A general platform for integrated opto-electronic sensor systems on silicon is proposed. The system is based on a hybridly integrated semiconductor laser, ZnO optical waveguides and monolithic photodiodes and electronic circuiry

Albers, H.

Bekman, H.H.P.Th.

Chalmers, J.

Holleman, J.

Ikkink, T.

Joppe, J.L.

Kranenburg, H. van

Krijger, A.J.T. de

Lambeck, P.V.

Zhou, M.-J.

de Krijger, A.J.T.

Chalmers, J.D.

Ikkink, T.J.

van Kranenburg, H.

Zhou, M.J.

University of Twente Research Information

}JBProceedings of the Dutch conferenceSensor Technology L994on Sensor Technology 1994University of TwenteEnschede, The NetherlandsFebruary 17 - 18, 1994Edited by P.V. LambeckThis conference has been held under the auspices of the Platform 'Sensor Technology'and tlre Duat'suerbat¿d-cornmittee 'Sensor Technology' as part of the STW/NWO Priority-Programme'Sensor Technology'.BASIC OPTO-ELECTRONICS ON SILICON FOR SENSORAPPLICATIONSJ.L. Joppe, H.H.P.Th. Belo¡utt and A.J.T. de l{rijgerTNO Pþsics and Electronics Laboratory (NGFEL)P.O. Box 96W, NL-2509JG, The Hague, The NaherlandsPhone: +31 70 3264221, Fax: *31 70 3ZUX|IP.V. Lotnbeck, H. Albers, J. Clulmcn, J. Holleman,T. Il&ink, H. van Kranenburg and M.J. ?,houMESA Research Insrtrute. Univerciry of Tluente,P.O. Box 217, NL-75æ AE, Enschcde, The NetlurlandsPhone: +31 53 8n76, Fax I3l 53 309547A general pladorm for integrated optoelectronic sensorsystems on silicon isproposed. The system is based on a hybridly integrated semiconductor laser, ZnOoptical waveguides and monolithic photodiodes and electronic circuiry.I. INTRODUCTIONThe development of innovative, miniaUrized sensorsystems is widely recognizedas being important for a modern and competitive industry. Therefore largenational and international activities in the fields of electrical, mechanical andoptical microsystems are being performed. Silicon has proved itself to be anexcællent material for the signal processing part of an integrated sensorsystem.Besides, the fabrication technologies for silicon based systems are highlydeveloped. It is therefore attractive to us€ silicon in various sensor integrationschemes [].Integrated optic microsensors are very attractive for detecting (bio-) chemicalsubstances as well as for many physical quantities [2]. Inægrated optical sensorscombine high sensitivity with the possibility of easy guidance and processing ofthe optical signal by the use of waveguides. They are smâll and rugged and offer awide choice of maûerials used for sensing. In combination with silicon this givesOPTICAL UAYEEUIDEIGNAT I NÊFígure I: (a) Possible loyout of the proposed integrued opto-electronicsensorsystem, (b) Functionalframewo* of the seworCHEMICAL DOMAINOPTICAL DOMAIN (circuitry) iôn, ôa, emission --, \Intensiry@pt) |190the prospect of monolithic smart multisensor systems and barchwise production.Chemo.optical sensors are most commonly based on a chemooptical transductionlayer. The optical properties of this transduction layer, like the real or imaginaryparts of the refractive index, change while detecting the chemical compound. Byusing e.g. the evanescent field of an optical waveguide mode, the presence of thechemical substance can be deæcæd as an intensity- or phaseshift of the opticalsignal. This paves the way for compact integraæd optical sensors for chemicaldetection and analysis.Ideally, a chemo-optical sensor has to be integrated with an opticål source anddetector and microelectronics. In a cooperation of the TNO Physics andElectronics L:boratory and several g¡oups of the University of Twente a siliconopto-electronic sensor pladorm is pursued. This cooperation is partly funded bythe IOP ElectroOptics in a six yeårs programme, initiated tn 1992. By suitabledesign of this platrorm a compact, flexible basic optoelectronic sensor circuit willbe created. The ach¡al implementation of a specific sensing principle will onlyaffect some final fabricationsteps of the chip. In this way we expect to achieve ahigh degree of standardization and cost effectiveness.II- BASIC OPTO-ELECTRONIC SENSOR PLATFORÀ{According to current ideas, the sensor pladorm will consist of a hybridlyintegrated semiconductor lasersource with a stabilizing optical feedback loop, anoptical waveguide system based on Zr'O, a monolithic detector subsystem using acoupling grating, a monolithic photodiode and UT-BiCMOS electronics fordriving the laserdiode and amplification of the detector signal (figure l). Thespecific optical sensing system will be implemented in the ZnO optical waveguidepart of the chip.elÊcfi)nic circuiLs opdcal intcrconncctionand phorodiodcFigure 2: Schcmatic cross sec'tion of the basic opto-elec'tronic circuitFor defining the specifications and a general process sequence ofthis device manyaspects have to b€ studied. These include pr(rcess compatibility and cross-talkeffects. The sensor plafform will be designed at 675 nm wavelength, although thehybrid integration scheme for the semiconductor laserdiode allows for otherwavelengths. Although a fast detector system is feasible, emphasis will be onsensitivity and dynamic range as required for the anticipated sensor applications.It w¿the Ionlystudifabri'proc(inclu9epomverSCVCItakerFiguCon¡BecamuslintrcAbiactirallorlnvesilicQqtepr-,bonrmetilayesoftgolcopel+gk*'oduction.transductionor imaginarYrmpound. BYese-nce of the'f the opticalfor chemic¿l¡l sor¡rce andPhvsics andcnté a siliconlv tunded bY:. By suitableor circuit willple wilt onlYI to achieve aIMf a hybridlYback loo'p, anvstem usrng afectronics forigure 1). Thccal waveguider*avcguidcitús device manYand cross-talkh, although thelows for othersis will be onapplications.r91III. SYSTEM INTEGRATIONA. Process CompatibilityIt was recognized in an early stage, that because of the reliability and flexibility ofthe BiCMOS technology all electronic elements have to be manufactu¡ed, withonly minor adjustments, before the optical ones. Therefore the compatibilitystudies focussed on possible influences on the electronics caused by the opticalfabrication steps. Beðides possible influences on the electronics by tti,r subsequentprocess steps, several physical interferences in the system were identified. Theseinclude asp€cts of thermal dissipation, electric¿l and optical isolation and ZnOdeposition on non-thermally oxidized substrates. In an accompanied paper theseinvestigations are further elaborated t3l. It can be concluded, that, althoughseveral influences have been identified, we anticipate, that these influences can beFigure 3: Electron microscope picrure of a laserdiode mounted on a ProgramControl Module chip containing several electronic tesl structuresB. Lightsource SubsystemBecause a lightsource cannot be fabricated in silicon, a semiconductor laserdiodemust be integraæd hybrittly. In earlier work [4] a new coupling mechanism wasintroduced, based on a smight well, accurately etched into the optical waveguide.A bare semiconductor laserchip was placed epi-down in the well. In this way theactive layer of the laserchip can be moved to the vicinity of the waveguide, thusallowing for an eff,icient coupling. For the laserbonding a new method has beeninvestigated. It appeared that a semiconductor laserdiode could be bonded to asilicon substrate by thermocompression.Quantum r#ell ridge waveguide type semiconduçr lasers (850 nm) were pressedepi-down on metallized silicon substrates at250 C for ten minutes. In this way abond was established between the gold layer on the laserdiode and a CrlAllPtJAumetâllization on tìe substrate. In this stack the ch¡omium serves as an adhesiontaken care of.194investigation. It is anticipated, that fhe thermocompression process can be appliedin this sensor system and that ioupring errrcrénciès ñp t" iöyã-rräiLìi¡r".C. Detector Subsystem.chip will consist of a mon erI inlerconnect between the w e.diffrculties a hybrid solution ispÌþto.unBnt (A)UE¡7aæa7uG{tzæa7ls{71.G47tooc{0buffer loyeßoloã¡&50æñæspholon ñux ånoto (0)Figyre 1: (a) Fast (Jd) and slow (Jp, Jn) contributions îo the photocunenr, (b)graring interconnect. N. B. A @) : *ei ¡6 1'@ephotodetectrthis solutio¡850nmasfor this sensThe photodThis ampliflow noise. '100 kHz. TlZnO is a pcand gas senelectronic iproces. Opthave beenshowed onldB/cm @ 6indicate thzaccompanieA.general rproposed. Toptical warexperimentsindicate, tluREFERENCIl. E. Voges, INeuch¡tel, Apr2. P.V. l-amh3. M.J. Zhou,P.V.l-embeck4. J.L. Jop'pe,5. J. Chalrcnó. H.H.P.Th.P.V. l-cmt€clr appliedaim is toilem willpo$,er lspaper, arrce. Thee crurenton therequiredamplifierotodiode.rsystem isCþrfier loyers,nent, (b)quantumditions fori substratee realized.ported viah is largerr effectivemally, the-like layer:equired inr redirect ita couplingnred to be,ted (figurethat almoste. This canùt and the1q3show however, thatan 850 nm. Aroundnm will be PursleddifficultY.The .by. aThis h- dYnlow be al0O the amPlifier is about 50 ¡rA'D- 7.rO Waveguide TechnologYv. coNcLUStONSsilicon islaser, ZnOuitrY. KeYthe sensors fe¿sible'R,EFERENCESl.E.Voge-s,H.BezzaouiandM'Hoffm¡¡n'EuropeanConferenceonlntegratedOptics'93'Neuch¡tel, April l8-22 (1993)'2. P.V. L¡mb€ck, S€nsors ¡nd Actuators B' 8' pp' 103-116 (192)'3. M.J. Zhou, T. Ikkink' J. Ch¡lmers, H. van Kr¡¡enbrrrg, H. Alben, J. Hollen¡an.P.V.l¡mbeck. ¡.1. ¡"pp"' ff 'np:fn' S"k-""' A'J' T d; Kri'ige¡' these pr<rcæedings ( 1994)'4. J.L. Joppe, A'J'T' de iä¡g"t -¿ ò f 'J'-NoonJmsn' Elec' L¡tt' ' 2'7 ' ip' 162-163 ( le9l )'5. J. ChalnBrs et al., these procæedings (1994)'6. H.H.P.Th. Bek¡ran, X'fi' ¡-o¡ti ¡'¡'C' u"¡ Bezooijen' J'L' Joppe' R G' lleirje¡nen endP.V. l-¡mbeck, these pnrceedings (1994)' an¡l references thereini4

Basic opto-electronics on silicon for sensor applications

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