Baseline and shaping pulse driving for microlight-emitting diode displays

Abstract

In addition to applying an operational drive power to drive the micro LEDs in an emitting state, the micro LED driver applies a low baseline power (i.e., baseline voltage or current) to pre-charge the micro LEDs in a nominally off (i.e., non-emitting) state. By pre-charging the micro LEDs prior to application of the operational drive power, the micro LED driver significantly reduces the time between application of the operational drive power and the onset of light emission from the micro LEDs. In some embodiments, the micro LED driver applies an operational drive power having multiple phases of current density to reduce the time between application of the operational drive power and the onset of light emission from the micro LEDs.

Description

[Background technology]

[0001] background A display panel contains an array of pixels arranged in rows and columns, typically having several thousand, or even tens of thousands, of rows and columns. Each pixel can be realized as a matrix of subpixels, such as a specific arrangement of red, green, and blue (RGB) subpixels, and each subpixel is controlled to emit light of the corresponding color at the corresponding brightness, and the combination of the color of the light and its brightness gives the pixel as a whole the intended brightness and color. A light-emitting diode (LED) display includes an array of LEDs forming subpixels and a driver employing pulse width modulation (PWM) to modulate the LEDs between off and on states to display an image, with the modulation frequency in the kHz range. The rise and fall times of the LEDs correspond to frequencies in the kHz range, providing sufficient response time to display an image at the PWM frequency. Future displays are expected to include microLEDs, which have pixels with a lateral dimension smaller than 50 μm. Microdisplays are expected to include light-emitting elements (i.e., microLEDs) and a driver that supplies current pulses to the light-emitting elements. [Overview of the Initiative] [Problems that the invention aims to solve]

[0002] The object of this disclosure is to provide an improved method for driving micro-LEDs that avoids or mitigates one or more problems associated with known methods, whether or not they are specified herein.

[0003] overview According to a general aspect, in addition to applying operational driving power for driving micro-LEDs in a light-emitting state, the micro-LED driver applies low baseline power (i.e., baseline voltage or current) to pre-charge micro-LEDs in a nominally off (i.e., non-light-emitting) state. By pre-charging the micro-LED before applying the operational driving power, the micro-LED driver significantly shortens the time between application of the operational driving power and initiation of light emission from the micro-LED. In some embodiments, the micro-LED driver applies operational driving power having a plurality of phases of current density to shorten the time between application of the operational driving power and initiation of light emission from the micro-LED.

[0004] According to a first aspect, there is provided a method comprising driving a first micro light emitting diode (micro LED) in a nominally off state, the first micro LED having a lateral dimension smaller than 20 μm, with a first baseline power greater than zero. The method further comprises driving the first micro LED in a light-emitting state with power greater than the first baseline power, wherein the amount of light emitted by the first micro LED in the nominally off state is negligibly small compared to the minimum amount of light emitted by the first micro LED in the light-emitting state.

[0005] Driving the first micro LED with the first baseline power may comprise applying the first baseline power before driving the first micro LED in the light-emitting state.

[0006] Driving the first micro LED in the nominally off state may be performed immediately before driving the first micro LED in the light-emitting state.

[0007] The method may further comprise driving a second micro LED in a nominally off state with a second baseline power greater than zero. The second baseline power may be different from the first baseline power. The method may further comprise driving the second micro LED in a light-emitting state with power greater than the second baseline power.

[0008] The first micro LED and the second micro LED can emit light of different colors from each other.

[0009] Driving the first micro LED in a light-emitting state may comprise driving the first micro LED with a current pulse including a first phase having a relatively high current density and a second phase having a relatively low current density. The first phase may be immediately before the second phase. The first phase may have a current density that is at least twice the current density of the second phase.

[0010] The method may further comprise driving the second micro LED in a light-emitting state. Driving the second micro LED in a light-emitting state may comprise driving the second micro LED with a current pulse including a first phase of the second micro LED having a relatively high current density and a second phase of the second micro LED having a relatively low current density. The first phase of the second micro LED may be immediately before the second phase of the second micro LED. The first phase of the second micro LED may have a current density that is at least twice the current density of the second phase of the second micro LED.

[0011] An amount of light emitted by a micro LED in a nominal off state may be less than 0.1% of a minimum amount of light emitted by the first micro LED in a light-emitting state, and the light-emitting state may be characterized by an internal quantum efficiency of at least 10%.

[0012] Driving the first micro LED in a nominal off state may comprise driving the first micro LED via a first power path. Driving the first micro LED in a light-emitting state may comprise driving the first micro LED via a second power path different from the first power path.

[0013] Driving the first micro-LED via the first power path may include supplying power to the first micro-LED via the first power path. Driving the first micro-LED via the second power path may include supplying power to the first micro-LED via the second power path.

[0014] The first power path may include at least one transistor or resistor. The turn-on time between the nominal off state and the illuminated state may be less than 500 ns.

[0015] In yet another embodiment, a method is provided for driving a first micro-light-emitting diode (micro-LED) of a display including an array of micro-LEDs, each micro-LED in the array having a lateral dimension less than 20 μm, and being in a light-emitting state including a first phase with a relatively high current density and a second phase with a relatively low current density, the current pulse having a duration of less than 1 microsecond, and the light-emitting state lasting for at least 50% of the current pulse duration.

[0016] The first phase may be immediately preceding the second phase. The first phase may have a current density at least twice that of the second phase.

[0017] The method may further include driving a first micro-LED in a nominally off state with a first baseline power greater than zero. The method may further include driving a first micro-LED in an illuminated state with a power greater than the first baseline power, such that the amount of light emitted by the nominally off micro-LED is negligibly small compared to the minimum amount of light emitted by the first micro-LED in an illuminated state.

[0018] Driving the first microLED with a first baseline power may include applying the first baseline power before driving the first microLED in the light-emitting state.

[0019] The first micro-LED in the nominally off state may be driven immediately before the first micro-LED in the illuminated state.

[0020] The method may further include driving a second micro-LED in a nominally off state with a second baseline power greater than zero, wherein the second baseline power is different from the first baseline power. The method may further include driving a second micro-LED in an illuminated state with a power greater than the second baseline power.

[0021] The first micro-LED and the second micro-LED are capable of emitting light of different colors from each other.

[0022] Driving the first microLED in the nominally off state may include driving the first microLED via a first power path. Driving the first microLED in the illuminated state may include driving the first microLED via a second power path different from the first power path.

[0023] Driving the first micro-LED via the first power path may include supplying power to the first micro-LED via the first power path. Driving the first micro-LED via the second power path may include supplying power to the first micro-LED via the second power path.

[0024] The amount of light emitted by a nominally off-state microLED may be less than 0.1% of the minimum amount of light emitted by a first microLED in an emitting state, and the emitting state may be characterized by an internal quantum efficiency of at least 10%.

[0025] In yet another embodiment, a device is provided comprising a first microlight-emitting diode (microLED) having a lateral dimension smaller than 20 μm, and a driver. The driver is configured to drive the first microLED in a nominally off state with a first baseline power greater than zero, and to drive the first microLED in an illuminated state with a power greater than the first baseline power, such that the amount of light emitted by the nominally off microLED is negligibly small compared to the minimum amount of light emitted by the first microLED in an illuminated state.

[0026] The driver may also be configured to apply baseline power to the first micro-LED before driving the first micro-LED in the illuminated state.

[0027] The driver may also be configured to apply a first baseline power to the first micro-LED immediately before driving the first micro-LED in the illuminated state.

[0028] The device may further include a second micro-LED. The driver may be configured to drive the second micro-LED in a nominally off state with a second baseline power greater than zero. The second baseline power may differ from the first baseline power. The first and second micro-LEDs may emit light of different colors from each other. The method may further include driving the second micro-LED in an illuminated state with a power greater than the second baseline power.

[0029] The driver may further be configured to drive a first micro-LED in an emitting state with a current pulse comprising a first phase having a relatively high current density and a second phase having a relatively low current density. The driver may further be configured to drive the micro-LED in an emitting state by applying a nonlinear conversion between a desired LED brightness and the current pulse duration.

[0030] The amount of light emitted by a nominally off-state microLED may be less than 0.1% of the minimum amount of light emitted by a first microLED in an emitting state, and the emitting state may be characterized by an internal quantum efficiency of at least 10%.

[0031] The driver may include a first power path for driving a first micro-LED in a nominal off state at a first baseline power, and a second power path different from the first power path for driving a first micro-LED in an illuminated state.

[0032] It will be understood that features described in the context of one aspect of this disclosure may be combined with features of other aspects of this disclosure. For example, features described in the context of one of the methods described above may be combined with features of the other methods described above. Similarly, features described in the context of any of the methods described above may be combined with features of the apparatus described above, and vice versa.

[0033] This disclosure will be better understood by referring to the accompanying drawings, and many of its features and advantages will become apparent to those skilled in the art. The use of the same reference numerals in different drawings indicates similar or identical items. [Brief explanation of the drawing]

[0034] [Figure 1] This figure shows a display composed of an array of pixels. [Figure 2] This block diagram shows a microLED display element, including a microLED driver that supplies baseline power and drive power pulses to a microLED, according to some embodiments. [Figure 3] This figure shows a timing scheme in which a microLED driver pre-charges a microLED at a baseline voltage, according to several embodiments. [Figure 4]This figure shows a comparison of the normalized light output from a microLED without precharging at the baseline voltage and the normalized light output from a microLED with precharging at the baseline voltage, according to several embodiments. [Figure 5] This figure shows a microLED driver according to some embodiments, comprising a first power path for applying pulse width modulation to illuminate a microLED and a second power path for applying a baseline current or voltage to the microLED. [Figure 6] This figure shows a micro-LED driver having a second power path including a resistor for converting a bias voltage into a baseline current to a micro-LED, according to some embodiments. [Figure 7] This figure shows a microLED driver having a second power path including a transistor for applying a baseline current to a microLED, according to some embodiments. [Figure 8] This figure shows multiple phases of current pulses for driving a light-emitting micro-LED according to several embodiments. [Figure 9] This figure shows the normalized light output from a microLED driven by current pulses of multiple phases, according to one embodiment. [Modes for carrying out the invention]

[0035] Detailed explanation The following description is intended to convey a thorough understanding of the Disclosure by providing several specific embodiments and details, including display systems utilizing micro-light-emitting diodes (micro-LEDs). However, it is understood that the Disclosure is not limited to these specific embodiments and details, which are merely illustrative, and that the scope of the Disclosure is intended to be limited accordingly only by the following claims and their equivalents. Furthermore, it is understood that those skilled in the art, in light of known systems and methods, will understand that the Disclosure can be used for its intended purposes and merits in any number of alternative embodiments, depending on the particular design and other needs.

[0036] In some display applications where the pixel architecture is implemented as microLEDs, such as augmented reality / virtual reality (AR / VR) systems, projectors, phones, tablets, laptops, televisions, and plasma displays, faster modulation speeds than those of conventional LED drivers in the kilohertz range are required. In some cases, pulses shorter than 1 μs, or even shorter than 100 ns, are necessary to meet specifications for a satisfactory user experience. Although microLEDs are small and therefore have low capacitance, the rise time of high-quality microLEDs from a completely off state to an on state where the microLED emits light is significantly longer than 100 ns with conventional driving technology, ranging from tens of seconds to hundreds of nanoseconds (ns).

[0037] Figures 1 to 9 illustrate techniques for driving microLEDs with lateral dimensions smaller than 20 μm to reduce the response time of the microLEDs. In some embodiments, the microLED driver applies low baseline power (i.e., baseline voltage or current) to precharge the nominally off (i.e., non-emitting) microLED, in addition to applying operating drive power to drive the microLED in the emitting state. By precharging the microLED with low baseline power before applying the operating drive power, the microLED driver significantly reduces the time between the application of the operating drive power and the start of emission from the microLED.

[0038] In some embodiments, the microLED driver conserves power by continuously applying low baseline power, while in other embodiments, it conserves power by continuously applying low baseline power only to specific areas of the display, such as a banner at the top of the display for displaying icons that remain lit while the rest of the display is off when the display is in a particular operating mode. In some embodiments, the microLED driver includes timing circuitry that applies low baseline power to a set of pixels shortly before the set of pixels becomes active. In some embodiments, the microLED driver applies low baseline power only to active pixels (i.e., non-dark pixels). In some embodiments, the microLED driver uses a primary power path to supply operational drive power to drive the microLEDs in an illuminating state and a secondary power path to supply baseline power to precharge the microLEDs before applying operational drive power.

[0039] In some embodiments, the microLED driver applies operating drive power having multiple phases of current density (referred to herein as “shaping pulses”) to reduce the time between the application of operating drive power and the start of light emission from the microLED. For example, by applying an initial phase with a relatively high current density followed by a second phase with a lower current density, the microLED driver reduces the capacitive charging time of the microLED. In some embodiments, the microLED driver applies shaping pulses instead of, or in addition to, low baseline power precharging of the microLED.

[0040] In various embodiments, the techniques described herein apply to time-dependent driving of photoelectron emitters, including LEDs, and more specifically, microLED displays. The terms pulse and power pulse are used herein to generally describe time-dependent driving schemes that alternate between relatively low input power (i.e., off or nearly off) and relatively high input power while light is emitted. The pulse may be a current pulse, a voltage pulse, or a power pulse. The examples disclosed herein consider III nitride LEDs. However, some of the techniques are applicable to other optoelectronic devices, including semiconductor LEDs (e.g., GaAs, AlInGaP, AlInGaAsP, III-V compounds, II-VI compounds), organic LEDs, perovskites, and other materials known in the art.

[0041] Figure 1 shows a display 100 composed of an array of pixels such as pixel 102. Each pixel includes a pixel circuit, such as pixel circuit 105, which includes three subpixels: a red (R) subpixel 105-1, a green (G) subpixel 105-2, and a blue (B) subpixel 105-3. Each subpixel includes a microLED driver and a microLED that emits light when the microLED driver applies power to the microLED. Thus, the R subpixel 105-1 includes an R microLED driver 110-1 that applies power to the R microLED 115-1 and causes the R microLED 115-1 to emit light. Similarly, the G subpixel 105-2 includes a G microLED driver 110-2 that applies power to the G microLED 115-2, and the B subpixel 105-3 includes a B microLED driver 110-3 that applies power to the B microLED 115-3. In some embodiments, the display 100 is used as a flat panel display, a mobile device display, a head-mounted display, or other display format. In some embodiments, the display 100 includes thousands of pixel circuits. In some embodiments, micro-LED drivers 110-1, 110-2, 110-3 improve the response time of micro-LEDs 115-1, 115-2, 115-3 by driving the corresponding micro-LEDs with baseline power when the micro-LEDs are nominally off, or by applying power pulses with a shaped current density to the micro-LEDs, where the baseline power is greater than zero power level. This can be better understood by referring to Figure 2.

[0042] Figure 2 is a block diagram showing a micro-LED display element 200 corresponding to one of the subpixels 105-1, 105-2, and 105-3 of Figure 1, according to several embodiments, the micro-LED display element 200 includes a micro-LED driver 205 corresponding to one of the micro-LED drivers 110-1, 110-2, and 110-3 of Figure 1, which supplies baseline power 230 and drive power pulses 235 to a micro-LED 210 corresponding to one of the micro-LEDs 115-1, 115-2, and 115-3 of Figure 1. The micro-LED 210 has a lateral dimension less than 20 μm and includes an n-contact layer 212 and a p-contact layer 224, an n-type layer 214 and a p-type layer 222, and an active (luminescent) region 225 including a core region 216, a quantum well 218, and an electron blocking layer 220. The micro-LED driver 205 applies a drive power pulse 235 to the micro-LED 210, causing the micro-LED 210 to emit light having an intensity corresponding to the amplitude of the drive power pulse 235. A portion of the current of the drive power pulse 235 is consumed by charging the active region 225, which is characterized by capacitance per unit area. The remaining current of the drive power pulse 235 is injected as free carriers in the core region 216, and the carriers can be captured by the light-emitting layer of the active region 225. Once in the light-emitting layer, the carriers are consumed by recombination.

[0043] However, the response of the micro-LED210 is limited by the time required to charge the capacitance of the micro-LED210 starting from the off state where no voltage or current is applied, which causes a delay in light emission. In addition, the recombination lifetime of the micro-LED210 is slow, especially during turn-on, which can limit the rise time of the light output. The micro-LED210 has a turn-on time τ on Characterized by this, the turn-on time is defined as the time required for the micro-LED 210 from the start of the drive power pulse 235 until the micro-LED 210 reaches 90% of the plateau level of the light output relative to the drive power pulse 235. The micro-LED 210 also has a turn-off time τ offCharacterized by this, the turn-off time is defined as the time required for the micro-LED 210 to reach 10% of its optical output plateau level after the end of the drive power pulse 235 (i.e., the start of the falling edge of the drive power pulse 235).

[0044] Some embodiments are characterized by an asymmetric time response in which the turn-off time and turn-on time are substantially different. In some embodiments, the micro-LED is driven by a power pulse and characterized by the turn-on time and turn-off time, with a ratio tau_on / tau_off that is greater than 1.5 (or 2, 5, 10) or less than 1 / 1.5 (or 1 / 2, 1 / 5, 1 / 10). Such asymmetric operation can distinguish the time response of some embodiments from the time response of conventional optoelectronic devices.

[0045] Some embodiments minimize the asymmetry of the time response by matching the rise time and fall time using the approach disclosed herein. Other embodiments use a substantially asymmetric response. Furthermore, by forming the current density of the drive power pulse 235, the micro-LED driver 205 further reduces the response time of the micro-LED 210 and the turn-off time τ off Control.

[0046] By supplying baseline power 230 to the micro LED 210, the micro LED driver 205 has a turn-on time τ onis shortened. The baseline power 230 is a current higher than zero and / or voltage that is applied when the microLED 210 is in a nominal off state where it is expected not to emit light. In some embodiments, the amplitude of the baseline power 230 is selected such that the amount of light emitted by the microLED 210 in the nominal off (baseline) state is negligibly small compared to the amount of light emitted by the microLED 210 in the on (emitting) state. For example, in some embodiments, the amount of light emitted in the nominal off state is 10% or less of the amount of light emitted in the light emitting state. In other embodiments, the amount of light emitted in the nominal off state is 1% or less of the amount of light emitted in the light emitting state. In still other embodiments, the amount of light emitted in the nominal off state is 0.1% or less of the amount of light emitted in the light emitting state. The amount of light emitted in the light emitting state may vary greatly. For example, light emission from a microLED pixel may reach a maximum of 1000cd / m 2 to a minimum of 0.1cd / m 2 can range. In some embodiments, the amount of light emitted in the baseline state is at most about 10% of the minimum emitted light amount (for example, if 0.1cd / m 2 is the minimum light emitted in the light emitting state, then in the baseline state, the microLED is limited to light emission of 0.01cd / m 2 or less).

[0047] In some embodiments, the structure of the microLED 210 is configured to improve time response, including time response associated with capacitance and / or associated with recombination time. In some embodiments, the LED is configured to achieve a desired capacitance per area, such as by maintaining the capacitance per area below a predetermined value. In some embodiments, the core region 216 of the microLED 210 has a thickness d (also referred to as depletion thickness d), and the space charge capacitance per unit area is approximately given by Csc=eps / d, where eps is the dielectric constant of the material. For example, in the case of GaN, eps is approximately 10*eps0 at zero bias (eps0 is the vacuum dielectric constant), and the value under forward bias is C=Csc*(1-V / Voc) -1 / 2(Voc is the open-circuit voltage) For example, it increases by about 2 times.

[0048] In some embodiments, the value of d is approximately equal to the thickness of the undoped region between the p region and the n region (i.e., d ~ tc).

[0049] By selecting the structure of the active region (e.g., quantum well (QW), barrier, or spacer), in some embodiments, it becomes easy to select tc independently of the active region thickness tw. This is in contrast to homojunction LEDs, where recombination occurs over a significant portion of the depletion thickness. A larger value of tc results in lower capacitance, while the value of tw can be selected to achieve appropriate efficiency. In some embodiments, the thickness of the depletion region is at least twice (or five, ten, or twenty times) the thickness of the light-emitting layer.

[0050] For example, some embodiments include only a few thin QWs and thin barriers, but have a value of d sufficient to reduce Csc. For this reason, some embodiments employ dummy QWs (i.e., QWs of a lower composition than the luminescent QWs, which promote carrier transport but do not emit light, thus ensuring that carriers reach the luminescent QWs) to increase d without adversely affecting the injection efficiency. The dummy QWs can be placed on the p-face, n-face, or both faces of the luminescent QWs, or interposed between them. In some embodiments, an epitaxial layer (not shown) is constructed to obtain the desired capacitance, regardless of the thickness of the luminescent QWs and barriers. In some embodiments, other active region designs are employed, including double heterostructures, layers of various compositions (staircase or gradient), and / or alloys of AlGaN, InGaN, AlInN, and AlInGaN.

[0051] In some embodiments, the value of d is selected to reduce the value of Csc. For example, Csc may be less than 1E-7F.cm⁻² (or 5E-8, 2E-8, 1E-8, 5E-9, 1E-9F.cm⁻²). In some embodiments, the value of d and the area A of the LED are selected to reduce the value of the net LED capacitance Csc*A. For example, the net LED capacitance is less than 1E-13F (or 5E-14, 1E-14, 5E-15, 1E-15, 5E-16, 1E-16F). In some embodiments, the microLED pixel or subpixel has a lateral dimension of less than 10um (or 5um, 3um, 2um, 1um).

[0052] In some embodiments, the rise time associated with capacitive charging is tau_charge = V * Csc / J (where V is the typical operating voltage (approximately 2.5-3V for a typical visible LED) and J is the current density). Therefore, in some embodiments, the LED configuration and the choice of operating current density together result in a sufficiently fast rise time. In some embodiments, the ratio Csc / J is less than 1E-8F / A (or 5E-9, 1E-9, 5E-10, 1E-10F / A). In some embodiments, tau_charge is less than 100ns (or 50ns, 10ns, 5ns, 1ns). In some embodiments, tau_charge is shorter than the pulse duration T (or shorter than 0.5*T, 0.2*T, or 0.1*T).

[0053] In some embodiments, the doping levels in the p-doped and n-doped regions 214 and 222 of the micro-LED 210 are selected to control the depletion width. In some embodiments, an abrupt transition from the undoped layer to the doped layer is formed. In some embodiments, the n-doped layer 214 (doping level of at least 1E18cm-3 or 1E19cm-3) is followed by a nominal undoped region containing the light-emitting layer (doping level of less than 1E17cm-3), followed by a p-doped active region 222 (doping level of at least 1E18cm-3 or 1E19cm-3). Such doping levels can be combined with other LED characteristics (such as the width of the undoped region) to obtain a desired capacitance value.

[0054] In some embodiments, the micro-LED 210 is configured to obtain a predetermined dynamic resistance rho = dV / dJ to facilitate avoidance of interaction with parasitic capacitance of the dynamic resistance, which could lead to further delays in the time response. In some embodiments, the dynamic resistance per unit area is maintained below a desired value for the nominal off state by, for example, applying a baseline low current to the micro-LED 210 in the nominal off state. In some embodiments, the nominal off state dynamic resistance is less than 100 Ω·cm² (or 10, 1, or 0.1 Ω·cm²).

[0055] In some cases, a trade-off can occur between material quality and response time. For example, a defective LED will operate inefficiently due to its low internal quantum efficiency (IQE), but its non-radiative recombination time will be faster due to SRH (Shockley-Read-Hall) recombination or other types of defect-related recombination (e.g., defect-induced leakage or tunneling), leading to an improved modulation speed. In some embodiments, the defect level is selected to facilitate operation at a given speed. For example, a desired modulation speed is selected, and the defect level of the LED is controlled to facilitate such a speed.

[0056] Several embodiments are designed to achieve a minimum IQE (or other relevant efficiency metric such as external quantum efficiency (EQE) or wall-plug efficiency (WPE)) such that the ON state is characterized by an IQE of at least 1% (or 5%, or 10%) and / or the baseline state is characterized by an IQE of less than 0.1% (or less than 0.01%). Thus, embodiments consist of a defect density low enough to achieve the minimum IQE. This leads to minimizing the rise / fall time of the active region. Thus, embodiments are driven with pulses longer than this minimum rise / fall time. Specifically, in some embodiments, the microLED210 is driven with pulses that have a non-radiative lifetime t_low (such as the SRH lifetime) at low current densities, and whose length is at least half (or 1, 2, 5, or 10 times tau_low).

[0057] In some embodiments, the turn-on time t_on is less than 500 ns (or 200 ns, 100 ns, 50 ns, 20 ns, 10 ns). In some embodiments, the SRH lifetime t_SRH (characterizing the active region) is greater than 100 ns and t_on is less than 50 ns. In some embodiments, t_on is less than t_SRH divided by 2 (or 3, 5, 10). In some embodiments, the charge time t_charge is longer than 10 ns and t_on is less than 10 ns. In some embodiments, t_on is less than t_charge divided by 2 (or 3, 5, 10). In some embodiments, t_on is less than t_charge + t_SRH divided by 2 (or 3, 5, 10). In some embodiments, the SRH lifetime is constrained to a sufficient IQE value as disclosed herein. In some embodiments, the IQE is at least 10%, and t_on is less than 500 ns (or 200 ns, 100 ns, 50 ns, 20 ns, 10 ns).

[0058] In some embodiments, the electrical pulse driving the on-state LED has a duration of less than 5us (or 2us, 1us, 500ns, 200ns, 100ns, 50ns, 10ns). In some embodiments, the on-state light emission occurs for a duration of at least 90% (or 80%, 50%, 20%, 10%) of the electrical pulse duration.

[0059] Figure 3 shows the baseline voltage V in some embodiments. BASELINE The baseline power 230, represented as 305, indicates the timing scheme in which the micro LED driver 205 pre-charges the micro LED 210. The drive power pulse 235 in Figure 2 is a pulse width modulation (PWM) voltage V PWM It is represented as 310. Figure 3 shows the baseline voltage V BASELINE 305. Pulse-width modulation (PWM) voltage V is the signal that drives the light output from the micro LED 210. PWM 310, and discharge voltage V DISCHARGE The time traces corresponding to example 315 are shown. For clarity, the time traces are offset perpendicularly from each other.

[0060] At time T1 320, the micro LED driver 205 operates at a baseline voltage V BASELINE 305 to Micro LED210 for time t charge The voltage is applied for 340 seconds. At time T2 325, the micro LED driver 205 operates at the baseline voltage V BASELINE Stop 305 and the PWM voltage V PWM Apply 310. The micro LED driver 205 uses a baseline voltage V BASELINE With the application of 305, the micro LED 210 begins charging, and the micro LED driver 205 uses the PWM voltage V PWM The capacity charging time after applying 310 is shortened, and as a result, the PWM voltage V PWM The time between the application of 310 and the start of light emission from the micro LED 210 is reduced. At time T3 330, the micro LED driver 205 uses the PWM voltage V PWMTo stop applying 310 and remove the charge from the micro LED 210, discharge voltage V DISCHARGE 315 for the period t discharge Apply for 345 seconds, until time T4 335 seconds.

[0061] Figure 4 shows a comparison of the normalized light output from a micro-LED without pre-charging with a baseline voltage and the normalized light output from a micro-LED with pre-charging with a baseline voltage, according to several embodiments. Curve 410 represents the normalized light output from a micro-LED 210 pre-charged with a baseline current density corresponding to the baseline voltage before applying the drive PWM current density corresponding to the drive PWM voltage at time 0 ns. Curve 420 represents the normalized light output from a micro-LED 210 that is not pre-charged with a baseline current density and is driven with a drive PWM current density corresponding to the drive PWM voltage that starts at time 0 ns. As shown, the start of light emission decreases from approximately 32 ns in curve 420 to approximately 3 ns in curve 410 by applying the baseline current density and baseline voltage. In the illustrated example, the baseline current density is 0.01 A / cm². 2 This corresponds to a baseline voltage of approximately 2.5V, and the drive PWM current density is 10A / cm². 2 This corresponds to a drive PWM voltage of approximately 2.7V. In the baseline (nominal off) state, the intensity of light emitted is very low (e.g., less than 10% of the light intensity emitted in the on state, or in some cases, about 3E-5 times the light intensity in the on state, calculated as the ratio of current × IQE), and the power consumption is very low (about 1E-4 times the power in the on state, calculated as the ratio of current). In some embodiments, the IQE in the baseline state is less than the IQE in the on state divided by 10 (or 20, 50, 100).

[0062] In some embodiments, controlling voltage can be easier than controlling very small currents, so the micro-LED driver 205 achieves the nominal off state by controlling the voltage applied to the micro-LED 210 and the ON state by controlling the current supplied to the micro-LED 210. In some embodiments, the micro-LED driver 205 uses a transistor, such as a field-effect transistor, or a resistor to control the baseline voltage to the micro-LED 210. In some embodiments, the micro-LED driver 205 maintains the baseline voltage for the nominal off state at a voltage higher than 2V and / or 1V lower than the drive PWM operating voltage.

[0063] Figure 5 shows a microLED driver 500 having a first path 505 (referred to as the first power path 505) for supplying power to a microLED to apply drive pulse width modulation for illuminating the microLED, and a second power path 510 for applying a baseline current or voltage to the microLED, according to some embodiments. In some embodiments, the driver is CMOS, TFT backbone, or other architecture. The first power path 505 supplies the column voltage V for the display. DD , and a digital gate control voltage (row selection) V for setting the voltage of capacitor 515 G This is supplied to the micro-LED. Capacitor 515 stores an analog voltage that turns on transistor 520, and in some embodiments, a current I, which has a time-dependent waveform, flows through the micro-LED. ON This provides the micro-LED to emit light when it is in the ON state. During this time, no power flows through the second power path 510. In the nominal OFF mode, no power flows through the first power path 505, but the baseline current I baseline or baseline voltage V baseline A baseline power consisting of these components is applied to the micro-LED through the second power path 510.

[0064] In some embodiments, the micro-LED driver 500 does not include a second power path 510, and instead drives the nominally off micro-LEDs (pixels) with a consistently low baseline power (voltage or current). In some embodiments, if only a specific area of ​​the display (i.e., a subset of micro-LEDs in the array) is used in a given operating mode to conserve power, the micro-LED driver 500 always applies baseline power only to the subset of micro-LEDs corresponding to the specific area of ​​the display being used. For example, in some operating modes, a banner at the top of the display is used to display icons, while the rest of the display is off. In such operating modes, the micro-LED driver 500 always applies baseline power only to the subset of micro-LEDs at the top of the display that form the banner.

[0065] In some embodiments, the micro-LED driver 500 drives nominally off micro-LEDs (pixels) in a single display frame at baseline power only if the nominally off pixel will be turned on in the next display frame. Thus, the display system considers the next frame when selecting the driving conditions for the current frame. That is, if a pixel is nominally off (i.e., dark) in the current frame but will be turned on in the next frame, the micro-LED driver 500 applies baseline power in the current frame to improve the response time of the next frame. Considering the next frame can increase latency because information about the next frame is needed before the current frame becomes displayable. Therefore, in some embodiments, the display system applies a high refresh rate (e.g., 90Hz or 120Hz or higher) to reduce latency.

[0066] Figure 6 shows a bias voltage V supplied to a micro LED according to several embodiments. bias Baseline current I baselineThis figure shows a micro LED driver 600 having a second power path 610 including a resistor 615 for converting to . Similar to Figure 5, the first power path 605 has a voltage V when the micro LED is on. DD This supplies power to the micro-LED. During this time, little power flows through the second power path 610 (for example, when the micro-LED is on, V bias If the current does not become zero, or does not flow through the second power path 610, and in some embodiments has a time-dependent waveform, then current I ON The current flows to the micro LED, causing it to emit light. In the nominal off mode, no power flows through the first power path 605, but the resistor is biased by voltage V bias Baseline current I baseline The current is converted to a second power path 610 and applied to the micro-LED. In some embodiments, V bias is V DD Equivalent to V in other embodiments bias is V DD It is different.

[0067] Figure 7 shows a baseline current I applied to a microLED according to several embodiments. baseline This figure shows a micro LED driver 700 having a second power path 710 including a transistor 715 for applying voltage V. In the illustrated example, transistor 715 is a parallel drive transistor. As in Figures 5 and 6, when the micro LED is in the ON state, the first power path 705 applies voltage V. DD This is supplied to the micro-LED. During this time, no power flows through the second power path 710, and in some embodiments, a current I having a time-dependent waveform is supplied. ON This current flows to the micro-LED, causing it to emit light. In the nominal off mode, no power flows through the first power path 705, and the baseline current I baseline This is generated by transistor 715, and its current value is V bias It is set by V in some embodiments. DD2 is V DD Equivalent to V in other embodiments DD2 is V DD It is different from V.bias In some embodiments, this is a direct current (DC) voltage, and in other embodiments, it is a time-dependent voltage.

[0068] In some embodiments, transistor 715 generates a photo-generating current I on When it is turned off, it is also used as a discharge transistor to remove charge from the micro-LED. In other embodiments, transistor 715 in the second power path 710 is used only as a charging transistor, and the micro-LED driver 700 includes a third power path (not shown) which includes a separate transistor (not shown) used as a discharge transistor.

[0069] The driver architectures shown in Figures 5 to 7 are examples of architectures that can be used to supply baseline power to the micro-LEDs 210. Those skilled in the art will understand that other architectures can be used, such as a combination of a second power path including a resistor and a third power path including a discharge transistor, as shown in Figure 6. In some embodiments, the driver architectures discussed herein relate to pixels of a display formed from an array of micro-LEDs. Each subpixel corresponds to a micro-LED and a micro-LED driver. In some embodiments, the baseline current or voltage varies per panel, per pixel region, per pixel, or per subpixel.

[0070] For example, (i) junction capacitance depends on the details of the epitaxial structure and may differ by color, and (ii) recombination lifetimes depend on color (at least different defect levels and different radiant lifetimes), so the time responses of LEDs of different colors (R, G, B, etc.) may differ. The capacitive charging time of one color may be at least twice that of another color. Similarly, the low-current recombination lifetime of one color may be at least twice that of another color. Thus, different colors may behave differently in response to the same pulse shape. Therefore, in some embodiments, the baseline current or voltage is different for subpixels of different colors (R, G, B, etc.). In some embodiments, the baseline current or voltage is less than the photon voltage of each subpixel (where photon voltage is defined as equal to the photon energy measured in electron volts) or less than some other threshold voltage. In some embodiments, different pulse shapes are used for different colors to individually improve the time response of each color. In some embodiments, the display has at least two colors and the display is configured such that the turn-on times of the two colors are no more than twice each other.

[0071] The micro LED driver has different voltages. bias The value, or shared V converted by different electronic components (such as resistors and transistors) bias By using different baseline power values, different baseline power can be achieved. In some embodiments, the micro-LED driver applies baseline power to facilitate uniformity correction and reduce non-uniformity of the display panel. In some embodiments, each pixel or group of pixels has different baseline conditions, resulting in a uniform light output under operation.

[0072] For example, in some embodiments, the second power path includes a resistive device that facilitates current leakage. For instance, an array may include one or more microLEDs of superior material quality that begin to emit light at lower currents than other microLEDs of inferior material quality, resulting in non-uniform brightness at low currents. Adding a small leakage path to every pixel prevents the microLEDs in the array from lighting up at low currents. The resistor is selected to produce a leakage current lower than the nominal on-current of the microLED, which facilitates the uniformity of the display's brightness and / or response time. In some embodiments, the display has multiple microLEDs with substantially different low-current non-radiative lifetimes (for example, due to different defect levels among the microLEDs). MicroLEDs with more non-radiative recombination may emit more light and respond more quickly at low currents, potentially leading to non-uniformity. Therefore, in some embodiments, a leakage path governing the response time and / or brightness at low currents is included to reduce non-uniformity.

[0073] In some embodiments, the microLED driver does not always apply baseline power (voltage or current). Instead, the microLED driver applies baseline power only for a suitable period of time before the pixel turns on. For example, the time τ required to drive the microLED from a completely off state to a baseline state. baseline If this occurs, the microLED driver will set the baseline power to at least τ so that the microLEDs are in the baseline state when the pixels (microLEDs) need to be lit. baseline Apply for the duration of time τ. baseline By applying baseline power during this period, the micro-LED driver reduces power consumption associated with the baseline state.

[0074] In addition to pre-charging the micro-LED 210 with a baseline power 230 before applying the drive (PWM) power pulse 235, or alternatively, the micro-LED driver 205 may shorten the response time of the micro-LED 210 (i.e., time to illumination start) by applying the drive power pulse 235, which is formed to vary in intensity or current density. In some embodiments, the micro-LED driver 205 applies a drive pulse characterized by a complex waveform (i.e., a shape more complex than a simple rectangular shape). For example, the current or voltage pulse may have peaks or ripples.

[0075] Figure 800 shows different examples of current pulses for driving a light-emitting micro-LED according to several embodiments. Different current pulses are superimposed to illustrate their differences. The total duration of each pulse is 100 ns. Current pulse 805 is J = 10 A / cm 2 It has a simple square profile of current density. Current pulse 810 is J = 50 A / cm 2 The current density is such that the first phase has a square profile with a duration of approximately 10 ns, and J = 10 A / cm². 2 The current density includes a second phase with a square profile and a duration of approximately 90 ns. Therefore, the total duration of current pulse 810 is approximately 100 ns. Current pulse 815 has a current density of J = 60 A / cm². 2 The current density is such that the first phase has a square profile with a duration of approximately 10 ns, and J = 10 A / cm². 2 It has a current density and a second phase with a square profile having a duration of approximately 90 ns. Thus, the total duration of current pulse 815 is approximately 100 ns. In each of current pulses 810 and 815, the first phase is immediately before the second phase.

[0076] Figure 9 shows the normalized light output from a micro-LED driven by different current pulses 805, 810, and 815 as shown in Figure 8, according to several embodiments. The normalized light output from each of the different current pulses is superimposed to illustrate their differences. For current pulse 805, the normalized light output is shown by curve 905. For current pulse 810, the normalized light output is shown by curve 910, and for current pulse 815, the normalized light output is shown by curve 915. As illustrated, high current peaks (current densities) such as those provided in the first phase of pulses 810 and 815 lead to faster charging of the micro-LED capacitance and faster accumulation of carriers in the active region, as shown by curves 910 and 915, respectively.

[0077] Depending on the length and magnitude of the current peak (i.e., the first phase), the normalized light output may show a peak because the carrier density in the micro-LED temporarily overshoots the plateau value, as shown for curve 915 corresponding to the third pulse 815. In some embodiments, the micro-LED driver configures the pulse shape to avoid or limit such overshoot peaks. By avoiding or limiting such peaks, the possibility of damage to the driver and / or micro-LED can be reduced. In some embodiments, within a pulse, the current pulse has a peak (i.e., the first phase) and a plateau (i.e., the second phase), and the micro-LED light output has corresponding peaks and plateaus such that the normalized light output peak is less than twice (or 1.5 times, 1.1 times) the value of the light output plateau. In some embodiments, the micro-LED driver configures pulses with complex shapes to improve the LED response time. In some embodiments, the current pulse has a duration shorter than 1 microsecond, and the light emission state extends for at least 50% of the current pulse duration. The waveform examples described above are provided for illustrative purposes only.

[0078] In some embodiments, the shape of the pulses supplying different colors differs. For example, in some embodiments, a blue pixel (microLED) has a first waveform with a first peak current and duration, a green pixel (microLED) has a second waveform with a second peak current and duration, and a red pixel (microLED) has a third waveform with a third peak current and duration, the peak current and duration being selected to reduce the turn-on delay to similar values. In some embodiments, a first microLED having a first color is driven by a first pulse having a charge time tau_charge_1, a first peak value and a first characteristic duration, and a second microLED having a second color is driven by a second pulse having a charge time tau_charge_2, a second peak intensity and a second characteristic duration, where tau_charge_2 is at least 2 (or 5, 10) times tau_charge_1, and the product (peak intensity * duration) is higher for the second microLED such that the time delay before the second microLED emits light is less than 2 times (or 1.5, 1.2, 3, 5, 10) compared to the first microLED.

[0079] The micro-LED driver applies pulse shaping to one or more of the power pulse, pre-charge baseline pulse, and discharge pulse that cause light output from the LED.

[0080] In some embodiments, a controller (not shown) of the micro-LED driver compensates for nonlinearity resulting from the time response by using a nonlinear transformation between the desired LED brightness and pulse shape (including pulse length and / or intensity and / or other aspects of the pulse shape). For example, in some embodiments, the nonlinear transformation is a lookup table that defines a given pulse width to achieve a given amount of light emission.

[0081] An example is shown in Table 1. This table applies to the micro-LED in Figure 2, and the current is 10A / cm². 2It is assumed that a simple rectangular wave of current density is applied as the drive power pulse 235. The bit depth is 8, corresponding to a maximum of 256 grayscale levels. Without nonlinear correction, the shortest pulse is 100 ns.

[0082] [Table 1]

[0083] In this example, an extra pulse length (or time offset) of 35 ns is applied to all tonal levels. This extra pulse length corrects the total amount of light emitted so that it is proportional to the target tonal level. Without such nonlinear correction, the tonal levels, especially at lower levels, could differ significantly from the desired values. In other words, (in the example above) increasing the length of all pulses by 35 ns allows for correction of the time it takes for emission to begin (or reach 90% of the total value).

[0084] Applying an arbitrary time offset to a pulse can be difficult if the time offset is not proportional to the base clock time of the display system. Therefore, some embodiments are configured so that the required time offset is close to the clock time. For example, in the example above, a clock time of 33.333 ns can produce time offsets very close to the values ​​in Table 1 (e.g., the shortest pulse lasts 4 clock cycles instead of 3). In some embodiments, other hardware, such as delay lines, is used to add a delay whose length is not determined by the clock period.

[0085] In this example, the extra pulse length is constant for all grayscale levels, and a complete lookup table is not required. However, other methods may require grayscale-dependent correction. This can occur, for example, when the pulse drive current depends on the grayscale level, or when hysteresis effects (i.e., the state of the pixel prior to the target pulse) are taken into account.

[0086] The lookup table may be finer or less finer, and may provide non-linear correction values ​​for more or fewer grayscale levels. For grayscale levels between levels in the lookup table, extra pulse lengths may be interpolated. The values ​​in such a lookup table may vary depending on the elements of the display (e.g., different regions, different pixels, different subpixels, different LED colors). Additional bits, for example, 12 bits (8 bits for display and 4 bits for correction), may be used to set the values ​​for individual elements.

[0087] In some embodiments, the controller applies nonlinear correction by itself or in combination with other teachings of the Disclosure. For example, the micro-LED and / or micro-LED driver may be configured to tolerate an approximate desired minimum pulse length (e.g., about 10 ns, 50 ns, 100 ns, 500 ns, or 1 us), and nonlinear correction may be applied to further control the light level and compensate for residual time response effects. In the above example, the micro-LED and micro-LED driver are configured to tolerate a minimum pulse of about 100 ns, and nonlinear correction is applied to precisely control the grayscale level. The pulse current density may also be set via a lookup table.

[0088] Table 1 assumes that the desired light intensity is strictly proportional to the bit depth. However, further gamma correction may be applied. Nonlinear correction may be configured to achieve the desired grayscale level after gamma correction. The lookup table may populate values ​​determined by applying a calibration process to the display, such as measuring light values ​​of different durations to determine how to change the pulse duration or pulse current density.

[0089] Embodiments include a method for configuring a driving scheme as disclosed herein to achieve a desired amount of light. This method may include the steps of determining a desired output (e.g., a nominal brightness level corresponding to a bit depth) and operating the display with a driving scheme (e.g., pulse shape and duration) suitable for achieving an actual output within a predetermined range of the desired output (e.g., within ±10% or 20% or 5% or 1%).

[0090] In some embodiments, certain aspects of the technology described above may be implemented by one or more processors of a processing system that executes the software. The software includes a set of one or more executable instructions stored in a non-temporary computer-readable storage medium, or otherwise embodied in a non-temporary computer-readable storage medium. The software may include instructions and specific data that, when executed by one or more processors, cause one or more processors to perform one or more aspects of the technology described above. The non-temporary computer-readable storage medium may include, for example, magnetic disks or optical disks, solid-state storage devices such as flash memory, caches, random-access memory (RAM), or other non-volatile memory devices or equipment. The executable instructions stored in the non-temporary computer-readable storage medium may be source code, assembly language code, object code, or other instruction forms that can be interpreted or otherwise executed by one or more processors.

[0091] It should be noted that not all of the actions or elements described above are necessary in general descriptions, and some parts of certain actions or devices may not be necessary. Furthermore, one or more additional actions or elements may be performed in addition to those described. Moreover, the order in which the actions are listed does not necessarily indicate the order in which they are performed. Concepts have also been described with reference to specific embodiments. However, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of this disclosure as set forth in the following claims. Accordingly, this specification and drawings should be considered illustrative rather than restrictive, and all such changes are intended to be within the scope of this disclosure.

[0092] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, benefits, advantages, solutions to problems, and any features(if any) that may produce or make more prominent any benefit, advantage, or solution should not be construed as essential, necessary, or required features of any or all of the claims. Furthermore, the subject matter disclosed above can be modified and implemented in different but equivalent ways that will be obvious to those skilled in the art who are interested in the teachings of this specification, so the specific embodiments disclosed above are merely illustrative. No limitations are intended to the details of the structure or design shown herein other than those set out in the following claims. It is therefore clear that the specific embodiments disclosed above can be modified or altered, and all such variations will be considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set out in the following claims.

Claims

1. To drive a first micro light-emitting diode (micro LED) with a lateral dimension smaller than 20 μm and nominally in the off state, with a first baseline power greater than zero, A method comprising driving the first microLED in an illuminating state with a power greater than the first baseline power, wherein the amount of light emitted by the first microLED in a nominally off state is negligibly small compared to the minimum amount of light emitted by the first microLED in an illuminating state.

2. The method according to claim 1, wherein driving the first microLED with the first baseline power includes applying the first baseline power before driving the first microLED in the light-emitting state.

3. The method according to claim 1 or 2, further comprising driving a second micro-LED in a nominal off state with a second baseline power greater than zero, wherein the second baseline power is different from the first baseline power.

4. The method according to any one of claims 1 to 3, wherein driving the first microLED in the light-emitting state is performed by driving the first microLED with a current pulse comprising a first phase having a relatively high current density and a second phase having a relatively low current density.

5. The method according to any one of claims 1 to 4, wherein the amount of light emitted by the nominally off-state microLED is less than 0.1% of the minimum amount of light emitted by the first microLED in the light-emitting state, and the light-emitting state is characterized by an internal quantum efficiency of at least 10%.

6. Driving the nominally off state of the first micro-LED includes driving the first micro-LED via a first power path, The method according to any one of claims 1 to 5, wherein driving the first microLED in the light-emitting state includes driving the first microLED via a second power path different from the first power path.

7. The method according to any one of claims 1 to 6, wherein the turn-on time between the nominal off state and the light-emitting state is less than 500 ns.

8. It is a method, The method includes driving a first microlight-emitting diode (microLED) of a display including an array of microLEDs, wherein each microLED in the array has a lateral dimension less than 20 μm and is in a light-emitting state including a first phase having a relatively high current density and a second phase having a relatively low current density. A method wherein the current pulse has a duration shorter than 1 microsecond, and the light emission state lasts for at least 50% of the current pulse duration.

9. The method according to claim 8, wherein the first phase has a current density at least twice that of the second phase.

10. The first micro-LED, which is nominally off, is driven with a first baseline power greater than zero, The method according to claim 8 or 9, further comprising driving the first microLED in the light-emitting state with a power greater than the first baseline power, wherein the amount of light emitted by the nominally off-state microLED is negligibly small compared to the minimum amount of light emitted by the first microLED in the light-emitting state.

11. The method according to claim 10, wherein driving the first microLED with the first baseline power includes applying the first baseline power before driving the first microLED in the light-emitting state.

12. The method according to claim 10 or 11, further comprising driving a second micro-LED of the array in a nominally off state with a second baseline power greater than zero, wherein the second baseline power is different from the first baseline power.

13. Driving the nominally off state of the first micro-LED includes driving the first micro-LED via a first power path, The method according to any one of claims 10 to 12, wherein driving the first micro-LED in the light-emitting state includes driving the first micro-LED via a second power path different from the first power path.

14. The method according to any one of claims 10 to 13, wherein the amount of light emitted by the nominally off-state microLED is less than 0.1% of the minimum amount of light emitted by the first microLED in the light-emitting state, and the light-emitting state is characterized by an internal quantum efficiency of at least 10%.

15. It is a device, A first micro light-emitting diode (micro LED) with a lateral dimension smaller than 20 μm, The driver comprises, The first micro-LED, which is nominally off, is driven with a first baseline power greater than zero. A device configured to drive the first microLED in an illuminating state with a power greater than the first baseline power, wherein the amount of light emitted by the nominally off-state microLED is negligibly small compared to the minimum amount of light emitted by the first microLED in an illuminating state.

16. The device according to claim 15, wherein the driver is further configured to apply a first baseline power to the first microLED before driving the first microLED in the light-emitting state.

17. The device according to claim 15 or 16, further comprising a second microLED, wherein the driver is configured to drive the nominally off second microLED with a second baseline power greater than zero, the second baseline power being different from the first baseline power.

18. The device according to any one of claims 15 to 17, wherein the driver is further configured to drive the first microLED in the light-emitting state with a current pulse comprising a first phase having a relatively high current density and a second phase having a relatively low current density.

19. The device according to any one of claims 15 to 18, wherein the amount of light emitted by the nominally off-state microLED is less than 0.1% of the minimum amount of light emitted by the first microLED in the light-emitting state, and the light-emitting state is characterized by an internal quantum efficiency of at least 10%.

20. The aforementioned driver A first power path for driving the nominally off first microLED with the first baseline power, The device according to any one of claims 15 to 19, further comprising a second power path different from the first power path for driving the first micro-LED in the light-emitting state.

21. A microLED having a horizontal dimension smaller than 20 μm, The system comprises a driver configured to drive the microLED with a current pulse to cause the microLED to emit a light pulse, wherein the current pulse includes a pulse profile having different amplitudes at different times, and the pulse profile is configured to trigger a turn-on time of less than 500 ns of the light pulse. The apparatus wherein the pulse profile includes a first phase having a high current density and a second phase having a low current density.

22. The apparatus according to claim 21, wherein the optical pulse has an optical output within + / - 10% of a predetermined value.

23. The apparatus according to claim 21 or 22, wherein the driver includes a plurality of power paths for generating the pulse profile.

24. A microLED having a horizontal dimension smaller than 20 μm, The system includes a driver configured to drive the microLED with an electric current pulse, causing the microLED to emit light pulses having a turn-on time and a turn-off time, The current pulse includes a pulse profile having different amplitudes at different times, and the turn-on time coincides with the turn-off time in the pulse profile. The apparatus wherein the pulse profile includes a first phase having a high current density and a second phase having a low current density.

25. The apparatus according to claim 24, wherein the optical pulse has an optical output within + / - 10% of a predetermined value.

26. The apparatus according to claim 24 or 25, wherein the current pulse has a pulse profile that includes a discharge pulse.

27. A microLED having a horizontal dimension smaller than 20 μm, The system comprises a driver configured to drive the microLED with a power pulse to cause the microLED to emit a light pulse, wherein the power pulse includes a pulse profile having different amplitudes at different times, and the pulse profile includes a discharge step that triggers a short turn-off time for the light pulse. The apparatus wherein the pulse profile includes a first phase having a high current density and a second phase having a low current density.

28. The apparatus according to claim 27, wherein the discharge step removes charge from the micro-LED.

29. It is a method, This includes driving a micro-LED having a lateral dimension smaller than 20 μm with an electric current pulse to cause the micro-LED to emit light pulses, The current pulse includes a pulse profile having different amplitudes at different times, The pulse profile is configured to trigger a turn-on time less than 500 ns of the optical pulse. The method wherein the pulse profile includes a first phase having a high current density and a second phase having a low current density.

30. This includes driving a micro-LED having a lateral dimension smaller than 20 μm with an electric current pulse, causing the micro-LED to emit light pulses having a turn-on time and a turn-off time. The current pulse includes a pulse profile having different amplitudes at different times, and the turn-on time coincides with the turn-off time in the pulse profile. The method wherein the pulse profile includes a first phase having a high current density and a second phase having a low current density.

31. It is a method, This includes driving a microLED with a power pulse to cause the microLED to emit a light pulse, The power pulse includes a pulse profile having different amplitudes at different times, The pulse profile includes a discharge step that triggers a short turn-off time for the optical pulse, The method wherein the pulse profile includes a first phase having a high current density and a second phase having a low current density.

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