Patent Application
20070089626
This invention relates generally to printed semiconductor devices and more particularly to functional inks and dielectric materials as used therewith.
Methods and apparatus that use such techniques as vacuum deposition to form semiconductor-based devices of various kinds are well known. Such techniques serve well for many purposes and can achieve high reliability, small size, and relative economy when applied in high volume settings. Recently, other techniques are being explored to yield semiconductor-based devices. For example, organic or inorganic semiconductor materials can be provided as a functional ink and used in conjunction with various printing techniques to yield printed semiconductor devices.
Printed semiconductor devices, however, yield considerably different end results and make use of considerably different fabrication techniques than those skilled in the art of semiconductor manufacture are prone to expect. For example, printed semiconductor devices tend to be considerably larger than typical semiconductor devices that are fabricated using more traditional techniques. As other examples, both the materials employed and the deposition techniques utilized are also well outside the norm of prior art expectations.
Due in part to such differences, in many cases existing materials and techniques are not suitable for use and deployment with respect to printed semiconductor devices. Further, in many cases, semiconductor device printing gives rise to challenges and difficulties that are without parallel in prior art practice. For example, one area of concern concerns the nature and quality of a dielectric layer as may be printed between a semiconductor layer and another device layer (or layers) (as when a dielectric layer serves to separate an organic semiconductor layer from a gate electrode and other device electrodes in a printed field effect transistor). Typically suggested polymer gate dielectric layers usually exhibit a relatively low dielectric constant (such as less than 5). This, in turn, can result in relatively low saturation current and therefore require higher device operating voltages. Higher operating voltage requirements can lead to numerous undesired design constraints.
In addition, the thickness of typical current dielectric layers is limited, at least in part, by the size of the filler particles that comprise a part of that dielectric layer. Such particles are normally larger than about 4 microns in diameter. It is also possible for the dielectric layer thickness to be at least partially set by the printing process itself. This relative thickness of the polymer dielectric layer further contributes (along with the aforementioned low dielectric constant) to an undesired low saturation current for a corresponding printed field effect transistor.
The above needs are at least partially met through provision of the functional ink apparatus and method described in the following detailed description, particularly when studied in conjunction with the drawings, wherein:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.
Generally speaking, pursuant to these various embodiments, a functional ink suitable for use as a dielectric layer in a printed semiconductor device comprises a dielectric carrier and a plurality of dielectric particles sized less than about 1,000 nanometers that are disposed within the dielectric carrier. In a preferred approach the dielectric carrier comprises a dielectric resin and the dielectric particles comprise a ferroelectric material (such as, but not limited to, BaTiO3). So provided, this functional ink can be applied to a substrate of choice through a printing technique of choice to thereby provide a resultant printed semiconductor device, such as a field effect transistor, having a dielectric layer comprised of this functional ink.
A corresponding resultant dielectric layer provides numerous advantages. These improvements include reducing the voltage required to operate the corresponding field effect transistor by increasing the saturation drain current. Benefits also include realizing a reduction in the thickness of the corresponding transistor. This functional ink tends to be compatible with numerous printing processes including both contact and non-contact printing and is also compatible with a variety of printing substrates including both substantially rigid and flexible plastic.
These and other benefits will become more evident to those skilled in the art upon making a thorough review and study of the following detailed description.
Referring now to the drawings, and in particular to
This process 100 further provides for the provision 102 of a functional ink comprising, preferably, a dielectric carrier having a plurality of dielectric particles sized less than about 1,000 nanometers disposed therein. (Those skilled in the printing arts are familiar with both graphic inks and so-called functional inks (wherein “ink” is generally understood to comprise a suspension, solution, or dispersant that is presented as a liquid, paste, or powder (such as a toner powder). These functional inks are further typically comprised of metallic, organic, or inorganic materials having any of a variety of shapes (spherical, flakes, fibers, tubes) and sizes ranging, for example, from micron to nanometer. Functional inks find application, for example, in the manufacture of some membrane keypads. Though graphic inks can be employed as appropriate in combination with this process, these inks are more likely, in a preferred embodiment, to comprise a functional ink.)
Referring momentarily to
In an optional though preferred approach, the functional ink 200 may further comprise additional contents 203 such as, but not limited to, one or more dispersants and/or one or more surfactants as are known in the art to aid, for example, in dispersing the dielectric particles 202 throughout the dielectric carrier 201.
The relative quantity of dielectric particles 202 to dielectric carrier 201 can be varied to suit the specific materials employed and/or the specifics of a given application setting. That said, in general, these elements are present in respective quantities such that, following application via printing and subsequent curing, the plurality of dielectric particles 202 will comprise about 60% by volume of the functional ink 200.
Referring again to
Referring now to
A dielectric layer 303 may then be printed over at least a substantial portion of the above-mentioned gate 302 using a functional ink 200 as has been described above.
Additional electrodes 304 and 305 are then again printed and cured using, for example, a copper or silver-based electrically conductive functional ink (such as, for example, DuPont's Ag 5028 with 2% 3610 thinner). These additional electrodes can comprise, for example, a source electrode 304 and a drain electrode 305. A semiconductor material ink, such as but not limited to an organic semiconductor material ink such as various formulations of polythiophene or a polythiophene-based material such as poly(3-hexylthiophene) or an inorganic semiconductor material ink such as SnO2, SnO, ZnO, Ge, Si, GaAs, InAs, InP, SiC, CdSe, and various forms of carbon (including carbon nanotubes), is then printed to provide an area of semiconductor material 306 that bridges a gap between the source electrode 304 and the drain electrode 305.
So configured the resultant dielectric layer will tend to be relatively thin. This, in turn, leads to an increased saturation drain current and a corresponding reduced operating voltage. These teachings are compatible with numerous printing processes and are also compatible with a variety of printing substrates including both substantially rigid substrates and flexible plastic substrates.
Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.
