Organic (plastic) Transistors Heal Themselves Over Time In A Vacuum

Zurich (Switzerland) - Researchers have found that organic transistors, those made of plastic, often have some form of molecular defects when created. This natural side effect of the manufacturing process can be fixed in many ways, however, by leaving the newly formed circuits in a high vacuum chamber for several days. Many of those defects actually heal themselves, resulting in increased performance and lower power consumption.

Taken from the published synopsis:
"We report on a healing of defects at room temperature in the organic semiconductor pentacene. This peculiar effect is a direct consequence of the weak intermolecular interaction which is characteristic of organic semiconductors. Pentacene thin-film transistors were fabricated and characterized by in situ gated four-terminal measurements. Under high vacuum conditions (base pressure of order 10E-8 mbar), the device performance is found to improve with time.

The effective field-effect mobility increases by as much as a factor of two and mobilities up to 0.45 cm2/Vs were achieved. In addition, the contact resistance decreases by more than an order of magnitude and there is a significant reduction in current hysteresis. Oxygen/nitrogen exposure and annealing experiments show the improvement of the electronic parameters to be driven by a thermally promoted process and not by chemical doping. In order to extract the spectral density of trap states from the transistor characteristics, we have implemented a powerful scheme which allows for a calculation of the trap densities with high accuracy in a straightforward fashion.

We show the performance improvement to be due to a reduction in the density of shallow traps <0.15 eV from the valence band edge, while the energetically deeper traps are essentially unaffected. This work contributes to an understanding of the shallow traps in organic semiconductors and identifies structural point defects within the grains of the polycrystalline thin films as a major cause."

Read more ... arXiv.org, 0711.1457, and download the PDF from that site (upper-right).

Summary
By leaving organic/plastic semiconductors in a vacuum chamber for about a week, many molecular defects heal themselves. Their power consumption is ultimately reduced by half, and their processing speed jumps up. It appears to increase by an undisclosed amount per application, such as some high level construct like an "ADD" operation within the CPU. It does appear to be a fixed, yet undisclosed, percentage increase at a per transistor level.