Do-Chan Choi

A 3.3-V single power supply 16-Mb nonvolatile virtual DRAM using a NAND flash memory technology

A 3.3-V 16-Mb nonvolatile memory having operation virtually identical to DRAM with package pin compatibility has been developed. Read and write operations are fully DRAM compatible except for a longer RAS precharge time after write. Fast random access time of 63 ns with the NAND flash memory cell is achieved by using a hierarchical row decoder scheme and a unique folded bit-line architecture which also allows bit-by-bit program verify and inhibit operation. Fast page mode with a column address access time of 21 ns is achieved by sensing and latching 4 k cells simultaneously. To allow byte alterability, nonvolatile restore operation with self-contained erase is developed. Self-contained erase is word-line based, and increased cell disturb due to the word-line based erase is relaxed by adding a boosted bit-line scheme to a conventional self-boosting technique. The device is fabricated in a 0.5-/spl mu/m triple-well, p-substrate CMOS process using two-metal and three-poly interconnect layers. A resulting die size is 86.6 mm/sup 2/, and the effective cell size including the overhead of string select transistors is 2.0 /spl mu/m/sup 2/.

Battery Operated 16m Dram With Post Package Programmable And Variable Self Refresh

with wide operating voltage range of 1.8~ to 3.6~ for battery based portable applications. Low power during data retention is obtained with Vcc and temperature variable self refresh which is programmable after packaging using electrical fuses. High performance is achieved at low voltage with dual VPPs for well bias and on-chip high voltage power supply, dual threshold voltages for NMOS and voltage variable sensing control. The 16M has a measured RAS access time of 58ns at 1.8~ and 83°C. This paper describes a I6M DRAM

A 35 ns 64 Mb DRAM using on-chip boosted power supply

An on-chip boosted power supply is necessary for ease of layout and high speed in high density DRAMs. The technique of TTL conversion is a key to designing high speed DRAMs for 3-V operation. The authors present the generation and regulation of an on-chip power supply (V/sub pp/) within 50 mV of the optimum level during operation for a given V/sub cc/. In addition to the regulated V/sub cc/ scheme, improved interface circuit techniques are employed to achieve fast input and output conversion with good noise margins. An experimental 64-Mb DRAM is designed. A typical access time of 35 ns is obtained by measurement.<<ETX>>

A 3.3 V 16 Mb nonvolatile virtual DRAM using a NAND flash memory technology

A 3.3V 16Mb nonvolatile memory has read and write operations fully DRAM-compatible except a longer RAS precharge time after write. Most systems with high-performance processors use a shadow nonvolatile memory uploaded to a fast DRAM to obtain zero wait-state performance. The introduced nonvolatile virtual DRAM (NVDRAM) eliminates the need for this redundancy, achieving high performance while reducing power consumption. Fast random access time (tRAC) with a NAND flash memory cell is achieved by using a folded bit-line architecture, and DRAM comparable column address access time (tkA) is achieved by sensing and latching 4k cells simultaneously.