摘要:
A method is provided for biasing a NAND array EEPROM during programming to allow the array to be scaled down further before reach punchthrough. The sources of the ground-select transistors of the NAND array are biased at V.sub.cc instead of ground to reduce the voltage drop across the source and drain of the ground-select transistors. As a result, the channel length of the ground-select transistors can be further shortened before punchthrough is obtained, resulting in a higher density EEPROM.
摘要:
A capacitor structure which exhibits a constant capacitance at non-negative voltages is provided by erasing a P-well floating gate NMOS transistor prior to its use as a capacitor. By erasing the transistor, a negative threshold voltage is obtained, thereby turning on the transistor and placing the transistor in an inversion state where the MOS capacitance is voltage-independent. Such transistors can be utilized as capacitors, whereby one plate of the capacitor corresponds to the control gate of the transistor and the other plate corresponds to the commonly connected source, drain, P-well, and deep N-well regions of the transistor, in voltage regulator circuits or other circuits in which node stabilization is desired. As a result, the capacitance is constant even at initialization when zero volts is applied.
摘要:
A flash memory including a page buffer with bias circuitry and a reference array enabling reading and verifying values stored on a word line of memory cells in parallel using the page buffer irrespective of temperature, Vcc, and process variations. The bias circuitry includes a cascode transistor having a source connected to the reference cell array which provides a single reference signal. The bias cascode couples the reference signal to an input of a bias inverter in the bias generator, while a bias load transistor in the bias generator couples Vcc to the bias inverter input. The page buffer includes a set of latches that are each coupled to a memory cell by a cascode. A first inverter in each latch has transistors with sizes matching the transistors in the bias inverter. A latch load transistor is connected between a pull-up and pull-down transistor of a second inverter in each latch and is sized to match the bias load transistor. Gates of the bias load transistor and the latch load transistor are both coupled to the output of the bias inverter enabling the first inverter of each latch to have an input mirroring the input of the bias inverter.
摘要:
The present invention provides a method of verifying that all flash EEPROM transistors in a NAND string are properly erased without overerasing by applying a bias voltage to the source of the bottom select gate of the NAND array and applying a non-negative erase verify voltage to the control gates of each transistor during an erase verify. The bias voltage is at least equal to the erased threshold voltage of the worst case transistor to ensure proper erase verification. If all transistors are not erased, then another erase operation is performed. Erasing is repeated until the erase verify operation indicates that all transistors are properly erased. By erasing and verifying according to the present invention, the NAND array is completely and properly erased while minimizing overerasing the array.
摘要:
A block decoder includes a p-well. A low voltage source is coupled to the p-well for asserting a body bias voltage to the p-well. An n-type word line pass transistor is positioned within the p-well and is coupled to a word line for passing programming voltages to the word line. A high voltage source is coupled to pass circuitry configured to assert a voltage on a gate of the pass transistor. The low voltage source is configured to apply a voltage of approximately 10 volts or more to the p-well during programming, thus reducing the voltage between the source and body region (and thus the threshold voltage as well) of NMOS transistors disposed within the p-well. Therefore, the amount of voltage needed to be applied to the pass transistors is reduced. Furthermore, the pass circuitry can work for lower supply voltages since the supply voltage is limited by the threshold voltage of the n-type transistors within the p-well.
摘要:
A memory system has the capability to adjust a program or erase voltage if the time to program or erase is excessive. The memory system comprises at least a memory cell, a voltage value storage device, a voltage source, and a voltage adjustment circuit. The voltage value storage device stores a voltage value. The voltage source receives and converts the voltage value into a voltage. The voltage source applies the voltage to at least one memory cell. The voltage adjustment circuit is also coupled to receive the stored voltage value. The voltage adjustment circuit determines the time required to program or erase at least one memory cell using the voltage value. If the time to program or erase at least one memory cell is excessive, the voltage adjustment circuit increments the voltage value stored in the voltage value storage device.
摘要:
A method is provided to determine erase threshold voltages of memory transistors and thereby identify unusable memory transistors. A voltage is applied to the common source of a selected memory transistor and gradually incremented until a logical HIGH bit is read as a logical LOW bit. By iteratively incrementing Vbias, the erase threshold voltage for each memory transistor can be determined. In one process, the erase threshold voltage for each memory transistor in a memory device is determined and then the memory device is put under stress tests to simulate normal operative conditions. After the stress tests, the erase threshold voltage of each memory transistor can be once again determined to ascertain the change in the erase threshold voltage, i.e., the data retention characteristic, of each memory transistor.
摘要:
In the programming of a non-volatile memory device, such as a NAND flash memory device 100, a positive bias voltage V.sub.bias is applied to a bit line 44 to set a respective memory gate 44a in a programmed state. In a further embodiment, the positive bias voltage V.sub.bias is obtained by dividing the select drain gate voltage V.sub.cc using two resistors 56 and 58 connected in series.
摘要:
A decoder for decoding from two sides of a memory array. The decoder is positioned on two sides of the memory array. The decoder includes driver circuits that are connected to routing lines from the memory array. To reduce the size of the decoder, some of the routing lines extend from one side of the memory array and the remaining routing lines extend from the other side of the memory array.
摘要:
An EEPROM NAND array has floating gate memory cells coupled in series, each having a control gate, a floating gate, a body region, and an insulating layer between the floating gate and the body region. A negative charge pump is coupled to the body region. In programming, the body region of the memory cell selected for programming is biased to a negative voltage by the negative charge pump while the control gate of the memory cell is biased to a predetermined positive voltage sufficient to induce Fowler-Nordheim tunneling from the body region into the floating gate. The present invention allows the programming voltage requirement at the control gate of a NAND EEPROM memory cell to be significantly reduced which allows for the peripheral voltage delivery circuitry in NAND EEPROM arrays to be designed for lower voltages than for conventional NAND EEPROM arrays.