F. Matsuoka

Autonomous refresh of floating body cell (FBC)

Physics of autonomous refresh of FBC is presented. Current input to the floating body by impact ionization and output by charge pumping can balance to make FBC refresh by itself without sense amplifier operation. Thanks to this feature, multiple cells on a BL can be refreshed simultaneously, leading to a drastic reduction of BL charging current compared to the conventional refresh. 600 muA refresh current for 1 G-bit memory is achieved in 32 nm technology node with 4 ms retention time. If gate direct tunneling current is used as output, FBC can realize static RAM without periodical refresh when retaining data.

Floating Body RAM Technology and its Scalability to 32nm Node and Beyond

Technologies and improved performance of the floating body RAM are demonstrated. Reducing SOI thickness to 43nm, a 16Mb chip yield of 68% has been obtained. Device simulation proves that the floating body cell is scalable to the 32nm node keeping signal margin (threshold voltage difference) and data retention time constant

Mobility improvement for 45nm node by combination of optimized stress and channel orientation design

Performance improvement of CMOSFET by adopting <100>-channel direction with high tensile stress gate capping layer (GC liner-SiN) was demonstrated. For pMOSFET, higher hole mobility of <100>-channel and lesser short channel effect (SCE) results in 20% improvement of I/sub on/. In addition, this improvement was not sensitive to local uniaxial strain. For nMOSFET, similar to <110>-channel, 10% improvement of I/sub on/ is realized in <100>-channel with high tensile stress gate capping layer. Thus, this technology can improve the performance of nMOSFET and pMOSFET without introducing specific additional processes for nMOSFET and pMOSFET.

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.

Analysis of hot-carrier-induced degradation mode on pMOSFET's

Hot-carrier-induced degradation surface-channel (p/sup +/ polysilicon gate) and buried-channel (n/sup +/ polysilicon gate) pMOSFETs is discussed. In the shallow gate bias region, a hot-carrier degradation mode by drain avalanche hot hole injection was found for the surface-channel pMOSFETs. Trapped holes and interface state generation, which were not observed in the buried-channel pMOSFETs, were detected. In this gate bias region, the degradation for the surface-channel structure is smaller than that for the buried-channel structure. Three reasons for the smaller degradation in the surface-channel structure are discussed. The deep-gate bias region was also investigated. In this region, an interface-state generation mode without the threshold-voltage shift was found for both surface- and buried-channel pMOSFETs. This interface state generation is caused by channel hot hole injection. >

Scaling scenario of floating body cell (FBC) suppressing V th variation due to random dopant fluctuation

A scaling scenario of fully-depleted floating body cell (FBC) is demonstrated in view of signal margin for stable array functionality. Measurement and numerical simulation reveal that the Vth variation of cell array transistors is mainly attributed to the random dopant fluctuation in channel region. By setting the channel impurity concentration in the order of 1016cm-3 or lower, Gbit array functionality is guaranteed for the 32nm node and further scaled generations.

FBC's Potential of 6F 2 Single Cell Operation in Multi-Gbit Memories Confirmed by a Newly Developed Method for Measuring Signal Sense Margin

A 6F2 single cell (one-cell-per-bit) operation of the floating body RAM (FBRAM) is successfully demonstrated for the first time with more than 60% yield of 16Mbit area in a wafer. The signal sense margin (SSM) at actual read conditions is found to well back up the functional results. The parasitic resistance in the source and drain formed under the FBCs spacers can be optimized for making the SSM as large as 8muA at plusmn 4.5sigma without sacrificing the retention time.

Array architecture of floating body cell (FBC) with quasi-shielded open bit line scheme for sub-40nm node

Cell array architecture for floating body RAM of 35 nm bit line half pitch is described. The quasi-non-destructive-read-out feature of floating body cell contributes to eliminating inter-bit line coupling noise in open bit line architecture without degrading the cycle time of the RAM.

Competitive and cost effective high-k based 28nm CMOS technology for low power applications

In this paper, we present a cost-effective 28nm CMOS technology for low power (LP) applications based on a high-k, single-metal-gate-first architecture. We report raw gate densities up to 4200 kGate/mm2, and, using the ARM Cortex-R4F as a reference, we report achievement of an overall 2.4x area reduction in 28nm from 45nm technology. Our high-density SRAM bit-cell (area= 0.120mm2) has a demonstrated Static Noise Margin (SNM) of 213mV at 1V. Fully compatible with power/leakage management techniques intensively used in low power designs, the transistor drive currents are increased +35% & +10%, for nFET and pFET respectively, with respect to a 28nm LP poly/SiON reference [3]. Compatible with LP system-on-chip requirements, ultra low-cost, high performance analog devices are reported which leverage a dramatic improvement in matching factor (AVT∼2mV.um) versus our previously-reported result [2]. An optimized interconnection scheme based on Extreme Low k (ELK) dielectric (k∼2.4) and advanced metallization allows high density wiring with competitive R-C versus our previous technology.

Interface state generation under long-term positive-bias temperature stress for a p/sup +/ poly gate MOS structure

The long-term reliability for a p/sup +/ poly gate MOS structure under low electric field bias temperature (BT) stress is studied. A significant increase in interface-state density was observed for such a structure under positive bias conditions. This phenomenon was not observed in the n/sup +/ poly gate case. The mechanism for this interface-state increase was investigated in detail. Several possible causes, such as mobile ions, excess boron concentration in the gate oxide, electron injection from the substrate, impact ionization in the gate oxide, and hole injection from the gate electrode, were considered. All of the possible causes, except hole injection, were obviated by experiments. Although hole injection current was too small to be detected, hole injection from the p/sup +/ poly gate is a possible cause, which could explain the interface-state generation under positive-bias temperature test. For a p/sup +/ poly gate in CMOS structures, care should be taken when positive bias is applied to the gate electrode. >