Patent Application
20090057662
The present invention relates generally to semiconductor devices, and more particularly, to devices where the semiconductive portion is made from nanoparticles and printed using a process that does not involve intense heating.
Conductive traces for electronic circuits and passive devices such as resistors and capacitors have long been formed using printing technology, such as screen printing. More recently, advanced printing techniques have been used to fabricate active devices, such as light emitting diodes and transistors. Printed electronics have historically been pursued utilizing various compositions of organic semiconducting materials, particularly solution-processable variants of conjugated hydrocarbons and aromatic hydrocarbons, such as polythiophenes and pentacene. The need for such materials has been based on the assumption that organic compositions are imperative for solution processability. While solution processes have been widely demonstrated for organic semiconductors, the performance of the semiconductive device, namely field effect mobility, has been shown to be several orders of magnitude lower than desired for applications requiring performance similar to that of amorphous silicon, particularly when moved to a graphic arts print press (where field effect mobility values less than 1 cm2/Vs are found). Although higher mobility values are possible with improved processing, organic semiconductors tend to be p-type, with n-type materials often of lower reliability and/or increased sensitivity to the environment. Inorganic semiconducting materials, including traditional silicon and germanium particles, semiconducting metal oxides (such as ZnO and SnO2) and other semiconductive binary metal chalcogenides (such as CdSe) have high mobility compared to organic semiconducting materials, but are traditionally deposited using high-temperature film growth processes, by means of gas-phase decomposition of precursors in chemical vapor deposition. ZnO semiconductor layers have also been formed by conventional vacuum deposition methods such as ion-beam sputtering, rf sputtering, or pulsed laser deposition. Devices formed using these inorganic semiconducting materials also depend heavily on a select few substrate surfaces and dielectrics (such as very thin and smooth SiO2), very thin semiconducting layers (30 nm or less), and/or high temperature annealing above 600° C. to improve crystallinity. These techniques are also not compatible with modern high speed printing techniques required to produce low cost products. It would be a significant addition to the art if a method to create printed semiconductive devices with inorganic semiconductors could be found that does not require high temperature treatments.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
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 of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method and apparatus components related to semiconductor devices, and in particular, low cost semiconductor devices that contain nanoparticles of the semiconductive element. Accordingly, the apparatus components and methods have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. The term “nanoparticle” as used herein refers to a particle with at least one dimension less than 100 nm.
A low-temperature process for creating a semiconductive device by printing a liquid composition containing semiconducting nanoparticles will now be described. The semiconductive device is formed on a polymeric substrate by printing a composition that contains nanoparticles of inorganic semiconductor suspended in a carrier, using a graphic arts printing method. The printed deposit is then heated to remove substantially all of the carrier from the printed deposit. The low-temperature process does not heat the substrate or the printed deposit above 300° C. The mobility of the resulting semiconductive device is between about 10 cm2/Vs and 200 cm2/Vs. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such semiconductive devices with minimal experimentation.
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The inorganic semiconducting devices and process described in this invention allow for improved electrical performance for non-polymeric semiconductor inks. These modifications allow for improved on/off ratio and improved current carrying capability for device structures using relatively thick printed dielectrics. The modifications also allow for environmental immunity for air or moisture sensitive semiconducting particles. These non-polymeric particle inks enable very high mobility devices, such as field effect transistors, to be fabricated using conventional printing processes.
In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
