Doped polyaniline polymer fuses: Electrically programmable read-only-memory elements
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We demonstrate polymeric electrically programmable read-only-memory elements based on camphorsulfonic-acid–doped polyaniline lines. Their working mechanism relies on irreversible reduction of the electrical conductivity by Joule heating like electrical safety fuses. The heating power is supplied electrically. The critical power required to “blow up” the fuse is strongly reduced by notches. The influence of the notch design can be predicted reasonably well using a simple thermal model. The critical power becomes less than 1 mW for fuses with notches narrower than 2 m. This power can be delivered by organic transistors already at modest voltages, opening the way of integration of these memory elements in all-polymer circuits.
I. INTRODUCTION
Organic electronic integrated circuits have been put forward for low-end, high-volume applications such as smart cards or radio-frequency price and identification tags.1–3 Recently, we reported a technology for fabrication of all-polymer integrated circuits.2,3 In this approach, all device layers are processed from solution by spin-coating and patterned using photolithographic techniques. Electrodes and interconnect lines are made from organic polymer conducting materials, such as polyaniline doped with camphorsulfonic acid (PANI/CSA)1–3 and poly(3,4-ethylenedioxithiophene) stabilized with poly(styrene-4-sulfonic acid).4–6 The technology has been demonstrated with 15-bit mechanically programmable code generators that contain an on-board clock generator, a 5-bit counter, decoder logic, and 15 programming pads.3 The digital code is stored in vertical PANI/CSA-isolator-PANI/CSA capacitors. An intact capacitor represents a Boolean 0, whereas a short-circuited (conducting) capacitor represents a Boolean 1. The data bits can be programmed either during manufacturing through mask design or afterwards by mechanically punching through intact capacitors to make them conducting. Both concepts are undesirable from the user’s point of view, and hence no viable organic programming method exists to date. Here we present an electrically programmable read-only element that fills
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0257 J. Mater. Res., Vol. 19, No. 7, Jul 2004
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this void. The memory can be integrated in a code generator without additional processing steps.
II. EXPERIMENTAL RESULTS
The operation of the memory elements is based on irreversible breakdown of the conductivity of PANI/CSA lines. In Fig. 1, we have plotted as a typical example I-V characteristics of a 200-m-long, 2-m-wide PANI/CSA line. It was made by photochemical patterning of PANI/ CSA films as described previously.3 A four-point probe geometry was used to minimize the effect of contact resistances between probe needles and the PANI/CSA contact pads in the measurements. In the first forward sweep, the current increases linearly with applied voltage. Thus, the line resistance is constant with a sheet resist
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