Patent Publication Number: US-11653509-B2

Title: Solar antenna array fabrication

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of co-pending U.S. patent application Ser. No. 15/682,646, filed on Aug. 22, 2017, which is a continuation-in-part of U.S. patent application Ser. No. 15/661,854, filed on Jul. 27, 2017, which is a continuation-in-part of U.S. patent application Ser. No. 15/411,396, filed on Jan. 20, 2017, which is a continuation-in-part of U.S. patent application Ser. No. 15/249,953, filed on Aug. 29, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 15/133,807, filed on Apr. 20, 2016, all of which are incorporated herein by reference. 
    
    
     FIELD OF ENDEAVOR 
     Various aspects of this disclosure may pertain to economical manufacturing processes of visible light rectenna arrays for the conversion of solar energy to electricity. 
     BACKGROUND 
     Rectifiers for AC to DC conversion of high frequency signals have been well known for decades. A particular type of diode rectifier when coupled to an antenna, called a rectenna, has also been known for decades. More specifically, over 20 years ago, Logan described using an array of rectennas to capture and convert microwaves into electrical energy in U.S. Pat. No. 5,043,739 granted Aug. 27, 1991. However, the dimensions of the antenna limited the frequency until recently, when Gritz, in U.S. Pat. No. 7,679,957 granted Mar. 16, 2010, described using a similar structure for converting infrared light into electricity, and Pietro Siciliano suggested that such a structure may be used for sunlight in “Nano-Rectenna For High Efficiency Direct Conversion of Sunlight to Electricity,” by Pietro Siciliano of The Institute for Microelectronics and Microsystems IMM-CNR, Lecce (Italy). 
     Still, the minimum dimensions required for such visible light rectennas are generally in the tens of nanometers. While these dimensions may be accomplished by today&#39;s deep submicron masking technology, such processing is typically far more expensive than the current solar cell processes, which require much larger dimensions. 
     Still, as Logan pointed out in U.S. Pat. No. 5,043,739, the efficiency of microwave rectennas can be as high as 40%, more than double that of typical single junction poly-silicon solar cell arrays, and when using metal-oxide-metal (MOM) rectifying diodes, as Pietro suggests, no semiconductor transistors are needed in the array core. 
     As such, it may be advantageous to be able to utilize the existing fine geometry processing capability of current semiconductor fabrication without incurring the cost of such manufacturing. 
     Also, recently, Rice University reported that their researchers created a carbon nanotube (CNT) thread with metallic-like electrical and thermal properties. Furthermore, carbon nanotube structures are becoming more manufacturable, as described by Rosenberger et al. in U.S. Pat. No. 7,354,977 granted Apr. 8, 2008. Various forms of continuous CNT growth may have also been contemplated, such as Lemaire et. al. repeatedly harvesting a CNT “forest’ while it is growing in U.S. Pat. No. 7,744,793 granted Jun. 29, 2010, and/or put into practice using techniques described by Predtechensky et al. in U.S. Pat. No. 8,137,653 granted Mar. 20, 2012. Grigorian et al. describes continuously pushing a carbon gas through a catalyst backed porous membrane to grow CNTs in U.S. Pat. No. 7,431,985 granted Oct. 7, 2008. 
     Furthermore, others have contemplated using CNTs for various structures such as Rice University&#39;s CNT thread as described in “Rice&#39;s carbon nanotube fibers outperform copper,” by Mike Williams, posted on Feb. 13, 2014 at: news.rice.edu/2014/02/13/rices-carbon-nanotube-fibers-outperform-copper-2; magnetic data storage as described by Tyson Winarski in U.S. Pat. No. 7,687,160 granted Mar. 30, 2010; and in particular, antenna-based solar cells, as described by Tadashi Ito et al. in US Patent Publication 2010/0244656 published Sep. 30, 2010. Still, Ito et al. did not describe methods to inexpensively construct carbon nanotube solar antennas for efficient conversion of solar energy. 
     SUMMARY OF VARIOUS EMBODIMENTS 
     Various aspects of the present disclosure may relate to ways to manufacture structures of CNT rectenna arrays for converting sunlight into electricity, which may utilize current IC manufacturing techniques and self-aligning process steps, and which may be successively used to achieve the molecular sized dimensions required for the antennas and the geometric diodes. 
     The structure of the rectenna array may include an array of CNT antennas connecting between interdigitated ground lines and negative voltage lines through geometric diodes. The antennas may be of varying lengths and orientations, distributed for maximum reception of the full spectrum of ambient sunlight, e.g., having ¼ wavelengths or harmonic multiples of ¼ wavelengths. Single ¼-wavelength antenna diode combinations may half-wave rectify the received light. Two coupled ¼-wavelength antenna diode combinations may full-wave rectify the received light. 
     In one aspect, the multi-walled carbon nanotube antennas may be constructed between interdigitated aluminum lines alternating from the ground and negative voltage lines, by growing from a nickel catalyst on the ground lines to the side walls of the negative voltage lines. 
     In another aspect, the diameters of the multi-walled carbon nanotubes may be determined by the processing of the catalyst coupled with the processing of the carbon nanotubes. 
     In another aspect, the carbon nanotubes may be subsequently used to form the geometric diodes at the tips of the carbon nanotubes through a thin layer of aluminum oxide. 
     In yet another aspect, the carbon nanotube antennas may be subsequently used to retain the geometric diode connections while growing a thicker protective layer of aluminum oxide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present disclosure will now be described in connection with the attached drawings, in which: 
         FIG.  1    is an electrical diagram of a combined diode and antenna according to an aspect of the present disclosure, 
         FIG.  2    is another electrical diagram of a pair of diodes and antennas according to an aspect of the present disclosure, 
         FIG.  3    is a logical diagram of an array of antennas and diodes according to an aspect of the present disclosure, and 
         FIG.  4    through  FIG.  6    are diagrams of cross-sections of an antenna array depicting multiple diode and carbon nanotube antennas according to aspects of the present disclosure. 
     
    
    
     DESCRIPTION OF VARIOUS ASPECTS OF THE PRESENT DISCLOSURE 
     Various aspects of the present disclosure are now described with reference to  FIG.  1    through  FIG.  6   , it being appreciated that the figures may illustrate the subject matter of various aspects and may not be to scale or to measure. 
     An electrical diagram  10  of a combined diode and antenna according to an aspect of the present disclosure is shown in  FIG.  1   . A diode  11  and a ¼-wavelength antenna  12  may be coupled together, with the antenna  12  further connected to a ground line  13  and the diode  11  connected to a negative voltage (−V) line  14 , to form a ½-wave rectified structure. Another electrical diagram  20  of a pair of diodes and antennas according to another aspect of the present disclosure, is shown in  FIG.  2   . Two structures  21 , each equivalent to the electrical diagram shown in  FIG.  1   , may be coupled to common ground and —V lines  22 , to form a full-wave rectified structure. 
     Reference is now made to  FIG.  3   , a conceptual diagram of an array of antennas and diodes according to an aspect of the present disclosure. The antenna  30  and diode  31  may be respectively connected to the ground line  32  and the power line  33  in a manner similar to the electrical diagram in  FIG.  1   . A second antenna  34  and diode  35  may be respectively connected to another side of the ground line  32  and another power line  36 , which may in turn be connected  37  to the original power line. Together, the antennas  30 ,  34  and diodes  31 ,  35  may be connected to the power  33 ,  36  and ground  32  lines in a manner similar to the electrical diagram in  FIG.  2   . The antennas may be of varying lengths and may be randomly placed between the diodes and the ground line  32 . The antennas may be metallic carbon nanotubes. 
     Reference is now made to  FIG.  4   , a diagram of a cross-section of an antenna array, depicting multiple diodes and CNT antennas according to an aspect of the present disclosure. The antennas  43  may be either single-walled metallic carbon nanotubes, or multi-walled carbon nanotubes, which may be attached to the ground lines  41  via a catalyst  44 . The catalyst may be used to grow the CNTs. The catalyst maybe composed of nickel, iron, cobalt, or some other suitable metal or alloy of metals. The catalyst may be a thin layer  44  formed by depositing and annealing the catalyst  44  on an oxide layer  45 . The oxide layer  45  may be sufficiently thick to form multiple sites for carbon nanotubes. The vertical sites may aid in growing adequate densities of carbon nanotube antennas. A thin layer of oxide  47 ,  49  may be grown or deposited on the metal lines  40 ,  41 . The tips  46  of the carbon nanotubes  43  may extend across a trench  48  to an oxide layer  47 , forming a contact between the tip of the carbon nanotube  43  and the oxide  47 . This structure may form a metal oxide carbon (MoC) diode coupling the carbon nanotube antennas  43  to the voltage line  40 . The oxide may be very thin, ˜one nanometer thick. The power  40  and ground  41  lines may be insulated from each other via a base  42 . The base  42  may be, for example, a ceramic, glass or a plastic material. The power  40  and ground  41  lines may be composed of one or more metals such as aluminum. The ground lines  41  may be electrically connected to the catalyst  44 . 
     Reference is now made to  FIG.  5   , another diagram of a cross-section of an antenna array depicting multiple diodes and CNT antennas according to another aspect of the present disclosure. Subsequent to the formation of the MoC diodes, a bias voltage may be applied to the CNT antennas  43  sufficient enough to migrate the metal  40  through the oxide  47  to the tips  52  of the CNT antennas  43 , to form geometric diodes. 
     Reference is now made to  FIG.  6   , another diagram of a cross-section of an antenna array depicting multiple diodes and CNT antennas according to another aspect of the present disclosure. Subsequent to the formation of geometric diodes, additional oxide may be grown to eliminate further migration of the metal from the carbon nanotube tip to the surface of the oxide. In order to accomplish this, one may allow the metal  40  and  41  to migrate through the oxide  47  and  49  respectively, until the migration naturally stops, without allowing the metal  40  to migrate from the tips  61  of the CNT antennas  43 . This may be performed by applying an electrical bias sufficient enough to hold the metal ions at the tip of the CNT antennas, while allowing the metal ions elsewhere to migrate to the surface of the oxide to form more oxide. For example aluminum oxide may grow on pure aluminum as aluminum ions migrate through the aluminum oxide to oxidize in the presence of oxygen in the air, but the process may typically stop after 3.5 to 4.5 nanometers of oxide has grown, when the natural electric fields are too weak to cause further migration. In this manner the tips  61  of the CNT antennas  43 , may be “anchored” in the oxide  47 , while also stabilizing the aluminum ion migration. 
     In order to efficiently rectify visible light, the diodes may need to have a cutoff frequency above 700 THz. This may require diodes  46  in  FIG.  4    with sufficiently small capacitance, which may be accomplished by growing CNTs approximately 15 nanometers in diameter to very thin oxides one to two nanometers thick. Nevertheless, even with such thin oxides, the turn-on voltage of the resulting diode may limit the rectification of infrared light. On the other hand, the small tip  51  of the CNT in  FIG.  5   , directly connecting to the large flat side of the power line may create a geometric diode, which may have a turn-on voltage close to zero, which may thus allow rectification of the entire spectrum of sunlight. Furthermore, the antennas&#39; lengths and directions may vary to cover substantially the entire spectrum of un-polarized sunlight. This may be accomplished by varying the distances the carbon nanotubes  43  cover from the ground  41  line to the power line  40 , such that the difference of the shortest to the longest carbon nanotube may be greater than the difference between a ¼ wavelength of ultraviolet light (˜80 nanometers) and ¼ wavelength of infrared light (˜640 nanometers). This may ensure that at least one harmonic of substantially all frequencies of sunlight may be covered by the range of CNT lengths. 
     Techniques for depositing and etching very thin layers of materials have been well known in the semiconductor industry for decades, but creating molecular-sized structures normally requires extremely expensive lithography equipment. In yet another aspect of the present disclosure, in the proper environment (alternating lines of metal that may have been mechanically patterned, polished and etched may be placed in a chemical vapor deposition machine), a plurality of first molecular-sized structures (e.g., CNT antennas) may be created (e.g., grown between lines of metal), and a plurality of second molecular-sized structures (e.g., geometric diodes) may be created using the first molecular-sized structures (e.g., by applying an electrical bias between the lines of metal and the CNT antennas), which may together form a final structure (e.g., a rectenna array), which may perform the desired function (which, in the present case, may be electrically rectifying sunlight), where each of the first molecular-sized structures may be self-aligned to a respective one of the second molecular-sized structures (e.g., the geometric diodes that may be formed at the tips of the CNT antennas). 
     Alternatively, in yet another aspect of the present disclosure, in the proper environment (alternating lines of metal that may have been mechanically patterned, polished, etched and oxidized, may be placed in a chemical vapor deposition machine), a plurality of first molecular-sized structures (e.g., CNT antennas) may be created (e.g., grown between lines of metals), a plurality of second molecular-sized structures (e.g., MoC diodes) may form in connection with the first molecular-sized structures (e.g., by coupling the tips of the CNTs to the oxide on the metal lines), and by using the first and second molecular-sized structures (e.g., by applying an electrical bias across the MoC diode), a plurality of third molecular-sized structures (e.g., geometric diodes), may be created in place of the second molecular-sized structures. The first and third molecular-sized structures together may form a final structure (e.g., a rectenna array), which may perform the desired function (e.g., electrically rectifying sunlight), where each of the first molecular-sized structures may be self-aligned to a respective one of the third molecular-sized structures (e.g., the geometric diodes that may be formed at the tips of the CNT antennas). 
     It is also contemplated that further processing using this resulting structure, which is a combination of two separate molecular-sized structures, may be used to preserve the resulting structure while enhancing the stability of the resulting structure by adding the additional oxide to stabilize and “anchor” the geometric diodes. 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and sub-combinations of various features described hereinabove as well as modifications and variations which would occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.