The local bit line (LCN) 504 may be coupled to a global bit line (GCN) 506 via a multiplexer (MUX) 508. The memory cell 12 may be biased by a source line driver 512. The source line driver 512 may be coupled to the memory cell 12 via a local source line (LEN) 510.
The hierarchical bit line configuration may include a plurality of local bit lines (LCNs) 504 coupled to the multiplexer (MUX) 508. In an exemplary embodiment, four local bit lines (LCNs) 504 may be coupled to the multiplexer (MUX) 508. The hierarchical bit line configurations may also include a global bit line (GCN) 506 coupled to a plurality of multiplexers (MUXs) 508. In an exemplary embodiment, the global bit line (GCN) 506 may be coupled to four multiplexers (MUXs) 508. The global bit line (GCN) 506 may be coupled to a plurality of local bit lines (LCNs) 504 via a plurality of multiplexers (MUXs) 508. In an exemplary embodiment, the global bit line (GCN) 506 may be coupled to sixteen local bit lines (LCNs) 504 via four multiplexers (MUXs) 508.
The source line driver 512 may be coupled to a plurality of memory cells 12. In an exemplary embodiment, the source line driver 512 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 the source line driver 512 may vary. For example, eight memory cells 12, sixteen memory cells 12, thirty-two memory cells 12, sixty-four memory cells 12 etc., may be coupled to the source line driver 512. In an exemplary embodiment, the number of memory cells 12 coupled to the source line driver 512 may be equal to the number of memory cells 12 coupled to the multiplexer (MUX) 508.
Referring to FIG. 6, there is shown a schematic diagram of a multiplexer 608 for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure. As shown in FIG. 6, a global bit line (GCN) 606 may be coupled to a plurality of local bit lines (LCNs) 604 via the multiplexer 608. In an exemplary embodiment, the multiplexer 608 may include a plurality of selection transistors (SELs) 614 coupled to the plurality of local bit lines (LCN) 604 and the global bit line (GCN) 606. The selection transistor 614 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). The plurality of selection transistors (SELs) 614 may be biased to selectively couple a local bit line (LCN) 604 to the global bit line (GCN) 606. In an exemplary embodiment, selection transistor (SEL<0>) 604 may be biased to couple the local bit line (LCN<0>) to the global bit line (GCN) 606, 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>) 604 from the global bit line (GCN) 606.
The multiplexer 608 may also include a biasing transistor pair 616. The 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). The biasing transistor pair 616 may be coupled to a global hold line (GHL) 610 and/or a global mask line (GML) 612. The biasing transistor pair 616 may include a hold transistor (HD) 618 and a mask transistor (MSK) 620. In an exemplary embodiment, the hold transistor (HD) 618 may be coupled to the global hold line (GHL) 610 and the 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 the memory cell 12 during a hold operation via the local bit line (LCN) 604. For example, when control signals may be 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 change to 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 the memory cells 12 via the local bit lines (LCN<0>, LCN<1>, LCN<2>, and LCN<3>).
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 the memory cell 12 during a read and/or write operation via the local bit line (LCN) 604. For example, when control signals may be applied to the gates of the mask transistors (MSK) 620, the control signals may cause the plurality of mask transistors (HD<0>, HD<1>, HD<2>, and/or HD<3>) 620 associated with unselected memory cells 12 to change to an “ON” state. Subsequently, the plurality of mask transistors (HD<0>, HD<1>, HD<2>, and/or HD<3>) 618 may output a masking voltage potential to the unselected memory cells 12 via the local bit lines (LCN<0>, LCN<1>, LCN<2>, and/or LCN<3>) associated with the unselected memory cells 12.
Referring to FIG. 7, there is shown a schematic diagram of a source line driver 708 for a hierarchical bit line configuration in accordance with an embodiment of the present disclosure. The source line driver 708 may include a plurality of biasing transistor pairs 716. Each biasing transistor pair 716 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 716 may be coupled to a global hold line (GHL) 710 and/or a global mask line (GML) 712. Each biasing transistor pair 716 may include a hold transistor (HD) 718 and a mask transistor (MSK) 720. In an exemplary embodiment, each hold transistor (HD) 718 may be coupled to the global hold line (GHL) 710 and each mask transistor (MSK) 720 may be coupled to the global mask line (GML) 712. Control signals may be applied to the gates of the hold transistor (HD) 718 to bias the hold transistors (HD) 718 in order to apply a holding voltage potential to memory cells 12 during a hold operation via a local bit line (LCN) 704. For example, when control signals are applied to the gates of the hold transistor (HD) 718, the control signals may cause the plurality of hold transistors (HD<0>, HD<1>, HD<2>, and HD<3>) 718 to change to an “ON” state. Subsequently, the plurality of hold transistors (HD<0>, HD<1>, HD<2>, and HD<3>) 718 may output a holding voltage potential to the memory cells 12 via the local bit lines (LCN<0>, LCN<1>, LCN<2>, and LCN<3>) 704.
Also, control signals may be applied to the gates of the mask transistors (MSK) 720 to bias the mask transistors (MSK) 720 in order to apply a masking voltage potential to the memory cell 12 during a read and/or write operation via the local bit line (LCN) 704. For example, when control signals are applied to the gates of the mask transistors (MSK) 720, the control signals may cause the plurality of mask transistors (HD<0>, HD<1>, HD<2>, and/or HD<3>) 720 associated with unselected memory cells 12 to change to an “ON” state. Subsequently, the plurality of mask transistors (HD<0>, HD<1>, HD<2>, and/or HD<3>) 718 may output a masking voltage potential to the unselected memory cells 12 via the local bit lines (LCN<0>, LCN<1>, LCN<2>, and/or LCN<3>) 704 associated with the unselected memory cells 12.
At this point it should be noted that providing a semiconductor memory device having hierarchical bit lines 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 providing a semiconductor memory device having hierarchical bit lines 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 providing a semiconductor memory device having hierarchical bit lines 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 semiconductor memory device comprising:
a plurality of memory cells;
a plurality of local bit lines coupled directly to the plurality of memory cells;
a multiplexer coupled to the plurality of local bit lines, wherein the multiplexer comprises a plurality of hold transistors each configured to apply a holding signal to a respective memory cell during a hold operation; and
a global bit line coupled to the multiplexer.

2. The semiconductor memory device according to claim 1, wherein four local bit lines are coupled directly to the multiplexer.

3. The semiconductor memory device according to claim 1, wherein the multiplexer is coupled to a global hold line.

4. The semiconductor memory device according to claim 1, wherein the multiplexer is coupled to a global mask line.

5. The semiconductor memory device according to claim 1, wherein the multiplexer further comprises a plurality of selection transistors.

6. The semiconductor memory device according to claim 5, wherein the plurality of selection transistors are coupled to the plurality of memory cells via the plurality of local bit lines.

7. The semiconductor memory device according to claim 5, wherein the plurality of selection transistors are coupled to the global bit line.

8. The semiconductor memory device according to claim 5, wherein each of the plurality of selection transistors is coupled to a respective one of the plurality of memory cells.

9. The semiconductor memory device according to claim 1, wherein the plurality of hold transistors are coupled to the plurality of local bit lines.

10. The semiconductor memory device according to claim 9, wherein each of the plurality of hold transistors are coupled to a respective one of the plurality of local bit lines.

11. The semiconductor memory device according to claim 1, wherein the plurality of hold transistors are coupled to a global hold line.

12. The semiconductor memory device according to claim 1, wherein the multiplexer further comprises a plurality of mask transistors.

13. The semiconductor memory device according to claim 12, wherein each of the plurality of mask transistors is coupled to a respective one of the plurality of local bit lines.

14. The semiconductor memory device according to claim 12, wherein the plurality of mask transistors are coupled to a global mask line.

15. The semiconductor memory device according to claim 1, wherein the multiplexer further comprises a plurality of selection transistors and a plurality of mask transistors.

16. The semiconductor memory device according to claim 15, wherein each of the plurality of selection transistors, each of the plurality of mask transistors, and each of the plurality of hold transistors is directly coupled to a respective one of the plurality of local bit lines.

17. The semiconductor memory device according to claim 15, wherein the plurality of mask transistors are coupled to a global mask line and the plurality of hold transistors are coupled to a global hold line.

18. The semiconductor memory device according to claim 17, wherein the global mask line is configured between adjacent global bit lines.

19. The semiconductor memory device according to claim 17, wherein the global hold line is configured between adjacent global bit lines.