Graphene Heat Spreaders Superior to Carbon Nanotubes and Diamond for Electronic and Photonic Devices ?

The reliability and speed of electronic and optoelectronic devices strongly depend on temperature . Materials with very high thermal conductivities are required to spread the heat generated locally in such devices . Bulk copper, which is widely used as heat spreader in computers, has a thermal conductivity of ∼400 W m−1 K−1 at room temperature, but copper thin films, used as electrical interconnects, can have lower thermal conductivity (below 250 W m−1 K−1). 

The search is thus on for materials with thermal conductivities higher than that of copper.Researchers at the University of California-Riverside Nano Device Laboratory  claim that that the thermal conductivity of graphene is greater than that of diamond and carbon nanotubes, and thus is an excellent material for thermal management. Use of graphene as a thermal management component makes heat removal more efficient, and thus the devices and circuits can use more power and with extended life.Pure-carbon materials such as diamond, graphite, and carbon nanotubes have very high thermal conductivities, because the strong covalent bonding between carbon atoms results in a large phonon (lattice vibration) contribution to the thermal conductivity. Recently, graphene has attracted much attention due to its unique properties, such as very high intrinsic charge carrier mobility. 

Researchers at UC-Riverside  developed a device and associated method of heat removal from electronic optoelectronic and photonic devices via incorporation of extremely high thermally conducting channels or embedded layers made of single-layer graphene (SLG), bi-layer graphene (BLG), or few-layer graphene (FLG). The heat spreading graphene layers and the manufacturing method are detailed in U.S. Patent20100085713.

There is a trend in industry to reduce the size of semiconductor devices and integrated circuits. At the same time, the devices and circuits are designed to perform more functions. To satisfy the demands for reduced size and increased functionality, it becomes necessary to include a greater number of circuits in a given unit area. As a consequence of increased functionality and density in packaging, the devices and circuits use more power. This power is typically dissipated as heat generated by the devices. The increased heat generation, coupled with the need to reduce size, leads to an increase in the amount of heat generated per unit area. The increase in the amount of heat generated in a given unit area leads to a demand to increase the rate at which heat is transferred from the devices and circuits to heat sinks or to ambient environment in order to prevent them from becoming damaged due to exposure to excessive heat.

Graphene may be used for thermal management and high-flux cooling of electronic devices and circuits, such as field-effect transistors (FETs), integrated circuits (ICs), printed circuit boards (PCBs), three-dimensional (3D) ICs, and optoelectronic devices, such as light-emitting diodes (LEDs), and related electronic, optoelectronic, and photonic devices and circuits

Graphene, as discovered by the inventors, is characterized by extremely high thermal conductivity, which allows it to be used for heat removal. The embodiments use the flat geometry of graphene, which allows it to be readily incorporated into the device structure. The embodiments allow for better thermal management of the electronic and optoelectronic devices and circuits and reduced power consumption

Graphene may be used as a heat spreader material and incorporated into device and chip designs in ways that are not possible with other materials. The proposed embodiments of graphene heat spreaders include graphene layers in MOSFETs, integrated circuit packages, printed circuit boards and as a filler material in TIMs (Thermal Interface Materials).

There are no known applications of graphene as a heat spreader material in semiconductor devices and circuits, integrated circuit packaging, or PCBs. Most manufactured semiconductor devices and integrated circuits do not include thermal management components embedded in the substrates. Traditional means of heat removal (micro liquid cooling, air blowing, and external heat sinks) still remain ineffective for hot-spot removal in the region near drain-source current or new interconnect wiring. That region absorbs most of the generated heat and remains to be a part of the device or circuit most likely to be damaged from excessive heat. Embedding a layer of the material with high thermal conductivity in the substrate provides an increase in tolerable heat flux. Moreover, the heat propagates laterally within the graphene plane, which results in an increase in the area of heat dissipation, reduction of the heat flux, and more uniform heat absorption by the substrate.

Graphene has more than twice the thermal conductivity of diamond, allowing an increase in the rate of heat removal. Graphene temperature processing requirements are lower than those for diamond. Employing graphene as a heat spreader material in semiconductor devices, chip packaging, and PCBs makes an increase of tolerable power possible.

Graphene is a one-atom-thick layer of carbon arranged in a honeycomb lattice. The material's high electron mobility and high thermal conductivity could lead to chips that are not only faster but also better at dissipating heat. This schematic shows a three-dimensional stacked chip with layers of graphene acting as heat spreaders. At present, though, graphene is extremely costly to manufacture.