Non-lead resistor composition

This invention relates to a composition for use in the production of resistors for electronic applications. The composition is prepared from non-lead materials that include lithium and ruthenium, and may be prepared in the form of a thick-film paste.

Existing conductive intermediates (such as ruthenium dioxide, silver/palladium solid solutions, and bismuth ruthenate) combined with non-lead frits can form the low-resistance end of an essentially lead-free resistor system (10 to 1000 ohms), while existing conductives (such as ruthenium dioxide, bismuth ruthenate and strontium ruthenate) with non-lead frits could be used to make a 10 kilohm member. Ceramic resistor systems commonly include individual decade members which range between 10 ohms/square and 1 megohm/square. Resistors in these series must be insensitive enough to variations in thermal process conditions to be used on high speed manufacturing lines. Currently, most commercial resistor systems in the 100 kilohm to 1 megohm range utilize lead-containing frits and/or lead-containing conductive phases, such as formulations containing either lead ruthenate, or RuO₂ and high-lead frits.

Fukaya and Matsuo (1997, 97 ISHM Symposia Proceedings, pp. 65-71) describe a RuO₂/sodium alkaline-earth alumino-borosilicate frit resistor system that can be fired on alumina substrates or an LTCC system as described therein. The resistance of the system extends generally from 10 ohms to 500 kilohms. ±100 ppm/° C. TCRs are reported from 100 ohms to 500 kilohms.

Hormadaly (2002, 02 IMAPS Symposia Proceedings, pp. 543-547) describes resistors composed of M_2−xCu_xRuO_7−β, where x is 0.2 to 0.4, β is 0 to 1, and M is a rare earth element. An example of a 6.15 megohm thick-film resistor is given.

Atsushi et al (2002, JP 2002-101903) describe a resistor composed of RuO₂ and a bismuth-bearing frit with or without bismuth ruthenate.

JP 2003-197405 describes RuO₂ and several ruthenates (such as CaRuO₃) combined with frits composed of many alkali and alkaline-earth borosilicates, and many transition metal drivers.

There nevertheless remains a need to find a non-lead conductive-oxide/frit combination that could provide resistor compositions in the 100 kilohm to 10 megohm range, and preferably with ±100 ppm/° C. TCRs.

In one embodiment, this invention provides a composition that includes particles of Li₂RuO₃ in which Li atoms have been exchanged for Al, Ga, K, Ca, Mn, Fe, H, Na, Cr, Co, Ni, V, Cu, Zn, or Ti atoms, or a combination thereof.

In another embodiment, this invention provides a composition described by formula as follows: M⁺¹_xM⁺²_yM⁺³_zLi_{2−x−2y−3z}RuO₃ where (x+2y+3z)≦1.5, and where M is selected from one or more members of the group consisting of Al, Ga, K, Ca, Mn, Fe, Na, H, Cr, Co, Ni, V, Cu, Zn, and Ti.

In a further embodiment, the above described compositions may be admixed with one or both of an alkali metal, zinc alumino-borosilicate frit, and an alkaline-earth metal, zinc alumino-borosilicate frit. The resulting composition may be fabricated as a resistor that has desirable sheet resistance and TCR properties, and the resistor so obtained may be used in an electronic device.

In yet another embodiment, this invention provides a method of preparing a Li₂RuO₃ composition by (a) providing Li₂RuO₃ particles having an average particle diameter between about 0.5 and about 5 microns; and (b) contacting the Li₂RuO₃ particles with a solution comprising ions prepared from one or more of the elements selected from the group consisting of Al, Ga, K, Ca, Mn, Fe, Na, H, Cr, Co, Ni, V, Cu, Zn, and Ti.

This invention provides a composition including particles of Li₂RuO₃ particles wherein the Li atoms at or near the particle surface have been replaced with atoms of other elements. Resistors comprising this material can be made which show high resistance and ±100 ppm/° C. TCRs without the use of toxic elements such as lead or cadmium.