DESC:FIELD OF INVENTION
[0001] The present invention relates to a field of heat management in the electronic industry. In particular, the present invention pertains to a graphene-based fast heat spreader for electronic applications addressing the challenge of rapid heat spreading in miniaturized electronic systems.

BACKGROUND
[0002] Next-generation electronic systems like tablets, laptops, phones, Micro-UAVs, integrated power converters, power electronics, and a variety of handheld computing platforms are constantly evolving, demanding aggressive scaling in size and efficient thermal management. The need for efficient thermal management is becoming increasingly pressing for both commercial (cell phones, laptops, data centers, etc.) and strategic electronic systems. Traditional engineering design practices are reaching their limits, as thermal management and heat spreading across the system contribute significantly to its size and weight.
[0003] The current approach to thermal management involves the use of graphite sheets, which have a limited thermal conductivity of around 1800 W/mK. However, in practical applications, the achieved thermal conductivity of composite graphite is typically only around 900-1200 W/mK. To overcome the limitations of conventional thermal management methods, there is a need to explore advanced materials such as graphene, which offers a much higher thermal conductivity of over 5000 W/mK.
[0004] Graphene’s exceptional thermal conductivity stems from its long mean free path (MFP) of acoustic phonons. The strong C-C bonds in graphene contribute to high acoustic phonon speed and a high phonon dispersion slope near the G-point (shown in FIG. 1), enabling phonon transport over long distances without significant scattering. Additionally, the absence of an energy gap between acoustic and optical phonons facilitates thermal exchange and the spreading of excess heat generated at hotspots.
[0005] While graphene has the potential to be an excellent heat spreader, a major challenge lies in efficiently removing excess heat from hotspots within electronic systems. Typically, these hotspots are metal lines (shown in FIGs. 2a-c) in the form of electrical or thermal vias. However, the cross-plane thermal conductivity between metal and graphene is poor, limiting overall heat spreading. This bottleneck is primarily due to the weak thermal coupling between graphene and metal caused by the lack of interplanar acoustic phonons.
[0006] There is, therefore, a need for a graphene-based fast heat spreader for electronic applications to enhance the cross-plane thermal coupling between metal and graphene.

SUMMARY
[0007] The present invention provides a unique solution called orbital overlap engineering. This engineering method enhances the thermal coupling between graphene and the metal, resulting in improved heat transfer. As a result, the temperature of generated hotspots is reduced by approximately 2.2 times, and the thermal decay time constant is improved by approximately 1.78 times. Furthermore, this engineering method allows for the fast spreading of heat, effectively removing generated hotspots. This invention offers a graphene-based fast heat spreader that can be utilized in modern electronic applications, addressing the need for efficient heat management in miniaturized electronic systems.

BRIEF DESCRIPTION OF DRAWINGS
[0008] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0009] FIG. 1 illustrates phonon band structure of graphene calculated using QuantumATK computational package (prior-art), in accordance with an embodiment of the present disclosure;
[0010] FIG. 2 is a schematic of a) graphene/h-BN stack (alternative layers of graphene and hBN), b) the graphene/h-BN stack integrated over a semiconductor chip for heat spreading application, and c) graphene/hBN heat spreader, heat to be taken out from the hotspots (encircled) of the thermal via (metal) line of an electronic system into graphene and spread to the sink through high thermal conductive graphene/hBN path (prior-art), in accordance with an embodiment of the present disclosure;
[0011] FIG. 3 illustrates a) schematic of line heater over graphene, b) heater with pointed spots to generate a hotspot, c) and d) are fabricated line and point heaters on patterned graphene over SiO2, in accordance with an embodiment of the present disclosure;
[0012] FIG. 4 illustrates thermal images of line heater on a) Sio2, b) full coverage graphene (over SiO2), and c) patterned graphene (over SiO2), d) thermal cross section temperature taken along the white dashed lines, in accordance with an embodiment of the present disclosure;
[0013] FIG. 5 illustrates hot spot temperature of the line heater on patterned graphene over SiO2, in accordance with an embodiment of the present disclosure; and
[0014] FIG. 6 illustrates a) steady state hotspot comparison of the heater over patterned graphene with and without contact engineering (CE); Transient measurements with heating time b) 1µs and c) 500ns; and d) comparison of thermal decay time constant in all condition, in accordance with an embodiment of the present disclosure.
[0015] FIG. 7 illustrates a block diagram illustrating a benefit of using a graphene-based heat spreader in heat removal, in accordance with an embodiment of the present disclosure.
[0016] FIG. 8A illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on the substrate, in accordance with an embodiment of the present disclosure.
[0017] FIG. 8B illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on and above, in accordance with an embodiment of the present disclosure.
[0018] FIG. 9A illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on the substrate and the device is connected to a heat sink, in accordance with an embodiment of the present disclosure.
[0019] FIG. 9B illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on the substrate and the device is connected to a heat sink at multiple locations, in accordance with an embodiment of the present disclosure.
[0020] FIG. 10 illustrates a flowchart for a method for forming a heat spreader to reduce temperature in an electronic device, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0021] The present invention provides a unique solution called orbital overlap engineering. This engineering method enhances the thermal coupling between graphene and the metal, resulting in improved heat transfer. As a result, the temperature of generated hotspots is reduced by approximately 2.2 times, and the thermal decay time constant is improved by approximately 1.78 times. Furthermore, this engineering method allows for the fast spreading of heat, effectively removing generated hotspots. This invention offers a graphene-based fast heat spreader that can be utilized in modern electronic applications, addressing the need for efficient heat management in miniaturized electronic systems.
[0022] In an aspect, the invention discloses a graphene-based heat spreader including micro-heaters of uniform heating lines fabricated on SiO2 substrate, patterned graphene on SiO2, or full coverage graphene on SiO2; wherein the micro-heaters include pointed heating lines fabricated on SiO2, patterned graphene on SiO2, or full coverage graphene on SiO2.
[0023] In various embodiments, characterization and investigation of the graphene-based heat spreader is carried out by subjecting graphene to vacancy engineering using a standard O2 plasma process, with varying exposure time (dose), to enhance thermal properties.
[0024] In certain embodiment, the invention discloses graphene/hBN based heat spreader and vacancy engineering is applied to carry out characterization and investigation of the graphene/hBN based heat spreader.
[0025] In some embodiments, the invention discloses a graphene/hBN based heat spreader using vacancy engineering to improve thermal transport properties, and characterization and investigation of the graphene/hBN based heat spreader.
[0026] In some embodiments, the invention discloses a vacancy engineering assisted thermal coupling enhancement between other metals and 2D materials, such as, without limitations, transition metal dichalcogenides, phosphorene etc., and their heterostructures. In one embodiment, the other metals are selected from a group consisting of gold, nickel, chromium, platinum, aluminium, palladium, and titanium, without limitations. In various embodiments, nanoscale time and spatial thermal characterizations are performed using a Microsanj NT 220 thermos-reflectance setup, based on the dependency of material reflectivity on temperature.
[0027] In various embodiment, nanoscale time and spatial thermal characterizations were performed using a Microsanj NT 220 thermos-reflectance setup, based on the dependency of material reflectivity on temperature.
[0028] In various embodiment, reflectance and temperature change are modelled using the equation ?R/R = Cth* ?T/T, where ?R/R represents the fractional change in reflectance, ?T/T represents the fractional change in temperature, and Cth is the calibrated thermal coefficient.
[0029] In various embodiment, calibration of the thermal coefficient (Cth) is conducted by mounting the sample on a controlled heater and determining the optimum wavelength for calibration purposes.
[0030] In one embodiment, the vacancy engineering of graphene is performed using an O2 plasma process with varying exposure time (dose) to create carbon vacancies and enhance the thermal properties of the graphene layer. During the O2 plasma process, graphene is subjected to a controlled exposure of oxygen plasma. The exposure time, or dose, is varied to achieve the desired level of vacancy creation. The plasma interacts with the carbon atoms in the graphene lattice, leading to the removal of some carbon atoms and the creation of vacancies. The created carbon vacancies within the graphene lattice have a significant impact on its thermal properties. The graphene’s exceptional thermal conductivity is mainly due to the long mean free path of acoustic phonons, which can travel long distances without significant scattering. The presence of carbon vacancies introduces scattering sites for acoustic phonons, which enhances their interaction and improves thermal transport within the graphene layer. By engineering the vacancies in the graphene layer, the thermal properties of graphene can be further optimized. The increased scattering of acoustic phonons due to carbon vacancies allows for more efficient thermal exchange and heat spreading. This, in turn, enhances the overall thermal management capabilities of the graphene-based heat spreader. The use of an O2 plasma process and varying exposure time provide control over the density and distribution of carbon vacancies within the graphene layer. This allows for fine-tuning of the thermal properties to suit the specific requirements of the heat spreading application.
[0031] In such embodiment, the nanoscale time and spatial thermal characterizations are performed using a Microsanj NT 220 thermos-reflectance setup, which measures the reflectivity change of the material to determine temperature variations with high spatial resolution. The thermos-reflectance technique is employed in this setup to analyze thermal characteristics at the nanoscale. It is based on the principle that the reflectivity of a material changes with temperature. By measuring the reflectivity change, it is possible to determine the corresponding temperature change in the material. The Microsanj NT 220 setup consists of a specialized microscope with a high-resolution imaging system. It is equipped with a sensitive detector that can detect minute changes in reflectivity. The setup is capable of capturing images and recording the reflected light intensity from the sample surface. To perform the nanoscale thermal characterizations, the sample, which includes the graphene-based heat spreader, is mounted on the Microsanj NT 220 setup. The setup then directs a controlled beam of light onto the sample surface. As the sample heats up, its reflectivity changes, which is detected by the setup's sensitive detector. By analyzing the changes in reflectivity, the Microsanj NT 220 setup can determine the corresponding temperature variations at a nanoscale resolution. This allows for precise mapping of temperature distribution across the sample surface, enabling the characterization of thermal behavior with high spatial resolution. The nanoscale time and spatial thermal characterizations using the Microsanj NT 220 setup provide valuable insights into the heat transfer dynamics of the graphene-based heat spreader. It allows researchers to understand how heat is distributed and dissipated within the material, identify potential hotspots, and optimize the design and performance of the heat spreader.
[0032] In such embodiment, the reflectance and temperature change are modelled using the equation ?R/R = Cth* ?T/T, where ?R/R represents the fractional change in reflectance, ?T/T represents the fractional change in temperature, and Cth is the calibrated thermal coefficient specific to the graphene material and wavelength used. Reflectance refers to the amount of light reflected by a material's surface. As the temperature of the material changes, there can be a corresponding change in its reflectance. By measuring the reflectance change, it is possible to indirectly determine the temperature change in the material. The equation ?R/R = Cth* ?T/T is used to model this relationship. ?R/R represents the fractional change in reflectance, which is the difference between the initial reflectance (R) and the reflectance at a given temperature change (?R), divided by the initial reflectance (R). ?T/T represents the fractional change in temperature, calculated by dividing the temperature change (?T) by the initial temperature (T). The thermal coefficient, Cth, is a calibrated value specific to the graphene material and the wavelength used for the measurements. It represents the relationship between the fractional change in reflectance and the fractional change in temperature for the specific material and wavelength. By calibrating Cth for the graphene material and the chosen wavelength, the equation can accurately model the reflectance change as a function of temperature change. This allows for the quantification of temperature variations based on reflectance measurements. The model based on this equation enables researchers to understand the thermal behavior of the graphene-based heat spreader. By measuring the reflectance change and applying the equation, they can determine the corresponding temperature changes within the material. This information is crucial for evaluating the effectiveness of the heat spreader and optimizing its thermal management capabilities.
[0033] In one embodiment, the thermal coefficient (Cth) is calibrated by mounting the sample on a controlled heater and determining the optimum wavelength that provides accurate calibration values for subsequent investigations. The controlled heater allows for precise control of the sample's temperature. By raising the temperature of the sample to known values, the relationship between the temperature change and the corresponding reflectance change can be established. This calibration process helps determine the specific thermal coefficient, Cth, for the graphene material used in the heat spreader. During the calibration process, different wavelengths of light are directed onto the sample surface. The reflectance change at each wavelength is measured and compared to the known temperature change. By analyzing the data, researchers can identify the wavelength that provides the most accurate and reliable calibration values. The optimum wavelength is selected based on several factors, including the sensitivity of the reflectance measurement system, the stability and repeatability of the calibration values, and the ability to accurately capture temperature variations. The wavelength that yields the most consistent and accurate results is chosen for subsequent investigations. Once the optimum wavelength is determined, the calibration values obtained are used to calculate the thermal coefficient, Cth, specific to the graphene material and the selected wavelength. This coefficient represents the relationship between the fractional change in reflectance and the fractional change in temperature for the material. By calibrating Cth through this process, researchers ensure that subsequent investigations and measurements involving the graphene-based heat spreader are accurate and reliable. The calibrated thermal coefficient allows for the precise determination of temperature variations based on reflectance measurements and contributes to a better understanding of the thermal behavior and performance of the heat spreader.
[0034] In various embodiment, the heat spreader effectively dissipates excess heat generated by micro-heaters, thereby enhancing heat management in electronic systems and reducing the temperature of hotspots. In electronic systems, such as integrated circuits or microprocessors, heat is generated as a by-product of their operation. This heat can lead to temperature increases, particularly in localized areas known as hotspots. If left unmanaged, these hotspots can negatively impact the performance and reliability of the electronic components. The graphene-based heat spreader plays a crucial role in managing this excess heat. It is designed to efficiently conduct and spread the heat away from the hotspots, thereby reducing their temperature. By doing so, the heat spreader helps prevent the hotspots from reaching critical temperatures that could cause device failure or performance degradation. The graphene, with its exceptional thermal conductivity properties, is an ideal material for a heat spreader. It can rapidly conduct heat across its surface, allowing for efficient heat dissipation. The vacancy engineering process used in creating the graphene-based heat spreader further enhances its thermal properties, making it even more effective in heat management. By effectively dissipating excess heat, the graphene-based heat spreader helps maintain lower and more uniform temperatures across the electronic system. This improves the overall thermal management of the system, preventing localized hotspots from forming and ensuring that the electronic components operate within safe temperature limits.
EXAMPLES
[0035] The present invention is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
Example 1
Fabrication of micro-heaters
[0036] Micro-heaters of uniform (FIG. 3a and 3c) and pointed heating lines (FIG. 3b and 3d) are fabricated. For detailed analysis, the heaters were fabricated on SiO2, patterned graphene on SiO2, and full coverage graphene on SiO2. Vacancy engineering was done in graphene using a standard O2 plasma process according to Meersha, et al., 2016, with varying exposure time (dose). The nanoscale time and spatial thermal characterizations were done using the Microsanj NT 220 thermos-reflectance setup. The characterization method is based on the dependency of the reflectivity of material with temperature. The reflectance and temperature change can be modeled for short-range temperature change as ?R/R = Cth* ?T/T according to Pavlidis et al., 2018, and Chaudhuri et al., 2021. Where ?R/R and ?T/T are fractional changes in reflectance and temperature, respectively. The Cth is the thermal coefficient that needs to be calibrated for a particular material and wavelength. The Sample was mounted on a controlled heater to calibrate and determine Cth for optimum wavelength. After calibration, the same wavelength with calibrated Cth values was used for further investigations. All the discussed temperature in the work is with respect to room temperature as a base.
[0037] FIG. 3 illustrates schematic of a) line heater over graphene, b) Pointed heater to generate a hotspot, c) and d) are the optical images of the fabricated line and point heaters on patterned graphene over SiO2, in accordance with an embodiment of the present disclosure. The heater can be driven through current /voltage as shown in the arrow path and generated heat flows towards patterned graphene.
Example 2
Graphene-metal cross-plane thermal coupling testing
[0038] The investigation begins with patterning line heaters on SiO2, and graphene over SiO2 to explore the heat spreading capability of graphene on different substrates. The line heaters reflect uniform heating under the same input power in both cases as expected (FIG. 4a and 4b). However, both heater shows comparable temperatures (~40 oC) under same input power. In fact, the thermal conductivity of graphene is very high ( >3000 W/m-K) than SiO2 (~1 W/m-K ). Thus, the heater on graphene should be colder than on SiO2. The possible cause of the anomalous behavior is due to less cross-plane thermal conductivity of metal-graphene than metal-SiO2.
[0039] Moving forward, the graphene was patterned to change the heat-spreading path (FIG. 4c), as the device shown in FIG. 3c. Interestingly, the metal region over graphene shows a higher temperature (~ 70 oC) than metal over SiO2, which further confirms graphene’s lower thermal spreading capability despite its high thermal conductivity.
[0040] FIG. 4 illustrates thermal images of line heater on a) Sio2, b) full coverage graphene (over SiO2), and c) patterned graphene (over SiO2), d) thermal cross section temperature taken along the white dashed lines in accordance with an embodiment of the present disclosure. The heater reflects hotspot over pattern graphene, which says heat is not transmitting rapidly from heater to graphene as it transfers from heater to SiO2.
Example 3
Plasma-assisted Cross-plane Thermal Engineering
[0041] Weak interplane bonding is the primary cause of weak cross-plane thermal coupling of metal with graphene than with SiO2. Graphene has very high thermal conductivity because of high-speed acoustic phonon and the availability of free electrons according to Kumar et al., 2022. However, it has no dangling bond to overlap with approaching metal on the surface. Thus, the graphene metal interface doesn’t offer acoustic phonon for interplanar heat transport. Additionally, due to the tunnel barrier at the interface, heat transport via electrons is also very weak. Carbon vacancy in graphene at the interface leaves unsaturated orbitals around the vacancy site. These unsaturated orbitals can overlap with approaching metal and enhance their bonding. Thus, creating carbon vacancy before the metal deposition can offer bonding enhancement and, eventually, partial acoustic phonon for thermal transport. Vacancy engineering also enhances cross-plane electron transmission probability due to a reduction in the tunnel barrier, which can also contribute to thermal transport.
[0042] Carbon vacancy (contact engineering) was created using oxygen plasma exposure before contact metal deposition, which offers metal graphene bond enhancement. Steady-state hotspot profile comparison shows a significant temperature reduction in contact-engineered devices (FIG. 5).
[0043] FIG. 5 illustrates hotspot temperature of the line heater on patterned graphene over SiO2, in accordance with an embodiment of the present disclosure. Heating comparison without (a1-c1) and with (a2-c2) contact engineering at different power. The comparison was made under the same power. Contact-engineered heater on (a2-c2) shows less heating than corresponding without an engineered heater (a1-c1) under similar drive power.
[0044] The hotspot temperature reduces up to ~1.5 and shows the potential for further reduction (FIG. 6a) with the rise in hotspot temperature (input power). The captured hotspot in nanoscale time evolution shows a significant reduction in hotspot temperature (FIG. 6b and 6c) and thermal decay time constant (Fig 6d). Hotspot temperature reduces by ~2.2 and the thermal decay time constant reduces by ~1.78 (FIG. 6d). Thus, the proposed vacancy engineering is a promising method to enhance the heat-spreading capability of devices.
[0045] FIG. 6 illustrates a) steady state hotspot comparison of the heater over patterned graphene with and without contact engineering (CE); Transient measurements with heating time b) 1µs and c) 500ns; and d) comparison of thermal decay time constant in all conditions, in accordance with an embodiment of the present disclosure. Figures reflect that contact-engineered graphene offers least temperature rise and rapid thermal decay due to better coupling with metal.
[0046] The present disclosure discloses the graphene-based heat spreader. The graphene-based heat spreader significantly improves heat spreading capabilities compared to conventional methods. By utilizing graphene's high thermal conductivity, the invention efficiently dissipates excess heat generated by micro-heaters, preventing hotspots and ensuring optimal temperature distribution. The invention offers a more effective solution for thermal management in electronic systems. By addressing the limitations of traditional materials like graphite, the graphene-based heat spreader provides superior heat transfer efficiency, reducing the risk of overheating and potential damage to electronic components. The use of graphene as a heat spreader allows for more compact and lightweight electronic systems. By efficiently spreading heat, the need for bulky and heavy cooling mechanisms is reduced, enabling the design of sleeker and more portable devices. Effective heat management is crucial for maintaining optimal performance and reliability of electronic systems. The invention ensures that hotspots are minimized, preventing performance degradation and increasing the lifespan of electronic components. The graphene-based heat spreader can be applied to various electronic systems, including tablets, laptops, phones, Micro-UAVs, integrated power converters, and power electronics. Its compatibility with different materials and fabrication processes makes it a versatile solution for diverse applications. The use of nanoscale time and spatial thermal characterizations provides precise and accurate temperature measurements. This enables better understanding and optimization of heat transfer within electronic systems, leading to improved design and performance. Graphene is a scalable and cost-effective material, making the invention commercially viable for mass production. Its integration into electronic systems can be achieved using existing manufacturing processes, ensuring feasibility and affordability.
[0047] FIG. 7 illustrates a block diagram illustrating a benefit of using a graphene-based heat spreader in heat removal, in accordance with an embodiment of the present disclosure. As mentioned, graphene-based heat spreader, specifically graphene, has a high thermal conductivity and represents a one-atom-planar sheet of carbon. The thickness of one plane of graphene is approximately 0.35 nm. In all embodiments, a single layer graphene (SLG) or few layer graphene (FLG) may be used depending on the device size, materials selection, graphene growth process. The number of graphene layers (e.g. total thickness of the overall graphene layer) is selected to achieve the optimum heat removal.
[0048] In an exemplary implementation, a graphene layer (704) placed within a semiconductor device above or below a heat source (702) causes the heat to quickly propagate (706) laterally through the graphene layer (704). Thereafter, the heat dissipates from the graphene layer into the substrate of the semiconductor device. The graphene layer increases the area (708) through which the heat dissipates into the substrate. Thus it reduces the heat to be removed per unit area per unit time (heat flux) (710). Moreover, the heat flux becomes more uniform. Also, a part of or a whole graphene layer may be placed on a bulk material which has high thermal conductivity, thus increasing the allowable rate at which the heat can be taken away from the heat source. As a result, the semiconductor device is able to use higher power per unit area.
[0049] Although, graphene may be employed as a heat removal component of a MOSFET, unlike diamond, graphene is an electrical conductor, and thus should be isolated from the active layer of the transistor. This can be done by placing an insulator (SiO2), hBN, diamond, amorphous carbon, diamond-like carbon, and the like) between the graphene and the material of the active layer (Si, GaN, InN, and the like).
[0050] FIG. 8A illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on the substrate, in accordance with an embodiment of the present disclosure.
[0051] This embodiment illustrates a graphene-based heat spreader (902) provided over a substrate (900). The insulating layer (806) may include a a layer of hBN, SiO2, synthetic polycrystalline diamond, or other electrically insulating heat conducting materials. The incorporation of graphene with the room-temperature thermal conductivity of up to ˜5000 Wm-1K-1 significantly improves the lateral heat spreading.
[0052] In an exemplary embodiment, an electrically insulating layer (806), having a thickness of, for example, between about 0.1 to 5 µm, is placed on top of the graphene layer 804. The insulating layer (806) separates the graphene layer (804), which is an electric conductor, from the active semiconductor layer (808) of the device. Finally, an insulative gate isolation layer 810 (typically SiO2) is applied over the active layer 808, as is well-known in the art.
[0053] Due to the extraordinarily high value of the graphene thermal conductivity (3100-5300 Wm-1K-1) and graphene's planar structure, the heat quickly propagates laterally through the graphene plane(s) and later dissipates into the substrate (802). The heat from the drain-source channel (812) is quickly removed, and the area of the heat dissipation is substantially increased, thereby reducing the heat flux and making it more uniform. Graphene’s incorporation allows hotspots to be removed and spreads the heat more uniformly.
[0054] Similar embodiments are possible with optoelectronic device structures, such as LEDs and semiconductor lasers, in which a graphene heat spreader may be incorporated within the optoelectronic device structure. The present disclosure and specific embodiments are to be implemented with many different materials and using different fabrication technologies. The present disclosure does not limit the choices for materials used for the substrate, the buffer layer, the insulating layer, and the active layer. Similarly, the disclosure does not limit the choices for processes used to fabricate a MOSFET with graphene as a component for heat removal.
[0055] FIG. 8B illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on and above, in accordance with an embodiment of the present disclosure.
[0056] FIG. 9A illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on the substrate and the device is connected to a heat sink, in accordance with an embodiment of the present disclosure. making grooves for the heat sink (1102) in the substrate wafer and placing these pieces in the grooves are done before bonding the substrate wafer.
[0057] In this embodiment the heat-generating semiconductor device (1004) where a graphene-based heat spreader (1004) is directly placed on the substrate (1000). In this embodiment, however, the substrate (1000) may be provided with a plurality of grooves (1006), into each of which a piece of thermally conductive material (1008), such as bulk graphite is disposed. The graphene layer(s) (1004) are formed on the substrate in a manner to contact the thermally conductive material (1008), which serves as heat sink. The thermal conductivity of the material 1008 may have a very broad range of values.
[0058] In the embodiment in which the thermally conductive material (1008) is bulk graphite, due to the excellent attachment of the graphene layers (1004) to the thermally conductive material (1008) (graphene is a single atomic layer of graphite), the problem of the thermal conductive resistance between the graphene lateral heat spreader (1004) and the heat sinks (1008) is avoided. That is because graphene forms a natural attachment to bulk graphite placed in the grooves (1006).
[0059] Accordingly, in an embodiment, an electronic or optoelectronic device is disclosed. The device includes a substrate (900) and a graphene-based heat spreader (902) positioned on the substrate (900). The graphene-based heat spreader includes at least one sheet of graphene film, and one or more microheaters integrated with at least one sheet of graphene film, wherein the microheaters include a plurality of heating lines distributed over the graphene film.
[0060] FIG. 9B illustrates a simplified schematic representation showing a heat-generating semiconductor device where a graphene-based heat spreader is directly placed on the substrate and the device is connected to a heat sink at multiple locations, in accordance with an embodiment of the present disclosure.
[0061] FIG. 10 illustrates a flowchart for a method for forming a heat spreader to reduce temperature in an electronic device, in accordance with an embodiment of the present disclosure.
[0062] At step 1002, a layer of a graphene-based heat spreader is formed on a substrate. The graphene-based heat spreader comprises at least one sheet of a graphene film, and incudes one or more microheaters having a plurality of heating lines over the at least one sheet of the graphene film.
[0063] At step 1004, a layer of an insulating material (806) is formed on top of the graphene-based heat spreader layer.
[0064] At step 1006, an active layer (808) of a semiconductor material is formed on top of the insulating layer.
[0065] At step 1008, device components are formed in the active layer to form the electronic device.
[0066] At step 1010, the graphene-based heat spreader layer is interfaced with one or more surfaces of heat sink to reduce the temperature in the electronic device.
[0067] In an exemplary embodiment, the graphene-based heat spreader can be designed using a single layer of graphene, multiple layers of graphene, or a combination of graphene and hBN (hexagonal boron nitride) in a stacked configuration.
[0068] In an exemplary embodiment, the plurality of heating lines is selected from any or a combination of uniform heating lines or pointed heating lines.
[0069] In an exemplary embodiment, the plurality of heating lines is fabricated on any or a combination of a Silicon dioxide (SiO2) substrate, a patterned graphene on SiO2, and a full coverage graphene on SiO2.
[0070] In an exemplary embodiment, the graphene-based heat spreader is processed for creating carbon vacancy or contact engineering in graphene using a plasma process wherein oxygen is used as the precursor gas and is channelled into the vacuum chamber with the graphene-based heat spreader and with varying exposure time (dose).
[0071] In an exemplary embodiment, introducing the carbon vacancy or the contact engineering is created before contact metal deposition.
[0072] In an exemplary embodiment, the graphene-based heat spreader comprises a first surface and a second surface, wherein the first surface of graphene-based heat spreader is in thermal contact with one or more heat sources, and further wherein the graphene-based heat spreader itself reduces the temperature.
[0073] In an exemplary embodiment, the graphene-based heat spreader is connected to one or more metal lines present in the form of electrical or thermal lines in the electronic device.
[0074] In an exemplary embodiment, the graphene film comprises a monolayer or multilayer structure.
[0075] In an exemplary embodiment, the microheaters are arranged in a pattern to optimize heat distribution across the graphene-based heat spreader.
[0076] In an exemplary embodiment, controlling the power supplied to the microheaters to achieve a desired thermal profile across the device.
[0077] In an exemplary embodiment, the substrate (900) is made of a thermally insulating material to enhance the efficiency of the graphene-based heat spreader.
[0078] In an exemplary embodiment, at least one sheet of graphene film used is synthesized by using a chemical vapor deposition (CVD) process.
[0079] In an exemplary embodiment, the plurality of heating lines comprises a metal or alloy selected from the group consisting of gold, nickel, palladium, aluminium, chromium, silver, platinum, and copper.
[0080] In an exemplary embodiment, the electronic or optoelectronic device is a semiconductor device, a display device, or a photovoltaic device.
[0081] In an exemplary embodiment, the graphene-based heat spreader is configured to reduce hot spots within the electronic or optoelectronic device during operation.
[0082] To summarize, the invention relates to an electronic or optoelectronic device designed to manage heat more effectively. This is achieved by incorporating a graphene-based heat spreader embedded within the device. The primary goal is to reduce the temperature and prevent overheating, which can lead to performance degradation or failure of electronic components.
[0083] Components and Working Principle:
[0084] Graphene-Based Heat Spreader:
[0085] Material Properties: Graphene is known for its exceptional thermal conductivity, which is much higher than traditional materials like copper or aluminium. This makes it ideal for spreading heat efficiently across the surface, reducing the occurrence of hot spots.
[0086] Structure: The heat spreader comprises at least one sheet of graphene film. This film may consist of a single layer (monolayer graphene) or multiple layers (multilayer graphene), depending on the specific thermal management requirements of the device.
[0087] Function: The graphene film spreads the heat generated by the electronic components more evenly across the substrate, preventing localized overheating and ensuring the device remains within safe operating temperatures.
[0088] Substrate (900):
[0089] Base Support: The substrate serves as the foundational layer upon which the graphene-based heat spreader may be applied. It could be made from various materials, such as silicon, glass, or other thermally insulating or conductive materials, depending on the application.
[0090] Thermal Management: The substrate works in conjunction with the graphene heat spreader to manage and dissipate heat. It may also influence the overall thermal resistance and efficiency of the heat management system.
[0091] Microheaters with Heating Lines:
[0092] Integrated Microheaters: Embedded within or on top of the graphene film are microheaters. These are small heating elements designed to generate localized heat, often used for precise thermal management or to activate certain processes within the device (e.g., defogging, thawing, or temperature control for specific components).
[0093] Heating Lines: The microheaters include a plurality of heating lines—thin conductive paths (typically made of metals like gold, nickel, chrominum, aluminium, palladium, silver, platinum, or copper) that carry electrical current to produce heat. The arrangement of these lines is crucial, as it ensures uniform heating and efficient heat transfer across the graphene sheet.
[0094] Controlled Heating: By applying a controlled current to these heating lines, the device can regulate the temperature of specific areas, further enhancing the effectiveness of the heat spreader. This can be particularly useful in optoelectronic devices, where temperature-sensitive components must be maintained within a narrow temperature range.
[0095] Operational Benefits:
[0096] Efficient Heat Dissipation: The combination of graphene’s high thermal conductivity ensures that heat is spread evenly across the device, preventing hot spots that could damage components.
[0097] Thermal Management Flexibility: The ability to adjust the operation of the microheaters allows for dynamic thermal management. For example, the device could increase heating in colder environments or reduce it during periods of lower power consumption.
[0098] Enhanced Device Longevity: By maintaining optimal temperatures, the device reduces thermal stress on electronic components, leading to improved reliability and a longer operational lifespan.
[0099] Compact Design: Graphene’s thin and lightweight nature means that the heat spreader adds minimal bulk to the device, allowing for more compact and lightweight electronic products.
[00100] While the foregoing description discloses various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
,CLAIMS:1. A method for forming a heat spreader to reduce temperature in an electronic device, the method comprising:
forming (1002) a layer of a graphene-based heat spreader provided above or below an active layer producing heat, wherein the graphene-based heat spreader comprises at least one sheet of a graphene film, and includes one or more microheaters having a plurality of heating lines over at least one sheet of the graphene film.
2. The method as claimed in claim 1, wherein the active layer comprises one or more semiconductor devices.
3. The method as claimed in claim 1, wherein the graphene-based heat spreader is designed using any or a combination of a single layer of graphene, multiple layers of graphene, and a combination of graphene and hBN (hexagonal boron nitride) in a stacked configuration.
4. The method as claimed in claim 1, wherein the plurality of heating lines is selected from any or a combination of uniform heating lines or pointed heating lines.
5. The method as claimed in claim 1, wherein the plurality of heating lines is fabricated on any or a combination of a Silicon dioxide (SiO2) substrate, a patterned graphene on SiO2, and a full coverage graphene on SiO2.
6. The method as claimed in claim 1, wherein the graphene-based heat spreader is processed for creating carbon vacancy or contact engineering in graphene using a plasma process wherein oxygen is used as the precursor gas and is channeled into the vacuum chamber with the graphene-based heat spreader and with varying exposure time (dose).
7. The method as claimed in claim 6, wherein the graphene-based heat spreader is processed for creating carbon vacancy, and wherein the carbon vacancies are creating by any or a combination of oxygen plasma, Argon (Ar) plasma, electron beam exposure, and Ar ion ashing.

8. The method as claimed in claim 6, wherein the method further comprising:
creating carbon vacancies are performed before deposition of the contact metal.
9. The method as claimed in claim 1, wherein the graphene-based heat spreader comprises a first surface and a second surface, wherein the first surface of graphene-based heat spreader is in thermal contact with one or more heat sources, and further wherein the graphene-based heat spreader itself reduces the temperature.
10. The method as claimed in claim 1, wherein the graphene-based heat spreader is connected to one or more metal lines present in the form of electrical or thermal lines in the electronic device.
11. The method as claimed in claim 1, wherein the method further comprising:
forming (1004) a layer of an insulating material (806) on top or bottom of the graphene-based heat spreader layer;
forming (1006) an active layer (808) of a semiconductor material on top or bottom of the insulating layer;
forming (1008) device components in the active layer to form the electronic device; and
interfacing (1010) the graphene-based heat spreader layer with one or more surfaces of heat sink to reduce the temperature in the electronic device.
12. An electronic or optoelectronic device (800) with an embedded graphene heat spreader to reduce temperature in an electronic device, the electronic or optoelectronic device comprising:
a substrate (900) having a first surface;
a layer of a graphene-based heat spreader (902) provided above or below an active layer producing heat, wherein the graphene-based heat spreader is designed using any or a combination of a single layer of graphene, multiple layers of graphene, and a combination of graphene and hBN (hexagonal boron nitride) in a stacked configuration; and
a heat sink, wherein the graphene-based heat spreader layer is interfaced with one or more surfaces of the heat sink to reduce the temperature in the electronic device;
wherein the substrate comprises a material that has a lattice structure matching a lattice structure of the graphene-based heat spreader layer;
the graphene-based heat spreader is based on any or a combination of a graphene, a hexagonal boron nitride (hBN).;
the plurality of heating lines is selected from any or a combination of uniform heating lines or pointed heating lines;
the plurality of heating lines is fabricated on any or a combination of a Silicon dioxide (SiO2) substrate, a patterned graphene on SiO2, and a full coverage graphene on SiO2; and
the graphene-based heat spreader is processed for creating carbon vacancy or contact engineering in graphene using a plasma process wherein oxygen is used as the precursor gas and is channeled into the vacuum chamber with the graphene-based heat spreader and with varying exposure time (dose).