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Sensors and Actuators A 136 (2007) 374384Development of various designs of low-power,MEMS valves for fluidic applicationsA.M. Cardenas-Valenciaa, J. Dlutowskia,b, J. Bumgarnera,C. Munoza,b, W. Wanga, R. Popuria, L. LangebrakeaaCenter for Ocean technology, University of South Florida, 140 Seventh Ave. S. St Petersburg FL 33701, United StatesbDepartment of Electrical Engineering, University of South Florida, 4202 E. Fowler Ave, Tampa FL 33620, United StatesReceived 11 July 2006; received in revised form 28 November 2006; accepted 19 December 2006Available online 22 December 2006AbstractAutomated, controlled fluid delivery is an important operation in micro-total analysis systems (?TAS). Actuated micro-valves have beenproposed to separate a pressurized fluid from the channel to be filled. This scheme greatly reduced the energy required to move the fluid. Thedesign,micro-fabricationandperformanceofarraysofsingle-usevalve,whichconstituteanintegralpartofthisactuationmechanism,ispresented.The addressable constituent of the valve is a thin metallic ohmic resistor, whose design dictates the actuation voltage. The resistor is patterned ona silicon nitride membrane that constitutes the flow barrier, which stands on a silicon wafer. Rapid heating via an electric pulse induces thermalstresses in the membrane/resistor, which in turn breaks the membrane opening the valves. The chosen processing steps allow for wafer-level devicefabrication using standard MEMS processing tools. Different size membranes with various thicknesses (1, 2 and 3?m) are tested. Valves thatwithstandapressuredifferentialofupto5bar(3mm3mm,3?m-thicksiliconnitridemembranes)werechosenforthestudy.Investigatedvalveswere activated with a potentials ranging between 14 and 140V and required activation energies from tens to hundreds of milliJoules. 2007 Elsevier B.V. All rights reserved.Keywords: Thermally actuated; Single-use; Micro-valves1. IntroductionMicro-fluidics has been included in various analyticalschemes that incorporate the well-known advantages of micro-scale transduction. A basic fluidic operation important in ?TASand Lab-on-a-chip applications is the controlled delivery ofminute fluid amounts. The purposes behind hermetic fluid stor-age and its on-demand delivery, even as a single-use operation,are manifold. For instance, a common micro-fluidic applica-tion involves the delivery of analytical reagents to a sample toinduce transductions that provide information on sample state,like presence or concentration of target chemicals 1,2. Intakeof samples in portable sensor systems that monitor water bodiesis another application that would benefit from automated fluidicdelivery 2,3. Additionally, automated fluid delivery has beenexploited as a way to produce energy “on-demand” by feedingelectrolytes into electrochemical cells 46.Corresponding author.E-mail address: (A.M. Cardenas-Valencia).Many works in literature exemplify fluidic delivery mecha-nisms,andthereferenceshereinareasmallsample714.Pneu-matically or inertiallly driven fluidic devices are preferred overelectrokinetic mechanisms due to their capacity to provide awider range of flow rates 1014. CD-styled platforms, basedoncentrifugalforcedactuation,areaclassicalexampleofmicro-fluidic schemes 11. Volume-expanding materials are anotheralternative that induce pneumatic differentials to obtain micro-flow 10,1214. Applications that involve remote, unattendedtransducers, for either analytical purposes or power production,have specific requirements that challenge the direct incorpo-ration of some of the available micro-fluidic schemes. Theseinclude,besidesreliability:low-powerrequirements,andingen-erallyshorttimeconstants.Alow-powerdevicerequiresthatthefluid delivery is done efficiently, thus providing longer opera-tional lives for the power sources and/or more operating devicecycles. Fast actuation ensures precise control of the desiredtransduction. In the case of sensors, reduction of temporal lagsguarantees real-time data. An attractive fluidic delivery actua-tion was proposed by Chien-Chong et al. 15: a pressurizedliquid reservoir that is contained by a valve, the controllable0924-4247/$ see front matter 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.sna.2006.12.016A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384375actuated component, that when opened, delivers a fluid to thedesired micro-channel. Micro-valves, generally activated withlow powers, can be utilized for such a scheme.There have been many reports on the design and fabrica-tion of micro-valves, and only a few are referenced herein1627. Polymeric and plastic valves and vents are innova-tions in micro-valving mechanisms that use non-silicon-basedprocessing15,2326.Reportsofvalvingschemesthatusecon-ventional fabrication processes are also common 16,18,27,28.Conventionalsilicon-MEMSfabricationtakesadvantagesofthetechnology derived from the integrated circuit industry, such ashigh yield processing and the capability of wafer-level devicefabrication, making low-cost production possible. Reductionof the energy required for actuation to fractions of a Joule isreported in thermally activated “burst-plug” valves by Muelleretal.27,28.Thedesignproposedhere,alsobasedonthermallyinduced stresses, differs from other works in that the valve isformed by a membrane on which a thin resistor is patterned(Fig. 1a). This design offers versatility, as the valves can befabricated with various dimensions (leading to valves capableof various operating conditions) and on different wafers thanthosewherethemicro-channelsand/orotherfluidiccomponentsare located. Hoses and fluidic ports, popular in micro-fluidicsresearchanddevelopment,easilyinterconnectdevices,asshowninFig.1b.Wellcharacterizedandcommonprocessingstepswereselectedwiththeaimofachievinghighyields.Ifimplementedasshown in Fig. 1b, the actuation energy requirements are dictatedby the consumed power of the valving mechanism. This workreports on the micro-valve fabrication and empirically studiesdesigns requiring low activation energies.2. Valves designs: practical and theoreticalconsiderations2.1. On the selection of materials for micro-valvefabricationThin resistors deposited on silicon nitride have been realizedfor various sensing applications (gas and pressure transducers)2934.Theceramic-likethermalpropertiesofthematerialandtheabilitytobedepositedasthinmembranesallowforthereduc-tion of the thermal mass of the device, favorable for the energyrequirements of many transducers. Platinum is commonly usedfor thermistors due to the high resistivity of the material relativeto other metals 3033. Even though there are several applica-tions using resistors on silicon nitride membranes, no reportshave been presented in which resistors with various dimen-sions and shapes are compared. In this work, platinum and goldmicro-fabricated resistors of various designs are presented. Theinfluence that these designs have on the power requirement foractivation is explored. Furthermore general guidelines to designand fabricate micro-valves that require different power specifi-cations, facilitating its potential integration in portable sensors,are shown.2.2. Theoretical background and resistor designsIfsingle-usevalves(anarrayisshowninFig.1)aretobeusedin a stored-pneumatic-energy fluidic mechanism, two impor-tant issues must be considered. On one hand a mechanicallystrong membrane to contain the pressurized fluid is desirable.The stronger the membrane, the higher the pressure differen-tial it can withstand, and the faster the liquid filling of thedesired channel/reservoir. On the other hand, the membranehas to be reliably broken with small amounts of energy and thebreakage time lag must be small. In this report, the maximumpressure that several size membranes can withstand is exper-imentally determined. Phenomenological mechanical models,solved generally using numerical techniques, are well docu-mented in literature 34,35. A simple descriptive model is usedherein to quantify the maximum pressure differential that themembranes can withstand. The descriptive model is valid for amembrane with large planar dimensions in comparison with itsthickness (which is the case herein) and can be used to relatethe required breakage pressure and the membrane dimensions36. A force balance can be written, when the pressures fac-ing each face of the membrane changes, as an equation of theform,Fig. 1. (a) Schematic illustrating the silicon membrane and a patterned resistor that constitute the single-use valves described here. (b) Conceptualization on theutilization of an array of the proposed single-use valves.376A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384Fig. 2. (a and b) Illustrations that show the shapes of the two basic resistors investigated herein.Table 1Dimensions of L- and P-types thin metal resistorsResistor designVaried dimensionsResistor designVaried dimensionsD1(mm)D2(mm)Width (?m)NTotal length (mm)W (mm)L (mm)L1(mm)L12.00.225522.0P12.02.550.225L22.50.225421.6P22.3752.550.225L32.50.225527.0P32.752.550.225L42.50.225632.4?F dA = D2?dP = 4tD + D2?a + bD2?(1)F is the perpendicular force, A the area of the membrane(considered constant and equal to D2), P the pressure, t themembrane thickness and D is the length of the membranesquare side. The left hand side term D2?dP represents auniform pneumatic force loading due to the average pressuredifferential; the term 4tD includes the maximum shear stress, and is the critical shearing force load at the membrane edges.The “b” in the last term, D2(a+b)/D2), is an offset (positiveor negative) force due to the membrane deviation from flatnessand residual stresses resulting from the membrane fabricationand “b/D2” encompass potential instrumental errors arisingfrom the utilized measurement set-up.To decide on the resistor designs, the basic coupled phe-nomenological equations that relate energetic and thermaleffectsareconsidered.First,thepower,Q,isgivenbythepoten-tial, V, and the resistance, R, of the ohmic resistor,Q =V2R(2)Second, the quantification of the resistors temperature incre-ment is estimated according to an energy balance that can begenerically written asQ = Changeinthermalenergy + Heatlossesviaconduction,convectionandradiation(3)Additionally, the temperature change in the resistor (TTo)induces a different resistance value, RT, that depends on thephysicochemicalcharacteristicsofthemetal(isthemetalresis-tivityandisthethermalresistivity)andonthedimensions(thelength, L and the cross-sectional area, Across)RT= (1 + (T To)LAcross(4)The thermal gradient (first term of the right hand side ofEq. (4) and the magnitude of the heat losses dictate the temper-aturereachedbythemembrane/resistorsystemaswellastherateof temperature increase. One way to reduce the thermal lossesis to increase the proximity of the resistor to the silicon nitrideedges. Fig. 2 shows the two basic resistor designs whose dimen-sions are varied to gain insight into the relative magnitude of theheatlosses.Thefirstdesign(labeledas“L”andshowninFig.2a)posses a square zigzag shape while the second resistor design(Fig. 2b), denoted here as “P”-type has two legs connected inparallel. Both designs (dimensions are shown in Table 1) aresymmetrically centered with respect to both the horizontal axisand the vertical axis. Four or five of each of the designs listedin Table 1 were distributed randomly in a 4in. diameter wafermask. It is expected that the first design type (L) would requireless current to heat to a certain temperature than the secondP-design (listed in Table 1). The parallel resistor design hashowever a smaller resistance, which permits the application ofsmallervoltagescomparedtothoserelativetotheL-typedesign.3. Micro-fabricationAn initial three step cleaning is performed for the siliconwafers (520?m-thick, 4in. diameter, ?100? crystal orienta-tion acquired from Montco Silicon), by rinsing (while wafersare spinning) thoroughly with first acetone, then methanol, andA.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384377Fig. 3. (a) Summary with the process flow for the fabrication of single-use valves. (b) Processing steps that show two fabrication routes for the silicon etching underthe valves.finallyDIwater,followedbyaspin-drystep.Themembranefab-ricationprocessflowisillustratedinFig.3aandstartsbyplacingthewafersintheTystarLPCVDovenfor3.3,6.6and10hresult-ing in coatings with thicknesses of 1, 2, and 3?m, respectively.Allphotolithographyandalignmentstepswereperformedusingan EV-620 aligner (EV Group Inc. Tempe AZ). The masks werebought from Precision Images Inc. (Largo, FL).3.1. Metals depositions and patterning of resistorsOne side of the wafers is patterned with the metal resistorsvia lift-off technique, and is schematically presented in Fig. 3a.A positive photo-resist 1813 (Rohm and Haas Elect. Mats) isdeposited at 3000rpm for 40s and then is exposed for 2.9sand immersion-developed (MF319 developer) for 3540s. Atitanium layer (approximately 10nm) is sputtered on the wafers(ANATC1800seriesfromAJAIntl.,sputteringtimeis1min)toserve as an adhesion layer for the subsequent platinum and golddeposition to the silicon wafers (Table 2). Immersion in acetone(J.T. Baker, NJ) for 20min completes the lift-off patterning.3.2. Etching through siliconSilicon etching on the backside of the wafer (cavity forma-tion step in Fig. 3a) followed the resistor patterning and wasperformed using two routes (labeled as A and B in Fig. 3b). Inroute A, backside silicon nitride layer etching was the first step,which in turn is used as a mask to perform batch chemical etch-ing through the silicon wafer. Negative photo-resist NR9-1500PY (Futurrex Inc., Franklin, NJ) was used with an appropriatefield mask to pattern squares in the silicon nitride on the backface of the wafer. The NR9-1500 PY was deposited, spun at1000rpm for 40s, and hot-plate baked at 150C for 80s. RD-6was used as the developer, after a predevelopment bake on thehot-plate for 80s at a temperature of 100C. The exposure timewas 20s, and the immersion development time was 15s. Theachieved photo-resist thickness with this procedure is approxi-mately 2.55?m, measured with a contact surface profiler modelTencor P10 (KLA Tencor, San Jose, California). The siliconnitride on the back of the wafer is then completely removedfrom the desired square areas by treating the wafers in a RIEtool (Uniaxis 790 series, Pf affikon SZ) for a total of 115min.A silicon nitride etch recipe with a volumetric ratio of CHF3toO2of 45:5 is used. At the end of that time the photo-resist layerwas drastically thined, and the silicon nitride received localizedattacks by the reactive etching. An immersion in 45% KOHsolution (J.T. Baker, Phillipsburg, NJ) at 90C, to completelyetch the silicon wafer, follows. The 500um through-holes areachieved after a 5h immersion while agitating at 250rpm in theKOH solution. The reported rate is about 100?m/h at 90CTable 2Deposition conditions to sputter the metals used to fabricate the thin resistorsMetalSputtering tool used for the depositionDeposition time (min)Average thickness (?m)PlatinumIn-house built tool40.090.025PlatinumIn-house built tool160.300.030GoldATC 1800 series (AJA International)150.150.015378A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384Fig. 4. Selected profiles that show the deviation from flatness of some of the fabricated membranes due to residual stresses. The profiles are in horizontal and verticallines that pass through the membrane center.37, for ?100? oriented wafers. In the second route (labeledas B in Fig. 3b) to create the through-holes on the wafer, thefirst step for the membrane fabrication is removing the sili-con nitride from the backsides of the wafer. This is done byexposing the wafers to reactive etching for 25min/?m of sil-icon nitride deposited. An aluminum mask is then patternedusing either lift-off or etching techniques with no apparent dif-ference on the yield and characteristics of final valve wafers.In the first case NR9 1000 PY is used to define the through-holes on the backside of the wafer. Then aluminum is sputteredfor 15min with an ATC 1800 series sputtering system (AJAInc. North Scituate, MA), resulting in a thickness of approxi-A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384379Fig. 5. Pressure testing set-up of valves (a) and calibration curves of the sensor (b).mately 0.270?m. The lift-off to pattern the aluminum requiredimmersion in acetone (J.T. Baker Phillipsburg, NJ) for 1h and15min. For the wafers in which aluminum is patterned via etch-ing, this metal is deposited first as described before, and etchedselectively. Acidic etching (aluminum etchant from J.T. BakerPhillipsburg, NJ) removes the aluminum. A 1813-photo-resistwas used (same as described above) to mask the aluminum. Athree solvent rinse is then performed and together with 1minoxygen plasma RIE removes any residues. Then the wafers aretaken to the DRIE tool (Uniaxis shuttlelock system, Pf affikonSZ), where the silicon is completely removed in 3mm3mmsquares under the patterned resistors after the wafers are sub-jected to 700 Bosch-processing cycles. Fig. 3b shows picturesoffabricatedmembranestakenwithaNikoneclipseL150opticalmicroscope (Kanagawa, Japan), with a 3.2.0 diagnostic instru-ment (Sterling Heights, MI) digital camera attached. All of themembranes (there were 45 devices per wafer) were successfullycompletedineachoftheprocessedwafersusingrouteB.A96%yield was obtained for valves on a single wafer using chemicaletching (route A), but one wafer became too fragile and brokewhile handling. For this reason route fabrication A was aban-doned even though it required a lesser number of processingsteps than route B.4. Equipment and protocols for testing, results anddiscussion4.1. Pressure testing of the membranesThe mechanical properties of the membrane can be used topredict the strength of the fabricated membranes. However, itis well known that a deposited membrane possesses intrinsicstresses related to the deposition technique and its conditions.Fig. 4 shows pictures generated with a NT3300 Wyko opticalprofiler (Veeco, NY, USA) that illustrate the bending of selectedmembrane due to residual stresses induced while fabricating thesquare membranes. These and other membranes with differentlateral sizes, D, will be utilized to test the maximum pressuresthattheycanwithstand.ThegraphsclearlyshowthattheLPCVDdeposition indeed induced intrinsic stresses to the fabricatedmembranes. The membranes, though, were strong enough forhandling with the rest of the wafer which indicates a residualstress with a value less than 0.1GPa as it has been numerouslyshown in other reports 3437.Inordertoobtainanestimateofthemaximumpressureunderwhich the fluid can be stored, various sized square membranes(side lengths equal to 1, 1.5, 2, 2.5, 3 and 4mm) and of variousthicknesses (1, 2, and 3?m-thick) were fabricated as describedabove.Fortesting,commerciallyavailablenanoports(UpchurchScientific)wereused.Aschematicoftheset-upusedtomeasurethe maximum pressure and obtain the calibration curve for thesensor (MSP-type sensors from Measurement specialties Inc.)is shown in Fig. 5. The pressure was induced via a compressorpump(CSAModelDOA-P704-AA,acquiredfromFisherScien-tific).Thecompressorwasturnedonwhiletheexhaustvalvewasopen,thisvalvewasclosedslowlyanddatawastakeneverysec-onduntilthemembranesfailed.Fig.6summarizesexperimentaldata points (as data markers) where breakage of the various sili-con nitride membranes occurred while applying pressure. In thefigure, it is clearly shown the dramatic increase in pneumaticstrength of the membrane as their dimensions are reduced. Thecontinuous line-curves represent a model that has been fitted tothe presented experimental data. Since only the largest mem-branes (D=4) with thicknesses equal to 3?m broke, the modelhas been calculated to compare only with membranes of mem-brane thicknesses of 1 and 2?m. This model is a simplificationFig. 6. Maximum pressure withstood by silicon nitride membranes of variousdimensions.380A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384Table 3Calculated and measured resistances (RTamb) at an ambient temperature of 1819C for the various resistor designs tested hereinResistor designCalculated resistances (?)Measured resistances (?)Platinuma(4)bPlatinuma(16)bGoldaPlatinuma(4)bPlatinuma(16)bGoldaL1896 320269 33119 121060 390268 15112 05L2880 310281 32117 11882 300281 35119 10L31100 400330 40146 151295 350332 41131 14L41320 480396 48176 181616 480400 50171 13P1104 8036 413 1158 11833 315 2P2111 8639 414 2167 10534 416 1P3119 9041 515 2173 8837 217 1aMaterial.bValue in brackets represents deposition time (min).of Eq. (1). It assumes a uniform pressure applied and equatesthepressureincrement,?P,tothemaximumshearstress,andthe membrane dimensions,?P =4t/D+k(5)The term k is an offset parameter that includes phenomeno-logical aspects explained in Section 2.2. As it is shown inFig. 6, the modeled curves are in fair agreement with that of theexperimental values obtained. Fig. 6 shows that the largest sizemembranes(withsidesequalsto4.0mm)breakatlowpressures,between0.25and0.60bar.Asformembraneswith3.0mmsides,several of the five tested membranes with 1 and 2?m thicknessbroke with a pressure in between 0.30 and 0.65bar, while onlyone (out of five tested) of the 3?m membranes broke whena pressure of 1.4bar was applied, while the other ones testedremainedunbrokenuptoapressureof5bar.Becauseofthelargepressure range of pressure for membranes with 3mm3mmsides and a thickness of 3?m this size was chosen to build thethermally activated valves.4.2. Power requirements to open the micro-valvesThermal efficiencies of micro-fabricated resistors are com-monly reported 14,33 as the required energy or the requiredapplicationtimeofacertainpowertoachieveacertaintempera-ture increment. In this work constant voltages are applied usingan E3612-A dc-power supply (Agilent Techn. Inc., Palo Alto,CA), while the resistors are placed on a Karl Suss probe station(from Suss Microtec Inc., Santa Clara, CA). Since the resistortemperature changes during heating, its resistance (and power,asstatedinEq.(2)alsovariesasheatingtakesplace.Inordertobe able to estimate the energy required for the resistor to reach acertain temperature an estimate of the resistance that represen-tatively estimates the change that takes place is necessary. Thisestimate, RT, calculated as an average, Rave, is shown below.Rave=RTamb+ Rhot2(6)The first resistance, RTamb, represent resistance values at ambi-ent temperature (18.9+(0.2)C) and are presented in Table 3,togetherwiththecalculatedones(usingEq.(4)foreachdesign.The resistance value at the higher temperature, Rhot, isobtained empirically. To do so, various voltages were used toheat the resistors at various temperatures (at least five poten-tials, resulting in temperature ranges between 18 and 700C,for each resistor). Fluke-189 Multimeters (Fluke corporation,Everett, WA) are used for recording the voltage and the elec-trical current flowing through the circuit (Fig. 7a). Current andvoltage are used to calculate the input power, as well as thesteady state resistance value (Ohms law) of the heated resistor,RT.TheRTvalueisthenusedwithEq.(7)(anexpressionderivedfrom Eq. (4) to estimate a steady state temperature, T, of theFig. 7. Testing set-ups for micro-fabricated valves. (a) For obtaining a thermal response to various input powers and (b) for applying electrical pulses to open thevalves.A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384381Fig.8. Experimentalresistortemperatureasafunctionofpower(opensymbols)andappliedpotential(filledmarkers).Continuousline-curvesrepresentmodeleddata as explained in text.resistors.T = T0+RT R0R0(7)Since it is a fact that a linear relationship exists between thepower and temperature for micro-fabricated resistors 14,33,Eq. (2) suggests a temperature versus potential expression ofthe form:T C = cV2+ dV + 18.5(8)Calculatedtemperaturesasafunctionofvoltagedatawereinputin a regression subroutine and the constants “c” and “d” inEq. (8) were obtained. In order to illustrate examples of theenergy required for heating that has been generated for theresistor designs, some of the data obtained with the L1-labeled,gold resistors has been summarized in Fig. 8. Fig. 8 shows thesteadystate(stabilized)temperaturethatisreachedasfunctionofpower(datapointsindicatedasopensymbols)andvoltage(indi-catedwithfilledmarkers).Thecurvesrepresentedbycontinuouslines are least square minimized curves that seem to adequatelydescribe the experimental data. As stated in the text tempera-ture increments are linearly related to the applied powers. Theaverage correlation coefficient, r, a value which closeness to 1indicates the goodness of the fitted line with the experimentaldata, has a value of 0.9820. The regressed curves that representan average temperature as a function of the applied voltage are asecond degree polynomial (Eq. (8). In that case, the calculatedaverage correlation coefficient is 0.9965. It should be pointedoutthatthefigureevidencesthatsmallertemperatureincrements(when compared to the other two valves) are achieved with thevalve labeled as 3 in Fig. 8. The most likely reason for this factis the position of this valve in the wafer. The valve is locatedin the edge of the wafer, position that exposes more area to theenvironmentataT=Tamb,inducingmoreconvectiveheatlosses(Eq. (3) and that results in less heating efficiency as shown inthe figure. Regression coefficients between 0.9682 and 0.9997confirm the validity of the mathematical form of Eq. (8) forall the other resistors. Eq. (8) allows then for the calculationof the expected Rhotvalue. The calculated Ravewas comparedwith a time-weighted resistor average value, Rave(t)(estimatedby numerical integration using the trapezoidal rule) of actualresistance variations, that were measured using a constant resis-tor and an oscilloscope. Experimentally it was observed for thesteady state temperatures for all the designs presented here, that|Rave Rave(t)|Rave(t) 10%(9)Since it was found that Raveis essentially equal to Rave(t),the contention of using RT=Raveas a constant in Eq. (2) toestimate the required power, to reach and maintain a steadystate temperature, T, can be used for the results presented inthis section.In order to estimate the required potential for opening eachof the valve designs, and based on previous observations thatsimilar silicon nitride diaphragms can withstand up to 650C34, voltages that would increase to temperature to around700C were used here. As a first step to test the opening ofthe valves, an estimation of the required time pulse for achiev-ingthesteadystatetemperaturewasobtained.Two-dimensionaldesigns similar to those in Fig. 2 were drawn in COMSOL,finite element method, FEM, software. The physicochemicalconstants of the materials together with Eqs. (2)(4) are usedfor the simulation models. These models provided an estimateoftherequiredtimetoachievethebreakingtemperature.Detailson 2D modeling are not reported here, but they are routinelydone in FEM modeling 38. The calculated voltage was thenapplied to the tested device first during either 30, 50 or 100ms(as indicated by the Femlab modeling results). If the valve didnot break the pulse was then incremented to 50ms and afterthat in steps of 50ms until the valve either opened (breakingthe silicon nitride membrane) or failed (resistor broke withoutbreakage of the membrane). Electrical pulses are produced viaTable 4Applied potentials, pulsing duration, and energetic requirements to open the valvesResistor designPlatinum (0.09?m)Platinum (0.30?m)Gold (0.15?m)Applied voltagePulse (ms)Energy (mJ)Applied voltagePulse (ms)Energy (mJ)Applied voltagePulse (ms)Energy (mJ)L1100200394475012313100140L27520066245304418200FailedL380200543555011625200FailedL41004008095010022525400658P120200235121001273100FailedP230200334161003165100FailedP335200490181004608100Failed382A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384Fig. 9. Experimental results obtained from the gold, L1-labeled resistor. Poten-tial drop measured through an external resistor during applied square pulses atthe shown potentials.a HexFET N-channel power MOSFET (International RectifierIRLD120)triggeredviaaSony-TektonixAFG320functiongen-erator. Table 4 shows the applied potential, the duration of theapplied pulse, and the estimated energy for opening the valve.The power estimation (as described above) assumes that steadystate temperatures were reached right before the resistor broke.The energy requirements were obtained by multiplying the cal-culated power by the pulsing time, tp.4.2.1. Further reduction of power requirements to open themicro-valvesA considered option to further decrease the required energyfor valve activation is to increase the potential applied to thedevices, which would decrease the heating time of the valve tothebreakingtemperature.HigherpotentialsthanthoseshowninTable 4, applied for shorter pulse times (1030ms) were thenchosen. In this case, it was expected that the breaking tempera-ture would not be the ultimate steady state temperature that theresistor could achieve. Because of this the required energy wascalculated by recording the electrical current as function of time(I(t) flowing through the resistor. This was done using a con-stant resistor (of similar magnitude that the design that is beingmeasured) and a Tektronix TDS 3032 digital oscilloscope. Thismeasurement also provided the pulsing time required for mem-branebreakage(tp).Theenergywasthenintegratednumericallyusing trapezoidal rule.Energy = V?I(t)dt(10)Potential drop measured through an external resistor duringapplied square pulses is shown in Fig. 9. The potential shownnext to each curve is the applied voltage to the resistor. Whenthetwohighervoltagesareapplied(13and17V),themembranebreaksopeningthevalve.Thecalculatedenergyrequiredtoopentheresistorsactuatedwith13Visoneorderofmagnitudehigher(about 4 times more) than that utilized with 17V. For that case,if integration of the power is performed as function of time, theenergyrequiredwasaround44mJ.Ifanaveragepoweriscalcu-lated and multiplied by the time required for breakage (22ms),theestimatedenergyrequiretoopenthevalvewas43J.Thefactthatthesevaluesdifferbylessthan1%showthatintegrationcanFig. 10. Energy required to break zigzag resistor designs in Table 1. (a) Plat-inum resistors with an average thickness of 0.090.025?m. (b) Platinumresistors with an average thickness of 0.300.030?m. (c) Gold resistors withan average thickness of 0.150.020?m. In parenthesis the applied potential aswell as the time during which the voltage was applied is shown.be avoided to obtain the valve energetic requirements, as statedin Section 4.2. Energetic requirements were calculated for allthe successful replicate cases (in all designs at least 3 out of 4or 4 out of 5 of the resistors broke together with the membrane)and are presented in Figs. 10 and 11. The calculated energy foreach device is shown as a function of their resistance. The fig-Fig.11. Energyrequiredtoopenvalveswithtwo-legs-in-parallelresistordesign.(a) Platinum resistors with an average thickness of 0.090.025?m (squares).(b) Platinum resistors with an average thickness of 0.300.030?m (rhombus).In parenthesis the applied potential as well as the duration of the applied voltageis shown.A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 374384383ures clearly show the effect of the resistor design. The averagepotential and pulse-time (with both a plus/minus voltage andduration of the successfully tested devices) has been includedclose to the corresponding data cluster for each design.5. Summary and conclusionsWe have presented the basis for the micro-fabrication pro-cess to produce reliable, single-use valve-arrays fabricated withmetals and silicon nitride, based on rapid thermal induction ofstresses. The presented thermal testing and characterization ofthe resistors on the valves serves as a guideline to design resis-tors with specific activation power requirements. The valves areactivated with low-power (in some cases with energetic require-mentsintheorderoftensofmilliJoules)anddifferentactivationvoltage/current pairs, potentially facilitating the implementa-tion in a device. Results for the maximum pressure that varioussized valves can withstand have been presented. Fabricated andtested valves with dimensions of 3mm3mm and 3?m thick-ness can withstand a pressure gradient of at least 5bar. Thelow-power requirements of single-use activated membranes is arequirement for the implementation of a valving mechanism areattractive for the development of remote and even portable sys-tems. Additionally, the fabrication steps ensure high-productionlevels (at least 75% of the produced devices were successfullytested)andlow-cost,makingthisfabricationmethodsuitableforthe production of expendable devices.It is acknowledged that a temperature of 700C may be toohot for certain applications; however, given the short durationof the pulse, it is likely that it is a temperature that will notaffect the pneumatic actuation illustrated in Fig. 1. In order toensurethatthistemperatureisreachedintheresistors,numericalsimulations are necessary. Modeling work including mechani-cal stresses of similarly heated transducers, with the objectiveof maintaining safe structural operational temperatures, haveappeared in the past 34,35. It is work in progress within ourresearch group to perform strict 3D modeling of the presentedvalves especially during the heating process to further improvethe performance of the micro-fabricated valves.AcknowledgementsDr. Cardenas-Valencia would like to continue acknowledg-ing the financial support from the Consejo Nacional de Cienciay Tecnologia and University of Guadalajara (Mexico) for hisdoctoral studies and for allowing him to take the post doctoralposition at COT at the University of South Florida, where hecurrently works and this work was developed.References1 M.A.Schwarz,P.C.Hauser,Recentdevelopmentsindetectionmethodsformicro fabricated analytical devices, Lab Chip (2001) 16.2 A.J. Tued os, G.A.J. Besselink, R.B.M. Schasfoort, Trends in miniaturizedtotal analysis systems for point-of-care testing in clinical chemistry, LabChip (2001) 8395.3 M.L. Janowiak, A.M. Cardenas-Valencia, M.L. Hall, D.P. Fries, Devel-opment of a mobile sensing system for in situ water analysis basedon solid-phase extraction-reflection spectroscopy, Meas. Sci. Technol. 16(2005) 729737.4 A.M. Cardenas-Valencia, V. Challa, D. Fries, L. Langebrake, R.F. Benson,S.Bhansali,Amicro-fluidicgalvaniccellasanon-chippowersource,Sens.Actuators B: Chem. 95 (2003) 406413.5 K.B. Lee, L. Lin, Electrolyte-based on-demand and disposable microbat-tery, J. Microelectromech. Syst. 12 (2003) 840847.6 A.M. Cardenas-Valencia, J. Dlutowski, J. Bumgarnenr, S. Knighton, C.Biver,L.Langebrake,Aluminum-anode,silicon-basedmicro-cellsforpow-ering expendable MEMS & lab-on-a-chip devices, Sens. and Act. B:Chemical, in press (corrected proof, available online 25 July 2006).7 A.vandenBerg,T.S.J.Lammerink,Micrototalanalysissystems:microflu-idic aspects, integration concepts and applications, Top. Curr. Chem. 194(1997) 2149.8 S.Shoji,Fluidsforsensorssystems,Top.Curr.Chem.194(1997)163188.9 J.E. Rem, T.J. Shepodd, E.F. Hasselbrink, Mobile flow control elementsfor high pressure micro-analytical systems fabricated using in-situ poly-merization, in: Proc. of the ?TAS 2001 Symposium, Monterey, CA, 2001,pp. 227228.10 A.M. Cardenas-Valencia, D.P. Fries, L.C. Langebrake, R.F. Benson, Rapiddesign, fabrication and optimization of a single shot thermo-pneumaticmicro-actuation for the delivery of minute amounts of liquids, in: Proc. ofthe Intern. Conf. on Microchannels and Minichannels, vol. 1, NY, USA,2003, pp. 801808.11 M.J.Madou,L.J.Lee,S.Daunert,S.Lai,C.-H.Shih,Designandfabricationof CD-like microfluidic platforms for diagnostics: microfluidic functions,Biomed. Microdev. 3 (2001) 245254.12 P. Griss, H. Andersson, G. Stemme, Liquid handling using expandablemicrospheres, in: The Fifteenth IEEE International Conference on MicroElectro Mechanical Systems, 2024 January, 2002, pp. 117120.13 C. Pang, Y.-C. Tai, J.W. Burdick, R.A. Andersen, Electrolysis-baseddiaphragm actuators, Nanotechnology 17 (2006) S64S68.14 C.-C. Hong, S. Murugesan, S. Kim, G. Beaucage, J.-W. Choi, C.H. Ahn, Afunctional on-chip pressure generator using solid chemical propellant fordisposable lab-on-a-chip, Lab Chip 3 (2003) 281286.15 H.Chien-Chong,C.Jin-Woo,C.H.Ahn,Disposableair-burstingdetonatorsas an alternative on-chip power source, Proc. of the 15th IEEE Int. Conf.on MEMS (2002) 240243.16 M. Felton, The new generation of microvalves, Anal. Chem. 75 (2003)429A432A.17 W.H. Grover, A.M. Skelley, C.N. Liu, E.T. Lagally, R.A. Mathies, Mono-lithic membrane valves and diaphragm pumps for practical large-scaleintegration into glass microfluidic devices, Sens. Actuators B: Chem. 89(2003) 315323.18 M. Hu, H. Du, S.-F. Ling, Y. Fu, Q. Chen, L. Chow, B. Li, A silicon-on-insulator based micro check valve, J. Micromech. Microeng. 14 (2004)382387.19 B. Xu, J. Castracane, R. Geer, Y. Yao, B. Altemus, Brace, process develop-ment and fabrication of application specific micro-valves, in: Proceedingsof SPIEThe International Society for Optical Engineering, vol. 4174,2000, pp. 299306.20 S.B ohm,G.J.Burger,M.T.Korthorst,F.Roseboom,Amicromachinedsil-icon valve driven by a miniature bi-stable electro-magnetic actuator, Sens.Actuators A: Phys. 80 (2000) 7783.21 H. Zhao, K. Stanley, Q.M. Jonathan Wu, E. Czyzewska, Structure andcharacterization of a planar normally closed bulk-micromachined piezo-electricvalveforfuelcellapplications,Sens.ActuatorsA:Phys.120(2005)134141.22 M.E. Piccini, B.C. Towe, A shape memory alloy microvalve with flowsensing, Sens. Actuators A: Phys. 128 (2006) 344349.23 J.S. Go, S. Shoji, A disposable, dead volume-free and leak-free in-planePDMS microvalve, Sens. Actuators A: Phys. 114 (2004) 438444.24 A.Gli ere,C.Delattre,Modelingandfabricationofcapillarystopvalvesforplanar microfluidic systems, Sens. and Act. A: Physical 130131 (2006)601608.25 N.-T. Nguyen, T.-Q. Truong, K.-K. Wong, S.-S. Ho, L.-N. Low, Microcheck valves for integration into polymeric microfluidic devices, J.Micromech. Microeng. 14 (2004) 6975.384A.M. Cardenas-Valencia et al. / Sensors and Actuators A 136 (2007) 37438426 K.W. Oh, C.H. Ahn, A review of microvalves, J. Micromech. Microeng.16 (2006) R13R39.27 J. Mueller, E.-H. Yang, A. Green, V. White, I. Chakraborty, R. Reinicke,DesignandfabricationofMEMS-basedmicropropulsiondevicesatJPL,in:Proceedings of SPIEThe International Society for Optical Engineering,vol. 4558, 2001, pp. 5771.28 J.Mueller,C.Marrese,J.Polk,E.-H.Yang,A.Green,V.White,D.Bame,I.Chadraborty, S. Vargo, R. Reinicke, An overview of MEMS-based micro-propulsion developments at JPL, Acta Astronautica 52 (2003) 881895.29 D. Briand, B. van der Schoot, N.F. de Rooij, H. Sundgren, I. Lundstrom,Low-power micromachined MOSFET gas sensor, J. Microelectromech.Syst. 9 (2000) 303308.30 C.-Y. Lee, G.-B. Lee, Micromachine-based humidity sensors with inte-grated temperature sensors for signal drift compensation, J. Micromech.Microeng. 13 (2003) 620627.31 C.-Y. Lee, G.-B. Lee, MEMS-based humidity sensors with integrated tem-perature sensors for signal drift compensation, in: Proceedings of IEEESensors, 1, 2003, pp. 384388.32 F. Mailly, A. Giani, R. Bonnot, P. Temple-Boyer, F. Pascal-Delannoy,A. Foucaran, A. Boyer, Anemometer with hot platinum thin film, Sens.Actuators A: Phys. 94 (2001) 3238.33 S. Wu, Q. Lin, Y. Yuen, Y.-C. Tai, MEMS flow sensors for nano-fluidicapplications, Sens. Actuators A: Phys. 89 (2001) 152158.34 J.Puigcorbe,D.Vogel,B.Michel,A.Vila,I.Gracia,C.Cane,J.R.Morante,J. Micromech. Microeng. 13 (2003) 548556.35 C. Rossi, E. Scheid, D. Esteve, Theoretical and experimental study ofsilicon micromachined heater with dielectric stacked membranes, Sens.Actuators A: Phys. 63 (1997) 183189.36 S. Timoshenko, S. Woinowsky-Krieger, Theory of Plates and Shells, Engi-neering Societes Monographs, second ed., Mc Graw-Hill Book Co., NewYork, 1959.37 H. Seidel, L. Csepregi, A. Heuberger, H. Baumg artel, Anisotropic etchingof crystalline silicon in alkaline solutions, J. Electrochem. Soc. 137 (11)(1990) 36123626.38 COMSOL Multiphysics 3.1, manual.BiographiesAndres M. Cardenas-Valencia earned a BS in chemical engineering (Univer-sityofGuadalajara,Mexico)publishingathesisonthecharacterizationofnovelpolymeric materials; and a PhD also in Chemical engineering (University ofSouth Florida, USF) focusing his dissertation on multiple scattering studies thatrelaxlimitationsinmultiangleandmultiwavelengthcharacterizationofcolloidalsystems. He participated in the prestigious Kauffman entrepreneurial internshipprogram, at Ocean Optics Inc. (Dunedin FL). After graduation, he joined theCenter for Ocean Technology, COT, located at the USF College of Marine Sci-ence in a postdoctoral position where he is currently employed. His researchinterestsincludeopticalsensors,microfluidics,powersourcedevelopment,poly-mer applications for MEMS, and miniaturization of sensing components andin-situ transduction systems