1,720,983 research outputs found
Characterization of TMAH Silicon Etchant Using Ammomium Persulfate as an Oxidizing Agent
No full textAmong the silicon anisotropic etchants, tetramethyl ammonium hydroxide [TMAH] is of great interest due to the absence of metal ions. Therefore using TMAH solutions at low concentrations has the advantage of being more economical, both in terms of cost and time. Unfortunately the surface quality of the etched silicon is strongly influenced by the concentration of the solution i.e. at low concentrations (less than 15%), the etched surfaces are very often covered with pyramidal-shaped hillocks, thus producing a very rough surface finish. Ammonium Persulfate (NH4)2S2O8 can be added to TMAH to suppress hillock formation. We investigated the effects of this additive under different oxidizer addition conditions. The influence of TMAH concentration and etchant temperature was evaluated
Characterization of Silicon Anisotropic TMAH Etch for Bulk Micromachining
No full textIn this paper the possibility to passivate the aluminum metalization in properly saturated TMAH solution is demostrated by doping the solution with appropiate amounts of silicic acid. This increases the range of application of this etchants simplifing both the post processing and the etch set-up configuration. We investigate the effect of these additives on the etch rate and the quality of (100) and (111) silicon sufaces obtained for different TMAH concentrations. We therefore also investigate the effect of ammonium persulfate (NH4)2S2O8 on the etch rate under different addition conditions for a 6.25wt.% TMAH doped by silicic acid in order to keep aluminum passivated
Characterization of TMAH Silicon Etchant Using Ammonium Persulfate as an Oxidizing Agent
No full textApplication of Dual Doped TMAH Silicon Etchant in the Fabrication of a Micromachined Aluminium Flexing Beam Actuator
No full textOne of the main goals of micromechanical systems (MEMS) fabrication is microdevice integration with standard integrated circuit (IC) technologies, such as bipolar or the more prevalent complementary metal oxide semiconductor (CMOS) processes. To that end, it has been found that the anisotropic silicon etchant tetra-methyl ammonium-hydroxide (TMAH) can be effectively used in a post-processing step with CMOS-based fabrication by doping it with silicic acid to prevent the unwanted etching of exposed alluminum. Furthermore, the addition of ammonium persulfate to the TMAH/silicic acid solution enhances etch rate and surface quality. The final etching solution, called dual-doped TMAH, is a CMOS-compatible, highly selective to silicon over aluminum, and can therefore allow an aluminum layer to be used as an etch mask. In this paper, we utilize dual-doped TMAH towards the fabrication of a microstructure made entirely of aluminum. A flexing beam microactuar suspended over a bulk micromachined silicon cavity is presented for use as a magnetomete
Low-Power Silicon Microheaters for Gas Sensors
No full textSilicon-based SnO2 gas sensors are commonly operated at relatively high temperatures (up to 400 °C and even beyond for specific applications), thus necessitating suitable heating modules to guarantee high temperature uniformity over the sensitive surface area with minimal power consumption. Silicon micromachining allows low-power microheaters to be fabricated, with a low-cost (for mass production) technology, which is potentially suitable for the integration of the sensor, the heating element, as well as the required electronics into the same battery-operated microsystem. In this paper, we report on the development of a microheater structure consisting of a dielectric stacked membrane micromachined from bulk silicon, with an embedded polysilicon resistor acting as the heating element, Different technological solutions in the fabrication process for the micromachined structures have been investigated. In particular, hoth uniform membranes and suspeded microbeam structures have been realized to characterize the different thermal behavior toward the ambient. The microheaters have been designed to enable temperatures in the excess of 500 °C to be reached on the hotplate with a power consumption lower than 50 mW. Extensive thermoelectric and thermomechanical finite-element numerical simulations have been carried out, to predict microheater temperature vs. electric-power characteristics and mechanical stability, respectively. Simulations have also provided helpful hints in view of the optimization of the proposed structures
Dual-doped TMAH silicon etchant for microelectromechanical structures and systems applications
No full textTetra-methyl ammonium-hydroxide (TMAH), is an anisotropic silicon etchant that is gaining considerable use in silicon micromachining due to its excellent silicon etch rate, etch selectivity to masking layers, degree of anisotropy, and relatively low toxicity. However, a shortcoming of TMAH is that it aggressively etches exposed aluminium layers. A dual-doped low concentration TMAH solution is presented, which incorporates a silicate additive for aluminium passivation and an oxidizer additive for improving etch rate and surface quality. Using etch and under-etch experiments, the dual-doped 5 wt% TMAH solution is shown to have characteristics comparable to those of high concentration TMAH solutions with the added benefit of improved etch rate, smoother etched surfaces, and selectivity to silicon over aluminium. Such an etchant can find effective use in batch fabrication and intergration of microelectromechanical systems within the framework of standard foundry processe
Electrochemical effects during anisotropic bulk-silicon etching with doped and undoped TMAHW solutions
No full textTetra-methyl ammonium hydroxide/water (TMAHW) solutions are gaining considerable interest as alternative anisotropic silicon etchant to the more usual KOH and EDP etchants because of their compatibility with CMOS processing and relatively low toxicity. TMAH exhibits a high etch rate for lower concentrations of solution, however this rate falls dramatically due to the inevitable formation of hillocks on the surface. For TMAH concentrations above approximately 20 wt.%, hillock formation is markedly reduced, however the intrinsic etch rate at these concentrations is low. Using TMAH at lower concentrations has the advantage of being more economical, both in terms of cost and time. Furthermore, it has been shown that oxidizing agents can be added to TMAH, such as ammonium persulfate (NH4)2S2O8 to eliminate hillock formation at these reduced concentrations. Our investigations have the aim to determine the effects of this additives on the silicon etch rate and anisotropy under different conditions, i.e. TMAH concentration, temperature, oxidizer concentration and frequency of oxidizer additions. In addition the role of the redox potential of the etchant solution is investigated and anomalous high silicon etch rates under anodic polarisation with respect to OCP, are reported and discussed
Polysilicon mesoscopic wires coated by Pd as high sensitivity H2 sensors
No full textA new class of H2 sensors made up of mesoscopic polysilicon wires coated by palladium is presented. Using surface micromachining combined with an usual microelectronic planar process, polysilicom wires of the following dimensions have been constructed: from 250 nm up to 3.7 um wide, from 100 um up to 140 um long, about 700 nm thick. Because of their high surface/volume ratio, these wires have shown a very high resistance percentage variation under hydrogen absorption. Enhanced resolution together with a low production cost are the most importand features of this devic
Feasibility study on fabrication of piezoresistive pressure sensors using silicon micromachining technology
No full textThis paper describes a feasibility study on design and fabrication of piezoresistive pressure sensors for the pressure range 0.5 - 350 bar, using silicon micromachining technology. Different technological steps are studied in order to optimize the fabrication process and the electro-mechanical parameters of the device. The sensing membrane is etched in (100)-oriented silicon by anisotropic etching using different concentration of TMAH (tetramethyl anmmnium hydroxide) in water solution. The software package ISE-TCAD. based on the finite element method (FEM), has been used to calculate the stress distribution on the membrane in order to provide information for the proper location of the piezoresistors.Devices with different membrane thickness (between 120 and 40 um) have been investigated. All devices show a good linearity (better than 1%) and their sensibility ranges from 3 to 58 mV/Vbar depending on the membrane thickness
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