Integration of 1GB/sec Silicon Lateral Trench Photodetector with High-Performance CMOS

Abstract

According to the ITRS, high-end microprocessors with 11.5-GHz on-chip clock frequency are within reach by the year 2010[1]. However, one of the biggest obstacles is the availability of an interconnection network capable of supporting multi-GHz-bandwidth, distortion- and interference-free data flow both on-chip and off-chip at the system level (Fig. 1). Optical links at wavelength of 850nm utilizing multimode fiber and vertical cavity surface emitting laser (VCSEL) have been widely used for short distance communication and have potential in high density parallel interconnects for cabinet-to-cabinet connections for large computer systems. However it is still questionable whether it can be applied to the next distance regimes: board-to-board, chip-to-chip or even on-chip global wiring. Existing high-bandwidth optical data links use hybrid integration, where III-V photodetectors and light-modulators are flip-chip or wire-bonded onto pre-fabricated silicon integrated circuits containing the drivers for the transmitters and receivers. In terms of cost and packaging complexity, monolithically integrated devices with Si VLSI technology are preferable. However, the speed of Si photodiodes is limited by the carrier transit time in the thick absorption layer due to the long absorption length in Si (>15μm at 850nm). Standard CMOS photodetectors suffer from low bandwidth, low efficiency and/or require high operating voltages (>10V) [2-4], Recently we developed the Si lateral trench detector (LTD), a CMOS-compatible photodiode capable of both high speed and high sensitivity at low operating voltages [5]. Open eye operation of a hybrid optical receiver, consisting of a LTD wire-bonded to a SiGe BiCMOS transimpedance amplifier (TIA), was demonstrated up to 6.5Gb/s. In the present work, we demonstrate the integration of optimized LTDs with 0.13μm CMOS technology. Excellent characteristics were achieved for both the photodiodes and the CMOS transistors. 10Gb/s operation was demonstrated at a supply voltage of only 1.5V.