Steven E. Ready

Additive jet printing of polymer thin-film transistors

Organic thin-film transistors were fabricated by direct patterning of solution-processable semiconductors consisting of either poly(9,9′-dioctyl-fluorene-co-bithiophene) or a regioregular poly(thiophene). Acoustic ink-jet printing was used to deposit the polymeric semiconductor onto patterned metal source-drain contacts. Printed and spin coated transistors performed identically. The regioregular poly(thiophene) exhibited a mobility of 0.1 cm2 V–1 s−1, on-off current ratios of ∼106 and low threshold voltage.

Printing Methods and Materials for Large-Area Electronic Devices

Two digital printing methods for the fabrication of active matrix thin-film transistor (AM-TFT) backplanes for displays are described. A process using printed resists layers, referred to as digital lithography, was used to fabricate arrays of hydrogenated amorphous silicon TFTs. TFTs were also fabricated using a combination of digital lithography to pattern metals and inkjet printing to pattern and deposit a polymeric semiconducting layer. The relative performance of amorphous silicon and polymer TFTs were evaluated. The utility of digital lithographic processing was demonstrated by the fabrication of prototype reflective displays using electrophoretic media.

Hydrogenated amorphous silicon thin-film transistor arrays fabricated by digital lithography

A jet-printed digital-lithographic method, in place of conventional photolithography, was used to fabricate 64 /spl times/ 64 pixel (300 /spl mu/m pitch) matrix addressing thin-film transistor (TFT) arrays. The average hydrogenated amorphous silicon TFT device within an array had a threshold voltage of /spl sim/3.5 V, carrier mobility of 0.7 cm/sup 2//V/spl middot/s, subthreshold slope of 0.76 V/decade, and an on/off ratio of 10/sup 8/.

Digital lithographic processing for large‐area electronics

— A non-contact jet-printed mask-patterning process is described. By combining digital imaging with jet printing, digital lithography was used to pattern a-Si:H-based electronics on glass and plastic substrates in place of conventional photolithography. This digital lithographic process is capable of layer-to-layer registration of ±5 μm using electronic mask files that are directly jet printed onto a surface. Aminimum feature size of 50 μm was used to create 180 × 180 element backplanes having 75-dpi resolution for display and image-sensor applications. By using a secondary mask process, the minimum feature size can be reduced down to ∼15 μm for fabrication of short-channel thin-film transistors. The same process was also used to pattern black-matrix wells in fabricating color-filter top plates in LCD panels.

Ink jet printing devices and circuits

For several years there have been many efforts to employ ink jet technologies in the fabrication of consumer electronics. The potential of displacing large and expensive pieces of electronic fabrication equipment and processes with seemingly appropriately scaled inexpensive alternatives is attractive. However, of course, the devil is in the details. Feature size, accuracy, registration and materials all have sever impacts on design rules, processing, performance and the types of devices appropriate to the technology. Here we present a look at some of the materials and deposition challenges along with solutions developed at PARC. The discussion will include the defining of printed features >5μm with ±1.5μm drop placement and layer to layer alignment accuracy, the materials characteristics of the generally complex functional fluids of interest required for reliable jetting and device performance. Examples of ink jet fabricated integrated circuits, working displays, imagers and RGB color filters for LCD displays will be shared.