Optical transmission losses in polycrystalline silicon strip waveguides: Effects of waveguide dimensions, thermal treatment, hydrogen passivation, and wavelength
Optical transmission losses in polycrystalline silicon strip waveguides: Effects of waveguide dimensions, thermal treatment, hydrogen passivation, and wavelength
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DOI：
10.1007/s11664-000-0122-4
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发表时间：
2000-12-01
影响因子：
2.1
通讯作者：
Kimerling, LC
中科院分区：
文献类型：
--
作者：
Liao, L;Lim, DR;Kimerling, LC
在不断缩小的超大规模集成电路（ULSI）中，信号传输延迟在门延迟中占主导地位。因此，基于硅的单片光电电路（SMOE）及其光速信号传播可以为未来几代微处理器提供独特的优势。对于这种SMOE电路，我们需要与硅技术兼容的光学互连。由包覆有SiO2的多晶硅（polySi）组成的条形波导提供了优异的光学限制和易于制造，是此类互连应用的理想选择。然而，使用这种材料系统的一个主要挑战是其插入损耗。在本文中，我们提供的技术，以尽量减少光传输损耗的多晶硅带波导。我们以前的工作，使用多晶硅带波导，表明在λ = 1.55 μ m的光传输损耗为15 dB/cm，这是一个通信波长的光纤中的选择，因为它代表了吸收最小值。在晶体硅条形波导中的类似测量产生小于1dB/cm的传输损耗。然而，在将损耗从77 dB/cm降低到15 dB/cm的过程中，我们通过改善膜表面形态来最小化表面散射的损耗，并且通过氢钝化来降低体吸收。在本文中，我们报告的剩余体积损耗从15 dB/cm到9 dB/cm的进一步减少。通过对不同波导芯尺寸的实验，我们发现体损耗对净传输损耗的贡献随波导芯厚度的增加而减小。此外，高温处理提供了在多晶硅中的应变消除，降低了传输损耗。不建议在氧气环境中退火，因为它总是增加传输损耗。氢钝化提高了透射率，这归因于存在于多晶硅晶界处的光吸收悬挂键缺陷位点的钝化。总之，这些方法在λ = 1.55 μ m时产生了最低测量损耗值9 dB/cm。由于集成的SiGe和Ge光电探测器在较短的波长，如λ = 1.32 μ m更有效，传输损耗也在λ = 1.32 μ m测量。当波导中的缺陷和应力最小化时，在两个波长（1.32 μ m和1.55 μ m）处的损耗相似。
Signal propagation delays dominate over gate delays in the ever-shrinking ultra large scale integrated (ULSI) circuits. Consequently, silicon-based monolithic optoelectronic circuits (SMOE) with their Light speed signal propagation can provide unique advantages for future generations of microprocessors. For such SMOE circuits, we need optical interconnects compatible with silicon technology. Strip waveguides consisting of polycrystalline silicon (polySi) clad with SiO2 offer excellent optical confinement and ease of fabrication that are ideal for such interconnect applications. One major challenge with using this material system, however, is its insertion loss. Tn this paper we provide techniques for minimizing optical transmission losses in polySi strip waveguides. Our previous work using polySi strip waveguides, showed an optical transmission loss of 15 dB/cm at lambda = 1.55 mum, which is a communication wavelength of choice in optical fibers because it represents an absorption minimum. Similar measurements in crystalline silicon strip waveguides' yielded transmission losses of less than 1 dB/cm. Hitherto, in decreasing loss from 77 dB/cm to 15 dB/cm, we had minimized loss from surface scattering by improving the film surface morphology, and decreased bulk absorption with hydrogen passivation. In this paper we report a further reduction in the residual bulk loss from 15 dB/cm to 9 dB/cm. By experimenting with different waveguide core dimensions, we find that the contribution of bulk loss towards net transmission loss decreases with waveguide core thickness. Additionally, high temperature treatment provides strain relief in the polySi, decreasing transmission loss. Annealing in an oxygen ambient is not recommended because it always increases transmission loss. Hydrogen passivation improves transmission, attributable to passivation of light-absorbing dangling bond defect sites present at polySi grain boundaries. Together, these methods have resulted in the lowest measured loss value of 9 dB/cm at lambda = 1.55 mum. Since integrated SiGe and Ge photodetectors are more efficient at shorter wavelengths like lambda = 1.32 mum, transmission loss is also measured at lambda = 1.32 mum. Losses at the two wavelengths (1.32 mum and 1.55 mum) are similar when defects and stress in the waveguides are minimized.