Thin metal resistors

Applications Although a wide range of metals can be sputtered, the method is often commercially restricted by the low rate of deposition. Applications include the coating of insulating surfaces, e.g. of crystal vibrators, to render them electrically conducting, and the manufacture of some selenium rectifiers. The micro-electronics industry now makes considerable use of sputtering in the production of thin-film resistors and capacitors . ... 

Thin metal films (e.g., copper films) on insulating materials are employed in remote-controlled resistors. The electrical resistance of such a film can be regulated in both directions, by cathodic growth of the film or by anodic dissolution of the film, leading to a decrease in film thickness. 

Early bolometers used, as thermometers, thermopiles, based on the thermoelectric effect (see Section 9.4) or Golay cells in which the heat absorbed in a thin metal film is transferred to a small volume of gas the resulting pressure increase moves a mirror in an optical amplifier. A historical review of the development of radiation detectors until 1994 can be found in ref. [59,60], The modern history of infrared bolometers starts with the introduction of the carbon resistor, as both bolometer sensor and absorber, by Boyle and Rogers [12], The device had a number of advantages over the Golay cell such as low cost, simplicity and relatively low heat capacity at low temperatures. 

A final alternative for metal patterning is the use of lasers to selectively and accurately etch small metal areas. Lasers are routinely used to trim thin-film resistors (126) they may also be used to repair defects or etch conductor lines by direct ablation in an inert atmosphere (127,129) or by laser-initiated etching in a reactive gas or liquid (128). 

The mixer was made by wet-chemical etching of glass substrates, following a photolithographic step, yielding channels for the fluid flow and for the electrodes. The electrodes (100 Q resistors) were made by an electron-beam evaporation process generating thin metallic films in the etched channels [92], Holes were drilled into the cover plate for inlet and outlet connection. Fusion bonding was used to seal the plates. 

Finally, the thermal stabiUty of the specific resistance of various films is demonstrated in Fig. 18, which shows the behavior of NiWP annealed at 400 °C for 1 h, NiReP annealed at 500 °C for 1 h, and NiMoP annealed at 500 °C for 1 h. The resistance of crystalline NiMoP heat-treated at 500 °C increases with rising temperature, which indicates that the thermal stability of NiMoP with a specific resistance of 147 pQ cm is inferior to that of the other materials. While the resistance of NiWP and NiReP films remains almost constant until about 500 °C, the resistance of NiReP is maintained at a more constant level than that of NiWP. The results shown in Fig. 18 indicate that NiReP containing a large amount of refractory metal (44 at% rhenium) is most suitable for a thin film resistor for use at temperatures below 500 °C, Specific resistance and TCR values of the respective films are listed in Table 7. 

Here we show an example of applying the EFS method to a non-silicon-based pressure sensor to operate at high pressure ranges. The membrane of many high-pressure sensors (Bosch, WIKA) is manufactured of steel, with thin-film metal resistors as a measurement signal pickup (Fig. 4.1.12). 

The sensor s transducer principle combines a membrane, as a mechanical transducer, with thin-film metal resistors forming a Wheatstone bridge, as an electromechanical transducer. The output voltage of the Wheatstone bridge is given by... 

It is fi quently observed that excess l/f noise is related to the microscopic sample structure and to the manufactural technology. This kind of noise is particularly sensitive to the surface and interface defects (Jones 1994). There are manufactural techniques which give small dispersion of the mean characteristic values, such as resistance or currents. On the other hand these devices can exhibit large dispersion ofthe noise characteristics. So, for example, metal thin film resistors have lower l/f noise than granular film resistors made from cermet thick films or carbon resistors. 

The histogram of reliability indicator Cq for ensemble of metallic thin film resistors of resistance 100 kS2 is shown in Fig. 11. The correlation with the normal distribution is given there. 

There are three major classes of palladium-based hydrogen sensors [4], The most popular class of palladium-based sensors is based on palladium resistors. A thin film of palladium deposited between two metal contacts shows a change in conductivity on exposure to hydrogen due to the phase transition in palladium. The palladium field-effect transistors (FETs) or capacitors constitute the second class, wherein the sensor architecture is in a transistor mode or capacitor configuration. The third class of palladium sensors includes optical sensors consisting of a layer of palladium coated on an optically active material that transforms the hydrogen concentration to an optical signal. 

Nevertheless the heat capacity of a carbon resistor was not so low as that of crystalline materials used later. More important, carbon resistors had an excess noise which limited the bolometer performance. In 1961, Low [61] proposed a bolometer which used a heavily doped Ge thermometer with much improved characteristics. This type of bolometer was rapidly applied to infrared astronomy as well also to laboratory spectroscopy. A further step in the development of bolometers came with improvements in the absorber. In the early superconducting bolometer built by Andrews et al. (1942) [62], the absorber was a blackened metal foil glued to the 7A thermometer. Low s original bolometer [61] was coated with black paint and Coron et al. [63] used a metal foil as substrate for the black-painted absorber. A definite improvement is due to J. Clarke, G. I. Hoffer, P. L. Richards [64] who used a thin low heat capacity dielectric substrate for the metal foil and used a bismuth film absorber instead of the black paint. 

Photo-resist technology is widely used for imaging processes in such applications in electronics. If it is wished to produce a metallic pattern of connections between many electronic components (resistors, capacitors, integrated circuits, etc.), this can be done by the selective etching of a thin copper plate deposited on an insulating base. The copper layer is protected by a resist which is a polymer, deposited in such a way that it prevents the attack of the metal by an etching solution which will solubilize only the unprotected, exposed copper (Figure 6.8). 

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