Light emitting diode integrated with lens, line printer head, and method of manufacturing the light emitting diode

Provided are a light emitting diode unit including a light emitting diode integrated with a lens, a line printer head using the light emitting diode, and a method of manufacturing the light emitting diode. The light emitting diode unit includes the light emitting diode layer bonded to a transparent substrate after removing a growth substrate on which the light emitting layer is grown, and a lens that refracts light emitted from the light emitting diode is formed on the transparent substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2009-0077633, filed on Aug. 21, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The embodiment relates to a light emitting diode integrated with a lens, a line printer head using the light emitting diode, and a method of manufacturing the light emitting diode.

2. Description of the Related Art

Light emitting diodes are a PN junction of compound semiconductors which emit light upon receiving a current. Unlike other light sources which use a filament, a light emitting diode does not have the problem of a short circuit caused by oxidization or heating. Also, the light emitting diode is an environment-friendly device which has a long lifespan and is driven with low power consumption. In addition, the light emitting diode has a high response speed of simultaneously responding to an applied current, and has excellent durability against temperature and shocks, and is manufactured in a semiconductor manufacturing process which is a batch process, and thus may be easily made compact and integrated.

With the commercialization of blue light emitting diodes, natural colors can be realized, and thus a light emitting diode is widely used not only in simple display devices (as previously used) but also in backlight units (BLU) of mobile phones, flat panel displays, outdoor electric signs, gauge boards of cars, taillights, traffic signals, lightscape lights, etc., and also in the environmental field or biotechnology in which water pollution or oxygen density in blood is measured. Furthermore, due to the improved product performance and reduced manufacturing costs, the application fields of light emitting diodes have gradually extended, and thus the light emitting diodes are also used as alternative illumination for home fluorescent lamps. Recently, as electrophotographic image forming apparatuses have high speed and high image quality, a line printer head (LPH) that uses a light emitting diode as a light source in order to overcome the limits of a laser scanning unit (LSU), which is a conventional exposure apparatus, has been developed. The LPH includes thousands of light emitting diodes arranged at intervals of several tens of microns, and each of the light emitting diodes changes light energy according to printing image data to transmit the printing image data to a photoreceptor that is disposed at a distance of several millimeters away from the light emitting diodes. In a conventional LPH, an optical system, which prevents lights emitted from adjacent light emitting diodes from overlapping, is further included.

SUMMARY

It is an aspect of the embodiment to provide a light emitting diode integrated with a lens that collimates emitted light or focuses light at a far distance, a line printer head (LPH) that uses the light emitting diode, and a method of manufacturing the light emitting diode.

The foregoing and/or other aspects may be achieved by providing a light emitting diode unit including: a light emitting diode; a transparent substrate bonded to the light emitting diode; and a lens that refracts light emitted from the light emitting diode, the lens being formed on the transparent substrate.

The light emitting diode may include a compound semiconductor layer that is grown on an opaque substrate and then separated from the opaque substrate.

The opaque substrate may be a GaAs substrate.

The light emitting diode may emit red light.

The light emitting diode may include: a first conductivity compound semiconductor layer bonded to the transparent substrate; an active layer formed on the first conductivity compound semiconductor layer; and a second conductivity compound semiconductor layer formed on the active layer.

The light emitting diode may be covered by a reflection layer.

The light emitting diode may include: a first electrode layer formed on a portion of the first conductivity compound semiconductor layer; and a second electrode layer formed on the second conductivity compound semiconductor layer.

The second electrode layer may cover a remaining portion of the first conductivity compound semiconductor layer except at the portion where the first electrode layer is formed, and an insulating layer is provided beneath the second electrode layer except at a portion where the second electrode layer contacts an upper surface of the second conductivity compound semiconductor layer.

A reflection layer may be inserted into the second conductivity compound semiconductor layer.

The light emitting diode may include a truncated pyramid shape.

The lens may have refractive power as a surface of the transparent substrate is curved. The lens may be formed of a polymer layer by molding the polymer layer and attaching the polymer layer to the transparent substrate. The lens may have refractive power as impurities have different densities according to positions in the transparent substrate.

A plurality of the light emitting diodes may be arranged on the transparent substrate. The plurality of light emitting diodes may be arranged in a row or in a plurality of rows.

The lens may include a micro-lens array which corresponds to the light emitting diodes that are arranged on the transparent substrate.

The foregoing and/or other aspects may be achieved by providing a line printer head exposing a photoreceptor in a main scanning direction, comprising the above-described light emitting diode unit.

The foregoing and/or other aspects may be achieved providing an electrophotographic image forming apparatus including: a photoreceptor; the above-described line printer head, which illustrates light onto an exposed surface of the photoreceptor to form an electrostatic latent image; and a developing unit supplying toner to the electrostatic latent image formed on the photoreceptor to develop the electrostatic latent image.

The foregoing and/or other aspects may be achieved by providing a method of manufacturing a light emitting diode unit, the method including: growing a light emitting diode layer on an opaque substrate; forming a transparent substrate having a lens formed on a surface; bonding an upper surface of the light emitting diode layer to a surface of the transparent substrate on which the lens is not formed; removing the opaque substrate from the light emitting diode layer; and forming an electrode layer structure on the light emitting diode layer.

The lens of the transparent substrate may be formed using a fusion molding method, a photolithography method, an imprinting method, or an impurity diffusion method.

The foregoing and/or other aspects may be achieved by providing a method of manufacturing a light emitting diode unit, the method comprising: growing a light emitting diode layer on an opaque substrate; bonding an upper surface of the light emitting diode layer to a transparent substrate; removing the opaque substrate from the light emitting diode layer; forming an electrode layer structure on the light emitting diode layer; and forming a lens on a surface of the transparent substrate, which is not bonded to the light emitting diode layer.

The lens of the transparent substrate may be formed using a photolithography method or an imprinting method.

A polymer layer may be formed on the transparent substrate, and a lens of the transparent substrate may be formed in the polymer layer.

The opaque substrate may include a GaAs substrate.

The method may further include forming a separation layer between the opaque substrate and the light emitting diode layer, wherein the separation layer is selectively etched to separate the opaque substrate from the light emitting diode layer.

The whole opaque substrate may be removed by selectively etching the opaque substrate from the light emitting diode layer.

The method may further include forming an etching stopper layer between the opaque substrate and the light emitting diode layer.

The transparent substrate and the light emitting diode layer may be bonded using a spin on glass (SOG).

DETAILED DESCRIPTION

The embodiments may be embodied in many different forms, and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concepts thereof to those of ordinary skill in the art.

FIG. 1is a side cross-sectional view illustrating a light emitting diode unit according to an embodiment. Referring toFIG. 1, the light emitting diode unit includes a transparent substrate110and a light emitting diode120that is bonded to the transparent substrate110.

The transparent substrate110includes a substrate bonding surface119on which the light emitting diode120is bonded and a lens surface115on which a lens115ais formed. The lens115amay be formed integrally with a body111of the transparent substrate110. The transparent substrate110is formed of a material which is substantially transparent to light emitted from the light emitting diode120. For example, when the light emitting diode120emits red light, the transparent substrate110may be formed of a material transparent to red light, such as glass, sapphire, GaP, plastic, or the like. The lens115arefracts the light emitted from the light emitting diode120to collimate the light or focus the light on a predetermined point according to an optical design. As described above, since the light emitting diode unit according to this embodiment may be a chip emitting parallel light or focused light, the optical configuration of the light emitting diode unit when used in different apparatuses may be simplified, and the light emitting diode unit may be made compact. Furthermore, since the lens115ais formed integrally with the body111, a distance between the lens surface115and the light emitting diode120may be very close and uniform, and thus a light extraction efficiency of the light emitting diode120may be increased and uniformity of light beams emitted from the light emitting diode120may be maintained.

The light emitting diode120includes a first conductivity compound semiconductor layer130that is bonded to the transparent substrate110, an active layer140formed on the first conductivity compound semiconductor layer130, a second conductivity compound semiconductor layer150formed on the active layer140, a first electrode layer180formed on a portion of the first conductivity compound semiconductor layer130, and a second electrode layer190formed on the second conductivity compound semiconductor layer150. The first and second electrode layers180and190are in ohmic contact with the first and second conductivity compound semiconductor layers130and150, respectively, to supply electrons or holes, and may be formed of a metal having good conductivity. For example, the first and second electrode layers180and190may each be formed of a single layer. Alternatively, each of the layers180and190may be formed of two layers. The metals may be, for example, Au, Ni, Ti, Al, or the like. When the transparent substrate110is formed of a conductive material such as GaP, the transparent substrate110may function as an electrode for the first conductivity compound semiconductor layer130, instead of the first electrode layer180. The second electrode layer190covers an upper portion of the second conductivity compound semiconductor layer150, thereby functioning as a reflection layer to reflect light emitted from the active layer140.

The first conductivity compound semiconductor layer130, the active layer140, and the second conductivity compound semiconductor layer150are epitaxial layers which are formed by epitaxy. The first conductivity compound semiconductor layer130may be formed of, for example, an N-doped compound semiconductor, and the second conductivity compound semiconductor layer150may be formed of, for example, a P-doped compound semiconductor, or vice versa. The active layer140may be formed of a P-doped, N-doped, or non-doped compound semiconductor, and may have a single quantum well structure or a multiple quantum well structure. Holes or electrons supplied from the first and second conductivity compound semiconductor layers130and150recombine in the active layer140, thereby emitting light.

A wavelength of light emitted from the light emitting diode120is determined according to energy band gaps of the epitaxial layers of the first conductivity compound semiconductor layer130, the active layer140, and the second conductivity compound semiconductor layer150, and due to lattice mismatching of the eptaxial layers, a selection of the growth substrate on which the epitaxial layers are grown is limited. For example, a compound semiconductor that emits red light is usually epitaxially grown in a GaAs substrate, and the GaAs substrate is opaque to light having red wavelengths. The epitaxial layers may be crystalline grown in the GaAs substrate, and may be a compound semiconductor that emits red light; in detail, the epitaxial layers may be a GaAsP, AlGaAs, InGaP, or InGaAIP compound semiconductors. As will be described later, after the epitaxial layers are grown, the GaAs substrate is removed.

FIG. 2is a side cross-sectional view illustrating a light emitting diode unit according to another embodiment.

Referring toFIG. 2, the light emitting diode unit includes the transparent substrate110and a light emitting diode120′ that is bonded to the transparent substrate110. The light emitting diode120′ includes the first conductivity compound semiconductor layer130that is bonded to the transparent substrate110, the active layer140formed on the first conductivity compound semiconductor layer130, the second conductivity compound semiconductor layer150formed on the active layer140, a reflection layer160inserted between the active layer140and the second conductivity compound semiconductor layer150, the first electrode layer180formed on a portion of the first conductivity compound semiconductor layer130, and the second electrode layer190formed on the second conductivity compound semiconductor layer150. The light emitting diode unit is substantially the same as that of the previous embodiment except that the reflection layer160is further formed in the light emitting diode120′, and therefore, not all of the elements are described again.

The reflection layer160reflects light that is isotropically emitted upwardly from the active layer140toward the transparent substrate110, thereby increasing light extraction efficiency. The reflection layer160may be, for example, a distributed Bragg reflector (DBR) layer, which is formed of materials having different refractive indices and are alternately stacked. A DBR layer is well known in the art and thus description thereof will be omitted here. InFIG. 2, the reflection layer160is inserted between the active layer140and the second conductivity compound semiconductor layer150; however the embodiments are not limited thereto and thus the reflection layer160may be inserted into the second conductivity compound semiconductor layer150or may also be formed on an upper surface of the second conductivity compound semiconductor layer150.

FIG. 3is a side cross-sectional view illustrating a light emitting diode unit according to another embodiment.

Referring toFIG. 3, the light emitting diode unit includes the transparent substrate110and a light emitting diode220bonded to the transparent substrate110. The light emitting diode220includes a first conductivity compound semiconductor layer230bonded to the transparent substrate110, an active layer240formed on the first conductivity compound semiconductor layer230, a second conductivity compound semiconductor layer250formed on the active layer240, the first electrode layer180formed on a portion of the first conductivity compound semiconductor layer230, and the second electrode layer190formed on the second conductivity compound semiconductor layer250. The light emitting diode unit ofFIG. 3is substantially the same as that ofFIG. 1, except that the light emitting220has a truncated pyramid shape.

The light emitting diode220has an inclined surface225that reflects light emitted from the active layer240toward the transparent substrate110, thereby improving light extraction efficiency. According to this embodiment, the light emitting diode220has a truncated pyramid shape, but is not limited thereto; the light emitting diode220may have various shapes for improving light extraction efficiency.

FIG. 4is a side cross-sectional view illustrating a light emitting diode unit according to another embodiment.

Referring toFIG. 4, the light emitting diode unit includes the transparent substrate110and a light emitting diode220′ bonded to the transparent substrate110. The light emitting diode220′ includes the first conductivity compound semiconductor layer230, the active layer240, the second conductivity compound semiconductor layer250, the first electrode layer180, the second electrode layer290, and an insulating layer260. The second electrode layer290covers an upper surface of the first conductivity compound semiconductor layer230, and also a side of the first conductivity compound semiconductor layer230, the active layer240, and the second conductivity compound semiconductor layer250, except at a portion where the first electrode layer180formed. The second electrode layer290contacts a top surface of the second conductivity compound semiconductor layer250. The insulating layer260is inserted beneath a portion of the second electrode layer290so that the insulating layer260insulates the second electrode layer290from the active layer240and the first conductivity compound semiconductor layer230. The insulating layer260may be formed of an insulating material such as SiO2. The light emitting diode unit according to this embodiment is substantially the same as the light emitting diode unit ofFIG. 3, except that the insulating layer260is included in the light emitting diode220′ and that the second electrode layer290covers the light emitting diode220′ except at the portion where the first electrode layer180is formed.

As the second electrode layer290substantially covers an upper surface the light emitting diode220′ except the portion where the first electrode layer180is formed, light emitted from the active layer240is reflected by the second electrode layer290and proceeds toward the transparent substrate110, thereby improving light extraction efficiency. To this end, the second electrode layer180may be formed of a metal having good reflection characteristics, and may be formed to have a sufficient thickness so that light is not transmitted therethrough.

FIG. 5is a side cross-sectional view illustrating a light emitting diode unit according to another embodiment.

Referring toFIG. 5, the light emitting diode unit includes a transparent substrate310including a lens layer315, and the light emitting diode120bonded to the transparent substrate310. The light emitting diode120includes the first conductivity compound semiconductor layer130that is bonded to the transparent substrate310, the active layer140formed on the first conductivity compound semiconductor layer130, the second conductivity compound semiconductor layer150formed on the active layer140, the first electrode layer180formed on a portion of the first conductivity compound semiconductor layer130, and the second electrode layer190formed on the second conductivity compound semiconductor layer150. The light emitting diode unit according to this embodiment is substantially the same as the light emitting diode unit ofFIG. 1, except that the transparent substrate310further includes the lens layer315.

A body311of the transparent substrate310includes a substrate bonding surface319that contacts the first conductivity compound semiconductor layer130, and another surface that contacts the lens layer315. The body311may be formed of a material such as glass, sapphire, GaP, or plastic. The lens layer315may be formed of polymer with which a lens315amay be easily formed. For example, when the lens layer315is formed of polymer, which can be formed using a low temperature process, the shape of the lens315amay be formed using an imprinting process after the transparent substrate310and the light emitting diode120are bonded to each other.

FIG. 6is a side cross-sectional view illustrating a light emitting diode unit according to another embodiment.

Referring toFIG. 6, the light emitting diode unit includes a transparent substrate410and the light emitting diode120that is bonded to the transparent substrate410. The light emitting diode120includes the first conductivity compound semiconductor layer130that is bonded to the transparent substrate410, the active layer140formed on the first conductivity compound semiconductor layer130, the second conductivity compound semiconductor layer150formed on the active layer140, the first electrode layer180formed on a portion of the first conductivity compound semiconductor layer130, and the second electrode layer190formed on the second conductivity compound semiconductor layer150. The light emitting diode unit according to this embodiment is substantially the same as the light emitting diode unit ofFIG. 1, except for the transparent substrate410.

The transparent substrate410is a flat lens having refractive power as a refractive index thereof is partially modulated. For example, impurities are diffused in a diameter direction419around a center C of the transparent substrate410to partially modulate a refractive index of the transparent substrate410so that the transparent substrate410has refractive power.

FIG. 7is a top view of a portion of a line printer head according to another embodiment,FIG. 8is a bottom view of the line printer head ofFIG. 7, andFIG. 9is a side cross-sectional view of the line printer head ofFIG. 7, taken along a line I-I′.

Referring toFIGS. 7 through 9, the line printer head has an array structure in which light emitting diodes520are arranged in two rows on an upper surface of a transparent substrate510. Also, lenses515are formed on a lower surface of the transparent substrate510to correspond to the light emitting diodes520. For example, the light emitting diodes520may each have a width of several tens of microns, and be arranged at intervals of several tens of microns. Also, a distance between the two rows of the light emitting diodes520may also be several tens of microns or less. The lenses515may also each have a width of several tens of microns and be arranged at intervals of several tens of microns to correspond to the size of the light emitting diodes520. The lenses515having a width of several tens of microns are referred to as a micro-lens array, and a method of manufacturing the micro-lens array is known well in the art.

In the line printer head, the two rows of the light emitting diodes520may be alternately arranged so that one row fills gaps of the other and so that light beams emitted from each of the light emitting diodes520may be accordingly densely emitted at equal distances without any gap due to the separation of the light emitting diodes520with respect to a side view. For example, light beams emitted from each of the light emitting diodes520may be emitted at intervals of several tens of microns. A thousand of the light emitting diodes520are arranged on one transparent substrate510. Accordingly, the line printer head according to the embodiment ofFIG. 7may be used as a line printer head of an image forming apparatus, as will be described later.

According to the embodiment ofFIG. 7, two rows of the light emitting diodes520are arranged, but the embodiment is not limited thereto. Alternatively, one row of the light emitting diodes520or three rows of the light emitting diodes520may be arranged, or the light emitting diodes520may also be disposed in another predetermined pattern.

Next, a method of manufacturing a light emitting diode, according to an embodiment, will be described.

FIGS. 10A through 10Eillustrate a method of manufacturing a light emitting diode unit, according to an embodiment.

Referring toFIG. 10A, epitaxial layers630are grown on an opaque substrate610. The epitaxial layers630are formed by sequentially stacking a second conductivity compound semiconductor layer640, an active layer650, and a first conductivity compound semiconductor layer660on the opaque substrate610. The epitaxial layers630may be grown by using a method such as a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, or a metal organic molecular beam epitaxy (MOMBE) method and using a compound semiconductor epitaxy apparatus.

Before growing the epitaxial layers630, a separation layer620may be formed on the opaque substrate610. The separation layer620, for example, AlAs, may be formed of a material having a higher etching selectivity than the epitaxial layers630. As will be described later, the separation layer620, e.g., a sacrificial layer or an etching stopper layer, may function as a layer separating the opaque substrate610and the epitaxial layers630.

Also, referring toFIG. 10B, a transparent substrate670having a lens675formed thereon is formed. The transparent substrate670may be formed of, for example, glass, plastic, or polymer. The lens675may be formed with, for example, a fusion molding method. Alternatively, the lens675may be formed on the transparent substrate670by using a photolithography method or an imprinting method. InFIG. 10B, the lens675is formed by processing a surface of the transparent substrate670as a lens surface having a predetermined curvature, but is not limited thereto. For example, a flat lens may be formed on the transparent substrate670by partially modulating a refractive index of transparent substrate670by diffusing impurities into the transparent substrate670.

Next, referring toFIG. 10C, an upper surface of the epitaxial layers630grown on the opaque substrate610is bonded to a surface of the transparent substrate670other than the surface thereof on which the lens675is formed. The upper surface of the epitaxial layers630may be bonded to the surface of the transparent substrate670by using, for example, heat and pressure. The surface of the transparent substrate670on which the lens675is not formed or the upper surface of the epitaxial layers630may be coated with a spin on glass (SOG) to facilitate the bonding.

Next, referring toFIG. 10D, the opaque substrate610is separated from the epitaxial layers630which are bonded to the transparent substrate670. For example, by using a difference in etching selectivities of the opaque substrate610and the epitaxial layers630, the whole opaque substrate610is etched, thereby removing the opaque substrate610. Alternatively, by removing the separation layer620by using a difference in the etching selectivities of the separation layer620and the epitaxial layers630and the opaque substrate610, the opaque substrate610may be separated from the epitaxial layers630.

Next, referring toFIG. 10E, the epitaxial layers630are formed into individual light emitting units by performing a photolithography process and a metal patterning process, thereby forming a plurality of electrode structures680.

FIGS. 11A through 11Eillustrate a method of manufacturing a light emitting diode unit according to another embodiment.

Referring toFIG. 11A, epitaxial layers730are grown on an opaque substrate710. The epitaxial layers730are formed by sequentially stacking a separation layer720, a second conductivity compound semiconductor layer740, an active layer750, and a first conductivity compound semiconductor layer760on the opaque substrate710. The above operations are substantially the same as described with reference toFIG. 10A.

Next, as illustrated inFIG. 11C, an upper surface of the epitaxial layers730grown on the opaque substrate710is bonded to the transparent substrate770. The bonding may be performed by using, for example, heat and pressure.

Next, as illustrated inFIG. 11D, the opaque substrate710is separated from the epitaxial layers730bonded to the transparent substrate770. The separation layer720may be used as an etching stopper layer or a sacrificial layer.

Next, as illustrated inFIG. 11E, a photolithography process and a metal patterning process are performed on the epitaxial layers730to form the epitaxial layers730into individual light emitting units and thus form a plurality of electrode structures780.

Next, as illustrated inFIG. 11F, a plurality of lenses775are formed on a surface of the transparent substrate770, which is not bonded to the epitaxial layers730. The lens775may be formed by using, for example, a photolithography process or an imprinting process. Alternatively, a surface of the transparent substrate770, which is not bonded to the epitaxial layers730, may be coated with a transparent polymer and then the transparent polymer may be processed to form a lens surface by using an imprinting process.

FIG. 12is a structural diagram illustrating an image forming apparatus in which an array of light emitting diodes according to embodiments is used in a line printer head810.FIG. 13is a perspective view illustrating one of the line printer heads810and one of a plurality of photosensitive drums830of the image forming apparatus ofFIG. 12.

Referring toFIG. 12, the image forming apparatus may include the line printer heads810, developing units820, the photosensitive drums830, charging rollers840, an intermediate transfer belt850, a transfer roller860, and a fixing unit870.

The line printer head810illustrates on the photosensitive drum830linear light L that is modulated according to image information, and may include the light emitting diode unit according to the above-described embodiments. The photosensitive drum830is an example of a photoreceptor, and includes a photosensitive layer having a predetermined thickness on an outer circumferential surface of a cylinder metal pipe. The outer circumferential surface of the photosensitive drum830is an exposed surface whereon the light L illustrated by the line printer head810forms an image. Also, a belt-type photosensitive belt may be used as a photoreceptor. A corresponding charging roller840is rotated while contacting the photosensitive drum830and charges the surface of the photosensitive drum830to a uniform electric potential. A charging bias voltage Vc is applied to the corresponding charging roller840. A corona charger (not shown) may be used instead of the corresponding charging roller840. Toner is contained in a corresponding developing unit820. The toner is transported to the photosensitive drum830in response to a developing bias voltage applied between the corresponding developing unit820and the photosensitive drum830and develops an electrostatic latent image into a visible toner image. The visible toner image formed on the photosensitive drum830is transferred to the intermediate transfer belt850. The toner image is then transferred to a paper P that is transported between the transfer roller860and the intermediate transfer belt850by applying a transfer bias voltage to the charging rollers840. The toner image transferred to the paper P is fixed on the paper P by heat and pressure from the fixing unit870, thereby completing formation of an image.

In order to print a color image, each of the line printer heads810, each of the developing units820, and each of the photosensitive drums830corresponding to one color are included. The line printer heads810respectively scan four light beams to the four photosensitive drums830. In the four photosensitive drums830, electrostatic latent images corresponding to image information of black (K), magenta (M), yellow (Y), and cyan (C) are formed. The four developing units820supply toner of black (K), magenta (M), yellow (Y), and cyan (C) colors to the photosensitive drums830to form toner images of black (K), magenta (M), yellow (Y), and cyan (C). The toner images of black (K), magenta (M), yellow (Y), and cyan (C) are transferred to the intermediate transfer belt850and overlapped thereon, and then are transferred to the paper P again.

Referring toFIG. 13, the line printer heads810are disposed from several to several tens of millimeters away from the photosensitive drums830, and emit a plurality of light beams L arranged in a main scanning direction onto an outer circumferential surface of the photosensitive drums830according to image information. The line printer head810exposes the photosensitive drum830line-by-line, and a two-dimensional electrostatic latent image is formed on the outer circumferential surface of the photosensitive drum830as the photosensitive drum830is rotated.

The line printer head810may have a structure as illustrated inFIGS. 7 through 9. That is, in the line printer head810, a plurality of light emitting diodes811are bonded to a transparent substrate812, and a plurality of micro-lenses815are arranged on the transparent substrate812to correspond to the plurality of the light emitting diodes811, respectively. Light beams are emitted through the plurality of micro-lenses815at equal distances, and may be focused on the outer circumferential surface of the photosensitive drum830according to the optical design of the micro-lenses815. According to conventional designs, a light beam emitted from the light emitting diode811has a large luminous view angle and is thus diverged, and in order to collimate or focus a plurality of the light beams that are usually arranged at several tens of microns, an expensive optical device such as a rod lens array (RLA) is needed. However, in the line printer head810, as a plurality of the micro-lenses815are arranged on the transparent substrate812, no optical unit is required. Accordingly, a simple light scanning optical system may be realized with reduced manufacturing costs. Also, since the line printer head810having a compact size may be manufactured, the degree of freedom of a system design of an image forming apparatus may also be increased.

According to the light emitting diode unit of the embodiments, light emitted from the light emitting diodes may proceed parallel or be efficiently focused at a predetermined distance. In addition, distances between the lens and the light emitting diodes may be kept as close as possible to a thickness of the transparent substrate and uniform. Thus, the light beam extraction efficiency of the light emitting diode may be increased and the uniformity of light beams emitted therefrom may be maintained.

According to the line printer head using the light emitting diode unit according to the embodiments, light may be focused on a scanning surface without using an RLA. Also, when the light emitting diode unit according to the embodiments is used in a line printer head, no RLA is required, and thus the manufacturing costs of the line printer head may be significantly reduced, and the size of the line printer head may also be reduced, thereby increasing the degree of freedom of a system design of a printer.

Also, according to the method of manufacturing the light emitting diode unit of the embodiments, a light emitting diode integrated with a lens may be manufactured in one process, thereby reducing manufacturing costs.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the embodiments, the scope of which is defined in the claims and their equivalents.