Fujitsu Corporation

Shouichi Kawamura

Yasushi Kasa

Takao Akaogi

Yasushige Ogawa

Kiyoshi Itano

Hiromi Kawashima

Masanobu Yoshida

Tetsuji Takeguchi

Ryoji Hagiwara

Nobuaki Takashina

Minoru Yamashita

Yasushige Oqawa

A semiconductor memory device has 2 word lines, a plurality of bit lines, a plurality of nonvolatile memory cells disposed at each intersection of the word lines and the bit lines, a write circuit for writing data to a memory cell located at an intersection of selected ones of the word lines and the bit lines, and a sense amplifier for reading data out of the memory cells. Further, the semiconductor memory device comprises a first unit for simultaneously selecting a block of 2 (n>m) word lines among the 2 word lines, and a second unit for not selecting a block of 2 (m>k) word lines among the 2 word lines. The second unit does not select the block of 2 word lines, and selects a block of 2 word lines prepared outside the 2 word lines when any one of the 2 word lines among the 2 word lines is defective. Consequently, redundant word lines are effectively employed, write and verify operations are stable, and thereby the yield and performance of the semiconductor memory device are improved.

Nonvolatile semiconductor memory device having electrically and collectively erasable characteristics

A semiconductor memory device has 2,word lines, a plurality of bit lines, a plurality of nonvolatile memory cells disposed at each intersection of the word lines and the bit lines, a write circuit for writing data to a memory cell located at an intersection of selected ones of the word lines and the bit lines, and a sense amplifier for reading data out of the memory cells. Further, the semiconductor memory device comprises a first unit for simultaneously selecting a block of 2,(n>m) word lines among the 2,word lines, and a second unit for not selecting a block of 2,(m>k) word lines among the 2,word lines. The second unit does not select the block of 2,word lines, and selects a block of 2,word lines prepared outside the 2,word lines when any one of the 2,word lines among the 2,word lines is defective. Consequently, redundant word lines are effectively employed, write and verify operations are stable, and thereby the yield and performance of the semiconductor memory device are improved.

A semiconductor memory device has 2.sup.n word lines, a plurality of bit lines, a plurality of nonvolatile memory cells disposed at each intersection of the word lines and the bit lines, a write circuit for writing data to a memory cell located at an intersection of selected ones of the word lines and the bit lines, and a sense amplifier for reading data out of the memory cells. Further, the semiconductor memory device comprises a first unit for simultaneously selecting a block of 2.sup.m (n&gt;m) word lines among the 2.sup.n word lines, and a second unit for not selecting a block of 2.sup.k (m&gt;k) word lines among the 2.sup.m word lines. The second unit does not select the block of 2.sup.k word lines, and selects a block of 2.sup.k word lines prepared outside the 2.sup.n word lines when any one of the 2.sup.k word lines among the 2.sup.m word lines is defective. Consequently, redundant word lines are effectively employed, write and verify operations are stable, and thereby the yield and performance of the semiconductor memory device are improved.

Semiconductor memory device with electrically controllable threshold

A flash memory performs channel erasing or source erasing by applying a negative voltage to a control gate. The device includes a voltage restriction device which restricts the negative voltage to be applied to the control gate so that the negative voltage will be a constant value relative to the voltage of the channel or source. Alternatively, two voltage restricting devices restrict the negative voltage applied to the control gate and the voltage to be applied to the source so that the voltages will be a constant value relative to a common reference voltage.

Flash memory with improved erasability and its circuitry

A negative-voltage circuit for realizing a flash memory is installed independently and is applied selectively to word lines in response to signals sent from row decoders. Row decoders for specifying word lines need not be installed in the negative voltage circuit. The negative circuit can therefore be reduced in scale.

Negative voltage circuit for a flash memory

The present invention relates to improvements in erasing a flash memory. An object of the present invention is to shorten the erasing time. During pre-erase writing, at least either word lines or bit lines are selected in units of multiple lines at a time, and data are written in multiple selective transistors simultaneously.

A nonvolatile semiconductor memory employs sense amplifiers, circuits for providing stabilized source voltages, and circuits for realizing high-speed and reliable read and write operations. The semiconductor memory has a matrix of nonvolatile erasable memory cell transistors. The semiconductor memory employs an arrangement for effectively using a plurality of source voltages and applying a verify voltage to sense amplifiers and word lines, a write verify arrangement for detecting an output of the sense amplifiers, an arrangement for comparing an output of the sense amplifiers with a reference value to determine whether or not a written state of the memory cell transistors is acceptable, an arrangement for adjusting an output of the sense amplifiers with use of inverters and transistors in response to a current flowing to the memory cell transistors, to improve a drive speed of the sense amplifiers, an internal source voltage generating arrangement using an n-channel depletion transistor connected to an external source voltage (Vcc), the gate of the transistor being connected to a low source voltage (Vss) to provide an internal source voltage (Vci), a combination of an arrangement for dropping the external source voltage (Vcc) for read to a predetermined value to drive a read circuit in the memory and an arrangement for dropping an external voltage (Vpp) for write, to generate a word line potential for a verify-after-write operation, an arrangement for setting a reference voltage (Vref) as a lower threshold (Vth) allowed for cell transistors (11.sub.00 to 11.sub.22), and comparing the voltage of a data bus (13) with the reference voltage (Vref), to simultaneously carry out an erase-verify operation on all memory cell transistors, and a pre-read arrangement for accessing the next address during a read time of the sense amplifiers, to improve a read speed.

Nonvolatile semiconductor memory

An object of the present invention is to ease the dielectric strength requirements for transistors forming power supply circuits or the like. A nonvolatile semiconductor memory of the present invention includes a plurality of memory cells, each of which is composed of a floating gate, a control gate, a drain, and a source, and a negative voltage generating means whose generated negative voltage is applied to the control gate for drawing a charge stored in the floating gate into a channel or the source when stored data is erased electrically. The nonvolatile memory of the present invention further includes positive erasure voltage generating means, and a positive voltage higher than a conventional supply voltage generated by the positive erasure voltage generating means is applied to the channel or the source.

Nonvolatile semiconductor memory that eases the dielectric strength

An exclusive OR circuit includes a first series circuit in which a source of a first pMIS transistor is connected to a positive-voltage power supply line. A drain of the first pMIS transistor is connected to a drain of a first nMIS transistor via a second nMIS transistor. The source of the first nMIS transistor is connected to a low-voltage power supply line via a fourth nMIS transistor. A second series circuit has a drain of a third nMIS transistor connected to a high-voltage power supply line via a second pMIS transistor. The source of the third nMIS transistor is connected to the source of a third pMIS transistor. The drain of the third pMIS transistor is connected to the low-voltage power supply line via a fourth pMIS transistor. The gates of the first and third nMIS transistors and the first and third pMIS transistors are connected to one another and provided with a first input. The gates of the second and fourth nMIS transistors and the second and fourth pMIS transistors are connected to one another and provided with a second input. The sources of the second and third nMIS transistors are connected to each other and provide the exclusive OR of the first and second inputs.

XOR CMOS logic gate

A semiconductor memory having address buffer means, memory cell means, word line selection means, bit line selection means, an output buffer, first address generation means connected to the address buffer means, for providing and address for specifying a group of data pieces, and second address generation means for providing addresses for specifying the data pieces, respectively, the semiconductor memory comprising first reading means for selecting and reading a group of data pieces through one of the word line selection means and bit line selection means according to an address provided by the first address generation means, second reading means for selecting the data pieces, which have been selected and read according to the address provided by the first address generation means, through one of the bit line selection means and word line selection means according addresses provided by the second address generation means and providing them to the output buffer; and pre-reading means for reading another group of data pieces according the another address to be provided by the first address generation means while the preceding data pieces are being read according to the preceding address provided by the first address generation means and being selectively provided to the output buffer according to the addresses provided by the second address generation means.

Nonvolatile semiconductor memory with pre-read means

When a current flows through a selected memory cell transistor at the time of data reading, the gate voltage of an n-channel MOS transistor, which makes up the current flowing through the load, rises. Thus, when a current flows through a selected memory cell transistor at the time of data reading, the current through the load is increased so that the time required for data reading when the current flows through the selected memory cell transistor can be shortened and the data reading can be effected at a high speed.

A nonvolatile semiconductor memory employs sense amplifiers, circuits for providing stabilized source voltages, and circuits for realizing high-speed and reliable read and write operations. The semiconductor memory has a matrix of nonvolatile erasable memory cell transistors. The semiconductor memory employs an arrangement for effectively using a plurality of source voltages and applying a verify voltage to sense amplifiers and word lines, a write verify arrangement for detecting an output of the sense amplifiers, an arrangement for comparing an output of the sense amplifiers with a reference value to determine whether or not a written state of the memory cell transistors is acceptable, an arrangement for adjusting an output of the sense amplifiers with use of inverters and transistors in response to a current flowing to the memory cell transistors, to improve a drive speed of the sense amplifiers, an internal source voltage generating arrangement using an n-channel depletion transistor connected to an external source voltage (V.sub.CC), the gate of the transistor being connected to a low source voltage (V.sub.ss) to provide an internal source voltage (V.sub.ci), a combination of an arrangement for dropping the external source voltage (V.sub.cc) for read to a predetermined value to drive a read circuit in the memory and an arrangement for dropping an external voltage (V.sub.pp) for write, to generate a word line potential for a verify-after-write operation, an arrangement for setting a reference voltage (V.sub.ref) as a lower threshold (V.sub.th) allowed for cell transistors (11.sub.00 to 11.sub.22), and comparing the voltage of a data bus (13) with the reference voltage (V.sub.ref), to simultaneously carry out an erase-verify operation on all memory cell transistors, and a pre-read arrangement for accessing the next address during a read time of the sense amplifiers, to improve a read speed.

The objects of the present invention are to enhance the operating speed by improving the access speed to a redundant memory, and also to enable a redundant address to be written into an electrically programmable memory device, which stores the redundant address, even for a semiconductor memory designed to operate with a low-voltage, single power supply. In a semiconductor memory according to a first aspect of the invention, an address detection circuit, which determines whether the access is for a replaced element, is constructed with a gate circuit that can be set either to such a state as to enable one of two complementary input signals for output or to a high impedance state, and a signal line, onto which a signal to inhibit the selection of normal memory cells is output upon detection of an address signal for redundancy, is directly controlled by an output of a redundancy memory circuit which stores the state of the redundancy function. Furthermore, in a semiconductor memory according to a second aspect of the invention, the write voltage for writing an address into a redundancy nonvolatile semiconductor memory is supplied from outside the semiconductor memory.

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Kawasaki, Japan

Shouichi Kawamura