Abstract: As for a variable resistive element including first and second electrodes, and a variable resistor containing a metal oxide between the first and second electrodes, in a case where a current path having a locally high current density of a current flowing between the both electrodes is formed in the metal oxide, and resistivity of at least one specific electrode having higher resistivity of the both electrodes is 100 ??cm or more, a dimension of a contact region of the specific electrode with the variable resistor in a short side or short axis direction is set to be more than 1.4 times as long as a film thickness of the specific electrode, which reduces variation in parasitic resistance generated in an electrode part due to process variation of the electrode, and prevents variation in resistance change characteristics of the variable resistive element generated due to the variation in parasitic resistance.

Abstract: A variable resistance element that can stably perform a switching operation with a property variation being reduced by suppressing a sharp current that accompanies completion of forming process, and a non-volatile semiconductor memory device including the variable resistance element are realized. The non-volatile semiconductor memory device uses the variable resistance element for storing information in which a resistance changing layer is interposed between a first electrode and a second electrode, and a buffer layer is inserted between the first electrode and the resistance changing layer where a switching interface is formed. The buffer layer and the resistance changing layer include n-type metal oxides, and materials of the buffer layer and the resistance changing layer are selected such that energy at a bottom of a conduction band of the n-type metal oxide configuring the buffer layer is lower than that of the n-type metal oxide configuring the resistance changing layer.

Abstract: A semiconductor memory device includes a memory cell array where a plurality of memory cells are arranged in a matrix, each of the memory cells serially connecting a two-terminal type memory element and a transistor for selection, a first voltage applying circuit that applies a write voltage pulse to a bit line, and a second voltage applying circuit that applies a precharge voltage to a bit line and a common line. In writing the memory cell, after the second voltage applying circuit has both terminals of the memory cell previously precharged to the same voltage, the first voltage applying circuit applies the write voltage pulse to one terminal of the writing target memory cell via the bit line, and while the write voltage pulse is applied, the second voltage applying circuit maintains the application of the precharge voltage to the other terminal of the memory cell via the common line.

Abstract: A three-dimensional memory cell array of memory cells with two terminals having a variable resistive element is formed such that: one ends of memory cells adjacent in Z direction are connected to one of middle selection lines extending in Z direction aligned in X and Y directions; the other ends of the memory cells located at the same point in Z direction are connected to one of third selection lines aligned in Z direction; a two-dimensional array where selection transistors are aligned in X and Y directions is adjacent to the memory cell array in Z direction; gates of selection transistors adjacent in X direction, drains of selection transistors adjacent in Y direction and sources of selection transistors are connected to same first selection line, second selection line, and different middle selection lines, respectively; and first, second and third selection lines are connected to X, Y and Z decoders, respectively.

Abstract: A large-capacity and inexpensive nonvolatile semiconductor memory device that prevents a leak current and is operated at high speed is implemented with a nonvolatile variable resistive element. A memory cell array includes the nonvolatile variable resistive elements each including a variable resistor composed of a metal oxide film to cause a resistance change according to an oxygen concentration in the film, an insulation film formed on the variable resistor, first and second electrodes to sandwich the variable resistor, and a third electrode opposite to the variable resistor across the insulation film. A writing operation is performed by applying a voltage to the third electrode to induce an electric field having a threshold value or more, in a direction perpendicular to an interface between the variable resistor and the insulation film, and a resistance state of the variable resistor is read by applying a voltage between the first and second electrodes.

Abstract: A memory cell array having a 1R structure is composed of nonvolatile variable resistive elements each including a variable resistor formed of a metal oxide film whose resistance changes depending on an oxygen concentration in the film, and first and second electrodes sandwiching the variable resistor. The first electrode and the variable resistor form a rectifier junction through a rectifier junction layer composed of an oxide layer and a layer (oxygen depletion layer) of the metal oxide film having an oxygen concentration lower than a stoichiometric composition. The oxygen moves between the first electrode and the metal oxide film when a voltage is applied, and a thickness of the oxygen depletion layer changes, so that the resistance of the metal oxide film changes and the rectifying properties are provided. A thickness of the oxygen depletion layer is set to allow the variable resistive element to show the sufficient rectifying properties.

Abstract: A nonvolatile semiconductor memory device includes a bit voltage adjusting circuit which, for each bit line, fixes potentials of a selected bit line and a non-selected bit line to a predetermined potential to perform a memory operation and a data voltage adjusting circuit which, for each data line, fixes potentials of a selected data line and a non-selected data line to a predetermined potential to perform a memory operation. Each of the voltage adjusting circuits includes an operational amplifier and a transistor, a voltage required for a memory operation is input to the non-inverted input terminal of the operational amplifier, and the inverted input terminal of the operational amplifier is connected to the bit line or the data line, so that the potential of the bit line or the data line is fixed to a potential of the non-inverted input terminal of the operational amplifier.

Abstract: A nonvolatile semiconductor memory device includes a memory cell array for storing user data provided by arranging memory cells each having a variable resistive element having a first electrode, a second electrode, and a variable resistor made of a metal oxide sandwiched between the first and second electrodes. The first and second electrodes are formed of a conductive material forming ohmic junction with the variable resistor and a conductive material forming non-ohmic junction with the variable resistor, respectively. The variable resistor changes between two or more different resistance states by applying a voltage between the electrodes. The resistance state after being changed is maintained in a nonvolatile manner. The variable resistive elements of all memory cells in the memory cell array are set to the highest of the two or more different resistance states in an unused state before the memory cell array is used to store the user data.

Abstract: The present invention provides a variable resistive element that can perform a stable switching operation at low voltage and low current, and also provides a low-power consumption large-capacity non-volatile semiconductor memory device including the variable resistive element. The non-volatile semiconductor memory device is a device using a variable resistive element, which includes a variable resistor between a first electrode and a second electrode, for storing information, wherein an oxygen concentration of a hafnium oxide (HfOx) film or a zirconium oxide (ZrOx) film constituting the variable resistor is optimized such that a stoichiometric composition ratio x of oxygen to Hf or Zr falls within a range of 1.7?x?1.97.

Abstract: In a semiconductor memory device using a variable resistive element made of a metal oxide for storing information, a voltage amplitude of a writing voltage pulse for changing the variable resistive element to a high resistance state is set within a voltage range in which the resistance value of the high resistance state after the change increases with time. The voltage amplitude is set within the voltage range in which the resistance value of the high resistance state after the change increases toward a predetermined peak with increase in voltage amplitude. When a data error is detected by the ECC circuit, it is estimated that the data that should be in the low resistance state changes to the high resistance state, and the variable resistive elements of all memory cells from which the error is detected are written to the low resistance state to correct the error bit.

Abstract: A large-capacity and inexpensive nonvolatile semiconductor memory device that prevents a leak current and is operated at high speed is implemented with a nonvolatile variable resistive element. A memory cell array includes the nonvolatile variable resistive elements each including a variable resistor composed of a metal oxide film to cause a resistance change according to an oxygen concentration in the film, an insulation film formed on the variable resistor, first and second electrodes to sandwich the variable resistor, and a third electrode opposite to the variable resistor across the insulation film. A writing operation is performed by applying a voltage to the third electrode to induce an electric field having a threshold value or more, in a direction perpendicular to an interface between the variable resistor and the insulation film, and a resistance state of the variable resistor is read by applying a voltage between the first and second electrodes.

Abstract: The invention realizes a semiconductor memory device that can efficiently execute a detection of a data error that might possibly occur in a continuous reading action, and a correction of the error data. The semiconductor memory device uses a variable resistive element made of a metal oxide for storing information. During a reading action of coded data with an ECC in the semiconductor memory device, when a data error is detected by an ECC circuit, a writing voltage pulse having a polarity opposite to a polarity of a reading voltage pulse is applied to all memory cells from which the error is detected so as to correct bits from which the error is detected, on an assumption that an erroneous writing has occurred due to the application of the writing voltage pulse having the polarity same as the polarity of the applied reading voltage pulse.

Abstract: A nonvolatile semiconductor memory device includes a memory cell array for storing user data provided by arranging memory cells each having a variable resistive element having a first electrode, a second electrode, and a variable resistor made of a metal oxide sandwiched between the first and second electrodes. The first and second electrodes are formed of a conductive material forming ohmic junction with the variable resistor and a conductive material forming non-ohmic junction with the variable resistor, respectively. The variable resistor changes between two or more different resistance states by applying a voltage between the electrodes. The resistance state after being changed is maintained in a nonvolatile manner. The variable resistive elements of all memory cells in the memory cell array are set to the highest of the two or more different resistance states in an unused state before the memory cell array is used to store the user data.

Abstract: The invention provides a semiconductor memory device including a variable resistance element capable of decreasing a variation of a resistance value of stored data due to a large number of times of switching operations and capable of performing a stable writing operation. The device has a circuit that applies a reforming voltage pulse to a memory cell including a variable resistance element of a degraded switching characteristic and a small read margin due to a large number of times of application of a write voltage pulse, to return each resistance state of the variable resistance element to an initial resistance state. By applying the reforming voltage pulse, the variable resistance element can recover at least one resistance state from a variation from the initial resistance state, and can recover the switching characteristic. Accordingly, there is obtained a semiconductor memory device in which a reduction of a read margin is suppressed.

Abstract: A variable resistance element that can stably perform a switching operation with a property variation being reduced by suppressing a sharp current that accompanies completion of forming process, and a non-volatile semiconductor memory device including the variable resistance element are realized. The non-volatile semiconductor memory device uses the variable resistance element for storing information in which a resistance changing layer is interposed between a first electrode and a second electrode, and a buffer layer is inserted between the first electrode and the resistance changing layer where a switching interface is formed. The buffer layer and the resistance changing layer include n-type metal oxides, and materials of the buffer layer and the resistance changing layer are selected such that energy at a bottom of a conduction band of the n-type metal oxide configuring the buffer layer is lower than that of the n-type metal oxide configuring the resistance changing layer.

Abstract: A semiconductor memory device includes a memory cell array where a plurality of memory cells are arranged in a matrix, each of the memory cells serially connecting a two-terminal type memory element and a transistor for selection, a first voltage applying circuit that applies a write voltage pulse to a bit line, and a second voltage applying circuit that applies a precharge voltage to a bit line and a common line. In writing the memory cell, after the second voltage applying circuit has both terminals of the memory cell previously precharged to the same voltage, the first voltage applying circuit applies the write voltage pulse to one terminal of the writing target memory cell via the bit line, and while the write voltage pulse is applied, the second voltage applying circuit maintains the application of the precharge voltage to the other terminal of the memory cell via the common line.

Abstract: A memory cell array having a 1R structure is composed of nonvolatile variable resistive elements each including a variable resistor formed of a metal oxide film whose resistance changes depending on an oxygen concentration in the film, and first and second electrodes sandwiching the variable resistor. The first electrode and the variable resistor form a rectifier junction through a rectifier junction layer composed of an oxide layer and a layer (oxygen depletion layer) of the metal oxide film having an oxygen concentration lower than a stoichiometric composition. The oxygen moves between the first electrode and the metal oxide film when a voltage is applied, and a thickness of the oxygen depletion layer changes, so that the resistance of the metal oxide film changes and the rectifying properties are provided. A thickness of the oxygen depletion layer is set to allow the variable resistive element to show the sufficient rectifying properties.

Abstract: Provided is a variable resistive element which performs high speed and low power consumption operation. The variable resistive element comprises a metal oxide layer between first and second electrodes wherein electrical resistance between the first and second electrodes reversibly changes in accordance with application of electrical stress across the first and second electrodes. The metal oxide layer has a filament, which is a current path where the density of a current flowing between the first and second electrodes locally increases. A portion including at least the vicinity of an interface between the certain electrode, which is one or both of the first and second electrodes, and the filament, on an interface between the certain electrode and the metal oxide layer is provided with an interface oxide which is an oxide of at least one element included in the certain electrode and different from the oxide of the metal oxide layer.

Abstract: An inexpensive nonvolatile memory having high performance which makes random write and readout possible an unlimited number of times is provided. A unit memory cell is formed of a MISFET having a channel body that is electrically isolated from a semiconductor substrate and a resistance change element having a two-terminal structure with one end electrically connected to a drain of the MISFET. The MISFET functions as a volatile memory element, and the resistance change element functions as a nonvolatile memory element, so that information stored in the MISFET is copied to the resistance change element before the power is turned OFF and information stored in the resistance change element is transferred to the MISFET when the power is turned ON, and thus, the MISFET is used as a volatile memory which makes random write and readout possible.

Abstract: A nonvolatile semiconductor memory device includes a bit voltage adjusting circuit which, for each bit line, fixes potentials of a selected bit line and a non-selected bit line to a predetermined potential to perform a memory operation and a data voltage adjusting circuit which, for each data line, fixes potentials of a selected data line and a non-selected data line to a predetermined potential to perform a memory operation. Each of the voltage adjusting circuits includes an operational amplifier and a transistor, a voltage required for a memory operation is input to the non-inverted input terminal of the operational amplifier, and the inverted input terminal of the operational amplifier is connected to the bit line or the data line, so that the potential of the bit line or the data line is fixed to a potential of the non-inverted input terminal of the operational amplifier.