Katsuhiro Suma

An SOI-DRAM with wide operating voltage range by CMOS/SIMOX technology

For future ULSI DRAMs beyond the 256 Mb generation, several circuit techniques and memory cell structures have been proposed to meet the requirement of high performance at low voltage. These solutions frequently involve complicated processing steps and/or the ultimate limitations of current Si-MOS devices. DRAM on silicon on insulator (SOI) substrate is a more simple solution to the problem. Thin-film SOI structures with isolation by implanted oxygen (SIMOX) process are under investigation for SRAM and logic. A SOI-DRAM test device with 100 nm thick SOI film has been fabricated in 0.5 /spl mu/m CMOS/SIMOX technology. With this 64 kb SOI-DRAM the bit-line to memory cell capacitance ratio Cb/Cs is reduced by 25% compared with the reference bulk-Si DRAM, because of the decreased junction capacitance. RAS access time tRAC is 70 ns at 2.7 VVcc, as fast as the equivalent bulk-Si device at 4 VVcc. The clock timing in this DRAM is not optimized, so access time should improve with well-tuned clocks. The boosted-level generator with body-contact structure enhances the upper Vcc margin and the reduced body-effect of sense-amplifier transistors improves the lower Vcc margin. The SOI-DRAM has an operating Vcc range from 2.3 V to 4.0 V. >

A 34-ns 16-Mb DRAM with controllable voltage down-converter

A high-speed 16-Mb DRAM with high reliability is reported. A multidivided column address decoding scheme and a fully embedded sense-amplifier driving scheme were used to meet the requirements for high speed. A low-power hybrid internal power supply voltage converter with an accelerated life-test function is also proposed and was demonstrated. A novel substrate engineering technology, a retrograded well structure formed by a megaelectronvolt ion-implantation process, provides a simple process sequence and high reliability in terms of soft error and latch-up immunity. >

Highly reliable testing of ULSI memories with on-chip voltage-down converters

Two testing techniques for ultra-large-scale integrated (ULSI) memories containing on-chip voltage downconverters (VDCs) are described. The first in an on-chip VDC tuning technique that adjusts internal V/sub CC/ to compensate for the monitored characteristics of the process parameters during repair analysis testing. The second is an operating-voltage margin test, performed at various internal V/sub CC/ levels during the water sort test (WT) and the final shipping test (FT).<<ETX>>