Small-area high-efficiency read-only memory (ROM) array and method for operating the same

A method for operating a small-area high-efficiency read-only memory (ROM) array, the small-area high-efficiency ROM array comprising a plurality of parallel bit lines, a plurality of parallel word common-source lines, and a plurality of sub-memory arrays, the plurality of parallel bit lines comprising a first bit line, a second bit line, a third bit line, and a fourth bit line adjacent to each other, the plurality of parallel word common-source lines, arranged perpendicular to the bit lines, comprising a first word common-source line, each of the plurality of sub-memory arrays connected to four of the bit lines and one of the word common-source lines, each of the plurality of sub-memory arrays comprises a first memory cell, a second memory cell, a third memory cell, and a fourth memory cell, the first memory cell connected to the first bit line and the first word common-source line, the second memory cell connected to the second bit line and the first word common-source line, the first memory cell and the second memory cell arranged adjacent to each other in a vertical direction, the third memory cell connected to the third bit line and the first word common-source line, the third memory cell and the first memory cell arranged adjacent to each other in a horizontal direction, the fourth memory cell connected to the fourth bit line and the first word common-source line and arranged at a point where the vertical direction corresponding to the third memory cell intersects the horizontal direction corresponding to the second memory cell, and the first memory cell, the second memory cell, the third memory cell, the fourth memory cell arranged between the first bit line and the fourth bit line, each of the first memory cell, second memory cell, third memory cell, and fourth memory cell comprises an N-type field-effect transistor in a P-type substrate or in a P-type well region, the first memory cell, second memory cell, third memory cell, and fourth memory cell are operation memory cells, one of the operation memory cells is chosen as a selected memory cell and remains of the operation memory cells are chosen as a plurality of unselected memory cells, wherein when operating on the selected memory cell, performing following voltage applications as required:

• providing a work power voltage Vdd,
• applying a substrate voltage Vsub to the P-type well region or the P-type substrate connecting to the selected memory cell,
• respectively applying a bit voltage Vb1 and a word common-source voltage Vws1 to the bit line and the word common-source line, which are connected to the selected memory cell, and
• respectively applying a bit voltage Vb2 and a word common-source voltage Vws2 to the bit line and the word common-source line, which are connected to each of the plurality of unselected memory cells;
• wherein in a write activity, the voltages satisfy following conditions:
• Vsub is grounded,
• Vb1 is equal to a medium voltage (MV) or 0 volt,
• Vws1 is equal to a high voltage (HV) or the MV,
• Vb2 is electrically floating, and
• Vws2=0 volt;
• wherein in an erase activity, the voltages satisfy following conditions:
• Vsub is grounded,
• Vb1 is equal to the HV,
• Vws1=0 volt,
• Vb2 is electrically floating, and
• Vws2 is equal to the MV;
• wherein in a read activity, the voltages satisfy following conditions:
• Vsub is grounded,
• Vws1>Vb1=0 volt,
• Vb2=Vws1, and
• Vws2 is grounded;
• wherein each of the first memory cell, the second memory cell, the third memory cell, and the fourth memory cell comprises a field-effect transistor (FET) with a drain, a source, and a gate;
• wherein the FETs of the first memory cell, the second memory cell, the third memory cell, and the fourth memory cell share a dielectric layer;
• wherein the dielectric layer partially overlaps the sources and the gates of the FETs;
• and
• wherein the source and the gate of each FET of the sub-memory array are each connected to the first word common-source line.

A method for operating a small-area high-efficiency read-only memory (ROM) array, the small-area high-efficiency ROM array comprising a plurality of parallel bit lines, a plurality of parallel word common-source lines, and a plurality of sub-memory arrays, the plurality of parallel bit lines comprising a first bit line, a second bit line, a third bit line, and a fourth bit line adjacent to each other, the plurality of parallel word common-source lines, arranged perpendicular to the bit lines, comprising a first word common-source line, each of the plurality of sub-memory arrays connected to four of the bit lines and one of the word common-source lines, each of the plurality of sub-memory arrays comprises a first memory cell, a second memory cell, a third memory cell, and a fourth memory cell, the first memory cell connected to the first bit line and the first word common-source line, the second memory cell connected to the second bit line and the first word common-source line, the first memory cell and the second memory cell arranged adjacent to each other in a vertical direction, the third memory cell connected to the third bit line and the first word common-source line, the third memory cell and the first memory cell arranged adjacent to each other in a horizontal direction, the fourth memory cell connected to the fourth bit line and the first word common-source line and arranged at a point where the vertical direction corresponding to the third memory cell intersects the horizontal direction corresponding to the second memory cell, and the first memory cell, the second memory cell, the third memory cell, the fourth memory cell arranged between the first bit line and the fourth bit line, each of the first memory cell, second memory cell, third memory cell, and fourth memory cell comprises a P-type field-effect transistor in an N-type substrate or in an N-type well region, the first memory cell, second memory cell, third memory cell, and fourth memory cell are operation memory cells, one of the operation memory cells is chosen as a selected memory cell and remains of the operation memory cells are chosen as a plurality of unselected memory cells, wherein when operating on the selected memory cell, performing following voltage applications as required:

• providing a work power voltage Vdd,
• applying a substrate voltage Vsub to the N-type well region or the N-type substrate connecting to the selected memory cell,
• respectively applying a bit voltage Vb1 and a word common-source voltage Vws1 to the bit line and the word common-source line, which are connected to the selected memory cell, and
• respectively applying a bit voltage Vb2 and a word common-source voltage Vws2 to the bit line and the word common-source line, which are connected to each of the plurality of unselected memory cells;
• wherein in a write activity, the voltages satisfy following conditions:
• Vsub is equal to a high voltage (HV),
• Vb1 is equal to a medium voltage (MV) or the HV,
• Vws1 is equal to 0 volt or the MV,
• Vb2 is electrically floating, and
• Vws2 is equal to the HV;
• wherein in an erase activity, the voltages satisfy following conditions:
• Vsub is equal to the HV,
• Vb1=0 volt,
• Vws1 is equal to the HV,
• Vb2 is electrically floating, and
• Vws2 is equal to the MV;
• wherein in a read activity, the voltages satisfy following conditions:
• Vsub=Vdd,
• Vb1>Vws1=0 volt, and
• Vws2=Vdd;
• wherein each of the first memory cell, the second memory cell, the third memory cell, and the fourth memory cell comprises a field-effect transistor (FET) with a drain, a source, and a gate;
• wherein the FETs of the first memory cell, the second memory cell, the third memory cell, and the fourth memory cell share a dielectric layer;
• wherein the dielectric layer partially overlaps the sources and the gates of the FETs;
• and
• wherein the source and the gate of each FET of the sub-memory array are each connected to the first word common-source line.