Hidehiro Shiga

A 1.6 GB/s DDR2 128 Mb Chain FeRAM With Scalable Octal Bitline and Sensing Schemes

An 87.7 mm2 1.6 GB/s 128 Mb chain FeRAM with 130 nm 4-metal CMOS process is demonstrated. In addition to small bitline capacitance inherent to chain FeRAM architecture, three new FeRAM scaling techniques - octal bitline architecture, small parasitic capacitance sensing scheme, and dual metal plateline scheme - reduce bitline capacitance from 100 fF to 60 fF. As a result, a cell signal of ±220 mV is achieved even with the small cell size of 0.252 ¿m2. An 800 Mb/s/pin read/write bandwidth at 400 MHz clock is realized by installing SDRAM compatible DDR2 interface, and performance is verified by simulation. The internal power-line bounce noise due to 400 MHz clock operation is suppressed to less than 50 mV by an event-driven current driver, which supplies several hundreds of mA of current within 2 ns response. The precise timing and voltage controls are achieved by using the data stored in a compact FeRAM-fuse, which consists of extra FeRAM memory cells placed in edge of normal array instead of conventional laser fuse links. This configuration minimizes area penalty to 0.2% without cell signal degradation.

A 64Mb Chain FeRAM with Quad-BL Architecture and 200MB/s Burst Mode

A 64Mb chain FeRAM implemented in 0.13mum 3M CMOS technology is described. A quad-BL architecture reduces the die area by 6.5% and realizes 87.5mm2 die with an effective cell-size of 0.7191mum2 while eliminating BL-BL coupling noise. A high-speed ECC circuit and cell data write-back scheme achieves read/write cycle time of 60ns and 200MB/S burst

A 64-Mb Chain FeRAM With Quad BL Architecture and 200 MB/s Burst Mode

A 64-Mb chain ferroelectric RAM (chainFeRAM) is fabricated using 130-nm 3-metal CMOS technology. A newly developed quad bitline architecture, which combines folded bitline configuration with shield bitline scheme, eliminates bitline-bitline (BL-BL) coupling noise. The quad bitline architecture also reduces the number of sense amplifiers and activated bitlines, resulting in the reduction of die size by 6.5% and cell array power consumption by 28%. Fast read/write of 60-ns cycle time as well as reliability improvement are realized by two high-speed error checking and correcting (ECC) techniques: 1) fast pre-parity calculation ECC sequence and 2) all-“0”-write-before-data-write scheme. Moreover, among nonvolatile memories reported so far, the 64 Mb chain FeRAM has achieved the highest read/write bandwidth of 200 MB/s with ECC. The chip size is 87.5 mm2 with average cell size of 0.7191 μm2.

Highly Reliable Reference Bitline Bias Designs for 64 Mb and 128 Mb Chain FeRAMs

This paper presents highly reliable reference bitline bias designs for 64 Mb and 128 Mb chain FeRAM™. The hysteresis shape deformation of ferroelectric capacitor due to temperature variation causes cell signal level shifts of both “1” and “0” data. The reference bitline bias of 64 Mb chip is designed to keep intermediate value of “1” and “0” data at any operating temperatures from -40^°C to 85 ^°C by introducing a modified band-gap reference circuit with 3 bit temperature coefficient trimmers and 6 bit digital-to-analog converter (DAC) using laser fuses. The measured result shows the improvement of tail-to-tail cell signal windows by ±22 mV. Moreover, a new reference bias circuit called the “elevator circuit” with 3 bit temperature coefficient trimmers using ferroelectric fuses installed in a 128 Mb chip compensates array operating voltage VAA fluctuation as well as temperature variation. The elevator circuit enables the temperature dependency control at low external VDD of 1.8 V. This improves cell signal window by ±40 mV. The elevator circuit also varies reference bitline bias with array operating voltage VAA variation, resulting in improvement of cell signal windows by ±44 mV in the range of 1.5 V ±0.2 V VAA.