Digitally controlled source side select gate offset in 3D NAND memory erase
First Claim
1. A monolithic three-dimensional non-volatile semiconductor memory device, comprising:
- a well structure formed in a silicon substrate;
one or more strings each formed along a common channel structure above the well structure and running in a vertical direction relative to the substrate, each of the strings having a plurality of memory cells connected in series between the well structure and a corresponding bit line respectively through source side and drain side select gates, where the memory cells each have a charge storage medium and are arranged in multiple physical levels above the silicon substrate; and
driver circuitry connected to receive a clock signal and connectable to apply voltage levels to the well structure and control gates of the memory cells, the source side select gates, and drain side select gates,wherein, when performing an erase operation on the strings, the driver circuitry applies to the well structure a first staircase waveform that begins with an initial level and increases in voltage with each of a first number of cycles of the clock signal and, after a delay of a second number of clock cycles subsequent to beginning to apply the first staircase waveform to the well structure, applies the first staircase waveform beginning with the initial level to the control gates of the source side select gates for the remainder of the first number of clock cycles.
2 Assignments
0 Petitions
Accused Products
Abstract
In 3D NAND type memory structures, such as of the BiCS type, the NAND strings have a channel that runs vertically up from the substrate between the memory cells and select gates. In an erase process, holes travel up from the well down at the substrate up towards the bit line in order to reach the cells to be erased. In such a process, the voltage applied to source side select gates should be low enough for the holes to pass through theses gates and up the column, but not so low as to result in device breakdown as the erase voltage is applied to the well. Techniques are presented to do this by controlling the source side select gate voltages so that the difference from the well voltage is kept largely constant during the erase process by use of a fixed offset during ramping and at the final level for the erase process.
-
Citations
14 Claims
-
1. A monolithic three-dimensional non-volatile semiconductor memory device, comprising:
-
a well structure formed in a silicon substrate; one or more strings each formed along a common channel structure above the well structure and running in a vertical direction relative to the substrate, each of the strings having a plurality of memory cells connected in series between the well structure and a corresponding bit line respectively through source side and drain side select gates, where the memory cells each have a charge storage medium and are arranged in multiple physical levels above the silicon substrate; and driver circuitry connected to receive a clock signal and connectable to apply voltage levels to the well structure and control gates of the memory cells, the source side select gates, and drain side select gates, wherein, when performing an erase operation on the strings, the driver circuitry applies to the well structure a first staircase waveform that begins with an initial level and increases in voltage with each of a first number of cycles of the clock signal and, after a delay of a second number of clock cycles subsequent to beginning to apply the first staircase waveform to the well structure, applies the first staircase waveform beginning with the initial level to the control gates of the source side select gates for the remainder of the first number of clock cycles. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
-
9. A method of performing erase operation on a monolithic three-dimensional non-volatile semiconductor memory device, where the memory device includes a well structure formed in a silicon substrate and one or more strings each formed along a common channel structure above the well structure and running in a vertical direction relative to the substrate, each of the strings having a plurality of memory cells connected in series between the well structure and a corresponding bit line respectively through source side and drain side select gates, where the memory cells each have a charge storage medium and are arranged in multiple physical levels above the silicon substrate, the method comprising:
-
applying to the well structure a first staircase waveform that begins with an initial level and increases in voltage with each of a first number of cycles of the clock signal; and after a delay of a second number of clock cycles subsequent to beginning to apply the first staircase waveform to the well structure, applying the first staircase waveform beginning with the initial level to the control gates of the source side select gates for the remainder of the first number of clock cycles. - View Dependent Claims (10, 11, 12, 13, 14)
-
Specification