• PDF / 323,559 Bytes
• 6 Pages / 420.48 x 639 pts Page_size
• 7 Downloads / 335 Views

DOWNLOAD

REPORT

---

ABSTRACT We report on the fabrication and analysis of silicon-oxynitride (SiON) as core material for silicon-based planar photonic waveguide circuits. Features of devices made of this particular SiON material are: (1) a silicon-compatible technology (low-cost perspective), (2) a waveguide structure with high dielectric index contrast, allowing a very compact device layout (approximately lOx smaller radius of curvature than conventional doped SiO 2 technology), (3) a low optical loss < 0.15 dB/cm, in the 1550 nm telecommunication window and (4) a negligible polarization dependence. The materials aspects and resulting analyses of the SiON layers as well as particular device properties are described. INTRODUCTION Analogous to fiber devices in optical telecommunication systems, silicon-based photonic integrated circuits (PIGs) have been actively pursued: the silicon-based fabrication, processing, and replication technology lends itself to mass production and is hence low-cost. Most notable in this area is the work on doped SiO 2 glass by the NTT and Lucent groups [1, 2] using either flame-hydrolysed or LPCVD-deposited doped-glass devices. These lowdoped glassy waveguide structures are very similar to well-known waveguiding glass fibers with respect to optical guiding (index contrast between core and cladding layers) and hence have very similar modal fields resulting in low coupling losses between the chip and standard single mode fiber. An inherent disadvantage of these low index-contrast glassy structures is the rather large radius of curvature allowable in circuits, typically greater than 10 mm [1]. We report on silicon-oxynitride (SiON) as an alternative silicon-based oxide for waveguide devices [3]. Owing to the nitrogen "doped" silicon-oxide compound, the dielectric value (refractive index) can be adjusted in a very flexible way to match other design criteria such as, e.g., achievable dimensions. In the work reported here, a relatively high effective lateral contrast in refractive index of 0.02 between the SiON (waveguiding) core layer and its surrounding (lower and upper) SiO 2 cladding layers is used (Fig. 1). This index contrast is approximately lOx higher than usual for Ge-doped SiC 2 waveguides [1, 2] and allows a lOx smaller radius of curvature (1.5 mm) to be used in our circuit layouts. The higher areal density results in a much more economical usage of wafer area and allows us to design multi-stage filter devices on 85 mm of chip length [4]. The high propagation loss at 1550 nm wavelength, usually associated with SiON compounds [5], is decreased to a value of 0.10 to 0.15 dB/cm via a high-temperature anneal process. By properly adjusting the mechanical film stress in the oxidic trilayer, a negligible polarization sensitivity of < 0.05 nm is obtained in channel waveguide filters.

255 Mat. Res. Soc. Symp. Proc. Vol. 574 01999 Materials Research Society

Material

] SiO2

SiO 2

Dimensions

5 p

.3

Refractive index

•m

19 P±m

ns=l.450I

ns=1.450

Si wafer [(001), n-type, 1-10 ohm-cm, 525 kin] Figure 1: S