Manufacturing of air gap areas in multi-component lens systems, device and head-mounted display device

Abstract

A device comprising: a first lens (115, 215, 310, 410), wherein the first lens (115, 215, 310, 410) includes a pattern of photoresist material (140, 230, 330); a second lens (125, 225, 305, 405) connected to the first lens (115, 215, 310, 410) by the photoresist material (140, 230, 330); an air gap region (160, 260, 460) between the first lens (115, 215, 310, 410) and the second lens (125, 225, 305, 405); wherein the photoresist pattern defines the air gap region (160, 260, 460) between the first lens (115, 215, 310, 410) and the second lens (125, 225, 305, 405); (115, 215, 310, 410) and the second lens (125, 225, 305, 405) defined, characterized in that the air gap region (160, 260, 460) is at least part of a light guide, wherein the air gap region (160, 260, 460) forms a volume with a low refractive index and serves as a sheath for total internal reflection.

Description

TECHNICAL AREA This disclosure relates generally to optical components and in particular, but not exclusively, to the fabrication of air gap regions in multi-component lens systems. BACKGROUND INFORMATION Creating air gaps between optical components of a multi-component lens system can be important in many optical applications. Air gap interfaces provide a low refractive index, which can serve as a shield for total internal reflection in embedded optical systems. However, the application of this component integration is limited because conventional methods require the use of low refractive index adhesives. Such adhesives are expensive, require complex processing, and have difficult mechanical properties for lens processing. In particular, defining an air gap in a specific area on a lens system requires that the binder pattern be patterned and excluded from the air gap area. Since the adhesive is applied in liquid form, its spatial control is not straightforward, thus complicating the manufacturing process for a lens system. US patent 2011 / 0 292 271 A1 discloses a camera module in which a photoresist is arranged between an image sensor device and a lens assembly of the camera module. Furthermore, US patent 9 213 178 B1 discloses a head-mounted display with two interconnected lenses. BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein, unless otherwise indicated, the same reference numerals refer to the same parts in the different views. The drawings are not necessarily to scale, with the emphasis instead on illustrating the described principles. Fig. 1 is a representation of a lens arrangement according to one embodiment; Fig. 2A illustrates a primary processing step in the fabrication of a lens arrangement according to one embodiment; Fig. 2B illustrates a photoresist application in the fabrication of a lens arrangement according to one embodiment; Fig. 2C illustrates a spatial modulation of light in the fabrication of a lens arrangement according to one embodiment; Fig. 2D illustrates photolithography in the fabrication of a lens arrangement according to one embodiment; Fig.Fig. 2E illustrates an application of photoresist winders in the fabrication of a lens assembly according to one embodiment; Fig. 2F illustrates the joining of lenses in the fabrication of a lens assembly according to one embodiment; Fig. 3A illustrates a front lens for the fabrication of a lens assembly according to one embodiment; Fig. 3B illustrates a rear lens for the fabrication of a lens assembly according to one embodiment; Fig. 3C illustrates the application of a photoresist coating in the fabrication of a lens assembly according to one embodiment; Fig. 3D illustrates spatial modulation of light with a masking element in the fabrication of a lens assembly according to one embodiment; Fig. 3E illustrates a lens with a remaining exposed photoresist for a lens assembly according to one embodiment; Fig.Figure 3F illustrates the joining of lenses in the fabrication of a lens assembly according to one embodiment; Figures 4A and 4B are representations of lens assemblies with air gaps produced using photoresist patterns according to one embodiment; and Figure 5 is a representation of a method for fabricating multi-component lenses according to one embodiment. DETAILED DESCRIPTION Embodiments of a device, a system and a method for producing air gap areas in multi-component lens systems. The following description presents numerous specific details to provide a thorough understanding of the embodiments. However, a person skilled in the relevant technology will recognize that the techniques described herein can be implemented without one or more of the specific details or using other methods, components, materials, etc. In other cases, known structures, materials, or operations are not shown or described in detail in order to avoid obscuring certain aspects. The reference in this specification to “an embodiment” means that a particular feature, structure, or property described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the use of the phrase “in an embodiment” at different points in this specification does not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or properties may be appropriately combined in one or more embodiments. As used herein, the following definitions apply: “Photoresist” or “resist” refers to a light-sensitive material that can be applied to form a patterned coating on a surface. "Negative tone photoresist" or "negative photoresist" refers to a photoresist in which the exposed photoresist (the portion of the photoresist that is exposed to light) is insoluble in a special photoresist developer, and the unexposed photoresist (the portion of the photoresist that is not exposed to light) is soluble in the photoresist developer. An example of a negative photoresist is SU-8 photoresist, a common epoxy-based negative photoresist dissolved in a specific organic solvent. “Positive tone photoresist” or “positive photoresist” refers to a photoresist in which the exposed photoresist (a part of the photoresist that is exposed to light) is soluble by a special photoresist developer and an unexposed photoresist (a part of the photoresist that is not exposed) is insoluble by the photoresist developer. In the fabrication of multi-component lenses, creating air gaps or cavities between the lens components is an important technique for providing low-refractive-index volumes. These low-refractive-index volumes can, for example, serve as a cladding for total internal reflection in embedded optical systems. Implementations can include, but are not limited to, head-mounted display optics for smart glass or virtual reality products. The concept of air gaps or cavities can also be used to maintain total internal reflection in a waveguide. A primary reason for creating an air gap is the refractive index required for the optical fiber optics to function correctly. The surface surrounding the optical fiber must have a significantly lower refractive index. Therefore, it is desirable for the optical fiber to operate in air with a refractive index of 1. Conventional methods for integrating lenses into a lens array, however, utilize low-refractive-index adhesives, which are difficult to apply and control, requiring sophisticated bonding, alignment, and dispensing of the optical adhesives. Conventional optical bonding requires pressure and either thermal or low-level radiation to fix the adhesive to the surfaces of the optical components. Fabrication using such an adhesive design is a well-defined process for standard optical composite systems. However, to introduce off-axis embedded optical fiber optics, the fabrication process using conventional adhesives becomes far more complex. In some embodiments, a device, system, or method provides for the generation of air gap regions while eliminating the need for conventional adhesive application and the advanced equipment required for adequate process control of conventional adhesives. In some embodiments, a device, system, or method uses a photoresist process to define both the air gap region and the bonding of lens components via photoresist-plastic interfaces. In some embodiments, a photoresist, for example, a negative photoresist, is used both as a structural component and as a bonding material for optical components. The use of photoresist construction for lens assemblies enables the fabrication of thin and lightweight devices. For example, fabricating a lens assembly using a photoresist construction can be particularly useful for manufacturing head-mounted display technology where thin and ophthalmic form factors are desired. Photoresist is a material that can be uniformly applied to a surface and deterministically patterned by photolithography. This material is common in the microchip industry, where photoresist defines the placement devices or features. For example, transistors in integrated circuits or microfluidic channels are patterned in photoresist and then etched into their respective substrates. The photoresist is then discarded by dissolving it in an etchant, leaving behind a patterned substrate. In some embodiments, a generated photoresist pattern is permanently embedded in a device or system, with the material becoming part of a final lens system. The ability to structure the photographic material enables a highly accurate (e.g., <0.5 micrometers) air gap definition, which generally exceeds the required accuracy for defining an air gap area. In some embodiments, a negative photoresist is applied to one or more lenses, wherein the photoresist material that is exposed is crosslinked and made permanent, while areas of the material that are not exposed remain uncrosslinked and can be dissolved in the appropriate photoresist developer. In contrast, a positive-tone photoresist behaves in the opposite way, with areas exposed to light being soluble in the developer and areas not exposed to light remaining intact. In some embodiments, a method for defining an air gap region using a photoresist bond is both simpler and more accurate compared to conventional methods. Furthermore, a large portion of the necessary processes, hardware, and chemistry for creating a lens array in one embodiment can be manufactured commercially or easily. Consequently, one implementation enables cost-effective fabrication, accurate air gap definition, and applicability to a variety of embedded optical fiber designs. In some embodiments, alternative implementations may include additional adhesives or photoresist to support the bonding of the optical fiber / carrier lens interface. In some embodiments, further variation in the activation of bonding regions via chemical, thermal, or electrical treatments may be employed, as appropriate for the specific photoresist material and lens material. Fig. 1 is a representation of a lens arrangement according to one embodiment. In some embodiments, a lens arrangement 100 comprises a combination of at least two lenses, namely a first lens 115 (also referred to as the rear lens or eye lens) located on a rear side 110 (near the eye of a user of the lens arrangement) of the lens arrangement and a second lens 125 (also referred to as the front lens or world lens) located on a front side 120 (farther away from the user's eye) of the lens arrangement 100. In some embodiments, the first lens 115 and the second lens 125 of the lens assembly are connected to each other using a photoresist 140 to create an air gap region 160. In some embodiments, the photoresist serves to define both the air gap region 160 and the bond between the lens components 115 and 125 via photoresist-plastic interfaces. The air gap region can, for example, be in the form of an air gap 460, as shown in Figures 4A and 4B. Figures 2A to 2F provide illustrations for the fabrication of a lens arrangement: Fig. 2A illustrates the primary processing step in the manufacture of a lens assembly according to one embodiment. In some embodiments, a manufacturing process may include a cleaning process for the lens elements to be combined to form a lens assembly. For example, two or more components forming a lens assembly are washed and dehydrated and may further be plasma-coated. In a particular example, a lens assembly consists of a first part (or first lens component) 215 and a second part (or second lens component) 225. In this example, the first part is a light-guiding lens, wherein the first part is located on a rear side of a lens assembly or near the eye of a user. Furthermore, in this example, the second part is a support lens, wherein the second part is located on a front side of a lens assembly or away from the eye.However, embodiments are not limited to a specific number of lens components and can include any number of two or more lens components. Fig. 2B illustrates a photoresist application in the fabrication of a lens assembly according to one embodiment. In some embodiments, a fabrication method may involve applying the photoresist to at least one side of a lens in a lens assembly. In some embodiments, the photoresist is a negative photoresist. In this implementation, the negative photoresist is uniformly coated (e.g., by spin, spray, or dip coating). However, embodiments are not limited to application processes that provide a uniform or complete coating with photoresist material. In other embodiments, a single photoresist may be used for multiple lenses to bond these lenses together. In a specific example, a negative photoresist coating 230 is applied to a convex side of a light-guiding lens (backside), which is shown as the first lens 215. In some embodiments, the thickness of the coating 230 determines the height of an air gap for a resulting lens arrangement, with the thickness generally ranging from 1 micron to 50 microns. In some embodiments, the one or more lenses onto which the photoresist coating is applied can be further processed if necessary, for example, by pre-exposure baking to remove excess solvents or similar processes according to a specific manufacturer's recommendation. However, embodiments are not limited to specific operations required for handling photoresist. Fig. 2C illustrates the spatial modulation of light during the fabrication of a lens assembly according to one embodiment. In some embodiments, a fabrication process may involve spatial modulation of light to direct exposure to desired sections of a photoresist coating. In some embodiments, the spatial modulation may, but is not limited to, masking areas of photoresist to allow desired sections to receive light exposure in order to define the air gap area in a lens assembly. In a specific example of a negative photoresist coating application, as shown in Fig. 2B, an area to be defined as the air gap region is covered, for example, by an aluminum-coated strip, a physical quartz mask, or another UV-absorbing material for photolithography on or above the photoresist-coated light guide lens. In one example, a photoresist mask or other blocking element 235 can be used, as shown in Fig. 2C. Embodiments are not limited to a specific photolithography process but can, for example, include contact, neighborhood, or projection photolithography. Fig. 2D illustrates photolithography in the fabrication of a lens assembly according to one embodiment. In some embodiments, a fabrication process may include photolithography to expose portions of the photoresist. In some embodiments, a first lens 215, for example, a light-guiding lens, is exposed to light, for example, UV / i-line (ultraviolet, where i-line refers to a wavelength of 365 nm (nanometers)) radiation 250 to crosslink the photoresist in the unmasked areas, i.e., areas not masked by the photoresist masking or other blocking elements 235. However, embodiments are not limited to a specific wavelength of exposure, the radiation wavelength depending on the specific photoresist material. Fig. 2E illustrates the application of photoresist developers in the fabrication of a lens arrangement according to one embodiment. In some embodiments, after radiation exposure, the mask 235 (if used to provide spatial modulation of the radiation) is removed from a first lens 215. In some embodiments, the photoresist developer 250 is then applied to the first lens 215, the application of photoresist developer to dissolve certain parts of the photoresist and to retain a photoresist pattern. In some embodiments, the first lens 215 can be baked after exposure (for example, at a temperature of about 65 degrees Celsius) or can be developed directly in a developer suggested by the manufacturer. Upon application of the photoresist developer, areas of the photoresist that were exposed to UV radiation remain on the lens 215, and areas of the photoresist that were protected prior to exposure by masking or other spatial modulation of the exposure dissolve and are completely removed. The lens with the remaining photoresist pattern can then be washed and dried. Fig. 2F illustrates the joining of lenses during the fabrication of a lens assembly according to one embodiment. In some embodiments, a fabrication method, as shown in Fig. 2E, may involve bonding the lens using a residual photoresist pattern after application of the photoresist developer. In some embodiments, a second lens 225, which may be cleaned and plasma-primed as described in conjunction with Fig. 2A, may be combined with the first lens 215. In some embodiments, a surface of the second lens 225, for example, a concave surface of such a lens, is brought into direct contact with a surface of the first lens 215, for example, a convex surface of the first lens 215. In some embodiments, the lenses are then joined together, for example by vacuum baking to apply pressure and heat 250. The use of vacuum bags or bubbles can be employed to impart uniform pressure over the entire surface of the lens. Critical parameters for joining the lens using photoresist adhesion include pressure, temperature, and time, which can be optimized for the specific photoresist, thereby enabling the two lenses to be incorporated into a lens assembly or lens unit 200. In some embodiments, the resulting lens assembly 200 includes a cavity or air gap 260, which is defined by the positioning and thickness of the photoresist pattern of the exposed photoresist 240. In some embodiments, the resulting lens arrangement 200 can then be cooled, for example, at room temperature, and cleaned if necessary. In some embodiments, additional methods can be used to ensure suitable curing of the photoresist. Embodiments are limited to specific methods for curing the photoresist but also include methods suitable for the respective photoresist material. Figures 3A to 3F provide illustrations for the fabrication of a lens arrangement: Fig. 3A illustrates a front lens for manufacturing a lens assembly according to one embodiment. Fig. 3B illustrates a rear lens for manufacturing a lens assembly according to one embodiment. In some embodiments, manufacturing a lens assembly involves joining two or more lens components, such as a front (world) lens 305 and a rear (eye) lens 310. In some embodiments, manufacturing the lens assembly creates an air gap, for example, an air gap to provide a light guide for the rear lens 310. Fig. 3C illustrates the application of a photoresist coating during the fabrication of a lens assembly according to one embodiment. In some embodiments, a negative photoresist 315 is applied to the front lens, for example, a negative photoresist coating applied by centrifugal coating or a spray of photoresist material. Fig. 3D shows the exposure of a photoresist coating during the fabrication of a lens assembly according to one embodiment. In some embodiments, the negative photoresist 315 is masked by one or more masking elements 320, and the unmasked portions of the photoresist 315 are exposed to light 325. Fig. 3E illustrates a lens with a remaining exposed photoresist for a lens arrangement according to one embodiment. In some embodiments, a photoresist developer is applied to the front lens 305, which leads to the removal of the unexposed portions of the negative photoresist, leaving the exposed photoresist 330 on the surface of the front lens 305. Fig. 3F illustrates a lens connection in the fabrication of a lens assembly according to one embodiment. In some embodiments, the rear lens 310 is connected to the front lens 305 using the exposed photoresist and applying heat and pressure to generate plasma activation. In some embodiments, the lens connection is intended to create an air gap defined by the photoresist pattern. Figures 4A and 4B show lens assemblies with air gaps produced using photoresist patterns according to one embodiment. In some embodiments, a photoresist pattern is produced by a process that includes coating a lens with a photoresist; applying light radiation to areas not protected from the radiation by masking or other spatial modulation of the radiation; and applying a photoresist developer to dissolve portions of the photoresist not intended for a photoresist pattern to bond two or more lens components and to create an air gap or cavity between these lens components. Figures 4A and 4B show views of lens assemblies, including air gaps, created using photoresist patterns in the lens assembly. In a first example, Figure 4A illustrates a top view of a front (world) lens 405 of a lens assembly that incorporates a photoresist pattern to create an air gap region 460. In a second example, Figure 4B illustrates a top view of a rear (eye) lens 410 that incorporates a photoresist pattern to create an air gap region 460. In some embodiments, the photoresist pattern 465 in Figures 4A and 4B can encompass the remaining portion of the surface of each lens except for the air gap region 460. The air gap region 460 can be created for use, for example, in a light guide implementation.However, embodiments are not limited to a specific photoresist pattern, but can also include any designed photoresist pattern that provides bonding for the lens of a lens arrangement and provides any required gap for the specific implementation. Fig. 5 is a representation of a method for manufacturing multi-component lenses according to one embodiment. In some embodiments, a process includes 500: 502: Cleaning of two or more lens components, wherein lens components include at least a first lens component and a second lens component. 504: Applying a photoresist coating to at least one side of at least one lens component, including applying photoresist to a first side of a first lens component. In one example, a negative photoresist coating is applied. The thickness of the applied photoresist coating is a determining factor for the height of a cavity or air gap between the lens components. 506: Additional processes for photoresist coating as required for the photoresist material, for example baking to remove excess solvent. 508: A spatial modulation of the light exposure, for example UV radiation, is applied to the photoresist coating. In one example, the spatial modulation may involve masking areas, but is not limited to producing the required photoresist pattern. 510: Exposure of the unmasked part of the photoresist coating by UV radiation or other light radiation as required for the photoresist material. 512: Removal of masking material if the spatial modulation involves the use of masking material. 514: The application of a suitable photoresist developer to the photoresist material to dissolve certain parts of the photoresist coating and to retain the photoresist pattern, for example with a negative photoresist, dissolving parts of the photoresist coating that were not exposed to UV irradiation. 516: Washing and drying the lens with the resulting photoresist pattern. 518: Bonding of the lens to the second lens using a photoresist pattern as a binder, which may involve the application of heat and pressure to provide a bonding effect. The processes described above are presented in terms of computer software and hardware. The techniques described can represent machine-executable instructions embodied in a physical or non-volatile machine-readable (e.g., computer-readable) storage medium, which, when executed by a machine, causes the machine to perform the described operations. Additionally, the processes can be executed in hardware, for example, an application-specific integrated circuit (ASIC), or in some other way. A machine-readable storage medium includes any mechanism that stores information in a non-volatile form accessible by a machine (e.g., a computer, a network device, a personal digital assistant, a manufacturing tool, any device with a set of one or more processors, etc.). A machine-readable storage medium includes, for example, writable / non-writable media (e.g., read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.). The foregoing description of the illustrated embodiments of the invention, including the one described in the abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments and examples of the invention are described herein for illustrative purposes, various modifications within the scope of the invention are possible, as those skilled in the art will recognize. These modifications can be made to the invention starting from the foregoing detailed description. The terms used in the following claims should not be interpreted as limiting the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention should be fully determined by the following claims, which are to be interpreted in accordance with established principles of claim interpretation. Reference symbol list 100 Lens arrangement 110 Back (near the eye) 115, 215 First lens 120 Front (away from the eye) 125, 225 Second lens 140, 230 Photoresist 160, 260 Pore or air gap 200 Resultant lens arrangement 235 Photoresist masking element or other blocking element 240 Remaining exposed photoresist 250 UV light, application of developer, application of pressure and heat 305 Front / world lenses 310 Back / eye lens 315 Negative photoresist 320 Masking 325 Light exposure 330 Exposed photoresist 405 Front lenses 410 Rear lenses 460 Air gap area 465 Photoresist pattern

Claims

A device comprising: a first lens (115, 215, 310, 410), wherein the first lens (115, 215, 310, 410) includes a pattern of photoresist material (140, 230, 330); a second lens (125, 225, 305, 405) connected to the first lens (115, 215, 310, 410) by the photoresist material (140, 230, 330); an air gap region (160, 260, 460) between the first lens (115, 215, 310, 410) and the second lens (125, 225, 305, 405); wherein the photoresist pattern defines the air gap region (160, 260, 460) between the first lens (115, 215, 310, 410) and the second lens (125, 225, 305, 405); (115, 215, 310, 410) and the second lens (125, 225, 305, 405) defined, characterized in that the air gap region (160, 260, 460) is at least part of a light guide, wherein the air gap region (160, 260, 460) forms a volume with a low refractive index and serves as a sheath for total internal reflection. Device according to claim 1, wherein the photoresist pattern further defines a height of the air gap area (160, 260, 460). Device according to claim 1 or 2, wherein the first lens (115, 215, 310, 410) is a light guiding lens and the second lens (125, 225, 305, 405) is a support lens. Device according to one of the preceding claims, wherein the photoresist pattern consists of a negative photoresist material, wherein the photoresist pattern has been exposed to light to crosslink the negative photoresist material. Device according to one of the preceding claims, further comprising a third lens coupled to the first lens (115, 215, 310, 410) or the second lens (125, 225, 305, 405), wherein a second photoresist pattern is used. Device according to one of the preceding claims, wherein the device comprises a head-mounted display optic. Device according to one of the preceding claims, wherein the first lens (115, 215, 310, 410) and the second lens (125, 225, 305, 405) are joined without the application of a separate adhesive in addition to the photoresist material (140, 230, 330). Method comprising: applying (504) a photoresist coating to at least one first side of a first lens component of a plurality of lens components; applying (508) spatial modulation of light radiation to define which areas of the photoresist coating are exposed to light radiation; applying (510) light radiation to the first lens component; applying (514) a photoresist developer to dissolve unexposed areas of the photoresist to produce a photoresist pattern;and connecting (518) a first side of a second lens component to the first side of the first lens component, wherein the photoresist pattern is to act as a binder and to define an air gap region (160, 260, 460) between the first lens component and the second lens component, characterized in that the air gap region (160, 260, 460) is at least a part of an optical fiber, wherein the air gap region (160, 260, 460) forms a volume with a low refractive index and serves as a sheath for total internal reflection. Method according to claim 8, wherein the application of the photoresist coating includes the application of a negative photoresist material. Method according to claim 8 or 9, wherein the application of light radiation involves the application of UV (ultraviolet) radiation to the exposed photoresist. Method according to any one of claims 8 to 10, wherein the application of spatial modulation includes the application of a mask to the first lens component prior to the application of the light radiation. The method of claim 11, further comprising removing the masking from the first lens component before applying the photoresist developer. Method according to any one of claims 8 to 12, wherein joining the second lens component to the first lens component involves applying heat and pressure to the first and the second lens component. Method according to any one of claims 8 to 13, wherein connecting the first side of the second lens component to the first side of the first lens component includes connecting to a clean surface of the second lens component. Method according to any one of claims 8 to 14, further comprising applying a second photoresist pattern to the first side of the second lens component, and wherein the joining of the first side of the second lens component to the first side of the first lens component at least partially joins the photoresist pattern to the second photoresist pattern. Method according to any one of claims 8 to 15, wherein joining the first side of the second lens component to the first side of the first lens component includes bonding without applying a separate adhesive in addition to the photoresist material. Head-mounted display optical device comprising: a multi-component lens system (100) comprising: a plurality of lenses (115, 215, 310, 410, 125, 225, 305, 405) comprising a waveguide lens component and a supporting lens component, wherein at least one first side of the waveguide lens component comprises a photoresist pattern, and an air gap region (160, 260, 460) between the waveguide lens component and the supporting lens component; wherein the waveguide lens component is connected to the supporting lens component by the photoresist pattern; and wherein the air gap region (160, 260, 460) is defined by the photoresist pattern, characterized thereby. that the air gap region (160, 260, 460) is at least part of an optical fiber, wherein the air gap region (160, 260, 460) forms a volume with a low refractive index and serves as a cladding for total internal reflection. Head-mounted display optics device according to claim 17, wherein the photoresist pattern consists of a negative photoresist material, wherein the photoresist pattern has been exposed to light to crosslink the negative photoresist material. Head-mounted display optics device according to claim 17 or 18, wherein the light-guiding lens component and the supporting lens component are joined without the application of a separate adhesive in addition to the photoresist material. Head-mounted display optics device according to one of claims 17 to 19, wherein the photoresist pattern further defines a height of the air gap area (160, 260, 460).

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