All-polymer RC filter circuits fabricated with inkjet printing technology
Introduction
The discovery of high conductivity in doped polyacetylene in 1977 [1] has been attracting considerable interests in the application of polymers as the semiconducting and conducting materials, and this made three scientists to win 2000 Nobel Prize in Chemistry. Since then a lot of researchers have been working on the mechanism of polymer conduction and polymer microelectronic devices. The first organic thin film transistor was reported in 1983 [2]. After that, the first all-polymer thin film transistor was fabricated in 1990 [3]. Garnier et al. [4] reported their first all-polymer transistor by screen-printing technology in 1994. By the end of 2000, large-scale and all-polymer integrated circuits [5] and complementary integrated circuits based on organic transistors [6] have also been demonstrated, providing the potential for a cheap alternative to amorphous silicon thin film transistor technology. Organic or polymer semiconductor devices are catching considerable attention due to their potential low cost and easy processing advantages. Within the last decade, the science and technology of conducting polymers have been greatly improved. The conductivity of some conjugated polymers has been made comparable to that of copper [35]. In addition to their potential low-cost feature and processing advantages, the processibility of some commonly used polymers is also increased. It is not surprising that conjugated polymers are of great interest both in industry and academia. They are potentially useful in a number of applications where high speeds are not essential, for example, low-cost memory devices, such as smart cards and electronic luggage tags [7], gas sensors [8], etc.
Being different from their solid-state counterparts, conducting polymers, often referred to as conjugated polymers, have different properties. Most of them have very low mobilities [25]. To date, the application of polymers is limited to low-speed areas. And because the chemical and physical properties are various among different polymers, several techniques have been employed in fabrication of polymer thin films, such as lithography, thermal evaporation, spin coating, dipping coating, printing, layer-by-layer self-assembly, and spraying coating [30], [31], [32], [33], [34].
Compared to various other printing techniques, such as screen-printing [9], [10], [11] and micro-contact printing [12], [13], inkjet printing [14], [15], [23] has caught more and more attention due to its unique characteristics, such as volatility, simplicity, compatibility with a lot of substrates, non-contact patterning and low cost. Inkjet printing has the promise to become a low cost manufacturing process, and has already been used to fabricate all-polymer transistors [14], [15], [16], [17], polymer light emitting diodes [18], [19], [20], and nanoparticle micro-electromechanical systems [21].
In this paper, the all-polymer RC filter circuit with inkjet printing technique is reported. To our knowledge, it is the first report about this kind of passive electronic component and circuit.
Section snippets
Analysis and simulation
Because our devices were made of polymer materials and fabricated by the inkjet printing technique, there are many variables to determine the circuit behaviors upon the outcoming of a realistic device. For example, the thicknesses of the printed polymer thin films are very important to determine the conductivity. Fluctuation in conductivity of thin films will result in unpredictable device characteristics. For RC filters, accurate parameters of resistors and capacitors are essential for
Materials
In order to use an inkjet printer to print out the polymer micro-electric devices, the material must be air-stable and solution processable. Two kinds of conductive polymers, PEDOT doped with PSS (Baytron P® from Bayer Company) and polynaniline (PANI) (from Aldrich company), have been used in the fabrication of devices.
PEDOT, a kind of polythiophene, has caught much attention during the last several years. Its high stability enables it to various applications, such as antistatic and
Experiments
The inkjet printer used in our experiments was the commercially available Epson Stylus color 480 SXU printer with a resolution of 720 by 720 dpi. Fig. 4 shows the structure of the all polymer capacitor and RC filter. First, two layers of PEDOT were printed to act as the bottom electrode. Each layer of PEDOT is heated on a hot plate at 50 °C for 2 min to dry it completely. In our other experiment, it is found that certain minutes of annealing immediately after printing helps make the thin film
Results and discussion
In our measurements, the HP54653A digital oscilloscope made by Hewlett-Packard Corporation was used to record our experimental data. The input signals were square waves generated by a function generator. In order to make the amplitudes of the output compatible with those of the input signals, 10× attenuation in the input amplitudes were employed.
In Fig. 6b, the waveform of the output signal is very similar to that of the input signal at high frequency. In other words, RC is much larger than the
Conclusions
The fabrication of all polymer capacitor and RC circuits has been demonstrated successfully with the all inkjet printing method. This is due to the solution processability and high performance of the conductive polymers, such as PANI and PEDOT/PSS. Theoretical analysis and experiment results show that the RC filter circuits function well. This means that inkjet printing can offer us potential lower cost over lithographic fabrication of micro-electronic devices, and may lead to new applications
Acknowledgements
This work is partially supported by the DARPA and CEnIT seed grant at Louisiana Tech University.
References (35)
- et al.
Sens. Actuators B
(2000) - et al.
Synth. Met.
(1993) - et al.
Synth. Met.
(2002) - et al.
Synth. Met.
(2001) - et al.
Phys. Rev. Lett.
(1977) - et al.
J. Appl. Phys.
(1983) - et al.
Adv. Mater.
(1990) - et al.
Science
(1994) - et al.
Appl. Phys. Lett.
(1998) - et al.
Nature
(2000)