Electrical and dielectric properties of solegel derived mullite doped with transition metals Debasis Roy, Biswajoy Bagchi, Sukhen Das * , Papiya Nandy Physics Department, Jadavpur University, Kolkata 700 032, India highlights < We have synthesized mullite composites with low dielectric constants. < Packaging substrate industry requires a material with low dielectric constant. < We think alumina can be replaced by the doped mullite. < The signal transmission delay time will be less. < The material we have synthesized is having dielectric constant of 3.15. article info Article history: Received 31 March 2012 Received in revised form 9 September 2012 Accepted 25 November 2012 Keywords: Nanostructures Solegel growth Grazing incidence X-ray diffraction Electron microscopy (SEM) Dielectric properties abstract Highly crystallized mullite composite has been synthesized at 1000  C and 1300  C via solegel technique in the presence of transition metal ions such as cobalt, nickel and copper. The dielectric properties (dielectric constant, loss tangent and a.c. conductivity) of the composites have been measured at room temperature and their variation with increasing frequency and concentration of the doped metals has been investigated. The composite doped with nickel exhibits minimum dielectric constant of 3.15 at 0.002(M) concentration at a frequency of 1.5 MHz. Experimental data shows a linear increase in a.c. conductivity with increasing concentration of metal doping ions .The dielectric constant and loss tangent of the composites are within the range of requirements for commercial use in electronics. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Mullite based ceramic composites have been continually gaining importance in the insulator/semiconductor industry. Apart from conventional uses as high temperature refractory materials, they are also appropriate candidates for high frequency circuit pack- aging and electronic substrate application due to their low dielec- tric constant (w6) and low thermal expansion coefficient. Earlier, alumina was used as substrate but the comparatively high dielectric constant (w9) increases the signal transmission delay time (t d ). The dielectric constant of the medium determines the speed of the electrical signal passing through it. The signal transmission delay time (t d ) is given by t d ¼ (ε r *s) 1/2 /c, where, ε r is the dielectric constant of the medium, s is the signal path length and c is the velocity of light. For high performance circuits ‘t d ’ should be as low as possible. Thus, mullite with its low dielectric constant is most suitable for such application. Controlled chip connections used in high package density logic devices requires a good compatibility of the thermal expansion coefficient (TCE) between substrate and Si chip. The mullite composite system has the required strength and much closer match of the TCE with Si chip than alumina [1e6]. There are several reports dealing with synthesis of mullite composites in presence of various ‘mineralizers’ which modify the mechano-chemical properties (densification, porosity, mechanical strength, sintering temperature, surface area etc.), however, liter- ature concerning the dielectric properties of these modified mullite composites are relatively few [7e13]. This paper deals with synthesis of mullite composites doped with varying concentrations of cobalt, nickel and copper ions and determines the effect of the same on the dielectric constant, loss tangent and a.c. conductivity of the composites at room tempera- ture. The results indicate that the composites have much lower dielectric constants at 1.5 MHz. Therefore, based on these results, it can be suitable for electronic packing applications. * Corresponding author. Tel.: þ91 9433091337. E-mail addresses: debasis35@yahoo.co.in (D. Roy), sukhendasju@gmail.com (S. Das). Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys 0254-0584/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matchemphys.2012.11.070 Materials Chemistry and Physics xxx (2012) 1e9 Please cite this article in press as: D. Roy, et al., Electrical and dielectric properties of solegel derived mullite doped with transition metals, Materials Chemistry and Physics (2012), http://dx.doi.org/10.1016/j.matchemphys.2012.11.070