Fabrication methods for thermoelectric phononic structures

Abstract

Phononic structures, devices related to phononic structures, and methods related to fabrication of the phononic structures are described. The phononic structure can include a sheet of material, where the sheet of material can include a plurality of regions. Adjacent regions in the sheet of material can have dissimilar phononic patterns.

What is claimed is: 
     
         1 . A method for fabricating a phononic structure, comprising:
 doping a sheet of a first material;   defining a plurality of regions in the sheet, wherein adjacent regions have dissimilar phononic patterns; and   etching the sheet to obtain the plurality of regions, thus fabricating the phononic structure.   
     
     
         2 . The method according to  claim 1 , wherein adjacent regions have dissimilar phonon energy band structures. 
     
     
         3 . The method according to  claim 1 , wherein each region has a length more than twice a phonon mean free path of the first material. 
     
     
         4 . The method according to  claim 1 , wherein defining a plurality of regions in the sheet comprises:
 defining at least a first region comprising holes in the first material; and   defining at least a second region adjacent to the first region, the second region comprising the first material devoid of holes.   
     
     
         5 . The method according to  claim 4 , wherein defining at least a first region comprises filling the holes with a second material different from the first material. 
     
     
         6 . The method according to  claim 1 , wherein defining a plurality of regions in the sheet comprises:
 defining at least a first region comprising holes in the first material, the holes having a first value for a characteristic; and   defining at least a second region adjacent to the first region, the second region comprising holes in the first material, the holes having a second value for the same characteristic.   
     
     
         7 . The method according to  claim 6 , wherein the characteristic is selected from the group consisting of hole size, pitch between holes, wall-to-wall distance between holes, and hole shape. 
     
     
         8 . The method according to  claim 6 , further comprising filling the holes in one or both of the first and second regions with a second material. 
     
     
         9 . The method according to  claim 6 , further comprising:
 filling the holes in the first region with a second material;   filling the holes in the second region with a third material different from the first material, the second material being different from the first and third material.   
     
     
         10 . The method according to  claim 5 , wherein the second material is selected from the group consisting of thermal insulators, polymers, glasses, ceramics, aerogels, natural materials, and epoxies. 
     
     
         11 . The method according to  claim 4 , wherein a distance between holes is not larger than twice a thickness of the sheet of the first material. 
     
     
         12 . The method according to  claim 4 , wherein a distance between holes is not larger than twice the phonon mean free path of the first material. 
     
     
         13 . The method according to  claim 1 , wherein the first material is selected from the group consisting of silicon, graphene, germanium, silicon-germanium, and lead-telluride. 
     
     
         14 . The method according to  claim 1 , wherein defining a plurality of regions in the sheet comprises:
 defining a first set of regions having a first phononic pattern; and   defining a second set of regions having a second phononic pattern dissimilar to the first phononic pattern,   wherein the phononic structure alternates between a region from the first set of regions and a region from the second set of regions.   
     
     
         15 . The method according to  claim 1 , wherein the phononic structure has a lower thermal conductivity than the first material. 
     
     
         16 . The method according to  claim 1 , wherein the phononic structure has a lower thermal conductivity than the first material and the phononic structure has substantially the same electrical conductivity as the first material. 
     
     
         17 . The method according to  claim 1 , wherein:
 adjacent regions are configured to carry a heat flow along a longitudinal axis of the phononic structure,   each region has a length perpendicularly to the longitudinal axis of the phononic structure, the length being more than twice a phonon mean free path of the first material, and   the plurality of regions comprises at least a first region and a second region adjacent the first region, the first region comprising a period pattern of holes in the first material and the second region comprising the first material devoid of holes.   
     
     
         18 . A method to fabricate a thermoelectric device, the method comprising:
 doping a first sheet of a semiconductor material;   defining a first plurality of regions in the first sheet, wherein adjacent regions have dissimilar phononic patterns;   etching the first sheet to obtain the first plurality of regions;   doping a second sheet of the semiconductor material;   defining a second plurality of regions in the second sheet, wherein adjacent regions have dissimilar phononic patterns;   etching the second sheet to obtain the second plurality of regions;   electrically coupling a first electrode to a first side of the first sheet;   electrically coupling a second electrode to a first side of the second sheet; and   electrically coupling a third electrode to a second side of the first sheet and the second sheet,   wherein, during operation of the thermoelectric device, the first and second sides of each sheet are adapted to exhibit different temperatures.