Materials For Monolithic Silicon Microphotonics
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L.M. GIOVANE, D.R. LIM, S. H. AHN, T. D. CHEN, J.S. FORESI, L. LIAO, E. J. OULETTE, A.M. AGARWAL, X. DUAN, J. MICHEL, A. THILDERKVIST AND L.C. KIMERLING Materials Processing Center, Massachusetts Institute of Technology, Cambridge, MA 02139,
[email protected] ABSTRACT The path for silicon materials development has been charted. By the year 2010 we will have fabricated integrated circuit chips containing 109 transistors with 40A thick gate oxides and 1000 A minimum feature sizes running at 4 GHz clock speeds. It is conceivable that incremental advances on the current chip architecture will satisfy the required materials and process improvements. The interconnection problem is the only challenge without a proposed solution. The signal propagation delay between devices is now longer than the individual device gate delay. The resistance and capacitance associated with fine line Al interconnects limit speed and increase power consumption and crosstalk. High power line drivers are limited by the reliability constraint of electromigration. There is no current paradigm for 4 GHz, electronic clock distribution. Optical interconnection can remove the electronic transmission bandwidth limit. The main challenge is development of a silicon-compatible, microphotonic technology. Rare earth doping has provided a means of sharp-line electroluminescence from silicon at X= 1.54 gm. Silicon's high index of refraction and low absorption in the near infrared yield an ideal optical waveguide. As with microelectronics, the silicon / silicon-dioxide materials system allows high levels of integration and functionality. The applications of silicon materials to light emission (Si:Er), optical waveguides (Si/SiO2), photonic switching (Si/SiO 2) and photon
detection (SiGe) are reviewed. These developments are discussed in the context of systems applications to communications and computation. 1. INTRODUCTION
Two dominant needs of the electronics industry are high speed interconnection for computation and wavelength division multiplexing (WDM) for telecommunications. The interconnection bottleneck in computing follows from the faster smaller devices contained in the latest technology microprocessor and DRAM chips. Speed of operation is limited by the propagation delay between transistors rather than the gate delay to switch an individual transistor. These same considerations limit the input/output bandwidth and the clock speed. Wavelength division multiplexing is a near term solution for slow electronics and the large imbedded fiber base of communication highways. WDM is also a long-term solution to providing unlimited bandwidth to the system. WDM devices are passive optical components that allow over a hundred different wavelengths (communications channels) to be coupled/decoupled from a single fiber transmission line. The number of channels is limited today, not by the properties of the fiber, but by the size and selectivity of the channel dropping filters.
45 Mat. Res. Soc. Symp. Proc. Vol. 486 © 1998 Materials Research Society
2. SILICON MI
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