ACKNOWLEDGMENTS This work is supported partially by the Young Scholar Foundation of Nanjing University of Science & Technology, the Excellent Young Teachers Program of Moe, PRC, and the Natural Science Foundation of China under contract no. 60271005. REFERENCES 1. S.D. Gedney and L. Hamilton, Full-wave CAD-based design of a finite ground CPW directional filter, Int J RF and Microwave CAE 10 (2000), 308 –318. 2. H.-H. Wu and Y.-J. Chan, High-Q inductors and low-loss band-pass filters on Al 2 O 3 substrates, Thin-film Technol Lett 20 (1999), 322– 326. 3. G.D. Alley, Interdigital capacitors and their application to lumped- element microwave integrated circuits, IEEE Trans Microwave Theory Techn 18 (1970), 1028 –1033. 4. J.L. Hobdell, Optimization of interdigital capacitors, IEEE Trans Mi- crowave Theory Techn 27 (1979), 788 –791. 5. I. Kneppo and J. Fabian, Microwave integrated circuits, Chapman & Hall, London. 6. M. Naghed and I. 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Howard Demuth and Mark Beale, Neural Network Toolbox for use with Matlab, User’s Guide, the Mathworks, Inc., Natick, MA, 1994. 16. F.D. Foresee and M.T. Hagan, Gauss–Newton approximation to Bayesian regularization, Proc Int Joint Conf on Neural Networks, 1997, pp. 1930 –1935. 17. Daniel S. Weile and Eric Michielssen, Genetic algorithm optimization applied to electromagetics: A Review, IEEE Trans Antennas Propa- gate 45 (1997), 343–353. © 2003 Wiley Periodicals, Inc. ANTENNA-COUPLED VOx THIN-FILM MICROBOLOMETER ARRAY F. J. Gonza ´ lez, M. Abdel-Rahman, and G. D. Boreman School of Optics/CREOL University of Central Florida 4000 Central Florida Blvd. Orlando, FL 32816-2700 Received 17 January 2003 ABSTRACT: Two-dimensional arrays of log-periodic antenna-coupled microbolometers were fabricated using VOx and Nb thin films as bolo- metric materials, which have different temperature coefficients of resis- tance. Noise, response, and angular characteristics of both types of mi- crobolometer arrays were measured and compared. VOx-based devices presented a 4.5better response and 5.5better signal-to-noise ratio than Nb-based devices. Radiation patterns show that a further increase in response can be obtained by better matching the VOx bolometer to the antenna elements. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 235–237, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11024 Key words: microbolometer; vanadium oxide; antenna-coupled detec- tors 1. INTRODUCTION Two-dimensional arrays of antenna-coupled microbolometers are used as fast infrared detectors that can be integrated into commer- cial readout integrated circuits (ROICs) [1], however, their mea- sured responsivity is lower than the required for commercial infrared imaging applications [2]. The voltage responsivity of a bolometer is given by [3]: v = | Z th | V bias , (1) where is the temperature coefficient of resistance of the bolom- eter, V bias is the dc bias voltage across the device, and Z th is the thermal impedance of the device. The temperature coefficient of resistance (TCR) is the material parameter used to quantify the temperature T dependence of the resistance R of the material and is defined as = 1 R dR dT . (2) As we can see form Eq. (1), the TCR of the bolometric material is directly proportional to the responsivity of the detector; there- fore, the choice of the thin-film heat-sensitive material is an important factor in achieving good response from the microbolom- eters. A thin films of sputtered Nb, which has a TCR close to 0.003K -1 , was used as bolometric material in [1]. Vanadium is a metal with a variable valence forming a large number of oxides which have a very narrow range of stability [4], films of vanadium oxide (VOx) consisting of a mixture of various oxides present a TCR 0.02K -1 and have been used in the past to fabricate microbolometers [5]. Films of stoichiometric VO 2 with TCRs greater than 0.05K -1 and a more involved deposition process have also been reported [6]. In this paper the performance of a VOx-based antenna-coupled microbolometer is evaluated and compared to a Nb-based device. 2. METHOD Two dimensional arrays of log-periodic-antenna-coupled microbo- lometers with a 50 m 50 m pixel area were used in this study MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 38, No. 3, August 5 2003 235