We present the results of our project for the design and construction and on-sky test of 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 with 363
grooves/mm and a blaze angle of 14 degrees has been eventually fabricated. The application of an
A/R coating on both the surfaces has been the last step: this procedure is critical because of the
groove geometry of the diffraction grating, whose performace might be compromised by the
coating. Then, the grism was inserted in the filter wheel of the Near Infrared camera NICS, at the
focal plane of the National Galileo Telescope (TNG), the 3.5 m Italian facility in the Canary Islands
(E). The result of the on-sky tests are given in detail.
Imaging arrays of direct detectors in the 0.5-5 THz range are being experimentally developed. Terahertz active imaging
with amplitude-modulated quantum cascade lasers emitting at 2.5 and 4.4 THz performed by using an antenna-coupled
superconducting microbolometer. We then present two room-temperature terahertz detector technologies compatible
with monolithic arrays: i) GaAs Schottky diodes with air-bridge sub-micron anodes; ii) high electron mobility transistors
with sub-micron Schottky gate. Performances, requirements and fabrication costs of the different detector technologies
The development of a miniaturized electrochemical cell for biosensor application regards both the structuring of an array of electrodes in a fluidic chamber and their connections to the control & processing unit The sensitivity of the chrono-amperometric measurement performed with the cell is increased by: (a) integrating the reference electrode on the same chip with the counter- and working- electrodes, (b) designing a specific pattern of the gold electrodes and (c) serially distributing them along the pipeline reservoir. Borosilicate glass is used as substrate for the electrodes, allowing, due to its transparency, an accurate and easy pad to pad alignment of the up-side-down chip versus a PCB soldered on a standard DIL 40 socket. This alignment is necessary to accomplish the elastomer-based-solderless electric contact, between chip and PCB. The solderless contact significantly improves both reliability and signal processing accuracy. The reservoir and its cover are micromachined out of silicone rubber respectively photosensitive glass in order to easy disassemble the fluidic chamber without any damage. Both thickness and elasticity of the photosensitive glass rend the device less brittle. A plug-in -plug-flow device with improved characteristics has been obtained with a modular structure that allows further extension of the number of electrodes.
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.
Er3+/Yb3+-codoped 95.8 SiO2-4.2 HfO2 planar waveguide was fabricated by the rf-sputtering technique. The sample was doped with 0.2 mol% Er and 0.2 mol% Yb. The thickness and the refractive indices of the waveguide were measured by an m-line apparatus operating at 543.5, 632.8, 1319 and 1542 nm. The losses, for the TE0 mode, were evaluated at 632.8, 1319 and 1542 nm. The structural properties were investigated with energy dispersive spectroscopy and Raman spectroscopy. The waveguide had a single-mode at 1.3 and 1.5 μm and an attenuation coefficient of 0.2 dB/cm at 1.5 μm was obtained. The emission of 4I13/2->4I15/2 of Er3+ ion transition with a 42 nm bandwidth was observed upon excitation in the TE0 mode at 980 and 514.5 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime of 4.6 ms. Back energy transfer from Er3+ to Yb3+ was demonstrated by measurement of Yb3+ emission upon Er3+ excitation at 514.5 nm. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb3+ ions. Channel waveguides in rib configuration were obtained by etching the active film by a wet etching process. Scanning Electron Microscopy was used to analyze the morphology of the waveguides.
Second harmonic generation (SHG) in the Cerenkov configuration is investigated in planar proton-exchanged lithium-niobate waveguides where the use of a linear grating fabricated on top of the waveguide reproduces a 1-D photonic band-gap structure. In such conditions the conversion efficiency is strongly enhanced, due to the high density of the fundamental guided mode in correspondence of the linear grating. Optimum parameters of the linear grating are determined for different waveguides in view of the fabrication of a very compact device for highly efficient frequency doubling.
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 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.
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.
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.
Erbium activated SiO2-HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-gel method. The films were deposited on v-SiO2 and silica-on-silicon substrates using dip-coating technique. The waveguides show high densification degree, effective intermingling of the two film components, and uniform surface morphology. The waveguide deposited on silica-on-silicon substrates shows one single propagation mode at 1.5μm, with a confinement coefficient of 0.81 and an attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuous-wave excitation at 980 nm or 514.5 nm. The shape of the emission band corresponding to the 4I13/2→4I15/2 transition is found to be almost independent both on erbium content and excitation wavelength, with a FWHM between 44 and 48 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1-6.6 ms, depending on the erbium concentration. Infrared to visible upconversion luminescence upon continuous-wave excitation at 980 nm was observed for all the samples. Channel waveguide in rib configuration was obtained by etching the active film in order to have a well confined mode at 1.5 μm.
SiO2-TiO2:Er3+-Yb3+ waveguides were prepared by rf-sputtering technique. The active films were deposited on silica-on-silicon and v-SiO2 substrates. The parameters of preparation were chosen in order to optimize the waveguides for operation in the NIR region with particular attention to the minimization of losses. The thickness of the waveguides and the refractive index at 632.8 and 543.5 nm were measured by an m-line apparatus. The losses, for the TE0 mode, were evaluated at 632.8 and 1300 nm. Roughness measurements were carried out by means of a stylus profilometer. The structural properties were investigated with several techniques such as Energy Dispersive Spectroscopy and Raman Spectroscopy. All waveguides were single-mode at 1550 nm. An attenuation coefficient equal or lower than 0.2 dB/cm was measured both at 632.8 nm and 1300 nm. The emission 4I13/2 →4I15/2 of Er3+ ion transition with a 40 nm bandwidth was observed upon excitation in the TE0 mode at 981 and 514.5 nm. Back energy transfer from Er3+ to Yb3+ was demonstrated by measurement of Yb3+ emission upon Er3+ excitation at 514.5 nm. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb3+ ions. Channel waveguides in rib configuration were obtained by etching the active film by a wet etching process. Scanning Electron Microscopy was used to analyze the morphology of the waveguides.
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.
Waveguide laser arrays operating at 1.5 micrometers have been fabricated on Er:Yb-doped glass substrates by a two-step silver-sodium ion-exchange process based on thermal diffusion followed by a field-assisted burial step. The fabrication parameters have been optimized to achieve low propagation losses and good mode matching between waveguide channels and standard single-mode output fibers. Each laser cavity is formed by two Bragg gratings butt-coupled to the two ends of the channel waveguide. Fiber-coupled output power in excess of 10 mW is readily available from a single channel, when pumped from both sides by two 980-nm laser diodes providing a maximum power of ~300 mW. Single-longitudinal mode operation with output power of the order of 1 mW has been achieved using narrow reflectivity band (<30 GHz) Bragg gratings with different laser configurations. The laser operating wavelength can be selected across the whole C-band of optical communications (1530-1565 nm) by changing the Bragg grating peak reflectivity wavelength. A relative intensity noise lower than -150 dB/Hz has been measured for frequencies larger than 2 MHz. Stability of single-frequency operation, low intensity noise and flexibility in the choice of the operating wavelength make this laser array particularly attractive for wavelength division multiplexing optical transmissions.
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.
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 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.
The aim of this paper is to determine an optimum nonselective etching solution in order to manufacture an as thin as possible, uniform and high quality GaAs membrane. Three different etching systems in various proportions of the components were analyzed. A high quality 10 micrometer thin GaAs membrane was obtained using the [1(H3PO4)]: [1(CH3OH)]: [3(H2O2)] etching solution. The micromachined GaAs membranes are manufactured to be used as support for microwave circuits as well as in high temperature sensor applications.
The effects of radio frequency radiation on the dc SQUID are examined. Simulations show how the shape of the SQUID transfer characteristic is distorted by radio frequency interference (RFI). How this affects three commonly used SQUID modulation methods is discussed, and the results explain why we experimentally observe the bias current reversing readout method to be the least susceptible to RFI. The commonly seen increase in the low frequency flux noise power spectrum of dc SQUIDs in unshielded environments is also explained.