Accelerated Publication Environmentally sustainable composite resistors with low temperature coefﬁcient of resistance Shweta Jagtap, Sunit Rane * , Dinesh Amalnerkar Thick Film Materials Laboratory, Centre for Materials for Electronics Technology, Panchawati, Off. Dr. Bhabha Road, Pune-411008, India article info Article history: Received 15 October 2008 Received in revised form 5 December 2008 Accepted 28 December 2008 Available online 17 January 2009 Keywords: Composite Thick ﬁlms Resistor Eco-friendly Temperature coefﬁcient of resistance abstract Temperature coefﬁcient of resistance (TCR) of thick ﬁlm resistors are based on ﬁred conducting grains and glass composites. Many analog sensor and control circuits require low (<100 ppm/°C) TCR value. To prepare resistors with low TCR value, knowledge of processing conditions and conduction mechanism parameters are of particular importance because TCR is ﬁnalised during ﬁring and cannot be trimmed in the latter stage to a target value as resistors can be. This paper reports the preparation and properties such as microstructural and electrical in particular to sheet resistance, TCR (hot and cold) of eco-friendly composite resistor paste compositions. Our resistor compositions showed the sheet resistance in the range of 1.18–1.38 KX/h and the hot and cold TCR of the compositions reduced substantially from 360 to 100 ppm/°C and 175 to 60 ppm/°C with the addition of TCR modiﬁer. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Use of thick ﬁlm resistive glazes is now widespread in the ﬁeld of hybrid microelectronics. The main requirements for thick ﬁlm resistors are long term stability, relatively narrow tolerances in the sheet resistance and a low temperature coefﬁcient of resistance (TCR). The commonly used mixed oxide technology is relatively simple and chemicals used in the process have a moderate cost. The traditional thick ﬁlm resistors are usually based on ruthenium dioxide (RuO 2 ) or ruthenate powders viz. lead ruthenate (Pb 2 Ru 2 O 6.5 ) or bismuth ruthenate (Bi 2 Ru 2 O 7 ) and the glass matrix is usually based on lead borosilicate system with some TCR modi- fying agents. The major part of the volume of chemicals used in manufacturing of thick ﬁlm resistors are lead and cadmium oxide. Both the oxides and their compounds are listed as toxic and haz- ardous to the environment not only in form of direct pollution originating from the waste produced but also because the products are not recyclable. Therefore, worldwide the electronics industry has been engaged in the development of new materials for the sus- tainable use of natural resources and waste to reduce the negative environmental effects resulting from the disposal of electronic goods and to conform the relevant legislation. Efforts are being made to develop eco-friendly electronic materials and as a result, eco-friendly solders, packages and thick ﬁlm conductive pastes for interconnect are currently available commercially. However, the developments of lead free thick ﬁlm resistor compositions for hybrid microelectronics is not a simple task and only partially sat- isfactory compositions based on RuO 2 or ruthenates (pyrochlore) have been obtained [1–3]. Their investigations revealed that prob- lems like devitriﬁcation and bleeding of glass, solubility of Ru and large reactivity of pyrochlore ruthenate with the glass in resistors developed with lead free glass based on RuO 2 or pyrochlore ruthe- nates. Some researchers used perovskite ruthenate (CaRuO 3 ) as a conductive phase for lead free resistors [4–7]. However, the above compositions studied showed high TCR of thick ﬁlm resistors that needs to be tailored. To the authors’ knowledge, lead free thick ﬁlm resistors series with characteristics comparable to ‘conventional’ thick ﬁlm resistors are not available commercially till today. The low temperature coefﬁcient of resistance (TCR) of thick ﬁlm resis- tors with high chemical stability is attractive for systems, which encounter wide range of service temperatures, or for use in high power applications such as automotive electronics and high-den- sity electronic packages. In this work, the effort was made to reduce the TCR value by adding TiO 2 as a TCR modifying agent in to the lead free composi- tion. We reported the morphological/microstructural and electrical properties such as sheet resistance, temperature coefﬁcient of resistance (TCR) of a perovskite ruthenate (CaRuO 3 ) based eco- friendly thick ﬁlm resistor compositions formulated indigenously. 2. Experimental techniques Composite resistor pastes were formulated by mixing the appropriate quantity of the calcium ruthenate powder and the lead free glass frit (SRG2P) with an organic vehicle. The details of 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.12.092 * Corresponding author. Tel.: +91 20 25899273; fax: +91 20 25898180. E-mail address: sunitrane@yahoo.com (S. Rane). Microelectronic Engineering 86 (2009) 2026–2029 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee