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VLSI papers weigh 65nm, new circuits

Posted: 23 Apr 2004 ?? ?Print Version ?Bookmark and Share

Keywords:vlsi technology? circuit? tsmc? nec? stmicroelectronics?

VLSI papers weigh 65nm, new circuits

While technologists look to 65-nanometer nodes, circuit designers by and large are two generations back. So it's no surprise that as a string of 65nm papers are delivered at the 2004 Symposium on VLSI Technology, fast circuits built at 130nm will take center stage at the accompanying VLSI Circuits Symposium.

The meetings are planned for the week of June 15 in Honolulu, preceded by a satellite IEEE Workshop on Silicon Nanoelectronics on June 13-14.

The 65nm process papers from NEC, STMicroelectronics, Texas Instruments, TSMC and others are clearly the highlight of the technology symposium. Researchers at NEC Corp.'s system devices research lab will discuss a 65nm technology with a variable supply voltage and back-bias control to keep power consumption under control. Texas Instruments Inc. engineers will present a 65nm technology with back-bias and voltage islands. A set of data-retention registers is used when the device is in sleep mode.

A team from the Crolles, France, development center of Motorola, Philips Semiconductors and STMicroelectronics will discuss its 65nm CMOS platform, aimed largely at low-power applications. The abstract includes performance metrics for a test SRAM array with a cell size of 0.5?m2, as well as for analog/mixed-signal transistors.

Taiwan Semiconductor Mfg Co. engineers will describe their 65nm CMOS transistors, with the high-speed, general-purpose and low-power flavors using gate lengths of 40-, 45- and 55nm, respectively. The paper details the advantages of using a laser spike anneal process step instead of conventional rapid thermal annealing. The process results in improved drive current and less polysilicon depletion at the gate.

A separate TSMC paper discusses the reliability concerns of using relatively porous low-k dielectrics, with a k-value of 2.2, for interconnects targeted at 65nm design rules.

TSMC also plans to describe a 45nm SRAM cell created with a silicon-on-insulator (SOI) technology. A six-transistor SRAM cell takes up only 0.296?m2 of area. The paper will discuss the advantages of SOI compared with bulk, including better control of the short-channel effects that plague such small devices. The transistors have gate lengths of 30nm and operate as low as 0.6V, though nominal voltages are in the 0.85V to 1V range.

Shinichi Takagi, one of Japan's leading researchers, will present work from Japan's government-supported MIRAI project that combines the advantages of silicon germanium - which creates higher mobility in the strained, active silicon layer - with the lower parasitics of SOI. The SiGe-on-insulator approach resulted in a 10x improvement in hole mobility in the PFET devices, the abstract reports.

IBM Corp. will present a 90nm SOI process to build millimeter-wave devices. Two papers will discuss moving to different crystal orientations: 100- and 110-crystalline structures, for the NMOS and PMOS devices respectively.

Intel Corp. will present details of the 90nm process technology it is now shipping, which includes local, or uniaxial, strained silicon. And Intel compares the advantages for mixed-signal and RF circuits of its NMOS technology with the silicon-germanium HBT approach to analog and mixed-signal circuits.

Micron Technology Inc. will present what appears to be the smallest DRAM cell size to date. By using a cell design that is six times "F" (F being the lithographically printable smallest feature), Micron engineers created a 0.036?m2 cell size, using a technology with a 78nm half-pitch created with a 193nm scanner.

Samsung engineers will describe a NOR flash cell that measures 0.049?m2. The approach requires pushing the ArF lithography tools to make contact holes that are 70nm in diameter.

Samsung also goes to the Symposium on VLSI Technology with an SRAM cell of 0.16?m2, using a stacked single-crystal technology and 80nm design rules. The SRAM design stacks the load-PMOS and pass-NMOS transistors over the planar-NMOS pull-down transistors, cutting the cell size sharply.

More than a dozen papers describe emerging memories, including one from Samsung that applies the FinFET transistor design to DRAM arrays. STMicroelectronics and Ovonyx Inc. engineers will discuss chalcogenide phase-change memory research, with a trench cell structure that is compatible with a CMOS process. The cell size is 0.32?m2 in 0.18?m technology.

More information about the symposium is available at the conference Web site.

- David Lammers

EE Times

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