SEMICONDUCTOR MEMORY DEVICE

Abstract: Address signals are decoded by partial decoders (18₀-18₇), to generate in-phase and complementary signals. These signals are selectively input to main decoders (19₀-19₁₅) consisting of NAND circuits (19₀-19₁₅). Further, these signals are fed via through programming fuse ele­ ments (23₀ to 23₇) to a NOR gate (22). The fuse elements and the NOR gate form a programmable spare decoder (30). When the bit selected by the main decoder is defective, the output of this main decoder is shut off. Further, the fuse ele­ ment of the spare decoder is opened corresponding to the main decoder to select the defective bit, thereby to replace the defective bit with the spare bit.

Description: This invention relates to semiconductor memory devices with redundancy circuits, and more particularly to an improvement of programmable spare decoders in semiconductor memory devices. In recent years, in semiconductor devices of a very high degree of integration, called "VLSI" (very large scale integration), with increase of integration density, the miniaturization of elements and the size increase of chips have been amazing. For this reason, the probability of a defective bit occurring in a semiconductor chip has become greater and the reduction of the manufacturing yield is present. In order to solve this problem, auxiliary decoders and spare bits are formed in the chip. Semiconductor integrated circuit devices have been developed in which, if there is a defective bit, it is replaced with a spare bit by means of an auxiliary decoder. These circuits are called "redundancy circuit". In order to replace the defective bit with a spare bit, the auxiliary decoder can be programmed so that the defective bit is disconnected from the device by a programmable fuse element, and the spare bit selected. A 288K CMOS EPROM with a nine-block cell array is disclosed in IEEE Journal of solid state circuits, Vol. SC-18(1983) Oct. No. 5, New York, USA. The device can be used as an 8 or 9 bit EPROM of which the ninth block can be used as a redundant block by electrically programmable polysilicon fuses. To eliminate failures due to defective word lines a redundant circuit for word replacement is included (Figure 8). The defective word line is switched by replacing the decoder which drives the defective word line with a redundant decoder. In this case the fuse corresponding to the defective address bit Ai and the fuse of the circuit to indicate enabling of the redundant word line are blown. To give a more detailed description of the basic structure of such semiconductor memory devices Fig. 1 shows a buffer circuit, a main decoder circuit and a programmable spare decoder circuit in a MOS (metal oxide semiconductor) dynamic RAM (random access memory). Address buffers 11₀, 11₁, 11₂, 11₃ are provided to receive address inputs Ai, Aj, Ak and Al. Each of the address buffers 11₀ to 11₃ outputs two signals, one in phase with its input signal, and the other out of phase, i.e. a complementary signal. Main decoders are composed of NOR circuits 12₀ to 12₁₅, which receive different combinations of two signals output from buffers 11₀ to 11₃. One of the decoders 12₀ to 12₁₅ is energized according to the logic of the address input, and the energized decoder energizes that of the bit lines B₀ to B₁₅ which is connected to the energized decoder. For example, if a defective bit is detected in the bit line B₀ connected to decoder 12₀ according to a known method, fuse 13₀ between decoder 12₀ and bit line B₀ is opened or burned according to a relevant known method to disconnect decoder 12₀ from the memory. The spare decoder 10 is comrised of fuses 15₀ to 15₇ coupled with all outputs Ai, Ai to Al, Al of address buffers 11₀ to 11₃ and a NOR circuit 14 coupled with those fuses. Spare decoder 10 designates an auxiliary or spare bit to repair the defective bit. To designate the auxiliary bit, it is necessary to program spare decoder 10 so that the logic of the spare decoder 10 be equal to that of the main decoder connected to the defective bit. This can be attained by selectively opening fuses 15₀ to 15₇ so as to have the same program. In this case, the number of fuses to be opended is the half of the buffer outputs Ai, Ai to Al, Al . In recent years, a laser has been used for opening or buring these fuse elements. Accuracy of opening operation is relatively improved, but is still insufficient. The number of opening errors increases as the number of fuses to be opening is large. Therefore, decrease of the number of the burned fuses leads to improvement of repairing accuracy of defective element. The main decoders 12₀ to 12₁₅ used in the conventional MOS dynamic RAM are constructed with NOR circuits. In all of these NOR circuits, in a precharge mode, their output nodes are precharded to logical high level. In an active mode, nodes other than a selected node are discharged to logical low level. The discharge of the non-select nodes consumes much power. Reduction of the power dissipation is a strong demand in this field. Accordingly, an object of this invention is to provide a semiconductor device which can effectively repair defective bits with low power dissipation by reducing the number of fuse elements. According to an aspect of this invention, there is provided a semiconductor memory device with a redundancy circuit comprising: address buffers each receiving an address signal and producing a signal in phase with the address signal and a signal out of phase with the address signal; partial decoders comprising logic circuits for receiving different combinations of the signals supplied from said address buffers and producing output signals; main decoders comprising logic circuits and fuse elements connected to the logic circuits, for receiving different combinations of the signals supplied from said partial decoders and producing output signals to select a bit designated by the address signals, a fuse element of a main decoder being opened or burnt to disconnect the main decoder from the memory if the defective bit is detected in the respective bit line; and a programmable decoder (30) comprising programming fuse circuits and a NOR-gate, the programmable decoder being programmed by opening fuse elements of the programming fuse circuits to have the same program as that of the main decoder being disconnected from the memory, so that when said defective bit is designated by the address signals, the programmable decoder selects a spare bit; characterized in that said programmable decoder, receives the output signals from said partial decoders so that when a bit selected by said main decoders is defective said programmable decoder selects the spare bit based on the program applied to said programmable decoder. According to another aspect of this invention, there is provided a semiconductor memory device with a redundancy circuit comprising: address buffers each receiving an address signal and producing a signal in phase with the address signal and a signal out of phase with the address signal; partial decoders comprising logic circuits for receiving different combinations of the signals supplied from said address buffers and producing output signals; main decoders comprising logic circuits for receiving different combinations of the signals supplied from said first partial decoders and producing output signals; fuse elements receiving the signals supplied from said main decoders and producing output signals to select a bit, designated by the address signals, a fuse element being opened or burnt to disconnect the main decoder from the memory if a defective bit is detected in the respective bit line; and a programmable decoder comprising programming fuse circuits and a NOR-gate, the programmable decoder being programmed by opening fuse elements of the programming fuse circuits to have the same program as the of the main decoder being disconnected from the memory, so that when said defective bit is designated by the address signals, the programmable decoder selects a spare bit; characterized in that said programmable decoder, receives the output signals from said main decoders so that when a bit selected by said main decoders is defective said programmable decoder selects the spare bit based on the program applied to said programmable decoder. According to a further aspect of this invention there is provided a semiconductor memory device with a redundancy circuit comprising: address buffers each receiving an address signal and producing a signal in phase with the address signal and a signal out of phase with the address signal: a plurality of stages of partial decoders the partial decoders of the first stage comprising logic circuits for receiving different combinations of the signals supplied from said address buffers and producing output signals, the partial decoders of the second and the following stages each comprising logic circuits for receiving different combinations of the signals supplied from the partial decoders of the preceding stage and producing output signals to the partial decoders of the following stage; fuse elements for receiving the signals supplied from the partial decoders of the final stage and producing output signals to select a bit designated by the address signals, a fuse element being opened or burnt to disconnect the partial decoders of the final stage from the memory if the defective bit is detected in the respective bit line; and a programmable decoder comprising programming fuse circuits the programmable decoder being programmed by opening a fuse element of the programming fuse circuits to have the same program as that of the partial decoders of the final stage being disconnected from the memory, so that when said defective bit is designated by the address signals, the programmable decoder selects a spare bit; characterized in that said programmable decoder receives the output signals from the partial decoders of the final stage so that when a bit selected by said partial decoders of the final stage is defective said programmable decoder selects the spare bit based on the program applied to said programmable decoder. This invention can be more fully understood from the following detailed description whent aken in conjunction with the accompanying drawings, in which: Fig. 1 is a logic circuit diagram showing one example of prior semiconductor devices; Fig. 2 is a logic circuit diagram of a semiconductor device according to an embodiment of this invention; and Fig. 3 is a logic circuit diagram of a semiconductor device according to another embodiment of this invention. An embodiment of this invention will be described referring to Fig. 2. In this embodiment, only four address inputs Ai, Aj, Ak and Aℓ are provided for simplicity of explanation. Four address buffers 11₀ to 11₃ are provided for receiving address inputs Ai, Aj, Ak and Aℓ, respectively. These buffers output signals that are in phase with their inputs and signals that are out of phase, i.e., complementary signals. Partial decoders 18₀ to 18₇ are each composed of a NAND circuit 16 and an inverter 17 connected to the output of the NAND circuit. Different paired signals or different combination of signals output from buffers 11₀ to 11₃ are supplied to these NAND circuits as the input signals. Different paired signals of outputs X0 - X7 of partial decoders 18₀ to 18₇ are input to main decoders 19₀ to 19₁₅, which are composed of NAND circuits. For example, if a defective bit is detected in the bit line B0 connected to decoder 19₀ according to a known method, fuse 21₀ between decoder 19₀ and bit line B0 is opened or burned according to the relevant known method to disconnect decoder 19₀ from the memory. The spare decoder 30 is comprised of programming fuses 23₀ to 23₇ coupled with all outputs of the partial decoders 18₀ to 18₇ coupled with those fuses. Spare decoder 30 designates an auxiliary or spare bit to repair the defective bit. To designate the auxiliary bit, it is necessary to program spare decoder 30 so that the logic of the spare decoder 30 be equal to that of the main decoder connected to the defective bit. This can be attained by opening only two fuses 23₀ and 23₄ of those 23₀ to 23₇. The fuses 23₀ and 23₄ are coupled with signals, which are input to NAND circuit 19₀ as the main decoder. Thus, opening of only two fuses of those eight fuses is merely needed for programming in this embodiment, while prior art needs the opening of the half of all of the fuses. That is to say, the number of opened fuses may be reduced 1/2 that of the prior art. In this respect, the opening error occurrence is remarkably reduced in this embodiment. NAND circuits are used for the main decoders 19₀ to 19₁₅. Therefore, in the active mode, only the output node of the selected decoder or the bit line connected to the selected decoder is discharged. The output nodes of the remaining decoders are left in the precharged state, i.e. logical high level. As a result, the power dissipation can be reduced. In the decoder of this embodiment, although the number of required fuses is equal to that of the prior decoder, the number of opened fuse elements is reduced half. In this respect, repairment of defective bits by the redundancy circuit can greatly be improved. Alternatively, second partial decoders are used, which are connected to the outputs of the partial decoders 18₀-18₇. The outputs of the second partial decoders are supplied to spare decoder 30 via programming fuses 23₀ to 23₃ of spare decoder 30. Such an approach is implemented in Fig. 3. In Fig. 3, same reference numerals are used for designating same equivalent portions in Fig. 2. As shown, in this embodiment, second partial decoders 28₀ to 28₁₅ each comprising a NAND gate 6 and an inverter 7 are provided. Applied to second partial decoders 28₀ to 28₁₅ are different pairs of outputs X0 to X7 issued from the first partial decoders 18₀-18₇. The outputs Y0 to Y15 of second decoders 28₀ to 28₁₅ are input to spare decoder 30 via programming fuses 23₀ to 23₁₅. For example, if a defective bit is detected in the bit line B0 connected to fuse 21₀ as a main decoder according to the known method, fuse 21₀ connected to bit line B0 is opened according to a relevant known method to disconnect the output Y0 from the memory. The spare decoder 30 is comprised of fuses 23₀ to 23₁₅ coupled with all outputs Y0 - Y15 of the second partial decoders 28₀ to 28₁₅, and a NOR circuit 22 coupled with those fuses. Spare decoder 30 designates an auxiliary or spare bit to repair the defective bit. To designate the auxiliary bit, it is necessary to program spare decoder 30 so that the logic of the spare decoder 30 be equal to that of the main decoder connected to the defective bit. This can be attained by opening only one fuse 23₀ of those 23₀ to 23₁₅. The fuse 23₀ is coupled with the signal Y0, which is input to the fuse 21₀ as the main decoder. Thus, in this embodiment, the opening of the one fuse is needed for programming, while the prior art needs the opening of the half of all of the fuses. That is to say, the number of open fuses may be reduced 1/4 that of the prior art. In this respect, the opening error occurrence is remarkable reduced in this embodiment. As described above, in this embodiment, no NAND circuits are used for she main decoders. Therefore, the charge or discharge does not occur. As the result, the power dissipation can be reduced. It should be understood that the number of partial decoder stages is not limited to one or two stages, but if necessary a desired number of the decoder stages may be used. The number of fuses to be opened is reduced 1/2 n that of the prior device shown in Fig. 1 (n is the number of stages of partial decoder). As will clearly be understood form the above, according to the invention, the production yield can be increased and the power dissipation can be reduced.

Claims: A semiconductor memory device with a redundancy circuit comprising: address buffers (11₀, ..., 11₃) each receiving an address signal (Ai, ..., Al) and producing a signal in phase with the address signal and a signal out of phase with the address signal; partial decoders (18₀, ..., 18₇) comprising logic circuits (16, 17) for receiving different combinations of the signals supplied from said address buffers and producing output signals (X₀, ..., X₇); main decoders comprising logic circuits (19₀, 20₀, ..., 19₁₅, 20₁₅) and fuse elements (21₀, ..., 21₁₅) connected to the logic circuits, for receiving different combinations of the signals supplied from said partial decoders and producing output signals to select a bit (B0, ..., B15) designated by the address signals, a fuse element of a main decoder being opened or burnt to disconnect the main decoder from the memory if the defective bit is detected in the respective bit line; and a programmable decoder (30) comprising programming fuse circuits (23₀, ..., 23₇,) and a NOR-gate (22), the programmable decoder being programmed by opening fuse elements (23₀, ..., 23₇) of the programming fuse circuits to have the same program as that of the main decoder being disconnected from the memory, so that when said defective bit is designated by the address signals the programmable decoder selects a spare bit; characterized in that: said programmable decoder receives the output signals from said partial decoders so that when a bit selected by said main decoders is defective said programmable decoder selects the spare bit based on the program applied to said programmable decoder. A semiconductor memory device according to claim 1, characterized in that said logic circuits of said partial decoders are NAND gates. A semiconductor memory device according to claims 1 or 2, characterized in that said logic circuit of said main decoders are NAND gates. A semiconductor memory device with a redundancy circuit comprising: address buffers (11₀, ..., 11₃) each receiving an address signal (Ai, ..., AI) and producing a signal in phase with the address signal and a signal out of phase with the address signal; partial decoders (18₀, ..., 18₇) comprising logic circuits (16, 17) for receiving different combinations of the signals supplied from said address buffers and producing output signals (X₀, ..., X₇); main decoders (28₀, ..., 28₁₅) comprising logic circuits (6, 7) for receiving different combinations of the signals supplied from said first partial decoders and producing output signals (Y0, ..., Y15); fuse elements (21₀, ..., 21₁₅) receiving the signals supplied from said main decoders and producing output signals to select a bit (B0, ..., B15) designated by the address signals, a fuse element being opened or burnt to disconnect the main decoder from the memory if a defective bit is detected in the respective bit line; and a programmable decoder (30) comprising programming fuse circuits (23₀, ..., 23₁₅,) and a NOR-gate (22), the programmable decoder being programmed by opening fuse elements (23₀, ..., 23₁₅) of the programming fuse circuits to have the same program as the of the main decoder being disconnected from the memory, so that when said defective bit is designated by the address signals, the programmable decoder selects a spare bit; characterized in that said programmable decoder receives the output signals from said main decoders so that when a bit selected by said main decoders is defective said programmable decoder selects the spare bit based on the program applied to said programmable decoder. A semiconductir memory device according to claim 4, characterized in that said logic circuits of said partial and main decoders are NAND gates. A semiconductor memory device with a redundancy circuit comprising: address buffers (11₀, ... 11₃) each receiving an address signal (Ai, ... AI) and producing a signal in phase with the address signal and a signal out of phase with the address signal; a plurality of stages of partial decoders (18₀, ..., 18₇; 28₀, ..., 28₁₅), the partial decoders (18₀, ..., 18₇) of the first stage comprising logic circuits (16, 17) for receiving different combinations of the signals supplied from said address buffers and producing output signals (X₀, ..., X₇), the partial decoders (28₀, ..., 28₁₅) of the second and the following stages each comprising logic circuits (6, 7) for receiving different combinations of the signals supplied from the partial decoders of the preceding stage and producing output signals (Yo, ..., Y15) to the partial decoders of the following stage; fuse elements (21₀, ..., 21₁₅) for receiving the signals supplied from the partial decoders of the final stage and producing output signals to select a bit (B0, ..., B15) designated by the address signals, a fuse element being opened or burnt to disconnect the partial decoders of the final stage from the memory if the defective bit is detected in the respective bit line; and a programmable decoder (30) comprising programming fuse circuits (23₀, ..., 23₁₅) and a NOR-gate (22) the programmable decoder being programmed by opening a fuse element of the programming fuse circuits to have the same program as that of the partial decoders of the final stage being disconnected from the memory, so that when said defective bit is designated by the address signals, the programmable decoder selects a spare bit; characterized in that said programmable decoder, receives the output signals from the partial decoders of the final stage so that when a bit selected by said partial decoders of the final stage is defective said programmable decoder selects the spare bit based on the program applied to said programmable decoder. A semiconductor memory device according to claim 6, characterized in that said logic circuits of said partial decoders are NAND gates.

Inventors: FUJII, SYUSO C/O PATENT DIVISION, SAITO, SHOZO C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1986
Main classification: G06F11
IPC codes: G11C29, G11C11