Operation scheme for programming charge trapping non-volatile memory
First Claim
1. A method for programming a multi-level charge storage memory cell having a first terminal and a second terminal acting as a source and a drain in a substrate, a charge storage element, and a control gate, comprising:
- determining a data value from one of more than two data values to be stored in the memory cell;
applying a gate voltage to the control gate relative to a reference voltage, a source voltage to the first terminal relative to the reference voltage, and a drain voltage to the second terminal relative to the reference voltage, in a program operation to induce charge transfer by hot electron injection to the charge storage element to establish a threshold voltage for the memory cell; and
holding the gate voltage substantially constant at one of a predetermined set of gate voltages in response to the determined data value during a portion of the program operation in which the voltage threshold converges on a target threshold corresponding with the determined data value.
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Abstract
A circuit and method for self-converging programming of a charge storage memory cell, such as NROM or floating gate flash. The method includes determining a data value from one of more than two data values to be stored in the memory cell, and applying a gate voltage to the control gate at one of a predetermined set of gate voltage levels selected in response to the determined data value. Programming parameters are controlled to establish a self-converging threshold state that is determined by the selected gate voltage. In this manner, the threshold voltage converges on a target threshold corresponding with the determined data value for the memory cell. Program verify operations are reduced or eliminated in various embodiments, reducing the overall time required for the program operation, and improving device performance. A second portion of the program operation can include verify operations to improve threshold margins across the array.
233 Citations
18 Claims
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1. A method for programming a multi-level charge storage memory cell having a first terminal and a second terminal acting as a source and a drain in a substrate, a charge storage element, and a control gate, comprising:
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determining a data value from one of more than two data values to be stored in the memory cell; applying a gate voltage to the control gate relative to a reference voltage, a source voltage to the first terminal relative to the reference voltage, and a drain voltage to the second terminal relative to the reference voltage, in a program operation to induce charge transfer by hot electron injection to the charge storage element to establish a threshold voltage for the memory cell; and holding the gate voltage substantially constant at one of a predetermined set of gate voltages in response to the determined data value during a portion of the program operation in which the voltage threshold converges on a target threshold corresponding with the determined data value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An integrated circuit, comprising:
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a memory array including decoding circuitry to select memory cells for programming, the memory cells having first and second terminals in a substrate acting as sources and drains, a charge storage element, and a control gate, wherein the memory cell is adapted to store more than two data values; a voltage supply circuit coupled to the memory array adapted to apply a gate voltage, a source voltage and a drain voltage to the control gate, first terminal and second terminal, respectively, of memory cells in the array; and a program controller coupled to the decoding circuitry and to the voltage supply circuit, the program controller adapted to execute a self-converging program operation for a selected memory cell to induce charge transfer by hot electron injection to the charge storage element and establish one of a set of threshold voltages corresponding with a respective one of the more than two data values in the selected memory cell, the program operation including determining a data value from one of more than two data values to be stored in the memory cell; applying a gate voltage to the control gate relative to a reference voltage, a source voltage to the first terminal relative to the reference voltage, and a drain voltage to the second terminal relative to the reference voltage, in a program operation to induce charge transfer by hot electron injection to the charge storage element to establish a threshold voltage for the memory cell; and holding the gate voltage substantially constant at one of a predetermined set of gate voltages in response to the determined data value during a portion of the program operation in which the voltage threshold converges on a target threshold corresponding with the determined data value. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification