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Peer Reviewed Articles School of Engineering

2012

Ion-Sensitive Field Effect Transistor as a PH Sensor

Lihong (Heidi) Jiao Grand Valley State University, [email protected]

Nael Barakat Grand Valley State University, [email protected]

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ScholarWorks Citation Jiao, Lihong (Heidi) and Barakat, Nael, "Ion-Sensitive Field Effect Transistor as a PH Sensor" (2012). Peer Reviewed Articles. 1. https://scholarworks.gvsu.edu/egr_articles/1

This Article is brought to you for free and open access by the School of Engineering at ScholarWorks@GVSU. It has been accepted for inclusion in Peer Reviewed Articles by an authorized administrator of ScholarWorks@GVSU. For more information, please contact [email protected]. RESEARCH ARTICLE - 2 1 2 Journal of -type silicon p , at the insula- Vol. 12, 1–5, 2012 eo Nanoscience and Nanotechnology 2.1 V to 0.5 V − across which the potential drop occurs. dl C -channel MOSFET whose gate is controlled by a n When the ISFET is placed in a solution (electrolyte), and Nael Barakat gate ISFETan biased by the AgCl reference electrode, controllable external voltagemode, and and operates a inand differential a MOSFET were read-out feedback fabricatedsubstrate circuitry. on using Both the the same same ISFET MOStwo fabrication transistors technology. The arenot identical have except a metal that gate the immediate ISFET to thethe does insulating surface layer. ofin the the insulator electrolyte, interactstor creating with surface a hydrogen and charge ions generating layer a on potential, the insula- tor/solution interface. This chargeionic layer charge is in opposedcapacitance the ( to solution, an which form a double layer A reference electrode, alsoterminal in allowing the the solution,way acts ISFET as as the to athe standard be gate ISFET MOSFET. biased consists The of in threshold two the voltage parts, of same the threshold voltage of electrolyte/insulator interface. Following thestatic behavior study of of the ISFETs,cially the the the dynamic threshold behavior, voltage espe- drift,pose was investigated. that We pro- thethe mechanism slow responding thathydration sites governs effect. in the The the driftprocessed output insulating with is layer signal a and both from low noise the the differential ISFET read-out was circuit. 2. STATIC MODELING The pH sensor system under study includes a SiO ∗ 1533-4880/2012/12/001/005 doi:10.1166/jnn.2012.6065 2 1 Based on this 6 Lihong (Heidi) Jiao -sensitive FET to bet- + ISFET, ThresholdCircuits. Voltage Drift, Hydration, Slow Responding Sites, Read-Out School of Engineering, Grand Valley State University, Grand Rapids, Mi 49504, USA -channel pH FET’s, it is difficult Although it can describe part of the n 5 4 The mechanism of the device instability, 2 Keywords: In this work, both thewere static studied. and The dynamic standard behaviorswas as NMOS used well to structure as model in the thechemistry signal ISFET conjunction occurring under read-out with study. circuits at The the of site-binding thedrift insulator-electrolyte ISFETs theory was insulator/electrolyte capacitor was further interface. incorporated explored. to We Theand propose describe mechanism hydration that the effects of to better need thetwo understand to threshold the exponential be drift, terms voltage considered. both had slow It toterm responding be was drift. sites employed found In with that, one addition,was to governing a carried better the low simulate initial out drift the noise using and voltage differential LTspice. the drift, signal The other read-out the output long circuit voltage was of designed the and system simulation changes from when the pH of the electrolyte changes from 12 to 0. Copyright © 2012 AmericanAll Scientific rights Publishers reserved Printed in the United States of America this type of device exhibit some non-ideal behav- Ion-Sensitive Field Effect Transistor as a PH Sensor 3 In this paper, a site-binding model was used to first Even though the technology of ISFET sensing sys- Author to whom correspondence should be addressed. ∗ ter understand the operation of ISFET. model, the ion-specific bindinginsulator sites is on the responsible surface for of the the potential changes at the especially the thresholdunclear. voltage Several drift hypotheses with havethese, time, been the was popular proposed. still one Among the is insulating layer. based on the hydration effect of drift behavior ofto the explain the initialconsidered. large drift with only hydration effect describe the static behavior of H J. Nanosci. Nanotechnol. 2012, Vol. 12, No. xx tem has progressed since1970, the first ISFET was reported in 1. INTRODUCTION Ion-Sensitive Field Effect Transistorwhere (ISFET) the is gate alytic oxide device solution. is Thisthe in type conventional electrodes of direct due device contactresponse to is time, its with high micro-size advantageous an sensitivity, andIt over fast is ana- on-chip useful circuit in continuous integration. in monitoring biological of and various ion chemical species sensing applications. iors, including the thresholdbeen voltage reported drift with that time. anhave It ISFET a has drift sensor of with 0.02–0.06be a pH/hour and even pH the higher. gate initial could drift could RESEARCH ARTICLE h ISFET; the lcrd tp .0 V); 0.205 (typ. electrode i.1. Fig. consists capacitor Gouy–Chapman capacitors. the tran- the Helmholtz capacitors, MOS part, and connected a chemical serially and two the part of In chemical a part. combines sistor It 1. Figure V MOSFET, the Sensor PH a as Transistor Effect Field Ion-Sensitive h iermd.Bsdo h OFTter,tedrain the theory, by: MOSFET given the is on current Based mode. linear the transistor. Since voltage, nefc,V insulator/electrolyte the interface, and electrolyte, the electrode, ence Hsniieoiesrae(SiO surface oxide sensitive a of pH consists System) (Silicon-Insulator-Electrolyte ISFET yia au f5 mV. with 50 pH, of the value of typical independent a solvent the of potential dipole ewe h eeec lcrd n h ouinwt a with solution mV; the 3 of and value electrode typical reference the between neulsiti h hehl otg,V voltage, threshold the in shift equal an h ehns epnil o h ufc oeta and potential surface the interface. for electrolyte/insulator responsible the mechanism at The potential surface the hc safnto fteslto pH; solution the of function a is which 2 tcnb enfo q 5 ht ihcntn ri current drain in constant with changes that, any (5) voltage, Eq. and from seen be can It where Where eragn q 4,w obtain we (4), Eq. Rearranging h SE a erpeetdb oe eitdin depicted model a by represented be can ISFET The h SE eiei omnybae ooeaein operate to biased commonly is device ISFET The sidctderir h hehl otg safce by affected is voltage threshold the earlier, indicated As V V h oe fteIFTue nteanalysis. the in used ISFET the of model The V DS DS V B th_chem GS <V <<

Gate voltage drift (mV) Id (mA) uptsga ftelwniedfeeta edotcrutfrp hnigo 2t 2. to 12 of changing pH for circuit read-out differential noise low the of signal Output response slow both considering time with drift voltage gate The at pH of function a as ISFET of current drain The 10 15 0.2 0.4 0.6 0.8 1.2 1.4 0 5 0 1 0040 0080 00 12000 10000 8000 6000 4000 2000 0 01234567891011121314 Time (sec) pH V D = 0 8V. hehl otg)dit h iuainrslsfrSiO turn for (in results voltage simulation gate The the incorporated drift. obtain were voltage) to (9) modeling threshold and static (8) the Eqs. in in terms The considered. varying were time effect hydration and insulator. at sites the (pzc) responding of surface pH the which charge on 4, charge zero net to of no 2 is drain point of there the the which region pH that to the 3 corresponding to is Figure sensitive from less seen is current be can It respectively. lcrd voltage, electrode w ude ilscnst . (pH V 0.1 to milliseconds hundred two h ttcbhvo fIFT.Fgr hw h drain the shows 3 Figure SiO ISFETs. of of current behavior simulate to static Matlab the in implemented were (3)–(7) Equations DISCUSSION AND RESULTS 5. . hr os a lee u yteButterworth the by and out filtered eliminated was was noise effect filter. Kherz body 1 V the electrolyte 0.1 the addition, show of from results In pH change in The signal. 2 a 5. to Figure is 12 signal in from there output change seen The the be input. with can that the circuit to the added of was noise Kherz 1 h it n egho h SE r 160 are ISFET the of length and a width kept The and were voltage voltage (reference) drain gate the The electrolytes. pH different ie r epnil o h nta otg rf n the of and potential drift. drift long-term the voltage for initial responsible is the effect responding for hydration slow responsible the dis- that are with found sites was terms It exponential constants. shape two time a by tinct Such explained the data. of be reported shape only the The can with (drift). agreement voltage, voltage in and gate is current in curve drain increase the a change and is no electrolyte is there there the though of even pH pH that seen in be a can It in 4. Figure kept ISFET, gate osmlt h hehl otg rf,bt slow both drift, voltage threshold the simulate To nodrt iuaetera-u ici,techemical the circuit, read-out the simulate to order In − 2 .2V(pH V 0.42 gt SE hntegt a xoe to exposed was gate the when ISFET -gate V .Nnsi aoeho.1,1–5 12, Nanotechnol. Nanosci. J. G a e ob .I diin . V 0.1 addition, In V. 2 be to set was , − = . o05Vi h output the in V 0.5 to V 2.1 = 2 a e ocag within change to set was 12) n . ,respectively. V, 0.8 and V 2 t lcrlt,i hw in shown is electrolyte, 9 = ioadBarakat and Jiao ) Reference 0). n 2 and m , 2012 m, 2 - RESEARCH ARTICLE 5 . , 978- (1997) . (1970) IEEE Transactions on IEEE Transactions on Chicago, June 1997 International Con- J. Chem. Soc. Faraday I BME-17, 70 Biosensors: Microelectrochem- . IEEE Transactions on Electron IEEE Sensors 2010 Conference IEEE Transactions on Circuits and (2007) 54 . . . . (1998) (1992) (1979) (2010) 39 45, . 69 IEEE Trans. Biomed. Eng. Ion-Sensitive Field Effect Transistor as a PH Sensor (1974) ED-26, 11 S. Sundaram and N. N. Sharma, M. Grattarola, G. Massobrio, andElectron S. Devices Martinoia, S. Jamasb, S. D.ference Collins, on Solid-State and Sensors R.D. and L. Actuators E. Smith, Yates, S.70, 1807 Levine, and T. W. Healy, S. Jamasb, S.Electron D. Devices Collins, and R. L. Smith, P. K. ChanSystems—I: and Regular Papers D. Y. Chen, M. Lambrechts and W. M.ical C. Devices Sansen, W. M. SiuDevices and R. S.P. Bergveld, C. Cobbold, 1-4244-8168-2/10/ 9. 8. 5. 6. 4. 7. References and Notes 1. 2. 3. the former graduatework student on LTspice Mykhayl simulation. Rybachek for the Received: 12 September 2011. Accepted: 30 November 2011. 4, in the < pH < 2012 The authors would like to acknowl- -gate ISFETs. The dynamic modeling showed 2 that both slow respondingresponsible sites for and the hydrationtion threshold effects effect voltage are governs drift.sites the While are long-term hydra- responsible for drift,was the designed slow initial and drift. responding proved A totrolyte. read-out be circuit It sensitive to eliminated pHwell the of as the influence any elec- background of noise the signal. body effect as Acknowledgments: edge the National Science Foundationport (NSF) of for this their work sup- through grant number NUE 0938434 and J. Nanosci. Nanotechnol. 12, 1–5, case of SiO The site-binding modelbehavior of was the ISFETs. used The derivedimplemented to sets in of describe equations Matlab. were It thestudy was static that found the from drainelectrolyte the near current sensitivity the is point less of zero sensitive charge, to 2 pH of the Jiao and Barakat 6. CONCLUSIONS