Nature of millimeter wave losses in low loss CVD diamonds

Dielectric losses in CVD diamonds in the millimeter-wave range at temperatures 300?900 K

“…Figure 4 shows the dependences of tan δ on the frequency f for several CVD-diamond windows by "De Beers" company. For specimens with relatively higher losses related to a greater number of defects (seen with a microscope), we observed that, as in [13][14][15], the losses at frequencies above 150 GHz exceed the values corresponding to the dependence 1/f describing losses due to conductance. Figure 5 shows the temperature dependences of tan δ in the specimen 56 22DB6 at frequencies 136 and 170 GHz.…”

“…Therefore, in contrast to Si:Au, the lowest losses observed in CVD diamonds significantly exceed the lowest theoretical limit tan δ ≤ 3 · 10 −8 [3,8,11,12,20] determined by the two-phonon intrinsic lattice losses in the corresponding perfect crystal. This also follows from the comparison performed in [14,15] between the temperature dependence of losses in the best CVD-diamond sample and the theoretical dependence of the intrinsic lattice losses, whence the upper estimate tan δ < 7 · 10 −7 was found for the intrinsic lattice losses in diamond at a frequency of about 150 GHz at room temperature [14,15]. Thus, the theoretical limit of losses is much lower than the levels observed in modern highest-quality CVD diamonds [1,14,15].…”

“…This also follows from the comparison performed in [14,15] between the temperature dependence of losses in the best CVD-diamond sample and the theoretical dependence of the intrinsic lattice losses, whence the upper estimate tan δ < 7 · 10 −7 was found for the intrinsic lattice losses in diamond at a frequency of about 150 GHz at room temperature [14,15]. Thus, the theoretical limit of losses is much lower than the levels observed in modern highest-quality CVD diamonds [1,14,15]. These losses are related to defects, impurities, and non-diamond inclusions, i.e., it is in principle possible to significantly decrease the losses by improving the growth technology.…”

“…Studying dielectric losses in polycrystalline diamonds grown by chemical vapor deposition (CVD) has become very topical in the millimeter-wave range because of considerable progress in the growth technology and the corresponding applications of this previously "exotic" material in modern engineering [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The grown diamond disks have a number of remarkable electrical and mechanical properties:…”

“…These losses are related to defects, impurities, and non-diamond inclusions, i.e., it is in principle possible to significantly decrease the losses by improving the growth technology. In this way, the lowest losses were reduced by 2 orders of magnitude during the last 10 years and continue to decrease [1,[4][5][6][7][8][9][10][11][12][13][14][15]. In the case of the further decrease in losses, it would be possible, e.g., to remove the water cooling system in windows for output and input of electromagnetic energy (see the above discussion), to significantly simplify their design, and thereby to enhance reliability of the entire facility.…”