Electrical capacitance of resistive film in plane-layered medium

The parasitic capaciences of film resistors can dramatically affect the output parameters of a microelectronic unit. A technique for computation of these capacitances is necessary for construction of mathematical models for CAD which are to be employed at the stage of circuit simulation, this stipulating the actuality of developing the technique for computations of the capacitances. The article presents analytic expressions for the capacitance of a current-carrying rectangular high-resistance film conductor (resistor), i. e., resistor stripe. The expressions describe the dependence of the capacitance on a non-uniformity of the charge distribution along the vector of the current density. The bounds within which the resistor’s capacitance changes with the ultimate change of the load resistance from 0 to ¥ are found. The estimation of the error caused by a computation of a resistor’s capacitance using formulae intended for a computation of a conductor capacitance is presented. A substantial nonlinearity of the input impedance of the film resistor is revealed. The nonlinearity is caused by a charge redistribution which takes place if the film resistor’s load resistance changes during the functioning of the integrated circuit.

Investigation towards the optimum of power capability, ageing stability and costs effectiveness on thick film resistor pastes for AlN ceramics

The focus of this work was the optimization of a 10 Ω/□ thick film resistor (TFR) paste composition to obtain increased power capability, aging stability and minimum use of ruthenium oxide for cost savings without changing the defined narrow sheet resistance (R□) and temperature coefficient of resistance (TCR) specifications. In times of highly fluctuating precious metal costs, the use of a minimum of the precious metal ruthenium respectively ruthenium dioxide is one essential part for cost-effectiveness. The thick film paste formulation consists of the electrically conducting phase ruthenium dioxide, a lead-free glass phase and two inorganic additives for tuning thermo-mechanical and electrical properties of the formed films. A phthalate free organic vehicle with ethyl cellulose polymer was used to formulate a screen printable ceramic thick film paste. For this paper, RuO2 powders with various specific surface area values (BET) were prepared by thermal annealing of a precipitated fine ruthenium dioxide powder. All other solid and liquid components of the paste were the same as used for IKTS 10 Ω/□ TFR paste FK9611 for AlN substrates. Furthermore, the content of ruthenium dioxide in the paste compositions was changed systematically around an assumed target content to achieve the desired sheet resistivity. Concurrent to the variation of the ruthenium dioxide content the inorganic additives had to be adapted too. The influence of the variations of raw material and paste composition on the film properties were investigated by screen printing 24 resistors of 2 mm × 1 mm dimension on an 1” × 1” AlN substrate, firing at 850 °C for 10 minutes in air atmosphere and subsequently measuring R□, TCR, the stability of resistance ΔR/R0 effected by artificial aging of the resistors (stored 100 up to 1000 hours @ 200°C) and the maximum rated power dissipation (MRPD) as well as short term overload voltage (STOL). The results are discussed in regard to find an optimum between all demands of the most important electrical film properties.