We present the results of our project aimed to design and construct silicon grisms. The fabrication of such devices is a
complex and critical process involving litho masking, anisotropic etching and direct bonding techniques. After the
successful fabrication of the silicon grating, we have optimized the bonding of the grating onto the hypotenuse of a
silicon prism to get the final prototype. After some critical phases during the experimentation a silicon grism has been
eventually fabricated with 363.6 grooves/mm and 14 degrees of blaze angle. The results of the cryo-optical laboratory
tests are reported, along with a general description of the adopted technological process. The positive results allows us to
offer to the international community a new capability in building such devices.
In order to obtain specific channels and reservoirs in glass for analytic systems, the structuring of borosilicate glass has been studied. We used wet etching in HF diluted solution for etching channels up to 150 μm depth. A mask obtained by successively wet etching of previously evaporated Au and Cr layers has been used. A thick SJR 5740 type resist has been spun-on in order to accomplish the optical transfer of the pattern. A normal underetching not larger than the depth, has been obtained when adding a small amount of nitric acid, and using an appropriate annealing process after metal deposition. Neither pinholes nor cracks have been noticed after getting an etching depth of 180 μm. Double side etching has been performed for penetrating the glass. The dependence of the etching rate vs. both HF and HNO3 concentration is outlined together with the etched surface quality.
The silicate spin-on-glass (SOG) assisted low temperature bonding of different types of glasses on silicon and silicon compounds substrates is widely used in micromachining of analytical devices. Two silicate spin-on glasses (SOG), potassium silicate KASIL 2130 and sodium silicate N/N CLEAR, both of them from PQ Inc., are used. Previous experiments have revealed the formation of clusters and voids in the cured glass layer, that diminishes the bonding quality. A quantitatively analysis of the bonding process in terms of work of adhesion and interfacial tensions enabled us to identify the hot points of the bonding process: the wettability of the surfaces to be bonded, the appropriate concentration of the soluble glass, the adhesion of the spin-on-glass on these surfaces in both liquid and solid state, the spun-on-glass curing process. To overcome these hot points appropriate technological steps are added to the bonding process: O2 plasma and hot HNO3 exposure of glass/silicon respectively silicon nitride surfaces, one minute delay of spinning after sog-deposition on the substrate, increasing up to 125°C the annealing temperature of the spun-on-glass. Smooth, uniform, reproducible glass layers, are obtained and the dependency of their thickness (ranging from 100 Å to 5000 Å) versus silicate concentration of the soluble glass is determined. In order to explain the clusters and voids formation, successively observations of the cured layer after the annealing treatment and after room temperature storage are performed, and show that room temperature storage of non-completely cured silicate layers leads to the formation of clusters. The effect of the concentration of the soluble silicates is qualitatively analyzed, by means of optical microscopy, showing that silicate solutions having 2-3% of wt. are suitable for bonding applications with best results when the obtained glass layer is thin enough.
The completion of the DNA sequence of several genomes, including the human one, has opened completely new scientific and technological frontiers. The huge amount of genetic information available requires the development of faster and cheaper analytical tools. This can be possible by miniaturising the analytical system itself and by the development of proper analytical procedures, involving fluidic processes. A precise genetic identifying technique is hybridization, that can be accomplished in an array format on very small bidimensional surfaces. In order to automate the fluidic process involved in the DNA hybridization, three micromachining techniques are approached by the authors team, for obtaining reservoirs with volumes ranging from 1nl to 2μl using different materials as polyimide, silicon and glass. Several configurations were proposed targeting a turbulence free fluid flow. A qualitatively fluid flow study was performed and the influence of the reservoir shape was revealed. One obtained device was tested in a Laser Induced Fluorescence detection set-up.
Waveguide laser arrays are fabricated on Er:Yb-doped phosphate glasses by a two-step ion exchange technique. The channel fabrication based on Ag-Na thermal diffusion followed by field assisted burial step is described. Single mode as well as multimode behavior of the laser is studied at four wavelengths representative of the telecom C-band between 1530-1565 nm. Each laser cavity is made by two fiber Bragg gratings butt-coupled to the waveguide. Fiber-coupled single-mode output powers > 0.8 mW and slope efficiency > 2% are obtained for all wavelengths.
Silicon grisms are suitable optical devices that allow for a spectroscopic mode able to effectively complement the natural
imaging mode of IR cameras, providing high spectral resolution
(R>5000) in the near infrared. We present a review of the fabrication process aimed to produce IR grisms with high refractive index. Such devices are intended to implement a high resolution mode in the Near IR Camera-Spectrograph, NICS, the user instrument at the focal plane of the Italian national telescope Galileo. Litho masking and anisotropic etching techniques have been employed to get, firstly, silicon gratings of suitable size for astronomical use, then warm bonding techniques have been used to obtain the final grisms in echelle configuration. The results and the problems encountered in the bonding procedure are presented along with a future implementation of silicon grisms in space instrumentation.
Silicon grisms are very attractive as devices for IR spectroscopy in terms of high resolving power and compactness, necessary for many astronomical applications and for implementation of spectroscopic modes in large telescopes respectively. We present the fabrication process of a silicon grism as composed by an IR transmission grating coupled to a silicon prism. The silicon gratings were manufactured using silicon micromachining techniques, as electron beam lithography and wet anisotropic etching, achieving good uniformity over all the large surface (32 X 32 mm2) and grating facets of excellent optical quality; the final grism was realized by means of direct bonding of the grating onto the prism face. The results of laboratory tests on the first prototype are presented.
Multidisciplinary efforts, combining microfabrication, chemistry and molecular biology, have been recently focused on the development of large electrode arrays loaded with oligonucleotide probe to allow rapid analysis of nucleic acid samples. Different micromachining techniques can be used for obtaining the inlet, outlet and main reservoirs for the analyte. In the present work silicon wafers are used as substrates for the microarrays, patterned by means of direct writing or optical lithography. Three methods are developed in order to obtain reservoirs with depths ranging from 5 microns to 200 microns, allowing an analyte volume in the range of 1 nl to 1 ml: reactive ion etching of a polyimide layer, wet anisotropic etching of silicon, respectively deep wet isotropic etching of the glass cover. The glass cover is bonded at low temperature, using spin-on glass as adhesive and ensures a protection of the analyte, as well as a rapid entering of the analyte in the reservoirs, increasing thus the speed of the analysis. A custom laser induced fluorescence set-up is used in order to perform the analysis. The fluorescent DNA molecules are concentrated and localized during an observation time of 60 seconds, proving the functionality of the device.
We report the fabrication process of a silicon target with a rectangular slit as an instrument for measuring the size and the angular divergence of high charge-density electron beams in particles accelerators. Bulk micromachining of silicon wafers by means of anisotropic etching allowed the definition of slits with parallel straight edges and low disuniformity. The disuniformities of the completed device evaluated by scanning electron microscopy were found to be tolerable with respect to the wavelength used in the experiments. Tests of the fabricated targets are in progress in the injector of ELETTRA, the synchrotron radiation facility in Trieste, Italy.
We present the first results of a fabrication process aimed to produce IR grisms with high refractive index. Such devices are intended to implement a high resolution mode in the near IR camera-spectrograph, a user instrument at the focal plane of the Italian national telescope Galileo. Litho masking and anisotropic etching techniques have been employed to get, firstly, silicon gratings of suitable size for astronomical use, then warm bonding techniques will be used to obtain the final grisms in echelle configuration. The results of the laboratory test on the first prototype are presented.
Ultrasonic transducers are generally based on the piezoelectric effect and they are used in a variety of applications (medical imaging, NDE, ranging). Some of the main reasons for choosing an alternative technology, based on electrostatic effect, are low impedance mismatch with air and in water, low energy density, high efficiency, low costs, good integration with control electronics. Capacitive ultrasonic transducer consists in a parallel plates capacitor (like a condensor microphone) with a fixed electrode and a free one (membrane). A cMUT (capacitive Micromachined Ultrasonic Transducer) consists of an array of capacitive ultrasonic transducer with a metallized membranes suspended on silicon bulk. The membrane thickness is 0.4 micrometers . Tests of these transducers ( 2.5 MHz) fabricated in our laboratories are in progress.