Organic electronic device having improved homogeneity Number:7,385,572 from the United States Patent and Trademark Office (PTO) owispatent A display for an electronic device may be calibrated and corrected for pixel-to-pixel variations in intensity. Radiation-sensing elements used for the calibration are not incorporated as circuit elements within the pixel circuits and may lie outside the pixels. Waveguides, reflectors, or the like may be used to optically couple the radiation-emitting elements of the pixels to the radiation-sensing elements. The radiation-sensing elements may be part of an apparatus separate from the electronic device or may be embedded within the electronic device. Many different methodologies may be used for correcting intensities to achieve better homogeneity in intensity among the pixels within a display.<H homogeneity, electronic, Organic, electro, 7385572.html, Patent, pto, 7385572

Title: Organic electronic device having improved homogeneity

Abstract: A display for an electronic device may be calibrated and corrected for pixel-to-pixel variations in intensity. Radiation-sensing elements used for the calibration are not incorporated as circuit elements within the pixel circuits and may lie outside the pixels. Waveguides, reflectors, or the like may be used to optically couple the radiation-emitting elements of the pixels to the radiation-sensing elements. The radiation-sensing elements may be part of an apparatus separate from the electronic device or may be embedded within the electronic device. Many different methodologies may be used for correcting intensities to achieve better homogeneity in intensity among the pixels within a display.

Patent Number: 7,385,572 Issued on 06/10/2008 to Yu, et al.

Inventors: Yu; Gang (Santa Barbara, CA), Wang; Jian (Goleta, CA), Zhang; Weixiao (Goleta, CA), Stevenson; Matthew (Santa Maria, CA)
Assignee: E.I du Pont de nemours and company (Wilmington, DE)

Appl. No.: 10/646,306

Filed: August 22, 2003

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60409172	Sep., 2002

Current U.S. Class: 345/76 ; 315/169.3; 345/81; 345/82

Field of Search: 345/36,55-100,204-207 315/169.1,169.3

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Primary Examiner: Lewis; David L.
Attorney, Agent or Firm: Lamming; John H.

Claims

What is claimed is:

1. An electronic device comprises: a first radiation-emitting element lying within a pixel; and a first radiation-sensing element for sensing radiation emitted from the first radiation-emitting element wherein: the first radiation-sensing element lies outside the pixel; the radiation-sensing element is part of a calibrating system; and the radiation-sensing element is not part of a radiation-emitting circuit; and the radiation-sensing element is located outside the projected area containing the radiation-emitting element.

2. The electronic device of claim 1, wherein the first radiation-sensing element lies at a location selected from: between the first radiation-emitting element and the user side of the electronic device; and farther from the user side of the electronic device compared to the first radiation-emitting element.

3. The electronic device of claim 1, further comprising a waveguide, wherein the waveguide optically couples the first radiation-emitting element to the first radiation-sensing element.

4. The electronic device of claim 3, wherein the waveguide lies at a location selected from: between the first radiation-emitting element and the user side of the electronic device; and farther from the user side of the electronic device compared to the first radiation-emitting element.

5. The electronic device of claim 3, wherein: the electronic device includes a plurality of radiation-emitting elements, including the first radiation-emitting element, within an array; the array has an array edge; the waveguide has a waveguide edge adjacent to the array edge; and the first radiation-sensing element is connected to the waveguide edge.

6. The electronic device of claim 3, wherein: the electronic device includes a plurality of radiation-emitting elements, including the first radiation-emitting element, within an array; the array has array edges; the waveguide has waveguide edges adjacent to the array edges; and a plurality of radiation-sensing elements, including the first radiation-sensing element, is connected to the waveguide edges.

7. The electronic device of claim 1, wherein the first radiation-emitting element is not electrically connected to the first radiation-sensing element.

8. The electronic device of claim 1, wherein the first radiation-emitting element is not electrically coupled to the first radiation-sensing element.

9. An electronic device comprises: a first radiation-emitting element; a waveguide; and a first radiation-sensing element, wherein: the waveguide optically couples the first radiation-emitting element to the first radiation-sensing element; the radiation-sensing element is not part of a radiation-emitting circuit; and the radiation-sensing element is part of a calibrating system; and the radiation-sensing element is located outside the projected area containing the radiation-emitting element.

10. The electronic device of claim 9, wherein the waveguide lies at a location selected from: between the first radiation-sensing element and the user side of the electronic device; and farther from the user side of the electronic device compared to the first radiation-sensing element.

11. The electronic device of claim 9, wherein: the electronic device includes a plurality of radiation-emitting elements, including the first radiation-emitting element within an array; the array has an array edge; the waveguide has a waveguide edge adjacent to the array edge; and the first radiation-sensing element is connected to the waveguide edge.

12. The electronic device of claim 9, wherein: the electronic device includes a plurality of radiation-emitting elements, including the first radiation-emitting element, within an array; the array has array edges; the waveguide has waveguide edges adjacent to the array edges; and a plurality of radiation-sensing elements, including the first radiation-sensing element, is connected to the waveguide edges.

13. The electronic device of claim 9, wherein the first radiation-emitting element comprises a transparent anode and a transparent cathode.

Description

FIELD OF THE INVENTION

This invention relates in general to electronic devices, and more particularly, to organic electronic devices comprising an array having radiation-emitting elements and methods of using them.

DESCRIPTION OF THE RELATED ART

Organic light-emitting diode and polymeric light-emitting diode (collectively, "OLED") technologies may be used for next generation flat-panel displays. An OLED device can be operated under constant current conditions. However, two lifetime effects are seen with OLEDs: (1) drift of electric characteristics and (2) intensity decrease.

One manifestation of lifetime effects for OLED technologies is related to extended operation of a stationary image that results in a burned-in pattern on the display, which reduces display quality considerably. The burned-in pattern corresponds to pixels having lower intensity emission when all pixels are operating at the same current because those burned-in pixels have been on disproportionately longer than other pixels in the display. Human eyes are extremely sensitive to light intensity variation, and therefore, variation of light intensity among pixels should be minimized. For example, an intensity variation of two percent translates to correct registration of 50 gray levels, which is close to 6-bit (i.e., 2.sup.6 or 64) digital grayscale. Note that uniformly increasing the current to all pixels to account for the overall intensity decrease does not address intensity differences among pixels in the same array.

Two approaches can be used to reduce the effects of burned-in image retention: (1) developing OLEDs with longer lifetimes (both light intensity and current-voltage stabilities) or (2) implementing a compensation mechanism in the display panel (e.g., pixel driver) or in peripheral driving electronics to drive each display pixel in a calibrated fashion that tries to maintain the display intensity homogeneity over the entire panel area. The former may require the development of new materials and is outside the scope of this specification. However, the latter may be accomplished with new circuitry.

One attempt to solve the problem includes a compensation approach that includes a series of amplifiers in parallel with the data driver (see, e.g., U.S. Patent Application Publication No. 2002/0030647). By probing the pixel current decay under a given voltage, the operation voltage of each pixel may be adjusted to its original current level. However, no compensation is provided for the intensity decrease related to constant current driving.

Another attempt to solve the problem, a photosensor thin-film transistor is incorporated into each pixel and detects the light being emitted at that pixel (see, e.g., U.S. Patent Application Publications No. 2001/0052597 and 2001/0055008). An electro-optic feedback system is created that can compensate for display intensity variation and degradation. However, the circuitry used for the OLED device is changed and may cause other complications. For example, the additional circuit element(s) within the pixel circuit may require a larger device, which is undesired.

In yet another attempt to solve the problem, a correction circuit using a current sensor or a photosensor may be used to adjust the voltage supplied to each display pixel to compensate for deterioration with time of the light output of each pixel (see, e.g., PCT Application Publication No. WO 98/40871). Similar to the photosensor thin-film transistor, the pixel circuit is changed and may cause other complications. For example, the additional circuit element(s) may require a larger device, which is undesired.

SUMMARY OF THE INVENTION

A display for an electronic device may be calibrated and corrected for pixel-to-pixel variations in intensity. Radiation-sensing elements used for the calibration are not incorporated as circuit elements within the pixel circuits and may lie outside the pixels. Waveguides, reflectors, or the like may be used to optically couple the radiation-emitting elements of the pixels to the radiation-sensing elements. The radiation-sensing elements may be part of an apparatus separate from the electronic device or may be embedded within the electronic device.

Many different methodologies may be used for correcting intensities to achieve better homogeneity in intensity among the pixels within a display. Using correction schemes of the invention, intensities of radiation emitted from nearby pixels in a display can be corrected to be within a range of approximately four percent of one another.

In one set of embodiments, an electronic device can comprise a first circuit comprising a radiation-emitting circuit element, and a second circuit comprising a radiation-sensing circuit element. The radiation-sensing element may not be part of the first circuit.

In another set of embodiments, an electronic device can comprise a radiation-emitting element lying within a pixel, and a radiation-sensing element for sensing radiation emitted from the radiation-emitting element. The radiation-sensing element may lie outside the pixel.

In still another set of embodiments, an electronic device can comprise a radiation-emitting element, a waveguide, and a radiation-sensing element. The waveguide can optically couple the radiation-emitting element to the radiation-sensing element.

In a further set of embodiments, a method of using an electronic device can comprise placing a radiation-sensing apparatus adjacent to a user side of the electronic device and activating radiation-emitting elements within an array. The method can also comprise measuring intensities of radiation emitted from the radiation-emitting elements. Measuring may be performed using the radiation-sensing apparatus. The method can further comprise removing the radiation-sensing apparatus away from the user side of the electronic device after measuring.

In still a further set of embodiments, a method of using an electronic device can comprise placing a reflector adjacent to a user side of the electronic device and activating radiation-emitting elements within an array. The method can also comprise measuring intensities of radiation emitted from the radiation-emitting elements. Measuring can be performed while the reflector is located adjacent to the user side of the electronic device. The method can further comprise removing the reflector away from the user side of the electronic device after measuring.

In yet another set of embodiments, a method of using an electronic device can comprise activating radiation-emitting elements within an array and measuring intensities of radiation emitted from the radiation-emitting elements during a most recent state. The method can also comprise determining correction factors for the radiation-emitting elements. The correction factor for a specific radiation-emitting element may be a function of (1) a change in intensity between a prior state and the most recent state of the specific radiation-emitting element, (2) a maximum change in intensity between the prior state and the most recent state of any radiation-emitting element in the array, (3) a maximum intensity of any radiation-emitting element in the array during the prior state, and (4) a minimum intensity of any radiation-emitting element in the array during the most recent state.

In another set of embodiments, a method of using an electronic device can comprise activating radiation-emitting elements within an array and measuring a calibration signal for the radiation-emitting elements during a most recent state. The method can also include determining correction factors for the radiation-emitting elements. The correction factor for a specific radiation-emitting element can be a function of the calibration signal. The method can further comprise determining data signals for the radiation-emitting elements. For each radiation-emitting element, the data signal can be a function of an input signal and the correction factor.

The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example and not limitation in the accompanying figures.

FIG. 1 includes a cross-sectional view of a portion of a radiation-emitting element.

FIG. 2 includes a schematic diagram of an active-matrix OLED.

FIG. 3 includes a schematic diagram of an alternative active-matrix OLED.

FIG. 4 includes a schematic diagram of a full-color active-matrix pixel.

FIG. 5 includes an illustration of a cross-sectional view of portions of an array of pixels and a radiation-sensing element.

FIG. 6 includes an illustration of a cross-sectional view of portions of an array of pixels, a radiation-sensing element, and a waveguide.

FIG. 7 includes an illustration of a cross-sectional view of portion of an electronic device that comprises an array of pixels, a waveguide, and a photodetector.

FIGS. 8 and 9 include illustrations of a cross-sectional view and a plan view, respectively, of portions of an electronic device that comprises an array of pixels, a waveguide, and photodetectors along edges of the waveguide.

FIG. 10 includes an illustration of a cross-sectional view of portions of a waveguide and an electronic device that comprises an array of pixels and photodiodes near the edges of the array.

FIG. 11 includes an illustration of a cross-sectional view of portions of a reflector and an electronic device that comprises an array of pixels and a buried photodetector.

FIG. 12 includes an illustration of a display after an initial-state calibration.

FIG. 13 includes an illustration of the display of FIG. 12 after images have been burned into the display.

FIG. 14 includes an illustration of the display of FIG. 12 after a most recent calibration performed to correct for the burned-in image seen in FIG. 13.

FIG. 15 includes an illustration of a hybrid cross-sectional view of a radiation-sensing apparatus, an electronic device being calibrated, and a process flow chart during a calibration operation.

FIG. 16 includes an illustration of a hybrid cross-sectional view of an electronic device after calibrating and a process flow chart during a regular operation of the electronic device.

Skilled artisans 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 invention.

DETAILED DESCRIPTION

Reference is now made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts (elements).

A display for an electronic device may be calibrated and corrected for pixel-to-pixel variations in intensity. Radiation-sensing elements used for the calibration are not incorporated as circuit elements within the pixel circuits and may lie outside the pixels. Waveguides, reflectors, or the like may be used to optically couple the radiation-emitting elements of the pixels to the radiation-sensing elements. The radiation-sensing elements may be part of an apparatus separate from the electronic device or may be embedded within the electronic device. Many different methodologies may be used for correcting intensities to achieve better homogeneity in intensity among the pixels within a display.

Before addressing details of embodiments described below, some terms are defined or clarified. As used herein, the terms "array," "peripheral circuitry" and "remote circuitry" are intended to mean different areas or components. For example, an array may include a number of pixels, cells, or other electronic devices within an orderly arrangement (usually designated by columns and rows) within a component. These electronic devices may be controlled locally on the component by peripheral circuitry, which may lie within the same component as the array but outside the array itself. Examples of peripheral circuits include column or row decoders, column or row array strobes, or the like. Remote circuitry typically lies within a different component and can send signals to or receive signals from the array (typically via the peripheral circuitry).

The term "circuit" is intended to mean a collection of circuit elements that collectively, when supplied the proper signal(s), perform a function. A circuit may include an active matrix pixel within an array of a display, a column or row decoder, a column or row array strobe, a sense amplifier, a signal or data driver, or the like. For the purposes of this specification, signal generators and power supplies that have signals sent to circuit elements may not be considered part of a circuit. For example, a data driver used to provide data to a pixel is not part of the pixel circuit, although the data driver has its own circuit. Likewise, a row array strobe used to activate a select (scan) line for a pixel is not part of the pixel circuit.

The term "circuit element" is intended to mean a lowest level unit of circuit that performs an electrical function. A circuit element may include a transistor, a diode, a resistor, a capacitor, or the like. A circuit element does not include parasitic resistance (e.g., resistance of a wire) or parasitic capacitance (e.g., capacitive coupling between two conductors connected to different circuit elements where a capacitor between the conductors is unintended or incidental).

The term "control electrode" is intended to mean an electrode used to control a transistor. In a field-effect transistor (e.g., junction field-effect transistor, metal-insulator-semiconductor field-effect transistor, etc.), the gate or gate electrode is the control electrode. In a bipolar transistor, the base or base region is the control electrode.

The term "coupled" is intended to mean a connection, linking, or association of two or more circuit elements, circuits, or systems in such a way that a potential or signal information may be transferred from one to another. Non-limiting examples of "coupled" can include direct connections between circuit elements, circuit elements with switch(es) (e.g., transistor(s)) connected between them, or the like.

The term "current-carrying electrode" is intended to mean an electrode used to carrying a current to or from a transistor. In a field-effect transistor (e.g., junction field-effect transistor, metal-insulator-semiconductor field-effect transistor, etc.), the source and drain (source region and drain region) are the current-carrying electrodes. In a bipolar transistor, the collector and emitter (collector region and emitter region) are the current-carrying electrodes.

The term "electron withdrawing" is synonymous with "hole injecting." Literally, holes represent a lack of electrons and are typically formed by removing electrons, thereby creating an illusion that positive charge carriers, called holes, are being created or injected. The holes migrate by a shift of electrons, so that an area with a lack of electrons is filled with electrons from an adjacent layer, which give the appearance that the holes are moving to that adjacent area. For simplicity, the terms holes, hole injecting, and their variants will be used.

The term "elevation" is intended to mean a plane substantially parallel to a reference plane. For electronic devices, the reference plane is typically the primary surface of a substrate. Elevations are typically used to note a distances from the primary surface.

The term "essentially X" is used to mean that the composition of a material is mainly X but may also contain other ingredients that do not detrimentally affect the functional properties of that material to a degree at which the material can no longer perform its intended purpose.

The term "low work function material" is intended to mean a material having a work function no greater than about 4.4 eV. The term "high work function material" is intended to mean a material having a work function of at least approximately 4.4 eV.

The term "pixel" is intended to mean the smallest complete unit of a display as observed by a user of the display. The term "subpixel" is intended to mean a portion of a pixel that makes up only a part, but not all, of a pixel. In a full-color display, a full-color pixel can comprise three sub-pixels with primary colors in red, green and blue spectral regions. A desired color can be obtained by combining the three primary colors with different intensities (gray levels). For instance, with 8-bit (256 level) gray levels for each sub-pixel, one can achieve 8.sup.3 or approximately 16.7 million color combinations. However, a red monochromatic display may only include red light-emitting elements. In the red monochromatic display, each red light-emitting element resides in a pixel. No subpixels are needed. Therefore, whether a light-emitting element is a pixel or subpixel depends on the application in which it is used.

The term "nearby pixels" is intended to refer to a relationship between a first pixel and the surrounding pixels in the plane of a display matrix. Nearby pixels are those that are approximately within a 25.times.25 pixel matrix wherein the first pixel is located at the center of the matrix.

The term "primary surface" is intended to mean a surface of a substrate from which an electronic device is subsequently formed.

The term "state" is intended to refer to information used for calibration factors at a point in time. For example, the first time an electronic device is calibrated may be an initial state. The second time the electronic device is calibrated may be the most recent state until the next calibration, and the initial state is now the prior state. A third calibration may include data collected for a most recent state, and information collected during the second calibration may now be the prior state.

The term "user side" of an electronic device refers to a side of the electronic device adjacent to a transparent electrode and principally used during normal operation of the electronic device. In the case of a display, the side of the electronic device having the display would be a user side. In the case of a detector or voltaic cell, the user side would be the side that principally receives radiation that is to be detected or converted to electrical energy.

The term "organic electronic device" is intended to mean a device including one or more semiconductor layers or materials. Organic electronic devices include: (1) devices that convert electrical energy into radiation (e.g., a light-emitting diode, light-emitting diode display, or diode laser), (2) devices that detect signals through electronics processes (e.g., photodetectors (e.g., photoconductive cells, photoresistors, photoswitches, phototransistors, phototubes), IR detectors), (3) devices that convert radiation into electrical energy (e.g., a photovoltaic device or solar cell), and (4) devices that include one or more electronic components that include one or more organic semi-conductor layers (e.g., a transistor or diode).

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, process, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but may include other elements not expressly listed or inherent to such method, process, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, use of the "a" or "an" are employed to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Group numbers corresponding to columns within the periodic table of the elements use the "New Notation" convention as seen in the CRC Handbook of Chemistry and Physics, 81.sup.st Edition (2000).

To the extent not described herein, many details regarding specific materials, processing acts, and circuits are conventional and may be found in textbooks and other sources within the organic light-emitting display, photodetector, semiconductor and microelectronic circuit arts. Details regarding radiation-emitting elements, pixels, subpixels, and pixel and subpixel circuitry will be addressed before turning to details of the radiation-sensing elements and circuitry.

FIG. 1 includes an illustration of a cross-sectional view of a radiation-emitting element 100 that can be used in electronic devices described herein. The radiation-emitting element 100 is typically a light-emitting element that has an emission maximum within the visible light spectrum (wavelengths in a range of 400-700 nm). As shown in FIG. 1, the radiation-emitting element can comprise an anode layer 110, a cathode layer 150, and an active layer 130. Adjacent to the anode layer 110 is an optional hole-injecting/transport layer 120, and adjacent to the cathode layer 150 is an optional electron-injection/transport layer 140. Layers 120 and 140 are examples of charge transport layers.

The radiation-emitting element 100 may be part of an electronic device and may be formed over a support or substrate (not shown) adjacent to the anode layer 110 or the cathode layer 150. Most frequently, the support is adjacent the anode layer 110. The support can be flexible or rigid, organic or inorganic. Generally, glass or flexible organic films are used as a support. The anode layer 110 is an electrode that is more efficient for injecting holes compared to the cathode layer 150. The anode can include materials containing a metal, mixed metal, alloy, metal oxide or mixed-metal oxide. Suitable metal elements within the anode layer 110 can include the Groups 4, 5, 6, and 8-11 transition metals. If the anode layer 110 is to be light transmitting, mixed-metal oxides of Groups 12, 13 and 14 metals, such as indium-tin-oxide, may be used. Some non-limiting, specific examples of materials for anode layer 110 include indium-tin-oxide ("ITO"), aluminum-tin-oxide, gold, silver, copper, nickel, and selenium.

The anode layer 110 may be formed by a chemical or physical vapor deposition process or spin-cast process. Chemical vapor deposition may be performed as a plasma-enhanced chemical vapor deposition ("PECVD") or metal organic chemical vapor deposition ("MOCVD"). Physical vapor deposition can include all forms of sputtering (e.g., ion beam sputtering), e-beam evaporation, and resistance evaporation. Specific forms of physical vapor deposition include rf magnetron sputtering or inductively-coupled plasma physical vapor deposition ("ICP-PVD"). These deposition techniques are well known within the semiconductor fabrication arts.

A hole-transport layer 120 may be adjacent the anode. Both hole transporting small molecule compounds and polymers can be used. Commonly used hole transporting molecules, in addition to N,N'-diphenyl-N,N'-bis (3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD) and bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP), include: 1,1-bis[(di-4-tolylamino) phenyl]cyclohexane (TAPC); N,N'-bis(4-methylphenyl)-N,N'-bis (4-ethylphenyl)-[1,1'-(3,3'-dimethyl)biphenyl]-4,4'-diamine (ETPD); tetrakis-(3-methylphenyl)-N,N,N',N'-2,5-phenylenediamine (PDA); a-phenyl-4-N,N-diphenylaminostyrene (TPS); p-(diethylamino)benzaldehyde diphenylhydrazone (DEH); triphenylamine (TPA); 1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline (PPR or DEASP); 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB); N,N,N',N'-tetrakis(4-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TTB); and porphyrinic compounds, such as copper phthalocyanine. Commonly used hole transporting polymers are polyvinylcarbazole, (phenylmethyl)polysilane, poly(3,4-ethylendioxythiophene) (PEDOT), and polyaniline. Hole-transporting polymers can be obtained by doping hole-transporting molecules such as those mentioned above into polymers, such as polystyrene and polycarbonate.

The hole-injection/transport layer 120 can be formed using any conventional means, including spin-coating, casting, and printing, such as gravure printing. The layer can also be applied by ink jet printing, thermal patterning, or chemical or physical vapor deposition.

Usually, the anode layer 110 and the hole-injection/transport layer 110 are patterned during the same lithographic operation. The pattern may vary as desired. The layers can be formed in a pattern by, for example, positioning a patterned mask or resist on the first flexible composite barrier structure prior to applying the first electrical contact layer material. Alternatively, the layers can be applied as an overall layer (also called blanket deposit) and subsequently patterned using, for example, a patterned resist layer and wet-chemical or dry-etching techniques. Other processes for patterning that are well known in the art can also be used. When the electronic devices are located within an array, the anode layer 110 and hole injection/transport layer 110 typically are formed into substantially parallel strips having lengths that extend in substantially the same direction.

The organic active layer 130 can comprise small molecule materials or polymeric materials. Small molecule materials may include those described in, for example, U.S. Pat. No. 4,356,429 ("Tang") and U.S. Pat. No. 4,539,507 ("Van Slyke"), the relevant portions of which are incorporated herein by reference. Alternatively, polymeric materials may include those described in U.S. Pat. No. 5,247,190 ("Friend"), U.S. Pat. No. 5,408,109 ("Heeger"), and U.S. Pat. No. 5,317,169 ("Nakano"), the relevant portions of which are incorporated herein by reference. Exemplary materials are semiconductive conjugated polymers. An example of such a polymer is poly (phenylenevinylene) referred to as "PPV." The light-emitting materials may be dispersed in a matrix of another material, with and without additives, but typically form a layer alone. The organic active layer 130 may comprise a semiconductive conjugated polymers and electro- and photo-luminescent materials. Specific examples include, but are not limited to, poly(2-methoxy,5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene) ("MEH-PPV") and MEH-PPV composites with CN-PPV.

An organic active layer 130 containing the organic active material can be applied from solution using a conventional means, including spin-coating, casting, and printing. The organic active materials can be applied directly by vapor deposition processes, depending upon the nature of the materials. An active polymer precursor can be applied and then converted to the polymer, typically by heating.

Optional layer 140 can function both to facilitate electron injection/transport, and also serve as a buffer layer or confinement layer to prevent quenching reactions at layer interfaces. More specifically, layer 140 may promote electron mobility and reduce the likelihood of a quenching reaction if layers 130 and 150 would otherwise be in direct contact. Examples of materials for optional layer 140 include metal-chelated oxinoid compounds (e.g., Alq.sub.3 or the like); phenanthroline-based compounds (e.g., 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ("DDPA"), 4,7-diphenyl-1,10-phenanthroline ("DPA"), or the like); azole compounds (e.g., 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole ("PBD" or the like), 3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole ("TAZ" or the like); other similar compounds; or any one or more combinations thereof. Alternatively, optional layer 140 may be inorganic and comprise BaO, LiF, Li.sub.2O, or the like.

The electron injection/transport layer 140 can be formed using any conventional means, including spin-coating, casting, and printing, such as gravure printing. The layer can also be applied by ink jet printing, thermal patterning, or chemical or physical vapor deposition.

The cathode layer 150 is an electrode that is particularly efficient for injecting electrons or negative charge carriers. The cathode layer 150 can be any metal or nonmetal having a lower work function than the first electrical contact layer (in this case, the anode layer 110). Materials for the second electrical contact layer can be selected from alkali metals of Group 1 (e.g., Li, Na, K, Rb, Cs,), the Group 2 (alkaline earth) metals, the Group 12 metals, the rare earths, the lanthanides (e.g., Ce, Sm, Eu, or the like), and the actinides. Materials, such as aluminum, indium, calcium, barium, yttrium, and magnesium, and combinations thereof, may also be used. Li-containing organometallic compounds, LiF, and Li.sub.2O can also be deposited between the organic layer and the cathode layer to lower the operating voltage. Specific non-limiting examples of materials for the cathode layer 150 include barium, lithium, cerium, cesium, europium, rubidium, yttrium, magnesium, or samarium.

The cathode layer 150 is usually formed by a chemical or physical vapor deposition process. The cathode layer can be patterned, as discussed above in reference to the anode layer 110 and optional hole-injecting layer 120. If the device lies within an array, the cathode layer 150 may be patterned into substantially parallel strips, where the lengths of the cathode layer strips extend in substantially the same direction and substantially perpendicular to the lengths of the anode layer strips. Electronic elements called radiation-emitting elements are formed at the cross points (where an anode layer strip intersects a cathode layer strip when the array is seen from a plan or top view). Alternatively, in the case of an active matrix display, the cathode layer can be an unpatterned common cathode layer that covers the entire pixel array. In this case, it is the patterned anode layer that defines the location and boundary of individual radiation-emitting elements.

In other embodiments, additional layer(s) may be present within organic electronic devices. For example, a layer (not shown) between the hole-injecting layer 120 and the active layer 130 may facilitate positive charge transport, band-gap matching of the layers, function as a protective layer, or the like. Similarly, additional layers (not shown) between the electron-injecting layer 140 and the cathode layer 150 may facilitate negative charge transport, band-gap matching between the layers, function as a protective layer, or the like. Layers that are known in the art can be used. Some or all of the layers may be surface treated to increase charge carrier transport efficiency. The choice of materials for each of the component layers may be determined by balancing the goals of providing a device with high device efficiency with the cost of manufacturing, manufacturing complexities, or potentially other factors.

Each functional layer may be made up of more than one layer. For example, the cathode layer may comprise a layer of a Group 1 metal and a layer of aluminum. The Group 1 metal may lie closer to the active layer 130, and the aluminum may help to protect the Group 1 metal from environmental contaminants, such as water.

Although not meant to limit, the different layers may have the following range of thicknesses: inorganic anode layer 110, usually no greater than approximately 500 nm, for example, approximately 50-200 nm; optional hole-injecting layer 120, usually no greater than approximately 100 nm, for example, approximately 50-200 nm; active layer 130, usually no greater than approximately 100 nm, for example, approximately 10-80 nm; optional electron-injecting layer 140, usually no greater than approximately 100 nm, for example, approximately 10-80 nm; and cathode layer 150, usually no greater than approximately 1000 nm, for example, approximately 30-500 nm. If the anode layer 110 or the cathode layer 150 needs to transmit at least some light, the thickness of such layer may not exceed approximately 100 nm.

In the radiation-emitting element 100, electrons and holes, injected from the cathode 150 and anode 110 layers, respectively, into the photoactive layer 130, form negative and positively charged polarons in the active layer 130. These polarons migrate under the influence of the applied electric field, forming a polaron exciton with an oppositely charged species and subsequently undergoing radiative recombination. A sufficient potential difference between the anode and cathode, usually less than approximately 20 volts, and in some instances no greater than approximately 5 volts, may be applied to the radiation-emitting element. The actual potential difference may depend on the use of the radiation-emitting element in a larger electronic component. In many embodiments, the anode layer 110 is biased to a positive voltage and the cathode layer 150 is at substantially ground potential or zero volts during the operation of the electronic device. In another embodiment, the cathode layer 150 may be biased using a negative potential.

The radiation-emitting element 100 may be part of a passive matrix or array or an active matrix or array. For a passive matrix, the radiation-emitting element 100 may be the pixel circuit. FIGS. 2 and 3 show exemplary pixel circuits for an electronic device with an active matrix display. After reading this specification, skilled artisans appreciate that many other pixels circuits may be used. When a pixel has one radiation-emitting element, the pixel may be used for a monochromatic display.

In FIG. 2, each pixel includes an n-channel transistor 222, a capacitor 226, a p-channel transistor 224, and the radiation-emitting element 100. The source of the n-channel transistor 222 is connected to the data line 202. The drain of the n-channel transistor 222 is connected to an electrode of the capacitor 226 and the gate of the p-channel transistor 224. The other electrode of the capacitor 224 is connected to the source of the p-channel transistor 224 and the Vdd line 206. The drain of the p-channel transistor 224 is connected to the anode of the light-emitting element 100. The cathode of the light-emitting element 100 is connected to the Vss line 208. All circuit elements in FIG. 2 except for the light-emitting element 100 form the pixel driver for that pixel circuit.

FIG. 3 is similar to FIG. 2 with a few exceptions. The p-channel transistor 224 is replaced by a second n-channel transistor 324. The other electrode for capacitor 226 is connected to the source of the second n-channel transistor 324 and the Vss line 208 instead of the Vdd line 206. The radiation-emitting element 100 has its anode connected to the Vdd line 206 and its cathode to the drain of the second n-channel transistor 324.

Either type of pixel circuit shown in FIG. 2 or 3 may be used in a full-color display. FIG. 4 includes a pixel 400 that includes a red subpixel 42, a green subpixel 44, and a blue subpixel 46. Each subpixel includes a light-emitting element (420, 440, 460) and a subpixel driver (422, 442, 462). Each of the subpixel drivers has the pixel driver circuit as described with respect to FIG. 2. Each of the subpixels (42, 44, 46) is connected to a common select (scan) line 410, a data line (424, 444, 4646), a Vdd line (426, 446, 466), and a Vss line (428, 448, 468). The potentials for the Vdd lines 426, 446, and 466 may be the same or different for the subpixels 42, 44, and 46. Similarly, the potentials for the Vss lines 428, 448, and 468 may be the same or different for the subpixels 42, 44, and 46. In an alternative embodiment, the pixel circuit 300 as shown in FIG. 3 could be used as a building block for the subpixel circuit. In that embodiment, the light-emitting element for a subpixel would lie between the Vdd line and subpixel driver for that subpixel.

As used in the subsequent figures, any of the pixels described in FIGS. 2-4 may be used. Each of the pixels will be represented by a block to simplify understanding of the embodiments described herein. In a display, the pixels can lie within an array. A two-dimensional array or matrix may be used to communicate information to a user of an electronic device. A focus of this specification is to improve homogeneity between radiation-emitting elements within an array without changing the pixel or subpixel circuit.

FIGS. 5-11 include illustrations of electronic devices and radiation-sensing elements used for calibrating displays of those devices. Calibrating systems may include radiation-sensing elements, waveguides, reflectors, or any combination thereof. The radiation-sensing elements, waveguides, reflectors, or any combination thereof may be part of a separate apparatus or embedded within the electronic device. The calibrating systems are better understood as described in more detail in FIGS. 5 through 11.

FIG. 5 includes an illustration of a cross-sectional view of a calibrating system that includes an electronic device 50 and a separate radiation-sensing element, such as photosensor 52. The electronic device can include a passivation layer or protective shield 502 and an array that is oriented in rows and columns of pixels 504. Each of the pixels 504 can emit radiation as illustrated by arrows 508 in FIG. 5. Dashed lines 506 represent edges of the array. A substrate 505 overlies the protective shield 502 and pixels 504. The protective shield 502 can protect the pixels 504 and other electronic circuits, if any, from environmental hazards or other conditions (e.g., scratches, moisture, mobile ions, other contamination, or the like). The electronic device 50 has a user side 500. Note that the radiation-emitting element 100 as illustrated in FIG. 1 may be oriented such that radiation can emit through the anode layer 110 and be seen by a user of the electronic device 50.

The photosensor 52 may be placed in contact with or otherwise adjacent to the user side 500. Notice that the photosensor 52 may be the same size or larger than the array because its edges 522 extend beyond the edges 506 of the array. The photosensor 52 may be a conventional photodiode or photosensitive transistor that may include a p-n junction. Although not shown, electrical connections and a sense amplifier may be connected to the photodiode. During calibration, typically one pixel 504 at a time will be activated with its light intensity measured by the radiation-sensing element, which is shown as photosensor 52 in FIG. 5.

FIG. 6 includes an illustration of a cross-sectional view of an alternative calibrating system. The apparatus 60 can be used to measure the intensity of radiation 508 from the pixels 504. Similar to FIG. 5, the apparatus 60 may be placed in contact with or otherwise adjacent to the user side 500 of the electronic device 50. In this embodiment, the apparatus 60 may include a photosensor 62 and a waveguide 64. The edges 642 of the waveguide 64 are adjacent to and extend beyond the edges 506 of the array. The waveguide 642 can include a material of relatively higher refractive index surrounded by a material of relatively lower refractive index. In one example, a quartz (i.e., silicon dioxide) block having a refractive index of approximately 1.45 may be surrounded by air having a refractive index of approximately 1.0. Alternatively, a block of silicon nitride (refractive index of approximate 2.0), polyethylene napthalate (refractive index in a range of approximately 1.65-1.90), polyimide (refractive index of approximately 1.5-1.7), or other materials could be used. Note that the refractive indices may vary depending on the composition of the material (including crystalinity or lack thereof) and the wavelength of radiation. The numbers for refractive indices are given to illustrate the general construction of a waveguide. The photosensor 62 is connected to one of the edges 642 of the waveguide 64. The waveguide 64 optically couples the pixels 504, each having a radiation-emitting element, to the radiation-sensing element 62. Similar to the system shown in FIG. 5, the pixels 504 are typically activated one at a time during a calibration operation.

FIG. 7 includes an illustration of a cross-sectional view of an electronic device 70 having an embedded calibrating system. The electronic device 70 may have a modified substrate 705, wherein a portion of the substrate can act as a waveguide 74. A photosensor 72 may lie within the substrate 705. A combination of the substrate 705 and air on the user side 700 of the electronic device 70 can act as a waveguide. Unlike the embodiments of FIGS. 5 and 6, the waveguide 74 does not have specific boundaries. Still, the effective edges of the waveguide 74 may correspond to portions of the substrate 705 extending from the photosensor 72 to a location at or just beyond the array edge 506 opposite the photosensor 72.

The photosensor 72 can be part of a sensing circuit, separate from the pixel (or subpixel) circuit. In other words, the photosensor 72 may not be part of the pixel (or subpixel) circuit. Further, the photosensor 72 and sensing circuit may not be electrically connected or, in some embodiments, coupled to the pixel (or subpixel) circuit. The connections and circuit elements for the sensing circuit and photosensor 72 are conventional.

Fabrication of portions of the electronic device 70 is briefly addressed. The substrate 705 may include conventional material(s) having conventional thickness(es). A location for the photosensor 72 may be etched into the substrate 705. The photosensor 72 may be formed by plasma-enhanced chemical vapor deposition or physical vapor deposition of a silicon material. In one embodiment, n-type and p-type doping may be performed in-situ during a portion of the deposition, may be performed subsequent to the deposition, or a combination thereof. A polishing operation may be used to remove the silicon material lying outside the recession within the substrate 705. A user of the electronic device 70 will see the user side 700. Other fabrication methods or sequences can be performed. For example, a deposition and etch process may be used. An electrically insulating material may be formed after forming the photosensor 72.

FIGS. 8 and 9 include an alternative embodiment similar to FIG. 7 except that the electronic device 80 includes a plurality of photosensors 822, 824, 826, and 828. Referring to FIG. 8, the photosensors 822 and 824 lie along opposite edges 842 of a waveguide 84. In this embodiment, the edges 842 of the waveguide 84 are better defined and can be that portion of the substrate 805 surrounded by the photosensors 822, 824, 826, and 828. The compositions of the substrate 805 and waveguide 84 may be the same or different from those describe with respect to FIG. 7. During a calibration operation, the pixels 504 can be activated one at a time. During regular operation, a plurality of pixels 504 may have light 508 emitted that passes through the substrate 805 and waveguide 84.

FIG. 9 includes a plan view of the electronic device 80 to better illustrate the positional relationships of some of the features of the device. The edges of the array are illustrated by dashed line 506 and generally correspond to the shape of a display for the electronic device 80. Although FIG. 9 shows one pixel 504, the array includes a plurality of pixels 504. Each pixel 504 may be designated by x- and y-coordinates. The waveguide 84 has edges 842 that have corresponding edges 506 in the array. The photosensors 822, 824, 826, and 828 are connected to the edges 842 of the waveguide 84.

In this particular environment, a pixel 504 lies closer to photosensor 824. Light emitted by the pixel 504 may be detected by the four photosensors, and more strongly detected by photosensor 824 compared to photosensor 822. The system illustrated in FIGS. 8 and 9 may have more accurate correction factors compared to the embodiment illustrated in FIG. 7 that has only one photosensor 72. When using signals from the photosensors in FIGS. 8 and 9, a detected composite signal for each pixel 504 may be a sum of all intensities measured by the photosensors, a product of those intensities, an average of those intensities, a geometric mean of those intensities, or the like.

FIG. 10 includes an illustration of a hybrid calibrating system. In this particular embodiment, the electronic device 1000 can include pixels 504, photosensors 1022, and a protective shield 502. A waveguide 1040 has edges 1042 extending at least to the photosensors 1022. The waveguide 1040 may be similar to the waveguide 64 in its composition. It may also be used in a similar manner. However, unlike the system shown in FIG. 6, the photosensors 1022 are embedded within the electronic device 1000, more specifically in the substrate 1005, as opposed to a separate apparatus. During calibration, light 508 from a pixel 504 may travel along the waveguide 1040 until it reaches the sensors 1022.

FIG. 11 includes an illustration of yet another hybrid calibrating system. An electronic device 1100 may include a photosensor 1122 that is buried within a passivation layer or protective shield 1102. During fabricatio