Stretchable display
By introducing a combination of auxiliary buffer layer and stretch buffer layer into the stretchable display, the problems of structural fracture and circuit breakage under stretching conditions are solved, thereby improving manufacturing yield and product reliability.
Patent Information
- Application Number
- CN202511130856.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-04-24
- Filing Date
- 2025-08-13
- Publication Date
- 2025-11-18
AI Technical Summary
Stretchable displays are prone to structural fractures and internal circuit breaks due to stress when stretched, affecting manufacturing yield and product reliability.
An auxiliary buffer layer is introduced into the stretchable display. The auxiliary buffer layer covers the edge of the island element and part of the circuit area. Combined with the stretch buffer layer, it reduces the strain at the junction of the island element and the conductor.
By designing an auxiliary buffer layer, the strain at the junction of the island component and the conductor is significantly reduced, improving manufacturing yield and product reliability.
Smart Images
Figure CN120977196A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to a display device, and more particularly to a stretchable display. Background Technology
[0002] With the rapid development of electronic technology, electronic products are constantly being innovated. To enable electronic products to be applied in various fields, the characteristics of stretchability, thinness, and unrestricted form factor are increasingly valued. In other words, electronic products are increasingly required to have different forms depending on the application method and environment. Therefore, electronic products need to be stretchable, such as stretchable displays or stretchable electronic devices, which have a special design architecture of active-matrix island / bridge-type stretchable arrays.
[0003] However, when stretched, stretchable displays or stretchable electronic devices may experience structural fractures due to stress, potentially leading to open circuits in internal wiring or damage to island edges. Therefore, ensuring good manufacturing yield and product reliability for stretchable electronic products is a pressing issue that needs to be addressed. Summary of the Invention
[0004] This disclosure relates to a stretchable display, comprising a substrate, an island element, a stretch buffer layer, an auxiliary buffer layer, conductive lines, and an insulating layer. The substrate has at least one pixel region and a circuit region, wherein the circuit region connects to the pixel region. The island element is disposed on the pixel region of the substrate and includes pixel driving circuitry and an edge. The stretch buffer layer covers at least a portion of the island element and the circuit region of the substrate. The auxiliary buffer layer covers at least a portion of the edge of the island element. The auxiliary buffer layer is disposed on at least a portion of the circuit region and extends to at least a portion of the pixel region. Conductors are disposed on the stretch buffer layer and electrically connected to the pixel driving circuitry of the island element. An insulating layer is disposed on the stretch buffer layer and covers the conductive lines and the island element.
[0005] In some embodiments, the conductor enters the island element from its edge, and the auxiliary buffer layer at least partially overlaps with the conductor. In the direction of edge extension, the width of the auxiliary buffer layer is greater than the width of the conductor.
[0006] In some implementations, the auxiliary buffer layer is located below the conductor and at least partially overlaps with the conductor.
[0007] In some embodiments, the island element further includes a top surface and sidewalls. An auxiliary buffer layer covers at least a portion of the top surface and at least a portion of the sidewalls of the island element.
[0008] In some embodiments, at least a portion of the auxiliary buffer layer is located between the island element and the stretch buffer layer. At least another portion of the auxiliary buffer layer is located between the stretch buffer layer and the routing area of the substrate.
[0009] In some implementations, an auxiliary buffer layer is disposed on the stretch buffer layer, and the auxiliary buffer layer and the conductor are in a continuous pattern.
[0010] In some embodiments, the stretch buffer layer includes a top surface and sidewalls. An auxiliary buffer layer covers at least a portion of the top surface and at least a portion of the sidewalls of the stretch buffer layer.
[0011] In some implementations, the auxiliary buffer layer is located above the conductor and at least partially overlaps with the conductor.
[0012] In some embodiments, the insulating layer includes a top surface and sidewalls. An auxiliary buffer layer covers at least a portion of the top surface and at least a portion of the sidewalls of the insulating layer.
[0013] In some implementations, at least a portion of the edge of the island-shaped element covered by the auxiliary buffer layer is not provided with wires.
[0014] In summary, the stretchable display disclosed herein includes an auxiliary buffer layer in addition to a stretching buffer layer, which can significantly reduce the strain at the junction of island components and conductors, thereby improving the manufacturing yield and product reliability of electronic products. Attached Figure Description
[0015] Figure 1A This is a top view schematic diagram of a stretchable display according to one embodiment of the present disclosure.
[0016] Figure 1B for Figure 1A A partially enlarged schematic diagram of the structure.
[0017] Figure 2A This is a cross-sectional schematic diagram of a stretchable display according to one embodiment of the present disclosure.
[0018] Figure 2B This is a detailed structural cross-sectional schematic diagram of a stretchable display according to one embodiment of the present disclosure.
[0019] Figure 3A This is a cross-sectional schematic diagram of a stretchable display according to another embodiment of the present disclosure.
[0020] Figure 3B This is a detailed structural cross-sectional schematic diagram of a stretchable display according to another embodiment of the present disclosure.
[0021] Figure 4AThis is a cross-sectional schematic diagram of a stretchable display according to yet another embodiment of the present disclosure.
[0022] Figure 4B This is a detailed structural cross-sectional schematic diagram of a stretchable display according to yet another embodiment of the present disclosure.
[0023] Figure 5 This is a top view schematic diagram of a stretchable display according to another embodiment of the present disclosure.
[0024] Explanation of reference numerals in the attached figures:
[0025] SD, SD-1, SD-2, SD-3: Stretchable Displays
[0026] PC: Pixel driving circuit
[0027] TFT: Thin Film Transistor
[0028] 100: Substrate
[0029] 110: Pixel area
[0030] 120: Line Area
[0031] 200: Island element
[0032] 201: Edge
[0033] 210: Buffer layer
[0034] 220: Semiconductor Pattern
[0035] 230: Gate insulation layer
[0036] 240: Control Terminal
[0037] 250: Interlayer dielectric layer
[0038] 260: First end
[0039] 270: Insulation layer
[0040] 280: Flattening layer
[0041] 310: Conductor
[0042] 320: Stretch buffer layer
[0043] 330, 330-1, 330-2, 330-3: Auxiliary buffer layers
[0044] 340: Conductive pattern
[0045] 350: Transparent conductive pattern
[0046] 360: Light Emitting Diode Components
[0047] 201a, 320a, 270a, 320a: Upper surface
[0048] 271a, 321a: First upper surface
[0049] 272a, 322a: Second upper surface
[0050] 201b, 210b, 230b, 250b, 270b, 320b: Sidewall
[0051] W1, W2: Width
[0052] A-A': Cut line
[0053] M1: Dashed line Detailed Implementation
[0054] Reference will now be made in detail to exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same element references are used in the drawings and description to denote the same or similar parts.
[0055] It should be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" or "connected" to another element, it may be directly on or connected to the other element, or intermediate elements may also be present. Conversely, when an element is referred to as being "directly on" or "directly connected" to another element, no intermediate elements are present. As used herein, "connection" can refer to physical and / or electrical connection. Furthermore, "electrical connection" or "coupling" may mean the presence of other elements between the two elements.
[0056] As used herein, “about,” “approximately,” or “substantially” includes the value and the average value within an acceptable range of deviations from a particular value as determined by one of ordinary skill in the art, taking into account the measurement under discussion and a particular number of errors associated with the measurement (i.e., limitations of the measurement system). For example, “about” may mean within one or more standard deviations of the value, or within ±30%, ±20%, ±10%, ±5%. Furthermore, the use of “about,” “approximately,” or “substantially” herein may be chosen based on the optical, etched, or other properties to select a more acceptable range of deviations or standard deviations, and may not require a single standard deviation to apply to all properties.
[0057] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the relevant technical context and this disclosure, and will not be interpreted as having idealized or overly formal meanings unless expressly defined herein.
[0058] Please see Figure 1A and Figure 1B . Figure 1A This is a top view of a stretchable display SD according to one embodiment. Figure 1B for Figure 1A The diagram shows a partially enlarged structural view of the stretchable display SD, enclosed by the dashed line M1. The stretchable display SD includes a substrate 100, island elements 200, conductive lines 310, a stretch buffer layer 320, and an auxiliary buffer layer 330. The island elements 200 are disposed on the substrate 100. Multiple conductive lines 310 enter from different edges of the island elements 200 and connect to them.
[0059] In some embodiments, the substrate 100 has a stretchable property. For example, the substrate 100 may be made of an organic polymer, such as polyimide (PI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonates (PC), polyether sulfone (PES), polyarylate, epoxy resin, polyurethane, polydimethylsiloxane, other suitable materials, or combinations of at least two of the foregoing materials.
[0060] In some embodiments, the wire 310 is made of a metallic material for conductivity considerations. In other embodiments, the wire 310 may also be made of other conductive materials. For example, alloys, nitrides of metallic materials, oxides of metallic materials, oxynitrides of metallic materials, or stacked layers of metallic materials and other conductive materials.
[0061] exist Figure 1BIn this embodiment, a stretch buffer layer 320 covers the island element 200, and a conductive line 310 is disposed on the stretch buffer layer 320. The stretch buffer layer 320 is configured on the island element 200 to reduce strain on the island element 200 during stretching of the stretchable display SD. The stretch buffer layer 320 can be made of various photosensitive materials with a buffering effect. For example, the Young's modulus of the stretch buffer layer 320 can be less than 10 GPa. The stretch buffer layer 320 can be made of photosensitive polyimide (PSPI), phenol-formaldehyde resin, epoxy resin, polyisoprene rubber, or other suitable materials. Considering process capabilities and material properties, the thickness of the stretch buffer layer 320 is less than 10 μm, but this disclosure is not limited thereto.
[0062] exist Figure 1B In this design, a conductor 310 enters the island element 200 from its edge 201, and an auxiliary buffer layer 330 is located at the point where the conductor 310 enters the island element 200 and crosses the conductor 310. In other words, at least a portion of the auxiliary buffer layer 330 overlaps with the edge 201 of the island element 200, and at least a portion of the auxiliary buffer layer 330 overlaps with the conductor 310. Along the extension direction of the edge 201, the auxiliary buffer layer 330 has a width W1, and the conductor 310 has a width W2, where width W1 is greater than width W2. The auxiliary buffer layer 330 may be located below, above, or in a continuous pattern with the conductor 310. The auxiliary buffer layer 330 is configured to reduce strain at the connection between the island element 200 and the conductor 310 when the stretchable display SD is stretched.
[0063] In some embodiments, the Young's modulus of the auxiliary buffer layer 330 can range from 30 GPa to 1000 GPa. The elongation at fracture of the auxiliary buffer layer 330 can range from 2% to 100%. Considering process capabilities and material properties, the thickness of the auxiliary buffer layer 330 can range from 1 nm to 10000 nm. The material of the auxiliary buffer layer 330 can be a metal, a metal oxide, a polymer, or a composite of the above materials. For example, the auxiliary buffer layer 330 can be titanium, aluminum, molybdenum, copper, tungsten, silver, indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), a composite of acrylate and silicon dioxide, a composite of polyimide and aluminum nitride, or other suitable materials.
[0064] Please see Figure 2A and Figure 2B , Figure 2A yes Figure 1A A cross-sectional view of a stretchable display SD. Figure 2B It is along Figure 1A The detailed structural cross-sectional diagram of the stretchable display SD is shown along section line A-A'. Figure 2A In the process, an island element 200 is disposed on a substrate 100, a stretch buffer layer 320 is disposed on at least a portion of the substrate 100 and covers the island element 200, a wire 310 is disposed on the stretch buffer layer 320 and connects the island element 200, and an auxiliary buffer layer 330 is located between the island element 200 and the stretch buffer layer 320.
[0065] exist Figure 2B In this embodiment, the substrate 100 has a plurality of pixel regions 110 and a line region 120, wherein the line region 120 is located between and connected to the plurality of pixel regions 110. The stretchable display SD includes a plurality of island elements 200, respectively disposed on the plurality of pixel regions 110 of the substrate 100. Each island element 200 includes a pixel driving circuit PC and has a top surface 201a and a sidewall 201b. Figure 2B In the middle, the sidewall 201b of the island element 200 and the boundary of the pixel area 110 are aligned with the line area 120.
[0066] exist Figure 2B In this embodiment, the pixel driving circuit PC of each island element 200 may include a thin-film transistor (TFT). The TFT includes a control terminal 240, a semiconductor pattern 220, a gate insulating layer 230 disposed between the control terminal 240 and the semiconductor pattern 220, and a first terminal 260 and a second terminal (not shown) electrically connected to two different regions of the semiconductor pattern 220, respectively. The sidewall 201b of the island element 200 may include the sidewall 230b of the gate insulating layer 230.
[0067] exist Figure 2B In this embodiment, each island element 200 may optionally include a buffer layer 210. The buffer layer 210 is disposed on the substrate 100, the thin-film transistor TFT is disposed on the buffer layer 210, and the sidewall 201b of the island element 200 may optionally include the sidewall 210b of the buffer layer 210. In this embodiment, each island element 200 may optionally include an interlayer dielectric layer 250. The interlayer dielectric layer 250 may be composed of a single film layer or multiple film layers stacked in phase. The interlayer dielectric layer 250 is disposed between the first terminal 260 and the control terminal 240 of the thin-film transistor TFT. The sidewall 201b of the island element 200 may optionally include the sidewall 250b of the interlayer dielectric layer 250.
[0068] exist Figure 2BIn this embodiment, the stretch buffer layer 320 is disposed on the line area 120 of the substrate 100 and extends at least to at least a portion of the pixel area 110. The stretch buffer layer 320 covers at least a portion of the sidewall 201b of the island element 200 and at least a portion of the upper surface 201a of the island element 200 facing away from the substrate 100.
[0069] exist Figure 2B In this embodiment, the wire 310 is disposed on the stretch buffer layer 320 and electrically connected to the plurality of pixel driving circuits PC of the plurality of island elements 200. For example, in this embodiment, the wire 310 may be a gate driving line electrically connected to the plurality of pixel driving circuits PC of the plurality of island elements 200, a common line electrically connected to the plurality of pixel driving circuits PC of the plurality of island elements 200, a power supply line electrically connected to the plurality of pixel driving circuits PC of the plurality of island elements 200, or a data line electrically connected to the plurality of pixel driving circuits PC of the plurality of island elements 200.
[0070] exist Figure 2B In this embodiment, the auxiliary buffer layer 330 is disposed on the line area 120 of the substrate 100 and extends at least to at least a portion of the pixel area 110. The auxiliary buffer layer 330 is located below the conductor 310 and between the island element 200 and the stretch buffer layer 320. The auxiliary buffer layer 330 covers at least a portion of the sidewall 201b of the island element 200 and at least a portion of the upper surface 201a of the island element 200 facing away from the substrate 100.
[0071] Specifically, the auxiliary buffer layer 330 is disposed between the stretch buffer layer 320 and at least a portion of the upper surface 201a of the island element 200. The auxiliary buffer layer 330 is further disposed between the stretch buffer layer 320 and at least a portion of the sidewall 201b of the island element 200. The auxiliary buffer layer 330 is further disposed between the stretch buffer layer 320 and the circuit area 120 of the substrate 100.
[0072] exist Figure 2B In this embodiment, the stretchable display SD further includes an insulating layer 270 covering the conductive lines 310 and the island elements 200. The insulating layer 270 may also be referred to as a protective layer. The material of the insulating layer 270 may be an inorganic material (e.g., silicon oxide, silicon nitride, silicon oxynitride, or a stack of at least two of the above materials), an organic material, or a combination thereof.
[0073] In some embodiments, the stretchable display SD may further include a conductive pattern 340 disposed on the insulating layer 270 and electrically connected to the pixel driving circuit PC of the island element 200. In some embodiments, the stretchable display SD may further include a planarization layer 280 disposed on the conductive pattern 340. In some embodiments, the stretchable display SD may further include a transparent conductive pattern 350 disposed on the planarization layer 280 and electrically connected to the conductive pattern 340. In some embodiments, the stretchable display SD may further include a light-emitting diode (LED) element 360. For example, the LED element 360 may be electrically connected to the pixel driving circuit PC of the island element 200 via the transparent conductive pattern 350 and the conductive pattern 340.
[0074] exist Figure 2B In this embodiment, each island element 200 may be provided with a light-emitting diode element 360 that emits a first color light, a second color light, or a third color light. The first color light, the second color light, and the third color light are, for example, red light, green light, and blue light, respectively.
[0075] exist Figure 2B In one embodiment, the stretch buffer layer 320 is disposed between the conductor 310 and at least a portion of the upper surface 201a of the island element 200, the stretch buffer layer 320 is further disposed between the conductor 310 and at least a portion of the sidewall 201b of the island element 200, and the stretch buffer layer 320 is further disposed between the conductor 310 and the line area 120 of the substrate 100.
[0076] It must be noted that the following embodiments use the component reference numerals and some content from the foregoing embodiments, with the same reference numerals used to represent the same or similar components, and descriptions of the same technical content omitted. For explanations of the omitted parts, please refer to the foregoing embodiments; these will not be repeated in the following embodiments.
[0077] Please see Figure 3A and Figure 3B , Figure 3A This is a cross-sectional schematic diagram of another embodiment of the stretchable display SD-1. Figure 3B A detailed cross-sectional view of the stretchable display SD-1 is shown. The stretchable display SD-1 is similar to the aforementioned stretchable display SD, the difference being that their auxiliary buffer layers 330-1 and 330 are different. Figure 3A In the middle, the auxiliary buffer layer 330-1 is disposed on the stretch buffer layer 320, and the pattern is continuous with that of the conductor 310.
[0078] exist Figure 3BIn this embodiment, the auxiliary buffer layer 330-1 is located between the tensile buffer layer 320 and the insulating layer 270. The tensile buffer layer 320 has an upper surface 320a and a sidewall 320b. The auxiliary buffer layer 330-1 covers at least a portion of the upper surface 320a and at least a portion of the sidewall 320b of the tensile buffer layer 320, and is a continuous pattern with the conductor 310. The auxiliary buffer layer 330-1 and the conductor 310 can be fabricated from the same processed electronic platform (PEP) and can be made of the same material.
[0079] Specifically, the upper surface 320a of the stretch buffer layer 320 includes a first upper surface 321a and a second upper surface 322a. The first upper surface 321a is located above the pixel region 110 of the substrate 100 and extends partially above the line region 120 of the substrate 100, and the second upper surface 322a is located above the line region 120, wherein the first upper surface 321a and the second upper surface 322a are connected by a sidewall 320b. An auxiliary buffer layer 330 is disposed between the insulating layer 270 and at least a portion of the first upper surface 321a of the stretch buffer layer 320. The auxiliary buffer layer 330 is further disposed between the insulating layer 270 and at least a portion of the sidewall 320b of the stretch buffer layer 320. The auxiliary buffer layer 330 is further disposed between the insulating layer 270 and the second upper surface 322a of the stretch buffer layer 320.
[0080] Please see Figure 4A and Figure 4B , Figure 4A This is a cross-sectional view of the SD-2 stretchable display. Figure 4B A detailed cross-sectional view of the stretchable display SD-2 is shown. The stretchable display SD-2 is similar to the aforementioned stretchable display SD, the difference being that their auxiliary buffer layers 330-2 and 330 are different. Figure 4A In the middle, the auxiliary buffer layer 330-2 is located above the conductor 310 and is disposed on the insulation layer 270.
[0081] exist Figure 4B In this embodiment, the auxiliary buffer layer 330-2 is disposed between the insulating layer 270 and the planarization layer 280. The insulating layer 270 has an upper surface 270a and a sidewall 270b, and the auxiliary buffer layer 330-2 covers at least a portion of the upper surface 270a and at least a portion of the sidewall 270b of the insulating layer 270.
[0082] Specifically, the upper surface 270a of the insulating layer 270 includes a first upper surface 271a and a second upper surface 272a. The first upper surface 271a is located above the pixel region 110 of the substrate 100 and extends partially above the line region 120 of the substrate 100, and the second upper surface 272a is located above the line region 120, wherein the first upper surface 271a and the second upper surface 272a are connected by a sidewall 270b. An auxiliary buffer layer 330 is disposed between at least a portion of the planarization layer 280 and the first upper surface 271a of the insulating layer 270. The auxiliary buffer layer 330-2 is further disposed between at least a portion of the planarization layer 280 and the sidewall 270b of the insulating layer 270. The auxiliary buffer layer 330 is further disposed between the planarization layer 280 and the second upper surface 272a of the insulating layer 270.
[0083] Please see Figure 5 , Figure 5 This is a top view of the SD-3 stretchable display. The SD-3 stretchable display is similar to the SD stretchable display mentioned above, the difference being that their auxiliary buffer layers 330-3 and 330 are different. Figure 5 In this embodiment, the auxiliary buffer layer 330-3 is disposed at the edge 201 of the island element 200 and does not overlap with any wires. In other words, at least a portion of the auxiliary buffer layer 330-3 overlaps with the edge 201 of the island element 200, and no wires are disposed in the portion of the auxiliary buffer layer 330-3 that overlaps with the edge 201.
[0084] The difference between the comparative example of the stretchable display (not shown) and the stretchable display SD of this disclosure is that the comparative example of the stretchable display does not include the auxiliary buffer layer 330 (please refer to the accompanying document). Figure 1A The comparative example of the stretchable display experienced a 1% strain at the junction of the island element 200 and the conductor 310, nearing the point of failure, making the overall structure unable to withstand further stretching. By adding an auxiliary buffer layer 330, the stretchable display SD can reduce the strain at the junction of the island element 200 and the conductor 310 to 0.65%. Compared to the comparative example of the stretchable display, the stretchable display SD shows a reduction of approximately 35% in strain at the junction of the island element 200 and the conductor 310.
[0085] In summary, the stretchable display disclosed herein includes an auxiliary buffer layer in addition to a stretching buffer layer, which can significantly reduce the strain at the junction of island components and conductors, thereby improving the manufacturing yield and product reliability of electronic products.
Claims
1. A stretchable display, comprising: A substrate having at least one pixel region and a line region, wherein the line region is connected to the at least one pixel region; An island-shaped element is disposed on the at least one pixel area of the substrate, wherein the island-shaped element includes a pixel driving circuit and an edge; A stretchable buffer layer covers at least a portion of the circuit area of the island element and the substrate; An auxiliary buffer layer covers at least a portion of the edge of the island element, wherein the auxiliary buffer layer is disposed on at least a portion of the line area and extends to at least a portion of the at least one pixel area; A wire is disposed on the stretch buffer layer and electrically connected to the pixel driving circuit of the island element; as well as An insulating layer is disposed on the tensile buffer layer and covers the conductor and the island element.
2. The stretchable display of claim 1, wherein the conductor enters the island element from the edge of the island element, and the auxiliary buffer layer at least partially overlaps the conductor, wherein a width of the auxiliary buffer layer is greater than a width of the conductor in an extension direction of the edge.
3. The stretchable display of claim 1, wherein the auxiliary buffer layer is located below the conductor and at least partially overlaps the conductor.
4. The stretchable display of claim 1, wherein the island element further comprises an upper surface and a sidewall, and the auxiliary buffer layer covers at least a portion of the upper surface and at least a portion of the sidewall of the island element.
5. The stretchable display of claim 1, wherein at least a portion of the auxiliary buffer layer is located between the island element and the stretch buffer layer, and at least another portion of the auxiliary buffer layer is located between the stretch buffer layer and the circuit area of the substrate.
6. The stretchable display as claimed in claim 1, wherein the auxiliary buffer layer is disposed on the stretch buffer layer, and the auxiliary buffer layer and the conductor form a continuous pattern.
7. The stretchable display of claim 1, wherein the stretch buffer layer comprises an upper surface and a sidewall, and the auxiliary buffer layer covers at least a portion of the upper surface and at least a portion of the sidewall of the stretch buffer layer.
8. The stretchable display of claim 1, wherein the auxiliary buffer layer is located above the conductor and at least partially overlaps the conductor.
9. The stretchable display of claim 1, wherein the insulating layer comprises an upper surface and a sidewall, and the auxiliary buffer layer covers at least a portion of the upper surface and at least a portion of the sidewall of the insulating layer.
10. The stretchable display of claim 1, wherein at least a portion of the edge of the island element covered by the auxiliary buffer layer is not provided with the conductor.