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US-12619020-B2 - Method of generating a spatially limited film stack on a light sensor element

US12619020B2US 12619020 B2US12619020 B2US 12619020B2US-12619020-B2

Abstract

The present invention relates to a method for manufacturing a spatially limited film stack comprising an optically anisotropic film on an optical sensor device with a light sensor element, such that the film stack covers the light sensor element but not the entire surface area of the optical sensor device. An electronic device manufactured according to the method of the invention can be used for analyzing the polarization state of light.

Inventors

  • David Pires
  • Richard Frantz

Assignees

  • Rolic Technologies AG

Dates

Publication Date
20260505
Application Date
20220126
Priority Date
20210202

Claims (15)

  1. 1 . A method for manufacturing a spatially limited film stack ( 14 , 21 a , 24 a ) comprising at least one optically anisotropic film ( 32 , 34 , 36 ) on a light sensor element ( 11 , 11 a , 11 b ) of an optical sensor device ( 10 a ), comprising a first light sensor element ( 11 a ) and a second light sensor element ( 11 b ), wherein the spatially limited film stack ( 14 , 21 a , 24 a ) covers the light sensor element ( 11 , 11 a , 11 b ) but not the entire surface area of the optical sensor device ( 10 a ), the method comprising the steps: providing the optical sensor device ( 10 a ) with a light sensor element ( 11 , 11 a , 11 b ), wherein the light sensor element ( 11 , 11 a , 11 b ) does not extend over the entire area of the optical sensor device ( 10 a ), preparing a film stack ( 21 ) comprising one or more oriented polymerized liquid crystal layer(s) ( 32 , 34 , 36 ) including a first oriented polymerized liquid crystal layer ( 32 , 36 ) on the optical sensor device ( 10 a ), wherein at least in one polymerized liquid crystal layer ( 34 , 36 ) an orientation pattern is generated, such that the orientation of the liquid crystals in the area above the first light sensor element ( 11 a ) is different from the orientation in the area above the second light sensor element ( 11 b ), and forming the spatially limited film stack ( 14 , 21 a , 24 a ) by selectively removing material from the film stack ( 21 ) by dry or wet etching.
  2. 2 . The method according to claim 1 , wherein the provided optical sensor device ( 10 a ) contains an electronic circuit, which provides signal processing and is preferably an integrated circuit ( 13 ).
  3. 3 . The method-according to claim 1 , wherein the first oriented polymerized liquid crystal layer ( 32 , 36 ) comprises anisotropically absorbing substances or a chiral dopant.
  4. 4 . The method according to claim 1 , wherein the film stack ( 21 ) is prepared, which comprises the first oriented polymerized liquid crystal layer ( 32 , 36 ) and a second oriented polymerized liquid crystal layer ( 34 ) on the optical sensor device ( 10 a ), wherein the second oriented polymerized liquid crystal layer ( 34 ) is preferably formed as a retarder layer.
  5. 5 . The method according to claim 1 , comprising the steps: providing the optical sensor device ( 10 a ) with the light sensor element ( 11 , 11 a , 11 b ), wherein the light sensor element ( 11 , 11 a , 11 b ) does not extend over the entire area of the optical sensor device ( 10 a ); preparing the film stack ( 21 ) comprising the first oriented polymerized liquid crystal layer ( 32 , 36 ) on the optical sensor device ( 10 a ); preparing a hard mask ( 23 ) with a pattern ( 23 a , 25 a ) on top of the film stack ( 21 ), which covers the area of the desired spatially limited film stack ( 14 , 21 a , 24 a ), wherein the hard mask ( 23 ) preferably comprises silicon nitride or inorganic oxides; and forming the spatially limited film stack ( 14 , 21 a , 24 a ) by selectively removing material from the film stack ( 21 ) by dry or wet etching the film stack ( 21 ) in the area which is not covered by the hard mask ( 23 ).
  6. 6 . The method according to claim 5 , wherein the hard mask comprises silicon oxides.
  7. 7 . The method according to claim 6 , wherein the hard mask comprises silicon dioxide.
  8. 8 . The method according to claim 1 , comprising the steps: providing the optical sensor device ( 10 a ) with a light sensor element ( 11 , 11 a , 11 b ), wherein the light sensor element ( 11 , 11 a , 11 b ) does not extend over the entire area of the optical sensor device ( 10 a ); preparing the film stack ( 21 ) comprising the first oriented polymerized liquid crystal layer ( 32 , 36 ) on the optical sensor device ( 10 a ); forming the spatially limited film stack ( 14 , 21 a , 24 a ) by selectively removing material from the film stack ( 21 ) by reactive ion etching (RIE), Inductively Coupled Plasma RIE (ICP-RIE) or plasma ashing, preferably using O2 plasma.
  9. 9 . An electronic device ( 20 ) comprising: an optical sensor device ( 10 a ) with a light sensor element ( 11 , 11 a , 11 b ) comprising a first light sensor element ( 11 a ) and a second light sensor element ( 11 b ); and a spatially limited film stack ( 14 , 21 a , 24 a ) comprising one or more oriented polymerized liquid crystal layer(s) ( 32 , 34 , 36 ), wherein the spatially limited film stack ( 14 , 21 a , 24 a ) covers both light sensor elements ( 11 a , 11 b ), but not the full area of the optical sensor device ( 10 a ), wherein at least in one polymerized liquid crystal layer ( 34 , 36 ) an orientation pattern is generated, such that the orientation of the liquid crystals in the area above the first light sensor element ( 11 a ) is different from the orientation in the area above the second light sensor element ( 11 b ).
  10. 10 . The electronic device ( 20 ) according to claim 9 , wherein the spatially limited film stack ( 14 , 21 a , 24 a ) comprises a first oriented polymerized liquid crystal layer ( 32 , 36 ) and a second oriented polymerized liquid crystal layer, and preferably a third oriented polymerized liquid crystal layer.
  11. 11 . The electronic device ( 20 ) according to claim 10 , wherein a second oriented polymerized liquid crystal layer ( 34 ) is a retarder layer, preferably with quarter wave or half wave retardance.
  12. 12 . The electronic device ( 20 ) according to claim 9 , wherein the optical sensor device ( 10 a ) contains an electronic circuit, which provides signal processing and is preferably an integrated circuit ( 13 ).
  13. 13 . The electronic device ( 20 ) according to claim 9 , wherein the first oriented polymerized liquid crystal layer ( 32 , 36 ) is a cholesteric LCP layer or acts as a linear polarizer.
  14. 14 . A method comprising use of an electronic device of claim 9 for analyzing a polarization state of light.
  15. 15 . A method comprising the use of the electronic device ( 20 ) of claim 9 in a display setup, located behind the display as seen from a viewer, as an ambient light sensor device ( 10 a ) for analyzing the intensity of ambient light.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a National Stage of Application No. PCT/EP2022/051668 filed Jan. 26, 2022, claiming priority based on European Patent Application No. 21154779.9 filed Feb. 2, 2021. TECHNICAL FIELD The invention relates to methods of spatially limiting optical elements comprising polymerized or cross-linked liquid crystals. BACKGROUND OF THE INVENTION Analysis of the polarization state of light has become important for many applications. In some applications light of different sources are encoded by the polarization state of light. Detection of the polarization state of light falling on a surface allows to determine the amount of light that comes, for example, from two different types of light sources. U.S. Pat. No. 9,612,152 B2 discloses a method for determining the amount of ambient light that falls on an organic light emitting diode (OLED) display with a light sensor device that is located behind the display screen, as seen from a viewer. Because the light that arrives at the sensor is a mixture of ambient light and light that is emitted from the OLED display, it is required to distinguish the light coming from the two different light sources. In one of the disclosed embodiments a circular polarizer consisting of a linear polarizer and a quarter wave retarder is arranged at the front side of the OLED display, which provides the additional benefit that reflections caused by the OLED structure are reduced. Incident ambient light that has passed the circular polarizer is circularly polarized, whereas light emitted from the OLED display is non-polarized. The light sensor device that is located at the rear side of the display has two channels. The first of the two channels detects both the ambient light and the light emitted by the display. The second channel is equipped with a circular polarizer with opposite handedness compared to the circular polarizer on the front side of the display. Accordingly, the circularly polarized ambient light is blocked in the second channel and only light emitted from the display is detected. The intensity of the ambient light can then be determined from the difference of the light intensities detected in the two channels. The light sensor device is therefore used as an ambient light sensor. However, the patent specification does not disclose how a circular polarizer is applied to the second channel of the light sensor device. US 2020191648 A1 also discloses an ambient light sensor element for an OLED display. Similar to the solution of U.S. Pat. No. 9,612,152 B2, a circular polarizer is arranged at the front side of the OLED display and an ambient light sensor comprising two channels is located at the rear side of the display. Both channels are equipped with circular polarizers but with opposite handedness. The circularly polarized ambient light is therefore blocked in one channel, whereas it can pass the circular polarizer in the other channel. The non-polarized light emitted from the OLED display is similarly detected by both channels. The intensity of the ambient light can be determined from the difference of the light intensities detected in the two channels. However, US 2020191648 A1 does not disclose how to apply circular polarizers with opposite handedness to the two channels of the light sensor device. In an optical sensor device such as for the use as ambient light sensor as explained above, one or more light sensor elements may occupy part of a semiconductor chip area. It may be desired that these parts of the chip are covered by an optical film, such as a circular polarizer film, while other areas of the chip, such as the bonding pads shall not be covered by the optical film. Moreover, in an optical sensor device comprising more than one light sensor element, for example an array of light sensor elements, optical films with mutually different optical properties may be required for individual light sensor elements. It is therefore necessary to precisely restrict an optical film or layer to specific areas of a substrate or a device. Further, for micro-optical applications, the effective optical areas to be covered by an optical film may be in the micrometre range. Therefore, it is almost impossible to use the standard optical films which have a thickness that is much larger than the dimension of the effective optical area to be covered. Therefore, methods are required that can generate or apply thin optical films or layers with anisotropic optical properties to areas in the micrometre range with very high positional precision and high resolution. Oriented liquid crystal polymers are known to provide high birefringence, which allows to manufacture retarder films, such as quarter wave or half wave retarders, with a layer thickness of only a few micrometers. Layers of liquid crystal polymers (LCP) can be made by coating a layer of liquid crystalline monomers on a substrate, which typically has a surface able to orient liquid cry