I. Field of the Disclosure
The field of the present disclosure relates to heat management in electronic devices employing integrated circuits (ICs).
II. Background
Electronic devices are manufactured using integrated circuits (ICs). These electronic devices require a power source to provide power to the ICs for operation. A common power source for portable electronic devices is a battery, which provides a power source for operating ICs within the portable electronic devices. Reducing power consumption in ICs, especially ICs in portable electronic devices, has been an area of concentration in designing ICs. Reduced power consumption results in longer battery life. Reduced power consumption can also result in lower heat generation that needs to be dissipated. Many electronic devices include various means to dissipate heat even if the devices have reduced power consumption demands.
One technique to reduce IC power consumption is to reduce the amount of time that active components (e.g., gates, registers, flip-flops) are exercised. Clock gating and power collapsing are two methods to reduce active component usage. In recent years, near threshold operation techniques have also been employed to reduce power consumption. Near threshold operation involves lowering the supply voltage to voltage values close to the threshold operational voltage of the gates to reduce consumed power. However, in any of these IC power reduction techniques, a certain amount of power inefficiency will be generated in the form of heat.
While power conservation techniques are actively being explored, there still remains a need for better power management, particularly in portable electronic devices where there is a strong need to maximize an amount of time available between battery recharging events.
Embodiments disclosed herein include systems and methods for harvesting dissipated heat from integrated circuits (ICs) in electronic devices into electrical energy for providing power. Energy transferred from one or more ICs in the form of dissipated heat is harvested to convert at least a portion of this dissipated heat into electricity. This power can be used to provide power to the ICs to reduce overall power consumption by the electronic device. The harvested dissipated heat can be supplied to ICs in the electronic device to provide power to the ICs. Alternatively, or in addition, the harvested dissipated heat can be stored in an energy storage device to provide power to the ICs at a later time. While it is expected that multiple ICs may be used concurrently the concepts remain applicable to a single IC.
In this regard, in an exemplary embodiment, a semiconductor package is disclosed. The semiconductor package comprises a semiconductor die disposed on a substrate. The semiconductor package further comprises a thermo-electric material distinct from and thermally coupled to at least a portion of the semiconductor die.
In another exemplary embodiment, an IC is disclosed. The IC comprises a semiconductor package. The semiconductor package comprises a semiconductor die disposed on a substrate and a thermo-electric material distinct from and thermally coupled to at least a portion of the semiconductor die, wherein the thermo-electrical material is configured to convert dissipated heat from the semiconductor die into electrical energy. The IC also comprises a voltage conditioning circuit configured to receive the converted electrical energy. The voltage conditioning circuit is also configured to condition the converted electrical energy to provide power to the IC.
In another exemplary embodiment, a printed circuit board (PCB) is disclosed. The PCB comprises a substrate. The PCB also comprises at least one thermo-electric material portion embedded in a portion of the substrate.
In another exemplary embodiment, a semiconductor package is disclosed. The semiconductor package comprises a semiconductor die disposed on a substrate. The semiconductor package also comprises a means for converting thermal energy to electrical energy distinct from and thermally coupled to at least a portion of the semiconductor die.
With reference now to the drawing figures, several exemplary embodiments of the present disclosure are described. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
Embodiments disclosed herein include systems and methods for harvesting dissipated heat from integrated circuits (ICs) in electronic devices and converting this harvested heat into electrical energy for providing power back to the ICs. Energy transferred from one or more ICs in the form of dissipated heat is harvested to convert at least a portion of this dissipated heat into electricity. This power can be used to provide power to the ICs to reduce overall power consumption by the electronic device. The harvested dissipated heat can be supplied to ICs in the electronic device to provide power to the ICs. Alternatively, or in addition, the harvested dissipated heat can be stored in an energy storage device to provide power to the ICs at a later time.
Before addressing the particulars of the heat harvesting techniques of the present disclosure, a discussion of the physics associated with thermoelectric behavior are provided with reference to the graphs of
Harvesting dissipated heat from ICs into electrical energy for providing power and converting this harvested heat back into electrical energy reduces the effective power consumption of the ICs of the electronic device. As noted above, reduction in the effective power consumption may extend battery life for mobile devices. Also, converting dissipated heat from the ICs into electrical energy can result in an equivalent reduction of heat released into the space within the electronic device. This heat release reduction can result in a lower substrate temperature of the ICs thereby possibly allowing the ICs to operate at higher frequencies without the IC substrate(s) temperature crossing over an undesired or dangerous temperature threshold. Such increases in frequency may allow faster operation.
The harvested heat converted into electrical energy can result in an effective reduction of IC power consumption by an amount equal to the efficiency of the energy harvesting system. For example, if the energy harvesting efficiency of the energy harvesting system is five percent (5%) (e.g., generating 5 mW of power from 100 mW of dissipated heat), the overall power consumption of the IC will be reduced by five percent (5%). A bit of additional background is provided.
Heat Engines, Thermoelectric Generators and Efficiencies
Energy harvesting is the process by which external sources of energy are converted to other forms of energy to be stored or used by electronic devices. Such external sources consist of, but are not limited to solar, wind, heat, kinetic or ambient radio frequency (RF) energy. In all such cases, a mechanism is employed by which part of the energy is absorbed and converted into either electrical or chemically stored energy.
In the case of heat, the material used to absorb and convert heat energy (temperature gradients) directly into electricity is called thermoelectric generator (or thermo-generator) and the direct conversion of temperature difference into electric voltage is called thermoelectric effect. Thermoelectric effect, in reality, encompasses three different effects: The Seebeck effect, Peltier effect and Thomson effect collectively referred to as Seebeck-Peltier Thomson effect.
The maximum efficiency (ηmax) of any heat engine, and therefore thermo-generators, is given by the Carnot's theorem, and is limited to:
where TC and TH are the cold and hot temperatures respectively given in units of Kelvin. As can be seen from Eq. 1, as the hot temperature increases the maximum theoretical efficiency approaches 1 or 100%. The maximum efficiency is plotted in graph 10 of
The efficiency of thermoelectric devices, however, contains additional terms as shown below:
is the figure of merit, and where ρ is the electrical resistivity, κ is the thermal conductivity,
Currently, the most efficient thermoelectric materials are formed as alloys of Bismuth Telluride (Bi2Te3.) The average thermoelectric figure of merit Z of crystals of Bismuth Telluride is between 2.8×10−3 and 3×10−3 l/K at 300K. Using this figure of merit for Z in Eq. 2 and plotting the efficiency η for various cold temperatures and temperature differentials (ΔT) as before, the family of curves shown in graph 12 of
Advances in material sciences are giving rise to thermoelectric materials with better efficiencies. Carbon nanotube. Gallium Manganese Arsenide (with thermo-spin effects) and a copper-selenium liquid-like crystal are a few examples of the latest research in finding more efficient thermoelectric material. Copper-selenium material, for example, has been found to have a thermoelectric figure of merit of ˜0.4 at 300K. The family of efficiency curves for a figure of merit of 0.4 has also been plotted in graph 12 of
Against the theoretical backdrop of the Carnot curves of
With continued reference to
With continued reference to
where x is the height of the material and A the cross sectional area. Therefore, the thermal differential ΔT is given by:
ΔT=Q(1−η)×RθJC Eq.4
where Q is the power dissipated by the IC, and η denotes the fraction of the power that is being harvested. As it can be seen from Eq. 4, the efficiency parameter η itself is a function of ΔT. Therefore, final ΔT is determined by substituting for η and solving for ΔT.
Using Eq. 5, one option is to use iterative algorithms and determine the final value of ΔT. Alternatively, the simplifying assumption that 2Tc>>ΔT is used to find a closed form solution for ΔT with a good approximation for the range of ΔTs of interest. Making this assumption, Eq. 5 can be re-written as
Eq. 6 can then be written as a quadratic equation in terms of ΔT, where its positive root is the solution for ΔT.
It is worth noting that according to the efficiency curves in
The junction temperature T of the die 22 is determined by the addition of the temperature difference in the thermoelectric casing 26 plus the ambient temperature (which is the temperature at which the cold side of the thermoelectric material or the thermoelectric casing 26 is maintained). Therefore, the junction temperature Tj of the die 22 is given by:
T
J
=T
AMB
+ΔT Eq. 8
The thermal conductivity of Bismuth Telluride is reported to be 1.20 (W/(° C. m)). Therefore, as an exemplary use case, for a typical cell phone power amplifier (PA) with package dimensions of 3 mm×3 mm×1 mm, the absolute thermal resistance of the casing made of Bismuth Telluride material would be
The power dissipated by the PA, on the other hand, at its maximum output power (and max efficiency of ˜40%) would result in a dissipated power of
and a temperature differential of
ΔT≈84° C.
and, assuming an ambient temperature of 25° C., a junction temperature of
T
J
=T
AMB
+ΔT=10° C.
The thermal efficiency of the thermoelectric casing 26 of such device, on the other hand, would be ˜4.22%. If the harvested energy is then put through VC circuitry 30 with an exemplary efficiency of 90%, the overall efficiency for the harvested electrical energy would be ˜3.8% of the dissipated power. In other words, the overall wasted power by the PA would be reduced by ˜3.8% resulting in an overall increase in the efficiency of the PA.
A greater benefit is realized when thermoelectric material with higher efficiency and lower thermal conductance (higher thermal resistance,) such as carbon nanotubes or copper-selenium is used. For example, if copper-selenium's reported figure of merit is accurate, and proceeding with the assumption that the absolute resistance remains the same (in reality, it is expected that copper-selenium has a lower thermal conductivity and, therefore, a higher absolute resistance for the same package size,) the thermoelectric efficiency number for the PA example above would be at ˜17%. Assuming the same 90% efficiency for the VC circuitry, this would reduce the overall power consumption of the PA by ˜10%, effectively increasing the PA efficiency to ˜45%.
It is also worth noting that for the example above with copper-selenium as the thermoelectric material, the temperature differential ΔT will be 71° C. instead of 84° C. for Bismuth Telluride. The decrease in temperature differential is, of course, directly related to the fact that the more efficient copper-selenium material harvests a bigger fraction of the heat energy, reducing the amount of energy wasted in the form of heat. Therefore, with more efficient material, not only is more energy extracted from the wasted heat energy, the chips remain cooler.
Data modem chips can serve as another example to better understand the power saving potentials of this disclosure. Currently, a typical data modem chip package is 8 mm×8 mm×1 mm. Assuming a power profile that dissipates ˜1.5 W of power and a thermoelectric package with a conservative thermal conductivity of 1.20 (W/(° C. m)) (that of Bismuth Telluride,) the temperature differential across the package would be ˜18° C. Assuming the thermoelectric package is made of copper-selenium, however, with a figure of merit of 0.4 and a 90% efficiency for the VC circuitry, the overall energy harvesting efficiency would be at ˜5%; effectively, reducing the power consumption of the data modem chip by the same amount.
It is also worth noting that as stated before, the absolute thermal resistivity of the thermoelectric material of the thermoelectric casing 26 can be increased by reducing its cross sectional area as deduced from Eq. 2.
In this regard,
With continued reference to
Another exemplary embodiment is illustrated in
As a final example, for the case of the modem chip above, if the absolute thermal resistance is increased (through reducing cross sectional area, increasing thickness or reducing the thermal conductivity) such that the temperature differential across the thermoelectric material reaches 95° C., the overall efficiency will increase to ˜20%.
The systems and methods for harvesting dissipated heat from ICs in electronic devices into electrical energy for providing power for the electronic devices according to embodiments disclosed herein may be provided in or integrated into any processor-based device. Examples, without limitation, include a set top box, an entertainment unit, a navigation device, a communications device, a fixed location data unit, a mobile location data unit, a mobile phone, a cellular phone, a computer, a portable computer, a desktop computer, a personal digital assistant (PDA), a monitor, a computer monitor, a television, a tuner, a radio, a satellite radio, a music player, a digital music player, a portable music player, a digital video player, a video player, a digital video disc (DVD) player, and a portable digital video player.
In this regard,
Other master and slave devices can be connected to the system bus 78. As illustrated in
The CPU(s) 72 may also be configured to access the display controller(s) 90 over the system bus 78 to control information sent to one or more displays 96. The display controller(s) 90 sends information to the display(s) 96 to be displayed via one or more video processors 98, which process the information to be displayed into a format suitable for the display(s) 96. The display(s) 96 can include any type of display, including but not limited to a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, etc.
Those of skill in the art will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithms described in connection with the embodiments disclosed herein may be implemented as electronic hardware, instructions stored in memory or in another computer-readable medium and executed by a processor or other processing device, or combinations of both. The arbiters, master devices, and slave devices described herein may be employed in any circuit, hardware component, IC, or IC chip, as examples. Memory disclosed herein may be any type and size of memory and may be configured to store any type of information desired. To clearly illustrate this interchangeability, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. How such functionality is implemented depends upon the particular application, design choices, and/or design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The embodiments disclosed herein may be embodied in hardware and in instructions that are stored in hardware, and may reside, for example, in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer readable medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a remote station. In the alternative, the processor and the storage medium may reside as discrete components in a remote station, base station, or server.
It is also noted that the operational steps described in any of the exemplary embodiments herein are described to provide examples and discussion. The operations described may be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step may actually be performed in a number of different steps. Additionally, one or more operational steps discussed in the exemplary embodiments may be combined. It is to be understood that the operational steps illustrated in the flow chart diagrams may be subject to numerous different modifications as will be readily apparent to one of skill in the art. Those of skill in the art will also understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/774,039, filed Mar. 7, 2013, entitled SYSTEMS AND METHODS FOR HARVESTING DISSIPATED HEAT FROM INTEGRATED CIRCUITS (IC) IN ELECTRONIC DEVICES INTO ELECTRICAL ENERGY FOR PROVIDING POWER FOR THE ELECTRONIC DEVICES, which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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61774039 | Mar 2013 | US |