Silicon oxynitride (SiON)- technology has been widely accepted for realizing integrated optical devices for application in optical telecommunication. Some of the severe requirements put in this field to devices and hence to technology are more relaxed in sensing applications, but other ones pop up in this area. These differences are explained from the general requirements put on the performance of integrated optical sensors performance and they are analyzed with respect to their consequences for applying SiON technology. Data about the technology are given. Application of the technology is illustrated on some chemo-optical sensors, a Mach-Zehnder interferometer, a polarimeter and a bend sensor, which have been developed in the MESA+-institute.
The mechanism of direct bonding at room temperature has been attributed to the short range inter-molecular and inter-atomic attraction forces, such as Van der Waals forces. Consequently, the wafer surface smoothness becomes one of the most critical parameters in this process. High surface roughness will result in small real area of contact, and therefore yield voids in the bonding interface. Usually, the root mean square roughness (RMS) or the mean roughness (Ra) are used as parameters to evaluate the wafer bondability. It was found from experience that for a bondable wafer surface the mean roughness must be in the subnanometer range, preferentially less than 0.5 nm. When the surface roughness exceeds a critical value, the wafers will not bond at all. However RMS and Ra were found to be not sufficient for evaluating the wafer bondability. Hence one tried to relate wafer bonding to the spatial spectrum of the wafer surface profile and indeed some empirical relations that have been found. The first, who proposed a theory on the problem of the closing gaps between contacted wafers was Stengl. This gap-closing theory was then further developed by Tong and Gosele. The elastomechanics theory was used to study the balance between the decrease of surface energy due to the bonding and the increase of elastic energy due to the distortion of the wafer. They considered the worst case by assuming that both wafers have a waviness, with a wavelength (lambda) and a height amplitude h, resulting in a gap height of 2h in a head to head position. This theory is simple and can be used in practice, for studying the formation of the voids, or for constructing design rules for the bonding of deliberately structured wafers. But it is insufficient to know what is the real area of contact in the wafer interface after contact at room temperature because the wafer surface always possesses a random distribution of the surface topography. Therefore Gui developed a continuous model on the influence of the surface roughness to wafer bonding, that is based on a statistical surface roughness model Pandraud demonstrated experimentally that direct bonding between processed glass wafers is possible. This result cannot be explained by considering the RMS value of the surfaces only, because the wafers used show a RMS value larger than 1 nm. Based on the approach exposed in reference six, a rigorous analysis of wafer bonding of these processed glass wafers is presented. We will discuss the relation between the bonding process and different waveguide technologies used for implementing optical waveguides into one or both glass wafers, and give examples of optical devices benefiting from such a bonding process.
Microsystems are presented in which a SiON based optical waveguiding system is monolithically integrated with photodiodes, which are implemented in the Si substrate. Coupling structures of various type enable to transfer whether (part of) the power of one selected mode or the power of all modi propagating through the waveguide, to the photodiode. Here we focus on coupling structures for use in integrated optical absorption sensor systems, where information can be obtained from both the TE0 and TM0 mode, propagating simultaneously through the waveguide system. The coupling into the photodiodes is achieved by thinning down the thickness of the core layer in the region above the photodiode, which results in a mode specific modewidth expansion of the propagating modi. It will be shown that in asymmetrical layer systems, within a certain interaction length all TM0 power can be absorbed by the Si detector, while the TE0 mode shows only a negligible attenuation. The selectivity of the coupling can be strongly enhanced by implementing an additional substrate layer, having a refractive index in between that of the TE0 and TM0 mode. Both theoretical and experimental results will be presented.
The curriculum in Electrical Engineering at the University of Twente has been recently adjusted in order to increase the proficiency in optics of the graduates, providing a general background and preparing especially for integrated optics and optical communication techniques. This involves mainly three undergraduate courses during the second through fourth year of the five-year curriculum. Two of these courses involve intensive use of computer aids. In the first one, Electrodynamics, Maple worksheets are extensively used for diminishing the tedium of the mathematics and for visualizing (using animation) of traveling and standing wave patterns. In the last course, computer programs (a slab mode solver and an implementation of the beam propagation method) are used as design tools. We describe the aims, contents, and the relationship between the courses and some organizational issues. It is concluded that the courses meet our requirements: undergraduate students become productive quite fast in the field of integrated optics when they work in an internship or in their MSc-project. The background thus provided to our graduates seems to be well received in the relevant industry.
A simple, efficient and reusable fiber-to-chip interconnect is presented. The interconnect is based on a V-groove (wet- chemically etched) in silicon, combined with a loose-mode Si3N4-channel waveguide. The loose-mode waveguide is adiabatically tapered to the integrated optical (sensor) circuitry. This adiabatic taper enables the dimensions of both the integrated optical sensor circuitry and the loose- mode waveguide section to be designed independently. The coupling efficiency of the `plug-it-in' interconnect is tunable between zero and the maximum obtainable value by tightening two adjustment screws. Coupling efficiencies up to 60% using TE-polarized light at wavelength of 632.8 nm have been reproducibly measured.
The thickness non-uniformity and refractive index in- homogeneity of silicon oxynitride thin films, grown by low pressure chemical vapor deposition, have been optimized. The present work was especially motivated by the application of these thin films as well defined waveguides in phase-matched second harmonic generating devices, which are well known for their extremely high requirements to uniformity and homogeneity. However, other demanding integrated optical components like gratings, sensor systems, telecommunication devices, etc., also strongly benefit from highly uniform waveguides.
Chemo-optical microsensing systems, whether based on fiber optics or integrated optics, show promising prospects. The physical principles underlying chemo-optical waveguide sensors are discussed with the accent on linear evanescent field sensors. The role of the chemo-optical transduction layer is emphasized. Restriction of the freedom of design by technological uncertainties is briefly dealt with. The structure of a complete micro-sensing system is discussed and illustrated by presenting various design of chemo-optical sensors based on surface plasmon resonance.