Patent Application
20230049337
The improvements generally relate to electronic circuits and more particularly relate to electronic circuits comprising graphene oxide paper.
Graphene oxide (GO) paper is a material consisting of superposed layers of oxidized graphene. In terms of physical properties, GO paper is a material generally known as exhibiting high ultimate tensile strength, high stiffness, low mass density, and high visco-elastic damping. Thanks to its oxidized composition, GO paper is also a highly insulating dielectric material. Thin layers of GO have been considered as additive layers atop electronic circuit substrates. In some studies, a polymer piece is used as a structural support to such thin layers of GO to form an electronic circuit substrate with GO as a constituent element. Although such polymer supported GO electronic circuit substrates have been found to be satisfactory to a certain degree, there remains room for improvement.
It was found that there was an incentive in the electronic circuit industry to benefit from the above-mentioned desirable physical properties of GO paper while avoiding the use of a structural, supporting polymer piece. For instance, as the thin layer of GO is supported on the polymer piece, recovery of the GO, conductive trace(s) and/or electronic component(s) has been found to be difficult and even impossible in at least some situations.
In an aspect, there is thus described a GO paper-based electronic circuit substrate allowing convenient recovery and re-use of the GO paper, the conductive trace(s) and/or the electronic component(s). More specifically, it was found that by providing a GO paper substrate having a structural thickness, the supporting polymer piece can be omitted, thereby allowing recovery of any of the components of the electronic circuit after its lifetime.
In accordance with a first aspect of the present disclosure, there is provided a method of recovering parts of an electronic circuit having a self-supporting substrate having graphene oxide (GO) paper and at least a conductive trace on said self-supporting substrate, the method comprising: immersing said electronic circuit into an environment-friendly solvent, said GO paper thereby dissociating from said conductive trace; and recovering at least one of said conductive trace and said GO paper from said environment-friendly solvent.
Further in accordance with the first aspect of the present disclosure, said immersing said electronic circuit into an environment-friendly solvent can for example comprise immersing said electronic circuit into water.
Still further in accordance with the first aspect of the present disclosure, said immersing can for example comprise said conductive trace settling to a bottom layer of said environment-friendly solvent and said GO paper forming a suspension within an upper layer of said environment-friendly solvent.
Still further in accordance with the first aspect of the present disclosure, said recovering can for example comprise isolating said top layer and said bottom layer from one another and removing said at least one of said conductive trace and said GO paper from said environment-friendly solvent.
Still further in accordance with the first aspect of the present disclosure, said recovering can for example comprise evaporating said environment-friendly solvent.
Still further in accordance with the first aspect of the present disclosure, said method can for example further comprise fabricating another electronic circuit using said recovered at least one of said conductive trace and said GO paper.
In accordance with a second aspect of the present disclosure, there is provided an electronic circuit comprising: a self-supporting substrate having GO paper with a structural thickness being equal or above a given thickness threshold; and at least a conductive trace on said self-supporting substrate.
Further in accordance with the second aspect of the present disclosure, said given thickness threshold can for example be at least 10 μm.
Still further in accordance with the second aspect of the present disclosure, said given thickness threshold can for example be at least 30 μm.
Still further in accordance with the second aspect of the present disclosure, said structural thickness can for example range between 10 μm and 3000 μm.
Still further in accordance with the second aspect of the present disclosure, said structural thickness can for example range between 30 μm and 300 μm.
Still further in accordance with the second aspect of the present disclosure, said conductive trace can for example be made of reduced graphene oxide (rGO).
Still further in accordance with the second aspect of the present disclosure, said conductive trace can for example be dissociable from said GO paper upon immersing said electronic circuit into an environment-friendly solvent.
In accordance with a third aspect of the present disclosure, there is provided a substrate for an electronic circuit, said substrate comprising: a self-supporting substrate having GO paper with a structural thickness being equal or above a given thickness threshold.
Further in accordance with the third aspect of the present disclosure, said given thickness threshold can for example be at least 10 μm.
Still further in accordance with the third aspect of the present disclosure, said given thickness threshold can for example be at least 30 μm.
Still further in accordance with the third aspect of the present disclosure, said structural thickness can for example range between 10 μm and 3000 μm.
Still further in accordance with the third aspect of the present disclosure, said structural thickness can for example range between 30 μm and 300 μm.
Still further in accordance with the third aspect of the present disclosure, said GO paper can for example be solvable in an environment-friendly solvent. In accordance with a fourth aspect of the present disclosure, there is provided a use of GO paper as a substrate for an electronic circuit, said substrate having said GO paper with a structural thickness being equal or above a given thickness threshold.
In accordance with a fifth aspect of the present disclosure, there is provided a method of manufacturing an electronic circuit, the method comprising: forming a self-supporting substrate of graphene oxide (GO) paper; and reducing the oxygen content of portions of said GO in one or more predetermined patterns to form one or more conductive traces running on said self-supporting substrate.
Further in accordance with the fifth aspect of the present disclosure, said reducing can for example comprise chemical reduction step(s), thermal reduction step(s), photoreduction step(s), or any combination thereof.
Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.
In the Figures,
As best seen in
As best seen in
Discrete electronic components can be soldered, or bonded on to the self-supporting substrate 100 using conductive adhesives in some embodiments. The ensemble combines the functionality of the discrete electronic components and integrated conductive traces with the functionality of the self-supporting substrate to create electronic circuits with greater functionality than the individual electronic components.
It is intended that the conductive trace(s) 106, and thereby any electronic component(s), are dissociable from the GO paper 102 upon immersion into an environment-friendly solvent, such as tap water, water with electrolytes, any other suitable inorganic solvents, and/or any other suitable organic solvents, thanks to an advantageous chemical property of the GO paper 102. Accordingly, the electronic circuit 104 can be separated into its fundamental components in a rather straightforward and eco-friendly manner. The temperature of the environment-friendly solvent can impact the rate at which the conductive trace(s) 106 and/or electronic component(s) may dissociate from the GO paper 102. For instance, in an experiment performed using tap water, the warmer the tap water was, the quicker the dissolution step could be performed. For instance, warm tap water at a temperature of about 69 degrees Celsius was found to be satisfactory to achieve a convenient dissolution rate. As such, there is described a method of recovering parts of the electronic circuit 104. More specifically, there is described a method of recovering the GO paper 102, the conductive trace(s) 106 and/or the electronic component(s), if any, from the electronic circuit 104. As shown in
As shown in the specific embodiment of
As will be described below, the conductive traces 106 can be made of metal, selectively reduced GO, or a combination thereof.
In embodiments where at least some of the conductive traces 106 are metallic, metal can be printed, deposited or otherwise mounted to the self-supporting substrate 100 in any satisfactory manner. Examples of such metals can include, but not limited to, Cu, Au, Ag, Pd and the like.
In embodiments where at least some of the conductive traces 106 are made of reduced GO (rGO), regions of the self-supporting substrate 100 can be selectively reduced (with reduced oxygen content than in GO) via selective area reduction (SAR), thereby rendering the regions of the GO paper 102 electrically conductive. Such an electronic circuit is referred to as a GO and rGO assembly in the following paragraphs. Such an assembly can be said to be monolithic as it consists only of unreduced and reduced graphene oxide. SAR can be used not only to form some of the conductive traces 106 but also to form a number of electronic components such as interconnects, capacitors, inductors, resistors, transmission lines, waveguides and antennas in some embodiments. The reduction of GO entails the removal of oxygen containing functional groups to partially or wholly recover the hexagonal lattice structure of graphene. Techniques to reduce regions of the GO paper 102 can vary from one embodiment to another. For instance, examples of such reduction can include, but not limited to, optical reduction, thermal reduction, electrical reduction, chemical reduction, any other suitable existing reduction technique, or a combination thereof.
For instance, chemical reduction is a method of reduction that relies on chemical reducing agents to eliminate oxygen functional groups. The functional groups containing oxygen react more readily with the reducing agents, creating free molecular species containing elements from the functional group. There are a wide variety of reducing agents that can be utilized. Selection of reducing agent often amounts to which functional group is targeted for removal. Certain reducing agents react more readily with one species of functional group than others. For example, borohydrides will more often reduce carbonyl functional groups. In this way, chemical selective reduction entails removing only particular functional groups. Other chemical reducing agents include aluminum hydrides, hydrohalic acids, alcohols, metals acids and even microorganisms, such as baker's yeast.
Thermal reduction is a method of reduction that relies on heating the GO sample under carbon-inert atmospheric conditions (e.g. ultra-high vacuum, argon, ammonia) to inhibit formation of new functional groups. Thermal reduction, unlike chemical reduction, allows for a higher degree of control over the final carbon to oxygen (C/O) ratio of the resulting rGO. The primary mechanism behind thermal reduction of GO is the dissociation of functional group with thermal energy elevated above that at room temperature.
Photoreduction is a method of reduction that uses electromagnetic radiation, most often in the ultra-violet, visible, and/or infra-red spectral regions, to eliminate functional groups. This method of reduction is often hailed as ‘green’ due to its lack of chemical agents and it's speed. The microscopic mechanisms in the process of photoreduction vary depending on the conditions of reduction. Mechanisms include solvated electron interactions and thermal reduction induced by optical energy transfer. Examples of photoreduction include, but are not limited to, laser lithography, flash lamp exposure and microwave exposure.
Hybrid reduction is a method of reduction referring to processes wherein a combination of two or more of the reduction methods listed above are combined.
Such monolithic GO and rGO assemblies can be designed to operate from DC through to radio frequency and microwave frequency bands. Monolithic construction can ease fabrication of a wide array of components on a single self-supporting substrate with a single material system. Such GO and rGO assemblies can be thin and flexible, yet mechanically robust. The GO and rGO assemblies can comprise earth abundant elements, primarily carbon, oxygen, and hydrogen in some embodiments. The physical properties of the above-described GO and rGO assembly, such as Young's modulus, ultimate tensile strength, electrical conductivity, can be tuned during the manufacturing process by physical and chemical means. In some embodiments, the GO and rGO assembly can be manufactured using aqueous processing methods, planar manufacturing methods, lamination methods, and/or roll-to-roll processes.
As described above, there can be environmental benefits of using such GO and rGO assemblies. As the GO paper 102 can be dissolved in water, the electronic components and the conductive traces 106 previously mounted to the self-supporting substrate 100 can be recovered at the end-of-life, which can greatly reduce cost and complexity of the disassembly process. The GO paper 102 generally degrades within the water to produce humic acid, which are large organic fragments that are weakly acidic. Natural humic acid is a component of humus, which is the primary constituent of peat bogs. The rGO of the GO/rGO assembly is itself a form of graphitic powder, as can be found in naturally occurring graphite ore deposits. The end-of-life products of GO and rGO assemblies are thus benign forms of earth abundant elements that can be recovered and processed without recourse to chemical processes that cause environmental and health risks such as highly hazardous acidic solvents.
Although an electronic circuit solely composed of GO and rGO has yet to be demonstrated, there are no apparent scientifically sound counter-indications why it would not work. Indeed, the rational basis supporting this hypothesis lies in that i) selective reduction techniques to reduce GO into reduced rGO are known in the art, and ii) reduced GO is known in the art to be electrically conductive. Accordingly, it is safe to assume that an electronic circuit having a self-supporting substrate having GO paper, and reduced GO provided in the form of traces could be functional. Further support was made in an experiment where laser-induced photoreduction was used to form conductive rGO traces. In this experiment, Ohmic resistivity measurements showed that the electrical resistivity of the resulting rGO traces was at least six orders of magnitude lower than the electrical resistivity of the surrounding unreduced GO paper, which is indicative that the rGO is conductive. In this experiment, although a 1064 nm, 25 W, YVO4 laser was used to laser-mark the rGO traces, it is believed that other suitable laser systems can be used. Moreover, X-ray photoelectron spectroscopy (XPS) measurements were performed both on the GO paper and on the laser-induced reduced GO traces. The RPX measurements showed that the relative carbon content increased in the laser-induced reduced GO traces as compare to GO paper, and that the relative oxygen content was considerably decreased in the laser-induced reduced GO traces. The lower oxygen content of the reduced GO traces shows that the laser-induced reduction technique reduced the amount of oxygen content in the GO paper, further indicating that the traces are electrically conductive rGO. More specifically, measurements of reduction was obtained by analyzing the C 1s XPS spectrum of the reduced surface. For this experiment the XPS spectrum was obtained using the K-Alpha XPS System. Results from the XPS analysis confirmed reduction occurred as the amount of oxygen on the remaining surfaces had been more than halved in the ablation process. The carbon-to-oxygen (C/O) ratio of the original GO was 0.88 and the C/O ratio of the resulting rGO was 2.31. XPS analysis of the spaces between these reduced areas revealed a lower C/O ratio of 0.91, proving that they were unreduced. Four-point measurements carried out on independent ones of the reduced GO traces yielded large resistances beyond measurement limits, thus proving that the discrete reduced structures of the matrix cells were electrically isolated from each other. Since XPS analysis was able to resolve differences in C/O ratio between reduced and unreduced areas, the depth of reduction could be inferred to be greater than the 2-5 nm depth of penetration for XPS in this specific experiment. These results independently show promise of optical reduction as a viable technique for reducing circuit patterns into GO wafers for printed circuit applications.
A reduction technique may include a combination of reduction steps or methods. For example, a first step of optical SAR can be used to define an rGO electrode array on opposite sides of a GO self-supporting substrate, followed by electrical stimulus applied to selected ones of the rGO electrodes across opposite sides of the GO self-supporting substrate to selectively reduce contacts between electrodes.
As can be understood, one or more electronic circuits as the ones described herein can be connected, superposed, stacked, integrated in any manner, shape or form that is best suited for a given application. A wide variation in functionality, ease of manufacture, and ease of recovery at the end of life can be achieved with variants of the proto-typical rGO and GO assemblies described herein. Further complexity can be achieved with multi-layer assemblies, whereby multiple GO and rGO assemblies are laminated together to realize more complex functionalities with a higher degree of interconnectivity. Lamination can be achieved by bonding with adhesives, or by the process of wetting and drying to effect bonding of GO paper layers one to another. Such GO and rGO assemblies can be used to realize capacitors, mutual inductors or analogs of multi-layer PCBs.
More specifically, in this example, the conductive traces including the conductive rows and columns 506a and 506b are made of rGO. It can be understood that resistance of the GO region 532 between an rGO row 506a and an rGO column 506b can be modulated by electrical stimulation to produce a GO/rGO region of variable electrical resistance, thus forming the memory element 534 therebetween. More specifically, electrical stimulation of two conductive traces selected from a crossed array of grid electrodes on obverse sides of a GO substrate can reduce the resistance between two conductive traces. The amplitude and duration of electrical stimulation can be used to tune the degree of GO reduction, and the resulting resistance between electrodes in the cross-bar array. Operated in analog mode, such a cross-bar array can be used for weighted response in neural network architectures where reinforcement learning is implement directly by electrical or electro-thermal reduction of GO between electrically activated electrodes. Operated in digital mode, such a cross-bar array can be used as a programmable digital memory device, where each intersection in the cross-bar array contains either highly resistive GO or highly conductive rGO, as determined by the application of electrical stimulus in an initial programming phase.
Accordingly, a scanning laser can be used to either create the rGO electrically conductive trace 606 or an etched hole or groove 636 by tuning the laser power, wavelength and exposure duration. Combining both methods can allow the fabrication of electromechanical structures such as a cantilever. Moreover, electronic circuits having a pattern of SAR and material processing (e.g., cutting) can be envisaged to form electromechanical elements including but not limited to electrostatically actuated elements and electrostatic transducers. By use of a laser scanning system with control over the directed output power, one may alternatively cut and reduce a GO substrate into a GO/rGO electromechanical device, with elements such as interdigitated comb structures that can be used for both actuation of mechanical motion with electrical stimulation, and transduction of mechanical motion into electrical signals. Such devices can be used for force sensing, acceleration measurement, liquid level measurement, pressure measurement, acoustic measurement, magnetic field measurement and any other sensor that is based on electromechanical coupling to transduce the stimulus being sensed into an electrical signal.
Optical detectors can be manufactured as well. For instance, the illumination of a self-supporting substrate having GO paper by optical radiation will cause SAR to occur with a spatial pattern corresponding to the spatial distribution of the optical radiation source. The optical dose delivered can be measured by monitoring, through electrical or optical means, the reduction of GO to rGO. In its simplest form, the reduction of GO by laser exposure can reveal itself through the different visual appearance of rGO (highly reflective of light) versus GO (highly absorptive of light), such that the GO substrate acts as a dosimeter.
Conventional wafer fabrication procedure was used to fabricate the GO wafer for this experiment. To manufacture the conductive section of the CPW, electron beam metal vapor deposition was used. Nickel was chosen as the conductor primarily because it has a lower sublimation temperature compared to copper and gold, while having a comparable conductivity (within the same order of magnitude). Using a metal with a lower sublimation temperature reduced the risk of accidentally reducing the GO substrate during the metal deposition process. Other reasons for choosing nickel included its low cost and availability.
A vector network analyzer (VNA) with the measurement frequency range of 100 MHz to 1.8 GHz, was used to measure the scattering parameters (S-parameters) of the transmissive CPW structure shown in
The resulting S-parameters are plotted by magnitude and phase in
The measured S-parameters were converted to RLGC transmission line parameters (including Z0, the characteristic impedance and γ, the complex propagation constant) using conventional techniques. Here, R is the conductor resistance per unit length, L is the inductance per unit length, G is the insulator conductance per unit length and C is the capacitance per unit length for the transmission line in an infinitesimal lumped element model.
The qualitative behaviours of both the complex characteristic impedance curve and the complex propagation constant as functions of frequency is what one would typically expect of CPW transmission lines. The magnitude of characteristic impedance of CPW transmission lines tend to decrease as frequency increases. In the case of the complex propagation constant (γ), the phase constant exhibits a linear trend, while the attenuation constant exhibits logarithmic growth and approaches a constant at higher frequencies.
The quantitative analyses pertinent to this study are those concerning loss and thus, the attenuation constant (α=Re{γ}). α is a measure of loss in strength of electromagnetic power propagating through a transmission line. It is a sum different loss mechanisms, most importantly: losses within the conductor (αc), and losses due to the dielectric (αd)
The total attenuation constant is low, reaching a value below 2 dB/cm. Secondarily important is the phase constant, β=Im{γ}, which is a measure of the change in phase versus distance of an EM wave propagating through a transmission line.
In the lumped circuit model for transmission lines, the per-unit length resistance generates resistive losses in the conductor, while the per-unit length conductance generates conductive losses in the dielectric. In the low loss limit, the ratios R/ωL and G/ωC are small compared to 1. Multiplying out the terms in the right-most square root in equation 5 and ignoring the term RG/ω2LC because it is small, the complex propagation constant can be approximated by:
The ratio R/L is the attenuation caused by the conductor, while G/C is proportional to the attenuation from the dielectric. As is readily evident in
As can be understood, the examples described above and illustrated are intended to be exemplary only. In some embodiments, the GO paper is made solely of oxidized graphene layers. In some embodiments, the GO paper can include at least 50% of oxidized graphene layers, with the remaining comprising oxidized graphene composite layers. The scope is indicated by the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2021/050066 | 1/22/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62964903 | Jan 2020 | US |
