CLIAMS:1. A thermoelectric generator comprising:
at least one n-type thermoelectric material, having first and second ends with a temperature gradient there across, at least one or more p-type thermoelectric material, having first and second ends with a same temperature gradient there across, wherein each of the n-type and the p-type thermoelectric material is a graphene with a predefined isotope; and
a first end of a first n-type thermoelectric material and a first end of a first p-type thermoelectric material form a series connection electrically, and a second end of the first p-type thermoelectric material and a second end of a second n-type thermoelectric material form a second series connection, and placing each pair of other at least one or more of n-type and p-type thermoelectric materials in series with one another to provide an electrical energy on an electric load connected across the at least one p-type and the at least one n-type thermoelectric materials in series based on the temperature gradient.
2. The thermoelectric generator as claimed in claim 1, wherein the predefined isotope is C13.

3. The thermoelectric generator as claimed in claim 2, wherein the graphene with isotope C13 is highly electrical conductive compared to other conventional material used for the thermoelectric devices.

4. The thermoelectric generator as claimed in claim 1 is assembled on an integrated circuit (IC) chip.

5. The thermoelectric generator as claimed in claim 4, wherein heat generated on the IC chip is converted into electrical energy by the thermoelectric generator.

6. The thermoelectric generator as claimed in claim 1, wherein the at least one of n-type and the at least one of p-type thermoelectric materials are spaced apart at a predetermined distance.

7. The thermoelectric generator as claimed in claim 1, wherein the electrical load comprises at least one of an electronic circuit.

8. The thermoelectric generator as claimed in claim 1, wherein the graphene is having higher thermoelectric efficiency (TE) compared to other conventional materials used in thermoelectric generators.

9. The thermoelectric generator as claimed in claim 8, wherein the TE efficiency of the graphene is enhanced by performing at least one of increasing n-type doping, p-type doping, and decreasing thermal conductivity of electrons and phonons in the thermoelectric material graphene by adding C13 isotopes, thereby increasing the electric energy generated from the temperature gradient.

10. The thermoelectric generator as claimed in claim 1, wherein the thermoelectric material is a single layer graphene.
,TagSPECI:TECHNICAL FIELD
The present disclosure relates to a single layer graphene based thermoelectric generator. In particular, the present disclosure relates to a thermoelectric generator using graphene with C13 isotope doping.
BACKGROUND
Presently, semiconductor industry has a bottleneck of increased power density/heating inside the chip because of reduced dimensions and increasing current density as a result of downscaling cannot be ignored. This demands devices to recover this excess heat from the chip and here comes the origin of in-chip thermoelectric generator that can be fabricated inside the chip for energy harvesting without adding any external moving parts to the chip for recovering the heat.
Thermoelectric (TE) materials are used as energy harvesting sources for many applications such as automobiles, handheld devices and any other device where standby power is the main concern. The fundamental aspect of TE materials is to optimize a variety of conflicting properties to achieve a high TE figure-of-merit (ZT), open circuit voltage (Voc) and power output. For past few decades, ZT is improved vastly which has resulted due to phonon mean-free-path engineering by introducing phonon scattering interfaces or surfaces in complex thermoelectric materials like Bi2Te3, CoSb3, etc., that exhibits a high ZT, i.e. approximately 1 near 400 K and approximately 0.8 near 800 K. However, conventional bulk materials like Bi, Te, Sb, Sn, alloys and thin films of these materials exhibits high ZT at room temperature, which are difficult to use as in-chip thermoelectric generators due to the compatibility issues with current silicon based CMOS technology.
With the increased hot-spots inside ICs, in-chip TE generators (TEGs) are in high demand because of their ability to drive other devices efficiently from the waste heat generated by the chip, where the temperature rise can be as high as 400 K. However, the abovementioned TE materials are difficult to use as in-chip thermoelectric generators due to the compatibility issues with present silicon based CMOS technology. Recently developments on TE and Si nanowires bundles have produced a large open-circuit voltage (Voc =27.9 mV), short circuit current (Isc = 67 µA) and power output (0.47 µW) under a temperature difference of 70 K. However, this is achieved at the cost of large integration of bundles, where the open-circuit voltage (Voc), ZT and efficiency (?) per wire could be very low. Therefore, thermoelectric material, which is adapted to CMOS technology and its relentless scaling, is in high demand for next generation “green” ICs.
Hence, there exists a need for a thermoelectric material which reduces the cost, size, improving ZT, thereby, achieving the desired results of converting the generated in-chip thermal energy into electrical energy.
SUMMARY
The shortcomings of the prior art are overcome and additional advantages are provided through the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
In one embodiment, the present disclosure relates to a thermoelectric (TE) generator. The TE generator comprises at least one n-type thermoelectric material, having first and second ends with a temperature gradient there across. Also, TE generator comprises at least one or more p-type thermoelectric material, having first and second ends with a same temperature gradient there across. Each of the n-type and the p-type thermoelectric material is a graphene with a predefined isotope. The predefined isotope is C13. A first end of a first n-type thermoelectric material and a first end of a first p-type thermoelectric material forms a series connection electrically. A second end of the first p-type thermoelectric material and a second end of a second n-type thermoelectric material forms a second series connection. Each pair of other at least one or more of n-type and p-type thermoelectric materials are placed in series with one another. An electric load is connected across the at least one p-type and the at least one n-type thermoelectric materials in series, which provides an electrical energy generated by the at least one p-type and the at least one n-type thermoelectric materials in series based on the temperature gradient.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects and features described above, further aspects, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features and characteristic of the disclosure are set forth in the appended claims. The embodiments of the disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings.

Fig. 1a illustrates a schematic arrangement of a thermoelectric generator (TEG) with a single thermoelectric material, in accordance with an embodiment of the present disclosure;

Fig. 1b illustrates a schematic arrangement of a thermoelectric generator (TEG) with an array of thermoelectric materials, in accordance with an exemplary embodiment of the present disclosure;

Fig. 2 shows a plot of Seebeck coefficient and electrical conductivity as a function of carrier concentration, in accordance with an embodiment of the present disclosure;

Fig. 3a shows a schematic illustration of an SLG sheet with dimension L × W, the contacts 1 and 2 are assumed to be ideal and at temperature TH and TL respectively, in accordance with an embodiment of the present disclosure;

Fig. 3b shows averaging the carrier back scattering length over the entire SLG sheet, in accordance with an embodiment of the present disclosure;

Fig. 4 illustrates a plot showing the variation of R as function of the temperature for different sheet concentration, in accordance with an embodiment of the present disclosure;

Fig. 5 illustrates a plot showing variation of the magnitude of SB with respect to T at different sheet concentration, in accordance with an embodiment of the present disclosure;

Fig. 6 illustrates a plot showing variation of ZT as a function of T with varying carrier concentration for isotopically impure sheet, in accordance with an embodiment of the present disclosure;

Fig. 7 illustrates a plot showing variation of ZT as a function of EF for both isotopically pure and impure SLG Sheet, in accordance with an embodiment of the present disclosure;

Fig. 8 illustrates a plot showing variation of the magnitude of Voc as function of TH for different sheet concentration, in accordance with an embodiment of the present disclosure;

Fig. 9 illustrates a plot showing TE efficiency as a function of n2D for both isotopically pure and impure SLG sheet, in accordance with an embodiment of the present disclosure;

Fig. 10 illustrates a plot showing short circuit current as function of temperature at contact 1 for different lengths and widths, in accordance with an embodiment of the present disclosure;

Fig. 11 illustrates a plot showing an output power as function of temperature at contact 1 for different lengths and widths, in accordance with an embodiment of the present disclosure; and

Fig. 12 illustrates a plot showing an output power as function of sheet concentration for different lengths when contact 1 is at 400 K, in accordance with an embodiment of the present disclosure

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described herein after which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific aspect disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.
The present disclosure provides a viable solution to the problem mentioned in the background by using C13 isotopes in single layer graphene based thermoelectric generator (TEG) system.
In one embodiment of the present disclosure relates to graphene with C13 isotope. Despite C13 extremely high thermal conductivity i.e. in the range of 600-7000 Wm-1K-1, as compared to Copper and Aluminum with thermal conductivity of about 400 Wm-1K-1 and 237 Wm-1K-1 respectively, graphene is a potential material for thermoelectric applications. Also, it is experimentally measured that Seebeck coefficient is highest among elemental semiconductors. However, as the thermal conductivity of graphene is mainly dominated by phonons, any TE application of graphene would require strong suppression of its phonon thermal conductivity. As an example embodiment, in case of SLG sheet since phonon thermal conductivity dominates over the electrons and thus, there remains scope to maximize the ZA phonon interactions in order to reduce phonon thermal conductivity significantly. However, with an addition of isotope impurity i.e. C13 over conventional isotope C12 atoms in graphene, decreases phonon thermal conductivity. Thus, there is a strong potential for C13 to severely increase the value of ZT and ? at room temperature. Therefore, by isotope doping it is possible to modulate the TE efficiency, Isc, Voc and output power of a single layer graphene, which has substantial role in recovering the waste-heat from the chip hot-spots.
In one embodiment, as an example under assumptions of strongly diffusive regime and using methods for ?ph inhibition i.e. isotope impurity scattering, thermoelectric performance of graphene is improved. The Voc thus found is about 14 mV, Isc = 200 µA, ZT = 0.17-1.02, ? = 3.2% and power output = 0.7 µW in the temperature range of 300 - 450 K and sheet concentration of 1016–1017 m-2 which further can be enhanced by the integration of these SLGs in the form of arrays. Thus, theoretical formulation of Voc and ZT may be compared with the experimental data from Si nanowire bundles arrays. Due to extremely high electronic and thermal conductivity, graphene and carbon nanotubes are being considered as alternative materials for interconnects in next-generation integrated circuits. Graphene is extremely scalable and may be used in flexible electronics. In an interconnect system where isotopically pure graphene sheets could be used to carry signals i.e. heat generated during an operation and sheets with extremely high isotopic impurity may be used as in-chip thermoelectric generators to convert the waste-heat into usable electric power for driving the circuits.
In one exemplary embodiment of the present disclosure relates to a thermoelectric (TE) generator. The TE generator comprises at least one n-type thermoelectric material, having first and second ends with a temperature gradient there across. Also, TE generator comprises at least one or more p-type thermoelectric material, having first and second ends with a same temperature gradient there across. Each of the n-type and the p-type thermoelectric material is a graphene with a predefined isotope. The predefined isotope is C13. A first end of a first n-type thermoelectric material and a first end of a first p-type thermoelectric material forms a series connection electrically. A second end of the first p-type thermoelectric material and a second end of a second n-type thermoelectric material forms a second series connection. Each pair of other at least one or more of n-type and p-type thermoelectric materials are placed in series with one another. An electric load is connected across the at least one p-type and the at least one n-type thermoelectric materials in series, which provides an electrical energy generated by the at least one p-type and the at least one n-type thermoelectric materials in series based on the temperature gradient. The graphene with isotope C13 is highly electrical conductive compared to other conventional material used for the thermoelectric devices.
The thermoelectric generators or Seebeck generators are devices that convert thermal energy i.e. temperature gradient or difference directly into electrical energy. Temperature gradient between the two ends of a material in an open circuit condition causes charge carriers in the material to diffuse from the hot side to the cold side and results in a voltage generation between the two ends, this effect is called Seebeck effect. The thermoelectric generator (TEG) is intended for conversion of waste heat from various sources such as, but not limited to a particular industry, heat engines, internal combustion engines, gas turbines, excess heat generated in electronic devices into electric energy. The TEG serves as a source of additional energy that can be used for internal needs and transferred into external electric circuit.

Fig. 1a shows a schematic arrangement of a thermoelectric generator (TEG) with a single thermoelectric material, in accordance with an embodiment of the present disclosure. As shown in Fig. 1a, n-type and p-type materials are connected electrically in series, but thermally shorted. The open-circuit voltage induced as a result of temperature difference between the two ends can be enhanced by repetition of such arrangement and making an array, in an alternative embodiment. The TE generator material used is graphene with C13 isotope, which increases TE efficiency substantially.
Fig. 1b shows a thermoelectric generator (TEG) with an array of thermoelectric materials, in an exemplary embodiment of the present disclosure. As shown in figure 1b, the TEG comprises an array of TE materials i.e. N times repetition of TE module made from n-p type TE material to integrate as an array, for obtaining higher Voc. The n-type and p-type TE material slabs are thermally shorted but are electrically in series connection to provide a continuous path for current to flow from one TE module to another TE module. The predefined isotope is graphene with isotope C13, which is highly electrical conductive compared to other conventional material used for the thermoelectric devices. The TEG may be embedded on an integrated circuit (IC). Also, the at least one of n-type and the at least one of p-type thermoelectric materials are spaced apart at a predetermined distance. The electrical load comprises at least one of an electronic circuit. The TE efficiency of the graphene is enhanced by performing at least one of increasing n-type doping, p-type doping, and decreasing thermal conductivity of electrons and phonons in the thermoelectric material graphene by adding C13 isotopes, thereby increasing the electric energy generated from the temperature gradient.
As shown in Figs. 1a and 1b, the operating principle of the TEG is based on the direct conversion of thermal energy into electric energy through the use of thermoelectricity. The efficiency of said generators is determined by a dimensionless figure-of-merit (ZT) and is given by:
(1)
where SB, s, T are the Seebeck-coefficient, electrical conductivity, absolute temperature respectively and ?e, ?ph are the thermal conductivity by electrons and phonons respectively. The transport coefficients are coupled with each other thereby optimizing ZT.
The TEG uses a material graphene with C13 isotope, by which the TE efficiency is substantially increased. The TE efficiency is defined by equation 1, in which the ZT can be enhanced by increasing s (n/p-type doping), or SB (n/p-type doping) or by decreasing ? (?e and ?ph). Since, s increases with carrier concentration and SB decreases with increasing carrier concentration, as shown in Fig. 2. Hence, it will be reasonable to optimize ZT by reducing the thermal conductivity. Fig. 2 shows a plot of Seebeck coefficient and electrical conductivity as a function of carrier concentration. As shown in Fig. 2, peak of dashed curve shows the optimized value of power factor. In case of graphene, thermal conductivity is phonon dominated (?e <