Patterning of thin tin oxide film with nano-size particle for two-dimensional micro-gas sensor array Wan-Young Chung a, * , Jun-Woo Lim b a School of Internet Engineering, Dongseo University, Busan 617-716, South Korea b Department of Electronic Engineering, Taegu Science College, Daegu 702-723, South Korea Received 7 February 2003; received in revised form 24 April 2003; accepted 24 April 2003 Abstract Thin tin oxide film with nano-size particle was prepared on silicon substrate by hydrothermal synthetic method and successive sol–gel spin coating method. The fabrication method of tin oxide film with ultrafine nano-size crystalline structure was tried to be applied to fabrication of micro-gas sensor array on silicon substrate. The tin oxide film on silicon substrate was well patterned by chemical etching upto 5 lm width and showed very uniform flatness. The tin oxide film preparation method and patterning method were successfully applied to newly proposed two-dimensional micro-sensor fabrication. Ó 2003 Elsevier B.V. All rights reserved. PACS: 72.80.Jc; 73.61.Le; 81.15.)z Keywords: Gas sensor; 2-D micro-gas sensor; Tin oxide; Thin film gas sensor A new trend of sensor array instrumentation using discrete sensor elements was begun in mid 1980s [1]. It aimed at increasing the selectivity of individual semi- conductor gas sensor firstly and nowadays discriminat- ing multiple gas components in a mixture with the aid of multivariate regression algorithms with a minimized loss inaccuracy.Recentlythisgasdiscriminationsystemhave been widely known to be applied for various applications such as the recognition of noxious gas leakage, measure- ment of air pollution and analysis of food quality [2]. Until now, most commonly used methods for the preparation of gas sensing film of silicon micro-sensors are physical methods such as r.f. sputtering and thermal evaporation. However, in most case when only its sensing properties were referred, the chemical prepara- tion methods such as sol–gel method [3,4] and spray method [5] has been known that they have many ad- vantages over the sensing films by physical methods al- though the fabrication processes for film are trouble some and difficult to standardization as followings; (i) catalyst and additive can easily and exactly incorpo- rated, (ii) the resultant films may possibly be charac- terized by an ultrafine and porous structure with a large specific area. Above all, chemical preparation method for the gas sensing film of metal oxide is considered to be an alternative method which could solve the lack of long-term stability of the metal oxide thin film prepared by physical method [6]. So the attempt for the thin film technology of sol–gel spin-coating on silicon substrate seems to contribute to develop more advanced micro-gas sensor array with good gas sensing performances. Moreover grain size effects on gas sensing properties of a polycrystalline metal oxide thin films are known to be very important. Therefore, by reducing the particle size, high gas sensi- tivity and short response times can be achieved [6]. The crystalline size of tin oxide was estimated to take a value of several tens nano-meter though very carefully pre- pared gas sensing films. The coating SnO 2 and Sb-doped SnO 2 solutions used were colloidal SnO 2 solution (SnO 2 content 8 wt.%, mean diameter of particles: about 3 nm) and colloidal SnO 2 (Sb) solution (SnO 2 content 10 wt.%, Sb content 0.6–0.7 wt.%, mean diameter of SnO 2 particles about 3 nm), prepared by means of the hydrothermal method described in detail elsewhere [3]. * Corresponding author. E-mail address: wychung@dongseo.ac.kr (W.-Y. Chung). 1567-1739/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1567-1739(03)00103-2 Current Applied Physics 3 (2003) 413–416 www.elsevier.com/locate/cap