Jet-printed Plastic Transistors

PARC plastic transistors can be jet-printed on flexible substrates and have high mobility, low leakage, and good stability

The flat panel display business is huge and still growing rapidly. However, along with the demand for ever larger display (e.g., the wall-sized TV) comes a big price tag, because large displays are still made by the same expensive photolithography techniques as the diminutive silicon chip.

What's needed: a completely new manufacturing approach that will dramatically lower the cost.

Polymeric, or plastic, semiconductors provide an exciting opportunity to solve the problem. Polymers can be dissolved in a liquid, thus creating a semiconducting ink. This ink can be printed using the same technology that is used in jet-printers that print documents. Printing has a low cost compared to photolithography for manufacturing of electronics because both material deposition and patterning are done simultaneously. Enormous progress has been made in recent years to develop plastic semiconductors that have electronic properties suitable to drive a display. Our collaborators at Xerox Research Center of Canada announced a new polymer in the polythiophene family, which has the best electrical properties of any reported plastic semiconductor and is ready for a printing technique to make devices.

PARC researchers have now succeeded in jet-printing this material and other polymer semiconductors to make transistors. Moreover, the jet-printed transistors made this way match the performance of the same material deposited by conventional spin-coating (which gives an unpatterned film) showing that the jet-printing process does not adversely affect the performance of the device. The transistors have exceptional performance for polymers, and meet all the requirements for addressing displays. Along with a high mobility, they have very low leakage and good stability.

PARC scientists have successfully integrated the jet-printed polymer into a prototype display circuit, in which printing techniques define all the patterns

There is much more involved in the fabrication of a low-cost transistor array than just printing the polymer semiconductor. As with any integrated electronic device, metals and insulators must also be deposited and patterned into a multi-layer structure that has the right electronic circuit and an appropriate physical size. PARC researchers have successfully integrated the jet-printed polymer into a prototype display circuit, in which printing techniques define all the patterns. The electronic properties and physical dimensions meet the needs of flat panel displays, and the complete absence of photolithography promises low cost manufacture. The PARC array design also solves key issues of unwanted interactions between pixels of the display, accurate layer-to-layer alignment, and materials compatibility.

While more development is needed, this breakthrough demonstration at PARC proves that it can be done successfully.