Patent Application
20200161509
The present disclosure relates to LED displays that use a quantum-dot backlight, and in particular relates to a quantum-dot LED backlight module for LED displays.
Quantum-dot (QD) material is used in some types of LED displays to provide enhanced backlighting. The QD material has the advantage that it obviates the need for wavelength filters to generate the R-G-B wavelengths of light needed to form a color display.
A downside of QD-based backlighting is that the QD material sensitive to temperature and light flux from the LED light source. These sensitivities require that the LED light source be separated from the QD material. But this separation runs counter to the need for the QD LED packages or “modules” that form the QD-based backlight to be compact and have a small footprint while also having high brightness.
An aspect of the disclosure relates to a QD LED display that uses an LED that emits blue light and a QD material having a color point on the color gamut (e.g., CIE 1931) that is shifted from the conventional QD color point (e.g., (0.28, 0.2) to the yellow or yellow-green portion of the color space (e.g., x>0.35, y>3.75). A first portion of the blue light from the LED does not pass through the color-shifted QD material. A second portion of the blue light is directed to the QD material and is used (i.e., converted by the QD material) to form green and red light. This configuration allows for the flux of blue light on the QD material to be reduced (e.g., by at least 10% and as much as 50%), which in turn increases the longevity and reduces the time to failure of the QD material, while also improving the overall backlighting brightness as compared to backlights that use conventional QD LED modules.
Other aspects of the disclosure include: 1) the use of at least one spacer layer and a support assembly that supports heat conduction away from the QD material and back to the circuit board that supports the LED, wherein the circuit board acts as a heat sink; 2) a scattering layer configured to substantially uniformize the blue light to avoid hot spots when irradiating the QD material; 3) a hermetic seal formed by a transparent cap that serves as a barrier to oxygen and moisture, which can reduce the performance of the QD material over time. The QD material can also be part of a hermetically sealed QD chiplet, obviating the need for the transparent cap.
An embodiment of the disclosure is directed to a QD LED module that includes: a circuit board; an LED operably supported by the circuit board, the LED having a surface that emits blue light; and a QD structure supported within the interior of the support assembly and axially spaced apart from the LED surface by a distance D1, the QD structure having an active area that includes at least one first region of QD material and at least one second region that has no QD material, wherein a first portion of the blue light from the LED passes through the at least one first region and is converted by the QD material to red and green light, and wherein a second portion of the blue light passes through the at least one second region.
Another embodiment of the disclosure is directed to a QD LED module that includes: a support assembly having an interior; a circuit board; an LED operably supported by the circuit board, the LED having a surface that emits blue light; a QD structure supported within the interior of the support assembly and axially spaced apart from the LED surface by a distance D1, the QD structure having an active area that includes at least one first region of QD material and at least one second region that has no QD material, wherein a first portion of the blue light from the LED passes through the at least one first region and is converted to red and green light, and wherein a second portion of the blue light passes through the at least one second region; and at least one spacer layer disposed between the LED and the QD structure so that there is no air space between the LED and the QD structure.
Another embodiment of the disclosure is directed to a QD LED module that includes: a support assembly having at first end, a second end at least one sidewall and an interior; a circuit board disposed at or adjacent the second end of the support assembly, wherein the circuit is in thermal contact with the at least one sidewall of the support assembly; an LED operably supported by the circuit board, the LED having a surface that emits blue light; a QD structure supported within the interior of the support assembly and axially spaced apart from the LED top surface by a distance D the QD structure having an active area that includes at least one first region that comprises QD material configured to receive and convert the blue light to red light and green light and at least one second region that does not include any QD material, wherein the QD material of the at least one first region has an (x,y) CIE color point of x>0.35 and y>0.375; and at least one spacer layer disposed between the LED and the QD structure and that is in thermal contact with the at least one sidewall so that there is no air space between the LED and the QD structure.
Another embodiment of the disclosure is directed to a method of forming white light using a QD material supported on a QD structure. The method includes: generating blue light from an LED; passing a first portion of the blue light through the QD material of the QD structure to form green and red light; passing a second portion of the blue light through the QD structure but not through any of the QD material; and combining the green and red light and the second portion of the blue light to form the white light.
Additional features and advantages are set forth in the Detailed Description that follows, and in part will be apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which:
Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.
The claims as set forth below are incorporated into and constitute part of this Detailed Description.
Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation.
The terms “downstream” and “upstream” refer to the relative locations of a component, element, etc., based on the direction of travel of light, so that A being downstream of B means that light is first incident on B and then on A. Likewise, A being upstream of B means that light is first incident on A and then on B.
The support assembly 40 operably supports within its interior 47 a QD structure 60 that includes a QD material 62. The QD structure 60 is sometimes referred to as a “QD chiplet.” In an example, the QD structure 60 comprises a polymer matrix and the QD material 62 is supported by (e.g., in or on) the polymer matrix. In an example, the QD structure can comprise a hermetic QD chiplet, which obviates the need to hermetically seal the QD LED module using a cap, as discussed below.
The distance from the top surface 32 of the LED 30 to the QD material 62 is measured along a vertical axis A1 and is denoted D1, and as discussed below is one of the main module dimensions. The QD material 62 is configured so that a portion of the blue light 36B is converted to red light 36R and green light 36G while a portion of the blue light is transmitted therethrough (i.e., is unconverted), thereby providing red, blue and green colors for use in the (color) QD LED display. The lens 50 can be used to redirect the red light 36R, green light 36G and blue light 36B to uniformize the light distribution for backlighting purposes.
The blue light 36B emitted by the LED 30 has an associated optical flux FL, which can be measured in units of Watts per meter squared (W/m2). The LED 30 also generates heat H that reaches the QD structure 60 and that causes the QD material 62 to have a temperature TF. QD LED displays require that the optical flux FL and the temperature TF experienced by the QD material 62 be well managed for long-life operation. This requires that the distance D1 be sufficient to reduce peak-shifting and peak-broadening emission degradation as well as yield reduction from prolonged high-temperature and high-flux operation.
Without being bound by theory, it is generally believed that degradation of QD material is due principally to QD-ligand and polymer matrix breakdown as well as defects formed in the surface of QDs. The type of LED 30 used in a QD LED module for backlighting apparatus typically produces an optical flux FL of about 100 W/cm2, which is too high for most QD materials. At the same time, cost requirements are such that QD-LED modules need to have a small footprint and be simple while also being easy to integrate with other modules. This is in addition to the QD LED module being hermetically sealed and enduring high-flux and high-temperature operation over a 10-year period.
A key requirement for a QD LED display is that it operate over 30,000+ hours with less than a 10% change in the color gamut. This requirement limits the amount of flux FL of blue light 36B incident upon the QD material 62 to be less than about 2.5 to 3 W/cm2. The typical 55″ TV with 1000 nits brightness requires about 435 W of blue light, assuming a luminous efficiency (LE) of 120 W/lm, or 290 W at 180 W/lm, from about 100 cm2 of the combined area of the QD material 62, regardless of how many individual LEDs 30 are used. It is noted here that the LE of a TV panel describes the ability of a panel to transform the incident light power (W) into light humans can perceive (lumens or lm), and plays a large role in the calculation for the total LED power required to construct a 1000 nit TV. The 290-520 W of power of blue light 36B used in the 55″ TV's LED-count calculation assumes a panel LE of at least 100 lumens/W. Some panels have LE values as high as 180 lumens/W.
Depending on the design of the LED 30, the minimum area of QD material 62 required is determined by the above considerations as well as by the limits of optical technology in distributing light from a finite number of LEDs. To determine the minimum area of the QD material 62 needed, the emission of blue light 36B needs to be close enough to the QD material to uniformly illuminate it but not be so close as to exceed the flux limit of FL<2.5 W/cm to 3 W/cm2.
It is also noted that increasing the brightness of QD LED displays means subjecting the QD material 62 to increasing amounts of heat H. Thus, another design consideration is how to dissipate the heat H generate by the LED 30 and that can reach the QD material 62 so that the temperature TF of the QD material 62 stays below a threshold temperature TTH, which in an example is 90° C. If the temperature TF of the QD material 62 exceeds the threshold temperature TTH, then the QD LED backlighting performance can degrade due to at least one of: a) a shifting emission peak (˜1 nm per 10° C.); b) peak width broadening (prefer to keep narrow, e.g., <24 nm); and c) accelerated aging of the QD material and polymer matrix breakdown.
Thus, some main design goals of the QD LED modules disclosed herein include one or more of: 1) the flux of the blue light 36 incident upon the QD material be substantially uniform and up to or close to the maximum allowable flux; 2) maximizing the LED brightness; and 3) stable output of red and green light from the QD material over a relatively long time duration, e.g., 10 years.
The QD LED module 10 of
A second spacer layer 100B resides immediately atop (i.e., downstream of) the first spacer layer 100A. The second spacer layer 100B is a scattering layer and has a thickness DB. In an example, the second spacer layer 100B is configured to scatter blue light 36B from the LED 30. In an example, the second spacer layer 100B comprises silicone along with scattering particles 130 (e.g., TiO2) embedded therein.
Thus, in an example, the first and second spacer layers 100A and 100B occupy the portion of the interior 47 of the support assembly 40 between the LED 30 and the QD structure 60 so that there is no air space between the LED 30 and the QD material 62. This configuration is used to promote the transfer of heat H away from the QD material by conducting the heat to the support assembly 40. In an example, at least one spacer layer 100A is employed, wherein the spacer layer has a thermal conduction greater than that of air. In an example, a single spacer layer 100 that includes scattering features sized to scatter the blue light 36B from the LED 30 can be employed, as described below. In an example, the QD material 62 has a thickness DQ.
In an example, the QD LED module 10 can include a cap 70 that resides on the top side 42 of the support assembly 40 and along with the support assembly serves to hermetically seal the interior 47 of the support assembly and the components therein, and in particular the QD structure 60. The cap 70 can also be attached directly to the QD structure 60 since only the QD material 62 needs to be hermetically sealed. In an example, the cap 70 can be in the form of the aforementioned lens element 50, which can be used to redirect the white light 36W to provide more uniform illumination from the QD LED module 10. Such lens elements 50 are sometimes referred to in the art as secondary lens elements. The QD structure 60 can also comprise a hermetically sealed QD chiplet, thereby obviating the need for the cap 70.
Thus, in an example, the non-scattering first spacer layer 100A serves as a first thermal conducting layer that conducts the heat H over to the sidewalls 42 of the support assembly 40. The sidewalls 46 of the support assembly 40 can be made of a material with a relatively high thermal conductivity, such as a metal, so that the heat H generated by the LED can be conducted back to the PCB 20 and then dissipated, as indicated by the arrows AH. In this case, the PCB 20 acts as a heat sink.
Example materials with a relatively high thermal conductivity (e.g., greater than 20% that of pure copper) include metals such as, aluminum, copper, stainless steel and other metal alloys, etc. In an example, the thermally conductive material or materials that make up the sidewalls 46 has or have a thermal conductivity of greater than 50 Wm−1K−1.
The second spacer layer 100B serves as a second thermal conducting layer that also conducts heat H to the sidewalls 46 of the support assembly 40. The second spacer layer 100B also acts to scatter and uniformize the blue light 36B to avoid “hot spots” forming at the QD material 62. In other words, the spatial intensity uniformity of the blue light 36B incident upon the QD structure 60 is improved by the second spacer layer 100B due its light-scattering properties.
The second spacer layer 100B also facilitates the substantially uniform generation of red and green light 36R and 36G by the QD material 62 while also facilitating the substantially uniform transmission of a portion of the blue light 36B through one or more regions of the QD structure that have no QD material, as described below.
In an example, the LED has dimension of 2 mm×2 mm while the thickness DA is between 1 mm and 8 mm and the thickness DB is between 0.05 and 0.5 mm.
The QD LED 10 of
With reference to
The examples of the QD LED 10 of
The light-homogenizing medium 200 resides at an axial distance DG from the top surface 32 of the LED 30. The distance DG constitutes a second main dimensional parameter of the QD LED module 10 (the first being the dimension D1 introduced and discussed above).
The example QD LED 10 of
In the example of the QD LED 10 of
The transmitted blue light 36B through region R1 and the newly generated red light 36R and green light 36G from region R2 are incident upon the scattering layer 160, which scatters the blue light 36B, the green light 36G and the red light 36R to make “initial” white light 36W′, i.e., white light that does not have a high degree of uniformity. The initial white light 36W′ is then incident upon the light-homogenizing medium 200, which acts to homogenize (i.e., mix, blend, etc.) the blue, red and green components of the initial white light 36W′ to form substantially uniformized white light 36W that ultimately exits the QD LED module 10 and that is used as backlight for a display (not shown).
In an example, the light-homogenizing medium 200 is configured to reflect some of the initial white light 36W′ back down to the PCB 20, whose top surface 22 is reflective so that initial white light 36W′ is reflected back through the scattering layer 160 and the light-homogenizing medium 200, thereby providing for greater uniformization of the white light 36W that is finally ultimately emitted by the QD LED 10. In an example, the reflectivity of the light-homogenizing medium 200 is in the range from 90% to 99% and the reflectivity of the top surface 22 of the PCB 20 is in the range from 85% to 99%. In an example, the support assembly 40 is configured such that the interior 47 allows for such reflection between the PCB 20 and the light-homogenizing layer 200. For example, the sidewalls 46 of the support assembly 40 can be made vertical rather than angled (see, e.g.,
Thus, the QD LED modules 10 of
Other distributions or configurations of the QD material 62 that define one or more first regions R1 and one or more second regions R2 are contemplated herein beyond just the few examples shown in
In an example, the amount of non-QD material area of the one or more regions R2 is in the range of 10% to 30% of the total active area AR of the QD structure 60.
For a particular QD material 62 with an initial concentration of red and green QDs, one can either double the concentration c of red and green QDs or double the thickness DQ to move the y CIE coordinate by 0.09 and the x CIE coordinate by 0.05. For example, for a CIE color point shift from (0.23, 2) to (0.47, 55) (which is the highest blue point in the CIE color space), one needs to increase the concentration c of red and green QDs by about 3.5× to 5×. For reference, the CIE color point (0.28, 0.24) is the target color point for FOS (“front of screen”) for white light in LED displays, with no picture and maximum white light throughput.
The QD LED module 10 can provide improved brightness as compared to conventional modules that used standard QD material. This is made possible because the QD LED module 10 disclosed herein can use a QD material 62 having a shifted CIE color point relative to that of a standard QD material used in conventional QD LED modules. For reference, a standard QD material 62 was obtained and its CIE color point measured to be (0.28, 0.20).
The QD LED module 10 that uses the first example QD material 62 has an average brightness that is greater by between 2× and 3× over QD LED modules associated with typical commercial displays (600≤nits ≤1000).
In a second example, the QD material 62 has a color point (x,y)=(0.41, 0.54), which is in the yellow-green portion of the CIE 1931 color space. This color point has a color point shift (Δx, Δy) measured relative to the measured CIE color point (0.28, 0.20) of Δx=0.13 and Δy=0.34.
In an example, the color point shift (Δx, Δy) of the color-shifted QD material 62 disclosed herein can be measured relative to the FOS color point (0.28, 0.24), in which case the color shift for the x coordinate is Δx>0.15 and for they coordinate is Δy>0.15. Also in an example, the (x,y) color point for the QD material 62 is in the range x>0.4 and y>0.45. In another example, the color point for the QD material is in the range x>0.35 and y>0.375.
A color point shift (Δx, Δy) in the CIE color point (x,y) of the QD material 62 relative to standard QD material (e.g., having a CIE color point of (x,y)=(0.28, 0.2) or (0.28, 0.24) enables a lower flux of blue light 36B on the QD material 62 of the QD structure 60 thereby enabling longer operation of the QD LED module 10. As noted above, it also can enable increased brightness as compared to conventional QD LED modules, e.g., by about 15%.
It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/527,205 filed on Jun. 30, 2017, the content of which is relied upon and incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/040208 | 6/29/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62527205 | Jun 2017 | US |
