Semiconductor memory device using only single-channel...

Details Semiconductor memory device using only single-channel... Semiconductor memory device using only single-channel...

2001-06-08

2003-09-16

Le, Thong (Department: 2818)

Static information storage and retrieval

Floating gate

Particular connection

C365S230030, C365S230060, C365S185110

Reexamination Certificate

active

06621735

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-173715, filed Jun. 9, 2000; and No. 2000-330972, filed Oct. 30, 2000, the entire contents of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor memory device and, more particularly to, a non-volatile semiconductor memory device such as a NAND cell-, NOR cell-, DINOR cell-, or AND cell-type EEPROM.
Conventionally, an electrically rewritable EEPROM is known as one of the semiconductor memory devices. Inter alia, a NAND cell-type EEPROM in which each NAND cell block is made up of a plurality of memory cells connected in series is attracting attention as a device that can have a high degree of integration.
Each memory cell of a NAND cell-type EEPROM has a FET-MOS structure in which a floating gate (charge storage layer) and a control gate are stacked with an insulating film there between on a semiconductor substrate. A plurality of adjacent memory cells share sources and drains and are connected in series to thereby make up a NAND cell, which is connected to a bit line as a unit. Such NAND cells are arranged in a matrix, thus constituting a memory array. The memory array is integrally formed in a p-type semiconductor substrate or in a p-type well.
Each drain positioned at one end of the NAND cells connected in series in a column direction of the memory cell array is commonly connected via a select gate transistor to a bit line, while each source positioned at the other end is also connected via a select gate transistor to a common source line. The control gates of the memory transistors and the gate electrode of the select gate transistors are commonly connected respectively as a control gate line (word line) and a select gate line in the row direction of the memory cell array.
This NAND cell-type EEPROM operates as follows. Data programming operations mainly start from a memory cell which is the most remote from the bit line contact. First, when the data programming operation starts, according to write-in data, the bit line is given 0V (for “1” data write-in bit line) or a power supply voltage Vcc (for “0” data write-in bit line) and the select gate line on the side of a selected bit line contact is given Vcc. In this case, in a selected NAND cell connected to the “1” data write-in bit line, its channel portion is fixed to 0V by way of a select gate transistor. In a selected NAND cell connected to the “0” data write-in bit line, on the other hand, its channel portion is charged via the select gate transistor up to [Vcc−Vtsg] (where Vtsg is a threshold voltage of the select gate transistor) and then enters a floating state. Subsequently, one control gate line in the selected memory cell in the selected NAND cell changes in potential from 0V to Vpp (=20V or so, which is a programming high voltage), while the other control gate line in the selected NAND cell changes in potential from 0V to Vmg (=10V or so, which is an intermediate voltage).
Since a selected NAND cell connected to the “1” data write-in bit line has its channel portion fixed at 0V, it has a large potential difference (=20V or so) between its selected memory cell's control gate line (=Vpp potential) and its channel portion (=0V), thus causing electrons to be injected from the channel portion to the floating gate. Accordingly, the threshold voltage of that selected memory cell shifts to the positive direction, thus completing write-in of data “1”.
A selected NAND cell connected to the “0” data write-in bit line, on the other hand, has its channel portion in a floating state, so that an influence of capacitive coupling between its control gate line and its channel portion raises a voltage of the control gate line (0V→Vpp, Vmg), which in turn raises a potential of the channel portion from a [Vcc−Vtsg] potential to Vmch (=8V or so) with that channel portion as held in the floating state. In this case, since a potential difference between the control gate line (=Vpp potential) and the channel portion (=Vmch) of the selected memory cell in the selected NAND cell is a relatively low value of 12V or so, thus electron injection is avoided. Therefore, the threshold voltage of the selected memory cell is held unchanged at a negative value.
Data erase is carried out to all of the memory cells in a selected NAND cell block. That is, 0V is applied to all the control gate lines of the selected NAND cell block, while a high voltage of 20V or so is applied to the bit lines, the source lines, the p-type well regions (or p-type semiconductor substrate), and the control gate lines and all the select gate lines in the non-selected NAND cell blocks. Thus, in all the memory cells in the selected NAND cell block, the electrons in the floating gate are emitted to the p-type well (or the p-type semiconductor substrate), thus shifting the threshold voltage to the negative direction.
Data read-out, on the other hand, is carried out by applying 0V to the control gate line of a selected memory cell and a read-out intermediate voltage Vread (4V or so) to the control gate line and the select gate line of the other memory cells to thereby detect whether a current flows through that selected memory cell.
As may be obvious from the above description, to write data into a NAND cell-type EEPROM, it is necessary to apply voltages higher than the power supply voltage, i.e. Vpp (20V or so) to a selected control gate line in a selected block and Vmg (10V or so) to a non-selected control gate line in that selected block.
To apply the above-mentioned voltages Vpp and Vmg, in a row decoder circuit, the current paths of two kinds of elements of an NMOS transistor (n-channel type MOS transistor) and a PMOS transistor (p-channel type MOS transistor) having different polarities are connected in parallel to the control gate line to conduct control so that both transistors may be turned ON and OFF in a selected block and in a non-selected block respectively.
FIG. 1
is a circuit diagram for showing a configuration example of part of the row decoder circuit in such a conventional semiconductor memory device.
In the circuit shown in
FIG. 1
, connected to each control gate line are one NMOS transistor (Qn
1
to Qn
8
)+one PMOS transistor (Qp
1
to Qp
8
). Those transistors Qn
1
to Qn
8
and Qp
1
to Qp
8
are supplied with complementary control signals from nodes N
1
and N
2
respectively.
For data write-in, the power supply node VPPRW and a selected control gate line have the same level in voltage like power supply node VPPRW=[selected control gate line voltage]=20V. In this case, connected to each control gate line are one NMOS transistor+one PMOS transistor, so that 20V can be applied to the control gate line even when the power supply node VPPRW is 20V. Accordingly, it is not necessary to raise the power supply node VPPRW to (20V+Vtn) in order to apply both voltages of 0V and Vpp in a selected block.
Note here that in the circuit shown in
FIG. 1
, memory cells M
1
to M
8
have their current paths connected in series, thus making up one NAND cell. One end of the each NAND cell is connected via the current path of the select gate transistor S
1
to the bit lines BL
1
to BLm and the other end, via the current path of the select gate transistor S
2
to the source line (Cell-Source) commonly. The control gate lines CG(
1
) to CG(
8
) are commonly connected to the control gates of the memory cells M
1
to M
8
respectively in each NAND cell, while the select gate lines SG(
1
) and SG(
2
) are commonly connected to the gates of the select gate transistors S
1
and S
2
respectively. The signal input nodes CGD
1
to CGD
8
, SGD, SGS, and SGDS are each supplied with a decode signal. Moreover, the row decoder activating signal RDEC is at Vcc during general data programming, read-out, and erase and at 0V

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