Patent ID: 12190790

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. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. 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.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Embodiments of the present disclosure provide light-emitting information displays and backlights that require less power. As used herein, the generic term ‘display’ refers to both an information display that shows information, such as an image, text, or video, to a viewer, such as a micro-LED display, and to a local-area-dimming backlight that provides structured illumination to a light-valve display, such as a liquid crystal display (LCD). Each pixel of a backlight can variably illuminate multiple pixels in an LCD thereby providing local-area dimming. For conciseness, the word ‘display’ is used in the following. Unless otherwise clear from context, where a ‘display’ is described, analogous embodiments of a backlight, with or without corresponding light control feature(s), such as an LCD layer, present, are also contemplated.

According to some embodiments of the present disclosure and as illustrated inFIGS.1,2A,2B, and2C, a current-selectable light-emitting diode (LED) display system90comprises display pixels24distributed in an array of rows and columns. Pixels24are grouped in mutually exclusive pixel clusters20so that no pixel24is in more than one cluster20and every pixel24is in a cluster20. A cluster controller22controls pixels24in each cluster20and each cluster controller22is connected to each pixel24in cluster20of pixels24so that pixels24emit light responsive to cluster row signals26and cluster column signals28. Each cluster controller22comprises a selectable current source30. A selectable current source30is responsive to a current-select signal40(discussed below with respect toFIGS.4A-4C) to select a current range provided to pixels24to emit light. The current range limits the maximum amount of current that can be supplied to pixels24and therefore limits the maximum brightness (luminance) of pixels24. Thus, selecting a different current range using current-select signal40can alter brightness characteristics of pixels24.

Cluster controllers22can receive control signals, for example display row signals17(e.g., row-select or timing signals) from a display row controller16and display column signals19(e.g., column-data, current-select signals40, or timing signals) from a display column controller18. Display row and column controllers16,18can receive display signals (e.g., display control signals) from a display controller14or can themselves constitute a display controller14. Display controller14can receive image data (image pixels) from an external source. Display row signals17and display column signals19can include data signals, row or column select signals, and timing signals, for example providing active-matrix control to pixel clusters20by providing image pixel data for each display pixel24from display column controller18through display column wires19to each cluster20in a row of clusters20selected by display row controller16through display row wires17. For illustrative clarity, display row signals17and display row wires17are designated with the same identifier since display row signals17are carried on display row wires17and are not easily distinguished in the drawings. Similarly, display column signals19and display column wires19are designated with the same identifier since display column signals19are carried on display column wires19and are not easily distinguished in the drawings.

Clusters20and pixels24can be disposed on a display substrate10, for example a glass or polymer substrate, within a display area12comprising all of pixels24and at least some of cluster controllers22. Display area12can be, for example, a convex hull of pixels24. Thus, in some embodiments, at least a portion of cluster controllers22are disposed between pixels24on display substrate10. In contrast, display row controller16, display column controller18, and display controller14can be disposed on display substrate10external to display area12, for example adjacent to the edges or sides of display area12. Display row controller16, display column controller18, and display controller14can be packaged integrated circuits mounted on display substrate10. According to some embodiments, display row controller16, display column controller18, and display controller14can each be one or more unpackaged bare die, for example disposed on display substrate10by micro-transfer printing, or a thin-film transistor circuit disposed on display substrate10.

As shown inFIG.2A, a cluster controller22of a cluster20can receive display row signals17and display column signals19from display row controller16and display column controller18, respectively. Cluster controller22can be directly connected to each pixel24in cluster20and can provide both cluster row signals26and cluster column signals28to provide either active- or passive-matrix control of pixels24. As shown inFIG.2B, pixels24in a cluster20can receive display row signals17and display column signals19from display row controller16and cluster controller22can receive display column signals19from display column controller18. According to the illustrations herein, a wire (e.g., display row wires17and display column wires19) incorporating dashes indicates that additional clusters not shown in the Figure can be connected to the wire e.g., as shown inFIGS.1,2B, and3, andFIGS.9A-9Bdiscussed below. As shown in more detail inFIGS.3A,3B, according to some embodiments, display row signals17from display row controller16can also serve as anode control lines for LEDs60.

According to some embodiments of the present disclosure and as illustrated inFIG.2C, cluster controller22can comprise multiple integrated circuits, for example unpackaged, micro-transfer printed, bare die disposed at least partly or completely between pixels24providing a cluster row controller22R and a cluster column controller22C to enable passive- or active-matrix control of pixels24.

According to embodiments of the present disclosure and as illustrated inFIGS.3A and3B, pixels24of clusters20can comprise one or more light emitters60, for example micro-light-emitting diodes60that each emit different colors of light, for example red LEDs that emit red light, green LEDs that emit green light, and blue LEDs that emit blue light when provided with enough current at a suitable voltage. Display row signals17(e.g., display row-select signals) or cluster row signals26(e.g., cluster row-select signals) and cluster column signals28(e.g., cluster column-data signals) can provide enough current at suitable voltages to drive each of LEDs60in each pixel24. Display or cluster row signals16,26and display column or cluster column signals18,28can comprise one or more of row-select, timing, column-data signals, or current-select signals40but are not limited to such and can implement any suitable control and data function desired.

As shown inFIG.3A, a separate selectable current source30is provided for each color of LEDs60and a common voltage provided either by cluster controller20or externally, for example by display row controller16. As shown inFIG.3B, a common selectable current source30is provided for all colors of LEDs60and different voltages provided for each color of LEDs can be provided either by cluster controller20or externally, for example by display row controller16. In some embodiments, both a common voltage and selectable current source30are provided to all of the different colors of LEDs60. In some embodiments, the colors of LEDs60are controlled in a color sequential fashion and a single selectable current source30is provided to all of the different colors of LEDs60in cluster20. By providing different voltages or selectable current sources to different colors of LEDs60, the realized efficiency of LEDs60can be improved, since different colors of LEDs60can have different efficiencies at different voltages and currents. Furthermore, a voltage provided to LEDs60(for example from display row controller16or cluster controller20) can be different from an operating voltage provided to cluster controller20. Since LEDs60and cluster controller20can comprise different semiconductor material (e.g., a compound semiconductor and silicon, respectively) that operate efficiently at different voltages, for example cluster controller22can operate at a lower voltage than LEDs60, providing different voltages can improve overall realized efficiency.

Pixels24can comprise light emitters60, for example light-emitting diodes60, for example inorganic light-emitting diodes60, for example micro-light emitting diodes60having a length or width no greater than one hundred microns, for example no greater than fifty microns, no greater than twenty microns, no greater than fifteen microns, no greater than twelve microns, or no greater than ten microns, and, optionally, a thickness no greater than fifty microns, for example no greater than twenty microns, no greater than ten microns, or no greater than five microns. As discussed further below, micro-light-emitting diodes60can be bare, unpackaged die, for example integrated circuit die, and can be micro-transfer printed from a micro-light-emitting diode source wafer to display substrate10and can comprise a broken (e.g., fractured) or separated LED tether61as a consequence of micro-transfer printing. Cluster controllers22can likewise be unpackaged bare die, for example integrated circuit die, and can be micro-transfer printed from a cluster controller source wafer to display substrate10and comprise a broken (e.g., fractured) or separated controller tether23as a consequence of micro-transfer printing. Cluster controllers22can have a length or width no greater than two hundred microns, for example no greater than one hundred microns, no greater than fifty microns or no greater than twenty microns, and, optionally, a thickness no greater than fifty microns, for example no greater than twenty microns, no greater than ten microns, or no greater than five microns. Micro-transfer printed integrated circuits, for example micro-LEDs60, are relatively small and can therefore be provided at a high density and resolution on display substrate10. Likewise, cluster controllers22can be very small and can therefore be provided between pixels24in display area12on or over display substrate10.

Each cluster controller22can comprise a single selectable current source30so that all of pixels24and LEDs60in each cluster20are driven with a single selected cluster current source36. In some embodiments, each cluster controller22can comprise a selectable current source30for each color of LED60(e.g., three selectable current sources30, one for each of the red-light emitting, green-light emitting, and blue-light emitting LEDs in a cluster20. In some embodiments a selectable current source30can be provided for each row or column of pixels60or for each color of LED60in each row or column of pixels in cluster20. In some embodiments, separate selectable current sources30can share some components but are nonetheless capable of providing different current ranges. For example, cluster current sources36can comprise a current reference and different current references can be provided for and shared by each color of LEDs60. Furthermore, the range of a cluster current source36can be specified by the input current reference. Different cluster current source36ranges can be provided by a programmable current source. Thus, current-select signal40can program a programmable current source, thereby selecting a cluster current source36range. As used herein, selecting a range of a cluster current source36is the same as selecting a cluster current source36.

A selectable current source30is a circuit that provides electrical current in two or more ranges that are selected by a current-select signal40. Current-select signal40can be a digital value presented on one or more wires to the selectable current source30circuit or current-select signal40can be an analog value. For example,FIGS.4A-4Cillustrate selectable current sources30according to embodiments of the present disclosure and Table 1 is a table illustrating example current ranges associated with each of four different current-select signals40presented as a two-bit binary value to selectable current source30. The ranges and circuits illustrated inFIGS.4A-4Cand Table 1 are exemplary and not limiting. Those knowledgeable in the digital and analog electronic arts will appreciate that there are many ways to implement selectable current source30and many possible current ranges that are useful in a display system90, such as a backlight.

As shown in Table 1, four different luminance values corresponding to the four different possible two-bit binary values selected by current-select signal40are each associated with one of four different current ranges: 0 to 1 μA, 0 to 4 μA, 0 to 16 μA, and 0 to 64 μA. These ranges are selected as suitable for micro-LEDs, but other ranges are possible and are included in the present disclosure. Moreover, the logarithmic progression of the different selectable current ranges is exemplary; some embodiments can comprise other progressions, for example linear or a power series. According to some embodiments of the present disclosure, one of current-select signals40can indicate no cluster current source36is selected so that all of the cluster current sources36are disabled or effectively turned off.

TABLE 100Luminance level 00 to 1 μA01Luminance level 10 to 4 μA10Luminance level 20 to 16 μA11Luminance level 30 to 64 μA

In some embodiments and as shown inFIG.4A, selectable current source30comprises four different cluster current sources36of different ranges with outputs connected in parallel and with a high-impedance output so that any one of cluster current sources36can be active at time, for example each providing a current range as illustrated in Table 1 and represented by current-source symbols of different sizes. A larger current-source symbol represents a cluster current source36that can provide current over a relatively larger range (not necessarily to scale). A demultiplexer32converts the binary current-select signal40into enable circuit control signals35that each enable a single different cluster current source36with respective enable circuit34.

In some embodiments and as shown inFIG.4B, selectable current source30comprises four cluster current sources36each having the same range (as illustrated with current-source symbols of the same size) connected in parallel. Enable circuits34enable one, two, three, or four of cluster current sources36in response to current-select signal40, thus providing 0 to 1 μA, 0 to 2 μA, 0 to 3 μA, or 0 to 4 μA (if each cluster current source36provides 0 to 1 μA while other ranges can be achieved with other cluster current sources36). In some embodiments, the same-range cluster current sources36ofFIG.4Bcould be replaced by the different-range cluster current sources36ofFIG.4A, providing different combinations of different current ranges, e.g., 0 to 5 μA (ranges 1 and 2 combined) or 0 to 21 μA (ranges 1, 2, and 3 combined).

In some embodiments and as shown inFIG.4C, in some embodiments selectable current source30can comprise multiple cluster current sources36and any one or combination of cluster current sources36can be active at the same time and can be connected in parallel so that the total cluster current sources36by selectable current source30is the sum of all of the activated cluster current sources36. The cluster current sources36can have the same range (e.g., as inFIG.4B) or have different ranges (e.g., as inFIGS.4A and4C).

Embodiments of the present disclosure can operate with any of a variety of cluster current sources36.FIG.5illustrates a generic cluster current source36that is enabled with enable circuit34, for example comprising two control transistors52A,52B responsive to enable circuit control signals35A and35B (collectively enable circuit control signal35), respectively and a transistor52C with a connected source and drain driving a capacitor C to form a sample and hold circuit that controls the gate of current source36(a transistor52). When the gate voltage control signal on current source36transistor52is low, leakage through capacitor C and the cluster current source36transistor52is reduced, saving power. In some embodiments, an optional control transistor52D responsive to enable circuit control signal35C can short capacitor C and ensure that the gate of current source36transistor52is grounded to further reduce leakage in capacitor C and current sources36. When the gate voltage is high current can flow through cluster current source36. The range of currents provided by cluster current source36can depend on the size of transistor52in cluster current source36(a larger transistor52can provide a greater current range) or current reference38. As shown inFIG.5, the gate control signal is connected to multiple cluster current sources36in parallel so that the multiple cluster current sources36are enabled in common. In some embodiments, enable circuit34drives only a single cluster current source36. According to some embodiments, current reference38can be part of enable circuit34or can be shared among multiple enable circuits34(as shown with the dotted line connection to the output of current reference38) in order to save circuitry. In some embodiments, one or more current reference38can be disposed in a display row controller16and connected to one or more cluster controller22, saving circuitry in cluster controller22.

Once cluster current source36is enabled, the provided current can be turned on or off with a switch50(for example comprising one or more transistors52) in response to a timing signal42and the current provided to a cluster row signal26or cluster column signal28to turn LEDs60on or off. According to some embodiments of the present disclosure, cluster controller22is a passive-matrix controller for pixels24in cluster20and timing signal42is a pulse-width modulation or pulse-density modulation signal that uses temporal modulation to control the luminance of pixels24at a constant current.

According to embodiments of the present disclosure, LEDs60emit light most efficiently at a particular current. This efficient current can be different for different LEDs, for example LEDs made with different materials or that emit different colors of light (e.g., due to having different compositions of a binary or ternary compound semiconductor). It is useful, therefore, to operate LEDs60at their most efficient current to provide a power-efficient display and to select different efficient currents for different corresponding types of LEDs60. Passive-matrix control can provide higher currents for shorter periods of time that, in some embodiments, match currents needed for efficient LED60operation.

LED60in pixel24can emit different amounts of light in response to a control signal (e.g., timing signal42) and the number of light levels (the luminance) is determined by the range of the control signal. However, if pixel24only operates within a subset of the range, the number of realized luminance levels is decreased. For example, if pixel24only operates at relatively low luminance levels, the higher luminance levels are never activated, and the reduced number of different luminance levels can lead to perceptible contouring (pixelization) in an image pixel. Thus, contouring is reduced if the actual luminance range of a display pixel24is matched to the desired luminance of a desired image pixel. Furthermore, transistors52(and some other components, such as capacitors) in cluster current sources36can leak current and the larger the transistor52(or other components) the more current can leak. Leakage can be reduced by reducing the voltage provided to a gate of a transistor or across a capacitor, for example by reducing the voltage output by enable circuit34. Although the leakage of a single transistor52can be relatively small, if the leakage occurs for every pixel24in a high-resolution display, the power wasted can be considerable, especially for portable display applications in which power efficiency is an important consideration. Thus, leakage is reduced if cluster current source36for an LED60provides only the current required for a desired LED luminance range. If additional current is provided but not used in a cluster current source36, additional current leakage also occurs, reducing efficiency.

Therefore, according to embodiments of the present disclosure, a current-selectable light-emitting-diode display comprises pixels24arranged and controlled in clusters20. Each cluster20has a selected range of electrical current necessary to operate pixels24in cluster20. The desired range can be determined by analyzing image pixel values input to cluster20, for example a portion of an image corresponding to cluster20, to determine the brightest image pixel in cluster20and selecting the smallest luminance range of selectable current source30that can provide the desired luminance in cluster20according to the brightest image pixel. By selecting the smallest luminance range, power leakage is reduced in selectable current source30and the number of luminance levels in each cluster20is maintained, improving power efficiency, and reducing image contouring. Use of a larger number of clusters20within display90of a given size can also enable further reductions in image contouring and improvements in efficiency (e.g., more clusters20decreases cluster size for a given resolution, thereby allowing for improved matching of luminance ranges to current sources36).

For example, and with reference to a simplified small example illustrated inFIG.6, an image can be divided into a four-by-four array of sixteen clusters20, labeled20A-20P. (In practice, for example, a 2k display might have 8192 clusters20each having 256 pixels24.) Clusters20A,20D,20E,20H,20I,20L,20M, and20P (dark clusters20) include only pixels24that are relatively dark and clusters20B,20C,20F,20G,20J,20K,20N, and20O (bright clusters20) include a range of pixels24that are both dark and light. Current for dark clusters20can be provided with a relatively small current range (e.g., 0 to 1 μA) and bright cluster20can be provided with a relatively large current range (e.g., 0 to 64 μA). Dark clusters20will therefore have reduced current leakage and current-selectable light-emitting-diode display system90will have increased power efficiency. Furthermore, pixels24in dark clusters20can have reduced contouring because the reduced luminance range (because of the reduced current range of dark clusters20) has the same number of luminance levels as clusters20with a greater luminance range. Since the human visual system has increased sensitivity to different luminance levels primarily in darker areas, embodiments of the present disclosure can provide displays with reduced visible contouring in darker areas without reducing luminance for a given image bit depth, and with reduced power usage and increased power efficiency. In effect, current-selectable light-emitting-diode display system90having clusters20provided with different current ranges can be a high-dynamic range (HDR) display.

For example, given an image with an eight-bit image pixel depth (256 luminance levels) and a two-bit current range corresponding to Table 1, the number of luminance levels at luminance level 0 is 256 and the number of additional luminance levels at each of luminance levels 1, 2, and 3 is 192 (because the lower luminance values in the larger current ranges are redundant with those of the lower current ranges) for a total of 832 luminance levels available (but only 256 are available in any one cluster20). Thus, in this example, an approximately four-fold increase in available luminance levels across display90is realized as compared to an equivalent display without selectable current sources30or clusters20. This example specifies eight bits, but as will be appreciated by those knowledgeable in the display arts, any number of bits greater than one can be used in a design according to embodiments of the present disclosure, for example ten bits or twelve bits.

Display systems90according to embodiments of the present disclosure can comprise light-emitting diodes (LEDs)60made with compound semiconductor materials and LED substrates separate, distinct, and individual from display substrate10. As shown inFIG.7A, each LED60can comprise a broken (e.g., fractured) or separated LED tether61broken (e.g., fractured) or separated as a consequence of micro-transfer printing LEDs60from an LED source wafer (e.g., a compound semiconductor substrate such as GaN or GaAs) to display substrate10. Similarly, cluster controller22can comprise a broken (e.g., fractured) or separated controller tether23broken (e.g., fractured) or separated as a consequence of micro-transfer printing cluster controller22from a cluster-controller source wafer (e.g., a semiconductor substrate such as silicon) to display substrate10. Thus, in some embodiments LEDs60and cluster controller22are disposed directly on display substrate10or directly on layers disposed on display substrate10.FIG.7Aillustrates one cluster20disposed on display substrate10but display systems90of the present disclosure can comprise multiple clusters20disposed on display substrate10, for example an array of clusters20defining a display area12, such as is shown inFIG.1.

In some embodiments, and as illustrated inFIG.7B, LEDs60and cluster controller22are micro-transfer printed onto a cluster substrate62that is separate, individual, and distinct from display substrate10and separate, individual, and distinct from LEDs60and any LED substrates and cluster controller22. LEDs60and a cluster controller22of a cluster20can be disposed on cluster substrate62. A single cluster20can be disposed on a single cluster substrate62or multiple clusters20can be disposed on a single cluster substrate62. Cluster substrates62can be disposed on display substrate10, for example by micro-transfer printing or other assembly processes, such as surface-mount technology. Clusters20on cluster substrates62can be surface-mount devices or can be micro-assembled, for example by micro-transfer printing cluster substrates62from a cluster source wafer to display substrate10so that cluster substrates62can comprise a broken (e.g., fractured) or separated cluster tether63as a consequence of micro-transfer printing. Clusters20on cluster substrates62can be packaged in order to be appropriately disposed by surface-mount technology. Cluster substrates62can comprise a same material as display substrate10or can be a different material.

As illustrated inFIG.7C, cluster controller22in each cluster20can be formed in or on and native to cluster substrate62rather than micro-assembled on cluster substrate62, for example where cluster substrate62is a semiconductor substrate such as a silicon substrate and by using photolithographic processes found in the integrated circuit industry. Cluster controller22can be an integrated circuit. As also illustrated inFIG.7C, pixels24with LEDs60can be micro-assembled on a pixel substrate64and pixel substrate64can be micro-assembled on cluster substrate62so that pixel substrate64can comprise a fractured or separated pixel tether65as a consequence of micro-assembling pixel substrate64from a pixel source wafer to cluster substrate62. Pixel substrates64can comprise material similar to or the same as cluster substrate62or display substrate10. One or more pixels24with pixel substrates64can be disposed directly on cluster controller22, so that cluster controller22can occupy a substantial amount of space on cluster substrate62or cluster controller22can be disposed between pixels24(e.g., as shown inFIG.7C). Cluster substrate62can be assembled on display substrate10or layers on display substrate10.

According to some embodiments and as shown inFIG.7D, cluster controller22can be formed in or on and native to display substrate10, for example where display substrate10is a semiconductor substrate and, e.g., with photolithographic processing and materials, for example a silicon substrate in a micro-display. LEDs60in pixels24can be assembled, for example by micro-transfer printing, directly on display substrate10or layers on display substrate10, as shown inFIG.7A, or can be disposed on pixel substrates64and pixel substrates64can be assembled, for example by micro-transfer printing, onto display substrate10or layers disposed on display substrate10, as shown inFIG.7D.

Embodiments of the present disclosure illustrate inFIGS.7B-7Duse cluster substrates62or pixel substrates64, or both, to provide a compound micro-assembled structure. Such structures can be tested before assembly on display substrate10. For example, clusters20on cluster substrates62as shown inFIGS.7B and7Ccan be tested before assembly on display substrate10. Similarly, pixels24disposed on pixel substrates64can be tested before micro-assembly on cluster substrates62or display substrate10. By testing clusters20or pixels24before assembly, any defective cluster controllers22or pixels24can be discarded and not assembled on display substrate10or cluster substrate62, thereby improving display system90yields and reducing costs. For example, either or both cluster substrate62or pixel substrate64can comprise probe pads for automated testing and micro-assembly systems can be programmed to discard or not assemble any defective clusters20or defective pixels24.

According to embodiments of the present disclosure and as illustrated inFIG.8A, display system90can operate by first providing a display system90in step100. Display system90then receives an image, for example display controller14receives an image comprising image pixel values arranged in rows and columns corresponding to display pixel24rows and columns, in step105. The image is then analyzed to determine the appropriate cluster current source36for each cluster20, for example by display controller14, in step110, and the corresponding current-select signal40chosen for each cluster20. The determination can be based on the current required to provide the greatest desired luminance of any display pixel24in each cluster20. The image data and current-select signal40are then sent to each cluster20, for example through display row and display column controllers16,18and display row wires17and display column wires19to cluster controllers22of each cluster20in step115. In response to received current-select signal40, cluster controller22enables circuit34to enable circuit control signal35to select cluster current source36. Timing signal42(for example provided by display row and display column controllers16,18or generated internally by cluster controller22) then controls switch50to display the received cluster image data with LEDs60in each cluster20in step125. Timing signal42can be a pulse-width modulation, pulse density modulation, or delta sigma signal that provides a constant current to LEDs60, thereby improving the efficiency of display system90. Cluster controller22can provide passive-matrix control to LEDs60, reducing the needed control circuits in cluster20.

Embodiments illustrated inFIG.8Acan use a display controller14to analyze the image data associated with each cluster20and determine the appropriate cluster current source36for each cluster20. According to some embodiments of the present disclosure and as illustrated inFIG.8B, the image data analysis to determine the appropriate cluster current source36for a cluster20is performed in cluster20. Thus, the analysis for each cluster20can be performed simultaneously and the communication bandwidth for cluster20is reduced, thereby increasing display system90frame rate. In some such embodiments, additional circuits must be provided in each cluster controller22to enable the analysis and determination, but since all that is necessary is to determine the greatest image pixel value of the cluster image data for each color or the colors together, e.g., find a greatest value, the circuitry can be simple and can be implemented directly in logic rather than requiring a stored-program machine (e.g., a computer or CPU and memory).

Therefore, according to embodiments of the present disclosure and as illustrated inFIG.8B, display system90can operate by first providing a display system90in step100. Display system90then receives an image, for example display controller14receives an image comprising image pixel values arranged in rows and columns corresponding to display pixels24, in step105. Image data for each cluster20is then communicated to each cluster20, for example through display row and display column controllers16,18and display row wires17and display column wires19to cluster controllers22of each cluster20in step114. The image is then analyzed in each cluster20to determine the appropriate cluster current source36for cluster20, for example by cluster controller22, in step112, and the corresponding current-select signal40chosen for each cluster20. The determination can be based on the current required to provide the greatest desired luminance of any display pixel24in each cluster20. In response to current-select signal40, each cluster controller22enables circuit34to enable circuit control signal35to select cluster current source36in step120. Timing signal42(for example provided by display row and display column controllers16,18or generated internally by cluster controller22) then controls switch50to display the received cluster image data with LEDs60in each cluster20in step125. Timing signal42can be a pulse-width modulation, pulse density modulation, or delta sigma signal that provides a constant current to LEDs60, thereby improving the efficiency of display system90. Cluster controller22can provide passive-matrix control to LEDs60, reducing the number and size needed in control circuits in cluster20. Thus, clusters20can be externally controlled, e.g., by display row and display column controllers16,18, using active-matrix circuits, each cluster20can control display pixels24in the cluster using passive-matrix circuits.

Display substrates10of large-format displays can have signal-carrying wires (e.g., display row wires17and display column wires19) that are lengthy (e.g., greater than one meter). Such long wires have a finite resistance and can experience parasitic capacitance and therefore signals carried on the wires can degrade significantly over the extent of display substrate10.FIG.9Aillustrates display row wires17and display column wires19directly connected to each cluster20and cluster controller22in an array of clusters20disposed over display substrate10. According to some embodiments and as illustrated inFIG.9B, display system90can comprise signal regeneration circuits70that regenerate signals (e.g., display row signals17and display column signals19) In some such embodiments, display row wires17and display column wires19each comprise separate wire segments that are indirectly electrically connected through signal regeneration circuits70. Thus, according to embodiments of the present disclosure and as shown inFIG.9B, a display system90can comprise an array of display pixels24distributed in rows and columns. A first wire segment (e.g., first display row wire segment17A or first display column wire segment19A) is electrically connected to a first cluster20or first cluster controller22and a second wire segment (e.g., second display row wire segment17B or second display column wire segment19B) is electrically connected to a second cluster20or second cluster controller22. Signal regeneration circuit70is operable to regenerate a signal conducted on the first wire segment and drive the regenerated signal onto the second wire segment.

FIG.10Aillustrates a simple signal regeneration circuit70. A gate of a transistor52is connected to first wire segments (e.g., first display row wire segment17A or first display column wire segment19A), transistor52source is connected to power P, the transistor52drain is connected through a resistor R to ground G and second wire segments (e.g., second display row wire segment17B or second display column wire segment19B). When a signal is received on the transistor52gate, transistor52is turned on and transistor52drain is pulled high to regenerate the signal connected to transistor52gate. As will be appreciated by those knowledgeable in electronic circuit design, many other signal regeneration circuits70are possible and are contemplated in various embodiments of the present disclosure. One or multiple clusters20or cluster controllers22can be connected to each first and to each second wire segment and embodiments of the present disclosure can comprise more than two wire segments (e.g., more than two display row wire segments17B or more than two display column wire segments19B) for each wire (e.g., display row wire17or display column wire19) and one or multiple clusters20or cluster controllers22can be connected to each of the more than two wire segments. Signal regeneration circuits70can be disposed on display substrate10separately from other circuits (for example signal regeneration circuits70can be unpackaged, bare integrated-circuit dies micro-transfer printed to display substrate10and can have broken (e.g., fractured) or separated tethers), as shown inFIG.9B. In some embodiments, signal regeneration circuits70can be disposed on cluster substrate62, either as a separate unpackaged, bare integrated circuit die or native to cluster substrate62, for example as shown inFIG.10B, or as a part of cluster controller22, for example as shown inFIG.10C. Signal regeneration circuits70can enable good signal propagation over large display substrate10and enable larger display systems90with faster frame rates and fewer display pixel errors.

Display substrate10can be any useful substrate on which cluster controllers22and an array of pixels24can be suitably disposed, for example glass, plastic, resin, fiberglass, semiconductor, ceramic, quartz, sapphire, or other substrates found in the display or integrated circuit industries. Display substrate10can be flexible or rigid and can be substantially flat. Display row wires17and display column wires19can be wires (e.g., photolithographically defined electrical conductors such as metal lines) disposed on display substrate10that conduct electrical current from display row controllers16and display column controllers18, respectively, to cluster controllers22. Similarly, cluster row wires26and cluster column wires28can be wires (e.g., photolithographically defined electrical conductors such as metal lines) disposed on display substrate10that conduct electrical current from cluster controllers22to pixels24and LEDs60.

Generally, display substrate10has two opposing smooth sides suitable for material deposition, photolithographic processing, or micro-transfer printing of micro-LEDs60or cluster controllers22. Display substrate10can have a size of a conventional display, for example a rectangle with a diagonal of a few centimeters to one or more meters. Display substrate10can include polymer, plastic, resin, polyimide, PEN, PET, metal, metal foil, glass, a semiconductor, or sapphire and have a transparency greater than or equal to 50%, 80%, 90%, or 95% for visible light. In some embodiments of the present disclosure, LEDs60emit light through display substrate10. In some embodiments, LEDs60emit light in a direction opposite display substrate10. Display substrate10can have a thickness from 5 microns to 20 mm (e.g., 5 to 10 microns, 10 to 50 microns, 50 to 100 microns, 100 to 200 microns, 200 to 500 microns, 500 microns to 0.5 mm, 0.5 to 1 mm, 1 mm to 5 mm, 5 mm to 10 mm, or 10 mm to 20 mm). According to some embodiments of the present disclosure, display substrate10can include layers formed on an underlying structure or substrate, for example a rigid or flexible glass or plastic substrate.

In some embodiments, display substrate10can have a single, connected, contiguous display area12(e.g., a convex hull including pixels24that each have a pixel functional area such as the light-emitting area of LEDs60in pixels24). The combined functional area of light emitters60can be less than or equal to one-quarter of display area12. In some embodiments, the combined functional areas of light emitters60is less than or equal to one eighth, one tenth, one twentieth, one fiftieth, one hundredth, one five-hundredth, one thousandth, one two-thousandth, or one ten-thousandth of the contiguous system substrate area. Thus, remaining area over display substrate10is available for additional functional elements such as cluster controllers22.

Cluster controller22can be, for example, a bare, unpackaged integrated circuit disposed between rows and columns of pixels24micro-transfer printing or formed in cluster substrate62or display substrate10that provides control, timing (e.g., clocks) or data signals (e.g., column-data signals) through cluster row wires26and cluster control wires28to pixels24to enable pixels24to emit light in display system90. Cluster controller22can comprise a single integrated circuit or can comprise multiple integrated circuits, e.g., electrically connected integrated circuits. The integrated circuit(s) can be micro-transfer printed as unpackaged dies and can comprise broken (e.g., fractured) or separated controller tether(s)23.

The array of pixels24can be a completely regular array (e.g., as shown inFIG.1) or can have pixel rows or pixel columns of pixels24that are offset from each other, so that pixel rows or pixel columns of pixels24are not disposed in a straight line and can, for example, form a zigzag line (not shown in the Figures) or, as another example, have non-uniform spacing(s). Cluster controllers22can be disposed between rows or columns of pixels24even when pixels24are arranged in a regular array, at least in part because cluster controllers22can be micro-integrated-circuits comprising bare, unpackaged die of a size that can be disposed between rows or columns, or both, of pixels24by micro-transfer printing.

Pixels24can be passive-matrix pixels24, can be analog or digital (e.g., including one or more analog or digital controllers), and can comprise one or more light-controlling or light-responsive elements, e.g., inorganic micro-light-emitting diodes60. Pixels24can comprise micro-light-emitting diodes60. Inorganic light-emitting diodes60can have a small area, for example having a length and a width each no greater than 20 microns, no greater than 50 microns, no greater than 100 microns, or no greater than 200 microns. Such small, light emitters60leave additional area on display substrate10for more or larger wires or additional functional elements such as cluster controllers22. When active, pixels24can be controlled at a constant current with timing signals42such as temporal pulse-width modulation signals provided by cluster controller22. Pixels24can comprise a red-light-emitting diode60that emits red light, a green-light-emitting diode60that emits green light, and a blue-light-emitting diode60that emits blue light (collectively light-emitting diodes60or LEDs60) under the control of cluster controller22. In certain embodiments, light emitters60that emit light of other color(s) are included in pixel24, such as a yellow light-emitting diode60. Light-emitting diodes60can be mini-LEDs60(e.g., having a largest dimension no greater than 500 microns) or micro-LEDs60(e.g., having a largest dimension of no greater than 100 microns). Pixels24can emit one color of light or white light (e.g., as in a black-and-white display) or multiple colors of light (e.g., red, green, and blue light as in a color display).

According to some embodiments of the present disclosure, pixels24comprise inorganic micro-light-emitting diodes60that have a length, a width, or both over array substrate10or pixel substrate64that is no greater than 100 microns (e.g., no greater than 50 microns, no greater than 20 microns, no greater than 15 microns, no greater than 12 microns, no greater than 10 microns, no greater than 8 microns, no greater than 5 microns, or no greater than 3 microns). Such relatively small, light emitters60disposed on a relatively large display substrate10(for example a laptop display, a monitor display, or a television display) take up relatively little area on display substrate10so that the fill factor of LEDs60on display substrate10(e.g., the aperture ratio or the ratio of the sum of the areas of LEDs60over display substrate10to the convex hull area of display substrate10that includes LEDs60or minimum rectangular area of the array of pixels24such as display area12) is no greater than 30% (e.g., no greater than 20%, no greater than 10%, no greater than 5%, no greater than 1%, no greater than 0.5%, no greater than 0.1%, no greater than 0.05%, or no greater than 0.01%). For example, an 8K display (having a display array12bounding 8192 by 4096 display pixels24) over a 2-meter diagonal 9:16 display with micro-LEDs60having a 15-micron length and 8-micron width has a fill factor of much less than 1%. An 8K display having 40-micron by 40-micron pixels24can have a fill factor of about 3%. According to some embodiments of the present disclosure, the remaining area not occupied by light emitters60is used at least partly to dispose cluster controllers22between light emitters60.

In contrast to embodiments of the present disclosure, existing prior-art flat-panel displays have a desirably large fill factor. For example, the lifetime of OLED displays is increased with a larger fill factor because such a larger fill factor reduces current density and improves organic material lifetimes. Similarly, liquid-crystal displays (LCDs) have a desirably large fill factor to reduce the necessary brightness of the backlight (because larger pixels transmit more light), improving the backlight lifetime and display power efficiency. Thus, prior displays cannot provide integrated cluster control because there is no space on their display substrates for additional or larger functional elements, such as cluster controllers22, in contrast to embodiments of the present disclosure.

In some embodiments, integrated circuits such as LEDs60or cluster controllers22are made in or on a native semiconductor wafer and have a semiconductor substrate and are micro-transfer printed to a non-native substrate, such as pixel substrate64, cluster substrate62, or display substrate10. Any of pixel substrate64, cluster substrate62, and display substrate10can include glass, resin, polymer, plastic, ceramic, or metal and can be non-elastomeric. Cluster substrate62can be a semiconductor substrate and cluster controller22can be formed in or on and native to cluster substrate62. Semiconductor materials (for example doped or undoped silicon, GaAs, or GaN) and processes for making small integrated circuits are well known in the integrated circuit arts. Likewise, backplanes such as display substrates10and means for interconnecting integrated circuit elements on the backplane are well known in the display and printed circuit board arts.

In a method according to some embodiments of the present disclosure, integrated circuits are disposed on the display substrate10by micro transfer printing. In some methods, integrated circuits (or portions thereof) or LEDs60are disposed on pixel substrate64to form a heterogeneous pixel24and pixel24is disposed on cluster substrate62or display substrate10using compound micro-assembly structures and methods, for example as described in U.S. patent application Ser. No. 14/822,868 filed Aug. 10, 2015, entitled Compound Micro-Assembly Strategies and Devices. However, since pixels24or clusters20can be larger than the integrated circuits included therein, in some methods of the present disclosure, pixels24or clusters20are disposed on display substrate10using pick-and-place methods found in the printed-circuit board industry, for example using vacuum grippers. Pixels24or clusters20can be interconnected on display substrate10using photolithographic methods and materials or printed circuit board methods and materials.

In certain embodiments, display substrate10includes material, for example glass or plastic, different from a material in an integrated-circuit substrate, for example a semiconductor material such as silicon or GaN. LEDs60can be formed separately on separate semiconductor substrates, assembled onto cluster substrates62or pixel substrates64to form pixels24and then the assembled units are located on the surface of cluster substrate62or display substrate10. This arrangement has an advantage that the integrated circuits, clusters20, or pixels24can be separately tested on cluster substrate62or pixel substrate64and the cluster20or pixel24modules accepted, repaired, or discarded before clusters22or pixels24are located on display substrate10, thus improving yields and reducing costs.

In some embodiments of the present disclosure, providing display system90, display substrate10, clusters20, or pixels24can include forming conductive wires (e.g., display row wire17, display column wire19, cluster row wire26, and cluster column wire28) on display substrate10, cluster substrate62, or pixel substrate64by using photolithographic and display-substrate processing techniques, for example photolithographic processes employing metal or metal oxide deposition using evaporation or sputtering, curable resin coatings (e.g. SU8), positive or negative photo-resist coating, radiation (e.g. ultraviolet radiation) exposure through a patterned mask, and etching methods to form patterned metal structures, vias, insulating layers, and electrical interconnections. Inkjet and screen-printing deposition processes and materials can be used to form patterned conductors or other electrical elements. The electrical interconnections, or wires, can be fine interconnections, for example having a width of less than fifty microns, less than twenty microns, less than ten microns, less than five microns, less than two microns, or less than one micron. Such fine interconnections are useful for interconnecting micro-integrated circuits, for example as bare dies with contact pads and used with cluster substrate62and pixel substrate64. Alternatively or additionally, wires can include one or more crude lithography interconnections having a width from 2 μm to 2 mm, wherein each crude lithography interconnection electrically interconnects circuits, device, or modules on display substrate10. For example, electrical interconnections cluster row wire26, and cluster column wire28can be formed with fine interconnections (e.g., relatively small high-resolution interconnections) while display row wire17and display column wire19are formed with crude interconnections (e.g., relatively large low-resolution interconnections).

In some embodiments, red, green, and blue LEDs (e.g., micro-LEDs50) are micro transfer printed to pixel substrates64, cluster substrate62, or display substrate10in one or more transfers and can comprise fractured or separated LED tethers61as a consequence of micro-transfer printing. For a discussion of micro-transfer printing techniques that can be used or adapted for use in methods disclosed herein, see U.S. Pat. Nos. 8,722,458, 7,622,367 and 8,506,867, each of which is hereby incorporated by reference in its entirety. The transferred light emitters60are then interconnected, for example with conductive wires and optionally including connection pads and other electrical connection structures.

In some embodiments of the present disclosure, an array of display pixels24(e.g., as inFIG.1) can include at least 40,000, 62,500, 100,000, 500,000, one million, two million, three million, six million, eight million, or thirty-two million display pixels24, for example for a quarter VGA, VGA, HD, 4K, 5K, 6K, or 8K display having various pixel densities (e.g., having at least 50, at least 75, at least 100, at least 150, at least 200, at least 300, or at least 400 pixels per inch (ppi)). In some embodiments of the present disclosure, light emitters60in pixels24can be considered integrated circuits, since they are formed in a substrate, for example a wafer substrate, or layer using integrated-circuit processes. The substrate or layer need not necessarily be silicon, for example III-V semiconductor wafers or layers can be used to form light emitters60using integrated-circuit processes. Light emitters60are considered integrated circuits (or portions thereof) in the context of this disclosure.

In some embodiments of the present disclosure, light emitters60are inorganic micro-light-emitting diodes60(micro-LEDs60), for example having light-emissive areas of less than 10, 20, 50, or 100 square microns. In some embodiments, light emitters60have physical dimensions that are less than 100 μm, for example having at least one of a width from 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm), a length from 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm), and a height from 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm). Light emitters60can have a size of, for example, one square micron to 500 square microns. Such micro-LEDs60have the advantage of a small light-emissive area compared to their brightness as well as color purity providing highly saturated display colors and a substantially Lambertian emission providing a wide viewing angle. Such small light emitters60also provide additional space on display substrate10for additional functional elements or larger wires.

In some embodiments, LEDs60are formed in substrates or on supports separate from display substrate10. For example, LEDs60can be made in a native compound semiconductor wafer. Similarly, cluster controllers22can be separately formed in a semiconductor wafer such as a silicon wafer e.g., in CMOS. LEDs60, or cluster controllers22are then removed from their respective source wafers and transferred, for example using micro-transfer printing, to display substrate10, cluster substrate62, or pixel substrate64. Such arrangements have the advantage of using a crystalline semiconductor substrate that provides higher-performance integrated circuit components than can be made in the amorphous or polysilicon semiconductor available in thin-film circuits on a large substrate such as display substrate10. Such micro-transferred LEDs60or cluster controllers22can comprise a broken (e.g., fractured) or separated LED tether61or controller tether23as a consequence of a micro-transfer printing process.

According to various embodiments, display system90can include a variety of designs having a variety of resolutions, light emitter60sizes, and display substrate10areas.

By employing a multi-step transfer or assembly process, increased yields are achieved and thus reduced costs for display systems90of the present disclosure. Additional details useful in understanding and performing aspects of the present disclosure are described in U.S. patent application Ser. No. 14/743,981, filed Jun. 18, 2015, entitled Micro Assembled Micro LED Displays and Lighting Elements, the disclosure of which is hereby incorporated by reference herein in its entirety.

As is understood by those skilled in the art, the terms “over”, “under”, “above”, “below”, “beneath”, and “on” are relative terms and can be interchanged in reference to different orientations of the layers, elements, and substrates included in the present disclosure. For example, a first layer on a second layer, in some embodiments means a first layer directly on and in contact with a second layer. In other embodiments, a first layer on a second layer can include another layer or layers there between.

As is also understood by those skilled in the art, the terms “column” and “row”, “horizontal” and “vertical”, and “x” and “y”, “top” and “bottom”, and “left” and “right” are arbitrary designations that can be interchanged (unless otherwise clear from context).

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.

It should be understood that the order of steps or order for performing certain action is immaterial so long as operability is maintained. Moreover, two or more steps or actions in some circumstances can be conducted simultaneously. The disclosure has been described in detail with particular express reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the following claims.

PARTS LIST

G groundP powerC capacitorR resistor10display substrate12display area14display controller16display row controller17display row signals/display row wires17A first display row wire segment17B second display row wire segment18display column controller19display column wire/display column signals19A first display column wire segment19B second display column wire segment20pixel cluster/cluster22cluster controller22C cluster column controller22R cluster row controller23controller tether24pixel/display pixel26cluster row wire/cluster row signal28cluster column wire/cluster column signal30selectable current source32demultiplexer34enable circuit35enable circuit control signal35A enable circuit control signal35B enable circuit control signal35B enable circuit control signal35C enable circuit control signal36cluster current source38current reference40current-select signal42timing signal50switch52transistor52A transistor52B transistor52C transistor52D transistor60light-emitting diode/LED/light emitter61LED tether62cluster substrate63cluster tether64pixel substrate65pixel tether70signal regeneration circuit90display or backlight system100provide display system step105receive image step110analyze image to determine current source for each cluster step112analyze cluster image data to determine current source for each cluster step114send image data to each cluster step115send image data and current-select signal to clusters step120each cluster selects current source step125each cluster displays image step