CHEMICAL REACTION AND ELECTRICAL PROPERTIES OF AMORPHOUS RuO-Ag-GLASS TERNARY SYSTEM

1) Iso-resistivity, iso-TCR and iso-noise index curves of the system are determined. They have a common feature with regard to their bending in the composition region containing less than about 10wt% Ag. 2) X-ray diffraction and thermal differential analysis reveals the solution of Ag into glass phase in addition to the crystallization of amorphous RuO2. 3) The triaxial diagram of isothermal section at 850 C is given. 4) Electrical isograms in the system are discussed in relation to the solubility of Ag into glass phase.


INTRODUCTION
Electrical properties of thick film resistor systems containing crystalline RuO2 have been investigated by many workers. 1,2It is known that none of the chemical reaction occurs during firing, unless lead rich Aluminoborosilicate glass is used as a binder with which crystalline RuO2 reacts to form Lead Ruthenate.However, these properties of the system containing amorphous RuO2 have not been reported.Consequently, we investigated the relation- ship between compositions and electrical properties, and the chemical reaction during firing of amorphous RuO2-Ag-Glass ternary systems.

EXPERIMENTAL PROCEDURES 2.1 Materials
Amorphous RuO2 powder was obtained from Nippon Engelhard Co.It was identified as RuO2" 2H20 by DTA, TGA and X-ray diffraction analysis.
Ag powder was prepared by reducing Ag20 which was precipitated from AgNO3 aq.solution by adding NaOH aq.solution.

2 Sample Preparation and Measurement
Pastes were prepared by mixing the base powders in the desired proportions with vehicle for 2 hours.
Vehicle used was 3% a-terpineol solution of 45 cps ethyl cellulose.Thick film resistors were prepared by printing the pastes on 96% AI: 03 substrate and firing at 850 C for 10 min.Electrode material used was Sumitomo Ag/Pd conductor C-4020.
Sample for X-ray diffraction and DTA were obtained by pressing the mixtures into disks, heating to selected temperatures and cooling to room temperature in air.
Temperature coefficient of resistance (TCR) was calculated from the resistance values at 25 C and 125 C. Noise indices were measured using a Quan-Teck resistor noise test instrument.

Electrical Properties
Resistor compositions investigated and their electrical properties are given in Table I.The  The resistivity of the ternary system exhibits a tendency to increase with increasing the content of Glass and the ratio of Ag to RuO2-2H20.However, the prominent feature of the iso-resistance curves is the shape like a flat S in the compositions containing less than about 10wt% Ag.Therefore, the resistivity in this composition region shows a complex variation with respect to the ratio of Ag to RuO'2H O.
The shape of iso-TCR curves closely resembles those of the iso-resistance curves shown in Figure (b).Since the zero TCR curve lies between the 10 k2/square curve and 1 k2/square curve, crossing No.a PROPERTIES OF RuO2-Ag-GLASS SYSTEM with the former near the RuO2 2H2 O-Glass side and with the latter near the Ag-Glass side of the triangle, the resistivity of compositions with zero TCR ranges from 1 k2/square to 10 k2/square.It is obvious by similar consideration that the resistivity of compositions with TCR + 200 ppm/deg, ranges from 0.1 to 100 k2/square.
The shape of the iso-noise index curves differ significantly from those of the iso-resistance curves and iso-TCR curves.However, it can be seen that there is a common feature with regard to their bending in the composition region containing less than 10wt% Ag.
3.2 X.ray Diffraction and DTA Figure 2 shows the change of X-ray diffraction pattern of composition No 24.Relative intensity of diffraction pattern of Ag decreases with increasing firing temperature and disappears completely above 500 C. The diffraction pattern of RuO2 appears from 500 C and increases its relative intensity with increasing firing temperature.Triaxial diagrams in Figure 4 show an iso-thermal section at 850 C in the system RuO2 "2H20-Ag- Glass.The ternary system is divided into three areas: area I where RuO:"2H O and Glass are present, area II characterized by coexistence of RuO2 and Ag with Glass phase, and area III in which Ag and Glass  3) Triaxial diagram of isothermal section at 850 C in the system were given.
4) The electrical properties of the system are closely related to the solubility of Ag into Glass.
ACKNOWLEDGEMENT Authors wish to thank John R. Cillag, Manager of electronic material division, Du Pont Far East Inc. for his helpful assistance.
1) Iso-resistivity, iso-TCR and iso.noise index curves of the RuO2" 2H O-Ag-Glass ternary system were determined.
2) X-ray diffraction and differential thermal FIGURE

Figure 3
Figure 3 compares the DTA curves of Glass used and the composition No 24 fired to 850 C. It is recognized that the characteristic points of Glass are lowered about 50 deg..by firing with Ag andRuO2"2Hz O.The changes of X-ray diffraction pattern and characteristic points of Glass indicate the solution of Ag into Glass.
FIGURE 4Results of X-ray diffraction analysis and phase relation in the system RuO2 2H O-Ag-Glass.
coexist.The line dividing area I and II indicates the solubility of Ag into the Glass used and coincides with the composition from where the isograms shown in Figure begin to bend.This fact should lead to further consideration that the complex change of isograms in the compositions containing less than about 10wt% Ag were caused by the change of electrical properties of Glass matrix due to the solution of Ag. 4. CONCLUSIONS analysis revealed the solution of Ag into glass phase in addition to the crystallization of RuO.2H O.

TABLE
Electrical properties of the compositions system RuO .2H20--Ag-Glass Noise index (dB).