摘要:
A nonvolatile memory array has a plurality of PMOS two transistor (2T) memory cells. Each 2T cell (40) includes a PMOS floating gate transistor (40a) and a PMOS select transistor (40b) and is connected between a bit line and a common source line. The select gate and the control gate of each 2T cell in a common row are connected to a word line and to a control gate line, respectively. The 2T cells of the array are programmed using a combination of FN tunneling and BTBT induced hot electron injection, and are erased using FN tunneling. In some embodiments, the array is divided into sectors, where each sector is defined by an n-well region and includes a predetermined number of rows of the 2T cells. Here, the source of each 2T cell in a sector is coupled to a common source line of the sector. In other embodiments, the bit lines of the array are segmented along sector boundaries.
摘要:
A semiconductor fabrication process allows for the fabrication of high-voltage transistors, logic transistors, and memory cells where, as required for sub-0.3 micron device geometries, the gate oxide of the logic transistors is thinner than the tunnel oxide thickness of the non-volatile memory cells without the undesirable contamination of the gate oxide of the logic transistors or contamination of the tunnel oxide of the memory cells. In one embodiment, the tunnel oxide of the memory cells is grown to a desired thickness. In a next step, a layer of doped polysilicon which will serve as the floating gate of the memory cell(s) is immediately deposited over the tunnel oxide of the memory cells, thereby protecting the tunnel oxide from contamination in subsequent masking and etching steps. The gate oxide of the logic transistors and the gate oxide of the high-voltage transistors are then grown to a desired thickness.
摘要:
A P-channel MOS memory cell has P+ source (14) and drain (16) regions formed in an N-well (18). A thin tunnel oxide (24) is provided between the well surface and an overlying floating gate (22). In one embodiment, the thin tunnel oxide (24) extends over a substantial portion of the active region (12) of the device. An overlying control gate (26) is insulated from the floating gate (22) by an insulating layer (28). The device is programmed via hot electron injection from the drain end of the channel region (12) to the floating gate (22), without avalanche breakdown, which allows the cell to be bit-selectable during programming. Erasing is accomplished by electron tunneling from the floating gate (22) to the N-well (18) with the source (14), drain (16), and N-well (18) regions equally biased. Since there is no high drain/well junction bias voltage, the channel length of the cell may be reduced without incurring and destructive junction stress.
摘要:
A nonvolatile memory array has a plurality of PMOS two transistor (2T) memory cells. Each 2T cell (40) includes a PMOS floating gate transistor (40a) and a PMOS select transistor (40b) and is connected between a bit line and a common source line. The select gate and the control gate of each 2T cell in a common row are connected to a word line and to a control gate line, respectively. The 2T cells of the array are programmed using a combination of FN tunneling and BTBT induced hot electron injection, and are erased using FN tunneling. In some embodiments, the array is divided into sectors, where each sector is defined by an n-well region and includes a predetermined number of rows of the 2T cells. Here, the source of each 2T cell in a sector is coupled to a common source line of the sector. In other embodiments, the bit lines of the array are segmented along sector boundaries.
摘要:
A P-channel MOS memory cell has P+ source (14) and drain (16) regions formed in an N-well (18). A thin tunnel oxide (24) is provided between the well surface and an overlying floating gate (22). In one embodiment, the thin tunnel oxide (24) extends over a substantial portion of the active region (12) of the device. An overlying control gate (26) is insulated from the floating gate (22) by an insulating layer (28). The device is programmed via hot electron injection from the drain end of the channel region (12) to the floating gate (22), without avalanche breakdown, which allows the cell to be bit-selectable during programming. Erasing is accomplished by electron tunneling from the floating gate (22) to the N-well (18) with the source (14), drain (16), and N-well (18) regions equally biased. Since there is no high drain/well junction bias voltage, the channel length of the cell may be reduced without incurring and destructive junction stress.
摘要:
A P-channel single-poly non-volatile memory cell (10) having P+ source (20) and P+ drain regions (22) and a channel (30) extending therebetween is formed in an N-type well (12). An overlying poly-silicon floating gate (26) is separated from the N-well by a thin oxide layer (34). A P-type diffusion region (36) is formed in a portion of the N-well underlying the floating gate (26) and is thereby capacitively coupled to the floating gate (26). This P-type diffusion area serves as the control gate for the cell. Programming is accomplished by coupling a sufficient voltage to the floating gate (26) via the control gate (36) while biasing the source (20) and drain (22) regions so as to cause the tunneling of electrons from the P+ drain region (22) of the cell to the floating gate (26). In some embodiments, an additional P-type diffusion region underlying the floating gate and separated therefrom by a layer of tunnel oxide serve as an erase gate for the memory cell. In such embodiments, erasing of the cell is accomplished by causing electrons to tunnel from the floating gate to the erase gate.
摘要:
A P-channel flash EEPROM cell (40) has P+ source (50) and P+ drain (52) regions, and a channel (51) extending therebetween, formed in an N-type well (42). A thin layer of tunnel oxide (62) is provided over the channel (51). A poly-silicon floating gate (56) and poly-silicon control gate (58), separated by a dielectric layer (57), overlie the tunnel oxide (62). Programming is accomplished via hot electron injection while erasing is realized by electron tunneling. The threshold voltage of the cell may be precisely controlled by the magnitude of voltage coupled to the floating gate (56) during programming. Since the injection of hot electrons into the floating gate (56) is independent of variations in the thickness of the tunnel oxide layer (62) and the coupling ratio between the floating gate (56) and the control gate (58), programming operations and data retention are not affected by process variations. In addition, PMOS devices conduct a gate current via hot electron injection over a narrow range of gate voltages, thereby allowing for precise control over the gate current and thus over the charging of the floating gate. This control over the gate current, as well as the independence of the cell's threshold voltage of process parameters, advantageously allows the threshold voltage of the cell to be more accurately controlled, thereby resulting in a more reliable cell capable of storing a greater number of bits of data.