Patent Application
20200043951
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/458785 filed on Feb. 14, 2017 the content of which is relied upon and incorporated herein by reference in its entirety.
The present specification generally relates to electronics assemblies and, more particularly, to electronics assemblies incorporating laminate substrates comprising polymer and glass-based material layers, and methods of their manufacture.
Active electronic devices on glass are commonly fabricated using silicon and metal oxide technology, such as is currently practiced in thin-film transistor (TFT) arrays used in liquid crystal and organic light emitting diode (OLED) displays. Current silicon and metal oxide technology requires high deposition temperatures (at least 400° C.) in order to achieve acceptable performance for commercialized display applications. However, low temperature processing alternatives exist in which organic TFTs are utilized rather than silicon or metal oxide. These other materials are processed at significantly lower temperatures than required for silicon or metal oxide, often well below 250° C.
Due to low processing temperatures, large area printed electronics, including roll-to-roll processing, becomes possible as new flexible substrates are a viable option. Many polymers are available in film format on rolls. However, polymer films have drawbacks when used as substrates for electronic devices. Such drawbacks include flatness, barrier properties, surface roughness, and dimensional stability. To make large area format, short pitch, small dimension electronics, such as are needed for high resolution displays, excellent dimensional stability is needed in order to maintain registration between different deposition processing steps, especially in lithographic processes. Polymer films cannot achieve such dimensional stability due to their propensity for plastic deformation under external load and low modulus and resulting stiffness. On the other hand, due to that very plastic nature, polymer films have excellent toughness. Even under stress, in the presence of defects, many polymer films mechanically fail by first irreversible plastic deformation instead of immediate fracture.
Accordingly, there exists a need for alternative thin, flexible substrates for electronic devices that have improved dimensional stability, particularly during device fabrication.
In one embodiment, an electronics assembly includes a glass-based substrate having a thickness of less than or equal to 300 μm, a first surface, and a second surface, at least one gate electrode disposed on the first surface of the glass-based substrate, and a polymer layer disposed on the first surface of the glass-based substrate such that the polymer layer contacts at least a portion of the at least one gate electrode. The electronics assembly further includes at least one source electrode disposed on a polymer surface of the polymer layer, at least one drain electrode disposed on the polymer surface, and a semiconductor material disposed on the polymer surface. The semiconductor material contacts at least a portion of the at least one source electrode and the at least one drain electrode. The polymer layer is configured to act as a dielectric material between the at least one gate electrode and the semiconductor material. The at least one gate electrode, a portion of the polymer layer, the at least one source electrode, the at least one drain electrode, and the semiconductor material define at least one electronic device.
In another embodiment, a method of fabricating an electronics assembly including an electronics device includes depositing at least one gate electrode on a first surface of a glass-based substrate, wherein the glass-based substrate has a thickness that is less than or equal to 300 μm, depositing a polymer layer on the first surface of the glass-based substrate such that the polymer layer contacts at least a portion of the at least one gate electrode, wherein the polymer layer comprises a polymer surface, and depositing at least one source electrode and at least one drain electrode on the polymer surface. The method further includes depositing a semiconductor material on the polymer surface such that the semiconductor material contacts at least a portion of the at least one source electrode and at least one drain electrode. The polymer layer is configured to act as a dielectric material between the at least one gate electrode and the semiconductor material. The at least one gate electrode, a portion of the polymer layer, the at least one source electrode, the at least one drain electrode, and the semiconductor material define at least one electronic device.
The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the representative embodiments.
The embodiments disclosed herein relate to electronics assemblies incorporating flexible, laminate substrates. Without limitation, the electronics assemblies described herein may be utilized in flexible displays, such as flexible displays incorporating organic thin-film transistors (TFT). Although polymer films are flexible and may thus be used as a substrate for electronic devices such as TFT, polymer films lack dimensional stability. Polymer films also have additional drawbacks, such as flatness, surface roughness, and barrier properties.
Embodiments of the present disclosure address these deficiencies of polymer films by utilizing thin form-factor glass-based substrates. Glass, such as glass sold by Corning Incorporated under the trade name Corning® Willow® glass, may solve the problems that exist with plastic substrates. Flexible glass is available in thin form factor, in both sheet and roll formats. Glass, glass-ceramics, and ceramics (herein referred to collectively as “glass-based substrates”) have excellent transparency, oxygen/water vapor barrier properties, durability, and dimensional stability. Glass-based substrates do not plastically deform under normal handling and moderate temperatures. Under these conditions, dimensional change of glass-based substrates is within the elastic regime. Further, glass-based substrates also do not dimensionally swell due to solvent or moisture absorption. Glass-based substrates may also possess exceptional quality surfaces, due to the fusion forming process. The use of glass-based substrates in such thin form factors may cause issues with respect to mechanical reliability during device fabrication as glass-based substrates may be susceptible to defect induced failures through crack propagation.
As examples, flexible glass-based substrates have advantages over thicker glass in areas of thickness, weight, and flexibility. Glass-based substrates about 300 μm or thinner may be used for flexible/conformable electronics applications and roll-to-roll manufacturing situations that thicker rigid glass is not mechanically compatible with. Thinner glass also has lower optical effects, such as parallax, and UV absorption. Compared to polymer film substrates, flexible glass-based substrates offer improved optical transmission, lower haze, lower surface roughness, higher thermal capability, higher barrier properties, process chemical compatibility, and overall dimensional stability. For example, a thin glass-based substrate as described herein can have an optical transmission of at least about 70%, at least about 80%, or at least about 90%, measured over a wavelength range of 400 nm to 800 nm. Additionally, or alternatively, a thin glass-based substrate as described herein can have a haze of at most about 1%, at most about 0.5%, at most about 0.2%, or at most about 0.1%, measured using a Byk-Gardner Haze-Gard LE04 Haze Meter. Additionally, or alternatively, a thin glass-based substrate as described herein can have a surface roughness of at most about 10 nm, at most about 5 nm, at most about 2 nm, at most about 1 nm, or at most about 0.5 nm, wherein the surface roughness is Ra surface roughness measured over an area of 100 μm×100 μm. Additionally, or alternatively, a thin glass-based substrate as described herein can have a thermal capability of at least about 200° C., at least about 400° C., at least about 500° C., or at least about 700° C. Additionally, or alternatively, a thin glass-based substrate as described herein can have a dimensional stability of at most about 20 μm, at most about 10 μm, or at most about 1 μm, wherein the dimensional stability is the dimensional change or distortion upon heating the glass-based substrate to a processing temperature and then returning it to room temperature. The dimensional stability, specifically, enables high performance devices made of multiple patterned layers that are registered to each other. Free-standing polymer substrates are known to unpredictably distort during processing due to situations of chemical/water absorption, low stiffness resulting in inability to compensate for thin film stresses or applied stress, and stress relaxation due to conditions near Tg. Utilizing a flexible substrate that includes one or more ultra-thin glass-based layers may enable achieving the dimensional stability needed to fabricate high resolution, high registration device structures.
Embodiments described herein combine a thin, glass-based substrate(s) with polymer layer(s) in laminate or coating structures to achieve the favorable properties of both material sets. The excellent dimensional stability and oxygen/water vapor barrier properties of the glass-based substrate may be taken advantage of, while the polymer layer imparts handleability and minimizes contact damage to the surface of the glass-based substrate. Accordingly, embodiments use thin glass-based substrates and polymer layers disposed adjacent to each other as enhanced substrates/superstrates for electronic devices, such as TFT arrays. The laminated structure can be used for sheet-to-sheet and roll-to-roll processes. In most cases, processes will be at low temperature to accommodate organic polymer material thermal properties. However, embodiments of the present disclosure do not exclude the use of these laminate substrates in higher temperature processes if thin glass-based substrate is laminated with high thermal stable polymers, such as, without limitation, polyimides.
The laminate substrates described herein may be utilized in organic TFT backplanes for display devices. Organic TFT structures include organic semiconductor materials, dielectric materials, and TFT designs. Embodiments of the present disclosure are further directed to optimized substrate-device combined structures. In some embodiments, one or more polymer layers disposed on a glass-based substrate may be configured as one or more dielectric layers for electronic devices (e.g., TFT devices) disposed on and/or in the flexible laminate substrate.
Various laminate substrates, electronic assemblies, and methods of fabricating electronics assemblies incorporating laminate substrates are described in detail below.
The laminate construction with two glass-based substrates 110A, 110B encompassing a central polymer layer as shown in
The glass-based substrates described herein 110 may be made of any glass, glass-ceramic, or ceramic material. As stated above, low temperature processing to fabricate TFT devices (e.g., maximum temperature less than or equal to 300° C.) enables the use of any composition of glass, glass-ceramic, and ceramic materials. Example glass materials include, but are not limited to, borosilicate glass (e.g., glass manufactured by Coming Incorporated of Corning, NY under the trade name Corning® Willow® Glass), alkaline Earth boro-aluminosilicate glass (e.g., glass manufactured by Corning Incorporated under the trade name EAGLE XG®), alkaline earth boro-aluminosilicate glass (e.g., glass manufactured by Corning Incorporated under the trade name Contego Glass), and ion-exchanged alkali-aluminosilicate (e.g., glass manufactured by Corning Incorporated under the trade name Gorilla® Glass). It should be understood that other flexible glass, glass ceramic, ceramic, multi-layers, or composite compositions may also be utilized.
However, high temperature processing of TFT devices (e.g., temperatures greater than 300° C.) may cause migration of alkali ions present within the glass-based substrate 110 into the TFT device, thereby affecting the performance and reliability of the TFT device. Thus, alkali-free glasses can be utilized for the glass-based substrate 110 in high-temperature processing applications where alkali contamination of TFTs is a concern. The presence of alkali ions in the glass-based substrate 110 will not be problematic for low temperature processing because the ions will remain in the glass.
In embodiments, the glass-based substrate 110 has a thickness such that it is flexible. Example thicknesses include, but are not limited to, less than about 300 μm, less than about 250 μm, less than about 200 μm, less than about 150 μm, less than about 100 μm, less than about 50 μm, and less than about 25 μm. For example, the glass-based substrate 110 has a thickness of about 10 μm to about 300 μm. Example glass-based substrates 110 described herein have the ability to bend at a radius of below 300 mm, or a radius below 200 mm, or a radius below 100 mm, or a radius below 75 mm, or a radius below 50 mm, or a radius below 25 mm.
The polymer layer 120 may be any suitably flexible polymer material that is capable of being secured to a surface of the glass-based substrate 110. In an example, the polymer layer 120 covers an entire surface of the glass-based substrate 110. In another example, one or more regions of the surface of the glass-based substrate 110 are not covered by the polymer layer 120. Example polymer materials include, but are not limited to, a polar elastomer, a polyimide, a polycarbonate, a polyvinybutyral, a poly(meth)acryolate. One non limiting example of a polar elastomer includes poly(vinylidene fluoride-co-hexafluoropropylene), as described in more detail below. The polymer layer 120 may be of any suitable thickness, such as, without limitation, within a range of, including endpoints, 0.5 m to 50 μm, or 0.5 μm to 40 μm, or 0.5 μm to 30 μm, or 0.5 μm to 20 μm, or 0.5 μm to 10 μm, or 0.5 μm to 5 μm, or 0.5 μm to 2.5 μm. The polymer layer 120 may have a Young's modulus of less than or equal to 20 GPa, less than or equal to 15 GPa, less than or equal to 10 GPa, or less than or equal to 5 GPa.
The polymer layer 120 may be included in the laminate substrate 100A for its toughness to protect the glass-based substrate 110, particularly during material handling in subsequent processing steps, such as fabrication of TFT devices on the laminate substrate 100A. The polymer layer 120 may minimize contact damage to the surface of the glass-based substrate 110. The polymer layer 120 can be used to accumulate mechanical defects caused by physical contact instead of them being formed in the surface of the glass-based substrate 110. In addition, the polymer layer 120 may act to maintain the integrity of the entire laminate substrate 100A if a mechanical failure occurs in the glass-based substrate 110. Thus, the polymer layer 120 disposed on the glass-based substrate 110 increases the mechanical robustness of the laminate substrate 100A.
The polymer layer 120 may be applied to the surface(s) of the glass-based substrate 110 by any suitable process. As shown in
As the glass-based substrate 110 may be a flexible material, the polymer layer 120 may be applied to the glass-based substrate 110 by a roll-to-roll process. Referring now to
The dielectric layer depositing system 130 may be any assembly or system capable of depositing the polymer material 122 onto the glass web 112. The glass web 112 may be any glass, glass-ceramic, or ceramic material, as described above. As an example and not a limitation,
Referring now to
As stated above, the polymer layer 120 may be applied to individual sheets of the glass-based substrate 110 rather than in a roll-to-roll process.
After application of the polymer material 122 to the glass substrate or web 111, the coated glass substrate/web 111 may then be severed into a plurality of laminate substrates having one or more desired shapes.
The laminate substrates described herein (e.g., laminate substrates 100A-100D) may be utilized as a substrate for an electronics assembly. In one non-limiting embodiment, the electronics assembly is an organic TFT backplane used in electronics devices, such as smart phones, for example. It should be understood that embodiments may be incorporated into other electronics assemblies, such as, without limitation, organic light emitting diode displays, organic field-effect transistors, OLED lighting, antennas, touch sensors, circuit board assemblies, photovoltaics, optical and opto-electronic devices, and sensors. Although embodiments are described herein in the context of organic TFT electronics assemblies, it should be understood that embodiments are not limited thereto.
The electronics assemblies described herein may include one or more electronic devices (e.g., TFT electronic device as described below) disposed on and/or in an exposed surface of the laminate substrate. As an example and not a limitation, an array of electronic devices, such as TFT electronic devices, may be disposed on and/or in one or more surfaces of the laminate substrate to provide a TFT backplane for an electronic display.
Referring to
It is noted that electronic devices built directly on the surface of the glass-based substrate 110, 110A make use of the excellent surface quality of the glass-based material and make best use of its dimensional stability. However, there may be potential applications in which it may be advantageous to have that high quality surface be presented outwards for interaction with the outside environment. In such cases, it would be viable to build the electronic devices (e.g., TFT arrays) on the surface of the polymer layer 120, 120A. There are also situations in which the polymer layer might impart other useful functionality of its own in terms of materials properties for outside interaction. In such cases, the laminate substrates 100B and 100D illustrated in
There are a number of various possible TFT configurations for the electronic devices that may be built on the laminate substrates 100A-100D illustrated in
The electronic device 150A further includes a dielectric layer 154 deposited or otherwise disposed on the surface 111, 121 of the glass-based substrate 110 or the polymer layer 120 such that it contacts at least a portion of the gate electrode 155. The dielectric layer 154 is chosen such that the gate is insulated from a source electrode 152, a drain electrode 153, and a semiconductor material 151. Example materials for the dielectric layer include, but are not limited to, non-conductive polymers, such as, fluoro-elastomers, polystyrene, polyvinylphenol, polymethylmethacrylate and polyimides.
An electrically conductive source electrode 152 and an electrically conductive drain electrode 153 are deposited or otherwise disposed on a surface of the dielectric layer 154. The source electrode 152 and the drain electrode 153 may be fabricated from the same electrically conductive materials as the gate electrode 155 (e.g., ITO), and the various electrodes of the electronic device 150A can be fabricated from the same or different materials. The electronic device 150A further includes a semiconductor material 151 deposited or otherwise disposed on a surface of the dielectric layer 154 such that the semiconductor material 151 contacts at least a portion of the source electrode 152 and the drain electrode 153. Example semiconductor materials include, but are not limited to, small molecule organic semi-conductors, polymeric organic semi-conductors, including fused thiophene and/or diketopyrrolopyrrole containing conjugated polymers and metal oxide semi-conductors. The various components of any of the electronic device described herein may be fabricated using any known or yet-to-be-developed TFT fabrication techniques.
An array of electronic devices (e.g., electronic devices 150A-150D depicted in
The example TFT electronic devices 150A and 150D depicted in
Referring now to
As shown in
Referring once again to
In some embodiments, the glass-based substrate 110 and the polymer layer 120 can be separated or debonded from each other. For example, the polymer layer 120 can be separated from the glass-based substrate 110 after deposition of the gate electrode 155, the polymer layer 120, the source electrode 152, the drain electrode 153, and/or the semiconductor material 151 as described herein. In some of such embodiments, the glass-based substrate 110 can serve as a carrier for forming the electronic device, and the electronic device can be removed from the carrier following processing. Additionally, or alternatively, the polymer layer 120 can protect the glass-based substrate 110 during the various processing steps as described herein.
Electronic assemblies with electronic devices disposed on both sides of a laminate substrate are also possible. In such embodiments, the laminate substrate may serve as an intra-state. These electronic devices on both sides of the substrate can be registered to each other (e.g., within ±10 μm, within ±5 μm, or within ±1 μm) or non-aligned. The electronic devices can also include categories of opto-electronic and optical devices. The electronic devices can also interact with each other electrically, optically, or through other methods. This interaction could make use of via holes in the substrate or the substrate's transparency. Referring now to
While exemplary embodiments have been described herein, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope encompassed by the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/018129 | 2/14/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62458785 | Feb 2017 | US |
