Masaki Tsukude

SOI-DRAM circuit technologies for low power high speed multigiga scale memories

This paper describes a silicon on insulator (SOI) DRAM which has a body bias controlling technique for high-speed circuit operation and a new type of redundancy for low standby power operation, aimed at high yield. The body bias controlling technique contributes to super-body synchronous sensing and body-bias controlled logic. The super-body synchronous sensing achieves 3.0 ns faster sensing than body synchronous sensing and the body-bias controlled logic realizes 8.0 ns faster peripheral logic operation compared with a conventional logic scheme, at 1.5 V in a 4 Gb-level SOI DRAM. The body-bias controlled logic also realizes a body-bias change current reduction of 1/20, compared with a bulk well-structure. A new type of redundancy that overcomes the standby current failure resulting from a wordline-bitline short is also discussed in respect of yield and area penalty.

Low voltage circuit design techniques for battery-operated and/or giga-scale DRAMs

This paper describes a charge-transferred well (CTW) sensing method for high-speed array circuit operation and a level-controllable local power line (LCL) structure for high-speed/low-power operation of peripheral logic circuits, aimed at low voltage operating and/or giga-scale DRAMs. The CTW method achieves 19% faster sensing and the LCL structure realizes 42% faster peripheral logic operation than the conventional scheme, at 1.2 V in 15 Mb-level devices. The LCL structure realizes a subthreshold leakage current reduction of three or four orders of magnitude in sleep mode, compared with a conventional hierarchical power line structure. A negative-voltage word line technique that overcomes the refresh degradation resulting from reduced storage charge (Q/sub s/) at low voltage operation for improved reliability is also discussed. An experimental 1.2 V 16 Mb DRAM with a RAS access time of 49 ns has been successfully developed using these technologies and a 0.4-/spl mu/m CMOS process. The chip size is 7.9/spl times/16.7 mm/sup 2/ and cell size is 1.35/spl times/2.8 /spl mu/m/sup 2/.

An experimental 256-Mb DRAM with boosted sense-ground scheme

In developing the 256-Mb DRAM, the data retention characteristics must inevitably be improved. In order for DRAMs to remain the semiconductor device with the largest production volume in the 256-Mb era, we must develop a cost effective device with a small chip size and a large process tolerance. In this paper, we propose the BSG (boosted sense-ground) scheme for data retention and FOGOS (folded global and open segment bit-line) structure for chip size reduction. We have fabricated an experimental 256-Mb DRAM with these technologies and obtained a chip size of 304 mm/sup 2/ and a performance of 34 ns access time. >

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. >

Circuit design techniques for low-voltage operating and/or giga-scale DRAMs

As use of battery-operated machines, such as hand-held computers and PDAs, becomes wider, low-voltage/low-power DRAMs are required. Low-voltage technologies are also required in giga-scale DRAMs with scaled-down voltage. This paper describes low-voltage circuit design techniques to meet these demands.

A 60-ns 3.3-V-only 16-Mbit DRAM with multipurpose register

A single 3.3-V 16-Mbit DRAM with a 135-mm/sup 2/ chip size has been fabricated using a 0.5- mu m twin-well process with double-metal wiring. The array architecture, based on the twisted-bit-line (TBL) array, includes suitable dummy and space word-line configurations which suppress the inter-bit-line noise and bring yield improvement. The multipurpose register (MPR) designed for the hierarchical data bus structure provides a line-mode test (LMT), copy write, and cache access capability. The LMT with on-chip test circuits using the MPR and a comparator creates a random test pattern and reduces the test time to 1/1000. A field shield isolation and a T-shaped stacked capacitor allow the layout of a 4.8- mu m/sup 2/ cell size with a storage capacitance of 35 fF. These techniques enable the 3.3-V 16-Mbit DRAM to achieve a 60-ns RAS access time and 300-mW power dissipation at 120-ns cycle time. >

A 1.2- to 3.3-V wide voltage-range/low-power DRAM with a charge-transfer presensing scheme

A charge-transfer presensing scheme (CTPS) for 0.8-V array operation with a 1/2 V/sub cc/ bit-line precharge achieves a five times larger readout voltage and 40% improvement in sensing speed compared with conventional sensing schemes. Operation over a 1.2- to 3.3-V range is achieved. A nonreset row block control scheme (NRBC) for power-consumption improvement in data-retention mode is proposed which decreases the charge/discharge number of the row block control circuit. By combining CTPS and NRBC, the data-retention current is reduced by 75%.

A new array architecture for parallel testing in VLSI memories

The authors describe a novel array architecture and its application to a 16-Mb DRAM (dynamic random-access memory) suitable for the line mode test (LMT) with test circuits consisting of a multipurpose register (MPR) and a comparator. The LMT can test all memory cells connected to a word line simultaneously. Testing with random patterns along a word line is easily realized by using the MPR as a pattern register after setting random test data in the MPR. Test time is reduced to approximately 1/1000. Owing to the MPR, the present LMT can achieve flexible testing with high fault coverage. The excess area penalty due to the circuits for the LMT is suppressed within 0.5% in application to the 16-Mb DRAM.<<ETX>>

High-speed/high-bandwidth design methodologies for on-chip DRAM core multimedia system LSI's

Recently, as multimedia large scale integrated devices (LSIs) have developed, there has been strongly increased demand for high-speed/high-bandwidth LSIs which integrate the DRAM core and logic elements (CPU etc.). However, the high-speed/high-bandwidth operation induces the large switching noise. This noise degrades the DRAMs operating margin, and especially its data retention characteristics. In this paper, we analyze the noise transmission model and propose DRAM and logic compatible design methodologies to maintain the reliability of high-speed/high-bandwidth system LSIs. We also show that good experimental results are obtained on the test device. Furthermore, we propose the most suitable V/sub DD//GND line scheme for on-chip DRAM system LSI.

A speed-enhanced DRAM array architecture with embedded ECC

An array architecture with countermeasures for the smaller signal charge caused by scaling down is proposed. Based on a new access model, the combination of a hierarchical data bus configuration and multipurpose register (MPR) provides high-speed array access. The MPR also includes practical array-embedded error checking and correcting (ECC) with little area penalty and no access overhead in the page mode. The array architecture is applied to a scaled-down 16-Mb DRAM and has achieved high performance. >