Micro OLED display device and preparation method thereof

Abstract

The application belongs to the technical field of micro organic light-emitting diode display, and provides a Micro OLED display device and a preparation method thereof. In the application, a photosensitive polyimide (PSPI) photoresist is used as a spacing medium of an optical strong microcavity structure, the thickness of the optical strong microcavity structure is accurately designed based on the refractive index of the PSPI photoresist, an optimal microcavity Q value is obtained, and color purity is improved. In the application, the PSPI photoresist is used as the spacing medium of the optical strong microcavity structure, optical interference enhancement is achieved by accurately controlling the height of the RGB color strong microcavity, the luminous efficiency is improved by more than 3%, the brightness is improved by more than 5%, the color purity is obviously optimized, the microcavity preparation process steps are reduced by more than 30%, the cost is obviously reduced, and the application is suitable for high-end display fields such as VR / AR.

Description

Technical Field

[0001] This invention relates to the field of micro organic light-emitting diode display technology, and more particularly to a Micro OLED display device and its fabrication method. Background Technology

[0002] Micro OLED (micro organic light-emitting diode) displays are widely used in high-end display fields such as virtual reality (VR), augmented reality (AR), and wearable devices due to their advantages such as high resolution, high contrast, high response speed, and low power consumption.

[0003] Strong microcavity structures are a key technology for improving the luminous efficiency, brightness, and color purity of Micro OLED displays. By precisely controlling the multiple reflections and interferences of light within the cavity, strong microcavity structures create standing wave enhancement for specific wavelengths of light within the microcavity, thereby significantly increasing the emission intensity of that wavelength of light while suppressing the emission of other wavelengths, achieving high color purity displays.

[0004] Currently, the strong microcavity structure in Micro OLED display manufacturing processes is generally fabricated using a multiple deposition-etching process with ITO and SiO2. This process involves repeatedly depositing ITO or SiO2 films, followed by multiple etching steps, to form an RGB strong microcavity structure. Traditional processes using ITO or SiO2 as the microcavity spacer have limited refractive index and thickness control, making it difficult to achieve the optimal microcavity Q value, thus requiring further improvement in color purity. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a Micro OLED display device and its fabrication method. This invention uses photosensitive polyimide (PSPI) photoresist as the spacer medium for an optically strong microcavity structure. Based on the refractive index of the PSPI photoresist, the thickness of the optically strong microcavity structure can be precisely designed, resulting in an optimal microcavity Q value and improved color purity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a Micro OLED display device, comprising: A CMOS driving substrate, the surface of which has a driving circuit and tungsten pillars; A metal reflective anode layer is disposed on the surface of the CMOS driving substrate and forms an ohmic contact with the tungsten pillar; An RGB strong microcavity structure is disposed on the surface of the metal reflective anode layer. The spacer medium of the RGB strong microcavity structure is a photosensitive polyimide photoresist. The photosensitive polyimide photoresist avoids the tungsten pillars, exposing the top of the tungsten pillars. The RGB strong microcavity structure includes an R-color strong microcavity structure, a G-color strong microcavity structure, and a B-color strong microcavity structure. A transparent anode layer is disposed on the surface of the RGB high-intensity microcavity structure and on the surface of the metal reflective anode layer in contact with the tungsten pillar; A pixel definition layer is disposed on the surface of the transparent anode layer and the surface of the CMOS driving substrate, and the pixel definition layer defines the boundary of the pixel light-emitting area through an opening; An organic light-emitting stack is disposed on the pixel light-emitting area enclosed by the pixel definition layer and on the surface of the pixel definition layer; A transparent cathode layer is disposed on the surface of the organic light-emitting stack.

[0007] Preferably, the metal reflective anode layer is a single-layer structure or a multi-layer stacked structure formed by an Ag layer, an Al layer or an Al alloy layer, wherein the Al alloy layer is an Al-Nd layer; The thickness of the metal reflective anode layer is 50~200nm, and its reflectivity to visible light is ≥70%. The contact resistance of the ohmic contact formed between the metal reflective anode layer and the tungsten pillar is ≤10. -4 Ω·cm 2 .

[0008] Preferably, the glass transition temperature of the photosensitive polyimide photoresist is independently ≥200℃, the ionic impurity content is independently <1ppm, the refractive index n in the range of 450~650nm is independently 1.60~1.85, and the transmittance in the visible light band is independently ≥85%.

[0009] Preferably, the height H of the R color intensity microcavity structure, G color intensity microcavity structure, and B color intensity microcavity structure satisfies: H = λ / (2n) × m; Where λ is the center wavelength of the corresponding color light, n is the refractive index of the photosensitive polyimide photoresist in the range of 450~650nm, and m is the interference order, and m is a positive integer.

[0010] Preferably, the transparent anode layer is made of ITO, IZO or AZO; the thickness of the transparent anode layer is 50~150nm, the sheet resistance is ≤100Ω, and the transmittance in the visible light band is ≥90%.

[0011] Preferably, the pixel definition layer is made of SiO2 or SiN; the thickness of the pixel definition layer is 0.01~3μm.

[0012] Preferably, the refractive index of the organic light-emitting stack is 1.6 to 1.9; The organic light-emitting stack includes a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, and an electron injection layer stacked sequentially, wherein the hole injection layer is in contact with the pixel definition layer.

[0013] The present invention also provides a method for fabricating the Micro OLED display device described in the above technical solution, comprising the following steps: A CMOS driving substrate is provided, the surface of which has a driving circuit and tungsten pillars; A metal reflective anode layer is fabricated on the surface of the CMOS driving substrate; Photosensitive polyimide photoresist is coated three times on the surface of the metal reflective anode layer. After each coating, pre-baking, exposure, development, and hard baking are performed sequentially to form R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures, respectively. The R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures precisely avoid the position of the tungsten pillars during the forming process, so that the top of the tungsten pillars is exposed. A transparent anode layer is prepared on the surface of the R-color-intensity microcavity structure, the G-color-intensity microcavity structure, the B-color-intensity microcavity structure, and the surface of the metal reflective anode layer in contact with the tungsten pillar; A pixel definition layer is prepared on the surface of the transparent anode layer; An organic light-emitting layer is prepared in the pixel light-emitting region enclosed by the pixel definition layer and on the surface of the pixel definition layer; A transparent cathode layer is fabricated on the surface of the organic light-emitting stack to obtain the Micro OLED display device.

[0014] Preferably, the metal reflective anode layer is prepared by physical vapor deposition, and the film formation temperature of the physical vapor deposition is room temperature to 150°C.

[0015] Preferably, the coating method is spin coating, and the spin coating speed is independently 300~5000 r / min; The thickness of the coating is independently 100~300nm; The photosensitive polyimide photoresist applied in three coats is applied using an overlay method, with an overlay error of ≤0.1μm between adjacent color-strong microcavity structures; The pre-baking temperature is independently 90~110℃, and the time is independently 5~15min; The photomask used for the exposure is a patterned photomask of a corresponding color, and the photomask contains a tungsten pillar avoidance pattern; The exposure dose is independently 100~300mJ / cm. 2 Each time is 10~30 seconds. The developing solution used is an alkaline developing solution, and the developing temperature is independently 20~30℃, and the developing time is independently 30~90s; The hard drying process includes a first drying and a second drying performed sequentially. The temperature of the first drying is independently 150~180℃ and the time is independently 10~20min. The temperature of the second drying is independently 200~250℃ and the time is independently 30~60min. Each time the photosensitive polyimide photoresist is hard baked and before the subsequent structure is prepared, a plasma treatment is also performed. The power of the plasma treatment is independently 100~300W and the time is independently 30~60s.

[0016] This invention provides a Micro OLED display device. The invention uses photosensitive polyimide (PSPI) photoresist as the spacer medium for an optically strong microcavity structure. Based on the refractive index of the PSPI photoresist, the thickness of the optically strong microcavity structure can be precisely designed, resulting in an optimal microcavity Q value and improved color purity.

[0017] The Micro OLED display device provided by this invention achieves significant advantages of strong microcavity: 1. Significantly improved luminous efficiency: The refractive index of PSPI photoresist at 450~650nm (1.60~1.85) matches the refractive index of organic light-emitting stack (1.6~1.9), reducing interface reflection loss; at the same time, the microcavity optical thickness based on the precise design of refractive index enables the formation of standing wave enhancement in the microcavity for specific wavelengths of light, improving luminous efficiency by more than 3%.

[0018] 2. Significantly enhanced brightness: The strong microcavity structure enhances the light interference effect, which multiplies the intensity of light emitted at a specific wavelength, resulting in a brightness increase of more than 5% for Micro OLED display devices.

[0019] 3. Significantly improved color purity: The selective wavelength enhancement effect of the microcavity structure suppresses the emission of non-target wavelengths, narrowing the full width at half maximum (FWHM) of the RGB colors and significantly improving color purity.

[0020] Furthermore: Synergistic conduction between the metal reflective anode layer and the transparent anode layer: The metal reflective anode layer provides an optical reflective surface with high reflectivity (≥85%), while the transparent anode layer provides excellent carrier injection capability and light transmittance. The two anode layers achieve electrical conduction through a tungsten pillar and work together.

[0021] The present invention also provides a method for fabricating the Micro OLED display device described in the above technical solution.

[0022] The preparation method of the present invention has the following advantages: (1) PSPI photoresist is used as the spacer medium for optically strong microcavity structures. PSPI photoresist is only used as the spacer medium for optically strong microcavity structures. It enhances optical interference based on its refractive index and thickness, and does not replace the function of the pixel definition layer.

[0023] (2) The height of the microcavity is precisely controllable: it is directly formed by step-by-step photolithography and curing. The height of each color microcavity is precisely controlled by the thickness of PSPI photoresist coating and exposure and development, avoiding the cumulative error introduced by multiple etching in traditional processes.

[0024] (3) Etching-free forming process: PSPI strong microcavity structure is formed directly by photolithography without the need for dry / wet etching, avoiding the roughening of the microcavity sidewalls and film damage caused by etching, improving the fabrication accuracy of strong microcavity structure, reducing light scattering loss, and enhancing the microcavity enhancement effect.

[0025] (4) Effective suppression of color deviation and brightness unevenness: The high degree of independent design and precise control of the strong microcavity structure of each color in RGB is ensured (error ≤ 5nm), which ensures that the microcavity effect of each color light is optimal and consistent, effectively suppressing the color deviation and brightness unevenness caused by the microcavity height deviation in traditional processes.

[0026] (5) Improved viewing angle characteristics: The precise molding of the microcavity structure formed by PSPI photoresist reduces sidewall roughness, reduces light scattering loss, and improves the viewing angle characteristics of the device.

[0027] (6) Production costs are significantly reduced: the number of steps in the preparation process of strong microcavity is reduced by more than 30% compared with the traditional process, the production cycle is shortened by 30%, the consumption of raw materials and the frequency of equipment use are reduced, the defect rate is reduced, and the production cost is reduced by more than 25%.

[0028] Furthermore, the pixel definition layer is fabricated independently: after the transparent anode layer is completed, an insulating material layer is deposited, and the pixel definition layer is formed by photolithography exposure and development opening. This is fabricated independently from the strong microcavity structure and optimized separately to ensure clear pixel boundaries and precise definition of the light-emitting area. Attached Figure Description

[0029] Figure 1 A schematic diagram of the structure of the Micro OLED display device provided by the present invention; Figure reference numerals: 1-CMOS driving substrate, 11-Tungsten pillar, 2-Metal reflective anode layer, 3-R color intensity microcavity structure, 4-G color intensity microcavity structure, 5-B color intensity microcavity structure, 6-Transparent anode layer, 7-Pixel definition layer, 8-Organic light-emitting stack, 9-Transparent cathode layer. Detailed Implementation

[0030] This invention provides a Micro OLED display device, comprising: A CMOS driving substrate, the surface of which has a driving circuit and tungsten pillars; A metal reflective anode layer is disposed on the surface of the CMOS driving substrate and forms an ohmic contact with the tungsten pillar; An RGB strong microcavity structure is disposed on the surface of the metal reflective anode layer. The spacer medium of the RGB strong microcavity structure is photosensitive polyimide (PSPI) photoresist. The photosensitive polyimide (PSPI) photoresist avoids the tungsten pillars, exposing the top of the tungsten pillars. A transparent anode layer is disposed on the surface of the RGB high-intensity microcavity structure and on the surface of the metal reflective anode layer in contact with the tungsten pillar; A pixel definition layer is disposed on the surface of the transparent anode layer and the surface of the CMOS driving substrate, and the pixel definition layer defines the boundary of the pixel light-emitting area through an opening; An organic light-emitting stack is disposed on the pixel light-emitting area enclosed by the pixel definition layer and on the surface of the pixel definition layer; A transparent cathode layer is disposed on the surface of the organic light-emitting stack.

[0031] The following is combined with Figure 1 The structure of the Micro OLED display device provided by the present invention will be described.

[0032] The Micro OLED display device provided by this invention includes a CMOS driving substrate 1, the surface of which has a driving circuit and tungsten pillars 11. In this invention, the CMOS driving substrate is preferably a single-crystal silicon substrate. In this invention, the driving circuit preferably includes pixel circuits and memory cells. In this invention, the tungsten pillars are preferably an integral structure of the CMOS driving substrate, used to enable the subsequent metal reflective anode layer to conduct electricity between the driving circuit and the substrate.

[0033] The Micro OLED display device provided by this invention includes a metal reflective anode layer 2, which is disposed on the surface of the CMOS driving substrate and forms an ohmic contact with the tungsten pillar. In this invention, the metal reflective anode layer covers a portion of the surface of the CMOS driving substrate. In this invention, the metal reflective anode layer is preferably a single-layer structure formed by an Ag layer, an Al layer, or an Al alloy layer, or a multi-layer stacked structure formed by multiple layers. In this invention, the Al alloy layer is preferably an Al-Nd alloy layer, and the Nd mass content in the Al-Nd alloy layer is preferably 1-3%, more preferably 2%. In this invention, the thickness of the metal reflective anode layer is preferably 50-200 nm, specifically preferably 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm. In this invention, the reflectivity of the metal reflective anode layer to visible light is preferably ≥70%, more preferably ≥85%, more preferably ≥88%, and can also be ≥90%. In this invention, the contact resistance of the ohmic contact formed between the metal reflective anode layer and the tungsten pillar is preferably ≤10 Ω. -4 Ω·cm 2 .

[0034] The Micro OLED display device provided by this invention includes an RGB strong microcavity structure disposed on the surface of the metal reflective anode layer. The spacer medium of the RGB strong microcavity structure is a photosensitive polyimide (PSPI) photoresist. The photosensitive polyimide (PSPI) photoresist avoids the tungsten pillars, exposing the tops of the tungsten pillars. The RGB strong microcavity structure includes an R-color strong microcavity structure, a G-color strong microcavity structure, and a B-color strong microcavity structure. In this invention, the RGB strong microcavity structure includes an R-color strong microcavity structure 3, a G-color strong microcavity structure 4, and a B-color strong microcavity structure 5.

[0035] In this invention, the height H of the R-intensity microcavity structure, G-intensity microcavity structure, and B-intensity microcavity structure satisfies: H = λ / (2n) × m; Wherein, λ is the center wavelength of the corresponding color light, n is the refractive index of the photosensitive polyimide photoresist in the range of 450~650nm, m is the interference order, and m is a positive integer, preferably 1.

[0036] In this invention, the height of the R-color intensity microcavity structure is preferably 180-300 nm, and can be preferably 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, or 300 nm. In this invention, the height of the G-color intensity microcavity structure is preferably 150-260 nm, and can be preferably 150 nm, 151 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, or 260 nm. In this invention, the height of the B-color-intensity microcavity structure is preferably 130~230nm, and can be preferably 130nm, 131nm, 135nm, 140nm, 150nm, 160nm, 165nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, or 230nm. In this invention, the spacer medium for the R-color-intensity microcavity structure 3, G-color-intensity microcavity structure 4, and B-color-intensity microcavity structure 5 is photosensitive polyimide (PSPI) photoresist, only differing in refractive index and thickness.

[0037] In this invention, the glass transition temperature (Tg) of the photosensitive polyimide photoresist is independently preferably ≥200℃, more preferably 200~300℃, and specifically preferably 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, or 300℃; the ionic impurity content is independently preferably <1ppm; the refractive index n at 450~650nm is independently preferably 1.60~1.85, and specifically preferably at 550nm is independently preferably 1.60~1.85. The preferred thicknesses are 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84, or 1.85. The refractive index n-value of the photosensitive polyimide photoresist fluctuates ≤0.03 in the 450~650nm range. The transmittance in the visible light band is preferably ≥85%, and more preferably ≥92%. In this invention, the PSPI photoresist serves as an optical microcavity spacer medium. Based on its refractive index and thickness, it enhances optical interference, obtains the optimal microcavity Q-value, and improves color purity. The PSPI photoresist has a refractive index (1.60~1.85) that matches the organic light-emitting stack, and a transmittance of ≥90%, giving it excellent physical properties as a spacer medium for optically strong microcavity structures.

[0038] The Micro OLED display device provided by this invention includes a transparent anode layer 6 disposed on the surface of the RGB strong cavity structure and on the surface of a metal reflective anode layer in contact with the tungsten pillar. In this invention, the transparent anode layer achieves electrical conduction with the metal reflective anode layer through the tungsten pillar. In this invention, the material of the transparent anode layer is preferably ITO, IZO, or AZO; the thickness of the transparent anode layer is preferably 50~150nm, specifically preferably 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, or 150nm. In this invention, the sheet resistance of the transparent anode layer is preferably ≤100Ω, and the transmittance in the visible light band is preferably ≥90%.

[0039] The Micro OLED display device provided by this invention includes a pixel definition layer 7 disposed on the surface of the transparent anode layer and the surface of the CMOS driving substrate. The pixel definition layer defines the boundary of the pixel light-emitting region through an opening. In this invention, the material of the pixel definition layer is preferably SiO2 or SiN; the thickness of the pixel definition layer is preferably 0.1~3μm, specifically preferably 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm or 3μm.

[0040] The Micro OLED display device provided by this invention includes an organic light-emitting stack 8, disposed in the pixel light-emitting region surrounded by the pixel definition layer and on the surface of the pixel definition layer. In this invention, the refractive index of the organic light-emitting stack is preferably 1.6 to 1.9, specifically preferably 1.6, 1.7, 1.8, or 1.9. In this invention, the organic light-emitting stack preferably includes a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, and an electron injection layer stacked sequentially. In this invention, the material of the hole injection layer is preferably MoO3, HAT-CN, or CuPc; the thickness of the hole injection layer is preferably 5 to 15 nm, specifically preferably 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, or 15 nm. In this invention, the material of the hole transport layer is preferably TAPC, NPB, or TCTA; the thickness of the hole transport layer is preferably 30 to 60 nm, specifically preferably 30 nm, 40 nm, 50 nm, or 60 nm. In this invention, the organic light-emitting layer is preferably made of CBP, mCP, or Bepp2; the thickness of the organic light-emitting layer is preferably 10-40 nm, specifically 10 nm, 20 nm, 30 nm, or 40 nm. In this invention, the electron transport layer is preferably made of one or more of TPBi, Bphen, and 3TPYMB; the thickness of the electron transport layer is preferably 20-60 nm, specifically 20 nm, 30 nm, 40 nm, 50 nm, or 60 nm. In this invention, the electron injection layer is preferably made of one or more of LiF, Liq, and Cs2CO3; the thickness of the electron injection layer is preferably 0.5-3 nm, specifically 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, or 3 nm. In this invention, the hole injection layer in the organic light-emitting stack is in contact with the pixel definition layer.

[0041] The Micro OLED display device provided by this invention includes a transparent cathode layer 9 disposed on the surface of the organic light-emitting stack. In this invention, the material of the transparent cathode layer is preferably Mg-Ag alloy or ITO; the mass content of silver in the Mg-Ag alloy is preferably 30-90%, specifically 30%, 40%, 50%, 60%, 70%, 80%, or 90%; the thickness of the transparent cathode layer is preferably 10-100 nm, specifically 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0042] The present invention also provides a method for fabricating the Micro OLED display device described in the above technical solution, comprising the following steps: A CMOS driving substrate is provided, the surface of which has a driving circuit and tungsten pillars; A metal reflective anode layer is fabricated on the surface of the CMOS driving substrate; Photosensitive polyimide (PSPI) photoresist is coated three times on the surface of the metal reflective anode layer. After each coating, pre-baking, exposure, development, and hard baking are performed sequentially to form R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures, respectively. The R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures precisely avoid the position of the tungsten pillars during the forming process, so that the top of the tungsten pillars is exposed. A transparent anode layer is prepared on the surface of the R-color-intensity microcavity structure, the G-color-intensity microcavity structure, the B-color-intensity microcavity structure, and the surface of the metal reflective anode layer in contact with the tungsten pillar; A pixel definition layer is prepared on the surface of the transparent anode layer; An organic light-emitting layer is prepared in the pixel light-emitting region enclosed by the pixel definition layer and on the surface of the pixel definition layer; A transparent cathode layer is fabricated on the surface of the organic light-emitting stack to obtain the Micro OLED display device.

[0043] This invention provides a CMOS driving substrate. In this invention, the surface of the CMOS driving substrate has a driving circuit and tungsten pillars. Preferably, the structure of the CMOS driving substrate in this invention is consistent with the above-described technical solution, and will not be repeated here.

[0044] In this invention, a metal reflective anode layer is prepared on the surface of a CMOS driving substrate. The metal reflective anode layer covers a portion of the surface of the CMOS driving substrate and forms an ohmic contact with the tungsten pillar. In this invention, the preparation method of the metal reflective anode layer is preferably physical vapor deposition (PVD). The film formation temperature of the PVD is preferably room temperature to 150°C, more preferably room temperature, i.e., requiring neither additional heating nor additional cooling.

[0045] After preparing the metal reflective anode layer, the present invention applies photosensitive polyimide (PSPI) photoresist to the surface of the metal reflective anode layer in three stages. After each application, pre-baking, exposure, development, and hard baking are performed sequentially to form R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures, respectively. The R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures precisely avoid the position of the tungsten pillars during the forming process, so that the top of the tungsten pillars is exposed.

[0046] In this invention, the coating method is preferably spin coating, and the spin coating speed is preferably 300~5000 r / min, specifically preferably 200 r / min, 500 r / min, 1000 r / min, 1500 r / min, 2000 r / min, 2500 r / min, 3000 r / min, 3500 r / min, 4000 r / min, 4500 r / min or 5000 r / min.

[0047] In this invention, the coating thickness is preferably designed independently based on the corresponding wavelength of light and the PSPI refractive index to meet the conditions for enhanced optical interference.

[0048] In this invention, the pre-baking temperature is preferably 90~110℃, specifically 90℃, 95℃, 100℃, 105℃ or 110℃; the time is preferably 5~15min, specifically 5min, 10min or 15min. In this invention, the pre-baking can remove the solvent in the PSPI photoresist.

[0049] In this invention, the mask used for exposure is preferably a patterned mask of a corresponding color, and the mask preferably includes a tungsten pillar avoidance pattern. In this invention, the exposure dose is independently preferably 100~300 mJ / cm². 2 Specifically, the preferred value is 100 mJ / cm. 2 150mJ / cm 2 200mJ / cm 2 250mJ / cm 2 or 300mJ / cm 2 The preferred time is 10-30 seconds, specifically 10 seconds, 15 seconds, 20 seconds, 25 seconds or 30 seconds.

[0050] In this invention, the developing solution used for development is preferably an alkaline developing solution, and the developing temperature is preferably 20~30℃, specifically 20℃, 25℃, or 30℃; the developing time is preferably 30~90s, specifically 30s, 40s, 50s, 60s, 70s, 80s, or 90s. After development, this invention preferably further includes rinsing with deionized water. In this invention, the development and deionized water rinsing can remove the PSPI photoresist in the unexposed areas while retaining the PSPI photoresist in the exposed areas, forming the prototype of a microcavity structure with corresponding color intensity.

[0051] In this invention, the hard drying preferably includes a first drying and a second drying performed sequentially. The temperature of the first drying is preferably 150~180℃, specifically 150℃, 160℃, 170℃, or 180℃; the time is preferably 10~20 min, specifically 15 min. The temperature of the second drying is preferably 200~250℃, specifically 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃; the time is preferably 30~60 min, specifically 30 min, 40 min, 45 min, 50 min, or 60 min. In this invention, the hard drying solidifies and shapes the preliminary microcavity structure.

[0052] In this invention, after each hard baking of the photosensitive polyimide (PSPI) photoresist and before fabricating subsequent structures, plasma treatment is preferably performed. The power of the plasma treatment is preferably 100-300W, specifically 100W, 150W, 200W, 250W, or 300W; the time is preferably 30-60s, specifically 30s, 40s, 45s, 50s, or 60s. In this invention, the plasma treatment enhances the interlayer bonding of the PSPI.

[0053] In this invention, the three-coating photosensitive polyimide (PSPI) photoresist is preferably applied using an overlay method, and the overlay error between adjacent color-strong microcavity structures is preferably ≤0.1μm, and more preferably ≤0.08μm.

[0054] In this invention, PSPI photoresist is a modified polymer material that combines high-temperature stability and photolithographic formability. Its molecular backbone consists of rigid benzene rings and imide rings, and its side chains are grafted with photosensitive functional groups. It can be directly formed through photolithography processes such as coating, exposure, development, and hard baking.

[0055] After obtaining the R-color intensity microcavity structure, G-color intensity microcavity structure, and B-color intensity microcavity structure, the present invention prepares a transparent anode layer on the surface of the R-color intensity microcavity structure, G-color intensity microcavity structure, and B-color intensity microcavity structure, as well as on the surface of the metal reflective anode layer in contact with the tungsten pillar.

[0056] In this invention, the preparation of a transparent anode layer on the surfaces of the R-intensity microcavity structure, G-intensity microcavity structure, B-intensity microcavity structure, and the surface of the metal reflective anode layer in contact with the tungsten pillar preferably includes the following steps: sputtering a transparent conductive film layer on the surfaces of the R-intensity microcavity structure, G-intensity microcavity structure, B-intensity microcavity structure, the surface of the metal reflective anode layer in contact with the tungsten pillar, and the surface of the CMOS driving substrate; patterning the transparent conductive film layer using dry etching, retaining the transparent conductive film layer in the regions corresponding to the R-intensity microcavity structure, G-intensity microcavity structure, B-intensity microcavity structure, and the surface of the metal reflective anode layer in contact with the tungsten pillar, thereby forming a transparent anode layer.

[0057] In this invention, the transparent conductive film is preferably subjected to plasma treatment before sputtering. The plasma treatment method is preferably the same as the above-described technical solution and will not be repeated here. In this invention, the sputtering method of the transparent conductive film is preferably magnetron sputtering deposition. The parameters of the magnetron sputtering deposition include: the sputtering temperature is preferably 150~200℃, specifically preferably 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃; the volume ratio of oxygen to argon during sputtering is preferably 1:5~1:10, specifically preferably 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10. This invention does not specifically limit the operation of the dry etching. In this invention, the dry etching can remove the transparent conductive film layer in excess areas, retain the transparent conductive film layer in the area corresponding to the RGB strong microcavity structure and the tungsten pillar connection area, and avoid short circuits between adjacent strong microcavity structures through the transparent conductive film layer.

[0058] After forming the transparent anode layer, the present invention prepares a pixel definition layer on the surface of the transparent anode layer.

[0059] In this invention, the preparation of a pixel definition layer on the surface of the transparent anode layer preferably includes the following steps: depositing an insulating material layer on the surface of the transparent anode layer and the surface of the CMOS driving substrate; and forming an opening in the insulating material layer by photolithography, exposure, and development to form the pixel definition layer. In this invention, the deposition method of the insulating material layer is preferably plasma-enhanced chemical vapor deposition (PECVD). This invention does not specifically limit the photolithography operation. In this invention, the size of the opening is preferably matched to the pixel light-emitting area, and the sidewalls of the opening are steep to ensure a clear boundary of the pixel light-emitting area.

[0060] After forming the pixel definition layer, the present invention prepares an organic light-emitting stack in the pixel light-emitting area enclosed by the pixel definition layer and on the surface of the pixel definition layer.

[0061] In this invention, the organic light-emitting layer is preferably prepared by vacuum evaporation. This invention does not specifically limit the vacuum evaporation method; any operation well-known to those skilled in the art can be used.

[0062] After forming the organic light-emitting stack, the present invention prepares a transparent cathode layer on the surface of the organic light-emitting stack to obtain the Micro OLED display device.

[0063] In this invention, the transparent cathode layer is preferably prepared by vapor deposition or sputtering. This invention does not specifically limit the vapor deposition or sputtering method; any operation well-known to those skilled in the art can be used.

[0064] In this invention, the fabrication process of the Micro OLED display device is summarized as follows: CMOS driving substrate preparation → Metal reflective anode layer preparation → First coating / pre-baking / exposure / development / hard baking of photosensitive polyimide (PSPI) photoresist → R-color high-intensity microcavity structure (including tungsten pillar avoidance) → Plasma treatment → Second coating / pre-baking / exposure / development / hard baking of photosensitive polyimide (PSPI) photoresist → G-color high-intensity microcavity structure (including tungsten pillar avoidance) → Plasma treatment → Third coating / pre-baking / exposure / development / hard baking of photosensitive polyimide (PSPI) photoresist → B-color high-intensity microcavity structure (including tungsten pillar avoidance) → Plasma treatment → ITO transparent conductive film sputtering → ITO transparent conductive film dry etching patterning to form transparent anode layer → Deposition of insulating material layer → Photolithography / exposure / development to prepare pixel definition layer → Organic light-emitting stack evaporation → Transparent cathode layer evaporation → Micro OLED display device finished product.

[0065] The Micro OLED display device and its fabrication method provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0066] Example 1 A method for fabricating a strong microcavity structure for a Micro OLED display includes the following steps: S1: Provides a single-crystal silicon CMOS driving substrate 1, on which an OLED display driving circuit has been fabricated, and has tungsten pillars 11.

[0067] S2: A metal reflective anode layer 2 is fabricated on the surface of the CMOS driving substrate 1 using PVD sputtering. An Ag film is selected and sputtered at room temperature to a thickness of 150 nm. The visible light reflectivity of the metal reflective anode layer 2 is ≥90%. The metal reflective anode layer 2 covers part of the surface of the CMOS driving substrate 1 and forms an ohmic contact with the tungsten pillar 7, with a contact resistance ≤10 Ω. -4 Ω·cm 2 .

[0068] S3: Perform the first PSPI coating on the surface of the metal reflective anode layer 2: use spin coating to coat high-temperature PSPI photoresist (Tg=260℃, ionic impurity content<1ppm, n=1.75@550nm, transmittance≥92%), spin coating speed is 4000r / min, coating thickness is 210nm; pre-baking temperature is 100℃, time is 10min.

[0069] Exposure was performed using an R-color patterned mask containing an R-color pixel pattern and tungsten pillar avoidance, with an exposure dose of 200 mJ / cm². 2 The exposure time was 20 seconds. The tungsten pillar was not exposed due to being blocked by the mask, and no PSPI residue was found after development, with the top of the tungsten pillar exposed.

[0070] Develop with alkaline developer (25℃) for 60 seconds, then rinse with deionized water.

[0071] Hard baking was performed using a stepped heating method: 160℃ for 15 min → 220℃ for 45 min, resulting in an R-color strong microcavity structure 3 with a height of 180 nm (corresponding to R-color light λ=630 nm, m=1, optical thickness=λ / (2n)×m =630 nm / (2×1.75)×1).

[0072] Before the second coating, plasma treatment was performed at a power of 200W for 45 seconds. The same PSPI photoresist was used, with a spin coating speed of 4000 r / min and a coating thickness of 180 nm. The pre-baking process parameters were the same as the first time. A G-color patterned mask (containing a tungsten pillar avoidance pattern) was used for exposure, and other exposure and development parameters were the same as the first time, resulting in a G-color strong microcavity structure 4 with a height of 151 nm (corresponding to G-color light λ=530 nm).

[0073] Before the third coating, plasma treatment was performed again with the same parameters as above; the coating thickness was 160nm, and the pre-baking process parameters were the same as the first time; a B-color pattern mask (containing tungsten pillar avoidance pattern) was used for exposure, and the other exposure parameters and development parameters were the same as the first time, resulting in a B-color strong microcavity structure 5 with a height of 131nm (corresponding to B-color light λ=460nm).

[0074] Each overlay error is ≤0.08μm, and the top of the tungsten pillar 11 is never covered by the PSPI microcavity structure.

[0075] S4: An ITO transparent conductive film layer with a thickness of 100 nm is deposited on the surface of the RGB high-intensity microcavity structure, the top of the exposed tungsten pillar 11, and the surface of the CMOS driving substrate by magnetron sputtering. The sputtering temperature is 180℃, and the volume ratio of oxygen to argon is 1:8. The sheet resistance of the ITO transparent conductive film layer is ≤100Ω, and the transmittance in the visible light band is ≥90%. It completely covers the surface of the RGB high-intensity microcavity structure, the top of the tungsten pillar 11, and the surface of the CMOS driving substrate. The ITO transparent conductive film layer achieves electrical conduction through the tungsten pillar 11 and the metal reflective anode layer 2.

[0076] S5: The ITO transparent conductive film layer is patterned by dry etching, removing excess areas and retaining the ITO transparent conductive film layer corresponding to the RGB strong microcavity structure and the tungsten pillar connection area to form the transparent anode layer 6.

[0077] S6: A SiO2 insulating material layer with a thickness of 2μm is deposited on the surface of the transparent anode layer 6 using PECVD. An opening is formed in the SiO2 insulating material layer by photolithography exposure and development to form a pixel definition layer 8. The size of the opening matches the pixel light-emitting area, defining the boundary of the pixel light-emitting area.

[0078] S7: On the surface of the pixel light-emitting region enclosed by the pixel definition layer 7 and the surface of the pixel definition layer 7, an organic light-emitting stack 8 (refractive index 1.6) is vacuum-deposited in sequence, consisting of a hole injection layer (MoO3 material, thickness 10nm) / a hole transport layer (TAPC material, thickness 50nm) / an organic light-emitting layer (CBP material, thickness 20nm) / an electron transport layer (TPBi material, thickness 40nm) / an electron injection layer (LiF material, thickness 2nm) and a transparent cathode layer 9 (Mg:Ag alloy (silver mass content 50%), thickness 15nm), thus completing the fabrication of the Micro OLED display device.

[0079] The strong microcavity structure prepared in this embodiment reduces the number of microcavity preparation steps by 35% compared to traditional processes, achieves a microcavity height accuracy error of ≤5nm, significantly optimizes color purity, and reduces production costs by 35%.

[0080] Example 2 A method for fabricating a Micro OLED display device includes the following steps: S1: A single-crystal silicon CMOS driving substrate 1 is provided, and the surface driving circuit and tungsten pillar 11 have been fabricated.

[0081] S2: The metal reflective anode layer 2 is prepared by PVD sputtering. An Al-Nd alloy (2wt% Nd content) at 120 nm is selected, with a visible light reflectivity ≥85%, forming an ohmic contact with the tungsten pillar 11. The contact resistance is preferably ≤10 Ω. -4 Ω·cm2 .

[0082] S3: The PSPI photoresist selected has a Tg of 250℃, n=1.68@550nm, and a visible light transmittance ≥85%. First coating: Spin coating speed 3000 r / min, coating thickness 190nm. Pre-baking temperature 90℃, time 15min. Exposure using an R-color patterned mask (containing tungsten pillar avoidance pattern), exposure dose 100mJ / cm². 2 The exposure time was 30 seconds. The alkaline developer was used at 20°C for 90 seconds. Hard baking was then performed at 150°C for 20 minutes, followed by hard baking at 200°C for 60 minutes, resulting in an R-color strong microcavity structure 3 with a height of 190 nm.

[0083] Before the second coating, plasma treatment was performed at a power of 150W for 60s. The coating thickness was 160nm, resulting in a G-color high-intensity microcavity structure 4 with a height of 160nm.

[0084] Plasma treatment was performed before the third coating, the same as before the second coating. The coating thickness was 140 nm, resulting in a B-color high-intensity microcavity structure 5 with a height of 140 nm.

[0085] The overlay error for each engraving is ≤0.1μm.

[0086] S4: An IZO transparent conductive film layer with a thickness of 50 nm is deposited by magnetron sputtering at a sputtering temperature of 150 °C and an oxygen to argon volume ratio of 1:5. The IZO transparent conductive film layer covers the surface of the RGB microcavity structure, the top of the tungsten pillar 7, and the surface of the CMOS driving substrate. The transparent conductive film layer is connected to the metal reflective anode layer 2 through the tungsten pillar 11.

[0087] S5: The IZO transparent conductive film layer is patterned by dry etching to remove the excess IZO transparent conductive film layer and avoid short circuits between adjacent strong microcavity structures through the IZO transparent conductive film layer; the IZO transparent conductive film layer corresponding to the RGB strong microcavity structure and the tungsten pillar connection area is retained to form the transparent anode layer 6.

[0088] S6: A SiN insulating layer with a thickness of 1.5 μm is deposited on the surface of the transparent anode layer 6 using PECVD. An opening is then created on the SiN insulating layer using photolithography and exposure development to form the pixel definition layer 7.

[0089] S7: An organic light-emitting stack 8 (same as in Example 1) and a transparent cathode layer 9 (ITO, 60nm thick) are deposited on the surface of the pixel light-emitting area enclosed by the pixel definition layer 7 and the surface of the pixel definition layer 7 to complete the fabrication of the Micro OLED display device.

[0090] The strong microcavity structure prepared in this embodiment has significantly optimized color purity and reduced production costs by 30%.

[0091] Example 3 A method for fabricating a Micro OLED display device includes the following steps: S1: Provides a single-crystal silicon CMOS driver substrate 1.

[0092] S2: The metal reflective anode layer 2 is prepared by PVD sputtering. A 200nm Al film is selected. The reflectivity is ≥88%, and it forms an ohmic contact with the tungsten pillar 11 with a contact resistance ≤10 Ω. -4 Ω·cm 2 .

[0093] S3: The PSPI photoresist selected has a Tg of 280℃, n=1.82@550nm, and a visible light transmittance ≥85%. First coating: Spin coating speed 5000 r / min, coating thickness 300nm. Pre-baking temperature 110℃, time 5min. Exposure using an R-color patterned mask (including tungsten pillar avoidance pattern), exposure dose 300mJ / cm². 2 Exposure time was 10s; alkaline developer was used at 30℃ for 30s. Hard baking: 180℃ for 10min → 250℃ for 30min to obtain R-color strong microcavity structure 3 with a height of 220nm.

[0094] Before the second coating, plasma treatment was performed at a power of 300W for 30s. The coating thickness was 260nm, resulting in a G-color strong microcavity structure 4 with a height of 180nm.

[0095] Plasma treatment was performed before the third coating, and the coating thickness was 230 nm, resulting in a B-color strong microcavity structure 5 with a height of 135 nm.

[0096] S4: An AZO transparent conductive film layer with a thickness of 150 nm is deposited by magnetron sputtering at a sputtering temperature of 200 °C and an oxygen to argon volume ratio of 1:10. The transparent conductive film layer covers the surface of the RGB microcavity structure, the top of the tungsten pillar 7, and the surface of the CMOS driving substrate. The transparent conductive film layer is connected to the metal reflective anode layer 2 through the tungsten pillar 11.

[0097] S5: The AZO transparent conductive film layer is patterned by dry etching to remove the excess AZO transparent conductive film layer and avoid short circuits between adjacent strong microcavity structures through the AZO transparent conductive film layer; the AZO transparent conductive film layer corresponding to the RGB strong microcavity structure and the tungsten pillar connection area is retained to form the transparent anode layer 6.

[0098] S6: A SiO2 insulating material layer with a thickness of 2.5 μm is deposited on the surface of the transparent anode layer 6 using PECVD. An opening is then created in the SiO2 insulating material layer by photolithography exposure and development to form the pixel definition layer 7.

[0099] S7: An organic light-emitting stack 8 (same as in Example 1) and a transparent cathode layer 10 (Mg:Ag=1:4, thickness of 10nm) are vapor-deposited on the surface of the pixel light-emitting area surrounded by the pixel definition layer 7 and on the surface of the pixel definition layer 7 to complete the fabrication of the Micro OLED display device.

[0100] The strong microcavity structure prepared in this embodiment has significantly improved color purity and reduced production costs by 35%.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Micro OLED display device, characterized in that, include: A CMOS driving substrate, the surface of which has a driving circuit and tungsten pillars; A metal reflective anode layer is disposed on the surface of the CMOS driving substrate and forms an ohmic contact with the tungsten pillar; An RGB strong microcavity structure is disposed on the surface of the metal reflective anode layer, and the spacer medium of the RGB strong microcavity structure is photosensitive polyimide photoresist; The photosensitive polyimide photoresist avoids the tungsten pillar, exposing the top of the tungsten pillar; the RGB strong microcavity structure includes an R color strong microcavity structure, a G color strong microcavity structure, and a B color strong microcavity structure; A transparent anode layer is disposed on the surface of the RGB high-intensity microcavity structure and on the surface of the metal reflective anode layer in contact with the tungsten pillar; A pixel definition layer is disposed on the surface of the transparent anode layer and the surface of the CMOS driving substrate, and the pixel definition layer defines the boundary of the pixel light-emitting area through an opening; An organic light-emitting stack is disposed on the pixel light-emitting area enclosed by the pixel definition layer and on the surface of the pixel definition layer; A transparent cathode layer is disposed on the surface of the organic light-emitting stack.

2. The Micro OLED display device according to claim 1, characterized in that, The metal reflective anode layer is a single-layer structure or a multi-layer stacked structure formed by Ag layer, Al layer or Al alloy layer, and the Al alloy layer is an Al-Nd layer. The thickness of the metal reflective anode layer is 50~200nm, and its reflectivity to visible light is ≥70%. The contact resistance of the ohmic contact formed between the metal reflective anode layer and the tungsten pillar is ≤10. -4 Ω·cm 2 .

3. The Micro OLED display device according to claim 1, characterized in that, The photosensitive polyimide photoresist has a glass transition temperature of ≥200℃, an ionic impurity content of <1ppm, a refractive index n of 1.60~1.85 in the 450~650nm range, and a transmittance of ≥85% in the visible light band.

4. The Micro OLED display device according to claim 1 or 3, characterized in that, The height H of the R-intensity microcavity structure, G-intensity microcavity structure, and B-intensity microcavity structure satisfies: H = λ / (2n) × m; Where λ is the center wavelength of the corresponding color light, n is the refractive index of the photosensitive polyimide photoresist in the range of 450~650nm, and m is the interference order, and m is a positive integer.

5. The Micro OLED display device according to claim 1, characterized in that, The transparent anode layer is made of ITO, IZO or AZO; the thickness of the transparent anode layer is 50~150nm, the sheet resistance is ≤100Ω, and the transmittance in the visible light band is ≥90%.

6. The Micro OLED display device according to claim 1, characterized in that, The pixel definition layer is made of SiO2 or SiN; the thickness of the pixel definition layer is 0.01~3μm.

7. The Micro OLED display device according to claim 1, characterized in that, The refractive index of the organic light-emitting stack is 1.6~1.9; The organic light-emitting stack includes a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, and an electron injection layer stacked sequentially, wherein the hole injection layer is in contact with the pixel definition layer.

8. A method for fabricating the Micro OLED display device according to any one of claims 1 to 7, characterized in that, Includes the following steps: A CMOS driving substrate is provided, the surface of which has a driving circuit and tungsten pillars; A metal reflective anode layer is fabricated on the surface of the CMOS driving substrate; Photosensitive polyimide photoresist is coated three times on the surface of the metal reflective anode layer. After each coating, pre-baking, exposure, development, and hard baking are performed sequentially to form R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures, respectively. The R-color strong microcavity structures, G-color strong microcavity structures, and B-color strong microcavity structures precisely avoid the position of the tungsten pillars during the forming process, so that the top of the tungsten pillars is exposed. A transparent anode layer is prepared on the surface of the R-color-intensity microcavity structure, the G-color-intensity microcavity structure, the B-color-intensity microcavity structure, and the surface of the metal reflective anode layer in contact with the tungsten pillar; A pixel definition layer is prepared on the surface of the transparent anode layer; An organic light-emitting layer is prepared in the pixel light-emitting region enclosed by the pixel definition layer and on the surface of the pixel definition layer; A transparent cathode layer is fabricated on the surface of the organic light-emitting stack to obtain the Micro OLED display device.

9. The preparation method according to claim 8, characterized in that, The metal reflective anode layer is prepared by physical vapor deposition, and the film formation temperature of the physical vapor deposition is room temperature to 150°C.

10. The preparation method according to claim 8, characterized in that, The coating method is spin coating, and the spin coating speed is independently 300~5000 r / min; The thickness of the coating is independently 100~300nm; The photosensitive polyimide photoresist applied in three coats is applied using an overlay method, with an overlay error of ≤0.1μm between adjacent color-strong microcavity structures; The pre-baking temperature is independently 90~110℃, and the time is independently 5~15min; The photomask used for the exposure is a patterned photomask of a corresponding color, and the photomask contains a tungsten pillar avoidance pattern; The exposure dose is independently 100~300mJ / cm. 2 Each time is 10~30 seconds. The developing solution used is an alkaline developing solution, and the developing temperature is independently 20~30℃, and the developing time is independently 30~90s; The hard drying process includes a first drying and a second drying performed sequentially. The temperature of the first drying is independently 150~180℃ and the time is independently 10~20min. The temperature of the second drying is independently 200~250℃ and the time is independently 30~60min. Each time the photosensitive polyimide photoresist is hard baked and before the subsequent structure is prepared, a plasma treatment is also performed. The power of the plasma treatment is independently 100~300W and the time is independently 30~60s.

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