CROSS REFERENCE TO RELATED APPLICATION

Reference is made to U.S. patent application Ser. No. 16/778,948, filed Jan. 31, 2020, entitled Micro-LED Color Display with Different Current Densities by Bower et al., the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to micro-light-emitting diode structures for transfer printing.

BACKGROUND

Large-format inorganic light-emitting diode (iLED) displays are used in outdoor and stadium displays. Because the iLEDs are relatively large, for example one square millimeter, they are restricted to relatively low-resolution displays. However, as iLED technology develops, there is increasing interest in applying smaller iLEDs to displays having higher resolution. Full-color displays typically include pixels with three (or more) emitters, usually red, green, and blue emitters, distributed in an array over the display surface. For example, inorganic light-emitting diodes used in flat-panel displays are disclosed in U.S. Pat. No. 9,818,725 entitled Inorganic-Light-Emitter Display with Integrated Black Matrix.

Inorganic light-emitting diodes are semiconductor light sources relying on p-n junctions to emit light when a suitable voltage is applied across the light-emitting diode. The color of the light emitted from the iLED corresponds to the energy bandgap of the semiconductor. Thus, different semiconductor materials can emit different colors of light when stimulated with suitably different voltages. Typical materials include InGaN (emitting blue light), AlGaP (emitting green light), and AlGaAs (emitting red light), among many other materials. Blue-light-emitting materials can emit light at voltages ranging from 2.5-3.7 volts, green-light-emitting materials can emit light at voltages ranging from 1.9-4 volts, and red-light-emitting materials can emit light at voltages ranging from 1.6-2 volts, for example as taught in U.S. Pat. No. 10,453,826, entitled Voltage Balanced Serial ILED Pixel and Display. Moreover, the efficiency with which the different materials emit light can depend on the density of the current passing through the materials.

In order to provide the different voltages and currents needed by the different light-emitting diodes emitting different colors of light in a full-color pixel, a separate power supply can supply power, ground, and control signals to each color light emitter in each multi-color pixel. By supplying the appropriate voltages and currents to each light emitter, the light emitters efficiently emit light. However, providing three (or more) different power, ground, and control signals to each multi-color pixel requires three times as many power supplies, lines, and connections, reducing the available space in the display and increasing costs.

Alternatively, a single power supply can provide power to all three different iLEDs in the full-color pixels. In this case any excess voltage is dropped across other circuit components, increasing heat and reducing overall display system power efficiency.

There is a need, therefore, for an improved pixel and LED structure that improves power efficiency and reduces circuitry, wiring, and assembly costs.

SUMMARY

According to some embodiments of the present disclosure, a multi-LED structure comprises a multi-LED native substrate and a patterned semiconductor layer comprising semiconductor portions disposed on or over the multi-LED native substrate. The multi-LED native substrate can be a single, unitary, and contiguous substrate on which is disposed the semiconductor portions. In some embodiments, the multi-LED native substrate is not divided into separate or distinct portions (e.g., each portion comprising a separate and independent individual semiconductor portion) that can be separately disposed in different locations and is therefore a single, unitary, and contiguous substrate. The semiconductor portions define at least a first LED and a second LED separate from the first LED. The first LED and the second LED each comprise (i) a first layer having a cantilever portion and a base portion, and (ii) a second layer disposed only over the base portion of the first layer and comprising an emission portion. In some embodiments, at least a portion of the first layer is shared between the first LED and the second LED. In some embodiments, at least a portion of the first layer is at least a portion of the multi-LED native substrate. An LED electrode is disposed on at least a portion of the multi-LED native substrate or disposed on at least a portion of a non-semiconductor structure in the semiconductor layer, or both. The LED electrode is also disposed on at least a portion of the first LED and on at least a portion of the second LED so that the LED electrode electrically connects the first LED to the second LED. In some embodiments, the cantilever portion of the first LED extends in a first direction and the base portion of the first LED extends in a second direction different from the first direction. In some embodiments, the cantilever portion of the first LED has a first cantilever length, the cantilever portion of the second LED has a second cantilever length, and an LED emission separation distance between the emission portion of the first LED and the emission portion of the second LED is less than or equal to the first cantilever length and less than or equal to the second cantilever length. In some embodiments, both are true.

The first LED and the second LED can be electrically connected in serial or electrically connected in parallel. The multi-LED structure can comprise more than two semiconductor portions and LEDs that are electrically connected in any combination of series and parallel for any combination of LEDs. For example, the semiconductor portions can define at least a third LED separate from the first LED and separate from the second LED. Separate LEDs have independent emission portions that can be spatially separate or electrically separate in the absence of electrodes. Separate LEDs can share at least a portion of a cantilever portion or can have separate cantilever portions. The first LED and the second LED can have any one or combination of substantially the same size, substantially the same area over the multi-LED substrate, and different size or same size light-emitting areas of the first LED and the second LED.

The multi-LED structure can comprise a tether or a broken or fractured tether. In embodiments, the first and second LEDs do not comprise a tether or portion of a tether. The multi-LED structure can be transfer printed, for example micro-transfer printed. The multi-LED structure can be a bare die without an enclosing package, e.g., a ceramic or plastic package.

According to embodiments of the present disclosure, the multi-LED native substrate has a surface and the first direction of the cantilever portion is orthogonal to the second direction of the base portion and both the first and the second directions are substantially parallel to the surface. According to some embodiments, the cantilever portion extends in a same direction as the base portion. According to some embodiments, the first LED and the second LED extend in substantially a same direction. According to some embodiments, the first LED and the second LED extend in substantially orthogonal directions.

According to embodiments of the present disclosure, the multi-LED structure can comprise a first LED contact disposed on the first LED and a second LED contact disposed on the second LED, the first LED contact and the second LED contact separate from the LED electrode and not electrically connected to the LED electrode. The LED contact separation distance between the first and second LED contacts separate from the LED electrode can be greater than a first LED length of the first LED, greater than a second LED length of the second LED, or greater than the larger of the first LED length and the second LED length. A length of an LED can be the longest dimension of the LED parallel to a surface of the multi-LED native substrate. The separate first and second LED contacts can be electrically connected to an external device through wires separate from the LED electrode. For example, the multi-LED structure can be disposed on a target substrate having target substrate wires that are electrically connected to the separate first and second LED contacts, for example using photolithographic methods and materials.

According to some embodiments of the present disclosure, the multi-LED native substrate has a center, a first edge, and a second edge different from the first edge. In some embodiments, the first LED contact separate from the LED electrode is disposed closer to the first edge than to the center and the second LED contact separate from the LED electrode is disposed closer to the second edge than to the center. In some embodiments, the multi-LED native substrate has a center, a first corner, and a second corner different from the first corner, and the first LED contact separate from the LED electrode is disposed closer to the first corner than to the center and the second LED contact separate from the LED electrode is disposed closer to the second corner than to the center.

According to some embodiments, the multi-LED native substrate is a first multi-LED native substrate and the multi-LED structure comprises a second multi-LED native substrate disposed on the first multi-LED substrate, comprises other LEDs separate and independent of the first and second LEDs disposed on the second multi-LED native substrate, or comprises both. The one or more LEDs (first and second LEDs) disposed on the first multi-LED native substrate and the other LEDs separate and independent of the first and second LEDs disposed on the second multi-LED native substrate comprise a semiconductor material different from a semiconductor material of the semiconductor layer, and can, for example can emit different colors of light than the first and second LEDs can emit.

According to some embodiments, one or more other LEDs separate from the first LED and separate from the second LED are disposed on the first multi-LED native substrate. The one or more LEDs (first and second LEDs) disposed on the first multi-LED native substrate and the other LEDs separate and independent of the first and second LEDs disposed on the first multi-LED native substrate comprise a semiconductor material different from a semiconductor material of the semiconductor layer, and can, for example can emit different colors of light than the first and second LEDs can emit.

According to some embodiments, the multi-LED native substrate comprises at least a portion of the first layer or the first layer comprises at least a portion of the multi-LED native substrate and the multi-LED native substrate is electrically conductive.

According to embodiments of the present disclosure, a multi-LED component structure comprises a component substrate and a first multi-LED structure is disposed on the component substrate. The multi-LED component structure can comprise a second multi-LED structure disposed on the component substrate, can comprise one or more other LEDs disposed on the component substrate, or can comprise both. In some embodiments, the first multi-LED structure and the second multi-LED structure can emit different colors of light. In some embodiments, the first multi-LED structure and the one or more other LEDs emit different colors of light. The first LED and the second LED of the first multi-LED structure can be electrically connected in series and the first LED and second LED of the second multi-LED structure can be electrically connected in parallel. For example, the first multi-LED structure can emit red light and the second multi-LED structure can emit green or blue light.

According to some embodiments, the multi-LED structure comprises a third individual and separate LED separate from the first and second LEDs of the multi-LED structure or a third multi-LED structure disposed on the component substrate and the third LED or third multi-LED structure emits a color of light different from a color of light emitted by the first and second LEDs of the first multi-LED structure and different from a color of light emitted by the one or more other LEDs or second multi-LED structure. According to some embodiments, the multi-LED component structure comprises another LED or second multi-LED structure disposed on the component substrate, a third LED or third multi-LED structure disposed on the component substrate, and a fourth LED or fourth multi-LED structure disposed on the component substrate. The one or more other LEDs or second multi-LED structure, the third LED or third multi-LED structure, and the fourth LED or fourth multi-LED structure can be electrically serially connected. According to some embodiments, the second LED or second multi-LED structure emits a second color of light, the third LED or third multi-LED structure emits a third color of light, and the fourth LED or fourth multi-LED structure emits a fourth color of light and the second, third, and fourth colors of light are all different. The second color of light can be red, the third color of light can be green, and the fourth color of light can be blue.

According to some embodiments, an LED wafer comprises a wafer comprising sacrificial portions separated by anchor portions and a multi-LED structure is disposed entirely and completely over each sacrificial portion and each multi-LED structure is physically connected to an anchor with a tether.

According to some embodiments of the present disclosure, a method of making a multi-LED structure comprises providing a multi-LED native substrate and disposing semiconductor layers on the multi-LED native substrate. The semiconductor layers are patterned to form spatially separated semiconductor portions. The semiconductor portions define at least a first LED and a second LED separate from the first LED. The first LED and the second LED each comprise a first layer having a cantilever portion and a base portion. A patterned second layer is disposed only over the base portion. An LED electrode is disposed on at least a portion of the multi-LED native substrate or on at least a portion of a non-semiconductor structure in the semiconductor layer. The LED electrode is also disposed on at least a portion of the first LED and on at least a portion of the second LED, so that the LED electrode electrically connects the first LED to the second LED. In some embodiments, the cantilever portion of the first LED extends in a first direction and the base portion of the first LED extends in a second direction different from the first direction. In some embodiments, the cantilever portion of the first LED has a first cantilever length, the cantilever portion of the second LED has a second cantilever length, and an LED emission separation distance between the emission portion of the first LED and the emission portion of the second LED is less than or equal to the first cantilever length and less than or equal to the second cantilever length. In some embodiments, both are true.

Methods of the present disclosure comprise providing an LED source wafer comprising sacrificial portions separated by anchor portions. A multi-LED structure is disposed entirely and completely over each sacrificial portion and each multi-LED structure is physically connected to an anchor with a tether. The sacrificial portions are etched to suspend each multi-LED structure over a corresponding sacrificial portion. A stamp and a target substrate are provided, and each multi-LED structure is micro-transfer printed from the multi-LED native substrate to the target substrate with the stamp.

According to an embodiment of the present disclosure, a multi-LED structure comprises an electrically conductive semiconductor layer comprising a cantilever portion and two or more spatially separated base portions, a separate emissive portion comprising a light-emissive semiconductor portion disposed on each base portion, and an LED contact pad disposed on each emissive portion. Each emissive portion emits light when electrical power is provided to the cantilever portion and the LED contact pad.

According to some embodiments of the present disclosure, a multi-LED component structure comprises a component substrate, a first multi-LED native substrate disposed on the component substrate, the first multi-LED native substrate having a first LED and a separate second LED disposed thereon, wherein the first LED and the second LED are native to the first multi-LED native substrate and electrically connected, and a second multi-LED native substrate having a third LED and a separate fourth LED disposed thereon, the third LED and the fourth LED are native to the second multi-LED native substrate and electrically connected, wherein the first LED, the second LED, the third LED, and the fourth LED are electrically connected to a common electrical connection. At least one of (i) the first LED and the second LED can be electrically connected in series and the third LED and the fourth LED can be electrically connected in parallel and (ii) the first LED and the second LED can emit a first color of light and the third LED and the fourth LED can emit a second color of light. The second multi-LED native substrate can be disposed on the first multi-LED native substrate.

According to some embodiments of the present disclosure, a multi-LED component structure further comprises a fifth LED non-native to the component substrate, the first multi-LED native substrate and the second multi-LED native substrate, wherein the fifth LED emits a different color of light from the first LED, the second LED, the third LED, and the fourth LED.

Embodiments of the present disclosure provide a display, lamps, pixels, or light emitters having improved optical characteristics and power efficiency and fewer separate components, control circuits, and electrical connections that can be constructed in fewer manufacturing steps.

