Light-emitting diode device and display device

A light-emitting diode (LED) device includes: an LED chip, a first lens, and a second lens. The first lens is disposed over the LED chip and configured to increase the light extraction efficiency of the LED device, and the first lens includes a first content of titanium dioxide. The second lens is disposed over the first lens and configured to alter the light pattern of the LED device, and the second lens includes a second content of titanium dioxide. The second content of titanium dioxide is more than the first content of titanium dioxide.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Taiwan Application Serial Number 108147251, filed Dec. 23, 2019, which is herein incorporated by reference in its entirety.

BACKGROUND

Field of Invention

The present disclosure relates to a package structure of a light-emitting diode device.

Description of Related Art

A light-emitting diode (LED) is a solid-state semiconductor device capable of converting electrical energy into light energy. Packaging the LED refers to encapsulating the LED chip in a particular structure which protects the LED chip and light can travel through.

FIG. 1Aillustrates a conventional package structure of an LED device10. The package structure of the LED device10is a flip-chip type of chip-scale package (CSP). An LED chip20is disposed on a printed circuit board (PCB)40and is electrically connected to the circuits of the PCB40through anodized pad22and a negative pad24. The outer part of the LED chip20is covered with an encapsulant30to protect the LED chip20. The material of the encapsulant30is often a silicone resin having a light refractive index of about 1.4 to 1.51.

In the conventional LED device10, non-epoxy-resin is often used as the encapsulant30. However, if the encapsulant30is exposed to ultraviolet (UV) lights emitted from the UV LED chip20for a long time, such encapsulant30will gradually yellow and affect the light extraction efficiency of the LED device10.

In addition,FIGS. 1B and 1Crespectively show the sample of traced rays and the Candela plot for light distribution of the LED device10shown inFIG. 1A. A high proportion of the light beams generated by the LED chip20are emitted from the upper side of the LED device10, and the light distribution pattern shown in the Candela plot is an elliptical shape. Therefore, the intensity distribution of the light field provided by the conventional LED device10is overly concentrated in the center, which results in poor performance of light uniformity and light emission angles. Because an LED device is a point light source, a conventional LED device often requires an additional design to diffuse the light beams emitted by the LED device more evenly. For example, a secondary optical lens can be added to the LED device in order to provide the desired light pattern.

For instance, LED devices are utilized in display devices. The applications of the display devices are gradually increasing, for example, a display device now can be integrated with multiple functions, such as various camera, communication, display, or other features. The resolutions of display devices are also gradually upgrading; for example, 4K resolution display devices are upgrading to 8K resolution display devices. Utilizing mini LED backlight modules in the display devices can not only provide more and smaller local dimming zones for the display devices, but also achieve high-contrast performance required for high dynamic range (HDR) imaging. In the direct type backlight modules of the existing display devices, which can be LCD TV or computer displays, a secondary optical lens is often disposed to cover the LED device in order to redistribute the light emitted by the LED device, so the light field can meet the requirements of the display devices containing optical cavities with heights more than 10 mm.

However, for the ultra-thin display devices, which contain optical cavities with heights equal to or smaller than 10 mm, the direct type backlight modules cannot be the conventional design mentioned above. Since the minimum height of the optical cavity is restricted by the conventional secondary optical lens for the LED devices, the ultra-thin display device having relatively tiny space inside cannot provide the secondary optical lenses enough light refraction distances and angles required for altering the light pattern of the LED devices, which will cause defects such as uneven mixing of light in the backlight modules.

SUMMARY

Some embodiments of the present disclosure provide an LED device including an LED chip, a first lens, and a second lens. The first lens is disposed over the LED chip and configured to increase the light extraction efficiency, and the first lens comprises a first content of titanium dioxide. A second lens is disposed over the first lens and configured to change the light pattern, and the second lens comprises a second content of titanium dioxide. In the LED device, the second content of titanium dioxide is more than the first content of titanium dioxide.

In some embodiments, the material of the first lens and the second lens includes a silicone epoxy resin.

In some embodiments, the first content of titanium dioxide in the first lens is more than 0.01 weight percent of the first lens.

In some embodiments, the first content of titanium dioxide in the first lens is less than 0.5 weight percent of the first lens.

In some embodiments, the second content of titanium dioxide in the second lens is more than 0.5 weight percent of the second lens.

In some embodiments, the second content of titanium dioxide in the second lens is less than 2 weight percent of the second lens.

In some embodiments, the average particle diameter of the titanium dioxide of the first lens and the titanium dioxide of the second lens is smaller than 1/10 of the wavelength of the emitted light of the LED chip.

In some embodiments, the average particle diameter of the titanium dioxide of the first lens and the titanium dioxide of the second lens is smaller than 40 nm.

In some embodiments, the LED chip is a blue light chip.

In some embodiments, the LED device is a chip-scale package structure.

Some embodiments of the present disclosure provide an LED device including an LED chip, a first lens, and a second lens. The first lens is disposed over the LED chip and includes titanium dioxide less than 0.5 weight percent of the first lens. The second lens is disposed over the first lens and includes titanium dioxide more than 0.5 weight percent of the second lens.

In some embodiments, the titanium dioxide of the first lens is dispersed in the first lens.

In some embodiments, the titanium dioxide of the second lens is dispersed in the second lens.

In some embodiments, the second lens includes a resin material, and the titanium dioxide of the second lens is formed as a thin film overlaying the resin material of the second lens.

In some embodiments, the first lens directly contacts the LED chip.

In some embodiments, the second lens directly contacts the first lens.

In some embodiments, the first lens is configured to increase the light refraction.

In some embodiments, the light refractive index of the second lens is smaller than the light refractive index of the first lens.

In some embodiments, the light transmittance of the second lens is less than the light transmittance of the first lens.

Some embodiments of the present disclosure provide a display device including any of the LED devices of the embodiments of the present disclosure, and the display device has an optical cavity having a height smaller than 10 mm.

In some embodiments, the LED device is a direct-light-type backlight module of a display device.

DETAILED DESCRIPTION

In view of the problems of conventional LED devices, such as undesired light pattern or uneven mixing of light, some embodiments of the present disclosure provide the solution, which can alter the light pattern and improve the light extraction efficiency of an LED device by disposing a two-layer lens, wherein the two layers have different content of titanium dioxide respectively.

FIG. 2shows the relationship between the various content of titanium dioxide in a silicone epoxy resin layer and light transmittance of the silicone epoxy resin layer. The particle diameters of the titanium dioxide in the tests shown inFIG. 2are smaller than 40 nm. As the tests shown inFIG. 2, the silicone epoxy resin layers with different content of titanium dioxide (TiO2), such as 0.01 weight percent, 0.1 weight percent, 0.5 weight percent, and 1 weight percent, were tested respectively for obtaining the light transmittance of the tested silicone epoxy resin layers at different light wavelengths.

The dotted line inFIG. 2is the wavelength of 450 nm, which is the applied wavelength of a typical blue LED chip.FIG. 2shows that increasing content of titanium dioxide particles leads to a significant reduction of light transmittance for the light with the wavelengths in the range of UV, such as the light with wavelengths shorter than 400 nm. Accordingly, a silicone epoxy resin layer mixed with titanium dioxide particles disposed on the LED chip can effectively filter a portion of the emitted UV light and improve the color purity of the blue light emitted from the LED device. In addition, a silicone epoxy resin layer has better resistance to UV light, so the silicone epoxy resin layer will not yellow as easily as the encapsulant30used in the conventional LED devices. The mixed titanium dioxide particles also reduce the transmittance of UV light and enhance absorption of UV light.

FIG. 2also shows that when 1 weight percent titanium dioxide was added into the silicone epoxy resin, the light transmittance at the wavelength of 450 nm was about 20%. When 0.5 weight percent titanium dioxide was added into the silicone epoxy resin, the light transmittance at the wavelength of 450 nm was about 65%. When 0.01 to 0.1 weight percent titanium dioxide was added into the silicone epoxy resin, the light transmittance at the wavelength of 450 nm was about 75% to 85%. Therefore, when less than 0.1 weight percent titanium dioxide is added into the silicone epoxy resin, the effect of altering the light transmittance made by the added titanium dioxide becomes smaller. According to the test results shown inFIG. 2, a silicone epoxy resin layer mixed with titanium dioxide particles disposed on the LED chip can provide the desired light transmittances or light patterns by adjusting the content of the titanium dioxide within the silicone epoxy resin layer.

FIG. 3shows the relationship of titanium dioxide content in a silicone epoxy resin layer and the refractive index for blue light with wavelengths from 445 to 450 nm in such silicone epoxy resin layer, wherein the diameters of the tested titanium dioxide particles are smaller than 40 nm. According toFIG. 3, when the silicone epoxy resin layer is not mixed with titanium dioxide particles, the refractive index for blue light in the silicone epoxy resin layer is about 1.5. When the content of titanium dioxide particles is gradually increased to 0.1 weight percent, the refractive index for blue light in the silicone epoxy resin layer increases as well. The highest refractive index for blue light, about 1.61 to 1.62, in the test is reached at 0.1 weight percent titanium dioxide particles mixed within the silicone epoxy resin layer. If the content of titanium dioxide particles is increased over 0.1 weight percent, the refractive index for blue light in the silicone epoxy resin layer decreases in contrast. For example, when the content of the titanium dioxide particles is gradually increased to 0.5 weight percent, the refractive index for blue light in the silicone epoxy resin layer gradually decreases to about 1.58.

According to the test results shown inFIGS. 2 and 3, the titanium dioxide powder having nanometer-scale particle size mixed in the encapsulant of silicone epoxy resin can provide various optical properties. When the content of titanium dioxide particles is low, e.g., less than 0.1 weight percent, the effect on the transmittance of light having wavelengths longer than 450 nm is small, i.e., there is not much reduction in transmittance while the content of titanium dioxide gradually increases to 0.1 weight percent. At the same time, the refractive index of the silicone epoxy resin layer mixed with titanium dioxide particles rises from 1.51 to about 1.61, while the content of titanium dioxide particles gradually increases to 0.1 weight percent. Alternatively, if the content of mixed titanium dioxide particles is more than 0.5 weight percent, the titanium dioxide particles will aggregate within the silicone epoxy resin and cannot maintain dispersion status, thereby the light extraction efficiency is no longer improved by the refractions between particles within the silicone epoxy resin layer. The aggregation phenomenon of particles may result in Rayleigh scattering and leads to a significant decrease in transmittance of blue light.

Therefore, a two-layer structure of lenses disposed in an LED device is disclosed according to some embodiments of the present disclosure, and different content of titanium dioxide particles are added into the silicone epoxy resin layers, wherein the first layer of the lenses is configured to increase the light extraction efficiency, and the second layer of the lenses is configured to alter the light pattern of the emitted light.

FIG. 4Aillustrates an LED device100according to some embodiments of the present disclosure. The LED device100includes a substrate110and an LED structure120which is disposed on the substrate110. The LED structure120includes a first pad132, a second pad134, an LED chip140, a first lens150, and a second lens160.

In some embodiments of the present disclosure, one or more LED structures120may be disposed on the substrate110, and the substrate110may be a printed circuit board (PCB), for example. In some embodiments, the substrate110is coated with white paint having 80% to 90% light reflectivity, so the light emitted from the LED chip140toward the substrate110will be reflected outward.

The LED chip140is disposed on the substrate110and is electrically connected to the circuits of the substrate110through the first pad132, such as an anode pad, and the second pad134, such as a cathode pad. In addition, in some embodiments, the LED chip140is fixed on the substrate110by an adhesive, such as epoxy resin.

In some embodiments of the present disclosure, the LED chip140is a blue light LED chip, such as a gallium nitride (GaN) chip or a gallium phosphide (GaP) chip, and the emitted light of the LED chip140has wavelengths between 430 and 480 nm, for example, 440 to 460 nm.

The first lens150is disposed over the LED chip140. In some embodiments, the first lens150directly contacts the LED chip140. The first lens150is made of silicone epoxy resin containing titanium dioxide particles dispersed therein, wherein the titanium dioxide particles are at a content in a range of about 0.01 to about 0.5 weight percent. The particle diameter of the titanium dioxide particles is smaller than 1/10 of the wavelength of the light emitted from the blue LED chip140, for example, smaller than 40 nm.

In some embodiments of the present disclosure, the titanium dioxide particles are mixed with the silicone epoxy resin which forms the first lens150on the LED chip140by a molding process.

In some embodiments of the present disclosure, the first lens150is configured to increase the light extraction efficiency of the LED device. According to Snell's Law, when the light is toward an optically rarer medium from an optically denser medium at an angle of incidence which is greater than the critical angle, the light will not refract through the optically rarer medium but reflect back to the optically denser medium. Such phenomenon refers to total internal reflection. For example, a gallium nitride (GaN) LED chip is used as the light source, which is the optically denser medium with the refractive indexes n=2.5. If the difference in refractive index between the encapsulant and the GaN LED chip covered by the encapsulant is too large, a large portion of the emitted light will be reflected back in the inside of the GaN LED chip in accordance with Snell's Law, and therefore the light extraction efficiency will be reduced. The refractive index of the encapsulating silicone resin contacting the LED chip in the prior art LED device is within the range from about 1.4 to about 1.51, so the light extraction efficiency of the conventional LED device is affected by the difference in the refractive indexes of materials.

Conversely, in the embodiments of the present disclosure, the first lens150in the LED structure120is made of silicone epoxy resin, wherein a particular proportion of titanium dioxide particles is added into the silicone epoxy resin, and silicone epoxy resin having titanium dioxide particles added forms the polygonal geometry shape of the first lens150which contacts the LED chip140directly. The first lens150can be formed by a molding process and thereby adhered to the LED chip140. As the first lens150is added with 0.01 to 0.5 weight percent titanium dioxide particles, the light refractive index of the first lens150is increased to about 1.61. Therefore, the light extraction efficiency of LED device100according to some embodiments of the present disclosure can be enhanced comparing to the prior art LED devices.

Please refer toFIG. 4Aagain, which illustrates the second lens160disposed on or outside the first lens150. In some embodiments of the present disclosure, the second lens160directly contacts the first lens150, and the second lens160is made of silicone epoxy resin having titanium dioxide particles dispersed within, wherein the titanium dioxide particles are at a content in a range of about 0.5 to about 0.2 weight percent. The particle diameter of the titanium dioxide particles is smaller than 1/10 of the wavelength of the light emitted from the blue LED chip140, for example, smaller than 40 nm.

In some embodiments of the present disclosure, the silicone epoxy resin layer having titanium dioxide particles dispersed therein forms the second lens160on the first lens150by a molding process. In other words, the forming process of the second lens160is similar to the forming process of the first lens150. The difference between the forming processes is that a higher content of titanium dioxide particles is mixed within the silicone epoxy resin layer of the second lens160.

In other embodiments of the present disclosure, the silicone epoxy resin layer is formed on the first lens150by a molding process. After that, a thin titanium dioxide film is deposited on the silicone epoxy resin layer by a vacuum deposition process, such that the structure of the thin titanium dioxide film overlaying the silicone epoxy resin layer forms the second lens160.

In other embodiments of the present disclosure, the second lens160is configured to alter the light pattern of the emitted light. The content of the titanium dioxide particles in the silicone epoxy resin layer is in the range of about 0.5 to about 2 weight percent, which makes the refractive index of the second lens160is smaller than that of the first lens150, so the light transmittance in silicone epoxy resin layer of the second lens160is decreased, and the effect of altering the light pattern can be achieved.

According to the test results shown inFIGS. 2 and 3, when the content of titanium dioxide particles in the silicone epoxy resin layer is higher than a critical proportion, the titanium dioxide particles aggregate and form large particles. Such large particles may have particle sizes larger than 1/10 of blue light wavelength, thereby resulting in Rayleigh scattering in the silicone epoxy resin layer and causing the transmittance of the blue light to be decreased. The second lens160is specifically designed to take advantage of Rayleigh scattering caused by the large titanium dioxide particles, such that the light scattering effect in the second lens160is increased and the transmittance of the light toward directly above from the second lens160is reduced. Furthermore, the light in the second lens160will be reflected more frequently, and part of the light will be refracted again, so the light distribution pattern of the light emitted from the lenses will be altered as the target of the design.

FIGS. 4B and 4Crespectively show the sample of traced rays and the Candela plot for light distribution of the LED device100illustrated inFIG. 4A. The transmittance of the light emitted from the upper side of the LED device100is reduced, and a part of the reflected light is refracted again by the lenses. Therefore, the light distribution pattern of the LED device100has a bat-wing shape, as shown inFIG. 4C. Accordingly, the LED device100is able to provide shorter light mixing distance, and thus the thinner backlight module design can be achieved with the LED device100.

Conversely, the conventional LED devices, such as the LED device10shown inFIG. 1A, are required to have secondary optical lenses covering the LED package to achieve the light distribution pattern similar as the one shown inFIG. 4C.

In some embodiments of the present disclosure, the concentration of the titanium dioxide particles dispersed in the second lens160can be adjusted in order to provide the desired light pattern. For example, when the light emitted toward directly above the LED device is required to have higher intensity, the content of titanium dioxide particles added during the process of forming the second lens160should be less. Alternatively, when light emitted toward directly above the LED device is required to have lower intensity, the content of titanium dioxide particles added during the process of forming the second lens160should be more.

In some embodiments of the present disclosure, the first lens150and the second lens160are two planar layers or layers having planar surfaces. In some other embodiments of the present disclosure, the first lens150and the second lens160may be two layers with arc shapes, for example, lenses with convex-shaped or concave-shaped structures.

In some embodiments of the present disclosure, the LED structure120is formed on the substrate110, such that the LED chip140is electrically connected to the substrate through the first pad132and the second pad134and adhered to the substrate110by an adhesive. After the LED structure120is formed, the first lens150is formed over or on the LED chip140, and the second lens160is formed over or on the first lens150.

In some other embodiments of the present disclosure, the first lens150is formed on the LED chip140, and then the second lens160is formed on the first lens150. After the lenses are formed, the LED structure120having the lenses is electrically connected to the substrate110through the first pad132and the second pad134, and the LED chip140is adhered to the substrate110by an adhesive.

FIG. 5Aillustrates an LED device200according to some embodiments of the present disclosure. In the LED device200, an LED package structure220is a full-encapsulation package. The first lens250and the second lens260encapsulate the top surface242and the side surfaces244of the LED chip240. The LED chip240is disposed on the substrate210and electrically connected to the circuits of the substrate210through the first pad232and the second pad234.

In some embodiments of the present disclosure, the LED chip240has a first dimension D1as the width, the second lens has a second dimension D2as the width, and the second dimension D2is smaller or equal to 1.2 times of the first dimension D1. Therefore, the LED package structure220is a chip-scale package LED structure.

FIG. 5Billustrates an LED device300according to some other embodiments of the present disclosure. In LED device300, the LED package structure320is a full-encapsulation package with a polygonal shape. The first lens350and the second lens360encapsulate the top surface and the side surfaces of the LED chip340. The LED chip340is disposed on the substrate310and is electrically connected to the circuits of the substrate through the first pad332and the second pad334.

The part of the first lens350encapsulating the top surface of the LED chip340has the first thickness T1, and the part of the first lens350encapsulating the side surface of the LED chip340has the second thickness T2. In some embodiments of the present disclosure, the first thickness T1may not equal to the second thickness T2. The first thickness T1and the second thickness T2of the first lens350may be adjusted respectively based on the design requirements, such that the desired or different light extraction efficiencies at the top and side surfaces of the LED package structure320can be achieved.

The part of the second lens360encapsulating the top surface of the LED chip340has the third thickness T3, and the part of the second lens360encapsulating the side surface of the LED chip340has the fourth thickness T4. In some embodiments of the present disclosure, the third thickness T3may not equal to the fourth thickness T4. In the embodiments that the second lens360is formed by a process of depositing a titanium dioxide film on the silicone epoxy resin layer, the thickness at different parts of the silicone epoxy resin layer can be adjusted during the process of forming the second lens360, such that the different parts of the second lens360can have the required contents of titanium dioxide particles respectively. The third thickness T3and the fourth thickness T4may be adjusted respectively based on the design requirements, such that the ideal light distribution patterns at the top and side surfaces of the LED package structure320can be achieved.

FIG. 6Aillustrates an LED package structure420according to some embodiments of the present disclosure. The main difference between the LED package structure420and the LED package structures220and320is that the LED package structure has a frame422, wherein the frame422may be made of a ceramic material or an epoxy resin material.

In the LED package structure420, the first pad432is electrically connected to the first extended pad426through a guide hole424in the frame422. The second pad434is electrically connected to the second extended pad428through another guide hole424in the frame422. The first lens450is located over the frame422and encapsulates the LED chip440. The second lens460is located over the frame422and encapsulates the first lens450.

FIG. 6Billustrates an LED package structure520according to some embodiments of the present disclosure. The LED package structure520is a single-sided illumination package structure. A protective layer570is located at the side544of the LED chip540, where the protective layer570is made of an opaque material. The first lens550is located on the protective layer570and encapsulates the top surface542of the LED chip540. The second lens560encapsulates the first lens550.

According to the LED device disclosed in the embodiments of the present disclosure, a two-layer micro-lenses structure, i.e., the first lens and the second lens, is disposed to encapsulate the LED chip. In some embodiments of the present disclosure, such structure can be applied to, for example, the encapsulation package of a mini LED package structure or a micro LED package structure, such as a chip-scale package or a wafer-scale package.

The LED devices disclosed in the embodiments of the present disclosure can be applied to, for example, display devices or lighting devices, but not limited to these. More specifically, the LED devices can be utilized in various lighting devices or components, at least including the backlight modules of the display devices, such as the direct-type backlight modules or the edge-lit backlight modules, the flash lamps, the projection instruments, the glare lighting fixtures, such as the car lights, the searchlights, the flashlights, the work lights, the outdoor high bay lights, and the landscape lights, the low-angle lights, and etc.

Given the backlight sources in a display device as an illustrative embodiment, the improvements provided by the present disclosure are expounded in Table 1 below, which compares the backlight module utilizing the LED device of the present disclosure to the one utilizing the conventional LED devices.

FIG. 7illustrates an exploded view of a backlight module700for a display device. The backlight module700includes a backplate710, a plurality light strips720, a backlight cavity730, and a plurality of optical films740.

A plurality of light strips720are disposed on the backplate710, and each of the light strips720includes a circuit board722and LED components724. The LED components724have the first lens and the second lens as described above.

The backlight cavity730is set over the backplate710and the light strips720. The bottom surface of the reflector, as the bottom of the backlight730, has a plurality of openings732respectively corresponding to the plurality of LED components724. In some embodiments of the present disclosure, the backlight module700can be applied in slim display devices or thin display devices, which require the height of the backlight cavity730to be less than 10 mm.

A plurality of optical films740are disposed over the backlight cavity730. The optical films may be, for example, a diffuser plate, a prism plate, a diffuser sheet, or the like, which can adjust the optical characteristics of the backlight module700as the requirements.

In some embodiments of the present disclosure, a thin display device is disclosed, which requires the height of the optical cavity within the display device is less than 10 mm. The backlight module of the display device includes the LED devices or the LED package structures of the embodiments illustrated inFIG. 4A, 5A, 5B, 6A, or6B. Therefore, the secondary optical lens required in the conventional LED devices can be omitted. In addition, the light extraction efficiency and the light-mixing effect of the thin display devices and the lighting devices having small optical cavity heights can be enhanced by utilizing the LED packages of the present disclosure.