Resistors, thick-film properties

Miscellaneous. Ruthenium dioxide-based thick-film resistors have been used as secondary thermometers below I K (92). Ruthenium dioxide-coated anodes ate the most widely used anode for chlorine production (93). Ruthenium(IV) oxide and other compounds ate used in the electronics industry as resistor material in apphcations where thick-film technology is used to print electrical circuits (94) (see Electronic materials). Ruthenium electroplate has similar properties to those of rhodium, but is much less expensive. Electrolytes used for mthenium electroplating (95) include [Ru2Clg(OH2)2N] Na2[Ru(N02)4(N0)0H] [13859-66-0] and (NH 2P uds(NO)] [13820-58-1], Several photocatalytic cycles that generate... 

Several kinds of conduction mechanisms are operative in ceramic thermistors, resistors, varistors, and chemical sensors. Negative temperature coefficient (NTC) thermistors make use of the semiconducting properties of heavily doped transition metal oxides such as tf-type Fe2 Ty03 and type Ni1 LyO. Thick film resistors are also made from transition-metal oxide solid solutions. Glass-bonded By 2 Pb2yRu207 having the pyrochlore [12174-36-6] structure is typical. 

A noise and nonlinearity of thin and thick film resistors are used as reliability indicators to make a prediction of resistor reliability. The resistor noise is proportional to the current density and this property makes it a valuable characteristic for detecting imperfections and abnormalities. The magnitude of the current noise is dependent upon many inherent properties of the resistor such as resistive material and technology factors as processing, size and shape. In the last decade l/f noise in resistive layers has been studied by many authors. It become evident that occurrence of l/f noise can serve as a measure of the technology standard. A problem which has been left consists in identification of the source of l/f noise. 

The conduction mechanisms in thick-film resistors are very complex and have not yet been well defined. Mechanisms with metallic, semiconductor, and insulator properties have all been identified. High ohmic value resistors tend to have more of the properties associated with semiconductors, whereas low ohmic values tend to have more of the properties associated with conductors ... 

The electrical properties of thin-film resistors are substantially better than thick-film resistors in terms of noise, stability, and precision. 

Ceramic thick films are most often used in applications where their electrical properties are exploited. In these applications, the ceramic thick films usually serve as either insulators, resistors, or capacitors. However, in many of these applications, especially those involving multilayer ceramics made from tape-cast films, the mechanical or thermal properties of the ceramic must also be considered. 

The particle size distribution of a thick-film paste is a compromise between screenability and the properties of the fir film. For screenability, it is desired to have very small particles, but very small particle sizes in thick-film resistors produce parameters that are skewed and not suitable for most circuit applications. Larger particles will obviously be more difficult to screen and may actually block one or more screen openings. 

Thick-film resistors can be processed with a tolerance of about 25%. Laser trimming increases the resistance value. Therefore, a resistor is designed to a lower value than desired and will be trimmed to its target value later on. Besides the resistance value required, the power dissipation density is required to design a thick-film resistor. The power dissipation density (Pdensiiy in mW/mm ) is a paste property, which is specified in the data sheet. It is typically related to a 50% trim cut (maximum allowable trim length) and application on prefired alumina. For a stable resistor, the minimum area Ag is determined by the maximmn circuit power dissipation requirement, as in Equation 9.3 ... 

Taketa, Y., The microstructure of RUO2 thick film resistors and influence of glass particles size on their electrical properties, IEEE Transactions, Vol. CHMT-7, No. 2, June 1984. 

Pike, G.E. and Seager C.H., Electrical properties and conduction mechanism of Ru-based thick film resistors. Journal cf Applied Physics, 48(12), 5152-5169, December 1977. 

G. E. Pike and C. H. Seager, Electrical properties and conduction mechanisms ofRu-based thick-film (cermet) resistors, J. Appl. Phys., Vol. 48, (1977), pp. 5152-68. 

DuPont Electronic Materials Division and Hughes Aircraft introduced the first LTCC materials system at the 1983 ISHM Conference in Philadelphia. DuPont then marketed a complete line of tapes and conductor systems with which to build complete systems. Solderable conductors and screened resistor inks soon followed. The properties of these DuPont materials are shown in Table 1.13. It can be seen that their properties are similar to those of alumina and thick film dielectrics. 

TABLE 8.20 Typical Properties of Thick Film Resistors... 

Statistical loading curve models have been proposed that take into account the segregated nature of thick-film resistors. A systematic microstmcture development study has been conducted by Vest for RuOj model thick-film resistors. Vest proposed a statistical loading curve to explain the sheet resistivity variation as a function of volume fraction of the conductive phase and particle sizes of both the conductive phase and glass. Several theoretical models have heen developed to explain the variation of resistivity as a function of volume fraction of the conductive phase. A comprehensive model to explain the sheet resistivity variation in thick-film resistors in terms of composition and physicochemical properties of powders over the entire resistance range has not heen developed to date. 

S. Vasudevan and A. Shaikh, Structure Property Modeling of Low Ohm Thick Film Resistors, Proc. Inti. Symp. Microelec., Dallas, pp. 685-694, 1993. 

Toshio Inokuma et al., The Microstructure of RUO2 Thick Film Resistors and the Influence of Glass Particle Size on Their Electrical Properties, IEEE Trans. CHMT, vol. 7, no. 2, pp. 166-175,1984. 

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