Suspended Conductive Polymer Bridges From Ion Implanted Polymers
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For practical electronic applications, the compatibility with conventional microlithographic processing procedures is required. This paper reports patterning and processing procedures to form small-geometry ion implanted polymer resistors. We also report here bridges of ion implanted conductive polymer films which are suspended from the substrate at the two contact ends (Figure 1). The ability to thermally isolate a film with a large temperature coefficient of resistance (TCR) is of interest for applications such as miniature bolometers and pirani gauges. 1 EXPERIMENT The precursor polymer, poly(styrene-acrylonitrile), PSA, was dissolved in diglyme, filtered through a 0.2 micrometer endpoint filter, and spin coated onto insulating substrates to form films with a thickness of 2000 angstroms. Conductivity was induced in the polymer by ion 2 implantation with 50 KeV nitrogen ions (N+) with a fluence in the range of I x 10)16 ions/cm to I x 1017 ions/cm 2 . Samples for the measurement of resistivity and resistance as a function of temperature were prepared on I" by 3" glass microscope slides. Electrical contact was made to high resistivity films with evaporated gold electrodes and resistance was measured by a two probe method using a Keithley 614 electrometer. A four point probe method was used to measure film resistances less than 10000 ohms. 329
Mat. Res. Soc. Symp. Proc. Vol. 396 e 1996 Materials Research Society
Patterned resistor matrices were prepared by spinning, coating, and baking poly(styrene-acrylonitrile) onto silicon dioxide wafers, which had gold electrodes patterned on them. After implantation, the conducting film was spin coated with Shipley 1470 positive photoresist. The resist was exposed through the appropriate mask in a Tamarack UV exposure system, and the pattern was developed in aqueous basic developer. The pattern was transferred to the implanted film by oxygen reactive ion etching (RIE) through the positive photoresist etch mask. Finally, the photoresist was removed with acetone. The wafer was cut into individual die; the die were bonded and packaged in standard dual in-line packages (DIP). When testing required exposure to the atmosphere, lids were The omitted from the packages. electrical configuration was a sixteenelement resistor array with one common bus line. To make conductive polymer bridges which were suspended between the two electrical contacts, resistors were prepared by the previous technique. The sacrificial layer of oxide underneath each resistor was removed by etching for 80 seconds in 50% HF solution. Following a water rinse and drying in a stream of dry nitrogen, bridges less than 30 jtm long remained suspended, while bridges longer than 30 gim often collapsed due to "stiction." Rinsing with acetone or isopropanol after the water rinse aided in drying and reduced stiction.
Figure 1. Suspended conductive polymer bridges made form ion implanted PSA. Top bridge is 20gtm x 20 jLim, bottom bridge is 30 jtm x 10 jtm. Large rectangular areas to each side of bridge are the gold int
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