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By Kelvin Yuk and Jorge Campos
Written: June 7, 2002
Even though research on Silicon-on-Insulator (SOI) devices has proven it to be the next technology that will significantly improve the performance of digital integrated circuits, many skeptics have labeled the “floating” body as one of the pitfalls of these devices. Digital integrated circuit layout strategies have consisted of a biased body for the past several decades, especially with the adoption of the CMOS design strategy, until now. Many of the advantages provided by the SOI technology require the transistors to be implemented with an un-biased body, including: low leakage current, high temperature operation, and high integration densities. Thus because of the dire need of integrated circuits with these features, the “floating” body may be more of a blessing than a burden.
One research cohort in particular, the Swiss-based Innovative Silicon Solutions (ISS) and the Swiss Federal Institute of Technology (EPFL), have recently developed a novel single-transistor DRAM cell that strictly relies on the floating body to provide the memory effect. They have adapted the previous one-transistor, one-capacitor (1T-1C) cell onto the Silicon-on-Insulator realm and created a one-transistor (1T) cell that replaces the capacitor by the floating body provided by the SOI technology. This 1T cell is projected to scale down to half the size (0.04 micron2) of 1T-1C cells at the 0.10 micron process node. An article by the EE Times mentions that this technology “bypasses the scaling problems of sub-100-nanometer technology DRAMs that were predicted by the International Technology Roadmap for Semiconductors (ITRS).”[1] ISS president Pierre C. Farzan mentioned to EE Times: “We wanted to provide a simple solution to the DRAM and embedded DRAM industry before they go below 100-nm features so that DRAM miniaturization can continue to follow Moore’s Law.”[1] This architecture was presented in a paper by Serguei Okhonin, chief scientist at EPFL, at an IEEE International SOI Conference in Durango, Colorado. The architecture was only implemented at a single-cell level that consists of 0.25 micron and 0.13 micron nodes, and resulted in read and write times of less than 3 ns[1].
The floating body characteristic of unbiased Silicon-on-Insulator transistors is also being exploited by devices meant to operate at high temperatures. A recent Sandia Lab News article discussed the accomplishments of a pair of researching engineers at the Sandia National Laboratories. Joe Henfling and Randy Normann of Geothermal Research Dept. 6211 have developed a “complete telemetry data acquisition” ASIC meant to operate at high temperatures. This device has been tested at 240ºC, where it measured real-time pressure and temperatures in a geothermal well. One of the significant accomplishments of this specific ASIC, besides the fact that it has been successfully operating at high temperatures, is that it has allowed research groups to acquire data never before thought possible. Japanese researchers at Unzen volcano used this prototype ASIC to measure pressure, temperature, and to detect the formation of fluid-filled fractures as well. This specific drilling attempt proved to be a useful method to determine potential production locations for geothermal energy by measuring pressure drops. These potential drops are a result of fluid running into the formation, “which means fluid could come back out of the hot rock to drive a geothermal power plant.”[2]
SOI in the Computing Industry
Many computing industries are employing SOI to improve the speed and power performance of their products.
AMD has just recently moved production of its Athlon Processors to the 0.13um technology to reduce space and power consumption of the processor. Due to the lower power comsumption of SOI technology, it is becoming the preferred technology in notebook computers. AMD hopes to implement low-power Athlon chips and the next generation processors into portable applications. In addition, AMD’s next generation processor codenamed “Hammer” due for release at the end of 2002 uses a 0.13micron SOI process. The processor is based on AMD’s x86-64 technology and will be the first 64-bit x86 processor produced.
IBM has also produced the 1-GHz G4 processors that utilizes SOI technology [6]. Although the processor is not used in the Apple Powermac G4 dual 1GHz machines, it is currently being used in IBM AS/400e servers [7]. The IBM iSeries Model 8XX is the industry’s first server family to deliver Silicon-on-Insulator techonology [8]. The combination of copper and SOI technology used in the iSeries increases processor performance by 25%-35%. In addition to IBM’s current utilization of SOI in their server technologies, it also plans to in a joint effort by IBM, Sony and Toshiba to produce Sony computer entertainment products.
Oki Electric Industry Co., Ltd. is currently manufacturing the world’s first low-power, high-performance, fully depleted SOI LSIs [5]. Oki has been successful in fabricating the SOI-based LSIs by using ultra-thin UNIBOND SOI wafers manufactured by Soitec. These LSIs . So far, Oki has used this technology in solar-powered watches that utilize the low-power benefits of SOI LSIs. Eventually, the LSIs will be implemented in communication and low-power devices such as cell phones, notebooks, PDAs, wireless and optical communications. The advantage that SOI technology has in RF circuits is the ability to maintain low power at high operating frequencies. The LSIs will be used in applications such as Bluetooth which enables wireless short-range high bandwidth data transfer. Oki has chosen to use fully depleted SOI technology over partially depleted devices due to the increased power reduction.
Seiko has also adopted SOI technology from Soitec and has applied it to their watches utilizing SPRING drive technology. The circuitry of the watches is fabricated using SOI UNIBOND process and is used for the driver circuit that controls the timing accuracy of the watch [3][4].
Although not many companies have SOI products available on the market at this time, there is much development on future projects based on SOI. Due to the debate over performance benefits and expensive fabrication processes, SOI has only begun to surface in the computing and IC industry. However, it shows potential in terms of speed and power performance and looks to be a promising solution to future computing needs.
References
[1] Paul Kallender, “Swiss Team Develops Single-Transistor SOI DRAM Cell”, EE Times Online, http://www.eetimes.com/story/OEG20011016S0099, Oct. 16, 2001.
[2] Bill Murphy, “Hot Electronics Could Boost Geothermal Industry, Earth Sciences”, Sandia Lab News, Vol. 53, No. 25, 2001. http://www.soisolutions.com/news.html [3] Seiko, http://www.soitec.com/pr33.htm [4] Seiko, http://www.seiko.co.jp/english/eco/kaihatsu.html [5] Oki, www.oki.com/semi/english/bt-soi.htm [6] IBM PowerPC G4, http://news.com.com/2100-1040-246841.html?legacy=cnet [7] IBM PowerPC G4, http://maccentral.macworld.com/news/0009/27.mot.shtml [8] IBM Server Information, http://commerce.www.ibm.com/cgi-bin/ncommerce/CategoryDisplay?cntrfnbr=107824&cgmenbr=24188&cntry=840&lang=en_US&scrfnbr=126&cgrfnbr=2051594&x=14&y=11
