Simulating flow in silicon Y-bifurcated microchannels

Microfluidic devices are excessively used for various biomedical, chemical, and engineering applications. The most common microfluidic platforms are obtained from polydimethylsiloxane (PDMS). Platforms based on etched silicon wafers anodically bonded to Pyrex glass are more mechanically rigid, have better sealing and there is no gas permeability compared to those obtained from PDMS [1,2]. The aim of our work is to numerically analyze fluid flow in anisotropically etched silicon microchannels sealed with Pyrex glass. We present simulations of fluid flow in Y-bifurcated microchannels fabricated from the etched {100} silicon in 25 wt% tetramethylammonium hydroxide (TMAH) water solution at the temperature of 80°C [3]. We have explored two symmetrical Y-bifurcations that are defined with acute angles of 36.8° and 19° with the sides that are along the and crystallographic directions in the masking layer [3], respectively. The angles between obtained sidewalls and {100} silicon of two ingoing microchannels for the first and second Y-bifurcation are 72.5° and 80.7°, respectively. The sidewalls of outgoing microchannel in both cases are defined with crystallographic directions and they are orthogonal to the surface of {100} silicon wafer. The appropriate widths of ingoing and outgoing microchannels are 300 and 400 μm, respectively. The depth of microchannels is 55 μm. All simulated flows are three-dimensional (3D), steady and laminar [4], while the investigated fluid is water. Velocities and pressure values are defined at the inlet and outlet boundaries, respectively. The resulting flows are illustrated by velocity contours. The obtained conclusions from fluid flow simulations of presented simple Y-bifurcations provide guidance for future fabrication of complex microfluidic platforms by a cost-effective process with good control over microchannel dimensions

Simulating flow in silicon Y-bifurcated microchannels

Microfluidic devices are excessively used for various biomedical, chemical, and engineering applications. The most common microfluidic platforms are obtained from polydimethylsiloxane (PDMS). Platforms based on etched silicon wafers anodically bonded to Pyrex glass are more mechanically rigid, have better sealing and there is no gas permeability compared to those obtained from PDMS [1,2]. The aim of our work is to numerically analyze fluid flow in anisotropically etched silicon microchannels sealed with Pyrex glass. We present simulations of fluid flow in Y-bifurcated microchannels fabricated from the etched {100} silicon in 25 wt% tetramethylammonium hydroxide (TMAH) water solution at the temperature of 80°C [3]. We have explored two symmetrical Y-bifurcations that are defined with acute angles of 36.8° and 19° with the sides that are along the and crystallographic directions in the masking layer [3], respectively. The angles between obtained sidewalls and {100} silicon of two ingoing microchannels for the first and second Y-bifurcation are 72.5° and 80.7°, respectively. The sidewalls of outgoing microchannel in both cases are defined with crystallographic directions and they are orthogonal to the surface of {100} silicon wafer. The appropriate widths of ingoing and outgoing microchannels are 300 and 400 μm, respectively. The depth of microchannels is 55 μm. All simulated flows are three-dimensional (3D), steady and laminar [4], while the investigated fluid is water. Velocities and pressure values are defined at the inlet and outlet boundaries, respectively. The resulting flows are illustrated by velocity contours. The obtained conclusions from fluid flow simulations of presented simple Y-bifurcations provide guidance for future fabrication of complex microfluidic platforms by a cost-effective process with good control over microchannel dimension

Two Color Photodiodes Mounted on the Micromachined Carrier

In this paper, two color detector based on silicon photodiodes is studied and fabricated. Standard IHTM photodiode’s design is modified to allow mounting one photodiode above another using special micromachined carrier. The carrier is fabricated using wet silicon etching in 25% TMAH water solution and anodic bonding of etched silicon and Pyrex glass. The fabricated carrier also allows easy wire thermocompression bonding from the photodiode’s pads to TO-5 housing. Output currents of the photodiodes were measured by applying light of 900 nm and 1060 nm. Obtained results verify applicability of the new packaging for two color detector

Etching of Uncompensated Convex Corners with Sides along <n10> and <100> in 25 wt% TMAH at 80 °C

This paper presents etching of convex corners with sides along and crystallographic directions in a 25 wt% tetramethylammonium hydroxide (TMAH) water solution at 80 °C. We analyzed parallelograms as the mask patterns for anisotropic wet etching of Si (100). The sides of the parallelograms were designed along and crystallographic directions (1 and crystallographic directions were smaller than 45°. All the crystallographic planes that appeared during etching in the experiment were determined. We found that the obtained types of 3D silicon shape sustain when n > 2. The convex corners were not distorted during etching. Therefore, no convex corner compensation is necessary. We fabricated three matrices of parallelograms with sides along crystallographic directions and as examples for possible applications. Additionally, the etching of matrices was simulated by the level set method. We obtained a good agreement between experiments and simulations

Etch rates of Si crystallographic planes in a 25 wt % TMAH water solution

Nagrizane su silicijumske strukture koje su na početku nagrizanja definisane kvadratnim ostrvima od termičkog silicijum dioksida. Stranice kvadrata su projektovane u različitim kristalografskim pravcima. Određene su kristalografske ravni koje se pojavljuju tokom nagrizanja ovih struktura u vodenom rastvoru TMAH koncentracije 25 tež. % na temperaturi od 80 0 C. Merenjem odgovarajućih parametara nagrizanih kristalografskih ravni sa vremenom odredili smo brzine nagrizanja uočenih kristalografskih ravni.We etched Si structures that had been defined at the beginning of etching by square islands of thermal SiO2. The sides of the squares were designed with orientations along various crystallographic directions. All the planes that appeared during etching of these Si structures in a 25 wt % TMAH water solution at a temperature of 80 deg C were determined. By measuring the time dependence of the appropriate parameters of the etched Si crystallographic planes we indirectly calculated their etch rates

Enhancement of the performance of multipurpose thermopile-based sensor using proprietary mems technology for soi piezoresistive pressure sensors fabrication

MEMS senzori na bazi Zebekovog efekta su tema dugogodišnjeg istraživanja u IHTM-CMTM-u. Oni su posebno interesantni zbog činjenice da imaju raznovrsnu primenu (senzori protoka, senzori vakuuma, termalni konvertori, IC detektori, akcelerometri, inklinometri, biološki i hemijski senzori, senzori vrste gasa, senzori sastava binarne smeše gasova, ...). U IHTM-u je do sada realizovano nekoliko varijanti ovog tipa senzora. Prilikom razvoja ovih senzora teži se da se iskoriste postojeći tehnološki procesi razvijeni za IHTM piezorezistivne senzore pritiska. Tako je poslednja generacija senzora sa temoparovima tehnološki kompatibilna sa IHTM Si piezorezistivnim senzorima pritiska. U medjuvremenu je osvojena tehnologija izrade SOI piezorezistivnih senzora pritiska koja će biti primenjena za realizaciju sledeće generacije termalnih senzora. U ovom radu je dat osvrt na dizajn, tehnologiju izrade i poboljšanje performansi koje se očekuje kod SOI višenamenskih senzora sa termoparovima.MEMS sensors based on Seebeck effect have been a part of the long-term research at IHTM-CMTM. They are of special interest because of the fact that they have broad range of applications (flow sensors, vacuum sensors, thermal converters, IR detectors, accelerometers, inclinometers, biological and chemical sensors, gas type sensors, binary gas mixture composition sensors, ...). Till now several types of this kind of sensors have been developed at IHTM. During the development process we aim at using aleady existing technological processes developed for IHTM piezoresistive pressure sensors. Thus, the last generation of thermopile-based sensors is technologicaly compatible with IHTM Si piezoresisitve pressure sensors. In the meantime, a technology of SOI piezoresistive pressure sensors have been conquered and it will be applied for realization of the next generation of thermal sensors. This paper gives overview of the design, fabrication technology and performance improvement expected to be reached with SOI multipurpose thermopile-based sensors

Study of possibilities of application of a thermopile-based gas sensor

The goal of this work is exploring the possibilities of application of a thermopile-based gas sensor. The main task was to study for which kind of gases this type of sensor would be suitable. For this purpose self-developed 1D analytical model was used. Modelling was done for multipurpose sensors developed at ICTM, but also for the same structure that would be fabricated on SOI substrate. Output signal of thermopile-based sensor depends on thermal conductivity of the surrounding gas. When this type of sensor is applied as a gas sensor, prerequisite is that the gases have different thermal conductivities so that the sensor can distinguish between them. According to simulation results, thermopile-based sensors could be applied for a number of gases which are important in industrial safety, homeland security, healthcare, domestic safety, etc. The results obtained for hydrogen detection were already presented, so in this work simulation data for other gases of interest will be given. This includes methane, ammonia, hydrogen sulfide, chlorine. Important conclusion is that thermopile-based sensor is capable to detect wide variety of gases

Characterization of PDMS membranes fabricated by bulkmicromachining on silicon wafers

In this paper we proposed microfabrication scheme for PDMS (Polydimethylsiloxane) thin membrane fabrication on Si micromachined cavities with square cross section. PDMS network samples for this research were synthesized with the same composition, which are Sylgard 184 (Dow Corning, USA) silicone elastomer base and silicone elastomer curing agent, volume ratio 10:1. Mechanical testing of PDMS elastic properties and bond strength between membranes and oxidized Si wafers, were investigated applying pressurized bulge testing In this paper experimentally determined dependence of the PDMS membrane deflection on pressure load for different membrane thicknesses and sizes of square cavities in Si wafers are given. Also, the influence of different types of Si wafer structuring by anisotropic wet chemical etching on membrane bonding strength were considered

Analytical modelling of the transient response of thermopile-based MEMS sensors

This work presents an analytical model dedicated to study of the transient response of multipurpose MEMS devices based on thermopile sensors. In general, thermopile sensors response depends on ambient temperature, thermal conductivity of the gas inside the housing and the pressure of the gas. The presented model takes into account all these parameters. This model was sucessfully implemented for the study of transient behaviour of our multifunctional sensors with p+Si/Al thermocouples and a bulk micromachined bilayered membrane. Simulations were performed for different gases of interest and conclusions were deduced regarding the influence of relevant parameters on the thermal time constant. This analytical approach is general and flexible enough to be implemented for analysis of the transient behaviour of thermopile-based sensors when used for different applications

Realization of Si microcantilevers by wet anisotropic etching on {100} oriented substrates applying <100> compensation beams

U ovom radu je prikazan način realizacije mikrogredica na Si supstratu {100} orijentacije postupcima zapreminskog mikromašinstva. Rastvor za anizotropno nagrizanje je bio vodeni rastvor 30 tež. % KOH na temperaturi od 80C. Istraživanje je skoncentrisano na određivanje dimenzija kompenzacione strukture u vidu trake orijentisane u pravcu kod koje postoji i bočno i čeono nagrizanje. Opisana je procedura za određivanje prirode najbrže nagrizajuće ravni i odnosa brzine nagrizanja ove ravni i podloge, jer su to parametri, osim dimenzija mikrogredice, koji se moraju poznavati da bi se odredile dimenzije kompenzacije konveksnih uglova pri anizotropnom hemijskom nagrizanju.This paper presents microcantilever fabrication on {100} oriented Si substrate using bulk micromachining techniques. Solution for anisotropic etching was water solution of 30 wt. % KOH on 80C temperature. Investigation concentrates on the study of compensation design for particular structure using a oriented beam with lateral and frontal etching. Determination procedures for the fastest etching plane and ratio of etching rate of this plane and the substrate plane were described. These data, together with microcantilever dimensions, are necessary for determination of compensating structure which prevents convex corners undercutting during the course of anisotropic etching