Abstract:
An apparatus and method for operating an array of NOR connected flash nonvolatile memory cells erases the array in increments of a page, block, sector, or the entire array while minimizing operational disturbances and providing bias operating conditions to prevent gate to source breakdown in peripheral devices. The apparatus has a row decoder circuit and a source decoder circuit for selecting the nonvolatile memory cells for providing biasing conditions for reading, programming, verifying, and erasing the selected nonvolatile memory cells while minimizing operational disturbances and preventing gate to source breakdown in peripheral devices.

Description:
This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application Ser. No. 61/131,554, filed on Jun. 9, 2008, which is herein incorporated by reference in its entirety. 
     This application claims priority under 35 U.S.C. §119 to U.S. Patent Application Ser. No. 61/132,122, filed on Jun. 16, 2008, assigned to the same assignee as the present invention, and incorporated herein by reference in its entirety. 
     This application claims priority under 35 U.S.C. §119 to U.S. Patent Application Ser. No. 61/132,628, filed on Jun. 20, 2008, assigned to the same assignee as the present invention, and incorporated herein by reference in its entirety. 
     RELATED PATENT APPLICATIONS 
     
         
         U.S. patent application Ser. No. 12/387,771, filed May 7, 2009. 
         U.S. patent application Ser. No. 12/455,337, filed Jun. 1, 2009. 
         U.S. patent application Ser. No. 12/456,354, filed Jun. 16, 2009. 
         U.S. patent application Ser. No. 12/456,744, filed Jun. 22, 2009. 
       
    
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to nonvolatile memory array structure and operation. More particularly, this invention relates to NOR nonvolatile memory device structures, peripheral circuits for NOR nonvolatile memory devices and methods for operation of NOR nonvolatile memory devices. 
     2. Description of Related Art 
     Nonvolatile memory is well known in the art. The different types of nonvolatile memory include Read-Only-Memory (ROM), Electrically Programmable Read Only Memory (EPROM), Electrically Erasable Programmable Read Only Memory (EEPROM), NOR Flash Memory, and NAND Flash Memory. In current applications such as personal digital assistants, cellular telephones, notebook and laptop computers, voice recorders, global positioning systems, etc., the Flash Memory has become one of the more popular types of Nonvolatile Memory. Flash Memory has the combined advantages of the high density, small silicon area, low cost, and can be repeatedly programmed and erased with a single low-voltage power supply voltage source. 
     The Flash Memory structures known in the art employ a charge retaining mechanism such as a charge storage phenomena and a charge trapping phenomena. In the charge storage mechanism, as with a floating gate nonvolatile memory, the charge representing digital data is stored on a floating gate of the device. The stored charge modifies the threshold voltage of the floating gate memory cell to determine the digital data stored. In a charge trapping mechanism, as in a Silicon-Oxide-Nitride Oxide-Silicon (SONOS) or Metal-Oxide-Nitride-Oxide-Silicon (MONOS) type cell, the charge is trapped in a charge trapping layer between two insulating layers. The charge trapping layer in the SONOS/MONOS devices has a relatively high dielectric constant (k) such as Silicon Nitride (SiN x ). 
     A present day flash nonvolatile memory is divided into two major product categories such as the fast random-access asynchronous NOR flash nonvolatile memory and the slower serial-access synchronous NAND flash nonvolatile memory. NOR flash nonvolatile memory devices, as presently designed are the high pin-count memory with multiple external address and data pins along with appropriate control signal pins. One disadvantage of NOR flash nonvolatile memory is, as the density is doubled, the number of the required external pin count increases by one due to the adding of one more external address pin. In contrast, NAND flash nonvolatile memory has an advantage of having a smaller pin-count than NOR with no address input pins. As density increases, the NAND flash nonvolatile memory pin count is always kept constant. Both main-streamed NAND and NOR flash nonvolatile memory cell structures in production today use a one charge retaining (charge storage or charge trapping) transistor memory cell that stores one bit of data as charge or as it commonly referred to as a single-level program cell (SLC). They are respectively referred as one-bit/one transistor NAND cell or NOR cell, storing a single-level programmed data in the cell. 
     The NAND and NOR flash nonvolatile memory provide the advantage of in-system program and erase capabilities and have a specification for providing at least 100K endurance cycles. In addition, both single-chip NAND and NOR flash nonvolatile memory product can provide giga-byte density because their highly-scalable cell sizes. For instance, presently a one-bit/one transistor NAND cell size is kept at ˜4λ 2  (A being a minimum feature size in a semiconductor process), while NOR cell size is ˜10λ 2 . Furthermore, in addition to storing data as a single-level program cell having two voltage thresholds (Vt 0  and Vt 1 ), both one transistor NAND and NOR flash nonvolatile memory cells are able to store at least two bits per cell or two bits/one transistor with four multi-level threshold voltages (Vt 0 , Vt 1 , Vt 2  and Vt 03 ) in one physical cell. 
     NOR flash memories cells are arranged in an array, of rows and columns in a NOR-like structure. All the NOR Flash cells on each row share the same word line. The drain electrodes that are common to two cells on each column are commonly connected to the bit line (BL) associated with each column. Sources of each of the NOR flash cells of each of the rows of the array are commonly connected to the source lines SL that are commonly connected and are often connected to the ground reference voltage source. 
     Currently, the highest-capacity of a single-chip double polycrystalline silicon gate NAND flash nonvolatile memory chip is 64 Gb. In contrast, a double polycrystalline silicon gate NOR flash nonvolatile memory chip has a density of 2 Gb. The big gap between NAND and NOR flash nonvolatile memory density is a result of the superior scalability of NAND flash nonvolatile memory cell over a NOR flash nonvolatile memory. A NOR flash nonvolatile memory cell requires 5.0V drain-to source (Vds) to maintain a high-current Channel-Hot-Electron (CHE) programming process. Alternately, a NAND flash nonvolatile memory cell requires a voltage difference between the drain to source of zero volts (0.0V) for a low-current Fowler Nordheim channel tunneling program process. This results in the one-bit/one transistor NAND flash nonvolatile memory cell size being approximately one-half that of a one bit/one transistor NOR flash nonvolatile memory cell. This permits a NAND flash nonvolatile memory device to be used in applications that require huge data storage. A NOR flash nonvolatile memory device is extensively used as a program-code storage memory which requires less data storage and requires fast and asynchronous random access. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a method for operating an array of NOR connected flash nonvolatile memory cells at increments of a page, block, sector, or an entire array while minimizing operational disturbances and providing bias operating conditions to prevent drain to source breakdown in peripheral devices. 
     Another object of this invention is to provide a row decoder circuit for selecting nonvolatile memory cells of an array of NOR connected nonvolatile memory cells for providing biasing conditions for reading, programming, verifying, and erasing the selected nonvolatile memory cells of the array of the NOR connected nonvolatile memory cells while minimizing operational disturbances and preventing drain to source breakdown in peripheral devices. 
     Further, another object of this invention is to provide a source decoder circuit for selecting and providing biasing conditions to selected nonvolatile memory cells of an array of NOR connected nonvolatile memory cells for reading, programming, verifying, and erasing the selected nonvolatile memory cells of the array of the NOR connected nonvolatile memory cells while minimizing operational disturbances and preventing drain to source breakdown of peripheral devices. 
     To accomplish at least one of these objects, a nonvolatile memory device includes an array of nonvolatile memory cells arranged in rows and columns. The nonvolatile memory cells are connected into a NOR configuration where the nonvolatile memory cells located on each column are connected such that the drains of each of the nonvolatile memory cells are commonly connected to a local bit line associated with each column. The nonvolatile memory cells on each row have their gates commonly connected to a word line. The nonvolatile memory cells on two adjacent rows have their sources commonly connected to a source line. The array of nonvolatile memory cells is partitioned into sectors, where each sector is placed in a first isolation well. Each sector of the array of the nonvolatile memory cells is divided into blocks and each block is divided into pages. Each page includes one row of the nonvolatile memory cells connected to a word line. 
     The nonvolatile memory device has a plurality of peripheral circuits that include a row decoder, a column decoder, and a source line decoder. The row decoder has a plurality of voltage isolators connected such that each voltage isolator is connected to the word lines of one block of the nonvolatile memory cells. Each voltage isolator is formed in a second isolation well such that biasing voltages as applied to the first and second isolation wells for reading, programming, erasing, and verifying selected nonvolatile memory cells do not exceed a low drain to source breakdown voltage of the peripheral circuits. Each of the peripheral circuit voltage isolators multiple pass gates are connected such that each pass gate transfers the operational signals to an associated word line for biasing control gates of charge retaining transistors of one row of the nonvolatile memory cells connected to the word line. 
     The row decoder has a first block selector that is activated when a block address indicates that a block is selected. The row decoder further includes a word line selector circuit connected to the first block selector, which, based on a row address, provides the word lines with word line operational voltage levels necessary for biasing the control gates of the nonvolatile memory cells for reading, programming, verifying, and erasing. The row decoder has a voltage level shifter for shifting a voltage level of a block select signal such that when the pass gates are activated, the operational voltage levels are transferred to the word lines of the selected block for biasing the control gates of the charge retaining transistors of the nonvolatile memory cells of the block for reading, programming, verifying, and erasing the selected nonvolatile memory cells. 
     The peripheral circuits of the nonvolatile memory device have a source decoder circuit that is connected to each source line within each block to transfer necessary source biasing voltage for reading, programming, verifying, and erasing selected nonvolatile memory cells to selected source lines. The source decoder circuit has a second block selector circuit that, when activated, selects the block being addressed. The block selector circuit is connected to a source voltage level shifter that shifts the voltage level of the block selector signals to transfer source line operational voltages to the source lines connected to the sources of the charge retaining transistors of the nonvolatile memory cells of the selected block for reading, programming, verifying, and erasing the selected nonvolatile memory cells. 
     The peripheral circuits of the nonvolatile memory device have a column decoder in communication with a local bit line for providing biasing voltages for reading, programming, verifying, and erasing selected nonvolatile memory cells. The row decoder, source decoder, and column decoder provide inhibit biasing voltage levels to all the non-selected nonvolatile memory cells to minimize disturbances resulting from the reading, programming, verifying, and erasing selected nonvolatile memory cells. 
     For reading a selected page of the array of nonvolatile memory cells, the row decoder transfers a voltage level of the power supply voltage source (VDD) to the word line of the selected nonvolatile memory cells for a single level program. The row decoder transfers an intermediate read voltage level to the word line of the selected nonvolatile memory cells for a multiple level program. The row decoder further transfers a ground reference voltage level to the word lines of the unselected nonvolatile memory cells. The column decoder transfers a first read biasing voltage of approximately +1.0V to the drains of the selected nonvolatile memory cells. The source decoder transfers the ground reference voltage level to the source lines of the selected nonvolatile memory cells and transfers a first source line read inhibit voltage to the source lines of unselected the nonvolatile memory cells. The magnitude of the power supply voltage source is either +1.8V or +3.0V. The magnitude of the first read inhibit voltage is approximately +1.0V 
     For erasing a selected page of the array of nonvolatile memory cells, a very high negative erase voltage is applied to the first isolation well into which the sector of nonvolatile memory cells is formed. A very high positive erase voltage is applied to the second isolation well into which the pass gate of the word line for the selected page of nonvolatile memory cells is formed. The ground reference voltage level is applied to the second isolation wells into which the pass gates of the word lines for the unselected pages of nonvolatile memory cells are formed. The row decoder of the selected page transfers a very high positive erase voltage to the word line of the selected nonvolatile memory cells and transfers the ground reference voltage level to the word lines of the unselected nonvolatile memory cells of the selected block. The row decoders of the unselected blocks of nonvolatile memory cells disconnect the word lines of the unselected nonvolatile memory cells so that the very high negative erase voltage is coupled from the isolation well to the word lines of the unselected nonvolatile memory cells in unselected blocks. The source line decoder transfers the very high negative erase voltage to the selected and unselected source lines. The voltage levels of the very high positive erase voltage and the very high negative erase voltage is less than or equal to the drain to source breakdown voltage level of approximately 10.0V for transistors forming the row decoder, column decoder, and the source line decoder. The magnitude of the very high positive erase voltage is from approximately +8.0V to approximately +10.0V and the magnitude of the very high negative erase voltage is from approximately −8.0V to approximately −10.0V. 
     For verifying a page erase, a selected page of the array of nonvolatile memory cells, the row decoder transfers a voltage level of a lower boundary of an erased threshold voltage level to the word line of the selected nonvolatile memory cells. The row decoder further transfers a ground reference voltage level to the word lines of the unselected nonvolatile memory cells. The column decoder transfers a second read biasing voltage to the drains of the selected nonvolatile memory cells. The source decoder transfers the ground reference voltage level to the source lines of the selected nonvolatile memory cells and transfers a second source line read inhibit voltage to the source lines of the unselected nonvolatile memory cells. The lower boundary of an erased threshold voltage level is approximately +5.0V for the single level cell program and the multiple level cell programming. The magnitude of the second read biasing voltage is pre-charged to approximately the magnitude of the power supply voltage source less a threshold voltage of an NMOS transistor. The magnitude of the second source line read inhibit voltage is approximately +1.0V. The pre-charged second read biasing voltage level is discharged to approximately 0.0V when the memory cell has not been successfully erased to have its threshold voltage level greater than the lower boundary of the erased threshold voltage level. If the nonvolatile memory cells are erased, the pre-charged level will be maintained. 
     For erasing a selected block of the array of nonvolatile memory cells, a very high negative erase voltage is applied to the first isolation well into which the sector of nonvolatile memory cells is formed. A very high positive erase voltage is applied to the second isolation wells into which the pass gates of the word lines for the selected block of nonvolatile memory cells are formed. The ground reference voltage level is applied to the second isolation wells into which the pass gates of the word lines for the unselected blocks of nonvolatile memory cells are formed. The row decoder transfers a very high positive erase voltage to the word lines of the nonvolatile memory cells of the selected block. The row decoders of the unselected blocks of nonvolatile memory cells disconnect the word lines of the unselected nonvolatile memory cells so that the very high negative erase voltage is coupled from the isolation well to the word lines of the unselected nonvolatile memory cells in unselected blocks. The source line decoder transfers the very high negative erase voltage to the selected and unselected source lines. The very high negative erase voltage is applied to the isolation well. The magnitude of the very high positive erase voltage and the very high negative erase voltage is less than or equal to the drain to source breakdown voltage level of approximately 10V for transistors forming the row decoder, column decoder, and the source line decoder. The magnitude of the very high positive erase voltage is from approximately +8.0V to approximately +10.0V and the magnitude of the very high negative erase voltage is from approximately −8.0V to approximately −10.0V. 
     For verifying a block erase, the row decoder transfers a voltage level of a lower boundary of an erased threshold voltage level to the word lines of the selected nonvolatile memory cells of the selected block. The row decoder further transfers a ground reference voltage level to the word lines of the unselected nonvolatile memory cells of the unselected block. The column decoder transfers the third read biasing voltage to the drains of the selected nonvolatile memory cells. The source decoder transfers the ground reference voltage level to the source lines of the selected nonvolatile memory cells and transfers the first source line read inhibit voltage to the source lines of the unselected nonvolatile memory cells. The lower boundary of an erased threshold voltage level is approximately +5.0V for the single level cell program and the multiple level cell programming. The magnitude of the third read biasing voltage is approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The magnitude of the first source line read inhibit voltage is approximately +1.0V. The lower boundary of an erased threshold voltage level is approximately +5.0V. The pre-charged level of the second read biasing voltage is discharged to approximately 0.0V when the memory cell has not been successfully erased to lower boundary of the erased threshold voltage level. If the nonvolatile memory cells are erased, the pre-charged level will be maintained when the threshold voltage of the erased nonvolatile memory cells is greater than the erased threshold voltage level. 
     For erasing a selected sector of the array of nonvolatile memory cells, a very high negative erase voltage is applied to the first isolation well into which the sector of nonvolatile memory cells is formed. A very high positive erase voltage is applied to the second isolation wells into which the pass gates of the word lines for the selected sector of nonvolatile memory cells are formed. The row decoder transfers a very high positive erase voltage to the word lines of the nonvolatile memory cells of the selected sector. The source line decoder transfers the very high negative erase voltage to the source lines. The magnitude of the very high positive erase voltage and the very high negative erase voltage is less than or equal to the drain to source breakdown voltage level of approximately 10V for transistors forming the row decoder, column decoder, and the source line decoder. The magnitude of the very high positive erase voltage is from approximately +8.0V to approximately +10.0V and the magnitude of the very high negative erase voltage is from approximately −8.0V to approximately −10.0V. 
     For verifying erasing a selected sector, the row decoder transfers the voltage level of a lower boundary of an erased threshold voltage level to the word lines of the selected nonvolatile memory cells. The row decoder further transfers a ground reference voltage level to the word lines of the unselected nonvolatile memory cells. The column decoder transfers the fourth read biasing voltage to the drains of the selected nonvolatile memory cells. The source decoder transfers the ground reference voltage level to the source lines of the selected sector of the nonvolatile memory cells. The lower boundary of an erased threshold voltage level is approximately 5.0V for the single level cell program and the multiple level cell programming. The magnitude of the fourth read biasing voltage is approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The lower boundary of an erased threshold voltage level is approximately +5.0V. The pre-charged level of the second read biasing voltage is discharged to approximately 0.0V when the memory cell has not been successfully erased to the erased threshold voltage level. If the nonvolatile memory cells are erased, the pre-charged read biasing voltage level will be maintained. 
     For programming a selected page of the array of nonvolatile memory cells, the ground reference voltage level is applied to the second isolation wells into which the pass gates of the word lines for the selected and unselected pages of nonvolatile memory cells are formed. The row decoder transfers a very high negative program voltage to the word line of the selected nonvolatile memory cells. The row decoder transfers a negative word line program inhibit voltage to the unselected word lines in the selected block and the unselected blocks of the array of nonvolatile memory cells. The column decoder transfers a high program select voltage to the bit lines and thus to the drains of the selected nonvolatile memory cells. The source line decoder transfers the ground reference voltage level to the source lines connected to the selected nonvolatile voltage cells. Alternately, the source line decoder disconnects the source lines connected to the selected nonvolatile voltage cells to allow them to float. The source line decoder transfers a source line program inhibit voltage to the source lines of the unselected nonvolatile memory cells. The magnitude of the very high negative program voltage is less than or equal to the breakdown voltage level of approximately 10.0V for transistors forming the row decoder. The magnitude of the high negative program voltage is from approximately −8.0V to approximately −10.0V. The magnitude of the negative word line program inhibit voltage is approximately −2.0V. The high program select voltage is approximately +5.0V. The source line program inhibit voltage is from approximately +1.5V to approximately +1.8V. 
     For verifying a page program, a selected page of the array of nonvolatile memory cells, the row decoder transfers a voltage level of an upper boundary of a programmed threshold voltage level to the word line of the selected nonvolatile memory cells when the array of nonvolatile memory cells are programmed for single level cell programming and iteratively transfers the upper boundaries of a first threshold voltage level, a second threshold voltage level and a third threshold voltage level when the array of nonvolatile memory cells are programmed for multiple level cell programming. The row decoder further transfers a ground reference voltage level to the word lines of the unselected nonvolatile memory cells. The column decoder transfers a fifth read biasing voltage to the drains of the selected nonvolatile memory cells. The source decoder transfers the ground reference voltage level to the source lines of the selected nonvolatile memory cells. The upper boundary of a programmed threshold voltage level is approximately +0.5V for the single level cell programming. The upper boundaries of a first threshold voltage level, a second threshold voltage level and a third threshold voltage level are respectively +0.5V, +2.0V, and +3.5V for the multiple level cell programming. The magnitude of the fifth read biasing voltage is approximately +5.0V. The magnitude of the second read inhibit voltage is pre-charged to approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The magnitude of the second source line read inhibit voltage is approximately +1.0V. The pre-charged level of the second read voltage is discharged to approximately 0.0V once memory cell has not been successfully programmed to the upper level of programmed threshold voltage level. If the nonvolatile memory cells are programmed, the pre-charged level will be maintained. 
     In other embodiments, a method for operating an array includes steps for providing the operating conditions for reading, page erasing, block erasing, sector erasing, page erase verifying, block erase verifying, sector erase verifying, page programming, and page program verifying of selected nonvolatile memory cells of the array of nonvolatile memory cells. In the step of reading a selected page of the array of nonvolatile memory cells, begins by transferring a voltage level of the power supply voltage source (VDD) to the word line of the selected nonvolatile memory cells when the array of nonvolatile memory cells are programmed with a single level program. An intermediate read voltage level is transferred to the word line of the selected nonvolatile memory cells when the array of nonvolatile memory cells is programmed with a multiple level program. A ground reference voltage level is transferred to the word lines of the unselected nonvolatile memory cells. A first read biasing voltage is transferred to the drains of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the source lines of the selected nonvolatile memory cells and a first source line read inhibit voltage is transferred to the source lines of the nonvolatile memory cells. The voltage level of the power supply voltage source (VDD) is either +1.8V or +3.0V. The magnitude of the first read biasing voltage is approximately +5.0V. The magnitude of the first source line read inhibit voltage is approximately +1.0V 
     In the step of erasing a selected page of the array of nonvolatile memory cells, a very high negative erase voltage is applied to the first isolation well into which the sector of nonvolatile memory cells is formed. A very high positive erase voltage is applied to the second isolation well into which the pass gate of the word line for the selected page of nonvolatile memory cells is formed. The ground reference voltage level is applied to the second isolation wells into which the pass gates of the word lines for the unselected pages of nonvolatile memory cells are formed. A very high positive erase voltage is transferred to the word line of the selected nonvolatile memory cells and the ground reference voltage level is transferred to the word lines of the unselected nonvolatile memory cells of the selected block. The step of erasing a selected pages continues with disconnecting the word lines of the unselected nonvolatile memory cells so that the very high negative erase voltage is coupled from the first isolation well to the word lines of the unselected nonvolatile memory cells in unselected blocks. The very high negative erase voltage is transferred to the selected and unselected source lines. The voltage levels of the very high positive erase voltage and the very high negative erase voltage are less than or equal to the drain to source breakdown voltage level of approximately WV for transistors forming the row decoder, column decoder, and the source line decoder. The magnitude of the very high positive erase voltage is from approximately +8.0V to approximately +10.0V and the magnitude of the very high negative erase voltage is from approximately −8.0V to approximately −10.0V. 
     In the step of verifying a page erase, a selected page of the array of nonvolatile memory cells, a voltage level of a lower boundary of an erased threshold voltage level is transferred to the word line of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the word lines of the unselected nonvolatile memory cells. A second read biasing voltage is transferred to the drains of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the source lines of the selected nonvolatile memory cells and a first source line read inhibit voltage is transferred to the source lines of the unselected nonvolatile memory cells. The lower boundary of an erased threshold voltage level is approximately +5.0V for the single level cell program and the multiple level cell is programming. The magnitude of the power supply voltage source is either +1.8V or +3.0V. The magnitude of the read biasing voltage is approximately +5.0V. The magnitude of the second read inhibit voltage is approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The magnitude of the first source line read inhibit voltage is approximately +1.0V. The pre charged level of the second read voltage is discharged to approximately 0.0V when the memory cell has not been successfully erased. If the nonvolatile memory cells are erased, the pre-charged second read biasing voltage level will be maintained. 
     In the step of erasing a selected block of the array of nonvolatile memory cells, a very high negative erase voltage is applied to the first isolation well into which the sector of nonvolatile memory cells is formed. A very high positive erase voltage is applied to the second isolation wells into which the pass gate of the word lines for the selected block of nonvolatile memory cells are formed. The ground reference voltage level is applied to the second isolation wells into which the pass gates of the word lines for the unselected blocks of nonvolatile memory cells are formed. A very high positive erase voltage is transferred to the word lines of the nonvolatile memory cells of the selected block. The word lines of the unselected nonvolatile memory cells are disconnected so that the very high negative erase voltage is coupled from the isolation well to the word lines of the unselected nonvolatile memory cells in unselected blocks. The very high negative erase voltage is transferred to the selected and unselected source lines. The voltage levels of the very high positive erase voltage and the very high negative erase voltage less than or equal to the drain to source breakdown voltage level of approximately 10V for transistors forming the row decoder, column decoder, and the source line decoder. The magnitude of the very high positive erase voltage is from approximately +8.0V to approximately +10.0V and the magnitude of the very high negative erase voltage is from approximately −8.0V to approximately −10.0V. 
     In the step of verifying a block erase, a voltage level of a lower boundary of an erased threshold voltage level is transferred to the word lines of the selected nonvolatile memory cells of the selected block. The ground reference voltage level is transferred to the word lines of the unselected nonvolatile memory cells of the unselected blocks. The third read biasing voltage is transferred to the drains of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the source lines of the selected block of the nonvolatile memory cells and a third source line read inhibit voltage is transferred to the source lines of the unselected nonvolatile memory cells. The magnitude of the second read biasing voltage is pre-charged to approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The magnitude of the third source line read inhibit voltage is approximately +1.0V. The pre-charged second read biasing voltage level of the second read voltage is discharged to approximately 0.0V when the memory cell has not been successfully erased. If the nonvolatile memory cells are erased, the pre charged level will be maintained. 
     In the step for erasing a selected sector of the array of nonvolatile memory cells, a very high negative erase voltage is applied to the first isolation well into which the sector of nonvolatile memory cells is formed. A very high positive erase voltage is applied to the second isolation wells into which the pass gates of the word lines for the selected sector of nonvolatile memory cells are formed. A very high positive erase voltage is transferred to the word lines of the nonvolatile memory cells of the selected sector. The very high negative erase voltage is transferred to the source lines. The very high negative erase voltage is applied to the isolation well. The voltage levels of the very high positive erase voltage and the very high negative erase voltage are less than or equal to the drain to source breakdown voltage level of approximately 10V for transistors forming the row decoder, column decoder, and the source line decoder. The magnitude of the very high positive erase voltage is from approximately +8.0V to approximately +10.0V and the magnitude of the very high negative erase voltage is from approximately −8.0V to approximately −10.0V. 
     For verifying erasing a sector, a voltage level of a lower boundary of an erased threshold voltage level is transferred to the word lines of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the word lines of the unselected nonvolatile memory cells. The fourth read biasing voltage is transferred to the drains of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the source lines of the selected nonvolatile memory cells. The magnitude of the fourth read biasing voltage is approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The pre charged fourth read biasing voltage level is discharged to approximately 0.0V when the memory cell has not been successfully erased. If the nonvolatile memory cells are erased, the pre-charged fourth read biasing voltage level will be maintained. 
     In the step for programming a selected page of the array of nonvolatile memory cells, a very high negative program voltage is transferred to the word line of the selected nonvolatile memory cells. A negative word line program inhibit voltage is transferred to the unselected word lines in the selected block and the unselected word lines of the unselected blocks of the array of nonvolatile memory cells. A high program select voltage is transferred to the bit lines and thus to the drains of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the source lines connected to the selected nonvolatile voltage cells. Alternately, the source lines connected to the selected nonvolatile voltage cells are disconnected to be floating. A source line program inhibit voltage is transferred to the source lines of the unselected nonvolatile memory cells. The voltage level of the very high negative program voltage is less than or equal to the drain to source breakdown voltage level of approximately 10.0V for transistors forming the row decoder. The magnitude of the high negative program voltage is from approximately −8.0V to approximately −10.0V. The magnitude of the negative bit line program inhibit voltage is approximately −2.0V. The high program select voltage is approximately +5.0V. The source line program inhibit voltage is from approximately +1.5V to approximately +1.8V. 
     In the step for verifying a page program, a selected page of the array of nonvolatile memory cells, The voltage level of an upper boundary of a programmed threshold voltage level is transferred to the word line of the selected nonvolatile memory cells when the array of nonvolatile memory cells are programmed with a single level cell programming and iteratively transfers the upper boundaries of a first threshold voltage level, a second threshold voltage level and a third threshold voltage level to the word line of the selected nonvolatile memory cells when the array of nonvolatile memory cells are programmed with multiple level cell programming. The ground reference voltage level is transferred to the word lines of the unselected nonvolatile memory cells. A fifth read biasing voltage is transferred to the drains of the selected nonvolatile memory cells. The ground reference voltage level is transferred to the source lines of the selected nonvolatile memory cells and transfers a fifth source line read inhibit voltage to the source lines of the unselected nonvolatile memory cells. The upper boundary of a programmed threshold voltage level is approximately +0.5V for the single level cell programming. The upper boundaries of a first threshold voltage level, a second threshold voltage level and a third threshold voltage level are respectively+0.5V, +2.5V, and +3.5V for the multiple level cell programming. The magnitude of the read biasing voltage is pre-charged to approximately the voltage level of the power supply voltage source less a threshold voltage of an NMOS transistor. The magnitude of the fifth source line read inhibit voltage is approximately +1.0V. The pre-charged level of the fifth read biasing voltage is discharged to approximately 0.0V when the memory cell has not been successfully erased. If the nonvolatile memory cells are erased, the pre charged fifth read biasing voltage level will be maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a top plan layout view of a single transistor floating-gate NMOS NOR flash cell of the prior art. 
         FIG. 1   b  is a cross sectional view of a single transistor floating-gate NMOS NOR flash cell of the prior art. 
         FIG. 1   c  is a schematic diagram of a single transistor floating-gate NMOS NOR flash cell of the prior art. 
         FIG. 1   d  is a graph of two threshold voltage distributions of a single transistor floating-gate NMOS NOR flash cell having a positive erase level and a single positive program level of the prior art. 
         FIG. 1   e  is a graph of four threshold voltage distributions of a single transistor floating-gate NMOS NOR flash cell having a positive erase level and three positive program levels of the prior art. 
         FIG. 2   a  is a schematic diagram of a serial string of floating-gate transistor NMOS NOR flash cells. 
         FIG. 2   b  is a top plan layout view of a serial string of floating-gate transistor NMOS NOR flash cells. 
         FIG. 2   c  is a cross sectional view of a floating-gate transistor NMOS NOR flash cell. 
         FIG. 2   d  is a plot of two threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell having a positive program level and a single positive erase level of one implementation embodying the principles of the present invention. 
         FIG. 2   e  is a plot of four threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell having a positive erase level and three positive program levels of one implementation embodying the principles of the present invention. 
         FIG. 2   f  is a plot of two threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell having a positive program level and a single positive erase level shifted while biasing the source line to a magnitude of approximately +1.0V. 
         FIG. 2   g  is a plot of four threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell having a positive erase level and three positive program levels shifted while biasing the source line to a magnitude of approximately +1.0V. 
         FIGS. 3   a - 3   c  are schematic diagrams of floating-gate transistor NMOS NOR flash cells illustrating the bias conditions reading, programming and page erasing of a floating-gate transistor NMOS NOR flash cells embodying the principles of the present invention. 
         FIG. 4  is a block diagram of a nonvolatile memory device embodying the principles of the present invention. 
         FIG. 5  is a schematic diagram illustrating an array of floating-gate transistor NMOS NOR flash cells. of  FIG. 4  embodying the principles of the present invention. 
         FIG. 6  is a schematic diagram of a block row decoder of the nonvolatile memory device of  FIG. 4  embodying the principles of the present invention. 
         FIG. 7  is a schematic diagram of a level shifter circuit of the block row decoders of  FIG. 6  embodying the principles of the present invention. 
         FIG. 8  is a schematic diagram of source line decoder of the nonvolatile memory device of  FIG. 4  embodying the principles of the present invention. 
         FIG. 9  is a schematic diagram of a source line selector/conditioner of the source line decoder of  FIG. 8  embodying the principles of this invention. 
         FIG. 10  is flow chart for the method for operating the nonvolatile memory device of  FIG. 4 . 
         FIG. 11  is flow chart for the method for erasing and erase verifying a page, block, or sector of the nonvolatile memory device of  FIG. 4 . 
         FIG. 12  is flow chart for the method for programming and program verifying a page of the nonvolatile memory device of  FIG. 4 . 
         FIG. 13   a  is a table illustrating the voltage conditions applied to an array of a floating-gate transistor NMOS NOR flash cells having single level programmed cells (SLC) embodying the principles of the present invention. 
         FIG. 13   b  is a table illustrating the voltage conditions applied to an array of a floating-gate transistor NMOS NOR flash cells having multiple-level programmed cells (MLC) embodying the principles of the present invention. 
         FIG. 14   a  is a table illustrating the voltage conditions applied to the row decoder of  FIG. 6  for the nonvolatile memory device having single level programmed cells (SLC) embodying the principles of the present invention. 
         FIG. 14   b  is a table illustrating the voltage conditions applied to the row decoder of  FIG. 6  for the nonvolatile memory device for nonvolatile memory device having multiple-level programmed cells (MLC) embodying the principles of the present invention. 
         FIG. 15  is a table illustrating the voltage conditions applied to the source line decoder of  FIG. 6  for the nonvolatile memory device for nonvolatile memory device embodying the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1   a  is a top plan view of a NMOS NOR flash floating-gate transistor  110  of the prior art.  FIG. 1   b  is a cross sectional view NMOS NOR flash floating-gate transistors  110  of the prior art.  FIG. 1   c  is the schematic symbol NMOS NOR flash floating-gate transistors  110  of the prior art. The floating-gate type NMOS NOR flash transistor cell  110  is formed in the top surface of a substrate  140 . An N-type material is diffused into the surface of the P-type substrate  140  to form a deep N-well  135 . A P-type material is then diffused into the surface of the deep N-well  135  to form a P-well  130  (commonly referred to as a triple P-well). The N-type material is then diffused into the surface of a P-type well  130  to form the drain (D)  115  and the self-aligned source (S)  120  of the NMOS NOR flash floating-gate transistor  110 . A first polycrystalline silicon layer is formed above the bulk region  132  of the P-type well  130  between the drain region  115  and the source region  120  to form the floating gate  145 . A second polycrystalline silicon layer is formed over the floating gate  145  to create a control gate (G)  125  of the NMOS NOR flash floating-gate transistors  110 . The self-aligned source  120  is formed self-aligned between two adjacent second polycrystalline silicon layers of two control gates  125  of a pair of NMOS NOR flash floating-gate transistors  110 . The self-aligned source  120  is commonly used in NMOS NOR flash floating-gate transistors  110  to reduce the source line pitch. 
     The gate length of the NMOS NOR flash floating-gate transistors  110  is the channel region  132  in the bulk region of P-type well  130  between drain region  115  and the source region  120 . The NMOS NOR flash floating-gate transistor&#39;s  110  channel width is determined by the width of the N-diffusion of the drain  115  and the source  120 . The typical unit size of the NMOS NOR flash floating-gate transistors  110  is about 10λ 2  to 12λ 2 . 
     The floating-gate layer  145  stores electron charges to modify the threshold voltage of the NMOS NOR flash floating-gate transistors  110 . In all operations, the P-type substrate  140  is connected to a ground reference voltage source (GND). The deep N-well  135  is connected to the power supply voltage source (VDD) in read and program operations and is connected to a large positive programming voltage level of approximately +10V in the Fowler-Nordheim channel erase operation. In present designs of NMOS NOR flash floating-gate transistors  110 , the power supply voltage source is either 1.8V or 3.0V. The triple P-type well  130  is connected to the ground reference voltage in normal read and program operation and is connected to a large positive erasing voltage level of approximately +10V during erase operation. In other words, during the Fowler-Nordheim channel erase operation, both the deep N-well  135  and the triple P-well  130  are biased with the same voltage of approximately +10V to avoid forward leakage current through the P/N junction through the deep N-well  135  and the triple P-well  130 . 
     In an array of NMOS NOR flash floating-gate transistors  110 , the NMOS NOR flash floating-gate transistors  110  are arranged in rows and columns. The second polycrystalline silicon layer  125  that is the control gate of the NMOS NOR flash floating gate transistors  110  is extended to form a word-line that connects to each of the NMOS NOR flash floating-gate transistors  110  on a row of the array. 
     A tunnel oxide  150  is formed on top of the channel region  132  between the drain region  115  and the source region  120  and the floating-gate  145 . The thickness of the tunnel oxide  150  typically 100 Å. The tunnel oxide  150  is the layer through which the electron charges pass during the high current channel-hot-electron programming and low current Fowler-Nordheim channel erasing. In a traditional NOR operation, Fowler-Nordheim channel erasing expels stored electrons from the floating gate  145  through the tunnel oxide  150  to cell&#39;s channel region  132  into the triple P-type well  130 . 
     After an erase operation, fewer electron charges are stored in the floating gate  145  that results in a decrease in the NMOS NOR flash floating-gate transistor&#39;s  110  first threshold voltage level (Vt 0 ) of less than approximately 2.5V. In contrast, in a channel-hot-electron program operation, electrons are attracted into floating-gate  145  so that the NMOS NOR flash floating-gate transistor&#39;s  110  second threshold voltage level (Vt 1 ) is set to the voltage greater than approximately 4.0V. The distributions of the first threshold voltage level (Vt 0 ) for an erased state with a wide distribution and the second threshold voltage level (Vt 1 ) for a programmed state with a narrow distribution are set to be positive to avoid any false reading induced by the NMOS NOR flash floating-gate transistors  110  having a negative threshold voltage level. 
       FIG. 1   d  is a graph of two threshold voltage distributions of a single transistor floating-gate NMOS NOR flash cell having a single program level. After an erase operation, there are fewer electron charges in the floating-gate  145  that result in lowering the threshold voltage of the NMOS NOR flash floating-gate transistors  110 . Normally, the erased NMOS NOR flash floating-gate transistors  110  has a maximum value of its threshold voltage set to approximately +2.5V. In contrast, in channel-hot electron-programming, electrons are attracted to the floating-gate  145  so that threshold voltage of the NMOS NOR flash floating-gate transistors  110  is increased to a minimum voltage level of approximately +4.0V. By convention, the erased voltage threshold (Vt 0 ) value of approximately +2.5V is designated as a logical data value of “1” and the programmed voltage threshold (Vt 1 ) of +4.0V is designated as a logical data value of “0”. The NMOS NOR flash floating-gate transistors  110  store a single bit of data is referred to as a one-bit/one-transistor NMOS NOR flash floating-gate cell ( 1   b   1 T). 
       FIG. 1   e  is a graph of four threshold voltage distributions of a single transistor floating-gate NMOS NOR flash cell having one erase level and three program levels. It is known in the art that by varying the program conditions more than two threshold voltage levels can be created based on the quantity of charge placed on the floating-gate  145  of the NMOS NOR flash floating-gate transistors  110 . This is commonly referred to as multiple level programming of a NMOS NOR flash floating-gate cell or multi-level programmed cell. In this example, there are four threshold voltage levels that can be programmed to the NMOS NOR flash floating-gate transistors  110 . The least positive wide-distribution threshold voltage level Vt 0  is the erased voltage level with a maximum value of +2.5V for storing a logical data value of “11”. The three positive narrow-distribution programmed voltage threshold voltage levels are set to be sufficiently spaced apart to allow accurate detection. In the present example, the first of the three positive voltage threshold levels Vt 1  has a nominal value of approximately −3.25V for storing a logical data value “10”. The second of the three voltage positive threshold levels Vt 2  has a nominal value of approximately +4.25V for storing a logical data value “01”. The third of the three positive voltage threshold level Vt 3  has a nominal value of approximately +5.25V for storing a logical data value “00”. Since each NMOS NOR flash floating-gate transistor  110  stores four distinctive positive threshold voltage states, each NMOS NOR flash floating-gate transistor  110  stores two bits binary data and is referred to as a two-bit/one-transistor NMOS NOR flash cell ( 2   b / 1 T). 
     The nominal values of threshold voltages Vt 1  and Vt 2  of the NMOS NOR flash floating-gate transistors  110  may vary by more than 1.0V among different designs. The nominal values of threshold voltages Vt 0  and Vt 3  can have a wider threshold voltage distribution. For example, the threshold voltage Vt 0  is may vary from approximately 1.0V to approximately 2.5V. The threshold voltage Vt 3  can have much wider distribution. It must have a voltage greater than approximately 4.5V to ensure that the NMOS NOR flash floating-gate transistors  110  is in a non-conduction state. The assigned designations of 2-bit data states for four threshold voltage states may also vary between NMOS NOR flash floating-gate cell designs as described above in the NMOS NAND flash floating-gate cell. 
       FIG. 2   a  is a schematic diagram of a serial string of floating-gate transistor NMOS NOR flash cells.  FIG. 2   b  is a top plan layout view of a serial string of floating gate transistor NMOS NOR flash cells.  FIG. 2   c  is a cross sectional view of a floating gate transistor NMOS NOR flash cell. The two-transistor floating-gate type NMOS NOR flash cell  210  is formed in a P-type well TPW  244  within a deep N-well DNW  242  that are formed in the top surface of a P-type substrate  240 . An N-type material is then diffused into the surface of the P-type well TPW  240  to form the drains (D)  215   a  and  215   b  of the two NMOS NOR floating gate transistors  205   a  and  205   b  and the self aligned source (S)  220 . The self-aligned source (S)  220  is shared by the two NMOS NOR floating gate transistors  205   a  and  205   b . A first polycrystalline silicon layer is formed over the bulk regions  230   a  and  230   b  between the drain regions  215   a  and  215   b  and the self-aligned source region  220  to form the floating gates  245   a  and  245   b . A second polycrystalline silicon layer is formed over the floating gates  245   a  and  245   b  to create the control gates (G)  225   a  and  225   b  of the floating-gate transistors  205   a  and  205   b . The self-aligned source  220  is formed self-aligned between two adjacent second polycrystalline silicon layers of two control gates  225   a  and  225   b  of a pair of NMOS NOR two floating gate transistors  205   a  and  205   b . The self-align source  220  is commonly used in NMOS NOR flash floating-gate transistors  210  to reduce the source line pitch. The drain regions  215   a  and  215   b  each have a metal contact  250   a  and  250   b.    
     Each of the control gates control gates  225   a  and  225   b  are connected to word lines  270   a  and  270   b . The word lines  270   a  and  270   b  connecting each of the control gates  225   a  and  225   b  of the floating gate transistors  205   a  and  205   b  located on a row of an array of the NMOS NOR floating gate transistors  205   a  and  205   b . The two metal contacts  250   a  and  250   b  are connected to and shorted by a common metal bit line  255 . The self-aligned source (S)  220  is connected to source line  260 . Having the sources  220  and drains  215   a  and  215   b  of each pair of the NMOS NOR flash floating-gate transistors  210  connected together places the devices essentially in parallel. 
       FIG. 2   d  is a plot of two threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell having a positive program level and a single positive erase level for a single level program cell (SLC) of one implementation embodying the principles of the present invention. The NMOS NOR floating gate transistors  205   a  or  205   b  may be programmed as single level program cells in which the source line  260  and the P-type well TPW  244  are biased to the voltage level of the ground reference voltage (0.0V). The programmed threshold voltage level Vt 0  is the programmed state for storing a datum of a logical “0”. The erased threshold voltage level Vt 1  is the erased state for storing a datum of a logical “1”. The programmed state is accomplished using a Fowler-Nordheim edge programming scheme and the erase state is accomplished using a Fowler-Nordheim channel erase scheme. The low and narrow programmed threshold voltage level Vt 0  is the result of a bit-by-bit and iterative program operation such that the programmed threshold voltage level Vt 0  is easily be controlled. A low and narrow distribution programmed threshold voltage level Vt 0  achieves a fast, low-voltage VDD read operation such that there is no requirement for boosted voltage applied to the word lines  270   a  and  270   b  voltage. In the prior art the word lines  270   a  and  270   b  are usually boosted to a voltage level that is higher than the voltage level of the power supply voltage source VDD by a charge-pump circuit. 
     The positive erased state of threshold voltage level Vt 1  for storing a datum of a logical “1” may have a wide distribution of threshold voltage levels between the floating gate transistors  205   a  and  205   b . The lower boundary of the distribution of the erased threshold voltage level Vt 1  is larger than approximately +5.0V. The programmed threshold voltage level Vt 0  for storing a datum of a logical “0” has distribution ranging from the lower boundary of the programmed threshold voltage level Vt 0 L of approximately 0.0V to an upper boundary of the programmed threshold voltage level Vt 0 H of approximately +0.5V. The nominal value of the programmed threshold voltage level Vt 0  is approximately +0.25V. The preferred word line  270   a  and  270   b  read voltage, VRWL to distinguish between a logical “0” and a logical “1” may be set to a voltage level of the power supply voltage source VDD. The word line read voltage level VRWL is set between upper boundary of the programmed threshold voltage Vt 0 H and the lower boundary of the erased threshold voltage level Vt 1 L for a single level programmed cell read operation. This permits the read operation to occur without having a boosted read voltage applied to the word lines  270   a  and  270   b.    
       FIG. 2   e  is a plot of four threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell having a positive erase level and three positive program levels for multiple level cell programming. The NMOS NOR floating gate transistors  205   a  or  205   b  may be programmed as multiple level program cells in which the source line  260  and the P-type well TPW  244  are biased to the voltage level of the ground reference voltage (0.0V). The four threshold voltages of this implementation include a high, wide, positive erased threshold voltage level Vt 3 , a first positive programmed state Vt 2 , a second positive programmed threshold voltage level Vt 1 , and a third positive programmed threshold voltage level Vt 0 . The positive erased threshold voltage level Vt 3  stores a data of a logical “11” of 2-bit digital data with a lower boundary of the positive erased threshold voltage level Vt 3  that is greater than +5.0V. The second threshold voltage level is a narrow programmed threshold voltage level Vt 2  for a storing a data of a logical “01”. The first programmed threshold voltage level Vt 2  has a nominal value of approximately +3.25V with a distribution of 0.5V about the nominal value. The lower boundary of the first programmed threshold voltage level Vt 2 L is approximately +3.0V and the upper boundary of the first programmed threshold voltage level Vt 2 H is approximately +3.5V. The third threshold voltage level is a narrow second positive programmed threshold voltage level Vt 1  for storing a data of a logical “10” of 2-bit digital data. The second positive programmed threshold voltage level Vt 1  has a nominal value of approximately +1.75V with a distribution of approximately 0.5V. The lower boundary of the second positive programmed threshold voltage level Vt 1 L is approximately +1.5 and the upper boundary of the second positive programmed threshold voltage level Vt 1 H is approximately +2.0V. The fourth threshold voltage level is a narrow third positive programmed threshold voltage level Vt 0  for storing a data of a logical “00” of 2-bit digital data. The third positive programmed threshold voltage level Vt 0  has a nominal value of approximately +0.25V with a distribution of approximately 0.5V. The lower boundary of the third positive programmed threshold voltage level Vt 0 L is approximately +0.0V and the upper boundary of the second positive programmed threshold voltage level Vt 0 H is approximately +0.5V. 
       FIG. 2   f  is a plot of two threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell that is shifted while biasing the source line to a magnitude of approximately 1.0V and having a positive program level and a single positive erase level. The programmed threshold voltage level Vt 0  and the erased threshold voltage level Vt 1  for the NMOS NOR floating gate transistors  205   a  or  205   b  are the same as those shown in  FIG. 2   d  except the source line  260  and is biased to a magnitude of approximately +1.0V. The threshold voltage shift of +1.0V in a positive direction does consider the NMOS body-effect. The programmed threshold voltage level Vt 0  has a distribution that varies from lower boundary of the programmed state Vt 0 L of approximately +1.0V to upper boundary of the programmed threshold voltage level Vt 0 H of approximately +1.5V. Similarly, the lower boundary of the distribution of the erased threshold voltage level Vt 1 L is shifted to approximately +6.0V. 
       FIG. 2   g  is a plot of four threshold voltage distributions of a floating-gate transistor NMOS NOR flash cell that is shifted while biasing the source line to a magnitude of approximately 1.0V and having a positive erased state Vt 3 , a first positive programmed state Vt 2 , a second positive programmed state Vt 1 , and a third positive programmed state Vt 0 . The threshold voltages Vt 3 , Vt 2 , Vt 1 , and Vt 0  have distributions that are similar to those described in  FIG. 2   e , except the source line  260  is biased to a magnitude of approximately +1.0V. Shifting the threshold voltage levels Vt 3 , Vt 2 , Vt 1 , and Vt 0  does not consider the NMOS body-effect. The positive erased threshold voltage level Vt 3  has the lower boundary Vt 3 L of approximately +6.0V. The first positive programmed threshold voltage level Vt 2  varies from the lower boundary Vt 2 L of approximately +4.0V to an upper boundary Vt 2 H of approximately +4.25V. The second positive programmed threshold voltage level Vt 1  varies from the lower boundary Vt 2 L of approximately +2.5V to an upper boundary Vt 0 H of approximately +3.0V. The third positive programmed threshold voltage level Vt 0  varies from the lower boundary Vt 0 L of approximately +1.0V to an upper boundary Vt 0 H of approximately +1.5V. 
       FIGS. 3   a - 3   c  are schematic diagrams of floating-gate transistor NMOS NOR flash cells illustrating the bias conditions for reading, programming and page erasing of a floating-gate transistor NMOS NOR flash cells embodying the principles of the present invention. The schematic diagrams of  FIGS. 3   a - 3   c  represent a sector  300  of an array of NOR flash cells  310   a , . . . ,  310   n  that include the NMOS floating gate transistors M 0 , M 1  and M 2 , and M 3 . The NMOS NOR flash floating gate transistors M 0 , M 1 , M 2 , and M 3  are arranged in rows and columns. The drains of the NMOS NOR flash floating gate transistors M 0  and M 1  are commonly connected to the local bit line LBL  325 . The sources of the NMOS NOR flash floating gate transistors M 0  and M 1  are commonly connected to the source line SL0  315   a . Similarly the drains of the NMOS NOR flash floating gate transistors M 2 , and M 3  are commonly connected to the local bit line LBL  325 . The sources of the NMOS NOR flash floating gate transistors M 2  and M 3  are commonly connected to the source line SLn  315   n.    
     The control gate of the NMOS NOR flash floating gate transistor M 0  of the block  310   a  is connected to the word line WL0  320   a  and the control gate of the NMOS NOR flash floating gate transistor M 1  of the block  310   a  is connected to the word line WL1  320   b . Similarly, the control gate of the NMOS NOR flash floating gate transistor M 0  of the block  310   n  is connected to the word line WL0  321   a  and the control gate of the NMOS NOR flash floating gate transistor M 1  of the block  310   n  is connected to the word line WL1  321   b.    
     The illustrated sector  300  of the NMOS NOR flash floating gate transistors M 0 , M 1 , M 2 , and M 3  are formed in a common P-type well  305 . The word lines  320   a , and  320   b , and  321   a , and  321   b  are connected to a row decoder that decodes a block and row address and applies the appropriate voltages to the word lines  320   a , and  320   b , and  321   a , and  321   b  for reading, programming, and erasing the block  310   a , . . . ,  310   n . The source lines  315   a , . . . ,  315   n  are connected to a source line decoder that decodes a block and row address and applies to the appropriate voltage levels to the source lines  315   a , . . . ,  315   n  for reading, programming, and erasing the block. The bit line  325  is connected to a column decoder that decodes a column address and applies the appropriate biasing for reading, programming, and erasing a block. 
       FIG. 3   a  illustrates the biasing voltages for selecting the NMOS NOR flash floating gate transistor M 0  of the block  310   a  for reading. The word line  320   a  connected to the selected page of the block  310   a  and containing the NMOS NOR flash floating gate transistor M 0  is set to the voltage level of the word line read voltage VRWL or approximately the level of the power supply voltage source VDD. The unselected word line  320   b  of the selected block  310   a  and the word lines  321   a  and  321   b  of the unselected block  310   n  are set to the voltage level of the of the ground reference voltage level (0.0V). The source line  315   a  connected to the selected NMOS NOR flash floating gate transistor M 0  is set to the voltage level of the ground reference voltage level (0.0V). The source line  315   n  that is connected to the unselected block  310   n  is set to a first source line inhibit biasing voltage VS 1  of approximately +1.0V. The bit line LBL  325  is set to the read biasing drain voltage VRB of approximately +1.0V. The P-type well TPW  305  is set to the voltage level of the ground reference voltage source (0.0V). If the selected NMOS NOR flash floating gate transistor M 0  of the block  310   a  is erased as a logical “1”, the selected NMOS NOR flash floating gate transistor M 0  will not turn on and a sense amplifier will detect the programmed level of the logical “1”. Alternately, if the selected NMOS NOR flash floating gate transistor M 0  of the block  310   a  is programmed with a logical “0”, the selected NMOS NOR flash floating gate transistor M 0  will turn on and a sense amplifier will detect the programmed level of the logical “0”. 
       FIG. 3   b  illustrates the biasing voltages for selecting the NMOS NOR flash floating gate transistor M 0  of the block  310   a  for programming. The word line  320   a  connected to the selected page of the block  310   a  and containing the NMOS NOR flash floating gate transistor M 0  is set to the voltage level of the very high negative program voltage NPVL. The very high negative program voltage NPVL has a magnitude of from approximately −8.0V to approximately −10.0V. The P-type well TPW  305  is set to the voltage level of the ground reference voltage source (0.0V). The unselected word line  320   b  of the selected block  310   a  and the word lines  321   a  and  321   b  of the unselected block  310   a  are set to program inhibit voltage PIVL. The program inhibit voltage PIVL has a magnitude of approximately −2.0V. The source line  315   a  that is connected to the selected NMOS NOR flash floating gate transistor M 0  is set to the voltage level of the ground reference voltage. The source line  315   n  that is connected to the unselected block  310   n  is set to a second source line inhibit biasing voltage VS 2  that has a magnitude of from approximately +1.5V to approximately 1.8V. The bit line LBL  325  is set to the high program select voltage PSV. The high program select voltage PSV has a magnitude of approximately +5.0V. If the selected NMOS NOR flash floating gate transistor M 0  is not to be programmed (i.e. remain erased), the bit line LBL  325  is set to the voltage level of the ground reference voltage to inhibit the programming of the NMOS NOR flash floating gate transistors that are to remain erased. 
       FIG. 3   c  illustrates the biasing voltages for selecting the NMOS NOR flash floating gate transistor M 0  of the block  310   a  for page erasing. The word line  320   a  connected to the selected page to be erased of the block  310   a  and containing the NMOS NOR flash floating gate transistor M 0  is set to the magnitude of the very high positive erase voltage PEVL. The positive erase voltage PEVL has a magnitude of from approximately +8.0V to approximately +10.0V. The P-type well TPW  305  is set to the voltage level of the very large negative erase voltage NEVL. The very large is negative erase voltage NEVL has a magnitude of from approximately −8.0V to approximately −10.0V. The unselected word line  320   b  of the selected block  310   a  is set to the ground reference voltage level to inhibit the unselected NMOS NOR flash floating gate transistor M 1  of the block  310   a  from erasure. The word lines  321   a  and  321   b  of the unselected block  310   n  are coupled through the P-type well TPW to the very large negative erase voltage NEVL to inhibit erasure of the unselected block  310   n . The source line  315   a  that is connected to the selected NMOS NOR flash floating gate transistor M 0  and the source line  315   n  that is connected to the unselected block  310   n  is set to the very large negative erase voltage NEVL of from approximately −8.0V to approximately −10.0V. The bit line LBL  325  is set to the very large negative erase voltage NEVL. In this example only the page containing the NMOS NOR flash floating gate transistor M 0  is erased and the unselected page containing the NMOS NOR flash floating gate transistor M 1  of the selected block  310   a  and the unselected block  310   n  are inhibited from erasing. 
       FIG. 4  is a block diagram of a nonvolatile memory device  400  embodying the principles of the present invention incorporating the various embodiments of NOR flash floating-gate transistors. The NOR flash nonvolatile memory device  400  includes an array  405  of NMOS flash floating-gate transistors arranged in a matrix of rows and columns. The array  405  is partitioned into a uniform number of sectors  410   a , . . . ,  410   m  and each sector is divided into a uniform number of blocks  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b , . . . ,  414   n , For instance, a 1 Gb memory array device may be divided into 1024 sectors. Each sector then becomes 128 KB and may be divided into a number blocks such as 8 blocks of 16 KB each. Further, the block is divided into pages. In this example, the page may have a size of 4 Kb such that one page is equivalent to one word line or row of the block or sub-array  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b ,  414   n . Thus, each block  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b , . . . ,  414   n  has 32 pages or word lines. 
     The column address decoder  445  receives a column address  440 , decodes the column address  440 , and from the decoded column address  440  selects which one of the data registers &amp; sense amplifiers  435  are being accessed. The column address decoder  445  activates the appropriate global bit lines  447   a , . . . ,  447   n  is for operating a selected sector  410   a , . . . ,  410   m . The appropriate global bit lines  447   a , . . . ,  447   n  are further connected to the data register and sense amplifier  435 . The data register and sense amplifier  435  receives the data signals through the global bit lines  447   a , . . . ,  447   n  from the selected sector  410   a , . . . ,  410   m  and senses and holds the data from the data signal for a read operation. In a program operation, the data is transferred from the data register and sense amplifier  435  through the global bit lines  447   a , . . . ,  447   n  to the selected sector  410   a , . . . ,  410   m . The data being read from or written (program and erase) to the array  405  of NOR NMOS flash floating-gate transistors is transferred to and from the data register and sense amplifier  435  through the column address decoder  445  from and to the data input/output bus  480 . 
     Each block  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b , . . . ,  414   n  of the array  405  of NOR NMOS flash floating-gate transistors is connected to a row decoder  420  through the word lines  432   a ,  432   b ,  432   n ,  434   a ,  434   b ,  434   n . Each sector  410   a , . . . ,  410   m  is connected to a sector row decoder  425   a , . . . ,  425   m  within the row decoder  420 . Each sector  410   a , . . . ,  410   m  is connected to one of the sector row decoder  425   a , . . . ,  425   m . The sector row decoders  425   a , . . . ,  425   m  further incorporate block row decoders  422   a ,  422   b , . . . ,  422   n , and  424   a ,  424   b ,  424   n  such that each block  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b , . . . ,  414   n  is connected with its own block row decoder  422   a ,  422   b , . . . ,  422   n , and  424   a ,  424   b ,  424   n  for providing the appropriate voltage levels to a selected page or word line for reading and programming selected NMOS flash floating-gate transistors. The row address  490  are transferred to each of the row decoders  422   a ,  422   b , . . . ,  422   n , and  424   a ,  424   b ,  424   n  select the page or word line and to provide the appropriate voltage levels for reading and programming the selected NMOS flash floating gate transistors. 
     Each block  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b , . . . ,  414   n  of the array  405  of NMOS NOR flash floating-gate transistors is connected to a source line decoder  415  through the source lines  426   a ,  426   b ,  426   n ,  427   a ,  427   b ,  427   n . The source line decoder  420  is formed of multiple sector source line decoders  416   a , . . . ,  416   m . Each sector source line decoder  416   a , . . . ,  416   m  has multiple block source line decoders  417   a ,  417   b , . . . ,  417   n , and  419   a ,  419   b , . . . ,  419   n  such that each block  412   a ,  412   b , . . . ,  412   n , and  414   a ,  414   b , . . . ,  414   n  is connected with its own source line decoder  417   a ,  417   b , . . . ,  417   n , and  419   a ,  419   b , . . . ,  419   n  for providing the appropriate voltage levels to a selected page or word line for reading and programming selected NMOS flash floating-gate transistors. The row address  490  is transferred to each of the source line decoders  417   a ,  417   b , . . . ,  417   n , and  419   a ,  419   b , . . . ,  419   n  to select the source line of the selected page to provide the appropriate voltage levels for reading, programming, and erasing the selected NMOS flash floating gate transistors. 
     Refer now to  FIG. 5  for a discussion of the structure of a sector  410   a  of the array  405  of  FIG. 4 . The sector  410   a  is exemplary of the all the sectors  410   a , . . . ,  410   m  of array  405 . The sector  410   a  is placed in a common P-type well (TPW 2 ) and contains all the NMOS floating gate transistors M 0 , . . . , Mn of the sector  410   a . The NMOS floating gate transistors M 0 , . . . , Mn are arranged in rows and columns to form the sub-array of the sector  410   a . The NMOS floating gate transistors M 0 , . . . , Mn are formed pair-wise to create a NOR flash nonvolatile memory cell  411 . The two NMOS floating gate transistors M 0  and M 1  of the NOR flash nonvolatile memory cell  411  have their drains commonly connected to a local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k . The sources of the two NMOS floating gate transistors M 0  and M 1  are connected to one source line  426   a , . . . ,  426   k  and  427   a , . . . ,  427   k . The source lines  426   a , . . . ,  426   m  and  427   a , . . . ,  427   m  of each block  412   a , . . . ,  412   n  are connected to the source line decoder  415  of  FIG. 4  to receive the appropriate source biasing voltages for reading, programming, and erasing selected NMOS floating gate transistors M 0 , . . . , Mn. The control gates of the two NMOS floating gate transistors M 0  and M 1  are connected to the word lines  432   a , . . . ,  432   n . The word lines  432   a , . . . ,  432   n  are connected to the row decoder  420  of  FIG. 4 . 
     The sector  410   a  is divided into multiple blocks  412   a , . . . ,  412   n  and each block  412   a , . . . ,  412   n  is further divided into pages  413 . The page  413  being a grouping of the NMOS floating gate transistors M 0 , . . . , Mn having their control gates connected commonly to a word line (WL0) of the word lines  432   a , . . . ,  432   n . Each local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  is connected to the source of a block select floating gate transistor MB0  460   a , . . . ,  460   k . The drains of the block select floating gate transistors MB0  460   a , . . . ,  460   k  are connected to the associated sector bit lines  455   a ,  455   b ,  455   k . The gate of each of the select floating gate transistors MB0  460   a , . . . ,  460   k  is connected to one of the block gate select lines  433   a ,  433   n  that provides the activation voltage to connect the NMOS floating gate transistors M 0 , . . . , Mn to its associated sector bit line  455   a ,  455   b ,  455   k.    
     Each of the sector bit lines  455   a ,  455   b ,  455   k  is connected to one of the sources of the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n  and each of the drains of the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n  is connected to one of the global bit lines  470   a , . . . ,  470   n . The gates of each of the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n  are connected to their associated global bit line select lines SLG[0]  467   a  and SLG[1]  467   b . The global bit lines  470   a , . . . ,  470   n  are connected to the column address decoder  445  and the data register and sense amplifier  435 . 
     When one row of the block select floating gate transistors MB0  460   a , . . . ,  460   k  is activated one of the blocks  412   a , . . . ,  412   n  is selected to be connected to the sector bit lines  455   a ,  455   b ,  455   k . One of a pair of columns of the selected block  412   a , . . . ,  412   n  is connected to the global bit lines when one grouping of the global bit line select lines SLG[0]  467   a  or SLG[1]  467   b  are activated to selectively turn on the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n . In a read and a program operation, one of the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n  is activated at a time to read or program the one column of the NMOS floating gate transistors M 0 , . . . , Mn follow deactivating the first of the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n  and activating the second of the global bit line gating transistors  465   a ,  465   n  and  466   a , . . . ,  466   n  to read or program the second column of the NMOS floating gate transistors M 0 , . . . , Mn. 
       FIG. 6  is a schematic diagram of a representative sector decoder  425  of the nonvolatile memory device of  FIG. 4 . Each sector decoder  425  is partitioned into a number of block row decoders  422   a ,  422   b , . . . ,  422   n  (Note that in  FIG. 4 , the row decoders are designated  422   a ,  422   b , . . . ,  422   n , and  424   a ,  424   b , . . . ,  424   n ). The number of block row decoders  422   a ,  422   b , . . . ,  422   n  in each sector decoder  425  is equal to the number of blocks of NMOS floating gate transistors M 0 , . . . , Mn in each sector  410   a , . . . ,  410   m  of  FIG. 4 . The logic gates  510   a , . . . ,  510   n  (a NAND gate in this embodiment) receive the block address  520  of the row address  490  of  FIG. 4 , decodes the block address  520  to select which of the block row decoders  422   a , . . . ,  422   n  are to be activated for reading, programming, or erasing. The output of each of the logic gates  510   a , . . . ,  510   n  is the block select signal RXD [0]  512   a , RXD [n]  512   n  that is the input to an input to one of the level shift circuits  515   a , . . . ,  515   n . The level shift circuits  515   a , . . . ,  515   n  receive the power supply voltage levels  525  that are used to shift the lower voltage logic level of the block select signals RXD [0]  512   a , RXD [n]  512   n  to the levels required for reading, programming, and erasing. The outputs of the level shift circuit  515   a , . . . ,  515   n  are the high voltage block select signals XD  530   a , . . . ,  530   n  and XDB  532   a , . . . ,  532   n  that are applied to the row decode circuit  540   a , . . . ,  540   n.    
     The row decode circuits  540   a , . . . ,  540   n  provide the appropriate voltage levels for transfer to the rows of the word lines  432   a , . . . ,  432   n  of the selected block  412   a , . . . ,  412   n  of  FIG. 4 . The voltage levels applied to row decode circuits  540   a , . . . ,  540   n  are provided by the high voltage power supply voltage lines  535 . Each of the high voltage power supply voltage lines  535  is associated with one of the word lines  432   a , . . . ,  432   n  and is set according to the operation (read, program, erase, or verify) to be executed and are discussed hereinafter. The row decode circuits  540   a , . . . ,  540   n  have the row pass devices formed of the high voltage PMOS transistors  541   a , . . . ,  541   n  and the high voltage NMOS transistors  542   a , . . . ,  442   n  connected pair-wise in parallel. The gates of the PMOS transistors  541   a , . . . ,  541   n  are each connected to one of the high voltage out of phase block select signals XDB  532   a , . . . ,  532   n . and the gates of the NMOS transistors  542   a , . . . ,  442   n  are each connected to one of the in-phase block select signals XD  530   a , . . . ,  530   n . The sources of the PMOS transistors  541   a , . . . ,  541   n  and the drains of the PMOS transistors  541   a , . . . ,  541   n  are connected to the high voltage power supply voltage line  535  associated with one of the word lines  432   a , . . . ,  432   n . The drains of the PMOS transistors  541   a , . . . ,  541   n  and the sources of the PMOS to transistors  541   a , . . . ,  541   n  are connected to the drain high voltage pass transistors  551   a , . . . ,  551   n  associated with one of the word lines  432   a , . . . ,  432   n . The drains of the PMOS transistors  541   a , . . . ,  541   n  and the sources of the PMOS transistors  541   a , . . . ,  541   n  are further connected to the drain of the NMOS transistors  543   a , . . . ,  543   n . The gate of the NMOS transistors  543   a , . . . ,  543   n  is connected to the out of phase block select signals XDB  532   a , . . . ,  532   n  and the sources of the NMOS transistors  543   a , . . . ,  543   n  are connected to the ground reference voltage source (0.0V). For the row decoders  422   a , . . . ,  422   n  of the unselected block  412   a , . . . ,  412   n , the level shift circuits  515   a , . . . ,  515   n  are deactivated and the out of phase block select signals XDB  532   a , . . . ,  532   n  are set to turn on the NMOS transistors  543   a , . . . ,  543   n  to set the drains of the NMOS transistors  543   a , . . . ,  543   n  to the voltage level of the ground reference voltage source (0.0V). 
     The high voltage PMOS pass transistors  551   a , . . . ,  551   n  form the PMOS high voltage isolators  550   a , . . . ,  550   n . The gates of the high voltage PMOS pass transistors  551   a , . . . ,  551   n  are connected together and to the isolation signal ISOB  566 . When activated, the high voltage pass transistors  551   a , . . . ,  551   n  connect the word lines  432   a , . . . ,  432   n  to the row decode circuits  540   a , . . . ,  540   n . When deactivated, the high voltage pass PMOS transistors  551   a , . . . ,  551   n  isolate the word lines  432   a , . . . ,  432   n  to the row decode circuits  540   a , . . . ,  540   n . It should be noted that the drain to source voltage of the transistors of the sector decoder never exceeds the +/−10V drain to source breakdown voltage. 
     The PMOS high voltage isolators  550   a , . . . ,  550   n  are each formed in an independent N-type well. The N-type well for each of the PMOS high voltage isolators  550   a , . . . ,  550   n  is connected to an N-type well switch  555   a , . . . ,  555   n  through the control lines  552   a , . . . ,  552   n  to individually charge or discharge the N-type wells. The N-type well switch  555   a , . . . ,  555   n  includes the PMOS transistors  556   a , . . . ,  556   n  and  557   a , . . . ,  557   n  and the NMOS transistors  558   a , . . . ,  558   n . The gates of the PMOS transistors  556   a , . . . ,  556   n  and the NMOS transistors  558   a , . . . ,  558   n  are connected to the out of phase block select signals XDB  532   a , . . . ,  532   n . The gates of the PMOS transistors  557   a , . . . ,  557   n  are connected to the out of phase read signal RDB  564 . The drains the PMOS transistors  556   a , . . . ,  556   n  and  557   a , . . . ,  557   n  and drains the NMOS transistors  558   a , . . . ,  558   n  are connected through the control lines  552   a , . . . ,  552   n  to the N-type wells. The sources of the PMOS transistors  556   a , . . . ,  556   n  and  557   a , . . . ,  557   n  are connected to the positive N-well biasing voltage source VP1  562  and the sources of the NMOS transistors  558   a , . . . ,  558   n  are connected to the negative N-well biasing voltage source VN1  560 . 
       FIG. 7  is a schematic diagram of a level shifter circuit of the row decoder of  FIG. 6 . Referring now to  FIG. 7 , the level shifter circuit  515  includes three sub-level-shifter circuits  570 ,  580 , and  590  to translate the low voltage level of the block select signal RXD  512  to a voltage level of a first positive high voltage power source VPX1  527   a . The voltage translation maintains the drain to source breakdown voltage of the peripheral circuitry of the nonvolatile memory device  400  of  FIG. 4  to be less than or equal to the drain to source breakdown voltage BVDSS approximately +/−10V. Maintaining the drain to source voltages of the sector decoder  425  of the nonvolatile memory device of  FIG. 4  less than the +/−10V eliminates the need for special high voltage devices. The first level shift circuit  570  has pair of cross connected PMOS transistors  571  and  572  that have their sources connected to a second positive high voltage power source VPX0  527   b . The bulk regions of the PMOS transistors  571  and  572  are connected to the second positive high voltage power source VPX0  527   b . The drain of the PMOS transistor  571  is connected to the gate of the PMOS transistor  572  and the drain of the PMOS transistor  572  is connected to the gate of the PMOS transistor  571 . The drain of the PMOS transistor  571  is connected to the drain of the NMOS transistor  575  and the drain of the PMOS transistor  572  is connected to the drain of the NMOS transistor  577 . The gate of the NMOS transistor  575  is connected to receive the block select signal RXD  512 . The block select signal RXD  512  is connected to the input of the inverter  576 . The output of the inverter  576  is connected to the gate of the NMOS transistor  577 . The sources of the NMOS transistors  575  and  577  are connected to the ground reference voltage source (0.0V). 
     The output nodes  573  and  574  of the first level shift circuit  570  are the input nodes of the second level shift circuit  580 . The second level shift circuit  580  has pair of PMOS transistors  581  and  582  that have their sources connected to a second high voltage power supply VPX0  527   b . The bulk regions of the PMOS transistors  581  and  582  are connected to the second high voltage power supply VPX0  527   b . The drain of the PMOS transistor  581  is connected to the gate of the PMOS transistor  582  and the drain of the PMOS transistors  582  is connected to the gate of the PMOS transistors  581 . The drain of the PMOS transistor  581  is connected to the drain of the NMOS transistor  585  and the drain of the PMOS transistor  582  is connected to the drain of the NMOS transistor  586 . The output node  573  of the first level shift circuit  570  is connected to the gate of the PMOS transistor  581  and the output node  574  of the first level shift circuit  570  is connected to the gate of the PMOS transistor  582 . The sources of the NMOS transistors are connected to the first negative high voltage source VNX0  526   a . The output node  583  is at the junction of the connection of the drains of the PMOS transistor  582  and the NMOS transistor  586 . The output node  584  is at the junction of the connection of the drains of the PMOS transistor  581  and the NMOS transistor  585 . 
     The output nodes  583  and  584  of the second level shift circuit  580  are the input nodes of the third level shift circuit  590 . The third level shift circuit  590  has pair of PMOS transistors  591  and  592  that have their sources connected to a second positive high voltage power supply VPX0  527   b . The drain of the PMOS transistors  591  is connected to the source of the PMOS transistor  593 . The drain of the PMOS transistors  592  is connected to the source of the PMOS transistor  594 . The output node  583  of the second level shift circuit  580  is connected to the gate of the PMOS transistor  591  and the output node  584  of the second level shift circuit  580  is connected to the gate of the PMOS transistor  592 . The gates of the PMOS transistors  593  and  594  are connected to the isolation signal ISOP  528 . The isolation signal ISOP  528  is used to isolate the drain of PMOS transistors  591  and  592  from the in-phase high voltage block select signal XD  530  and the inverse high voltage block select signal XDB  532  at the program mode. If the PMOS transistors  593  and  594  were to be removed or eliminated, the voltage level of the power supply voltage source VDD would be applied to the output node  583  or the output node  584  during a program operation. This causes a voltage level of the power supply voltage source VDD plus the very high positive erase voltage to be applied from the gate to the drain of the PMOS transistors  591  or  592 . The drain of the PMOS transistor  594  is connected to the drain of the NMOS transistor  596  and the gate of the NMOS transistor  595 . The bulk regions of the PMOS transistors  591 ,  592 ,  593 , and  595  are connected to the second high voltage power supply VPX1  527   a . The sources of the NMOS transistors are connected to the second negative high voltage source VNX1  526   b . The high voltage block select signal XD  530  is present at the junction of the connection of the drains of the PMOS transistor  594  and the NMOS transistor  596 . The inverse high voltage block select signal XDB  532  is present at the junction of the connection of the drains of the PMOS transistor  593  and the NMOS transistor  595 . 
       FIG. 8  is a schematic diagram of sector source line decoder of the nonvolatile memory device of  FIG. 4 . The sector source line decoder  416   a  is divided into multiple block source line decoders  417   a , . . . ,  417   n . Each of the block source line decoders  417   a , . . . ,  417   n  has a logic gate  600   a , . . . ,  600   n  (a NAND gate in this embodiment) that receives and decodes the block address  520  of the row address  490  of  FIG. 4 . The output of the block source line decoders  417   a , . . . ,  417   n  is the block source line selection signal  610   a , . . . ,  610   n  that is the input to the source line selector/conditioner  605   a , . . . ,  605   n . The source line selector/conditioner  605   a , . . . ,  605   n  is connected to the source lines  426   a , . . . ,  426   n  to apply the correct voltage levels to the source lines  426   a , . . . ,  426   n  for reading, programming, and erasing the selected NMOS floating gate transistors M 0 , . . . , Mn. The source line selector/conditioner  605   a , . . . ,  605   n  is connected to the block gate select lines  433   a ,  433   n  to provide the activation signal for activating the block select floating gate transistor MB0  460   a , . . . ,  460   n  of  FIG. 5  to connect the selected NMOS floating gate transistors M 0 , . . . , Mn to the associated sector bit lines  455   a ,  455   b ,  455   k . The out-of-phase erase signal ERSB  615 , positive high voltage source VP2  616 , the in-phase program signal PG  618 , and the out-of-phase program signal PGB  619  provide the activation signals for setting the appropriate voltage levels to the source lines  426   a , . . . ,  426   n  and the block gate select lines  433   a ,  433   n  from the source line address lines ST[0]  620   a , ST[1]  620   b , and ST[3]  620   c  and the source line select line SLS  632 . The source line address lines ST[0]  620   a , ST[1]  620   b , and ST[3]  620   c  are connected to the drains of the NMOS transistors  625   a ,  625   b , and  625   c . The sources of the NMOS transistors  625   a ,  625   b , and  625   c  are connected to the source line decoders  605   a , . . . ,  605   n . The gates of the NMOS transistors  625   a ,  625   b , and  625   c  are connected to the source line isolation signal DISE  630  to isolate the source line address lines ST[0]  620   a , ST[1]  620   b , and ST[3]  620   c  from the source line decoders  605   a , . . . ,  605   n  during an erase operation. The transistors of the source line decoders  605   a , . . . ,  605   n  are subject to drain to source voltage levels that are less than or equal to a drain to source breakdown voltage BVDSS of approximately +/−10V. 
       FIG. 9  is a schematic diagram of a source line selector/conditioner of the source line decoder  605   a , . . . ,  605   n  of  FIG. 8 . The source line selector/conditioner  605  has a voltage level shifter  640  that receives the block selection signal  610  and translates the voltage level of the block selection signal  610  to those required by the source lines  426  and the block gate select signal  433 . The voltage level shifter  640  has a logic gate  641  (a NAND circuit in this embodiment) that receives the block selection signal  610  and the out of phase of the erase command signal  615 . The output of the logic gate  641  is an input to a logic gate  642  (a NAND circuit in this embodiment). The second input of the logic gate  642  is the erase command signal  615 . The output of the logic gate  641  is connected to the input of the NMOS transistor  644 . The output of the logic gate  642  is the input of the NMOS transistor  643 . The sources of the NMOS transistors  643  and  644  are connected to the ground reference voltage source (0.0V). The drain of the NMOS transistor  643  is connected to the drain of the PMOS transistor  646  and the gate of the PMOS transistor  645 . The drain of the NMOS transistor  644  is connected to the drain of the PMOS transistor  645  and the gate of the PMOS transistor  646 . The sources of the PMOS transistors  645  and  646  are connected to the positive high voltage source VP2  616 . The in-phase output SD  650  of the voltage level shifter  640  is generated at the junction of the connection of the drains of the NMOS transistor  644  and the PMOS transistor  645 . The out-of-phase output SDB  652  of the voltage level shifter  640  is generated at the junction of the connection of the drains of the NMOS transistor  643  and the PMOS transistor  646 . 
     The in-phase output SD  650  and out-of-phase output SDB  652  of the voltage level shifter  640  are connected to the inputs of the source line decoder  635 . The source line decoder  635  is formed of pairs of NMOS transistors  655   a , . . . ,  655   n  and  657   a , . . . ,  657   n . The gates of the NMOS transistors  655   a , . . . ,  655   n  are connected to the in-phase output SD  650  of the voltage level shifter  640  and the gates of the NMOS transistors  657   a , . . . ,  657   n  are connected to the out-of-phase output SDB  652  in-phase output SD  650 . The sources of the NMOS transistors  655   a , . . . ,  655   n  and the drains of the NMOS transistors  657   a , . . . ,  657   n  are connected to the source lines  426 . The drains of the NMOS transistors  655   a , . . . ,  655   n  are connected to the source line address lines ST[0]  620   a , ST[1]  620   b , and ST[3]  620   c . The sources of the NMOS transistors  657   a , . . . ,  657   n  are connected to the source line select line SLS  632 . 
     The in-phase program command signal PG  618  and the out-of-phase program command signal PGB  619  are connected to the pass gate circuits  660  and  665 . The NMOS transistor  661  and the PMOS transistor  662  are placed in parallel to form the pass gate circuit  660  and the PMOS transistor  666  and the NMOS transistor  667  are placed in parallel to form the pass gate circuit  665 . The out-of-phase program command signal PGB  619  is connected to the gates of the NMOS transistor  661  and the PMOS transistor  666  and the in-phase program command signal PG  618  is connected to the PMOS transistors  662  and  667 . The sources of the NMOS transistor  661  and the PMOS transistor  662  are connected to the positive high voltage source VP2  616 . The drains of the NMOS transistor  661  and the PMOS transistor  662  are connected to the sources of the PMOS transistor  666  and the NMOS transistor  667  and to the block gate select line  433  of each block to selectively activate the block select floating gate transistors MB0  460   a , . . . ,  460   n  of  FIG. 5 . The sources of the PMOS transistor  666  and the NMOS transistor  667  are connected to the gates of the NMOS transistors  655   a , . . . ,  655   n  to transfer the decoded in-phase output SD  650  to activate one of the NMOS transistors  655   a , . . . ,  655   n  when the of the voltage level shifter  640  is active during a program operation. 
       FIG. 10  is flow chart for the method for operating the nonvolatile memory device of  FIG. 4 .  FIG. 11  is flow chart of the method for erasing and erase verifying a page, block, or sector of the nonvolatile memory device of  FIG. 4 .  FIG. 12  is flow chart of the method for programming and program verifying a page of the nonvolatile memory device of  FIG. 4 . Refer now to  FIGS. 4-12 ,  13   a ,  13   b ,  14   a ,  14   b , and  15  for a discussion of the operating voltage levels required for the reading, programming, erasing, and verification of the nonvolatile memory device. The method begins by determining (Box  700 ) if the operation is an erase. If the operation is an erase operation, the erase is determined (Box  705 ) to be a page, block, or sector erase. If the operation is to be a page erase, the page to be erased is selected (Box  710 ) and the page is erased (Box  725 ). The voltage levels for the array  405  of the NMOS floating gate transistors M 0 , . . . , Mn are shown in  FIG. 13   a  for a single level cell program and  FIG. 13   b  for a multiple level cell program. For the page erase the voltage levels are the same for the single level cell program and the multiple level cell program. The word lines  432 U of the unselected blocks  412 U of the selected sectors have the very high negative erase voltage coupled from the P-type well TPW  244 S of the selected sector. The very high negative erase voltage, as applied to the P-type well TPW  244 S, is from approximately −8.0V to approximately −10.0V. In the unselected sectors  410   a , . . . ,  410   m  of the array  405 , the P-type well TPW  244 U is set to approximately the voltage level of the ground reference voltage source (0.0V). The selected word line  432 S of the selected block is set to a very high positive erase voltage. The very high positive erase voltage is from approximately +8.0V to approximately +10.0V. The unselected word line  432 SU in the selected block  412 S is set to the approximately the voltage level of the ground reference voltage source (0.0V). The selected local bit line  450 S is set to the very high negative erase voltage. The block gate select lines  433 S are set to the high erase select voltage of approximately +5.0V to couple the local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  to the associated sector bit lines  455   a ,  455   b ,  455   k . The selected source line  426 S are set to the very high negative erase voltage. The selected global bit line select lines  467 S are set to the very high negative erase voltage to connect the sector bit lines  455   a ,  455   b ,  455   k  to the global bit lines  470   a , . . . ,  470   n.    
     To establish the page erase values as just described the row decoders  422   a ,  422   b , . . . ,  422   n , and  424   a ,  424   b ,  424   n  of the selected sector have voltage levels described in  FIGS. 14   a  and  14   b . The single level cell program signal of  FIG. 14   a  and the multiple level cell program signals of  FIG. 14   b  are identical for a page erase operation The selected word line  432 S must be set to the very high positive erase voltage and the unselected word lines  432 SU of the selected block are set to the approximately the voltage level of the ground reference voltage source (0.0V). The unselected word lines  432 U of the unselected blocks are coupled to the very high negative erase voltage from the P-type well TPW  244 S. To accomplish these levels, the row decoders  422   a ,  422   b , . . . ,  422   n  of the selected blocks  412 S have their selected high voltage power supply voltage line XT  535 S associated with the selected word line  432 S set to the very high positive erase voltage to be fed through the row decode circuit  540   a , . . . ,  540   n  and the PMOS high voltage isolators  550   a , . . . ,  550   n  to the selected word line  432 . The unselected high voltage power supply voltage line  535 U associated with the selected word line  432 SU set to the voltage level of the ground reference voltage level to be fed through the row decode circuit  540   a , . . . ,  540   n  and the PMOS high voltage isolators  550   a , . . . ,  550   n  to the unselected word line  432 SU. The voltage level of the selected in-phase block select signals XD  530 S, indicating that a block  412 S is selected, is set to the very high positive erase voltage and the voltage level of the out-of-phase block select signals XD  530 U, indicating that a block  412 U is unselected, is set to approximately the voltage level of the ground reference voltage source (0.0V) to be coupled from the row decode circuit  540   a , . . . ,  540   n  through the PMOS high voltage isolators  550   a , . . . ,  550   n  such that the unselected word lines  432 U are coupled to the very high negative erase voltage from the P-type well TPW  244 S. The N-type wells  552 S of the selected block  412 S are connected to the very high positive erase voltage to avoid voltage breakdown in the PMOS high voltage isolators  550   a , . . . ,  550   n  and the N-type well switch  555   a , . . . ,  555   n . The N-type wells  552 U of the selected block  412 U are connected to the voltage level of the ground reference voltage source (0.0V). 
     To transfer the very high positive erase voltage present on the selected high voltage power supply voltage line XT  535 S to the selected word line  432 S, the PMOS high voltage isolators  550   a , . . . ,  550   n  are activated with the isolation signal ISOB  566  is set to the voltage level of the ground reference voltage source (0.0V). The out of phase read signal RDB  564 , first positive high voltage power source VPX1  527   a , the second high voltage power source VPX0  527   b , and the positive N-well biasing voltage source VP1  562  are set to the very high positive erase voltage to set the selected word line  432 S to the voltage level of the very high positive erase voltage. The first high negative voltage source VNX0  526   a , the second negative high voltage source VNX1  526   b , the negative N-well biasing voltage source VN1  560  and isolation signal ISOP  528  are set to the voltage level of the ground reference voltage source (0.0V) to set the unselected word lines  432 SU of the selected block  412 S to approximately the voltage level of the ground reference voltage source (0.0V). 
       FIG. 15  illustrates the voltage levels of both the single level cell program and the multiple level cell program to generate the biasing voltages for the source lines for the page, block, or sector erase. In the erase operation for the page, block, sector all the source lines  426 S,  426 SU, and  426 U are selected and set to the very high negative erase voltage level, because the very high negative erase voltage applied to the P-type well TPW  244 S is transferred from source line select line SLS  632 . All the source line address lines ST  620 S and  620 U are selected and set to approximately the voltage level of the ground reference voltage source (0.0V). All the block source line selection signals  610 S and  610 U are selected and set to the voltage level of the power supply voltage source VDD. All the block gate select lines BLG  433 S and  433 U are selected and set to approximately the voltage level of the ground reference voltage source (0.0V). The out of phase erase command signal  615 , the positive high voltage source VP2  616 , and the in-phase program command signal PG  618  are set to approximately the voltage level of the ground reference voltage source (0.0V). The source line select line SLS  632  and the source line erase isolation signal DISE  630  are set to the very high negative erase voltage level. The out-of-phase program command signal PGB  619  is set to the voltage level of the power supply voltage source. The very high negative erase voltage level as applied to the source line select line SLS  632  is fed to the selected source lines  426 S, but to prevent the very high negative erase voltage level from passing to all the source lines  426 U,  426 SU, and  426 U in a selected sector the source line address lines ST  620 S, the NMOS transistors  625   a ,  625   b , and  625   c  must be turned off. The source line erase isolation signal DISE  630  is set to the very high negative erase voltage level to turn off the NMOS transistors  625   a ,  625   b , and  625   c.    
     Returning now to  FIG. 11 , after the completion of the erase operation (Box  725 ), the page erase verify operation is executed (Box  730 ) to determine if the erase has been successfully accomplished. If the erase is not successful, a loop counter is to tested (Box  735 ) to assess that the maximum number of erasure trials is not exceeded. If the maximum number of erasure trials is not exceeded, the loop counter is incremented (Box  740 ) and the page erase operation is executed repetitively until the maximum number of erasure trials is exceeded and the nonvolatile memory device is declared as having failed (Box  745 ) or the erasure is a success and the nonvolatile memory device is declared as having successfully been erased (Box  750 ). 
     The voltage levels for the page erase verification for the array  405  of the NMOS floating gate transistors M 0 , . . . , Mn are shown in  FIG. 13   a  for a single level cell program and  FIG. 13   b  for a multiple level cell program. Referring to  FIGS. 13   a  and  13   b , the unselected word lines  432 U of the unselected blocks  412 U and the unselected word lines  432 SU of the selected blocks  412 S are set to the voltage level of the ground reference voltage source (0.0V). The selected word line  432 S is set to a voltage level of the lower boundary of the erase threshold voltage Vt 1 L or approximately +5.0V for the single level cell program as shown in  FIG. 13   a . The selected word line  432 S is set to a voltage level of the lower boundary of the erase threshold voltage Vt 3 L or approximately +5.0V for the multiple level cell program as shown in  FIG. 13   b.    
     Referring to  FIGS. 14   a  and  14   b , the selected word line  432 S is set to the lower boundary of the erase threshold voltage Vt 1 L by setting selected high voltage power supply voltage line XT  535 S to the voltage level of the lower boundary of the erase threshold voltage level. The voltage level of the selected in-phase block select signals XD  530 S, the first positive high voltage power source VPX1  527   a , the second high voltage power source VPX0  527   b , negative N-well biasing voltage source VN1  560 , and the positive N-well biasing voltage source VP1  562  are set to lower boundary of the erase threshold voltage Vt 1 L to pass the lower boundary of the erase threshold voltage Vt 1 L to the selected word line  432 S. The out of phase read signal RDB  564 , the first high negative voltage source VNX0  526   a , the second negative high voltage source VNX1  526   b , and the isolation signal ISOP  528  are set to the voltage level of the ground reference voltage source (0.0V). These voltage levels, as described, pass the lower boundary of the erase threshold voltage Vt 1 L from the selected high voltage power supply voltage line XT  535 S to the selected word line  432 S. Further, the voltage levels, as described, pass the voltage level of the ground reference voltage source (0.0V) from the unselected high voltage power supply voltage line XT  535 U to the unselected word line  432 U. 
     The local bit lines  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  as shown in  FIG. 5  are selectively connected to the associated sector bit lines  455   a ,  455   b ,  455   k . Two of the sector bit lines  455   a ,  455   b ,  455   k  are selectively connected to one of the global bit lines  470   a , . . . ,  470   n . The local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  of one column is read or verified followed by reading the second local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  of the adjacent associated column. To accomplish this, the selected bit lines LBL  450 S for the column being read is pre-charged to the pre-charge voltage level of the power supply voltage source VDD less the threshold voltage Vt (VDD−Vt) for sensing the status of the selected NMOS floating gate transistors M 0 , . . . , Mn on the activated column. The pre-charge voltage level (VDD−Vt) will be discharged to 0V when the NMOS floating gate transistor M 0 , . . . , Mn has not been successfully erased. If the NMOS floating gate transistors M 0 , . . . , Mn are erased, the pre-charged level will be maintained. Since all the local bit lines  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  are tested during the erase verify operation, there are no unselected local bit lines  450 U. The selected block gate select lines  433 S for all the blocks of the selected sector are set to the voltage level of the high read select voltage HV″ of approximately +5.0V to fully couple the local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  to the associated sector bit lines  455   a ,  455   b , . . . ,  455   k.    
     The selected source line  426 S in the selected sector  412 S are set to the voltage level of the ground reference voltage source (0.0V). The unselected source lines  426 U is set first read inhibit voltage is approximately +1.0V. The selected global bit line select line  467 S of the selected sector  4105  are set to the voltage level of the power supply voltage source VDD to connect a first set of sector bit lines  455   a ,  455   b , . . . ,  455   k  to the associated global bit lines  470   a , . . . ,  470   n . The unselected global bit line select line  467 U of the selected sector  410 S are set to the voltage level of the power supply voltage source VDD to disconnect a second set of sector bit lines  455   a ,  455   b , . . . ,  455   k  from the associated global bit lines  470   a , . . . ,  470   n . The P-type well TPW  244 S selected sector  410 S and the P-type well TPW  244 U unselected sectors  410 U are set to the voltage level of the ground reference voltage source (0.0V). 
     To establish the voltage levels as described for the erase verification in  FIGS. 13   a  and  13   b , the source line decoder  415  has the voltage levels shown in  FIG. 15 . Referring to  FIG. 15 , the selected source line  426 S is set to the voltage level of the is ground reference voltage source (0.0V) and the unselected source lines  426 SU and  426 U are set to the first read inhibit voltage VS 1 *(approximately +1.0V). Further, the selected block gate select line  433 S and the unselected block gate select lines  433 U are to be set to the voltage level of the high source line select voltage HV″ (approximately +5.0V). To accomplish these voltage levels, the selected source line address line ST  620 S for the selected source line  426 S is set to the voltage level of the ground reference voltage source (0.0V) and the unselected source line address line ST  620 U is set to the first read inhibit voltage VS 1 *. The selected block source line selection signal SXD  610 S is set to the voltage level of the power supply voltage source VDD and the unselected block source line selection signal SXD  610 U is set to the voltage level of the ground reference voltage source (0.0V). The out of phase erase command signal ERSB  615  is set to the voltage level of the power supply voltage source VDD. The positive high voltage source VP2  616  and the out-of-phase program command signal PGB  619  are set to voltage level of the high source line select voltage HV″. The source line select line SLS  632  is set to the voltage level of the first read inhibit voltage VS 1 *. The source line erase isolation signal DISE  630  is set to the voltage level of the power supply voltage source VDD. The in-phase program command signal PG  618  is set to approximately the voltage level of the ground reference voltage source (0.0V). 
     Return now to  FIG. 11 . If the operation is to be a block erase, the block to be erased is selected (Box  715 ) and the block is erased (Box  725 ). Referring now to  FIGS. 14   a  and  14   b , the voltage levels for the block erase are identical to that of the page erase described above except that there are no unselected word lines  432 SU in the selected block  412 S. All the word lines  432 S are now selected for erasure and placed at the very high positive erase voltage level of from approximately +8.0V to approximately +10.0V to accomplish the block erase. 
     Returning now to  FIG. 11 , after the completion of the erase operation (Box  725 ), the block erase verify operation is executed (Box  730 ) to determine if the erase has been successfully accomplished. The block erase verify is identical to the page erase verify, except, again, there are no unselected word lines  432 U. The selected word lines  432 S are set to a voltage level of the lower boundary of the erase threshold is voltage Vt 1 L or approximately +5.0V for the single level cell program as shown in  FIG. 13   a . The selected word lines  432 S are set to a voltage level of the lower boundary of the erase threshold voltage Vt 3 L or approximately +5.0V for the multiple level cell program as shown in  FIG. 13   b.    
     Returning to  FIG. 11 , if the block erase is not successful, a loop counter is tested (Box  735 ) to assess that the maximum number of erasure trials is not exceeded. If the maximum number of erasure trials is not exceeded, the loop counter is incremented (Box  740 ) and the page erase operation is executed repetitively until the maximum number of erasure trials is exceeded and the nonvolatile memory device is declared as having failed (Box  745 ) or the erasure is a success and the nonvolatile memory device is declared as having successfully been erased (Box  750 ). 
     Return now to  FIG. 11 . If the operation is to be a sector erase, the sector to be erased is selected (Box  715 ) and the sector is erased (Box  725 ). Referring now to  FIGS. 14   a  and  14   b , the voltage levels for the sector erase are identical to that of the page erase and block erase described above except that there are no unselected word lines  432 SU or  432 U. All the word lines  432 S are now selected for erasure and placed at the very high positive erase voltage level of from approximately +8.0V to approximately +10.0V to accomplish the sector erase. 
     Returning now to  FIG. 11 , after the completion of the erase operation (Box  725 ), the sector erase verify operation is executed (Box  730 ) to determine if the erase has been successfully accomplished. The sector erase verify is identical to the page erase verify, except, again, there are no unselected word lines  432 SU or  432 U. All the selected word lines  432 S are set to a voltage level of the lower boundary of the erase threshold voltage Vt 1 L or approximately +5.0V for the single level cell program as shown in  FIG. 13   a . The selected word lines  432 S are set to a voltage level of the lower boundary of the erase threshold voltage Vt 3 L or approximately +6.0V for the multiple level cell program as shown in  FIG. 13   b . Returning to  FIG. 11 , if the sector erase is not successful, a loop counter is tested (Box  735 ) to assess that the maximum number of erasure trials is not exceeded. If the maximum number of erasure trials is not exceeded, the loop counter is incremented (Box  740 ) and the page erase operation is executed repetitively until the maximum number of erasure trials is exceeded and the nonvolatile memory device is declared as having failed (Box  745 ) or the erasure is a success and the nonvolatile memory device is declared as having successfully been erased (Box  750 ). 
     Returning now to  FIG. 10 , if the operation is determined (Box  700 ) not to be an erase operation, the operation is determine (Box  755 ) if it is a program operation. If the operation is determined (Box  755 ) to be a program operation (referring to  FIG. 12 ), data is loaded (Box  756 ) to the data register and sense amplifier  435  and the page to be programmed is selected (Box  758 ). The selected page is then programmed (Box  760 ) with the voltage levels applied as shown in  FIGS. 13   a ,  13   b ,  14   a ,  14   b , and  15 . Referring to  FIGS. 13   a  and  13   b , the unselected word lines  432 U of the unselected blocks  412 U and the unselected word lines  432 SU of the selected block  412 S are set to the negative program inhibit voltage that is approximately −2.0V. The selected word line  432 S is set to the high negative program voltage level that is from approximately −8.0V to approximately −10. The high negative program voltage level is less than or equal to the drain to source breakdown voltage BVDSS of approximately 10V for the transistors of the row decoder  420  of  FIG. 4 . The selected local bit lines LBL  450 S for the columns that are to be programmed are set to the high program voltage that is approximately +5.0V for the single level program cell ( FIG. 13   a ). The selected local bit lines LBL  450 S for the columns that are to be programmed are set to one of the program voltages that establish the desired threshold voltage representing the data to be programmed. The program voltages, as shown in  FIG. 13   b , are approximately +4.0V for the first level programmed threshold voltage Vt 2 , approximately +5.0V for the first level programmed threshold voltage Vt 1 , and approximately +6.0V for the first level programmed threshold voltage Vt 0 . The unselected local bit lines LBL  450 U and the program inhibit of the selected local bit lines LBL  450 S for the columns that are to remain erased are set to a voltage level of approximately the ground reference voltage source (0.0V) or alternately disconnected and allowed to float. To insure that the program voltages are passed from the column address decoder  445  to the global bit lines  447   a , . . . ,  447   n  to the sector bit lines  455   a ,  455   b ,  455   k  to the local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k , the is selected block gate select line  433 S for the selected block  412 S and the sector gate select line  467 S for the selected sector  410 S is set to the high program select voltage that is from approximately +8.0V to approximately +10.0V. The unselected block select gate lines  433 U for the unselected blocks  412 U and the unselected sector gate select lines  467 U for the unselected sectors  410 U are set to the voltage level of the ground reference voltage source. The selected source line  426 S connected to the selected page of the selected block  412 S is set to the voltage level of the ground reference voltage source. The unselected source lines  426 U of the selected sector  410 S are set to the source line program inhibit voltage that is from approximately +1.5V to approximately 1.8V. The selected P-type well TPW  244 S in which the selected sector  410 S is formed and the unselected P-type wells TPW  244 U in which the unselected sectors  410 U are formed are set to the voltage level of the ground reference voltage source. 
     To establish the voltage level as described for the programming in  FIGS. 13   a  and  13   b , the row decoder  420  has the voltage levels shown in  FIGS. 14   a  and  14   b . To have the selected word line  432 S set to the high negative program voltage, the selected high voltage power supply voltage line XT  535 S associated with the selected word line  432 S set to the very high negative program voltage. To have the unselected word lines  432 SU and  432 U set to the negative program inhibit voltage that is approximately −2.0V, the unselected high voltage power supply voltage line XT  535 U associated with the unselected word lines  432 U set to the negative program inhibit voltage. The voltage level of the selected in-phase block select signals XD  530 S, indicating that a block  412 S is selected is set to approximately the voltage level of the ground reference voltage source (0.0V) such that the very high negative program voltage is coupled from the row decode circuit  540   a , . . . ,  540   n  through the PMOS high voltage isolators  550   a , . . . ,  550   n  to the selected word line  432 S. The voltage level of the out-of-phase block select signals XD  530 U, indicating that a block  412 U is unselected, is set to the very high negative program voltage to couple the negative program inhibit voltage to the unselected high voltage power supply voltage line XT  535 U to the unselected word line  432 SU and  432 U. The N-type wells  552 S of the selected block  412 S and the N-type wells  552 U of the unselected blocks  412 U is connected to the voltage level of approximately the ground reference voltage source (0.0V). 
     To establish the voltage level as described for the programming in  FIGS. 13   a  and  13   b , the source line decoder  415  has the voltage levels shown in  FIG. 15 . Referring to  FIG. 15 , the selected source line  426 S is set to the voltage level of the ground reference voltage source (0.0V) or disconnected and allowed to float. The unselected source lines  426 SU and  426 U are set to the source line program inhibit voltage VS 2 ** that is from approximately +1.5V to approximately 1.8V. Further, the selected block gate select lines  433 S is to be set to the voltage level of very high program voltage and the unselected block gate select lines  433 U is to be set to the voltage level of approximately the ground reference voltage source (0.0V). 
     To accomplish these voltage levels, the selected source line address line ST  620 S for the selected source line  426 S is set to the voltage level of the ground reference voltage source (0.0V) or disconnected and allowed to float. The unselected source line address line ST  620 U is set to the source line inhibit voltage VS 2 **. The selected block source line selection signal SXD  610 S is set to the voltage level of the power supply voltage source VDD and the unselected block source line selection signal SXD  610 U is set to the voltage level of the ground reference voltage source (0.0V). The out of phase erase command signal ERSB  615  is set to the voltage level of the power supply voltage source VDD. The positive high voltage source VP2  616  and the in-phase program command signal PG  618  are set to the very high program voltage. The source line select line SLS  632  is set to the voltage level of the source line program inhibit voltage VS 2 **. The source line erase isolation signal DISE  630  is set to the voltage level of the high program select voltage that is approximately +5.0V. The out-of-phase program command signal PGB  619  is set to approximately the voltage level of the ground reference voltage source (0.0V). 
     Returning now to  FIG. 11 , after the completion of the program operation (Box  760 ), the page program verify operation is executed (Box  765 ) to determine if the program has been successfully accomplished. If the program is not successful, a loop counter is tested (Box  770 ) to assess that the maximum number of program trials is not exceeded. If the maximum number of program trials is not exceeded, the loop counter is incremented (Box  775 ) and the page program operation is executed repetitively until the maximum number of program trials is exceeded and the nonvolatile memory device is declared as having failed (Box  780 ) or the programming is a success and the nonvolatile memory device is declared as having successfully been erased (Box  785 ). 
     The program verify (Box  765 ) is essentially the same as the erase verify (Box  730 ) of  FIG. 11  except the selected word line  432 S of the single level program cell of  FIG. 13   a  is set to the upper boundary of the threshold voltage Vt 0 H to evaluate the programmed threshold voltage of the selected NMOS floating gate transistors M 0 , . . . , Mn. In the case of the multiple level program cell of  FIG. 13   b , selected word line  432 S is iteratively set to the upper boundary of the first threshold voltage Vt 0 H, second threshold voltage Vt 1 H, and the third threshold voltage Vt 2 H to evaluate the programmed threshold voltage of the selected NMOS floating gate transistors M 0 , . . . , Mn. 
     Returning now to  FIG. 10 , if the operation is determined (Box  755 ) not to be a program operation, the operation is a read operation and the read operation is executed (Box  790 ). The selected page is then read with the voltage levels applied as shown in  FIGS. 13   a ,  13   b ,  14   a ,  14   b , and  15 . Referring to  FIGS. 13   a  and  13   b , the unselected word lines  432 U of the unselected blocks  412 U and the unselected word lines  432 SU of the selected block  432 S are voltage level of the ground reference voltage source (0.0V). The selected word line  412 S is set to the voltage level of the power supply voltage source VDD. The selected local bit lines LBL  450 S for the columns that are to be read are set to the first read biasing voltage of approximately +1.0V for the single level program cell ( FIG. 13   a ) and the multiple level program cell ( FIG. 13   b ). The unselected local bit lines LBL  450 U for the columns that are set to a voltage level of approximately the ground reference voltage source (0.0V). To insure that the voltages are passed from the column address decoder  445  to the global bit lines  447   a , . . . ,  447   n  to the sector bit lines  455   a ,  455   b ,  455   k  to the local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k , the selected block gate select line  433 S for the selected block  412 S is set to the high read select voltage HV″ of approximately +5.0V to fully couple the local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  to the associated sector bit lines  455   a ,  455   b ,  455   k . The sector gate select line  467 S for the selected sector  410 S is set to voltage level of the power supply voltage source VDD. The unselected sector gate select lines  467 U for the unselected sectors  410 U are set to the voltage level of the ground reference voltage source. The selected source line  426 S connected to the selected page of the selected block  412 S is set to the voltage level of the ground reference voltage source. The unselected source lines  426 U of the selected block  412 S is set to the source line read inhibit voltage that is approximately +1.0V. The selected P-type well TPW  244 S in which the selected sector is formed and the unselected P-type wells TPW  244 U in which the unselected sectors are formed are set to the voltage level of the ground reference voltage source. 
     To establish the read voltages of  FIGS. 13   a  and  13   b  (referring to  FIGS. 14   a  and  14   b ), the selected word line  432 S is set to the voltage level of the power supply voltage source VDD by setting selected high voltage power supply voltage line XT  535 S to the voltage level of the voltage level of the power supply voltage source VDD. The voltage level of the selected in-phase block select signals XD  530 S, the first positive high voltage power source VPX1  527   a , the second high voltage power source VPX0  527   b , negative N-well biasing voltage source VN1  560 , and the positive N-well biasing voltage source VP1  562  are set to the voltage level of the power supply voltage source VDD to pass the voltage level of the power supply voltage source VDD to the selected word line  432 S. The out of phase read signal RDB  564 , the first high negative voltage source VNX0  526   a , the second negative high voltage source VNX1  526   b , and the isolation signal ISOP  528  are set to the voltage level of the ground reference voltage source (0.0V). These voltage levels, as described, pass the voltage level of the power supply voltage source VDD from the selected high voltage power supply voltage line XT  535 S to the selected word line  432 S. Further, The voltage levels, as described, pass the voltage level of the ground reference voltage source (0.0V) from the unselected high voltage power supply voltage line XT  535 U to the unselected word line  432 U. 
     The local bit lines  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  as shown in  FIG. 5  are selectively connected to the associated sector bit lines  455   a ,  455   b ,  455   k . Two of the sector bit lines  455   a ,  455   b ,  455   k  are selectively connected to one of the global bit lines  470   a , . . . ,  470   n . The local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  of one column is read or verified followed by reading the second local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  of the adjacent associated column. To accomplish this, the selected bit lines LBL  450 S for the column being read is set to the voltage level of the read sense voltage that is approximately +1.0V for sensing the status of the selected NMOS floating gate transistors M 0 , . . . , Mn on the activated column. The unselected bit lines LBL  450 U for the column not being read is set to the voltage level of the ground reference voltage source (0.0V) to disable the column not being read. The selected block gate select line  433 S and the unselected block gate select line  433 U for the selected sector is set to the voltage level of the high read select voltage HV″ of approximately +5.0V to fully couple the local bit line  450   a , . . . ,  450   k  and  451   a , . . . ,  451   k  to the associated sector bit lines  455   a ,  455   b ,  455   k.    
     The selected source line  426 S in the selected sector  412 S are set to the voltage level of the ground reference voltage source (0.0V). The unselected source lines  426 U is set to the first read inhibit voltage that is approximately +1.0V. The selected global bit line select line  467 S of the selected sector  410 S are set to the voltage level of the power supply voltage source VDD to connect a first set of sector bit lines  455   a ,  455   b ,  455   k  to the associated global bit lines  470   a , . . . ,  470   n . The unselected global bit line select lines  467 U of the selected sector  410 S are set to the voltage level of the ground reference voltage source (0.0V) to disconnect a second set of sector bit lines  455   a ,  455   b ,  455   k  from the associated global bit lines  470   a , . . . ,  470   n . For the read and program verify operations, the enabled global bit line select lines SLG[0]  467   a  and SLG[1]  467   b  will determine the sequence (order) of the reading or verifying of the adjacent columns of the NMOS floating gate transistors M 0 , . . . , Mn. The split program and program verify operations are done according to the order of activation of the associated global bit line select lines SLG[0]  467   a  and SLG[1]  467   b . The P-type well TPW  244 S selected sector  410 S and the P-type well TPW  244 U unselected sectors  410 U are set to the voltage level of the ground reference voltage source (0.0V). 
     To establish the voltage levels as described for the read operation in  FIGS. 13   a  and  13   b , the source line decoder  415  has the voltage levels shown in  FIG. 15 . Referring to  FIG. 15 , the selected source line  426 S is set to the voltage level of the ground reference voltage source (0.0V) and the unselected source lines  426 SU and  426 U are set to the source line read inhibit voltage VS 1 * that is approximately +1.0V. 
     Further, the selected block gate select line  433 S and unselected block gate select lines  433 U are to be set to the voltage level of the high source line select voltage HV″ that is approximately +5.0V. To accomplish these voltage levels, the selected source line address line ST  620 S for the selected source line  426 S is set to the voltage level of the ground reference voltage source (0.0V) and the unselected source line address line ST  620 U is set to the source line read inhibit voltage VS 1 *. The selected block source line selection signal SXD  610 S is set to the voltage level of the power supply voltage source VDD and the unselected block source line selection signal SXD  610 U is set to the voltage level of the ground reference voltage source (0.0V). The out of phase erase command signal ERSB  615  is set to the voltage level of the power supply voltage source VDD. The positive high voltage source VP2  616  and the out-of-phase program command signal PGB  619  are set to voltage level of the high source line select voltage HV″ that is approximately +5.0V. The source line select line SLS  632  is set to the voltage level of the first read inhibit voltage VS 1 *. The source line erase isolation signal DISE  630  is set to the voltage level of the power supply voltage source VDD. The in phase program command signal PG  618  is set to approximately the voltage level of the ground reference voltage source (0.0V). 
     In other embodiments of this invention, nonvolatile memory device  400  incorporating NOR flash floating-gate transistors may have NAND flash floating gate transistor cells and be in keeping with the intent of this invention. Further, the description of the nonvolatile memory device  400  incorporating NOR flash floating-gate transistors may also be NOR or NAND flash charge trapping transistor formed with a charge trapping layer formed of a first layer of silicon dioxide, a layer of silicon nitride, and a second layer of silicon oxide commonly referred to as a SONOS charge trapping transistor. 
     While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.