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Mar 13, 2003 - A method 10 produce photo-patternable optical chemical senior mateds is reponed .... ELECTRONICS LEmERS 12th June 2003 Vol. 39 No. 12.

K. Murase, M. Hirata, K. Fujimoto, Y.Takeo. H. Taira, S. Moriyama, N. Tsuji and S. Kurita for their support. Q IEE 2003 13 March 2003 Elerlronics Letterr Online No: 20030596 D o l : 111.104Y/e1:20030596 K. Ishii, H. Nakajima, H. Nosaka, M. Ida, K. Kurishima, S. Yamahata, T. Enoki and T. Shibata ( N I T Photonics Labomtoria, NTT Corporation. 3-1. Morinosato Atrugi-shi, Kanaguwa 2 4 3 - 0 1 ~ nJ. ~ ~ ~ ~ ) E-mail: [email protected]

References MOKHTARI,M., FIELDS. c., and RAJAVEL, R.D.:

‘loo+ FHz static divide-by2 circuit in InP-DHBT technology’. GaAr IC Symp. Tech. Dig., Scottsdale, AZ, USA, 2002, pp. 291-293 ISHI,. K.. NOSAKA, It., IDA. M., KURISHIMA, K., ENOKI, T.. SHIBATA,?., and SANO, E.: ‘High-input-sensitiviry, low-power 43 Gbit/s decision circuit using InP/lnGaAs DHRTs’, Elecrmn. Len., 2002, 38, pp. 557-558

Despite the strong interest in exploiting this material system for telecom and datacom devices, there has been no report to date of the use of these materials far sensor applications. We report in this Letter the first demonstration of doped UV-pattemable sol-gel-derived materials for optical chemical sensor applications. In panicular, we have developed novel materials formulations which exhibit two imponant fearurcs. First, we show that the photo-patremability of this materials system enables the fabrication of a range of sensor configurations on planar substrates. Secondly, we demonstrate the ability to rune the sensor sensitivity by varying the nanostructure ofthe sol-gel materials. The combination of these two features provides a versatile capability which has significant implications for micro-system and integrated optic sensor applications. To demonstrate these principles, we have employed the well-known luminescent oxygen indicator ms-(4,7-diphenyl)- 1, 10 phenanthroline ruthenium(l1) chloride [abbreviated as Ru(dpp),CI,] as a dopant in the sol-gel material [4]. The sensor function relies on the reversible quenching by oxygen of the luminescence emitted by the ruthenium complex, when excited in the blue spectral region. The relation between the luminescence signal in the absence (lo)and presence (0of oxygen of concentration [O,] is described by the Stem-Volmer equation:


snecd multidener: a 50 Obls 4:1 MUX in InP HRT technoloev’. GaAs ~r~~ IC Symp. Tech. Dig., Monterey, CA, USA, 1999, pp. 189-192 ~~




far 40 Gb/s fiber-optic applications’. IEEE ISSCC Dig. Tech. Papers, San Francisco, CA. USA, 2000, pp. 6 M 5 HENDARMAN. A , SOVERO,E A., xu. x.,and w i n , K : ‘STS-768multiplexer with full rate output data retimer in InP UBT’ GaAs IC Symp. Tech. Dig., Sconsdale, AZ. USA, 2002, pp. 211-214 IUA.M., KURISHIMA, K., NAKAJtMA, H., WATANABE,N., and SAMAHATA. S.: ‘Undoped-eminer InP/lnGaAs HRTs for high-speed and low power applications’, Tech. Dig. InL Elecrron D d c e Mtg IIEDM)), 2000, pp. 85G856 ISHII, K., NOSAKA. H., NAKAIIMA. H., KURISHIMA. K., IDA, M., \FATANABE, N., YAMANE. Y., SANO. E., and ENOKI. T.: ‘Low-power 1:16 DEMUX and one-chip CDR with 1:4 DEMUX using InP-InFaAs heterqlunction bipolar transistors’,IEEE J Solid-Slaie Circnils, 2002,37, pp. 114&1151

Photo-patternable optical chemical sensors based on hybrid sol-gel materials S. Aubonnet, H.F. Barry, C. von Biiltzingslowen, .I.-M. Sabattie and B.D. MacCraith A method

10 produce photo-patternable optical chemical senior mateds is reponed and demonstrated for the first time. Hybrid inorganic-organic $01-gel formulations, doped with an oxygensensitive luminescent mthcnium complex, were used to produce both ridge waveguide and spot array configurations. The ability to

tune the sensitivity

of thcsc sensor materials was also demonsmted.

where K,, is the Stem-Volmer quenching constant, which depends directly on the diffusion coefficient of oxygen in the sensor material. The value of K,, may he used to characterise the sensitivity of the sensor.

Materids preparation: The sol-gel process enables the preparation of glass-like materials from alkoxide precursors at room temperature. The hydrolysis and condensation reaction rates of the precursors i r e inHuenced strongly by the pH of the sol and the water:precursor ratio. By varying those two parameters the final StmCruTe and porosity of the sol-gel materials can he tuned for particular applications IS]. The starting point of our work was a UV-pattemable sol-gel preparation which was developed to produce integrated optic components for telecom applications [6]. The sol-gel precursors used in that preparation were 3-(trimethaxysilyl)-propylmethacrjlate and zircaniumprapoxide. Methacrylic acid was added to complex the zirconium precursor. The photoinitiator used for the radical polymerisation was Irgacure 184. The absence of residual porosity is an important property of materials used in telecom components. In contrast, it is an essential property of chemical sensor materials based on entrapped indicators. Therefore, to make photo-patternable chemical sensor materials, we have made significant changes to the original formulation. A tetra-ethoxy silane precursor was added, because it is known to produce porous sol-gel materials [4]. To control the resultant porosity, the water content and pH were varied from the original formulation. lrgacure 1800 was used as a photoinitiator for the photo-patterning of the waveguiding Structure.

Table 1: pH of sols measured after 45 min SOIS

Sample A

Introduction: The fabrication of integrated optic devices using hybrid silica sol-gel materials has been widely reported in recent years [I]. The hybrid sol-gel process is an attractive low-cost alternative technology to more conventional silica-on-silicon processes such as Rame hydrolysis deposition and reactive ion etching [2]. Organicinorganic sol-gel materials can he produced by molecular ‘mixing’ of metal alkoxides and organic components. The resulting hybrid materials exhibit the Hexibility and functionality of organics and many of the useful properties of inorganic materials including stability, hardness and chemical resistance. One of the major advantages of hybrid sol-gel materials is their photo-pattrmability due to the presence of photopolymerisable organic functionalities. The non-exposed materials arc soluble in a wide range of benign solvents (e.g. isopropanol) and can be rinsed away easily. This technology, with the use of appropriate photomasks, allows the creation of very accurate patterns, similar to negative resist patterns obtained with standard photolithographic methods [3].


samnte B

1 Catalyst 1 Conc. [mol cm-’] I




I 0.1


I 0.30 I


To investigate the feasibility of tuning the sensor response through adjustment of porosity, we prepared a range of sals ofdifferent pH using either an acid (HCI) or a base (NaOH) catalyst. The concentration of the oxygen indicator Ru(dpp),C12 in the sol was 2 . 7 ~ mol cm-’. The pH of the sol was measured (Table 1) using a combined antimony pH electrode (Coleparmer). These measurements were made when the silica precursors had been mixed with the catalyst and stirred for 45 min to allow for good homogenisation.

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A range of sensor configurations was investigated, including ridge waveguides and spot arrays. Films of the doped sol were dip-coated on a glass substrate at a rate of 3 mm s-' and dried at 70°C for 1 h. The waveguides wcre produced by illuminating a film through a contact mask with rectangular openings for 40 min using a UV-lamp which provided an intensity of 100 mW cm-* in the 3 2 0 4 0 0 nm region. The non-illuminated areas of the sol-gcl films were rinsed away with propan-2-01. Ridge waveguides with an average thickness of 14.5 pm were obtained as can be seen in Fig. 1". The 3D mapping was carried out with a Dektak surface profiler. Spot arrays, demonstrating another potential configuration for our sensor, are shown in Fig. Ih.

materials system enabler control of the porosity via the initial pH of the sol, thereby facilitating sensitivity optiinisarion for different applications. The results reported here have significant implications for the fabrication of sensor arrays, micro-total-analysis systems (pTAS), and integrated optic sensors.







% 02

Fig. 2 Stern-Yolmer plots ,for ,films pmpored with di/feerenr ucidlbase corolysrs Inset: K,,

against pH o f initial sol

For example, this approach will enable the production a m y s of dopcd spots for multi-sensor arrays (e.g. within a microfluidic channel) or multiple-replicate sensing devices. It is also'compatible with the fabrication of [email protected] sensor chips using fluorescent sensor spots deposited on top of undoped multimode waveguides [8]. Such waveguiding s t m ~ h l r ecan ~ be designcd to enhance the collection efficiency by coupling into the waveguides to obtain highly sensitive sensor chips [9].


Fig. I 3D-mop and emisrim pntrrm /km waveguides 3D-map of ridge sol-gel waveguides b Spot arrays c Emission panem f" waveguides U

0 IEE 2003 Resalts: Sensor samples were placed in

gas flow cell though which controlled miXNreS of oxygen and nitrogen werc passed. Using blue LED (i,,, at 450nm) excitation, the emitted luminescence was measured against oxygcn conccnmtion. Fig. I C shows the emission at the end face of the doped waveguides, which was imaged with a CCD camera. The lumincscence dependence of O2 concentrations was examined for a range of samples produced ai different pH. The resultant data against Yo 02) where the slope of were plotted as Stem-Volmer plots (lo/l the plot yields the Stem-Volmer sensitivity constant, K,, (Fig. 2). It is clear f " these data that the sensitivity varies significantly with the pH value of the starting sol. It is also significant that the original formulation used far telecom components exhibits the lowest sensitivity, indicating very low, although nonzero, porosity. In Fig. 2 (inset) the explicit dependence of the'Stem-Volmer constant on pH is plotted. These'data show that, for the formulation reported here, the sensitivity of sensor material depends almost linearly on the pH ofthe starting sol, within the pH range evaluated. This dependence reflects the influence of pH an the material porosity and the diffusionbased nature of the oxygen sensing function [7]. Acidic catalysis promotes the hydrolysis reaction of the silica precursor preferentially to the condensation reaction whereas the base catalyst will favourably enhance the polycondensation ofthe sol. The silica network obtained in the latter casc contains much larger pores because aggregation of the silica particles is favoured much morc than in the acid catalyst case. This feature, which facilitates hming ofthe sensor response function, is very attractive for sensor design and, whcn combined with phatopattemability properties,' makes the materials formulation- described he+ very significant far sensor fabrication. B

S. Aubonnet, H.F. Barry, C. von Biiltzingsliiwcn, 1.-M. Sabatti6 and B.D. MacCraith (National Centre for Sen-or Research, School "/ Physical Sciences. Dublin Cily Univrrsi&, Glosnevin, Dublin 9, Ireland) E-mail: [email protected]


sol-gel materials that can be panemed to yield a range of possible sensor configurations. Moreover, the versatility of the sol-gel


r. ETIBNNE, P., ponouc, J., MOREAU, Y, and NAJAFI, s.I.: 'Integrated optical devices achieved by sol-gcl process', SPIE, 1998, 3278, pp. 252-258 LI. Y.P., and IILNRY, C H : 'Silica-based optical integrated circuits'. IEE Pmc., Optoelecrron., 1996, 143, pp. 263-280 RANTALA, J.T., LEVY. R., KIVIMAKI. L., and DESCOUR. M.R.: 'Direct UV patteming of thick hybrid glass films for micro- opto-mechanical stmclures', Eiecr,on. Lei,., 2000, 36, pp. 530-531 MCBVOY, A.K., MCDONAGH. C.M., and MACCRAITH. B.D.: 'Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive ruthenium complexes immobilized in sol-gel-denved porous silica coatings', Analyst. 1996, 121, pp. 785-788 RRINKER. C.J., and SCIIERER. C . : 'Sol-gel Science: the physics and chemistry of sol-gel processing' (Academic Press, San Diego, 1990) ETIENNE, P., COUDRAY, P., MOREAU. y.. and PORQUE, I.: 'Photocurable sol-gel coatings: channel waveguides for use at I.55 mum'. L Sol-Gel Sci. k h n o l . , 1998, 13. pp. 523-527 RANTALA, 1. and AYRAS, P : 'Binayphase zone-plate arrays bascd on hybrid sol-gel glass', Opt. lelt., 1998, 23, p. 1939 FELDSTEM, M.J., MACCRAITH. B.O., and LIGLER. F.S.: 'Integrating multiwaveguide SCIISOT'. US Patent 6,137,117, 2000 GOUIN. J.F., DOYLE. A., and MACCRAITH. RD.: 'Fluorescence capture by planar waveguide as platform for optical sensors', Elecrmn. Lert.. 1998, 34, pp. 1685-1687


2 3 4



7 8

Conclusions: We have developed innovative formulations for hybrid

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electronic.^ Lerters Online No: 20030618 DOI: 1 ~ . 1 ~ 4 9 / ~ 1 : 2 n n 3 n 6 1 8



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