Hyung-Kyu Lim

A 3.3 V 32 Mb NAND flash memory with incremental step pulse programming scheme

While the performance of flash memory exceeds hard disk drives in almost every category, the cost of flash memory must come down in order to gain wider acceptance in mass storage applications. This paper describes a 3.3 V-only 32 Mb NAND flash memory that achieves not only high performance but also low cost with a 94.9 mm/sup 2/ die size, improved yields, and a simple process with 0.5 /spl mu/m CMOS technology. Die size is reduced by eliminating high voltage operation on the bitlines through a self boosted program inhibit voltage generation scheme. Incremental-step-pulse programming results in a 2.3 MB/s program data rate as well as improved process variation tolerance. Interleaved data paths and a boosted wordline results in a 25 ns burst cycle time and a 24 MB/s read data rate. Maximum operating current is less than 8 mA.

A 117-mm/sup 2/ 3.3-V only 128-Mb multilevel NAND flash memory for mass storage applications

For a quantum step in further cost reduction, the multilevel cell concept has been combined with the NAND flash memory. Key requirements of mass storage, low cost, and high serial access throughput have been achieved by sacrificing fast random access performance. This paper describes a 128-Mb multilevel NAND flash memory storing 2 b per cell. Multilevel storage is achieved through tight cell threshold voltage distribution of 0.4 V and is made practical by significantly reducing program disturbance by using a local self-boosting scheme. An intelligent page buffer enables cell-by-cell and state-by-state program and inhibit operations. A read throughput of 14.0 MB/s and a program throughput of 0.5 MB/s are achieved. The device has been fabricated with 0.4-/spl mu/m CMOS technology, resulting in a 117 mm/sup 2/ die size and a 1.1 /spl mu/m/sup 2/ effective cell size.

A 3.3 V 128 Mb multi-level NAND flash memory for mass storage applications

The NAND flash memory was originally designed to target solid-state mass storage applications. Key requirements of mass storage, low cost and high serial access throughput, have been achieved by sacrificing a non-critical feature, fast random access. For a quantum step in cost reduction, the multi-level cell is combined with NAND flash memory. This 128 Mb multi-level NAND flash memory stores two bits per cell by tight programmed cell threshold voltage (Vth) control and is made practical by significantly reducing program disturbs.The NAND flash memory was originally designed to target solid-state mass storage applications. Key requirements of mass storage, low cost and high serial access throughput, have been achieved by sacrificing a non-critical feature, fast random access. For a quantum step in cost reduction, the multi-level cell is combined with NAND flash memory. This 128 Mb multi-level NAND flash memory stores two bits per cell by tight programmed cell threshold voltage (Vth) control and is made practical by significantly reducing program disturbs.

A 32-bank 1 Gb self-strobing synchronous DRAM with 1 GByte/s bandwidth

This paper describes a 32-bank 1 Gb DRAM achieving 1 Gbyte/s (500 Mb/s/DQ pin) data bandwidth and the access time from RAS of 31 ns at V/sub cc/=2.0 V and 25/spl deg/C. The chip employs (1) a merged multibank architecture to minimize die area; (2) an extended small swing read operation and a single I/O line driving write scheme to reduce power consumption; (3) a self-strobing I/O schemes to achieve high bandwidth with low power dissipation; and (4) a block redundancy scheme with increased flexibility. The nonstitched chip with an area of 652 mm/sup 2/ has been fabricated using 0.16 /spl mu/m four-poly, four-metal CMOS process technology.

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/.

A 32-bank 1 Gb DRAM with 1 GB/s bandwidth

This 32-bank 1 Gb DRAM features: (1) a merged bank architecture (MBA) that results in only 3% die area penalty for 32-bank operation; (2) a source-synchronous I/O interface (SSI) that achieves 1 GB/s bandwidth with low power consumption; (3) flexible block redundancy that allows freedom of repair to anywhere within each half-Gb array; and (4) extended small swing read and single-I/O line driving write which result in 30% power reduction. The DRAM chip is implemented in a 0.16 /spl mu/m twin-well CMOS process.

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 256MB synchronous-burst DDR SRAM with hierarchical bit-line architecture for mobile applications

RZ current switches are added to a current steering DAC for high-frequency wideband applications to achieve 800MHz bandwidth at 1/sup st/ and 2/sup nd/ Nyquist band without the need for a reverse sinc equalization filter. Implemented in a GaAs HBT process with 4.5 /spl mu/m/sup 2/ minimum emitter area, the DAC dissipates 1.2W at -5V with a 1.6GHz clock and 0dBm typical output power.

A novel NAND structure with a BJT contact for the high density mask ROMs

A novel NAND cell structure with a PNP BJT, which amplifies the cell current, was proposed and fabricated. Its typical current gain is around 10 and the measured cell current is about 180 /spl mu/A at 25/spl deg/C. This amount is extremely high compared to that of the conventional NAND cell structure. This structure also keeps good current driving capability regardless of temperature variation while full MOS type degrades the characteristics. This results indicate that this new structure is a strong candidate for high performance and high density mask ROMs.<<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.