A charge-recycling circuit and system that reuses the energy between two or more stacked CPUs is proposed in order to double the life of a battery. In this architecture, CPUs are divided into upper and lower load groups, and electrical charges are shared among the stacked CPUs and a tank capacitor. Charges are temporarily stored in the tank capacitor and are then reused. To control divided loads, a high-speed and energy-efficient regulator is needed. Internal circuit voltage variation between the upper and lower modules is determined by seven low-drop-out (LDO) regulators, a voltage-boosting capacitor circuit, and the tank capacitor. As a result, stable voltage can be supplied to each CPU, even if the upper and lower loads are different or a battery is being used. The LDOs improve the margin of collection in the tank capacitor or task schedule operation, and power efficiency is raised even further. The circuit can be implemented on silicon without a large external control circuit and inductor such as a switching regulator. This circuit was applied to an in-vehicle lock-step system because the upper and lower loads and tasks are the same. Additionally, by using the proposed task scheduling to maximize efficiency, this circuit can be applied not only to lock-step systems but also to general systems. Test chips were fabricated using 90-nm standard CMOS technology. Although the maximum power efficiency of a conventional circuit with a simple LDO is 44.4%, efficiency of the proposed charge-recycling circuit turned out to be as high as 87.1% with the test chips.

This paper proposes a novel approach for implementing an ultra-low-power voltage reference using the structure of self-cascode MOSFET, operating in the subthreshold region with a self-biased body effect. The difference between the two gate-source voltages in the structure enables the voltage reference circuit to produce a low output voltage below the threshold voltage. The circuit is designed with only MOSFETs and fabricated in standard 0.18-mu m CMOS technology. Measurements show that the reference voltage is about 107.5 mV, and the temperature coefficient is about 40 ppm/degrees C, at a range from -20 degrees C to 80 degrees C. The voltage line sensitivity is 0.017%/V. The minimum supply voltage is 0.85 V, and the supply current is approximately 24 nA at 80 degrees C. The occupied chip area is around 0.028 mm(2).

This paper presents the method of searching optimized PID controller's coefficients for Buck converter using PSO-particle swarm optimization. Recently, PSO, which can be used for parameter optimization, becomes attractive because its computation simplicity relative to other evolutionary algorithms such as GA. A problem is that PID controller's coefficients found with PSO may be not suitable which causes large overshoot and bad robustness. This paper proposed a method to solve this problem by improving the ratio of the proportion term through changing evolution conditions. According to the experimental results, the proposed method is feasible and the effect is good. © 2013 IEEE.

In this paper, the charge pump efficiency is discussed, and a charge pump with continuous frequency charge sharing scheme is presented. The proposed charge sharing clock generator is able to recover the charge from parasitic-capacitor charging and discharging, so that the dynamic power loss is reduced by half. Furthermore, the proposed frequency regulation structure is able to keep the efficiency of charge pump at the theoretical maximum value without effect of load current. The simulation results show a maximum 10% efficiency increase and the efficiency is kept around 68% when load current decreases, while efficiency of conventional charge pump drops to 23% when load current is 10uA. © 2013 IEEE.

This paper presents a Processing Engine (PE) which is used in Low Density Parity Codec (LDPC) application with a novel charge-recovery logic called pseudo-NMOS boost logic (pNBL), to achieve high-speed and low power dissipation. pNBL is a high-overdriven and low area consuming charge recovery logic, which belongs to boost logic family. Proposed Processing Engine is used in LDPC circuit to reduce operating power dissipation and increase the processing speed. To demonstrate the performance of proposed PE, a test chip is designed and fabricated with 0.18 mu m CMOS technology. Simulation results indicate that proposed PE with pNBL dissipates only 1 pJ/cycle when working at the frequency of 403 MHz, which is only 36% of PE with the conventional static CMOS gates. The measurement results show that the test chip can work as high as 609 MHz with the energy dissipation of 2.1 pJ/cycle.

In this paper, the charge pump efficiency is discussed, and a dual charge pump circuit with complementary architecture using charge sharing clock scheme is presented. The proposed charge sharing clock generator is able to recover the charge from parasitic-capacitor charging and discharging, so that the dynamic power loss in the pumping process is reduced by a half. To preserve the overlapping period of the four-phase clock used for threshold cancellation technique, two complementary sets of clocks are generated from the proposed clock generator, and each set feeds a certain branch of the dual charge pump to achieve the between-branch charge sharing. A test chip is fabricated in 0.18 mu m process, and the area penalty of the proposed charge sharing clock generator is 1%. From the measurement results, the proposed charge pump shows an overall power efficiency increase with a peak value of 63.7% comparing to 52.3% of a conventional single charge pump without charge sharing, and the proposed clock scheme shows no degradation on the driving capability while the output ripple voltage is reduced by 43%.

An area efficiency hybrid decoupling scheme is proposed to suppress the charge pump noise during F-N tunneling program in nonvolatile memory (NVM). The proposed scheme is focused on suppressing the average noise power in frequency domain aspect, which is more suitable for the program error reduction in NVMs. The concept of active capacitor is utilized. Feed forward effect of the amplifier is firstly considered in the impedance analysis, and a trade-off relation between in-band and out-band frequency noise decoupling performance is shown. A fast optimization based on average noise power is made to achieve minimum error in the F-N tunneling program. Simulation results show very stable output voltage in different load conditions, the average ripple voltage is 17 mV with up to 20 dB noise-suppression-ratio (NSR), and the F-N tunneling program error is less than 5 mV for a 800 mu s program pulse. A test chip is also fabricated in 0.18 mu m technology. The area overhead of the proposed scheme is 2%. The measurement results show 24.4 mV average ripple voltage compared to 72.3 mV of the conventional one with the same decoupling capacitance size, while the noise power suppression achieves 15.4 dB.

A novel charge-recovery logic structure called Pulse Boost Logic (PBL) is proposed in this paper. PBL is a high-speed low-energy-dissipation charge-recovery logic with dual-rail evaluation tree structure. It is driven by 2-phase non-overlap clock, and requires no DC power supply. PBL belongs to boost logic family, which includes boost logic, enhanced boost logic and subthreshold boost logic. In this paper, PBL has been compared with other charge-recovery logic technologies. To demonstrate the performance of PBL structure, a 4-bit pipeline multiplier is designed and fabricated with 0.18 mu m CMOS process technology. The simulation results indicate that the 4-bit multiplier can work at a frequency of 1.8 GHz, while the measurement of test chip is at operation frequency of 161 MHz, and the power dissipation at 161 MHz is 772 mu W.

A 4-phase cross-coupled charge pump with charge sharing clock scheme is proposed in this paper. Four phase clock is utilized to prevent the reverse leakage current. A charge sharing clock control circuit is constructed, and the consumption in charging or discharging the bottom plate parasitic capacitance of the boost capacitors is reduced by half. The proposed charge pump is overstress free and compatible for standard CMOS process. Simulation results show a maximum 10% efficiency increase more than that of conventional charge pump without charge sharing. © 2011 IEEE.

In this paper, we propose a new energy saving boost logic structure named Invert Boost Logic(IBL). This design belongs to the Boost Logic family and inherits the same two-phase structure. Transistor numbers, layout area and power consumption reduce significantly by virtue of this novel design. Driven by two opposite phased power clocks, it can maximize its gate drivability by increasing the logic power supply voltage thanks to the recycling ability of the AC energy sources as well as two latches. Energy cut could be as high as 60% at GHz-Class frequencies. © 2011 IEEE.

In this paper a wireless power transmission system is designed and implemented with 0.18μm CMOS technology. A novel structure without rectifier is developed in order to improve the power transmission efficiency. The coupled inductors are a pair of highly optimized 700μmx700μm on-chip inductors, and with the proposed structure, simulation achieves wireless transmitted power of 32mW, while the measurement of test chip shows the achieved transmission power is 22mW. © 2011 IEEE.

This paper presents one error control scheme for NAND Flash memories with error correction code (ECC). With the increasing array bit error rates, multi bits ECCs like binary Bose-Chaudhuri-Hocquenghem (BCH) code, have been used widely to improve endurance and improve retention. However, with the correction ability and codeword length raise, the parity bits cost increase at the same time. With erasure concept, which means the read data is unstable for erasure cells, this paper proposes a codeword error decrease scheme for NAND Flash memories. This method with no more bits cost could provides more than 70% error decrease by altering reading data if errors exceed correction capability. It could be combined with BCH code or one-bits ECC like hamming code, for both 1-bit/cell or multi-bits/cell memories. © 2011 IEEE.

Two novel voltage reference using self-biased body effect are discussed in this paper. The proposed circuits based on the weighted difference of two gate-source voltages of two MOSFETs operated in subthreshold region and one of them with forward-biased body effect, can generate two ultra-low reference voltages of 171.1 mV and 243.2 mV with temperature coefficients of 15.6 ppm/°C and 14.8 ppm/°C in a range from -25°C∼80°C, respectively. The voltage line sensitivities are 0.0025%/V and 0.0019%/V. The power supply rejection ratio (PSRR) are -110 dB and -105 dB at 100 Hz. The power dissipations are 0.74 W and 1.4 μW at a 1.4-V power supply. The circuits were designed and simulated in 0.18 μm CMOS technology. The layouts illustrate the chip area are 0.016 mm 2 and 0.014 mm 2. © 2011 IEEE.

This paper presents a Processing Engine (PE) which is used in Low Density Parity Codec (LDPC) application with a novel charge-recovery logic called pseudo-NMOS boost logic (pNBL), to achieve high-speed and low power dissipation. pNBL is a high-overdriven, low area consuming charge recovery logic, which belongs to boost logic family. Proposed Processing Engine is used in LDPC circuit to reduce power dissipation and increase the processing speed. To demonstrate the performance of proposed PE, a test chip is designed and fabricated with 0.18μm CMOS technology. Simulation results indicate that proposed PE with pNBL dissipates only 1pJ/cycle when working at the frequency of 403MHz, which is only 36% of PE with conventional static CMOS gates. The measurement results shows that the test chip can work as high as 609MHz with the energy dissipation of 2.1pJ/cycle. © 2011 IEEE.

This paper proposes a novel soft-switching PV inverter formed by a ZVT-PWM boost converter, a ZVS-ZCS-PWM buck converter and a low frequency full-bridge inverter. The ZVT-PWM boost converter maintains the dc-bus voltage and provides an auxiliary current source for the soft-switching cell of the buck converter. The buck converter consists of a main switch and an auxiliary switch, with ZVS and ZCS features respectively, which generates a semi-sinusoidal current output. The semi-sinusoidal current is inverted into sinusoidal and fed to the utility grid by the low frequency full-bridge inverter. The overall efficiency is improved and the size is dramatically reduced due to high frequency operation. The operating principles are presented and the circuit is implemented to a 1000W prototype machine. The experimental results with a maximum overall efficiency up to 97% at 100 kHz, about 1.5%'s improvement compared to the hard-switching one, verify the proposal. © 2011 IEEE.

Power dissipation performance of distributed differential oscillator (DDO) is investigated. The architecture of DDO and factors affecting performance are introduced. Power dissipation analysis with a physical model was implemented. The relationship between power dissipation performance and quality factor Q is discussed. Moreover, the result is compared with nonresonant clocking system to demonstrate DDO has a better power dissipation performance. Simulation is implemented to examine whether power dissipation performance is consistent to the analysis result. ©2010 IEEE.

The conventional SRAMs, namely four-transistor SRAM (4T) and six-transistor SRAM (6T), suffered from the external noise, because they have direct paths through bit-line(BL) to their storage nodes. This paper proposes seven-transistor (7T) SRAM which has no direct path through BL to the data storage nodes and has higher endurance against external noise. The proposed cell is composed of two separate data access mechanisms
one is for the read operation and another is for the write one. Based upon our SRAM design, data destruction never occurs in the read operation. Simulation result shows that the read Static-Noise-Margin (SNM) of the proposed cell is enhanced by 1.6X and 0.31X with the conventional 4T and 6T SRAM cell respectively. We also manufactured a chip and confirmed its performance. ©2010 IEEE.

A novel charge-recovery logic structure called Pulse Boost Logic (PBL) is proposed in this paper. PBL is a highspeed low-energy-dissipation charge-recovery logic with dual-rail evaluation tree structure. It is driven by 2-phase non-overlap clock, and requires no DC power supply. To demonstrate the performance of PBL structure, 4-bit counters designed with both PBL gates and conventional static CMOS. Post-layout simulation is applied to compare energy dissipation performance between PBL and conventional static CMOS in a frequency range of 500MHz to 1GHz. The simulation result indicates that PBL dissipates only 15% energy per cycle at 1GHz, and for sequential circuits such as counter, PBL is less area consuming than static CMOS. © 2010 IEEE.

NAND Flash memory is widely used in recent SoCs. High density NAND Flash requires Error Correcting Code (ECC) mechanism to guarantee data integrity. We propose an efficient ECC model which decrease multi bit errors by considering the Flash memory's characteristic. According to the Flash memory mechanism, 0's error is more likely to happen than 1's error. The proposed error control code counts the number of '1' in a word and inverts all bits to keep the number of 1 is more than that of 0s, which signify a high quantity of Hamming weight. We confirm that the proposed method is not only effective for single error but also dramatically effective for multi bit error. ©2010 IEEE.

A charge sharing clock scheme is proposed to feed a 5-stage double charge pump circuit. By reusing the charges in charging or discharging the parasitic capacitance during the pumping process, dynamic power loss is able to be reduced by nearly a half. Under 1V supply, simulation results show a maximum 10% efficiency increase, and the ripple noise is also reduced by a half comparing to the conventional charge pumps. ©2010 IEEE.

A high area efficiency hybrid decoupling scheme using both passive and active capacitors is designed to suppress the program noise of charge pump in non-volatile memory. Through the decoupling impedance analysis and noise power calculation, an optimized ratio between the passive and active capacitors is obtained to achieve maximum noise suppression performance. The proposed hybrid decoupling charge pump is fabricated in 0.18μm technology with 1V supply voltage. The results show a nearly 20dB noise-suppression-ratio (NSR) to the conventional method and the ripple voltage reduction is 73%. The area overhead is only 2%. ©2010 IEEE.

In this paper a 4-bit pipeline multiplier is designed using a novel charge-recovery logic technology called Pulse Boost Logic (PBL), and fabricated out with Rohm 0.18μm CMOS process. Cadence Spectre simulation indicates that energy dissipation of proposed PBL multiplier is 79% of Enhanced Boost Logic with almost the same number of transistors. The test chip is using a LC resonant system for AC power supply, since PBL structure requires two phase non-overlap clock as power supply. The measurement result shows that operation frequency of PBL 4-bit pipeline multiplier is up to 161MHz, while the energy dissipation is 4.81pJ/cycle. ©2010 IEEE.

We propose a wafer level burn-in (WLBI) mode, a leak-bit redundancy and a small, highly reliable Cu E-trim fuse repair for an embedded 6T-SRAM to achieve a known good die (KGD) SoC. We fabricated a 16 Mb SRAM with these techniques using 65 nm LSTP technology, and confirmed the efficient operations of these techniques. The WLBI mode enables simultaneous write operation for 6T-SRAM, and has no area penalty and a speed penalty of only 50 ps. The leak-bit redundancy for 6T-SRAM can reduce the infant mortality of the bare die, and improves the standby current distribution. The area penalty is less than 2%. The Cu E-trim fuse can be used beyond the 45 nm advanced process technology. The fuse requires no additional wafer process steps. Using only 1.2 V core transistors will allow CMOS technology scaling to enable fuse circuit size reduction. The trimming transistor is placed under the fuse due to there being no cracking around the trimmed position. We achieve the small fuse circuit size of 6 x 36 mu m(2) using 65 nm technology.

The simulation of a thermal-neutron-induced single-event upset (SEU) was performed on a 0.4-mu m-design-rule 4 Mbit static 14 random access memory (SRAM) using particle and heavy-ion transport code system (PHITS). The SEU rates obtained by the simulation were in very good agreement with the result of experiments. PHITS is a useful tool for simulating SEUs in semiconductor devices. To further improve the accuracy of the simulation, additional methods for tallying the energy deposition are required for PHITS.

In the sub-100-nm CMOS generation, a large local Vth variability degrades the 6T-SRAM cell stability, so that we have to consider this local variability as well as the global variability to achieve high-yield SRAM products. Therefore, we need to employ some assist circuits to expand the SRAM operating margin. We propose a variability-tolerant 6T-SRAM cell layout and new circuit techniques to improve both the read and the write operating margins in the presence of a large Vth variability. By applying these circuit techniques to a 0.494-mu m(2) SRAM cell with a beta ratio of 1, which is an extremely small cell size, we can achieve a high-yield 8M-SRAM for a wide range of Vth values using a 65-nm low stand-by power (LSTP) CMOS technology.

A 16Mbit Low power SRAM with 0.98um^2 cells using 0.15um DRAM and TFT technology has been developed. A new type memory cell technology achieves enough low power, low cost and high soft error immunity with out large investment. By these improved characteristics some customers at industrial machines and handy devices decided to use this new type of SRAM by compatibility with SRAM.

The voltage margin of an embedded DRAM's sense operation has been shrinking with the scaling of process technology. A method to estimate this margin would be a key to optimizing the memory array configuration and the size of the sense transistor. In this paper, the voltage margin of the sense operation is theoretically analyzed. The accuracy of the proposed voltage margin model was confirmed on a 0.13-mu m eDRAM test chip, and the results of calculation were generally in agreement with the measured results.

This paper describes a dynamic TCAM architecture with planar complementary capacitors, transparently scheduled refresh (TSR), autonomous power management (APM) and address-input-free writing scheme. The complementary cell structure of the planar dynamic TCAM (PD-TCAM) allows small cell size of 4.79 mu m(2) in 130 nm CMOS technology, and realizes stable TCAM operation even with very small storage capacitance. Due to the TSR architecture, the PD-TCAM maintains functional compatibility with a conventional SRAM-based TCAM. The combined effects of the compact PD-TCAM array matrix and the APM technique result in up to 50% reduction of the total power consumption during search operation. In addition, an intelligent address-input-free writing scheme is also introduced to facilitate the PD-TCAM application for the user. Consequently the proposed architecture is quite attractive for realizing compact and low-power embedded TCAM macros for the design of system VLSI solutions in the field of networking applications.

An embedded DRAM macro with a self-adjustable timing control (STC) scheme, a negative edge transmission scheme (NET), and a power-down data retention (PDDR) mode is developed. A 13.98-mm(2) 16-Mb embedded DRAM macro is fabricated in 0.13 mum logic-based embedded DRAM process. Co-salicide word lines and MIM capacitors are used for high-speed array operation. The delay timing variation of 36% for an RC delay can be reduced to 3.8% by using the STC scheme. The NET scheme transfers array control signals to local array blocks with high accuracy. Thereby, the test chip achieves 1.2-V 312-MHz random cycle operation even in the low-power process. 73-muW data retention power is realized by using the PDDR mode, which is 5% of conventional schemes.

This paper describes a 4.5-Mb dynamic ternary CAM (DTCAM) which is suitable for networking applications. A dynamic TCAM cell structure in 130-nm embedded DRAM technology is used to realize the small cell size of 3.59 mum(2). In addition, a novel array architecture of TCAM, the pipelined hierarchical searching (PHS) architecture, is proposed. The PHS architecture is found to be suitable for realizing small area penalty high-throughput searching and low-voltage operation simultaneously. With the combination of the DTCAM cell and the PHS architecture, small silicon area of 32 mm(2) for a fabricated 4.5-Mb DTCAM chip, high performance of 143 M searches per second and low power dissipation of 1.1 W have been achieved. To Improve the yield of TCAMs, a novel shift redundancy technique is applied and estimated to result in 3.6-times yield improvement. These techniques and architectures described in this report are attractive for realizing cost-efficient, large-scale, high-performance TCAM chips.

This paper describes an all-digital delay-locked loop (DLL) architecture for over 667 Mb/s operating double-data-rate (DDR) type SDRAMs, which suppresses skews and jitters. Two novel replica adjusting techniques are introduced, in which timing skews caused by the clock input and data output circuits Are reduced by a hierarchical phase comparing architecture and a replica check method with slow tester. Further, an improved phase interpolating method, suppresses jitters caused by a boundary of the fine and coarse delays.-A 512-Mb test device is fabricated using a 0.13-mum DRAM process technology, in which skew and jitter suppressed 667-Mb/s (333-MHz) DDR operation has been verified.

This paper presents an efficient layout method for a high-speed multiplier. The Wallace-tree method is generally used far high-speed multipliers. In the conventional Wallace tree, however, every partial product is added in a single direction from top to bottom. Therefore, the number of adders increases as the adding stage moves forward, As a result, it generates a dead area when the multiplier is laid out in a rectangle.
To solve this problem, we propose a rectangular Wallace-tree construction method. In our method, the partial products are divided into two groups and added in the opposite direction. The partial products in the first group are added downward, and the partial products in the second group are added upward. Using this method, we eliminate the dead area. Also, we optimized the carry propagation between the two groups to realize high speed and a simple layout. We applied it to a 54 x 54-bit multiplier. The 980 mum x 1000 I-tm area size and the 600-MHz clock speed have been achieved using 0.18-mum CMOS technology.

This paper proposes the virtual-socket architecture in order to reduce the design turn-around time (TAT) of the embedded DRAM. The required memory density and the function of the embedded DRAM are system dependent. In the conventional design, the DRAM control circuitry with the DRAM memory array is handled as a hardware macro, resulting in the increase in design TAT,On the other hand, our proposed architecture provides the DRAM control circuitry as a software macro to take advantage of the automated tools based on synchronous circuit design. With array-generator technology, this architecture can achieve high quality and quick turn-around time (QTAT) of flexible embedded DRAM that is almost the same as the CMOS ASIC.
We applied this virtual-socket architecture to the development of the 64-Mb synchronous DRAM core using 0.18-mum design rule and confirmed the high-speed operation, 166 MHz at CAS latency of two, and 180 MHz at that of three. The experimental results show that our proposed architecture can be applied to the development of the high-performance embedded DRAM with design QTAT.

A 200-MHz double-data-rate synchronous-DRAM (DDR-SDRAM) was developed. The chip contains. a delay-locked loop (DLL) which performs over a wide range of operating conditions. Post-mold-tuning allows precise replica programming. A 200-MHz intra-chip data bus is suitable for DDR operation.

A precharged-capacitor-assisted sensing (PCAS) scheme suitable for Low-power DRAM using boosted-sense ground (BSG) is proposed. In this scheme, the data on bitlines are sensed with the assistance of precharged capacitors. Precise data Level generation is achieved with sense speed 4.2 ns faster than the conventional scheme in the case that bitline swing is 1.4 V, Necessary decoupling capacitors can be efficiently implemented in memory arrays by using junction capacitors between well and substrate so that the area penalty of decoupling capacitors can be minimized. To keep sensed data stable, two types of level controllers are introduced. A voltage downconverter (VDC) with a current mirror discharger (CMD) compensates for the change of both data levels during write/read operations. A level controller with charge transfer amplifier (CTA) prevents the BSG level from falling during the row active period. The two level controllers greatly improve data-retention characteristics.

This paper presents the high-performance DRAM array and logic architecture for a sub-1.2-V embedded silicon-on-insulator (SOI) DRAM, The degradation of the transistor performance caused by boosted wordline voltage level is distinctly apparent in the low voltage range, In our proposed stressless SOT DRAM array, the applied electric field to the gate oxide of the memory-cell transistor can be relaxed. The crucial problem that the gate oxide of the embedded-DRAM process must be thicker than that of the logic process can be solved. As a result, the performance degradation of the logic transistor can be avoided without forming the gate oxides of the memory-cell array and the logic circuits individually. In addition, the data retention characteristics can be improved. Secondly, we propose the body-bias-controlled SOI-circuit architecture which enhances the performance of the logic circuit at sub-1.2-V power supply voltage. Experimental results verify that the proposed circuit architecture has the potential to reduce the gate-delay time up to 30% compared to the conventional one. This proposed architecture could provide high performance in the low-voltage embedded SOI DRAM.

This paper describes a 16:1 multiplexer using 0.18 mu m SOI-CMOS technology. To realize ultra-high-speed operations, the multiplexer adapts a pipeline structure and a phase shift technique together with a selector architecture, This architecture takes advantage of the small junction capacitances of the SOI-CMOS devices, The multiplexer achieves 3.6 Gbls at a supply voltage of 2.0 V, while dissipating only 30 mW at the core circuit and 340 mW for the whole chip which includes the I/O buffers.

An SOI-DRAM test device (64-Kb scale) with 100-nm-thick SOI film has been fabricated in 0.5-mu m CMOS/SIMOX technology and the basic DRAM function has been successfully observed. A partially depleted transistor was used to solve the floating-body effect, resulting in improved operation. The newly introduced body-synchronized sensing scheme enhances the lower V-cc margin.
The p-n junction capacitance between source/drain and a substrate for SOI structure is reduced by 25%. RAS access time tRAC is 70 ns with a 2.7-V power supply, which is as fast as the equivalent bulk-Si device with a 4-V power supply. The active current consumption is 1.1 mA (V-cc = 3.0 V, 260-ns cycle) for this SOI-DRAM, which is a reduction of 65%, compared with 3.2 mA for the reference bulk-Si DRAM. The mean value of data retention time for this chip at 80 degrees C is longer than 20 s (V-cc = 3.3 V), which is the same value as mass-produced 16-Mb DRAM's. The SOI-DRAM has an operating V-cc range from 2.3 V to 4.0 V. The observed speed enhancement and the wide operating voltage range indicate high performance at the low voltage operation suitable for battery-operated DRAM's.

In developing the 256-Mb DRAM, the data retention characteristics must inevitably be improved. In order for DRAM's 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(2) and a performance of 34 ns access time.

A memory array architecture and row decoding scheme for a 3 V only DINOR (divided bit line NOR) flash memory has been designed. A new sector organization realizes one word line driver per two word lines, which is conformable to tight word line pitch. A hierarchical negative voltage switching row decoder and a compact source line driver have been developed for 1 K byte sector erase without increasing the chip size. A bit-by-bit programming control and a low threshold voltage detection circuit provide a high speed random access time at low V(cc) and a narrow program threshold voltage distribution. A 4 Mb DINOR flash memory test device was fabricated from 0.5 mum, double-layer metal, triple polysilicon, triple well CMOS process. The cell measures 1.8 x 1.6 mum2 and the chip measures 5.8 x 5.0 mm2. The divided bit line structure realizes a small NOR type memory cell.

A 4-Mb cache DRAM (CDRAM), which integrates 16-kb SRAM as a cache memory and 4-Mb DRAM into a monolithic circuit, will be described. This CDRAM has a 100-MHz operating cache, newly proposed fast copy-back (FCB) scheme that realizes a three times faster miss access time over with the conventional copy-back method, and maximized mapping flexibility. The process technology is a quad-polysilicon double-metal 0.7-mum CMOS process, which is the same as used in a conventional 4-Mb DRAM. The chip size of 82.9 mm2 is only a 7% increase over the conventional 4-Mb DRAM. The simulated system performance indicated better performance than a conventional cache system with eight times the cache capacity.

An erase and program control system has been implemented in a 60-ns 16-Mb flash EEPROM. The memory array is divided into 64 blocks, and in each block, erase pulse application and erase-verify operation are employed individually. The erase and program sequence is controlled by an internal sequence controller which is composed of a synchronous circuit with an on-chip oscillator. A 60-ns access time has been achieved with a differential sensing scheme utilizing dummy cells. The cell size is 1.8-mu-m x 2.0-mu-m and the chip size is 6.5 mm x 18.4 mm using a simple stacked gate cell structure and 0.6-mu-m CMOS process.

A single 3.3-V 64-Mb DRAM with a chip size of 233.8 mm2 has been fabricated using 0.4-mu-m CMOS technology with double-level metallization. The dual-cell-plate (DCP) cell structure is applied with a cell size of 1.7-mu-m2, and 30-fF cell capacitance has been achieved using an oxynitride layer (t(eff) = 5 nm) as the gate insulator. The RAM implements a new data-line architecture called the merged match-line test (MMT) to achieve faster access time and shorter test time with the least chip-area penalty. The MMT architecture makes it possible to get an RAS access time of 45 ns, and reduces test time by 1/16000. A parallel MMT technique, which is an extended mode of MMT, leads to the further test-time reduction of 1/64000. Therefore, all 64 Mb are tested in only 1024 cycles, and the test time is only 150-mu-s with 150-ns cycle time.

A novel high-speed page mode sense scheme for EPROMs and flash EEPROMs has been developed. A divided bit line architecture makes it possible to adopt a folded bit line architecture in which sense amplifiers are located at the end of the bit lines. Dynamic sensing avoids the soft write problem by reducing bit line voltage and the current flow through the memory cell. An experimental 1-Mb flash EEPROM using a 0.6-μm design rule has been designed. Simulated results show that a high-speed address access time of 60 ns and a page mode access time of 15 ns can be achieved.

— A high-speed parallel sensing architecture for high-density 5-V-only flash E&lt
sup&gt
2&lt
/sup&gt
PROM’s is described. A source-biasing technique enhances the cell current while minimizing the read disturbance problem. Flip-flop-type differential sense amplifiers are arranged between every two pairs of bit lines, so that half the memory cells on the same word line are sensed simultaneously. Self-timed dynamic sensing was developed for high speed and stable sensing and also decreases read disturbance and operating current. Simulated results show that a sub-10- μA cell current is successfully sensed in 40 ns. In the program mode, the differential amplifier acts as a column latch, which substantially reduces the chip size. © 1990 IEEE

Portable computers operated by batteries have become popular these days, and there is a great demand for low-power LSI memories for battery backup application. This paper describes a DRAM with a battery-backup (BBU) mode, which enables automatic data retention with extremely reduced power consumption. The circuit techniques to reduce the refresh current and the back-bias-generator current are developed, and the dissipated current required for data retention of 44 uA is achieved under typical conditions. This DRAM was fabricated with quad-poly and double-metal CMOS process technology. The memory array is divided into 4X32 subarrays. This finely divided array architecture is suitable for the fast access time and the multibit test mode. © 1990 IEEE