In this paper, we present both a theoretical evaluation and the fabrication of a novel polymerase chain reaction (PCR) microdevice. This microdevice contains elements for both thermal cycling and fluorescence detection. The proposed device is composed of a reaction chamber with integrated temperature sensor, heaters, p-n diode and optical filter. The advantage of combining these in a single structure is that real time detection of DNA amplification will be possible using a small volume of the PCR solution. The photodiode is covered by a thin film optical filter in order to block out the light which is used to excite the fluorophore dyes. CdS is used for the first time for such a filter and the complete micro-fabrication process is described.
Injection strategies have been employed in the field of fluidic MEMS using piezo electric or thermal actuators. A very popular application for such technology is inkjet printing. Largely this technology is used to produce droplets of fluid in air; the aim of this investigation is to produce an injection device for the precise dispensing of nanolitre volumes of fluid. A novel technique for dispensing fluid using superparamagnetic beads has been investigated. The beads used (Dynal Biotech) contain a homogeneous dispersion of Fe2O3, allowing for easy control with a magnet. This magnetic property is exploited, by a plug of approximately 60 000 beads within a micro channel. This is accomplished by applying a non-uniform magnetic field from a bullet magnet within close proximity of the bead plug. Once the plug is formed it can be moved along the micro channel by moving the magnet and thus, provide a plunger-like action.
Previous work has demonstrated a bead plug device is able to dispense fluid from a micro channel at rates up to 7.2μlmin-1. This is an investigation using silicon and Pyrex fabricated micro channels with smaller dimensions, such that the dimensions will be similar to those which will be used to produce a pipette device. Here results are presented using these fabricated micro channels, where the effects of using differently sized bead plugs and varying velocities are examined. The results follow our proposed theory; further analysis is required to determine the operation of a bead plug during all states of movement.
The recent interest in silicon based photonics, and the trend to reduced device dimensions in photonic circuits generally, has led to the need for mode converters to couple from optical fibres to such small devices. A range of structures have been proposed and in some cases demonstrated, including three dimensional tapers, inverted tapers and micromachined prisms. We have previously reported theoretical analyses of a Dual Grating Assisted Directional Coupler (DGADC), which promises high efficiency coupling over modest spectral linewidths. In this paper we report preliminary experimental results on the fabrication of such devices, together with an evaluation of the coupling efficiency. The approach has been to fabricate a demonstrator device for a particular arrangement of waveguide coupling parameters, i.e. we have fabricated a device that couples easily from fibre, because the input waveguide is approximately 5μm in cross sectional dimensions. The mode converter then couples to a 0.25μm silicon waveguide, primarily because comparisons exist in the literature. These results are compared with the predicted efficiency, and the results are discussed both in terms of the constituent parts of the DGADC, as well as the fabrication limitations. Whilst our device is not optimised we demonstrate that it has promise for very high efficiency coupling.
Recently there has been a strong trend to fabricate smaller photonic devices. In the literature, the problem of coupling optical fibres with thin semiconductor waveguides has not been solved sufficiently well to obtain both high coupling efficiency and good fabrication tolerances. This paper discusses a new approach, the Dual Grating-Assisted Directional Coupling (DGADC), which can result in a robust and very efficient device, with relaxed fabrication tolerances. Theoretical investigation of the coupler is presented. Coupling efficiency and device length are determined as functions of layer thicknesses and refractive indices, grating periods, depths and duty ratios, and finally wavelength. Fabrication of the coupler is also given, as well as preliminary experimental results.
In silicon based photonic circuits, optical modulation is usually performed via the plasma dispersion effect or via the thermo-optic effect, both of which are relatively slow processes. Until relatively recently, the majority of the work in Silicon-on-Insulator (SOI) was based upon waveguides with cross sectional dimensions of several microns. This limits the speed of devices based on the plasma dispersion effect due to the finite transit time of charge carriers, and on the thermo-optic effect due to the volume of the silicon device. Consequently moving to smaller dimensions will increase device speed, as well as providing other advantages of closer packing density, smaller bend radius, and cost effective fabrication. As a result, the trend in recent years has been a move to smaller waveguides, of the order of 1 micron in cross sectional dimensions. In this paper we discuss both the design of small waveguide modulators (of the order of ~1 micron) together with a presentation of preliminary experimental results. In particular two approaches to modulation are discussed, based on injection of free carriers via a p-i-n device, and via thermal modulation of a ring resonator.
Waveguide based Bragg grating devices have the potential of integration with passive or active optical components. A narrow bandwidth Bragg reflection filter or Fabry-Perot resonant structures can be realised using the approach of periodic refractive index modulation in waveguide gratings to form reflective structures. Most authors have considered 1st order Bragg gratings with periods of the order of 228nm operating at 1550nm but at the expense of complexity and high cost of fabrication. This paper describes the design of Silicon-On-Insulator (SOI) rib waveguides operating in the single mode regime that exhibit low polarisation dependence. A rigorous leaky mode propagation method (LMP) has been used to investigate the influence of etch depth in 3rd order Bragg gratings on the reflectance and bandwidth in the waveguides.
In silicon based photonic circuits, optical modulation is usually performed via the plasma dispersion effect, which is a relatively slow process. Until recently, most reserachers utilized Silicon on Insulator (SOI) waveguides with cross secitonal dimensions of the order of 5 microns. This limits the speed of devices based on the plasma dispersion effect due to the finite transit time of charge carriers. Consequently moving to smaller dimensions will increase device speed, as well as providing other advantages of closer packaging density, smaller bend radius, and cost effective fabrication. As a result, the trend in recent years has been a move to smaller waveguides, of the order of 1 micron in cross sectional dimensions. However, coupling light to such small waveguides is relatively inefficient. In the literature, the problem of coupling optical fibers to thin semiconductor waveguides has not been solved sufficiently well to obtain both high coupling efficiency and good fabrication tolerances, due to large difference between the fiber and the waveguide in both dimensions and refractive indices. In this paper, we discuss both the desing of small waveguide modulators (of the order of ~1 micron) together with a novel theoretical solution to the coupling problem. An example of coupling light to a thin silicon waveguide is given, as well as a discussion of a number of modulator design issues.
Silicon-based optical modulators are expected to be important components in some optical networks. The optical modulation mechanism can be achieved either via the plasma dispersion effect, or by thermal means. Both are relatively slow processes when utilized in large (multi micron) waveguide structures, which researchers tend to concentrate on for ease of coupling. Using large waveguide structures limits the operating speed and hence excludes the applicability of these devices in areas where higher speeds are required. This limitation could be overcomed by using smaller waveguides (of the order of 1Rm). In this paper, we present the basic operating mechanism, design, and fabrication details of an optimum three terminal p-i-n diode based optical phase modulator based on Silicon-On-Insulator (501). The device was optimised via electrical and optical modeling and is predicted to operated at 1 .3GHz with a power reduction of900%, as compared to previously published designs.
It is well documented that optical sensors offer many advantages over conventional electronic devices for some applications because they are more versatile, lighter, smaller, immune to electrical interference and can be densely multiplexed. However, to date, many optical sensor instrument systems have been insufficiently robust for use in harsh environments and relatively expensive due to the use of discrete optical components. Hence the primary aim of this work is to develop a physically robust and cost effective interrogation system for fibre Bragg grating strain sensors by integrating a system on a silicon chip. Therefore it will be possible to replace many of the costly discrete components. Related improvements will be the reduction of size and weight, an increase in robustness, and performance in relatively harsh environments. This work will focus on the development of a Micro Electro Mechanical System (MEMS) tunable Fabry-Perot optical filter, together with an integrated optical circuit fabricated on silicon-on-insulator (SOT) to deliver the signal to the Bragg gratings and to detectors based in the same optical circuit. In this paper we discuss the requirements for integration, as well as reviewing the principles of strain measurement using fibre Bragg gratings. The latter will include a brief discussion of the merits of multiplexing via single or multiple fibres
Silicon-on-insulator (SOI) technology offers tremendous potential for the integration of optoelectronic functions on a silicon substrate. In this research, we report on the fabrication process of a Mach-Zehnder interferometer on an SOI with 0.5μm wide waveguides in a Si layer of the order of ~1μm thick. These small dimensions increase the speed of these devices. However, with these small dimensions several fabrication difficulties such as alignment and thickness accuracy are present.
Silicon Carbide is a potentially useful compound for use in silicon based photonics because cubic silicon carbide (3C- SiC), possesses a first order electro-optic (Pockels) effect, something absent in pure silicon. This means the material is potentially suitable for high speed optical modulation. Furthermore, the wide bandgap (2.2 eV) of 3C-SiC makes the devices suitable for use over the visible and near infrared spectrum range as well as the longer communication wavelengths, and also means the material can tolerate high temperatures. However, relatively little work has been carried out in SiC for photonics applications. In this paper we will discuss design and fabrication of both SiC waveguides and modulators for silicon based photonics. The fabrication process utilizes ion implantation of oxygen into SiC to form the lower waveguide boundary. Subsequently, ribs are etched and contacts are added to form the optical modulators. Consideration of both Pockels modulators and plasma dispersion modulators has been made, and both will be discussed here. These devices have potential for optical modulation, but are also compatible with silicon processing technology. We have demonstrated waveguiding in 3C-SiC, established a processing recipe for the SiC wafers which enables fabrication of 3-dimensional devices, and demonstrated optical modulation. Performance of the resultant devices is compared to other silicon based devices in terms of operating speed and efficiency.
We have designed and fabricated waveguide optical modulators using cubic silicon carbide-(3C-SiC)-on-insulator rib waveguides. A refractive index change is induced in the rib via the plasma dispersion effect. These types of devices have potential for relatively high-speed silicon-based photonics compatible with silicon processing technology, as compared to pure silicon. Furthermore, the wide bandgap (2.2 eV) of 3C-SiC makes the devices suitable for use over the visible and near infrared spectrum range as well as the longer communication wavelengths. We have demonstrated waveguiding in 3C-SiC, fabricating the waveguides by ion implantation of oxygen into a silicon carbide layer. We have also established a processing recipe for the SiC wafers which enables fabrication of 3- dimensional devices. The work reported here describes the fabrication of the devices and presents preliminary experimental results for the waveguide losses and the modulation of the refractive index as a function of applied current. An efficient waveguide modulator for a single polarization is reported.
We have investigated different techniques to deposit 1 micrometers to 2 micrometers thick aluminium onto sidewalls of trenches etched into silicon. This process is required for the fabrication of thermally excited vertical bimorph actuators. First, aluminium is deposited covering both horizontal surfaces and sidewalls. Then an etch-step removes the aluminium from the horizontal surfaces, retaining only aluminium spacers on the sidewalls. Sputtering of aluminium and a subsequent anisotropic dry-etch yields spacers of a thickness less than 0.5 microns having a rough surface. Evaporation of aluminium at a shallow angle between the wafer and the aluminium source allows controlling the thickness of the deposits on the sidewalls compared to those on the horizontal surfaces. Thus, the dry-etch time can be reduced resulting in aluminium spacers up to 2 microns thick and of improved surface quality. If the deposit on the sidewall is thicker than on the horizontal surfaces, isotropic wet-etching can be used to remove the aluminium on the horizontal surfaces, where as on the sidewalls it is only thinned by about the thickness of the aluminium on the horizontal surfaces. Spacers of up to 2.5 microns thickness with good surface quality have been achieved.
This paper reports the design, fabrication and testing of silicon based micropump for liquid and gases. This piezoelectrically driven membrane pump is designed to be tolerant to gas-bubbles and to be suitable for self-priming. Reducing the dead volume within the pump, and thus increasing the compression ration, achieves the gas pumping. The main advantage of the pump described in the paper is the self-aligning of the membrane unit to the valve unit and the possibility of using screen printed PZT as actuator, which enables mass production and thus very low-cost micropumps. Dynamic passive valves are used, as those valves are very reliable having no moving parts and being not sensitive to smaller particles. Furthermore they can follow high frequencies, hence allowing the pump to run at resonance frequency enabling the maximum deflection of the diaphragm. First tests carried out on the micropump have produced promising results.
This paper presents the concept and design of a new lateral scanning system for an integrated atomic force microscope (AFM). The core part of the scanner is formed by vertical bimorph beams, which are reported for the first time in this paper. They consist of silicon beams side-coated with aluminium, which bend upon heating causing movement in the horizontal plane. Combining vertical bimorphs with planar bimorphs allows three-dimensional actuation. Theoretical analyses comprising electro-thermal and thermo-eleastic calculations show that large actuation movements are possible at low electrical input power and low input voltage. A process has been developed to deposit aluminium onto sidewalls of silicon beams. Furthermore, the fabrication process for the actuator is described.
This paper reports the design, fabrication and packaging of a micro machined silicon/Pyrex based chip for the polymerase chain reaction. Anodic bonding is used for sealing the chambers of 1 (mu) l volume with a Pyrex glass wafer. Platinum resistors on the back of the wafer are used as heaters and temperature sensors. The chip is externally cooled by forced air to achieve rapid temperature cycling. The transparency of the Pyrex makes it possible for using optical readout methods. The packaging is especially designed for easy handling, filling, power connection, temperature regulation and optical readout. The mass production of such silicon reactors could make single-shot, disposable devices economically viable.
Grating couplers can be more efficient than end-fire coupling, in coupling light into a thin film waveguide. The aim of this work is to fabricate a low cost, highly efficient silicon waveguide grating coupler which is to be use data the telecommunication wavelength of 1.3 micrometers . Silicon-on-insulator (SOI) is chosen for fabricating the gratings as it is low cost using the exiting silicon technology. Unibond wafers were used because they offer flexibility in the choice of the thickness' of both the silicon film and the buried oxide layer, and they have low optical waveguide loss. The wafers used in this work have a Si film thickness of 1.14 μm and a SiO2 buried layer thickness of 0.67 μm. Gratings that have asymmetrical profiles, such as blazed gratings are known to have higher directionality than the symmetrical rectangular gratings, and hence a higher output efficiency. Using perturbation theory, Si blazed gratings with an optimum grating height were predicted to have a maximum output efficiency of the order of 90% towards the substrate. The design and fabrication of the blazed gratings will be discussed in this paper.
In this work planar and rib (beta) -SiC-on-insulator waveguides were investigated. The waveguides were fabricated by two different methods. In the first a technological process similar to that of SIMOX was used, a buried SiO2 layer was formed by a two-step high-energy ion implantation of oxygen in SiC/Si wafers. For the second type of waveguides we used heteroepitaxy of SiC on SOI. The losses have been measured at 1.3 and 1.55micrometers . Rib waveguides were fabricated using dry-etching. These types of waveguides have great potential for high-speed silicon-based photonic devices compatible with silicon technology.
In integrated optics, grating couplers are used when conventional end-fire methods are cumbersome and less efficient in coupling light in and out of thin-film waveguides. Our aim is to fabricate a high efficiency grating coupler for integrated optics applications at infra-red wavelengths and for thin-film waveguides which can be used for sensor applications. In this paper, theoretical output efficiencies of silicon (Si) rectangular, ideal right-angled blazed and non-ideal trapezoidal gratings are presented. Using perturbation theory, Si rectangular gratings with optimum grating heights exhibit a maximum predicted output efficiency towards the surface at the order of 80% and Si right-angled blazed gratings have predicted efficiencies approaching 100%. The fabrication method consists of using electron beam lithography and reactive ion etching. Ion beam milling is also considered with the aim of creating blazed profiles by tilting the silicon-on-insulator (SOI) wafer. In our work, smart cut SOI Unibond wafers are used as the base material for fabricating the grating couplers as they offer good flexibility in choosing the guiding layer and buried layer thickness'. These waveguides are chosen to have an Si film thickness of 0.92 micrometer and an SiO2 buried layer thickness of 0.67 micrometer in order to use the transverse resonance effect to improve the output coupling efficiency. Si rectangular with various grating heights, designed at the first order of diffraction, were fabricated and characterized. The highest efficiency grating yet reported in SOI was produced, having the coupling efficiency in excess of 70%.
We have designed waveguide modulators using (beta) -SiC-on- insulator waveguides and the Pockels effect. A 2D semiconductor device simulator was used to determine the electric field configuration in a double-Schottky diode structure. This allowed us to evaluate the local modulation of the refractive index as a function of applied external bias and to determine the effective index modulation of the guided mode. The optical simulations were performed using the Spectral Index and the Effective Index methods. Different 2D geometries are analyzed and the material parameters needed for fabricating such a device are determined. Application to Mach- Zehnder intensity modulators is described. Such devices have potential for high-speed Si-based photonic devices compatible with silicon technology.
In this work planar planar (beta) -SiC-on-insulator waveguides were investigated. The waveguides were fabricated by two different methods. In the first a technological process similar to that of SIMOX was used, and therefore a buried SiO2 layer was formed by high energy ion implantation of oxygen in SiC/Si wafers. For the second type of waveguides we used heteroepitaxy of SiC on SOI(SIMOX). The losses have been measured at 0.633, 1.3 and 1.55 micrometer in both TE and TM polarization. A detailed analysis of the different loss mechanisms is presented. These types of waveguides have potential for high-speed silicon-based photonic devices compatible with silicon technology.
A simple grating mask has been used in an ordinary 5:1 projection stepper equipment to fabricate microscopic parabolic topographies in thick positive photoresist. The microparabolic surfaces created were coated with reflective material to form parabolic reflectors. Measurement values of focal length were in agreement with the expected theoretical values. The simple parabola forms the basis for the fabrication of compound parabolic reflector which can be used for beam steering. Normal incidence beam can be redirected by the compound parabolic reflector onto device areas in the vicinity of the focus.