Patent Description:
The present invention relates to displays with inorganic light-emitting diode pixels.

Flat-panel displays are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a display substrate to display images, graphics, or text. In a color display, each pixel includes light emitters that emit light of different colors, such as red, green, and blue. For example, liquid crystal displays (LCDs) employ liquid crystals to block or transmit light from a backlight behind the liquid crystals and organic light-emitting diode (OLED) displays rely on passing current through a layer of organic material that glows in response to the current. Displays using inorganic light emitting diodes (LEDs) are also in widespread use for outdoor signage and have been demonstrated in a <NUM>-inch television.

Inorganic light-emitting diode displays using inorganic micro-LEDs on a display substrate are also known. Micro-LEDs can have an area less than <NUM> square, less than <NUM> microns square, or less than <NUM> microns square or have an area small enough that it is not visible to an unaided observer of the display at a designed viewing distance. <CIT> entitled Optical Systems Fabricated by Printing-Based Assembly teaches transferring light-emitting, light-sensing, or light-collecting semiconductor elements from a wafer substrate to a destination substrate.

In any application requiring many elements, it is important that each element is reliable to ensure good manufacturing yields and performance. Active-matrix control circuits, as well as the controlled element (e.g., a light emitter) are subject to failure. Because no manufacturing process is perfect, any large system can have defective elements. In particular, inorganic light-emitting diodes are subject to manufacturing defects that increase the amount of current passing through the LED when provided with power, resulting in an undesirable brightness, power usage, or system control problems.

An undesired increase in current can also overheat the LEDs. One approach to preventing such overheating is to provide each LED pixel with a resistor or group of resistors in series with the LED, as is described in <CIT>. <CIT> discloses a current-limiting diode in an LED circuit for a lighting system with both forward-biased and reverse-biased LEDs and a polarity switching device. Circuits for sensing current levels and reducing power dissipation are also known, for example as taught in <CIT> and <CIT> as are voltage control circuits, for example as described in <CIT>. However, these approaches either require complex or expensive circuit components in association with each LED or result in diminished light output.

Alternatively, to ensure that large multi-element systems are reliably manufactured and operated, such systems can employ redundant elements. For example, displays are sometimes designed with redundant light emitters. <CIT> describes an LCD with redundant pixel electrodes and thin-film transistors to reduce defects. In another approach described in <CIT>, an extra row or column of pixels is provided to replace any defective row or column. An alternative approach to improving display yields uses additional, redundant light-emitting elements, for example two light emitters for every desired light emitter in the display. <CIT> discloses a pixel circuit with two sub-pixels and circuitry to determine whether a sub-pixel is to be enabled, for example if another sub-pixel is faulty. Similarly, <CIT> teaches an LED-based lighting system that includes a primary light source and at least one redundant light source. The primary light source is activated by itself and the performance of the light source is measured to determine whether or not to drive the redundant light source. The redundant light source is activated when the performance measurements indicate that a performance characteristic is not being met by the primary light source alone. The first light system can be activated in combination with the redundant light source once the decision is made to activate the redundant light source. <CIT> discloses redundant pairs of micro LED devices driven by a common transistor. <CIT> describes separately controlled micro-LED devices. However, the use of redundant emitters is expensive and does not address problems with LEDs that conduct too much current.

The following documents have been cited against the application:.

There is a need, therefore, for LED pixel circuits that can control or avoid problems resulting from LEDs in a display that undesirably conduct too much current.

The present invention includes embodiments of a display having an array of fused light-emitting diodes as defined in the appended claims. In more detail, a micro-transfer printable pixel component includes an LED having first and second LED electrical contacts for providing power to the LED to cause the LED to emit light, and a fuse having first and second fuse electrical contacts, the first fuse electrical contact electrically connected in series with the first LED electrical contact. A first electrical conductor is connected to the second fuse electrical contact and a second electrical conductor is connected to the second LED electrical contact.

In another embodiment, a micro-transfer printable pixel component wafer includes a pixel wafer having a patterned sacrificial layer forming an array of sacrificial portions separated by anchors and a plurality of pixel components. Each pixel component is disposed entirely on or over a corresponding sacrificial portion.

A fuse is an electrically conductive, sacrificial, low-resistance resistor providing overcurrent protection that becomes permanently non-conductive when a pre-determined current passes through the fuse.

The pixel components can each include a plurality of LEDs and a corresponding plurality of electrical fuses, each electrical fuse electrically connected in series with a corresponding LED. The plurality of LEDs can include red, green, and blue light-emitting diodes forming full-color pixel components in a full-color pixel of a display. Each different color of LED can have a fuse that has a different current rating. Alternatively, a single electrical fuse can be electrically connected in series with multiple LEDs.

The LEDs can be tested for short circuits (for example, an improperly large electrical conduction resulting in an overcurrent when electrical power is supplied) with a forward-biased voltage or with a reverse-biased voltage. If too much current flows through the LED, too much current also flows through the fuse, the fuse is blown, and the LED will no longer operate in an LED control circuit.

The LEDs in the display are operated, tested, or rendered non-conductive with a fuse controller. The fuse controller is a circuit that provides sufficient electrical current to blow the fuse as part of a test. The fuse controller also operates the LEDs in the display to display an image. The fuse controller can be, or be part of, a passive-matrix display controller or an active-matrix display controller for a matrix-addressed display, and can be or can include row or column controllers, or both. If the fuse controller is an active-matrix display controller, the pixel components can include a pixel controller to provide local pixel information storage and pixel control. The pixel controller is electrically connected to the one or more LEDs and fuses in a pixel component and can also provide sufficient current to render the fuses non-conductive.

The LEDs or fuses, or both, can be provided as micro-transfer printable components, either in individual packages or together in one component. In another embodiment, the LED and fuse, or multiple LEDs and one or more fuses such as in a full-color display pixel, are mounted and electrically connected on a pixel substrate separate, independent, and distinct from the display substrate. The pixel substrate is then mounted on the display substrate. The pixel substrate can also be a micro-transfer printable component. The LEDs, fuses, or pixel substrates, or any combination of the LEDs, fuses, and pixel substrates, can be provided in components with connection posts that enable electrical connections to electrical conductors on a destination substrate (such as a display substrate) on which the component is micro-transfer printed.

A method of making a micro-transfer printable pixel component includes providing a pixel wafer having a patterned sacrificial layer forming an array of sacrificial portions separated by anchors. One or more LEDs are disposed on the pixel wafer entirely in, on, or over a sacrificial portion, for example by micro-transfer printing. Each LED has first and second LED electrical contacts for providing power to the LED to cause the LED to emit light. One or more fuses having first and second fuse electrical contacts are also disposed entirely in, on, or over the sacrificial portion. The fuse(s) can be disposed by micro-transfer printing or by forming the fuse over the sacrificial portion using photolithographic methods. At least one first fuse electrical contact is electrically connected in series with the first LED electrical contact. A first electrical conductor is provided and electrically connected to the second fuse electrical contact and a second electrical conductor is provided and electrically connected to the second LED electrical contact.

Embodiments of the present invention provide a simple way to overcome LED manufacturing faults in a display and enables simple detection, correction, and repair.

In certain embodiments, the fuse controller provides electrical power to the LEDS in a forward-biased direction.

In certain embodiments, the fuse controller provides electrical power to the LEDS in a reverse-biased direction.

In certain embodiments, the display includes a redundant pixel component electrically connected to each combination of row conductors and column conductors in parallel with each pixel component, each redundant pixel component comprising a light-emitting diode and an electrical fuse electrically connected in series with the light-emitting diode.

In certain embodiments, the fuses, the LEDs, or the pixel components are provided in a micro-transfer printable component.

In certain embodiments, each pixel component is provided in a micro-transfer printable component and either or both of the fuses and the LEDs are provided in a micro-transfer printable component.

In certain embodiments, the fuses, the LEDs, or the pixel components are replaceable.

In another aspect, the disclosed technology includes a method of operating a display having fused light-emitting diodes (LEDs), including: providing a display, the display comprising a display substrate and an array of pixel components disposed on, over, or in the display substrate, each pixel component comprising a light-emitting diode and an electrical fuse electrically connected in series with the corresponding light-emitting diode; operating the display to determine the operational status of the LEDs; determining the LEDs that have an electrical short; and providing an electrical current through the shorted LEDs and through the corresponding fuses electrically connected in series to the shorted LEDs that renders the fuses non-conductive.

In certain embodiments, the method includes operating the display so that the LEDs emit light, measuring the luminance of each LED, and comparing the light emitted from the LEDs to a predetermined desired luminance to determine the operational status of the LEDs.

In certain embodiments, the method includes operating the display so that the LEDs conduct electrical current, measuring the current conducted through each LED or the voltage across each LED or pixel component, and comparing the current conducted through each LED to a predetermined desired current to determine the operational status of the LEDs or comparing the voltage across each LED or pixel component to a predetermined desired voltage to determine the operational status of the LEDs.

In certain embodiments, the method includes operating all of the LEDs in the display at a time, operating all of the LEDS in a row at a time and sequentially operating rows of LEDS, operating all of the LEDS in a column at a time and sequentially operating columns of LEDS, or sequentially operating the LEDS.

In certain embodiments, the method includes providing an electrical current through all of the shorted LEDs and corresponding fuses electrically connected to the shorted LEDs at a time, providing an electrical current through all of the shorted LEDs and corresponding fuses electrically connected to the shorted LEDs in a row or column at a time, or sequentially providing an electrical current through each of the shorted LEDs and corresponding fuses electrically connected to the shorted LEDs.

In certain embodiments, the method includes providing the electrical current in a forward-biased direction.

In certain embodiments, the method includes providing the electrical current in a reverse-biased direction.

In certain embodiments, the method includes replacing shorted LEDs and the corresponding fuse.

In certain embodiments, the method includes providing a redundant pixel component in parallel with a shorted pixel component.

In certain embodiments, the steps of operating the display to determine the operational status of the LEDs and determining the LEDs that have an electrical short are provided in a common step with providing an electrical current through the shorted LEDs and through the corresponding fuses electrically connected in series to the shorted LEDs that renders the fuses non-conductive.

In another aspect, the disclosed technology includes a micro-transfer printable pixel component, including: an LED having first and second LED electrical contacts for providing power to the LED to cause the LED to emit light; a fuse having first and second fuse electrical contacts, the first fuse electrical contact electrically connected in series with the first LED electrical contact; a first electrode connected to the second fuse electrical contact; and a second electrode connected to the second LED electrical contact.

In certain embodiments, the micro-transfer printable pixel component includes first and second connection posts and wherein the first connection post is electrically connected to the first electrode or the second connection post is electrically connected to the second electrode.

In certain embodiments, the micro-transfer printable pixel component includes a plurality of LEDs, each LED of the plurality of LEDs having first and second LED electrical contacts for providing power to the LED to cause the LED to emit light, and a corresponding plurality of fuses, each fuse having first and second fuse electrical contacts, the first fuse electrical contact of each fuse electrically connected in series with the first LED electrical contact of a corresponding LED.

In certain embodiments, the micro-transfer printable pixel component includes a pixel substrate on which the LED, the fuse, the first electrode, and the second electrode are disposed.

In certain embodiments, the micro-transfer printable pixel component includes a pixel controller, the pixel controller electrically connected to any one or to any combination of the first LED electrical contact, the second LED electrical contact, the first fuse electrical contact, or the second fuse electrical contact.

In certain embodiments, the micro-transfer printable pixel component includes first and second connection posts and wherein the first connection post is electrically connected to the first electrode or the pixel controller or wherein the second connection post is electrically connected to the second electrode or the pixel controller.

In certain embodiments, the micro-transfer printable pixel component includes a redundant LED having first and second redundant LED electrical contacts for providing power to the redundant LED to cause the redundant LED to emit light; a redundant fuse having first and second redundant fuse electrical contacts, the first redundant fuse electrical contact electrically connected in series with the first redundant LED electrical contact; the first electrode connected to the second redundant fuse electrical contact; and the second electrode connected to the second redundant LED electrical contact.

In certain embodiments, the fuse is a distance greater than or equal to one times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, or <NUM> times the length or width of the LED from the LED.

In another aspect, the disclosed technology includes a method of making a micro-transfer printable pixel component, including: providing a pixel wafer having a patterned sacrificial layer forming an array of sacrificial portions separated by anchors; disposing an LED on the pixel wafer entirely in, on, or over a sacrificial portion, the LED having first and second LED electrical contacts for providing power to the LED to cause the LED to emit light; disposing a fuse having first and second fuse electrical contacts entirely in, on, or over the sacrificial portion; electrically connecting the first fuse electrical contact in series with the first LED electrical contact; providing a first electrode and electrically connecting the first electrode to the second fuse electrical contact; and providing a second electrode and electrically connecting the second electrode to the second LED electrical contact.

In certain embodiments, the method includes disposing the LED on or over the sacrificial portion by micro-transfer printing the LED on or over the sacrificial portion or disposing the fuse on or over the sacrificial portion by micro-transfer printing the fuse on or over the sacrificial portion.

In certain embodiments, the method includes disposing a redundant LED on the pixel wafer entirely in, on, or over the sacrificial portion, the redundant LED having first and second redundant LED electrical contacts for providing power to the redundant LED to cause the redundant LED to emit light; disposing a redundant fuse having first and second redundant fuse electrical contacts entirely in, on, or over the sacrificial portion; electrically connecting the first redundant fuse electrical contact in series with the first redundant LED electrical contact; electrically connecting the first electrode to the second redundant fuse electrical contact; and electrically connecting the second electrode to the second redundant LED electrical contact.

In another aspect, the disclosed technology includes a micro-transfer printable pixel component wafer, including: a pixel wafer having a patterned sacrificial layer forming an array of sacrificial portions separated by anchors; a plurality of pixel components, each pixel component disposed entirely on or over a corresponding sacrificial portion, wherein the plurality of pixel components comprises a redundant pixel component in parallel with a shorted pixel component.

In certain embodiments, the micro-transfer printable pixel component wafer includes first and second connection posts and wherein the first connection post is electrically connected to the first electrode or the second connection post is electrically connected to the second electrode.

In certain embodiments, the micro-transfer printable pixel component wafer includes a plurality of LEDs, each LED of the plurality of LEDs having first and second LED electrical contacts for providing power to the LED to cause the LED to emit light, and a corresponding plurality of fuses, each fuse having first and second fuse electrical contacts, the first fuse electrical contact of each fuse electrically connected in series with the first LED electrical contact of a corresponding LED.

In certain embodiments, the micro-transfer printable pixel component wafer includes a pixel substrate on which the LED, the fuse, the first electrical conductor, and the second electrical conductor are disposed.

In certain embodiments, the micro-transfer printable pixel component wafer includes a pixel controller, the pixel controller electrically connected to any one or to any combination of the first LED electrical contact, the second LED electrical contact, the first fuse electrical contact, or the second fuse electrical contact.

In another aspect, the disclosed technology includes a method of operating a display having fused light-emitting diodes (LEDs), including: providing a display, the display comprising a display substrate and an array of pixel components disposed on, over, or in the display substrate, each pixel component comprising a light-emitting diode and an electrical fuse electrically connected in series with the corresponding light-emitting diode; and providing an electrical current through one or more of the pixel components so that the fuse of any of the pixel components that has an LED with an electrical short is rendered non-conductive.

In certain embodiments, the micro-transfer printable pixel component wafer includes providing a forward-biased electrical current.

In certain embodiments, the micro-transfer printable pixel component wafer includes providing a reverse-biased electrical current.

In certain embodiments, the micro-transfer printable pixel component wafer includes sequentially providing an electrical current through each of the pixel components at a time, providing an electrical current through rows or columns of the pixel components at a time, or providing an electrical current through all of the pixel components at a time.

The foregoing and other objects, aspects, features, and advantages of the present disclosure will become more apparent and better understood by referring to the following description taken in conjunction with the accompanying drawings, in which:.

The features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. The figures are not drawn to scale since the variation in size of various elements in the Figures is too great to permit depiction to scale.

The present invention includes embodiments of a display <NUM> having an array of fused light-emitting diodes (LEDs) <NUM>, as illustrated in <FIG>. The display <NUM> includes a display substrate <NUM> with an array of pixel components <NUM> disposed on the display substrate <NUM>. Each pixel component <NUM> has at least one light-emitting diode <NUM> and at least one electrical fuse <NUM>. Each fuse <NUM> is electrically connected in series to at least one light-emitting diode <NUM>, for example, with an electrode <NUM>. Each fuse <NUM> can include fuse electrical contacts <NUM> for providing electrical connections to the fuse <NUM>. The electrodes <NUM> can be or provide the fuse electrical contacts <NUM> or the fuse electrical contacts <NUM> can be or provide a portion of the electrodes <NUM>. The electrodes <NUM> and the fuse electrical contacts <NUM> are electrical conductors and can be made of metal patterned with photolithographic methods, tools, and materials.

The display <NUM> can include an array of row conductors <NUM> formed on, in, or over the display substrate <NUM>, the row conductors <NUM> extending in a row direction. An array of column conductors <NUM> are also formed on, in, or over the display substrate <NUM>. The column conductors <NUM> extend in a column direction different from the row direction and and are not directly electrically connected to the row conductors <NUM> so that the row conductors <NUM> and the column conductors <NUM> can conduct different electrical signals at the same time. A pixel component <NUM> is electrically connected to each combination of the row conductors <NUM> and the column conductors <NUM> to form an array of the pixel components <NUM> disposed on or over the display substrate <NUM> that are matrix-addressed through the row and column conductors <NUM>, <NUM> in a display <NUM>. A column controller <NUM> and a row controller <NUM> provide signals to the column conductors <NUM> and the row conductors <NUM>, respectively, through busses <NUM> to display images on the display <NUM>. In various embodiments, the column conductors <NUM> and the row conductors <NUM> can also provide test signals to the pixel components <NUM> or can render the fuses <NUM> in the pixel components <NUM> non-conductive.

The display substrate <NUM> can be a glass, polymer, ceramic, or metal substrate having at least one side suitable for constructing the row and column conductors <NUM>, <NUM> and receiving or forming the pixel components <NUM>, or elements of the pixel components <NUM> such as the LEDs <NUM> and fuses <NUM>, and electrodes <NUM> thereon. The display substrate <NUM> can have a thickness from <NUM> to <NUM> microns, <NUM> to <NUM> microns, <NUM> to <NUM> microns, <NUM> to <NUM> microns, <NUM> to <NUM> microns, <NUM> microns to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM> and can be, but is not necessarily, transparent.

The light-emitting diodes <NUM> can be inorganic light-emitting diodes made in a semiconductor material, such as a compound semiconductor (e.g., GaN). The semiconductor material can be crystalline. Any one or each of the LEDs <NUM> or the fuses <NUM> can have a width from <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>, has a length from <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>, or has a height from <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>.

The row and column conductors <NUM>, <NUM> can be electrically conductive metal wires formed, or disposed on, the display substrate <NUM> using, for example, photolithographic methods, tools, and materials. The row and column controllers <NUM>, <NUM> can be integrated circuits and provided external to the display substrate <NUM> or on the display substrate <NUM> and electrically connected using printed circuit board tools, methods, and materials.

The fuse <NUM> is an electrically conductive element that becomes permanently non-conductive when a pre-determined current passes through the fuse and is a type of sacrificial low-resistance resistor providing overcurrent protection. The essential component of the fuse <NUM> is a low-resistance electrical conductor that melts, oxidizes, vaporizes, sublimates, reacts, or otherwise loses conductivity when too much current flows through the fuse <NUM>, referred to herein as melting although fuses <NUM> of the present invention are not limited to fuses <NUM> that melt. The fuse <NUM> can have a melting temperature that is greater than the maximum rated operating temperature of the LEDs <NUM> or the display <NUM>. According to an embodiment of the present invention, the fuse <NUM> includes a metal wire or strip. As used herein, a fuse <NUM> that is rendered non-conductive is a blown fuse <NUM> and the process of rendering the fuse <NUM> non-conductive is the process of blowing the fuse <NUM>. The current at which a fuse <NUM> is blown is its rated current or current rating. In an embodiment, the rated current is greater than or equal to <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, or <NUM> times the maximum desired LED <NUM> current.

The electrical fuses <NUM> can be metal wires formed in a pre-determined shape and size, such as a shape and size providing a cross section designed to melt when conducting a desired current. The fuse <NUM> can be made, for example, of a metal such as zinc, copper, silver, aluminum, nickel, chrome, or tin, or metal alloys such as nickel-chromium that include these or other metals. In other embodiments, the fuses <NUM> can be made of most degenerate semiconductors that are highly doped and conduct current in a manner similar to a native metal. The fuses <NUM> can be made of or in a semiconductor and can be polysilicon. In an embodiment, the fuse <NUM> has a different cross section but is made of the same materials as the fuse electrical contacts <NUM>, the electrodes <NUM>, or the LED electrical contacts <NUM>. The fuse <NUM> can have a cross section that is small or smaller than the cross section of other electrical conductors with which the fuse <NUM> is electrically connected in series, such as the electrodes <NUM>, the LED electrical contacts <NUM>, and the fuse electrical contacts <NUM>. The fuse <NUM> can be a joint between two other electrical conductors. If the LED <NUM> is too conductive (i.e., shorted), for example if the LED <NUM> has an electrical short or short circuit (whether or not the LED <NUM> emits any light, too much light, too little light, or no light), the fuse <NUM> will cease to conduct any current at all. The term 'shorted' or 'short' refers to an electrical short circuit in a component, in this case an LED <NUM> in a pixel component <NUM>. A pixel component <NUM> having a shorted LED <NUM> is referred to as a shorted pixel component <NUM>, as discussed below.

Referring to <FIG>, in an embodiment one or more full-color pixel components <NUM> comprise a plurality of the LEDs <NUM>, each LED <NUM> having a separate electrical fuse <NUM> electrically connected in series with the LED <NUM>. As shown in <FIG>, each of the full-color pixel components <NUM> includes a red LED 22R that emits red light, a green LED <NUM> that emits green light, and a blue LED 22B that emits blue light (collectively LEDs <NUM>). A full-color pixel component <NUM> is also a pixel component <NUM>. In an embodiment, the red, green, and blue LEDs 22R, <NUM>, 22B are electrically connected to a common electrical connection (as shown in <FIG>, described below). Alternatively, the separate electrical fuses <NUM> are electrically connected to a common electrical connection <NUM> (as shown, column conductor <NUM>, but in another embodiment row conductor <NUM>). These connections can enable matrix-addressed control of the pixel components <NUM> through the row and column conductors <NUM>, <NUM>.

Furthermore, each of the differently colored red, green, and blue LEDs 22R, <NUM>, 22B can have a different optimal or maximum desired current. Thus, in an embodiment, the red LED 22R is electrically connected in series with a red electrical fuse (red fuse 24R), the green LED <NUM> is electrically connected in series with a green electrical fuse (green fuse <NUM>), and the blue LED 22B is electrically connected in series with a blue electrical fuse (blue fuse 24B), and at least one of the red, green, and blue fuses 24R, <NUM>, 24B is rendered non-conductive with a different amount of electrical power than another of the red, green, or blue fuses 24R, <NUM>, 24B. Thus, the fuses <NUM> can be customized to the particular LED <NUM> with which it is electrically in series.

Referring to <FIG>, in another embodiment one or more of the pixel components <NUM> comprises a plurality of LEDs <NUM> electrically connected in parallel. In this embodiment, the plurality of LEDs <NUM> includes red, green, and blue LEDs 22R, <NUM>, 22B to form a full-color pixel component <NUM>. An electrical fuse <NUM> is electrically connected in common with the common electrical connection <NUM> and electrically in series with each of the LEDs <NUM> in the plurality of LEDs <NUM>. Referring to <FIG>, the plurality of LEDs <NUM> are electrically connected in series and form a monochrome pixel component <NUM>. The electrical fuse <NUM> is electrically connected in common with the common electrical connection <NUM> and electrically in series with the series-connected LEDs <NUM>. This reduces the number of fuses <NUM> that are necessary and still provides protection against electrically shorted LEDs <NUM>.

In an embodiment, the row and column controllers <NUM>, <NUM> control the LEDs <NUM> to display an image and also comprise a fuse controller <NUM> that provides image control signals that cause the array of LEDs <NUM> to display an image and fuse control signals that can provide sufficient electrical power to test the LEDs <NUM> or blow the fuses <NUM>. In one embodiment, the fuse controller <NUM> provides electrical power to the LEDs <NUM> in a forward-biased direction. In another embodiment, the fuse controller <NUM> provides electrical power to the LEDs <NUM> in a reverse-biased direction. Providing current to the LEDs <NUM> and the fuses <NUM> in a forward-biased direction to blow the fuses <NUM> and display an image requires a simpler circuit than using a forward-biased current to display an image and a reverse-biased current to blow the fuses <NUM>. However, a reverse-biased current can employ a larger voltage (but a voltage less than the breakdown voltage of the light-emitting diode), rendering the fuses <NUM> less sensitive to operating parameters. Thus, in this embodiment, the shorted LED <NUM> conducts a large reverse-biased current at a voltage less than the reverse breakdown voltage of the other non-shorted LEDs <NUM> in order to blow the fuse of the shorted LED <NUM> without damaging the non-shorted LEDs <NUM>.

Referring to <FIG>, in an embodiment one or more of the fuses <NUM> includes separate conductors connected in parallel. Such an arrangement can provide a more accurately controlled rated current.

In one embodiment of the present invention, the fuse controller <NUM> is a passive-matrix controller, as shown in <FIG>. In another embodiment, referring to <FIG>, the fuse controller <NUM> (or row and column controllers <NUM>, <NUM> together or individually) is an active-matrix controller and each pixel component <NUM> comprises a pixel controller <NUM> electrically connected to the LED(s) <NUM> and that can provide active-matrix pixel control to the LED(s) <NUM>. The pixel controller <NUM> can also include circuitry that, in combination with the fuse controller <NUM> (or row and column controllers <NUM>, <NUM> together or individually), provides sufficient electrical power to blow each fuse <NUM> and render it non-conductive. As shown in <FIG>, a full-color pixel component <NUM> can include red, green, and blue LEDs 22R, <NUM>, 22B controlled by the pixel controller <NUM> and red, green, and blue fuses 24R, <NUM>, 24B connected in series with the red, green, and blue LEDs 22R, <NUM>, 22B between the pixel controller <NUM> and the red, green, and blue LEDs 22R, <NUM>, 22B. The red, green, and blue LEDs 22R, <NUM>, 22B are electrically connected in common to the column conductor <NUM>. In the embodiment of <FIG>, the red, green, and blue LEDs 22R, <NUM>, 22B are connected in series with the red, green, and blue fuses 24R, <NUM>, 24B between the pixel controller <NUM> and the red, green, and blue fuses 24R, <NUM>, 24B. The red, green, and blue fuses 24R, <NUM>, 24B are electrically connected in common to the column conductor <NUM>. In both embodiments, the different row conductors <NUM> can be electrically connected to the pixel controller <NUM> to provide active-matrix control to the full-color pixel component <NUM>. Alternatively, a row conductor <NUM> can be connected in common and different column conductors <NUM> can be electrically connected to the pixel controller <NUM> to provide active-matrix control. As will be understood by those knowledgeable in the art, 'row' and 'column' are arbitrary designations that can be exchanged in alternative embodiments of the present invention.

As shown in <FIG> and <FIG>, the LEDs <NUM> and the fuses <NUM> are disposed directly on a display substrate <NUM>. In an embodiment of the invention as shown in <FIG>, the LEDs <NUM> and the fuses <NUM> are disposed on a pixel substrate <NUM> that is separate, independent, distinct from the display substrate <NUM>. The pixel substrates <NUM> are then disposed on the display substrate <NUM>. Use of pixel substrates <NUM> can provide a more modular display architecture that is more readily tested, repaired, or replaced.

Referring to <FIG>, one or more of the fuses <NUM>, the LEDs <NUM>, the pixel controllers <NUM>, or the pixel components <NUM> are provided in a micro-transfer printable component. As shown in <FIG>, the LED <NUM> has LED electrical contacts <NUM> for providing electrical power to the LED <NUM> and cause the LED <NUM> to emit light. The LED electrical contacts <NUM> can be electrical contact pads or simply designated portions of the LED <NUM>. Electrodes <NUM> are electrical conductors that electrically connect the LED electrical contacts <NUM> and LED <NUM> to the row and column conductors <NUM>, <NUM> on the display substrate <NUM>. Optionally, in an embodiment, the LED <NUM> has an underlying pixel substrate <NUM> and connection posts <NUM> that enable electrical connections between the electrodes <NUM> and the row or column conductors <NUM>, <NUM> to be made during the micro-transfer printing process. As shown in the embodiment of <FIG>, the fuse <NUM> can be incorporated in a common micro-transfer printable component with the LED <NUM> with fuse electrical contacts <NUM> electrically connected to the electrode <NUM>. In a different embodiment, the LED <NUM> is provided in a micro-transfer printable component independent of and separate from the fuse <NUM>. According to another embodiment of the present invention illustrated in <FIG>, the underlying pixel substrate <NUM> includes vias <NUM> electrically connecting the electrodes <NUM> and the connection posts <NUM>. An adhesive layer <NUM> can adhere the pixel component <NUM> to the display substrate <NUM>. An encapsulation layer <NUM> can encapsulate the pixel components <NUM> of <FIG> and <FIG>.

As shown in another embodiment in <FIG>, the fuse <NUM> is a micro-transfer printable component independent of the LED <NUM>. In an optional embodiment, the fuse <NUM> has an underlying pixel substrate <NUM> and connection posts <NUM> that enable electrical connections with the row or column conductors <NUM>, <NUM> to be made during a micro-transfer printing process. An encapsulation layer <NUM> can encapsulate the fuse <NUM> (not shown). In particular, in an embodiment, the fuse <NUM> can also serve as a jumper over the display substrate <NUM> connecting different row conductors <NUM> on opposite sides of a column conductor <NUM>, as shown, or connecting different column conductors <NUM> on opposite sides of a row conductor <NUM>, not shown. Micro-transfer printable LEDs <NUM>, fuses <NUM>, or pixel components <NUM> can be removable or replaceable. In another embodiment, the fuses <NUM> are formed separately from the LEDs <NUM> using photolithographic techniques, for example, made in a common step with electrodes <NUM> electrically connected to the connection posts <NUM>.

As shown in the cross sections of <FIG> and <FIG>, with reference to the schematic illustrations of <FIG> and <FIG>, and as noted above, individual red, green, and blue light-emitting pixel components 20R, <NUM>, 20B can be disposed directly on the display substrate <NUM> using micro-transfer printing and connection posts <NUM> to provide electrical connections between the LEDs <NUM> and the row and column conductors <NUM>, <NUM>. Alternatively, referring to <FIG> and with reference to <FIG>, and <FIG>, a micro-transfer printable pixel component <NUM> (for example, a full-color pixel component <NUM>) includes a pixel substrate <NUM> separate, independent, and distinct from the display substrate <NUM>. One or more LEDs <NUM>, each having first and second LED electrical contacts <NUM> (<FIG>) for providing power to the LED <NUM> to cause the LED <NUM> to emit light are disposed on the pixel substrate <NUM>. One or more fuses <NUM> each have first and second fuse electrical contacts <NUM>. The first fuse electrical contact <NUM> is electrically connected in series with the first LED electrical contact <NUM>, a first electrode <NUM> is electrically connected to the second fuse electrical contact <NUM>, and a second electrode <NUM> is electrically connected to the second LED electrical contact <NUM>. As shown in <FIG>, the pixel component <NUM> can be a full-color pixel component <NUM> and can comprise a plurality of LEDs <NUM>, each LED <NUM> of the plurality of LEDs <NUM> having first and second LED electrical contacts <NUM> for providing power to the LED <NUM> to cause the LED <NUM> to emit light. A corresponding plurality of fuses <NUM> have first and second fuse electrical contacts <NUM>, one of which is electrically connected in series with an LED electrical contact <NUM> of a corresponding LED <NUM>. As shown in <FIG>, the full-color pixel component <NUM> includes a plurality of different single-color pixel components <NUM>, red pixel component 20R, green pixel component <NUM>, and blue pixel component 20B.

In an embodiment, the micro-transfer printable pixel component <NUM> includes first and second connection posts <NUM>. The first connection post <NUM> is electrically connected to the first electrode <NUM> or the second connection post <NUM> is electrically connected to the second electrode <NUM>. Thus, in an embodiment, pixel components <NUM>, LEDs <NUM>, or fuses <NUM> can be micro-transfer printed onto the pixel substrate <NUM> to form a full-color pixel component <NUM> and the full-color pixel component <NUM> can itself be micro-transfer printed. The pixel component <NUM> can also include a pixel controller <NUM> that is electrically connected to any one or to any combination of the LED electrical contacts <NUM> or fuse electrical contacts <NUM>. The connection posts <NUM> can be electrically connected to any one of or to any combination of the electrodes <NUM> or the pixel controller <NUM>. <FIG> is a perspective of an array of full-color pixel components <NUM>, each including red, green, and blue pixel components 20R, <NUM>, 20B micro-transfer printed on a pixel substrate <NUM> with a pixel controller <NUM>. The full-color pixel components 21are disposed on a display substrate <NUM> of a display <NUM>.

Referring to <FIG>, in a method, a micro-transfer printable pixel component <NUM> and pixel component wafer is made by providing a pixel wafer <NUM> (<FIG>). A sacrificial layer <NUM> is patterned in, on, or over the pixel wafer <NUM> to form sacrificial portions <NUM> separated by portions of the pixel wafer <NUM> forming anchors <NUM> (<FIG>) using photolithographic materials and methods. The pixel wafer <NUM> can be a substrate such as a semiconductor, glass, polymer, metal, or ceramic wafer. Connection post forms <NUM> are etched into the sacrificial portions <NUM> (<FIG>). As shown in <FIG>, an LED <NUM> is provided by forming or disposing an LED <NUM> entirely on the sacrificial portion <NUM>, for example, by micro-transfer printing the LED <NUM> from an LED source wafer onto the sacrificial portion <NUM>. The LED <NUM> has first and second LED electrical contacts <NUM> for providing power to the LED <NUM> to cause the LED <NUM> to emit light. A patterned dielectric structure <NUM> is formed or otherwise disposed on the LED <NUM> to protect the LED <NUM> and LED electrical contacts <NUM>. Electrical conductors, such as electrodes <NUM>, are formed in electrical contact with the LED electrical contacts <NUM> over the sacrificial portion <NUM> and the connection post form <NUM> to form connection posts <NUM>. The patterned dielectric structure <NUM> can be, for example, silicon dioxide and the electrical conducting electrodes <NUM> can be metal deposited and patterned using photolithographic materials, tools, and methods such as coating, sputtering, or evaporation, and etching with patterned photoresist.

A fuse <NUM> having first and second fuse electrical contacts <NUM> is disposed entirely in, on, or over the sacrificial portion <NUM> (<FIG>). In one embodiment, the fuse <NUM> (or LED <NUM>) is formed on the sacrificial portion <NUM> of the pixel wafer <NUM> using photolithographic processes and can be made, partially or entirely, in a common step with the electrodes <NUM> and using the same materials or including at least some of the same materials. Alternatively, the fuse <NUM> can be provided by micro-transfer printing the fuse <NUM> (<FIG>) from a fuse source wafer. Either or both the LED <NUM> and fuse <NUM> can have connection posts <NUM> to enable electrical connections in, on, or over the pixel substrate <NUM> or otherwise in the pixel component <NUM>. The first fuse electrical contact <NUM> is electrically connected in series with the first LED electrical contact <NUM>, for example, using an electrode <NUM>. A first electrode <NUM> is provided and electrically connected to the second fuse electrical contact <NUM> and a second electrode <NUM> is provided and electrically connected to the second LED electrical contact <NUM>. In an embodiment, the electrodes <NUM> coat the connection post form <NUM> to make the connection posts <NUM>.

The electrodes <NUM>, the fuse <NUM>, and the first and second fuse electrical contacts <NUM> can be made in one step with common materials, or can be at least partially formed in a common step with some common materials using photolithography. For example, the fuse <NUM> can be made with a desired cross section together with a portion of the first and second fuse electrical contacts <NUM>, electrodes <NUM>, and connection posts <NUM>. In a following step additional material can be provided to the first and second fuse electrical contacts <NUM>, electrodes <NUM>, and connection posts <NUM> to increase their cross section and electrical conductivity compared to the fuse <NUM>. These elements form the pixel component <NUM> and are all shown in <FIG>. An optional encapsulation layer <NUM> is provided over the LED <NUM>, electrodes <NUM>, and fuse <NUM> (<FIG>).

The sacrificial portion <NUM> can be etched to form tethers <NUM> connecting the pixel component <NUM> to the anchor <NUM> and a gap between the pixel component <NUM> and the pixel wafer <NUM> (<FIG>), enabling the pixel component <NUM> to be micro-transfer printed with a transfer stamp. The sacrificial portions <NUM> can be, for example, an oxide layer or a designated anisotropically etchable portion of the pixel wafer <NUM>, or, once etched, the gap between the pixel component <NUM> and the pixel wafer <NUM>. In an embodiment, the optional encapsulation layer <NUM> is patterned (as shown) and can include an oxide or nitride such as silicon nitride and can form at least a portion of the tether <NUM>.

In another embodiment, a plurality of LEDs <NUM> and fuses <NUM> are formed or disposed entirely over a common sacrificial portion <NUM>. Optionally, a pixel controller <NUM> is also disposed entirely on the common sacrificial portion <NUM>, for example by micro-transfer printing, to make the full-color pixel component <NUM> structure of <FIG>, <FIG>, or <FIG>. The pixel wafer <NUM> can include a plurality of sacrificial portions <NUM> and corresponding plurality of pixel components <NUM> disposed on the sacrificial portions <NUM>, each pixel component <NUM> having one or more LEDs <NUM>, one or more fuses <NUM> electrically connected in series with a corresponding LED <NUM>, and optionally first and second connection posts <NUM> for making electrical connections to the pixel components <NUM>.

In one embodiment, the micro-transfer printable pixel component <NUM> is then transfer printed to the display substrate <NUM> to form the structures illustrated in <FIG>, <FIG>, or <FIG>. The encapsulation layer <NUM> and the electrodes <NUM> can provide sufficient mechanical and structural rigidity to the pixel component <NUM> that the pixel component <NUM> can be micro-transfer printed without additional support. In an embodiment and as shown in <FIG>, the sacrificial layer <NUM> provides a surface with sufficient mechanical rigidity to enable LEDs <NUM>, fuses <NUM>, or pixel controllers <NUM> to be micro-transfer printed thereon and electrodes <NUM> formed using photolithographic processes. The electrodes <NUM> and encapsulation layer <NUM> provide enough mechanical structure and rigidity to enable micro-transfer printing the pixel component <NUM> from the pixel wafer <NUM>. Alternatively, an optional pixel substrate <NUM> can be provided on which LEDs <NUM>, fuses <NUM>, pixel controllers <NUM>, or electrodes <NUM> can be disposed, micro-transfer printed, or otherwise formed. Referring to <FIG>, a pixel substrate <NUM>, for example an oxide or nitride layer such as a silicon dioxide layer can be formed on or over the sacrificial portions <NUM>, for example, after the steps illustrated in <FIG>, using photolithographic processes, tools, and materials. <FIG> illustrates a released pixel component <NUM> having the pixel substrate <NUM> (corresponding to <FIG>).

Referring to <FIG>, an array of the pixel components <NUM> are illustrated with matrix-addressed row and column conductors <NUM>, <NUM>, controlled by the row and column controllers <NUM>, <NUM>, respectively (not shown), corresponding to <FIG>. (In <FIG>, the fuses <NUM> are not illustrated for clarity. ) The dashed row or column conductors <NUM>, <NUM> are not provided with a forward-biased voltage differential while the center row and column conductors <NUM>, <NUM> are shown with a thicker, solid line to illustrate that they are provided with a forward-biased voltage differential. In normal operation with functional pixel components <NUM>, the center pixel component <NUM> (indicated with a dashed circle) will conduct current from the center row conductor <NUM> to the center column conductor <NUM> and emit light. The remaining pixel components <NUM> in the center column do not emit light because there is no voltage difference with the corresponding row conductor <NUM>. The other pixel components <NUM> in the center row and connected to the other columns do not emit light because they are reverse biased.

Referring to <FIG>, however, if a pixel component <NUM> is shorted to form a shorted pixel component <NUM>, the row in which the shorted pixel component <NUM> is electrically connected will be provided with power from the corresponding column conductor <NUM> through the shorted pixel component <NUM>. The pixel component <NUM> in the center column and the row with the shorted pixel component <NUM> will therefore also emit light. If all of the column conductors <NUM> except that of the shorted pixel component <NUM> are powered to emit light from all of the pixel components <NUM> in the center row, then all of the pixel components <NUM> in the row that includes the shorted pixel component <NUM> will emit light (except the shorted pixel component <NUM>). Thus, shorted pixel components <NUM> can cause other, functional pixel components <NUM> to emit light and render the display <NUM> unusable. A row having a shorted pixel component <NUM> has been demonstrated to undesirably cause the remaining pixels in the row to emit light and the removal of a conductor in series with the shorted pixel component <NUM> (electrically equivalent to blowing a fuse <NUM>) has been demonstrated to prevent the undesirable light emission.

According to embodiments of the present invention, this electrically shorted LEDs in a display <NUM> can be mitigated by blowing the fuse <NUM> of the shorted pixel component <NUM> having the shorted LED. This can be accomplished in a variety of ways. In one method of the present invention, referring to <FIG>, the display is provided in step <NUM> and operated in step <NUM> so that the pixel components <NUM> emit light. An operational parameter of each pixel component <NUM> is measured in step <NUM> (for example light output or current through each pixel component <NUM>). The shorted pixel components <NUM> are determined in step <NUM> and the fuses <NUM> of the shorted pixel components <NUM> are blown in step <NUM>.

Referring to <FIG>, shorted pixel components <NUM> can be determined by measuring the light output of each pixel component <NUM> (step <NUM>) and comparing it to an expected light output (step <NUM>). Shorted pixel components <NUM> typically do not emit light and they can be distinguished from open pixel components <NUM> (pixel components <NUM> that do not conduct current and do not emit light), by controlling the pixel components <NUM> in a common row or column with the non-light-emitting pixel component <NUM> as described above with respect to <FIG>. Referring to <FIG>, shorted pixel components <NUM> can also be determined by measuring (step <NUM>) the current through each LED <NUM> individually and comparing the measured current to an expected standard (step <NUM>). Shorted pixel components <NUM> can conduct more current than functional pixel components <NUM>, for example when provided with a voltage difference that is less than the expected voltage drop for the LED <NUM>, when provided with a reverse-biased voltage differential, or by noting a greater-than-expected current when driven with a predetermined operating voltage. In another embodiment, a shorted pixel component <NUM> is determined by passing a current through the shorted pixel component <NUM> and measuring the voltage across the shorted pixel component <NUM>. An electrical short can be measured as a very low voltage drop in comparison with a good pixel component <NUM>, which can have a voltage drop exceeding two volts. For example, an electrical short can be measured as a voltage drop across the power supply lines (power and ground lines) of a shorted pixel component <NUM> of less than two volts, less than <NUM> volts, less than <NUM> volts, less than <NUM> volts, or less than <NUM> volts.

The fuses <NUM> of the shorted pixel components <NUM> can be blown by providing a reverse-biased current across the shorted pixel components <NUM> with a voltage that is greater than the normal operating voltage but less than the breakdown voltage of the LEDs <NUM>, to avoid destroying functional pixel components <NUM>. Alternatively, as noted above with respect to <FIG>, a shorted pixel component <NUM> can conduct enough current to drive a row of functional pixel components <NUM>. By setting the fuse <NUM> current rating at a current level greater than the current necessary to operate a single functional pixel component <NUM> but less than the current necessary to operate multiple pixel components <NUM>, the fuse <NUM> of a shorted pixel component <NUM> can be blown by controlling the row to emit light from all of the other pixel components <NUM> in the row.

The display <NUM> can be operated in various ways to determine any shorted pixel components <NUM>. In one way, each LED <NUM> is sequentially operated and its operating characteristics measured. In another way, all of the LEDs <NUM> in a row or a column are operated at a time and the rows or columns sequentially operated. In yet another way, all of the LEDs <NUM> are operated at the same time.

Similarly, the fuses <NUM> of shorted pixel components <NUM> can be blown in different ways. In one way, each fuse <NUM> of the shorted pixel components <NUM> is sequentially blown. In another way, all of the fuses <NUM> of the shorted pixel components <NUM> in a row or a column are blown at a time and the rows or columns sequentially activated. In yet another way, all of the fuses <NUM> of the shorted pixel components <NUM> are blown at the same time. For example, by providing all of the pixel components <NUM> in the display (sequentially, in rows or columns, or all at once) with a reverse-biased voltage and enough current to blow the fuses <NUM>, all of the fuses <NUM> can be blown one after the other, in rows or columns at a time, or all at once. (Fuses <NUM> can be blown by using either or both passive-matrix control or active-matrix control. ) In another example, by operating all of the pixel components <NUM> in a row or column at a time, a forward-biased low-resistance shorted pixel component <NUM> will conduct more current than the normally functional pixel components <NUM> in a common row or column and will blow the fuse <NUM> of the shorted pixel component <NUM>.

In an embodiment of the present invention, the step <NUM> of blowing a fuse <NUM> is a common step with measuring the operational parameter in step <NUM> and determining the shorted LEDs <NUM> (shorted pixel components <NUM>) in step <NUM>, and can even be the same step <NUM> as operating the display <NUM>. By providing a fuse <NUM> with a predetermined current rating and providing an image or fuse signal to the pixel components <NUM> with sufficient current to blow the fuse <NUM> of a shorted pixel component <NUM> and leave the functional pixel components <NUM> operational the current is inherently compared to the rated current (step <NUM>) and if the fuse <NUM> of a shorted pixel component <NUM> is blown, the blown fuses <NUM> determine the shorted LEDs <NUM> of the electrically shorted pixel components <NUM>. Hence, in an embodiment, the display <NUM> is rendered properly functional by providing the display in step <NUM> according to embodiments of the present invention, and then providing a fuse signal that deactivates any shorted pixel components <NUM> the display by blowing its associated fuse <NUM> in step <NUM> and leaving the remaining pixel components <NUM> functional.

The current rating of a fuse <NUM> can depend, at least in part, on the temperature of the fuse <NUM>. Since an operational LED <NUM> can have an elevated temperature, the associated fuse <NUM> can also have an elevated temperature that affects its current rating. Hence, referring to <FIG>, the spatial location of the fuse <NUM> with respect to its corresponding LED <NUM> can be selected to reduce changes in the fuse <NUM> current rating due to temperature changes in the LED <NUM>. As shown in <FIG>, a fuse <NUM> is located a distance D from its associated LED <NUM>. The associated LED <NUM> has a length L and width W over the display substrate <NUM> (<FIG>). In an embodiment, the distance D is greater than or equal to the length L or width W. In other embodiments, the distance D is greater than or equal to <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, or <NUM> times the length L or width W. The rated current of the fuse <NUM> can be set to compensate for the operating temperature of the LED <NUM>, pixel component <NUM>, or display <NUM>.

Once the fuse <NUM> of a shorted pixel component <NUM> is blown, the shorted pixel component <NUM> cannot conduct current and therefore cannot emit light, if it ever did. Consequently, the display <NUM> will have a missing pixel. This can be corrected, referring to <FIG>, by removing the shorted LED <NUM> and fuse <NUM> (for example, in a pixel component <NUM> such as is illustrated in <FIG>) in step <NUM>. The removed shorted pixel component <NUM> can be replaced with a new pixel component <NUM> in step <NUM>. The shorted pixel component <NUM> can be manually removed and a new pixel component <NUM> can be micro-transfer printed into place and electrically connected, either using connection posts <NUM> or with photolithographic methods. Alternatively, referring to <FIG> and <FIG>, a redundant LED 22E and fuse 24E (for example, in a common pixel component <NUM>) can be added in step <NUM>. The redundant pixel component <NUM> can be added after the shorted pixel component <NUM> is removed or before. Hence, in an embodiment and as shown in <FIG>, a redundant pixel component <NUM> can be provided for each pixel component <NUM> and electrically connected in parallel with the corresponding pixel component <NUM> as part of the display <NUM> manufacturing process and before the display <NUM> is tested.

If an LED <NUM> is electrically open, a redundant pixel component <NUM> can provide the needed light output. If the LED <NUM> is electrically shorted, the fuse <NUM> of the shorted pixel component <NUM> is blown providing a blown pixel component <NUM> and the redundant pixel component <NUM> provides the needed light output. Therefore, as shown in <FIG>, the display <NUM> includes a redundant pixel component <NUM> at each juncture of a row conductor <NUM> and column conductor <NUM> pixel component <NUM> site. The fuses <NUM> of the shorted pixel components <NUM> are blown and the redundant pixel components <NUM> are operated to provide the needed pixel emission. If both the pixel component <NUM> and the redundant pixel component <NUM> are functional, they are both operated together to provide the desired light output together (for example, by driving each pixel component <NUM> and redundant pixel component <NUM> at half the desired brightness). If the redundant pixel component <NUM> is a shorted pixel component <NUM>, the redundant fuse <NUM> of the redundant pixel component <NUM> can be blown as described above with respect to the pixel components <NUM>.

The row conductors <NUM> can include an electrically conductive conductor extension <NUM> to provide a space over the display substrate <NUM> in which the redundant pixel components <NUM> can be disposed and electrically connected to the row and column conductors <NUM>, <NUM>. The conductor extension <NUM> can be an electrical conductor (for example, made of metal or the same material used for the row or column conductors <NUM>, <NUM> and made in the same step or using similar photolithographic processes), that is electrically connected to the row conductor <NUM> and is substantially parallel to the column conductor <NUM>. As shown in <FIG>, multiple conductor extensions <NUM> can be provided and can be substantially parallel to either the row conductor <NUM> or column conductor <NUM>. The redundant pixel component <NUM> can be provided and electrically connected in similar or the same steps as the pixel component <NUM> is provided and electrically connected.

As will be apparent to those skilled in the art of substrate and component layout, alternative arrangements of the pixel components <NUM> and redundant pixel components <NUM> are possible, for example as illustrated in <FIG>.

In an alternative embodiment and referring to <FIG>, each pixel component <NUM> includes a redundant LED 22E and associated redundant fuse 24E electrically connected in series with the redundant LED 22E. The redundant LED 22E and redundant fuse 24E are electrically connected in parallel with the LED <NUM> and fuse <NUM>. Thus a micro-transfer printable pixel component <NUM> of the present invention comprises a redundant LED 22E having first and second redundant LED electrical contacts <NUM> for providing power to the redundant LED 22E to cause the redundant LED 22E to emit light. A redundant fuse 24E has first and second redundant fuse electrical contacts <NUM>. The first redundant fuse electrical contact <NUM> is electrically connected in series with the first redundant LED electrical contact <NUM>. The first electrode <NUM> is connected to the second redundant fuse electrical contact <NUM> and the second electrode <NUM> is connected to the second redundant LED electrical contact <NUM>. The redundant LED 22E and redundant fuse 24E can be provided and electrically connected in similar or the same steps as the LED <NUM> and fuse <NUM> are provided and electrically connected.

Thus, methods and structures of the present invention can enable fully functional LED displays such as displays incorporating matrix-addressed arrays of inorganic LEDs.

In some embodiments of the present invention, the LEDs <NUM>, fuses <NUM>, or pixel components <NUM> (collectively referred to below as elements) have a thin substrate with a thickness of only a few microns, for example less than or equal to <NUM> microns, less than or equal to <NUM> microns, or less than or equal to <NUM> microns, and a width or length of <NUM>-<NUM> microns, <NUM>-<NUM> microns, <NUM>-<NUM> microns, or <NUM>-<NUM> microns. Such micro-transfer printable elements can be made in a semiconductor source wafer (e.g., a silicon or GaN wafer) having a process side and a back side used to handle and transport the wafer. The elements are formed using lithographic processes in an active layer on or in the process side of a source wafer. An empty release layer space (corresponding to sacrificial portion <NUM> in <FIG> or <FIG>) is formed beneath the micro-transfer printable elements with tethers <NUM> connecting the micro-transfer printable elements to the source wafer (e.g., pixel wafer <NUM>, LED source wafer, or fuse source wafer) in such a way that pressure applied against the micro-transfer printable elements with a transfer stamp breaks the tethers <NUM> to release the micro-transfer printable elements from the source wafer. The elements are then micro-transfer printed to a destination substrate such as a pixel wafer <NUM> or display substrate <NUM>. Lithographic processes in the integrated circuit art for forming micro-transfer printable elements in a source wafer, for example transistors, LEDS, wires, and capacitors, can be used. The same etching and transfer process can be used to micro-transfer print the assembled or constructed elements onto the pixel wafer <NUM> or display substrate <NUM>.

Methods of forming such micro-transfer printable structures are described, for example, in the paper AMOLED Displays using Transfer-Printed integrated Circuits and <CIT>, referenced above. For a discussion of micro-transfer printing techniques see, <CIT>,<CIT> and <CIT>. Micro-transfer printing using compound micro-assembly structures and methods can also be used with the present invention, for example, as described in <CIT>, entitled Compound Micro-Assembly Strategies and Devices. In an embodiment, the pixel component <NUM> is a compound micro-assembled device.

According to various embodiments of the present invention, the pixel wafer <NUM> can be provided with the LEDs <NUM>, release layer (sacrificial layer <NUM>), tethers <NUM>, and connection posts <NUM> already formed, or they can be constructed as part of the process of the present invention. Similarly, any source wafers having micro-transfer printable LEDs <NUM> thereon can be constructed or transfer printed as part of the process of the present invention.

Connection posts <NUM> are electrical connections formed on a side of a micro-transfer printable element such as the LED <NUM>, fuse <NUM>, or pixel component <NUM> that extend generally perpendicular to a surface of the element. Such connection posts <NUM> can be formed from metals such as aluminum, titanium, tungsten, copper, silver, gold, or other conductive metals. In some embodiments, the connection posts <NUM> are made of one or more high elastic modulus metals, such as tungsten. As used herein, a high elastic modulus is an elastic modulus sufficient to maintain the function and structure of the connection posts <NUM> when pressed into a display substrate <NUM> row conductors <NUM> or column conductors <NUM> (which can include electrical contact pads as discussed below).

The connection posts <NUM> can be formed by repeated masking and deposition processes that build up three-dimensional structures, for example, by etching one or more layers of metal evaporated or sputtered on the process side of the element. Such structures can also be made by forming a layer above the element surface (e.g., sacrificial layer <NUM>), etching a well into the surface to form a connection post form <NUM>, filling or covering it with a patterned conductive material such as metal, and then removing the layer. The connection posts <NUM> can have a variety of aspect ratios and typically have a peak area smaller than a base area. The connection posts <NUM> can have a sharp point for embedding in or piercing electrical contact pads electrically connected to the row conductors <NUM> or column conductors <NUM>, electrodes <NUM>, or fuse electrical contacts <NUM>. The connection posts <NUM> can include a post material coated with an electrically conductive material different from the post material. The post material can be an electrically conductive metal or a doped or undoped semiconductor or an electrically insulating polymer, for example a resin, cured, resin, or epoxy and can have any of a variety of hardness or elastic modulus values. In an embodiment, the post material is softer than the conductive material so that the conductive material can crumple when the connection post <NUM> is under mechanical pressure. Alternatively, the conductive material is softer than the post material so that it deforms before the post material when under mechanical pressure. By deform is meant that the connection posts <NUM>, the contact pads, or the conductive material change shape as a consequence of the transfer printing. The connection post <NUM> or post material can be a semiconductor material, such as silicon or GaN, formed by etching material from around the connection post <NUM>. Coatings, such as the conductive material can be evaporated or sputtered over the post material structure and then pattern-wise etched to form the connection post <NUM>. The conductive material can be a solder or other metal or metal alloy that flows under a relatively low temperature, for example less than <NUM> degrees C. In particular, the conductive material can have a melting point less than the melting point of the post material.

In certain embodiments, the two or more adjacent connection posts <NUM> comprise a first and a second connection post <NUM> of different heights. In certain embodiments, the distance between two or more connection posts <NUM> is less than a width or length of the contact pads in a direction parallel to the display substrate <NUM>. In certain embodiments, the connection posts <NUM> are disposed in groups, the connection posts <NUM> within a group are electrically connected to a common contact pad and the connection posts <NUM> in different groups are electrically connected to different contact pads. In certain embodiments, the connection posts <NUM> are disposed in groups and a spacing between adjacent connection posts <NUM> within a given group is less than a spacing between adjacent groups. In certain embodiments, the connection posts <NUM> within a group are electrically shorted together. In certain embodiments, each of the two or more connection posts <NUM> is a multi-layer connection post <NUM>. In certain embodiments, the contact pads comprise a material that is the same material as a material included in the connection post <NUM>.

In certain embodiments, the contact pads comprise a material that is softer than that of the connection post <NUM>. In certain embodiments, the connection posts <NUM> comprise a material that is softer than that of the contact pads. In certain embodiments, a conductive material other than a material of the contact pad or the connection post <NUM> adheres or electrically connects, or both, the contact pad to the connection post <NUM>. In certain embodiments, at least a portion of the contact pad has a first conductive layer and a second conductive layer over the first conductive layer, and the second conductive layer has a lower melting temperature than the first conductive layer. In embodiments, the contact pad is coated with a non-conductive layer or the contact pad is formed on a compliant non-conductive layer. In certain embodiments, the second conductive layer is a solder. In certain embodiments, the contact pad is welded to the connection post <NUM>. In certain embodiments, the contact pads are non-planar and the connection posts <NUM> are inserted into the contact pads.

The display substrate <NUM> contact pads can be made of or include a relatively soft metal, such as tin, solder, or tin-based solder, to assist in forming good electrical contact with the connection posts <NUM> and adhesion with the elements. As used herein, a soft metal may refer to a metal into which a connection post <NUM> can be pressed to form an electrical connection between the connection post <NUM> and the contact pad. In this arrangement, the contact pad can plastically deform and flow under mechanical pressure to provide a good electrical connection between the connection post <NUM> and the contact pad.

In another embodiment of the present invention, the connection posts <NUM> can include a soft metal and the contact pads include a high elastic modulus metal. In this arrangement, the connection posts <NUM> can plastically deform and flow under mechanical pressure to provide a good electrical connection between the connection post <NUM> and the contact pads.

If an optional layer of adhesive is formed on the display substrate <NUM>, the connection posts <NUM> can be driven through the adhesive layer to form an electrical connection with the contact pads beneath the adhesive layer. The adhesive layer can be cured to more firmly adhere the element and maintain a robust electrical connection between the connection posts <NUM> and contact pads in the presence of mechanical stress. The adhesive layer can undergo some shrinkage during the curing process that can further strengthen the electrical connectivity and adhesion between the connection post <NUM> and the contact pads.

In alternative embodiments of the present invention, the connection posts <NUM> of are in contact with, are embedded in, or pierce the contact pads of the element. In other or additional embodiments, either or both one or more of the connection posts <NUM> and the contact pads are deformed or crumpled into a non-planar shape or are deformed so that the surfaces of the connection posts <NUM> and the contact pads change shape on contact with each other. The deformation or crumpling can improve the electrical connection between the connection posts <NUM> and the contact pads by increasing the surface area that is in contact between the connection posts <NUM> and the contact pads. To facilitate deformation, in an embodiment the connection posts <NUM> have a composition softer than that of the contact pads or the contact pads have a composition softer than the connection posts <NUM>.

In another embodiment, the contact pads are coated with an optional polymer layer that can be patterned. The connection posts <NUM> are driven through the polymer layer to make electrical contact with the contact pads. The polymer layer can protect the contact pads and serves to embed the connection posts <NUM> in the contact pads by adhering to the connection posts <NUM>. Alternatively, a compliant polymer layer is formed beneath the contact pads to facilitate the mechanical contact made when the connection posts <NUM> are embedded in the contact pads. For example, a metal or metal alloy containing as gold, tin, silver, or aluminum, can be formed over a polymer layer or a polymer layer coated over a metal or metal alloy containing gold, tin, silver, or aluminum. The compliant polymer layer can also serve to adhere the connection posts <NUM> to the contact pads.

In some embodiments, the pixel components <NUM> include small integrated circuits (e.g., the pixel controller <NUM>) or assemblies of such small integrated circuits formed in or disposed on a semiconductor wafer, for example gallium arsenide or silicon, which can have a crystalline structure. Processing technologies for these materials typically employ high heat and reactive chemicals. However, by employing transfer technologies that do not stress the pixel component <NUM> or substrate materials, more benign environmental conditions can be used compared to thin-film manufacturing processes. Thus, the present invention has an advantage in that flexible substrates, such as polymeric substrates, that are intolerant of extreme processing conditions (e.g. heat, chemical, or mechanical processes) can be employed for the display substrates <NUM> or pixel components <NUM>. Furthermore, it has been demonstrated that crystalline semiconductor substrates have strong mechanical properties and, in small sizes, can be relatively flexible and tolerant of mechanical stress. This is particularly true for substrates having <NUM>-micron, <NUM>-micron, <NUM>-micron, <NUM>-micron, or even <NUM>-micron thicknesses. Alternatively, the printable LED components <NUM> can be formed in a microcrystalline, polycrystalline, or amorphous semiconductor layer.

The micro-transfer printable elements of the present invention can be constructed using foundry fabrication processes used in the art. Layers of materials can be used, including materials such as metals, oxides, nitrides and other materials used in the integrated-circuit art. Each element can be or include a complete semiconductor integrated circuit and can include, for example, transistors. The elements can have different sizes, for example, <NUM> square microns or <NUM>,<NUM> square microns, <NUM>,<NUM> square microns, or <NUM> square mm, or larger, and can have variable aspect ratios, for example <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, or <NUM>:<NUM>. The elements can be rectangular or can have other shapes.

Embodiments of the present invention provide advantages over other printing methods described in the prior art. By employing connection posts <NUM> and a printing method that provides micro-transfer printable element on a destination substrate and connection posts <NUM> adjacent to the destination substrate, a low-cost method for printing elements in large quantities over a destination substrate is provided. Furthermore, additional process steps for electrically connecting the micro-transfer printable elements to the destination substrate are obviated.

The element source wafer and micro-transfer printable elements, micro-transfer printing stamps, and destination substrates can be made separately and at different times or in different temporal orders or locations and provided in various process states.

The method can be iteratively applied to a single or multiple destination substrates. By repeatedly transferring sub-arrays of micro-transfer printable elements from a transfer stamp to a destination substrate and relatively moving the transfer stamp and destination substrates between stamping operations by a distance equal to the spacing of the selected micro-transfer printable elements in the transferred sub-array between each transfer of micro-transfer printable elements, an array of micro-transfer printable elements formed at a high density on a source wafer (e.g., pixel wafer <NUM>) can be transferred to a destination substrate (e.g., the display substrate <NUM>) at a much lower density. In practice, the source wafer is likely to be expensive, and forming micro-transfer printable elements with a high density on the source wafer will reduce the cost of the micro-transfer printable elements, especially as compared to micro-transfer printable elements on the destination substrate.

In particular, in the case wherein the active micro-transfer printable elements are or include an integrated circuit formed in a crystalline semiconductor material, the integrated circuit substrate provides sufficient cohesion, strength, and flexibility that it can adhere to the destination substrate without breaking as the transfer stamp is removed.

In comparison to thin-film manufacturing methods, using densely populated source substrate wafers and transferring micro-transfer printable elements to a destination substrate that requires only a sparse array of micro-transfer printable elements located thereon does not waste or require active layer material on a destination substrate. The present invention can also be used in transferring micro-transfer printable elements made with crystalline semiconductor materials that have higher performance than thin-film active components. Furthermore, the flatness, smoothness, chemical stability, and heat stability requirements for a destination substrate used in embodiments of the present invention may be reduced because the adhesion and transfer process is not substantially limited by the material properties of the destination substrate. Manufacturing and material costs may be reduced because of high utilization rates of more expensive materials (e.g., the source substrate) and reduced material and processing requirements for the destination substrate.

As is understood by those skilled in the art, the terms "over" and "under" are relative terms and can be interchanged in reference to different orientations of the layers, elements, and substrates included in the present invention. For example, a first layer on a second layer, in some implementations means a first layer directly on and in contact with a second layer. In other implementations a first layer on a second layer includes a first layer and a second layer with another layer therebetween.

The terms row and column are arbitrary and relative designations and can be exchanged in embodiments of the present invention.

Having described certain implementations of embodiments, it will now become apparent to one of skill in the art that other implementations incorporating the concepts of the disclosure may be used. Therefore, the disclosure should not be limited to certain implementations, but rather should be limited only by the scope of the following claims.

The various described embodiments of the invention may be used in conjunction with one or more other embodiments unless technically incompatible.

Throughout the description, where apparatus and systems are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are apparatus, and systems of the disclosed technology that consist essentially of, or consist of, the recited components, and that there are processes and methods according to the disclosed technology that consist essentially of, or consist of, the recited processing steps.

Claim 1:
A display having fused light-emitting diodes (LEDs), comprising:
a display substrate (<NUM>);
an array of pixel components (<NUM>) disposed on the display substrate, each pixel component comprising a pixel substrate (<NUM>) separate, independent, distinct from the display substrate, an inorganic light-emitting diode (<NUM>), and an electrical fuse (<NUM>) electrically connected in series with the light-emitting diode, wherein the light-emitting diode and the fuse are disposed on the pixel substrate; and
a fuse controller adapted to provide image control signals that cause the array of pixel components to display an image and fuse control signals providing sufficient electrical power to render each fuse non-conductive,
wherein the pixel substrates are disposed on the display substrate.