Semiconductor memory device and method for program operation having program loops by step voltage
Provided herein are a semiconductor memory device and a method of operating the semiconductor memory device. The semiconductor memory device includes a memory cell array including a memory cell array including a plurality of memory cells, a peripheral circuit configured to perform a program operation, which includes a plurality of program loops, on selected memory cells among the plurality of memory cells and a control circuit configured to control the peripheral circuit so that a program voltage applied to a selected word line, to which the selected memory cells are coupled, is stepwisely increased from a program start voltage to a target program voltage by a step voltage, which is a voltage increment of the program voltage, during a preset time period of a respective program loop.
1. A semiconductor memory device, comprising:
a memory cell array including a plurality of memory cells;
a peripheral circuit configured to perform a program operation, which includes a plurality of program loops, on selected memory cells among the plurality of memory cells; and
a control circuit configured to control the peripheral circuit so that a program voltage applied to a selected word line, to which the selected memory cells are coupled, is stepwisely increased from a program start voltage to a target program voltage by a step voltage, which is a voltage increment of the program voltage, during a preset time period of a respective program loop,
wherein the control circuit comprises a program voltage control unit configured to update the step voltage according to Equation 1 at a start of each step interval defined by Equation 2 given a total of 2 N steps corresponding to the preset time period as follows:
Vstep
(
n
)
=
(
VPGM_TARGET
-
VCURRENT
)
REMAINING
STEPS
,
[
Equation
1
]
where “VPGM TARGET” represents the target program voltage, “VCURRENT” represents a current program voltage of the selected word line, “REMAINING STEPS” represents a number of remaining steps in the total steps at the start of each step interval, and “n” is a natural number ranging from 1 to N+1; and
n
th
step
interval
(
unit
:
step
)
=
{
2
N
+
1
-
n
-
2
N
-
n
n
=
1
N
1
n
=
N
+
1
,
[
Equation
2
]
where “n” is a natural number ranging from 1 to N+1.
2. The semiconductor memory device according to claim 1 , wherein the program voltage control unit comprises:
a step counter circuit configured to count the number of remaining steps as the program voltage is applied to the selected word line; and
a step voltage calculation unit configured to update the step voltage according to the equation 1.
3. The semiconductor memory device according to claim 1 , wherein the preset time period is equally applied to the plurality of program loops.
4. The semiconductor memory device according to claim 1 , wherein each of the total steps has a length corresponding to one of one period and a half period of a clock signal of the semiconductor memory device.
5. A method for operating a semiconductor memory device, comprising:
applying a pass voltage to all word lines;
when a voltage of the word lines reaches the pass voltage, applying a program start voltage higher than the pass voltage to a selected word line among the word lines; and
when the voltage of the selected word line reaches the program start voltage, applying a program voltage to the selected word line during a preset time period of each of a plurality of program loops,
wherein the program voltage is stepwisely increased from the program start voltage to a target program voltage by a step voltage, which is a voltage increment of the program voltage, during the preset time period, and
wherein the applying the program voltage comprises updating the step voltage according to Equation 1 at a start of each step interval defined by Equation 2 given a total of 2 N steps corresponding to the preset time period as follows:
Vstep
(
n
)
=
(
VPGM_TARGET
-
VCURRENT
)
REMAINING
STEPS
,
[
Equation
1
]
where “VPGM TARGET” represents the target program voltage, “VCURRENT” represents a current program voltage of the selected word line, “REMAINING STEPS” represents a number of remaining steps in the total steps at the start of each step interval, and “n” is a natural number ranging from 1 to N+1; and
n
th
step
interval
(
unit
:
step
)
=
{
2
N
+
1
-
n
-
2
N
-
n
n
=
1
N
1
n
=
N
+
1
,
[
Equation
2
]
where “n” is a natural number ranging from 1 to N+1.
6. The method according to claim 5 , wherein the preset time is equally applied to the plurality of program loops.
7. The method according to claim 5 , wherein each of the total steps has a length corresponding to one of one period and a half period of a clock signal of the semiconductor memory device.