Patent Grant
9723711
Flexible electronics are expected to revolutionize the next generation of devices. Due to the high degree of flexibility of flexible electronics, they can be integrated into many different shapes. This flexibility and diverse integration options can provide for a large number of useful device configurations that would not be possible with the more rigid electronics that are fabricated based on silicon. Applications envisioned for flexible electronics include thin, flexible mobile devices, bendable and conformable displays, rollable and foldable flexible displays, and paper-like displays. Additionally, new forms of flexible electronic enable significant strain or stretch.
Some portions of such flexible electronics may be fabricated in solution. In addition, flexible substrates may be used in the fabrication of the flexible electronics. The flexible substrates enable fabrication by high speed printing techniques capable of generating electronic devices over large substrate at low cost. The flexible electronics also may be fabricated using independent fabricated components followed by assembly onto a single device substrate.
Fabricating flexible electronics that exhibit good electronic performance can be challenging. For example, fabrication techniques developed for the semiconductor fabrication industry are incompatible with some flexible materials. The temperatures used to generate high quality inorganic semiconductor components (for example, temperatures greater than 1000 degrees Celsius) are incompatible with many polymers, plastics and elastomeric materials. In addition, inorganic semiconductors are poorly soluble in the types of solvents that facilitate formation of the flexible electronics. While amorphous forms of silicon are fabricated using lower temperatures, it may not be compatible with the flexible electronic structure. Organic or hybrid organic-inorganic semiconductors can be processed at relatively low temperatures; however these materials do not form electronic structures with the performance capability needed for the next generation of flexible, foldable and bendable products.
Flexible electronics may be formed through incorporating inorganic semiconductor components into a polymer-based matrix. The flexible electronics can be fabricated on a rigid substrate or a flexible substrate. At one or more stages in the fabrication process, the flexible electronics is subjected to processing in solvents that are incompatible with the inorganic components. Therefore, polymer encapsulation of the inorganic device components has been suggested.
A challenge to large-scale production of the flexible electronics is the difficulty with separating the fabricated flexible electronics from the substrate on which the flexible electronics are fabricated. Mechanical removal may damage the flexible electronics by introducing stresses in the structure. Many chemical-based methods of separating the fabricated flexible electronics from the support substrate can cause damage to the flexible electronics.
In view of the foregoing, the Inventors have recognized and appreciated various significant improvements to fabrication processes for flexible electronics that facilitate higher yield and generally improve the integrity of electronics devices resulting from the fabrication process. One example of such an improvement involves a “sacrificial release layer” disposed on a substrate on which some portion of the flexible electronics are fabricated. In particular, the Inventors have recognized and appreciated that, when fabricating electronic, optical, or mechanical systems, it is desirable to construct the system over a substrate that has a sacrificial release layer disposed on its surface. In one exemplary implementation illustrating the inventive concepts disclosed herein, such an electronic, optical and/or mechanical system is built (i.e., fabricated) on top of the sacrificial release layer, and the sacrificial release layer is then selectively removed (by etching) so that the system is either free-standing, floating or sufficiently de-adhered from the substrate, such that it can be separated from the substrate.
Fabrication processes according to various embodiments of the present invention involving such a sacrificial release layer may be used in the fabrication of stretchable electronic systems. The deformable electronics can be manufactured in a highly planar format, after which the deformable electronics may be separated from the original support substrate via removal of a sacrificial release layer (e.g., by an etch process). In some instances, the removal process involving the sacrificial release layer may be difficult to control and may lead to loss of the deformable electronics upon separation from the original support substrate (e.g., the deformable electronics may float away in an etchant and become twisted, tangled or broken as a result).
To mitigate the foregoing problems that may arise in some fabrication processes involving a sacrificial release layer, various embodiments of the invention disclosed herein relate generally to fabrication methods in which a loss of deformable electronics arising from separation of the deformable electronics from their original support substrate (e.g., by over etching) is significantly reduced or substantially prevented. In some embodiments, systems and devices fabricated using these inventive processes are also provided.
For example, according to one embodiment of an inventive fabrication process for deformable electronics involving a sacrificial release layer, a plurality of anchors is formed between an encapsulated electronic device array and a substrate. In one aspect, the anchors serve to adhere the encapsulated electronic device array to the substrate, and keep the encapsulated electronic device array substantially attached to the substrate when the sacrificial layer is removed. In another aspect, the encapsulated electronic device array can be separated from the substrate when a force is applied. In one example implementation, the force is applied using an elastomeric transfer stamp, as disclosed in U.S. Publication No. 20090199960 entitled “Pattern Transfer Printing by Kinetic Control of Adhesion to an Elastomeric Stamp” filed Jun. 9, 2006, which publication is hereby incorporated herein by reference it is entirety.
An example method for fabricating the flexible electronic structures can include applying a first layer to a portion of a substrate, removing selected portions of the first layer to provide a plurality of vias such that a portion of the vias extend substantially to a surface of the substrate, and disposing a second polymer layer, such that portions of the second polymer layer conform to a dimension of at least one of the plurality of vias and forms a plurality of anchors that contact at least a portion of the substrate. The second polymer layer is more resistant to a selective etchant than the first layer. The example method can further include disposing at least one electronic device layer above a portion of the first layer and/or the second polymer layer, forming at least one trench through the second polymer layer and the at least one electronic device layer to expose at least a portion of the first layer, exposing at least a portion of the first layer to the selective etchant through the at least one trench, and removing, by the selective etchant, portions of the first layer, thereby providing the flexible electronic structure. At least one anchor of the plurality of anchors can remains in contact with at least a portion of the substrate.
In an example, a method for fabricating the flexible electronic structure can further include applying a third polymer layer to at least a portion of the at least one electronic device layer; and forming the at least one trench through the third polymer layer, the second polymer layer, and the at least one electronic device layer to expose at least a portion of the first layer.
In an example, the first layer can include polymethylmethacrylate, silicon dioxide, chromium, or titanium. In an example, the second polymer layer can include polyimide, polyethylene naphthalate, polybenzobisoxazole, benzocyclobutene, siloxane, or a liquid crystal polymer.
In an example, an average width of each of the plurality of vias can be in a range from about 10 μm to about 50 μm. In another example, an average width of each of the plurality of vias is in a range from about 0.1 μm to about 1000 μm.
In an example, respective ones of the plurality of vias can be spaced apart by an average separation ranging from about 50 μm to about 1,000 μm. In another example, respective ones of the plurality of vias are spaced apart by an average separation ranging from about 0.2 to about 10,000 μm. In yet another example, respective ones of the plurality of vias are spaced apart by an average separation ranging from about 200 to about 800 μm.
In an example, a method for fabricating the flexible electronic structures can include applying a first layer to a portion of a substrate, removing selected portions of the first layer to provide a plurality of vias such that a portion of the vias extend substantially to a surface of the substrate, and disposing a second polymer layer, such that portions of the second polymer layer conform to a dimension of at least one of the plurality of vias and forms a plurality of anchors that contact at least a portion of the substrate. The second polymer layer is more resistant to a selective etchant than the first layer. The example method can further include disposing at least one electronic device layer above a portion of the first layer and/or the second polymer layer, forming at least one trench through the second polymer layer and the at least one electronic device layer to expose at least a portion of the first layer, exposing at least a portion of the first layer to the selective etchant through the at least one trench, and removing, by the selective etchant, portions of the first layer, thereby providing the flexible electronic structure. At least one anchor of the plurality of anchors can remain in contact with at least a portion of the substrate. The example method can further include separating the flexible electronic structure from the substrate.
A flexible electronic structure fabricated according to one embodiment of an inventive fabrication process can include a second polymer layer having a first surface and a second surface, where the first surface includes a plurality of anchors, and at least one electronic device layer disposed above the second surface of the second polymer layer.
In another example, the flexible electronic structure can include a base polymer layer having a first surface and a second surface, where the first surface includes a plurality of anchors, and at least one electronic device layer disposed above a portion of the second surface of the base polymer.
In another example, the flexible electronic structure can include a base polymer layer having a first surface and a second surface, where the first surface includes a plurality of anchors, at least one electronic device layer disposed above a portion of the second surface of the base polymer, and a top polymer layer that is disposed above at least a portion of the at least one electronic device layer.
In another example, the flexible electronic structure can include a base polymer layer having a first surface and a second surface, where the first surface includes a plurality of anchors, and wherein at least one of the plurality of anchors contacts a substrate, and at least one electronic device layer disposed above a portion of the second surface of the base polymer.
In another example, the flexible electronic structure can include a base polymer layer having a first surface and a second surface, where the first surface includes a plurality of anchors, and wherein at least one of the plurality of anchors contacts a substrate, at least one electronic device layer disposed above a portion of the second surface of the base polymer, and a top polymer layer that is disposed above at least a portion of the at least one electronic device layer.
In another example, a flexible electronic structure disposed on a substrate is provided. The flexible electronic structure can include a first layer disposed on a portion of the substrate and a second polymer layer having a first surface and a second surface. The first surface can include a plurality of anchors. The plurality of anchors can extend through selected portions of the first layer and contact at least a portion of the substrate. The flexible electronic structure can further include at least one electronic device layer disposed above the second surface of the second polymer layer.
In another example, a flexible electronic structure disposed on a substrate can include a first layer disposed on a portion of the substrate, a second polymer layer having a first surface and a second surface, at least one electronic device layer disposed above the second surface of the second polymer layer, and a third polymer layer disposed above at least a portion of the at least one electronic device layer. The first surface of the second layer can include a plurality of anchors. The plurality of anchors extends through selected portions of the first layer and contact at least a portion of the substrate.
A flexible electronic structure disposed on a substrate and fabricated according to one embodiment of an inventive fabrication process herein can include a first layer disposed on a portion of the substrate, a second polymer layer having a first surface and a second surface, and at least one electronic device layer disposed above the second surface of the second polymer layer. The first surface of the second polymer can include a plurality of anchors, and the plurality of anchors can extend through selected portions of the first layer and contact at least a portion of the substrate. The plurality of anchors can have a diameter of about 50 μm and have a pitch ranging from about 200 μm to about 800 μm.
A flexible electronic structure fabricated according to one embodiment of an inventive fabrication process herein can include a base polymer layer having a first surface and a second surface and at least one electronic device layer disposed above the second surface of the base polymer layer. The first surface can include a plurality of anchors that have a diameter of about 50 μm and have a pitch ranging from about 200 μm to about 800 μm.
Any other applicable technique may be employed to fabricate a device according to the principles described herein. As non-limiting examples, the following patent publications (which are hereby incorporated herein by reference in their entireties, including drawings) describe applicable techniques that can be used, all or in part, in tandem with various inventive concepts disclosed herein, for device fabrication according to various embodiments of the present invention:
U.S. publication no. 2006 0038182-A1, published Feb. 23, 2006, filed Jun. 2, 2005, and entitled “STRETCHABLE SEMICONDUCTOR ELEMENTS AND STRETCHABLE ELECTRICAL CIRCUITS;”
U.S. publication no. 2008 0157234-A1, published Jul. 3, 2008, filed Sep. 6, 2006, and entitled “CONTROLLED BUCKLING STRUCTURES IN SEMICONDUCTOR INTERCONNECTS AND NANOMEMBRANES FOR STRETCHABLE ELECTRONICS;”
U.S. publication no. 2010 0002402-A1, published Jan. 7, 2010, filed Mar. 5, 2009, and entitled “STRETCHABLE AND FOLDABLE ELECTRONIC DEVICES;”
U.S. publication no. 2010 0087782-A1, published Apr. 8, 2010, filed Oct. 7, 2009, and entitled “CATHETER BALLOON HAVING STRETCHABLE INTEGRATED CIRCUITRY AND SENSOR ARRAY;”
U.S. publication no. 2010 0116526-A1, published May 13, 2010, filed Nov. 12, 2009, and entitled “EXTREMELY STRETCHABLE ELECTRONICS;”
U.S. publication no. 2010 0178722-A1, published Jul. 15, 2010, filed Jan. 12, 2010, and entitled “METHODS AND APPLICATIONS OF NON-PLANAR IMAGING ARRAYS;”
U.S. publication no. 2010 027119-A1, published Oct. 28, 2010, filed Nov. 24, 2009, and entitled “SYSTEMS, DEVICES, AND METHODS UTILIZING STRETCHABLE ELECTRONICS TO MEASURE TIRE OR ROAD SURFACE CONDITIONS;”
U.S. publication no. 2010-0298895, published Nov. 25, 2010, filed Dec. 11, 2009, and entitled “SYSTEMS, METHODS AND DEVICES USING STRETCHABLE OR FLEXIBLE ELECTRONICS FOR MEDICAL APPLICATIONS;” and
PCT publication no. WO 2010/102310, published Sep. 10, 2010, filed Mar. 12, 2010, and entitled “SYSTEMS, METHODS, AND DEVICES HAVING STRETCHABLE INTEGRATED CIRCUITRY FOR SENSING AND DELIVERING THERAPY.”
It should be appreciated that all combinations of the foregoing concepts and additional concepts described in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter described herein. All combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter described herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts described herein.
The skilled artisan will understand that the figures, described herein, are for illustration purposes only, and that the drawings are not intended to limit the scope of the described teachings in any way. In some instances, various aspects or features may be shown exaggerated or enlarged to facilitate an understanding of the inventive concepts described herein (the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the teachings). In the drawings, like reference characters generally refer to like features, functionally similar and/or structurally similar elements throughout the various figures.
Following below are more detailed descriptions of various concepts related to, and examples of, electronic, optical and/or mechanical apparatus and systems, and methods for fabricating same involving sacrificial release layers and associated anchors. It should be appreciated that various concepts introduced above and described in greater detail below may be implemented in any of numerous ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.
As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on.
With respect to description herein concerning the surface(s) of a substrate a layer, any references to “top” surface and “bottom” surface are used primarily to indicate relative position, alignment and/or orientation of various elements/components with respect to the substrate and each other, and these terms do not necessarily indicate any particular frame of reference (e.g., a gravitational frame of reference). Thus, reference to a “bottom surface of a substrate” does not necessarily require that the indicated surface be facing a ground surface. Similarly, terms such as “over,” “under,” “above,” “beneath” and the like do not necessarily indicate any particular frame of reference, such as a gravitational frame of reference, but rather are used primarily to indicate relative position, alignment and/or orientation of various elements/components with respect to the substrate and each other.
Provided herein are methods for selectively anchoring an array of electronic devices to a supporting substrate. In an example, a method includes providing a sacrificial layer on the supporting substrate, patterning trenches in the sacrificial layer, and providing a first encapsulating layer to support the array of electronic devices whereby the first encapsulating layer comes into contact with the supporting substrate via the trenches. An array of electronic devices is fabricated on the first encapsulating layer. The array of electronic devices are sealed with a second encapsulating layer. The sacrificial layer is removed by immersion in a suitable solvent. The encapsulated electronic devices can remain adhered to the support substrate due to forces of adhesion between the encapsulating layer and the support substrate.
In an example, the electronic structure is a flexible electronic structure.
As shown in the cross-sectional view of
In an example, the third polymer layer is the top layer of the electronic structure.
In an example, the thickness of the third polymer layer (or, in an example, the top layer) is configured to cause the location of a resultant neutral mechanical plane of the electronic structure to correspond to strain-sensitive layers of the electronic structure. The neutral mechanical plane is a region of the electronic structure where a strain-sensitive layer can be isolated from stresses and strains applied to the electronic structure, e.g., from bending, rolling, or folding. For example, the thickness of the third polymer layer (or, in an example, the top layer) can be selected such that the at least one electronic device layer is located at or near a neutral mechanical plane of the electronic structure.
At least one trench 9 is formed through the third polymer layer 8 and the second polymer layer 4 to expose at least a portion of the first layer 2 (see cross-sectional view of
The structure of
In an example, the flexible electronic structure can include an integrated circuit, a semiconductor, a transistor, a diode, a logic gate, arrays of electronic components, an optical system, a temperature sensors, a pressure sensor, electrical-conductivity sensors, electrodes for pH sensors, chemical sensors, sensors for enzymatic activity, resistors, capacitors, passive devices, light emitting diodes (LEDs), photodiodes (PDs), photodetectors, a battery, a transducer, an emitter, a receiver, or a transceiver.
In another example, the at least one electronic device layer includes at least one of a multifunctional sensor (including a temperature, strain, and/or electrophysiological sensor), a microscale light-emitting diode (LED), an active to passive circuit elements (including a transistor, a diode, a resistor, and/or a memristor), wireless power coils, and devices for radio frequency (RF) communications (including a high-frequency inductor, capacitor, oscillator, and/or antenna). The active elements of the at least one electronic device layer can include electronic materials such as silicon and gallium arsenide in the form of filamentary serpentine nanoribbons and micro- and nano-membranes. In an example, the at least one electronic device layer includes may be configured to provide solar cells and/or wireless coils to serve as a power supply.
The electronic structures herein, which can include interconnects, can exhibit ultrathin layouts, and employ neutral mechanical plane configurations and optimized geometrical designs.
In the example of
In an example of the process, the electronic device layer 5 may be formed with multiple layers, including several layers and/or several portions of metal, electronic devices, polymers, semiconductor material, dielectric material, and any other material used for creating electronic devices. For example, as shown in
As shown in
In an example, the first polymer 2 is a sacrificial release layer. Removal of the sacrificial release facilitates the fabrication of the electronic structure. In an example, the electronic structure 10 is a stretchable electronic system. In the manufacture of a stretchable electronic system, deformable electronics can fabricated initially in a planar format and are released from the original substrate 1 by an etch process. This etch process can be difficult to control and may lead to loss of electronic arrays that may float away in the etchant, and become twisted, tangled or broken as a result. The processes, systems and devices described herein can prevent this loss of devices by preventing over etching. The anchors 3 can be created from portions of the second polymer layer 4 or can be formed from a different polymer material. The second polymer layer 4 can be an electric/electronic array encapsulation. The anchors 3 provide enough adhesion to keep the stretchable electronic system arrays attached to the support substrate 1 when the sacrificial layer is removed. The stretchable electronic system arrays may be readily separated from the support substrate 1 when an external force is applied (as a non-limiting example, a force applied by elastomeric transfer stamp as disclosed in United States Published Patent Application No. 20090199960 entitled “Pattern Transfer Printing by Kinetic Control of Adhesion to an Elastomeric Stamp” filed Jun. 9, 2006, which is incorporated herein by reference it is entirety).
In an example, vias 6 are patterned in the sacrificial layer 2 prior to fabrication of the electronic device layer 5. The vias 6 may begin at the surface of the sacrificial layer and end at the interface with the support substrate 1. The support substrate 1 may be a silicon wafer in an example. A non-limiting example of a suitable material to form a first layer, and in some examples, to serve as a sacrificial layer, is polymethylmethacrylate (PMMA). In another non-limiting example, the first layer is formed from silicon dioxide, chromium, or titanium. A non-limiting example of a suitable material to form a second polymer layer, and in some examples, to serve as an encapsulation layer, is polyimide. In another non-limiting example, the second polymer layer can be formed from polyethylene naphthalate, polybenzobisoxazole, benzocyclobutene, siloxane, or a liquid crystal polymer
The Young's modulus of the substrate can be greater than that of the first layer (e.g., PMMA with a Young's modulus of 1800-3100 MPa) and the second polymer layer (e.g., polyimide with a Young's modulus of 2.5 GPa).
The PMMA can be selectively etched in acetone without affecting the polyimide. In a non-limiting example, the vias 6 (shown in
The vias or anchors may be in any two-dimensional geometry. As a non-limiting example, they can be formed as a circular cross-section, which may be easier to fabricate. Any other cross-sectional geometry of the vias or anchors is within the scope of this disclosure, such as but not limited to a hexagonal, oval or rectangular cross-section, or any polygonal or non-polygonal shape. In an example, the diameter of this circular cross-section can be between about 10 μm and about 50 μm. In an example, the width of the vias (or anchors) is selected such that the anchors provide sufficient adhesive force with the substrate to not separate during the etching of the first layer. In an example, the width of the vias (or anchors) also can be selected such that the anchors do not generate an adhesive force that prevents the array of electronics structure from being separated from the substrate, such as but not limited to in a transfer printing step, after the sacrificial release layer is removed. Although the range of the width of the vias or anchors can be between about 10 μm and about 50 μm, smaller diameters and larger diameters can be used. For example, the width of the vias or anchors can be selected based on the adhesive strength between the material of the anchor (such as but not limited to polyimide) and the substrate (such as but not limited to silicon). In an example, the width of the vias or anchors can range from about 0.1 μm to about 1000 μm.
The spacing of the vias or anchors also can be selected based on the intended adhesive strength between the anchors and the substrate. In an example, the number and spacing of vias or anchors can be determined based on the adhesive force to maintain the geometry of the array of electronic structures, and to substantially prevent distorting during the etching to remove the first layer (e.g., a sacrificial release layer). In an example, the number and spacing of vias or anchors is determined such that the total adhesive force of the anchors does not prevent separation of the array of electronic structures from the substrate, e.g., in a later transfer printing after the sacrificial etch. The exact pattern and placement of the vias or anchors can depend on the geometry of the array of electronic structures (including on the geometry of the array of electronic device layer 5). As a non-limiting example, the vias or anchors may be placed along the pattern of interconnected device islands. In an example, the vias or anchors can have a pitch between about 50 μm and about 1000 μm, i.e., they vias or anchors can be spaced apart by an average distance of between about 50 μm and about 1000 μm. In another example, the vias or anchors can be spaced apart by an average distance (a pitch) of between about 0.2 μm and about 10000 μm.
In a non-limiting example, the vias or anchors are cylindrical in shape, have a diameter of about 50 μm, and are spaced apart with spacing (a pitch) ranging from about 200 μm to about 800 μm. These anchors may be positioned along the pattern of interconnected device islands.
When a second polymer layer material is deposited onto the first layer, it can conform to the dimensions of the vias and contact the support substrate to form the anchor 3 (see, for example,
In an example, a mask may be deposited onto the topmost layer of the electronic structure before further processing. In an example, the mask is created using a photolithographic patterning and etching process. In an example, the mask is an oxide layer. The mask can be used to control the further processing. For example, the mask can be used to prevent over-etching of an encapsulant polymer region that is being used to protecting the electronic devices and interconnects of the at least one electronic device layer 5.
In an example, an adhesion-promoting layer can be included between the first layer and the substrate (e.g., when it is used as a sacrificial layer). For example, where the first layer is PMMA, adhesion-promoting layer can be included between the PMMA and the substrate to ensure adequate bonding of the PMMA to the substrate. In an example, the substrate is a Si support substrate. In the absence of an adhesion-promoting layer, the vias patterned into the PMMA may distort. For example, the width of the vias in the PMMA may expand by a factor of about 5 to about 10 when the second polymer layer material is subjected to further processing. The coefficient of thermal expansion of PMMA is higher than polyimide or silicon; therefore it may undergo greater dimensions or volume changes than the polyimide or the silicon with temperature. As a result, portions of the structure may delaminate from the silicon substrate. In a non-limiting example, where the second polymer layer is a polyimide encapsulation layer, and the vias are formed in PMMA, curing the polyimide (e.g., at greater than 140° C., and more typically about 200-250° C.) can cause the change in dimension of the resulting anchors as compared to the original width of the vias. As a result, the anchors may not be formed with the intended dimensions. In a non-limiting example, the adhesion-promoting layer can be formed from hexamethyldisilazane (HMDS).
In an example where the second layer is cured at a higher temperature than the first layer, precautions can be taken to avoid out gassing, which can induce roughness in the encapsulating layer. For example, polyimide, which can be used to form the second polymer layer, cures at 250° C., whereas PMMA (which can be used to form the first layer) may be cured at a lower temperature, e.g., at 180° C. To avoid out-gassing of the first layer if a curing is performed on the second polymer layer, the first layer first may be cured at the cure temperature of the second polymer layer to evolve the more volatile components that may evaporate at the higher temperature. As a result, little or no out-gassing can occur from the first layer. There is less disturbance of the second polymer layer, creating an advantageously smoother surface for the deposition and patterning of electronic materials in the at least one electronic device layer 5. In another example, a slow ramped baking (e.g., about 100° C. per hour) from room temperature to the cure temperature of the second polymer layer (e.g., 250° C. for polyimide) also can improve the uniformity of the second polymer layer.
After any encapsulation, patterning, and isolation steps are complete in the fabrication, the first layer can then be removed using a selective etchant. The selective etchant is selected such that the other polymer materials in the structure are more resistant to the selective etchant than the first layer. As non-limiting examples, the selective etchant can be a solvent, a mixture of solvents, a plasma technique, or any other applicable technique in the art that can be used to selectively remove the first layer. For example, where the first layer is formed from PMMA, hot acetone may be used as the selective etchant to effectively separate the electronic structure from the substrate. In an example where the first layer is a silicon dioxide, the selective etchant can include hydroflouric acid. In an example where the first layer is a chromium, the selective etchant can include cerric ammonium nitrate. In an example where the first layer is a titanium, the selective etchant can include hydroflouric acid or hydrochloric acid. During the process for removing the first layer, the anchors are configured to remain substantially undisturbed and effectively hold the array of electronic structures in place relative to one another and to the substrate.
In an example, the structures can be subjected to a longer process for removing the first layer. For example, the structures may be left in a release bath for a long time the array of electronic structures being separated from the substrate or losing registration with the substrate. This process of preparing flexible electronics structures, which in an example includes stretchable electronics structures, is suited for subsequent transfer printing using any applicable technique in the art.
A second polymer layer (e.g., of an encapsulating polymer 300) can be applied to the structure. In an example, the second polymer material is applied to fill a number of the vias 201 and create anchors 302 (shown in
The vias 201 or anchors 302 may be in any two-dimensional geometry. For example, as shown in
The spacing of the vias 201 (or anchors 302) also can be selected based on the intended adhesive strength between the anchors 302 and the substrate 100. For example, the number and spacing of vias 201 (or anchors 302) can be selected to provide sufficient adhesive force to maintain the geometry of the array of electronic structures, and to substantially prevent distortion during removal of the first layer 101. In another example, the number and spacing of vias 201 (or anchors 302) is determined such that the total adhesive force of the anchors 302 does not impede separation of the array of electronic structures from the substrate 100. The pattern and placement of the vias 201 (or anchors 302) can depend on the geometry of the array of electronic structures. As a non-limiting example, the vias 201 (or anchors 302) may be placed along the pattern of interconnected device islands. In an example, the vias 201 (or anchors 302) may be spaced apart (i.e., have a pitch) by an average distance of between about 50 μm and about 1000 μm. In another example, the vias 201 (or anchors 302) may be spaced apart by an average distance of between about 0.2 μm and about 10000 μm.
In a non-limiting example, the vias 201 (or anchors 302) are cylindrical in shape, have a diameter of about 50 μm, and are spaced apart with spacing ranging from about 200 μm to about 800 μm.
As described above, an adhesion-promoting layer may be applied to ensure adequate bonding of the first layer 101 to the substrate 100. In an example where the first layer 101 is PMMA, the adhesion-promoting layer can be formed from a polymeric material. As a non-limiting example, the adhesion-promoting layer can be formed from hexamethyldisilazane (HMDS).
As described above, where the second polymer layer material 300 has a higher cure temperature than the first layer material 101, the first layer can be cured at the cure temperature of the second polymer layer material prior to application of the second polymer layer.
In an example, as shown in
In a non-limiting example, the at least one electronic device layer can include a metal, a semiconductor, a dielectric, a micro electro mechanical system (MEMS) component, and any other device component.
An oxide or polymer layer, such as layer 600 or layer 800, can be deposited prior to photolithographic patterning and etching, or other processing. The oxide or polymer layer helps to control the etch process and prevents over etching of the encapsulating regions of the electronic device layer, thus protecting the electronic devices and interconnects that are part of the electronic device layer.
As illustrated in
As shown in
As shown in
Once chemical access to the first layer is created, the selective etchant can act to remove remaining portions of the first layer. This results in cavities 1200 being formed beneath the electronic structure and exposing the anchors 302 (see
Transfer printing may be performed using any applicable technique in the art to separate the electronic structure described herein from the substrate after removal of the remaining portions of the first layer. In an example, the transfer printing can be performed using a removable medium, including an elastomeric stamp or cylinder, a selectively adhesive tape, or a tape that can be removed, after transfer, with an oxygen plasma etch, UV light, application of heat, or dissolving in a solvent or mixture of solvents (including water). In an example, regions of the electronic structure where large bulk areas of the polymer layer are in contact with the substrate may not be removed during a transfer process.
In an example, the transfer printing can be performed to transfer the arrays of the electronic structures from one substrate to another, e.g, from a carrier substrate to a final device substrate. For example, the arrays of the electronic structures may be fabricated on a rigid substrate and then transferred using transfer printing to a soft, flexible, and or stretchable substrate (including polydimethylsiloxane (PDMS,), ECOFLEX® (BASF Chemical Company, Florham Park, N.J.), or any other elastomer, rubber, plastic, fabric or polymer material). The transfer process may introduce additional defects (including breakage and incomplete transfer), resulting in low yield. The operation can be sensitive to differences in the adhesive forces between the array-to-stamp interface and the anchor-to-substrate interface. They may be difficult to accurately and consistently control. In addition, transferring the array from the stamp to the second (stretchable) substrate may require that the adhesive forces for the array-to-second substrate contact are greater than the forces at the array-to-stamp contact. The stamp-to-second substrate adhesive forces can be small enough to remove the stamp without damaging the second substrate. Covalent bonding forces may be used between a silicon dioxide layer on the array and an oxygen-terminated surface of the second (stretchable) substrate to obtain a strong bond for device mechanical durability. This process can result in the stamp becoming too strongly bonded to the second (stretchable) substrate, and as a result, removing the stamp can damage the array.
A removable medium can be used to separate the array of electronic structure from the support substrate. The removable medium can present a large adhesion force. For example, the removable medium to array adhesive forces can be greater than the pattern to substrate forces. Therefore, the removable medium can be used to separate the array from the substrate. In addition, where the removable medium is a water-dissolvable medium, it can be dissolved in water. Therefore, the second transfer process (i.e., from removable medium to ECOFLEX® substrate may not depend on any difference in forces whatsoever. In addition, if a strong bond (i.e., oxygen bonding as described above) is used for the second transfer process, the removable medium is removed easily and substantially without residue, using only water regardless of the strength of the removable medium to second substrate bond strength.
In a non-limiting example, the arrays of the electronic structures may be removed from the substrate using a removable medium. In an example, the removable medium may be a selectively adhesive tape, a tape that can be removed by exposure to UV light, with application of heat, using an oxygen plasma etch, or by dissolving in a solvent or mixture of solvents (including water). In an example, the removable medium may be an elastomeric stamp or cylinder. In an example, the removable medium is a water-dissolvable tape.
In an example, the electronic structures are separated from the substrate by applying a removable medium on a portion of the top layer of the electronic structure, and applying a force to the removable medium to separate the anchors of the electronic structure from the substrate. The removable medium can be selected such that its adhesion strength to the top layer of the electronic structure is greater than the adhesion strength of the anchors to the substrate.
A removable medium 1400 can be selected based on its adhesion characteristics for a specific layer material. For example, removable medium 1400 can be selected based on its adhesion characteristics such that the removable medium to electronic structure adhesion force is greater than the anchors to substrate force. The arrays of electronic structures 1303 may be removed from the substrate, and remain contacted with the removable medium 1400, without causing defects in the electronic devices of the electronic structure or causing breakage.
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In
A non-limiting example of a process for fabricating an electronic structure that is contacted to a substrate using anchors is as follows:
1 RCA clean silicon wafer
2 Spin coat PMMA sacrificial layer coating (˜100 nm)
3 Cure PMMA at 250° C.
4 Pattern PMMA
5 Spin coat PI to create posts in PMMA vias (˜10 μm)
6 Cure PI at 250° C.
7 Deposit Cr/Au (˜100 Å/5000 Å)
8 Spin coat photoresist (PR)
9 Soft bake PR
10 Expose PR using patterned mask of metal design
11 Develop PR
12 Rinse wafers
13 Etch gold in potassium iodide
14 Etch chromium in cerric ammonium nitrate
15 Rinse wafers in De-ionised Water (DIW)
16 Strip PR
17 Spin coat PI to encapsulate gold pattern (˜10 μm)
18 Cure PI at 250° C.
19 Deposit SiO2 hard mask layer (50-100 nm)
20 Spin PR
21 Softbake PR
22 Expose PR using patterned mask of PI encapsulation design
23 Develop PR
24 Rinse wafers in DIW
25 Etch SiO2 layer/PI exposed by PR pattern in CF4/O2 Reactive Ion Etch (RIE) respectively
26 Etch PMMA layer using hot acetone bath
27 Remove encapsulated metal from Si support by suitable transfer printing methods (e.g., Soft Lithography or tape)
Another non-limiting example of a process fabricate an electronic structure that is contacted to a substrate using anchors is as follows:
1 Clean rigid carrier substrate
2 Apply sacrificial layer material
3 Anneal sacrificial layer @T1 (where T1 is a cure temperature for a material in the electronic structure)
4 Pattern sacrificial layer to create vias to the substrate
5 Apply base layer polymer to create posts in sacrificial layer vias
6 Cure polymer layer @T1 or lower
7 Electronic processing (varying levels of complexity)
8 Apply top layer polymer to encapsulate electronics
9 Cure polymer layer @T1 or lower
10 Deposit masking material
11 Pattern masking material
12 Etch trenches to define device geometry and access sacrificial layer
13 Etch sacrificial layer using selective etchant that won't attack any of the device elements
14 Remove encapsulated electronic system from carrier substrate support by suitable transfer printing methods (e.g., soft Lithography or tape)
Any other applicable technique may be employed to fabricate a device according to the principles described herein.
While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
The above-described embodiments of the invention can be implemented in any of numerous ways. For example, some embodiments may be implemented using hardware, software or a combination thereof. When any aspect of an embodiment is implemented at least in part in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.
In this respect, various aspects of the invention may be embodied at least in part as a computer readable storage medium (or multiple computer readable storage media) (e.g., a computer memory, one or more floppy disks, compact disks, optical disks, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium or non-transitory medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the technology described above. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present technology as described above.
The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of the present technology as described above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present technology need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present technology.
Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.
Also, the technology described herein may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.
As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.
This application is a continuation of U.S. patent application Ser. No. 13/481,843, filed May 27, 2012, which claims priority to and the benefit of U.S. Provisional Application No. 61/490,826, filed on May 27, 2011, entitled “METHODS FOR FABRICATING ELECTRONIC, OPTICAL AND/OR MECHANICAL APPARATUS AND SYSTEMS” both of which are incorporated herein by reference in their entireties.
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| Number | Date | Country | |
|---|---|---|---|
| 20150342036 A1 | Nov 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61490826 | May 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13481843 | May 2012 | US |
| Child | 14819040 | US |
