2-bit/cell type nonvolatile semiconductor memory

A nonvolatile semiconductor memory comprising:

• a semiconductor substrate of a first conductivity type;
• a number of nonvolatile semiconductor memory cells formed in a surface layer of said semiconductor substrate, said nonvolatile semiconductor memory cells being disposed in a matrix form of m rows and n columns and serially connected along a row direction, each memory cell including first and second diffusion regions of a second conductivity type formed in the surface layer of said semiconductor substrate to define a channel region therebetween, a gate insulating film formed on the channel region and including a carrier trap layer capable of trapping charge carriers, and a gate electrode formed on the gate insulating film;
• m word lines for connecting the gate electrodes of nonvolatile memory cells of a same row;
• (n+1) bit lines for connecting first or second diffusion regions of nonvolatile semiconductor memory cells of a same column and, if there is an adjacent column to said first or second diffusion regions of said same column, for connecting second or first diffusion regions of nonvolatile semiconductor memory cells of the adjacent column;
• and
• a control circuit for controlling:
• in writing data at a memory position of an i-th row, j-th column nonvolatile semiconductor memory cell only on a (j+1)-th bit line side, to apply a high level voltage to an i-th word line, a low level voltage to a j-th bit line, and a high level voltage to the (j+1)-th bit line to inject charge carriers of the second conductivity type in the carrier trap layer near the diffusion region connected to the (j+1)-th bit line of the semiconductor memory cell, and in erasing the written data, to apply a low level voltage or an opposite polarity voltage to the i-th word line, a low level voltage to the i-th bit line, and a high level voltage to the (j+1)-th bit line to inject carriers of the first conductivity type generated by an interband tunneling effect, into the carrier trap layer near the diffusion region connected to the (j+1)-th bit line of the semiconductor memory cell, and neutralize charge carriers of the second conductive type.

A control method for a nonvolatile semiconductor memory having a number of nonvolatile semiconductor memory cells formed on a semiconductor substrate of a first conductivity type and disposed in m rows and n columns, the memory cells in a row direction being connected serially, each memory cell including a gate insulating film formed on a surface of the semiconductor substrate and including a carrier trap layer capable of trapping charge carriers,a gate electrode formed on the gate insulating film, and first and second diffusion regions of a second conductivity type formed in the semiconductor substrate on both sides of the gate electrode, the nonvolatile memory having m word lines for connecting the gate electrodes of nonvolatile memory cells of a same row, and (n+1) bit lines for connecting first or second diffusion regions of nonvolatile semiconductor memory cells of a same column and, if there is an adjacent column to said first or second diffusion regions of said same column, for connecting second or first diffusion regions of nonvolatile semiconductor memory cells of the adjacent column, the control method comprising:

• a data write step capable of writing two bits per one semiconductor memory cell, said data write step writing data by applying a low level voltage to one of the first and second diffusion regions of each semiconductor memory cell, a high level voltage to the other of the first and second diffusion regions, and a high level voltage to the gate electrode to trap charge carriers of the second conductivity in the carrier trap layer near the other of the first and second diffusion regions;
• and
• a data erase step capable of selectively controlling erase/non-erase on a bit unit basis, said data erase step selectively injecting carriers of the first conductivity type in the carrier trap layer by setting a potential of one of the first and second diffusion regions on an erase side to a high level, a potential of the other of the first and second diffusion regions to a low level, or to a high level or a floating level, and a potential of the gate electrode to a low level or an opposite polarity level.

A control method for a nonvolatile semiconductor memory having a number of nonvolatile semiconductor memory cells formed on a semiconductor substrate of a first conductivity type and disposed in m rows and n columns, the memory cells in a row direction being connected serially, each memory cell including a gate insulating film formed on a surface of the semiconductor substrate and including a carrier trap layer capable of trapping charge carriers, a gate electrode formed on the gate insulating film, and first and second diffusion regions of a second conductivity type formed in the semiconductor substrate on both sides of the gate electrode, and the nonvolatile memory having m word lines for connecting the gate electrodes of nonvolatile memory cells of a same row, and (n+1) bit lines for connecting first or second diffusion regions of nonvolatile semiconductor memory cells of a same column and, if there is an adjacent column to said first or second diffusion regions of said same column, for connecting second or first diffusion regions of nonvolatile semiconductor memory cells of the adjacent column, the control method comprising:

• an erase step of, when carriers of the second conductivity type written in an i-th row, j-th column nonvolatile semiconductor memory cell near the diffusion region connected to a (j+1)-th bit line are to be erased, applying a low level voltage or an opposite polarity voltage to an i-th word line, applying a low level voltage to first to (j−1)-th bit lines or setting the first to (j−1)-th bit lines to a floating state, applying a low level voltage to a j-th bit line, applying a high level voltage to the (j+1)-th bit line, and applying a high level signal to (j+2)-th and succeeding bit lines or setting the (j+2)-th and succeeding bit lines to a floating state, to inject carriers of the first conductivity type generated by an interband tunneling effect into the semiconductor memory cell near the diffusion region connected to the (j+1)-th bit line.