A novel redundancy method suitable for an ultra-high-speed SRAM with logic gates is proposed. Fuse decoders are used to reduce the number of fuses, thus suppressing the access time degradation. This makes it possible to flip chip bond an SRAM with logic gates, which has a high pin count and operates at a very high frequency. To combine the new redundancy method and an ECL decoder circuit with a BiCMOS inverter, several schemes for disabling a defective cell and enabling a spare one are discussed. A 1-Mb ECL-CMOS SRAM with 120-k logic gates was fabricated using 0.3-µm BiCMOS technology. This SRAM consists of 16 RAM macros, and the RAM macro had an access time of only 0.65 ns. The access time degradation after repair was less than 50 ps.

An ultrahigh-speed 72-kb ECL-CMOS RAM macro for a 1-Mb SRAM with 0.65-ns address-access time, 0.80-ns write-pulse width, and 30.24-µm2 memory cells has been developed using 0.3-µm BiCMOS technology. Two key techniques for achieving ultrahigh speed are an ECL decoder/driver circuit with a BiCMOS inverter and a write-pulse generator with a replica memory cell. These circuit techniques can reduce access time and write-pulse width of the 72-kb RAM macro to 71% and 58% of those of RAM macros with conventional circuits. In order to reduce crosstalk noise for CMOS memory-cell arrays driven at extremely high speeds, a twisted bit-line structure with a normally on MOS equalizer is proposed. These techniques are especially useful for realizing ultrahigh-speed, high-density SRAM's, which have been used as cache and control storages in mainframe computers.