JPH065364A - End face luminescence type el element - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the light intensity of an edge-emitting EL device. [Structure] The active layer 12 of the edge-emitting type EL device 11 is formed of a thin film layer having a higher refractive index toward the center than both sides in the film thickness direction,
The light generated in the active layer 12 and traveling outward from the center of the film thickness is focused on the center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge emitting EL element used as a light emitting element of a line head of an electrophotographic apparatus.

[0002]

2. Description of the Related Art Currently, as a light emitting element used in a line head of an electrophotographic apparatus, for example, an EL (Electro Lumin
There is a luminescence element, but there is a demand for improvement of the emission brightness, which tends to be insufficient. Therefore, an edge-emitting type EL has been developed which exhibits a light emission luminance about 100 times that of a conventional EL in which the surface of the thin film layer emits light. This is a thin-film active layer made of zinc sulfide containing an active element surrounded by a dielectric layer to form an optical waveguide, and an extremely flat light is emitted from the end face of the active layer. Due to its high brightness, it is expected to be used for printer heads and the like.

Therefore, a conventional example of this edge emitting EL element will be described with reference to FIGS. First, in the conventional edge-emitting EL device 1, as illustrated in FIG. 5, the thin film-like active layer 3 forming the optical waveguide 2 is formed from above and below the dielectric layers 4, 4.
5, and the electrode layers 6 are formed on the upper and lower surfaces of the dielectric layers 4 and 5.
7 is formed. More specifically, the active layer 3 comprises EB (Electron Bea) of a phosphor material such as ZnS in which about 0.5 (wt%) of an emission center material such as Mn is mixed.
m) The dielectric layers 4 and 5 are formed by a vapor deposition method or a sputtering method, and the dielectric layers 4 and 5 are formed of Y ₂ O ₃ , SiO ₂ , Ta ₂ O ₅ , and Al ₂ O _3.
The electrode layers 6 and 7 are formed as transparent electrodes by a sputtering method such as Al or ITO (Indium-Tin Oxide). Therefore,
As illustrated in FIG. 6, it is possible to form a line head 9 of an electrophotographic apparatus by arranging a large number of edge emitting EL elements 1 on a glass substrate 8 in series.

With this structure, in the edge-emitting EL device 1, when an AC voltage is applied between the electrode layers 6 and 7 by the AC power supply 10, electrons induced in the active layer 3 made of ZnS: Mn are generated. The electrons are accelerated in a high electric field to become hot electrons, which collide with each other to excite outer shell electrons of Mn atoms. Then, when the outer shell electrons of the Mn atom return to the ground state, light emission occurs, so that extremely flat light is emitted from the end surface of the active layer 3 of the edge emitting EL element 1. At this time, in the edge emitting EL element 1,
As illustrated in FIG. 5, it is considered that light generated in the active layer 3 is sequentially propagated by repeating total reflection at boundaries between the dielectric layers 4 and 5 having different refractive indexes. The light intensity of the emitted light emitted from the end surface of the active layer 3 is about 100 times that of the conventional EL element in which the surface of the thin film layer emits light.

[0005]

The edge emitting EL elements 1 as described above can be used for the line head 9 or the like by emitting light individually by connecting them in an array.

However, in reality, a part of the light generated in the active layer 3 is transmitted through the boundary surface between the dielectric layers 4 and 5 and each of the layers 4 to 4.
When the line head 9 is formed with this edge-emitting EL element 1, it is emitted from the edge surface of the active layer 3 and is used for image formation because it is radiated to the outside from the edge surface of 7 and the surfaces of the electrode layers 6 and 7. The intensity of the emitted light is decreasing. Therefore, in order to improve the light intensity of the edge-emitting type EL element 1, the driving power of the AC power supply 10 is set to a high voltage of 250 (V) and a high frequency of 5 (KHz). Weight reduction and power saving will be hindered. Further, when the driving power is increased in this way to secure the light intensity of the emitted light of the edge emitting EL element 1, the light emitted from other than the edge of the active layer 3 becomes noise and the print quality of the electrophotographic apparatus. Is inhibited, which is not preferable.

Here, the edge emitting EL device 1 has an active layer 3
Since it has a structure in which the light generated inside is propagated in the longitudinal direction and is emitted from the end face, it is considered that the light intensity is improved by extending the length. However, in reality, the light attenuation rate of zinc sulfide or the like forming the active layer 3 of the edge-emitting type EL device 1 is about 5 to 50 (cm to ¹ ), so that the light generated in the active layer 3 is generated. The intensity of is attenuated by a factor of 10 in a few millimeters. Therefore, the edge emitting EL
Even if the length of the element 1 is extended, the increment of the light intensity is minute and the upper limit is fixed.

The present invention is directed to an edge-emitting type E which emits light with high intensity.
The L element is obtained.

[0009]

In an edge-emitting type EL device in which electrode layers facing each other are formed on the outer surface of a dielectric layer surrounding a thin film active layer, a thin film having a higher refractive index in the center than on both sides in the film thickness direction. The layers formed the active layer.

[0010]

The light generated in the active layer is deflected to the center according to the refractive index distribution in the process from the center to the both sides in the film thickness direction. Therefore, the intensity of the light emitted from the end face of the active layer is improved and the light other than the end face is improved. It is possible to reduce the optical noise emitted from the device.

[0011]

Embodiments of the present invention will be described with reference to FIGS. First, in this edge-emitting EL device 11, as illustrated in FIGS. 1 and 2, a thin-film active layer 12 forming an optical waveguide is surrounded from above and below by dielectric layers 13 to 16 having a double structure. In this structure, electrode layers 17 and 18 are formed on the upper and lower surfaces of the dielectric layers 13 to 16, respectively. In the edge-emitting EL device 11 of the present embodiment, the active layer 12 is formed by laminating a large number of thin film layers having different refractive indexes in sequence, so that the active layer 12 has an equivalent refractive index. The center is higher than both sides of the direction.

Therefore, the active layer 1 having such a refractive index distribution is used.
A specific example of a method of manufacturing the edge-emitting EL device 11 having 2 will be described in detail below. First, an aluminum film having a film thickness of 2000 (Å) formed by vapor deposition or the like on a glass substrate 19 is patterned by etching or the like to a width of about 100 (μm) in the main scanning direction to form a lower electrode layer 18 to be an individual electrode. SiO ₂ having a film thickness of 500 (Å) to be the lower first dielectric layer 16 and Ta ₂ having a film thickness of 2500 (Å) to be the second lower dielectric layer 14 are formed thereon.
O ₅ and O ₅ are sequentially formed by RF (Radio-Frequency) sputtering or the like. As a method of forming the active layer 12 having a refractive index sequentially different in the film thickness direction on the dielectric layer 14 thus formed, for example, there is a hot wall epitaxy method, a plasma control type sputtering method, or the like. .

Therefore, here, a film forming apparatus 20 for carrying out the hot wall epitaxy method will be described with reference to FIG. First, in this film forming apparatus 20, three stainless steel pipes 23 to 25 for heat insulation are sequentially erected on the inner bottom surface of a bell jar 22 to which a vacuum pump (not shown) is connected by an exhaust pipe 21. In the upper half of the stainless tubes 23 to 25, quartz glass crucibles 29 to 31 are arranged via tungsten heaters 26 to 28. A substrate holder 32 is movably provided at a position sequentially facing the upper openings of these crucibles 29 to 31, and the substrate holder 32 is provided on the bottom of a housing 34 having an infrared heater 33 built therein. The structure is such that an opening 35 in which 19 is set is formed.

Therefore, when the active layer 12 of the edge emitting EL element 11 is formed by the hot wall epitaxy method using the film forming apparatus 20 as described above, first, the lower electrode layer 18 is formed as described above. The glass substrate 19 in which the dielectric layer 16 and the dielectric layer 16 are sequentially formed is set in the opening 35 of the substrate holder 32. For example, ZnS and ZnTe which are phosphor substances and Mn which is an emission center substance are placed in the crucibles 29 to 31. The strips 36 to 38 of and are respectively put. Therefore, the vacuum pump is driven to evacuate the bell jar 22 to about 5.0 × 10 to ⁶ (Torr), and the tungsten heaters 26 to 28 are driven to drive the crucible 29.
Strips 36-38 of ZnS, ZnTe and Mn in
Sublimate. Therefore, the glass substrate 19 heated by the infrared heater 33 is placed in a predetermined crucible 29 to 31 by the substrate holder 32.
When placed on top, the strips 36-3 in the crucibles 29-31
8 thin film layers on the dielectric layer 14 of the glass substrate 19 1.
The film is formed at a speed of about 0 (Å). Therefore, here, by controlling the time for disposing the glass substrate 19 on each of the crucibles 29 to 31, a large number of thin film layers in which Mn, ZnS, and ZnTe are mixed at a predetermined ratio are laminated to form an equivalent film thickness. The active layer 12 having a different refractive index in each direction is formed.

That is, at the start of film formation, the film formation of ZnS to 10 (Å) and then the film formation of Mn to 0.5 (Å) are repeated 100 times. Membrane, Mn 0.
Deposition of 5 (Å), 100 times, 10 (Å) of ZnTe, 0.5 (Å) of Mn, 20 times, 10 times of ZnS
(Å) film formation, Mn 0.5 (Å) film formation, 60 times, Z
nTe 10 (Å) film, Mn 0.5 (Å) film, 40 times, ZnS 10 (Å) film, Mn 0.5 (Å) film, 40 times ZnTe 10 (Å) film formation, Mn 0.
5 (Å) film formation, 60 times of this, ZnS 10 (Å) film formation,
Mn 0.5 (Å) film formation, this 20 times, ZnTe 10
(Å) film formation, Mn 0.5 (Å) film formation, 80 times, Z
The nTe film formation of 10 (Å) and Mn film formation of 0.5 (Å) are repeated 100 times. Since the lower half of the active layer 12 is formed in this way, the formation of the active layer 12 is completed by reversing the order of repetition in the following process. In the active layer 12 thus formed, the density of ZnTe is high in the center of the thickness direction and the density of ZnS is high on both sides of the active layer 12, so that the refractive index is equivalently higher in the center than in both sides in the thickness direction. .

When the formation of the active layer 12 by the hot wall epitaxy method is completed as described above, the glass substrate 19 is removed from the film forming apparatus 20 and Ta ₂ having a film thickness of 2500 (Å) is formed on the glass substrate 19. O ₅ and S of film thickness 500 (Å)
io ₂ and SiO ₂ are sequentially formed by RF sputtering or the like to form the upper dielectric layers 13 and 15, and an aluminum film having a thickness of 2000 (Å) formed by vapor deposition or the like is formed on the dielectric layers 13 and 15 to have a width of 0.5 in the optical axis direction.
The upper electrode layer 17 to be a common electrode is formed by patterning to about 5.0 (mm) by etching or the like. Therefore, here, the light emitting end surface of the edge emitting EL element 11 is formed by cutting the glass substrate 19 together with each thin film layer at the position of the end of the electrode layer 17.

In such a structure, the edge emitting EL element 11 is induced in the active layer 12 made of ZnS: Mn and ZnTe: Mn when an AC voltage is applied between the electrode layers 17 and 18 by an AC power source. The generated electrons are accelerated in a high electric field to become hot electrons, which collide with each other to excite outer shell electrons of Mn atoms. And this Mn
Light emission occurs when the outer shell electrons of the atoms return to the ground state, so that extremely flat light is emitted from the end surface of the active layer 12 of the edge emitting EL element 11. At this time, in the edge-emitting type EL device 11, since the refractive index of the active layer 12 is higher in the center than on both sides in the film thickness direction, light generated in the active layer 12 has a film thickness as illustrated in FIG. In the process of going from the center of the direction to both sides, the light will be refracted toward the center. That is, in this edge-emitting EL device 11, the light components that have been transmitted from the active layer 12 through the boundary surface between the dielectric layers 13 and 14 and were emitted to the outside are also collected toward the end surface of the active layer 12. As a result, the light intensity of the light emitted from this end face is improved and the optical noise emitted from other than the end face is reduced. Therefore, such an edge-emitting type E
By forming the line head (not shown) of the electrophotographic apparatus by connecting the L elements 11 in series, it is possible to reduce the size and weight of the AC power supply (not shown) and save power, and also to reduce optical noise. It is also possible to contribute to the improvement of print quality by reducing

The applicant of the present invention produced a prototype to evaluate the characteristics of the active layer 12 of the edge-emitting EL device 11 as described above, and measured the emission intensity. The length of the upper electrode layer 17 was measured. It was confirmed that the luminescence intensity changed with the increase.

Further, the edge emitting EL element 11 of this embodiment is used.
Then, ZnS and ZnTe are used as phosphor materials of the active layer 12.
However, a compound semiconductor of the 2-6 group of the periodic table can be used as such a phosphor substance, and for example, ZnSe, CdS, CdSe,
CdTe, SrS, etc. can also be implemented. Therefore, in the edge-emitting type EL device 11 of the present embodiment, ZnS and ZnTe having different refractive indices are selected as the material of the active layer 12, so that the refractive index between the center and both sides in the film thickness direction is largely changed. I was allowed to. The refractive index of such a semiconductor can be obtained from the dielectric constant, which is a physical property value. If the dielectric constant is ε when the lattice frequency is high, the refractive index n is n ² = ε. Then, since the dielectric constants of ZnS and ZnTe are 5.07 and 8.26, the refractive indexes thereof are 2.25 and 2.87.

Further, in the edge-emitting type EL device 11, the wavelength of the emitted light is determined by the material of the emission center substance added to the active layer 12, and therefore the emission center substance is Mn and the peak is 585 (nm). It is assumed that emitted light is generated.
For example, when such an emission center substance is TbF ₃ , the peak of emitted light is 540 to 550 (nm), and SmF ₃ is 650 (nm). Here, in the edge-emitting type EL device 11, there is a relationship of Eg = (1239.8) / λ (λ: nm Eg: eV) between the energy gap Eg of the phosphor substance and the wavelength λ of the emitted light. The phosphor substance needs to have an energy gap larger than the emission energy of the emission center substance. Therefore, in the edge-emitting type EL device 11 of the present embodiment, ZnS having a refractive index of about 2.3 and an energy gap of about 3.4 (eV) as the fluorescent substance of the active layer 12 and an energy gap of about 2.8 having an energy gap of about 2.8. The above conditions are satisfied by using ZnTe of 2.26 (eV) and Mn having an emission energy of 2.1 as the emission center substance.

Further, here, as another method for forming the active layer 12 whose refractive index sequentially differs in the film thickness direction, a plasma control type sputtering method which is a variation of the magnetron sputtering method will be described with reference to FIG. First, in the plasma-controlled sputtering film forming apparatus 39,
A cylindrical magnetic yoke 43 containing an annular electromagnetic coil 42 is attached to the bottom of a vacuum chamber 41 connected to an exhaust pipe 40 by a vacuum pump (not shown). In the vacuum chamber 41, disk-shaped and ring-shaped targets 44 and 45 of ZnTe and ZnS are arranged coaxially. A glass substrate 19 having a lower electrode layer 18 and dielectric layers 14 and 16 formed thereon is arranged at a position facing the targets 44 and 45 from above. An annular electromagnetic coil 46 is provided at a position surrounding the space between the target 19 and the targets 44 and 45. In addition,
Here, since the fluorescent substance of the active layer 12 is prepared as the targets 44 and 45 arranged coaxially, the emission center substance Mn of the fluorescent substance is converted into the target 44, 45 as a predetermined amount of strips 47.
It will be placed on 45.

Therefore, when the active layer 12 of the edge-emitting EL element 11 is formed by the plasma-controlled sputtering method using the film forming apparatus 39, first, the vacuum pump is driven to move the inside of the vacuum chamber 41. Is evacuated to about 5.0 × 10 to ⁶ (Torr), and argon gas is introduced to about 5.0 × 10 to ³ (Torr). Then, by moving each of the electromagnetic coils 42 and 46 at a predetermined voltage, the moving direction of the argon ions is adjusted to collide with the predetermined position of the targets 44 and 45, and ZnS: M
Releases n and ZnTe: Mn ions. Therefore, here, by controlling the voltage of the driving power of each electromagnetic coil 42, 46 in a time-division manner, a large number of thin film layers in which ZnS: Mn and ZnTe: Mn are mixed at a predetermined ratio are laminated to form an equivalent film. The active layer 12 having a different refractive index in the thickness direction is formed.

That is, at the start of film formation, argon ions in the plasma state are guided to the outer peripheral portion of the target 45 and Zn
By depositing S: Mn and moving the induction position of the argon ions sequentially toward the center of the target 44, a mixture of ZnS: Mn and ZnTe: Mn or Zn
Te: Mn is sequentially formed. By doing so, the lower half of the active layer 12 is formed, so that the formation of the active layer 12 is completed by reversing the order in the following process.
In the active layer 12 thus formed, the density of ZnTe is high in the center of the film thickness direction and the density of ZnS is high on both sides of the active layer 12, so the refractive index is equivalently higher in the center than in both sides in the film thickness direction. .

In this embodiment, the hot wall epitaxy method and the plasma-controlled sputtering method are used to sequentially stack thin film layers having different refractive indexes, and the active layer having a higher refractive index in the center than both sides in the film thickness direction. Although the formation of the layer 12 has been illustrated, it is also possible to thermally diffuse the refractive index variable substance from the outer peripheral portion to the preformed active layer 12 such as a graded index type optical fiber. In this case, for example, a sulfur thin film, which is a variable refractive index material, is formed on the dielectric layer 14 and then the active layer 12 is formed, and after the sulfur thin film is formed on this, the whole is heated to form the active layer 12. It will be to diffuse sulfur from the outside. However, in this case, sulfur is also thermally diffused in the dielectric layer 14, and it is difficult to control the amount of diffusion, and it is difficult to control the refractive index distribution of the active layer 12. Further, it is also possible to form thin film layers having different refractive indexes sequentially by a general electron beam vapor deposition or sputtering method to form the active layer 12 having a higher refractive index in the center of both sides in the film thickness direction. However, in this case, since it is necessary to prepare a vapor deposition material and a target for each thin film layer having a different refractive index, the number of manufacturing steps increases and the productivity decreases. Therefore, in the present embodiment, as a method of forming the active layer 12 having a higher refractive index toward the center from both sides in the film thickness direction without causing the above problems, the hot wall epitaxy method and the plasma control type sputtering method are exemplified. did.

[0025]

As described above, according to the present invention, in an edge-emitting EL element in which electrode layers facing each other are formed on the outer surface of a dielectric layer surrounding a thin film active layer, refraction proceeds from both sides in the film thickness direction toward the center. By forming the active layer with a thin film layer having a high refractive index, the light generated in the active layer is deflected to the center according to the refractive index distribution in the process from the center to the both sides in the film thickness direction. It has the effect of improving the intensity of light emitted from the device and reducing the optical noise emitted from other than the end face.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an embodiment of the present invention.

FIG. 2 is a front view.

FIG. 3 is a vertical sectional front view showing a film forming apparatus of a hot wall epitaxy method.

FIG. 4 is a vertical sectional front view showing a film forming apparatus of a plasma control type sputtering method.

FIG. 5 is a vertical sectional side view showing a conventional example.

FIG. 6 is a perspective view.

[Explanation of symbols]

 11 Edge-Emitting EL Element 12 Active Layers 13 to 16 Dielectric Layers 17 and 18 Electrode Layers

Claims (1)

[Claims] 1. In an edge-emitting EL device in which electrode layers facing each other are formed on the outer surface of a dielectric layer surrounding a thin film active layer, the active layer is a thin film layer having a refractive index higher toward the center than on both sides in the film thickness direction. Edge emitting EL having a layer formed
element.