Fabrication of infrared and optical antennas requires high-resolution lithography so that thin films of the required materials can be deposited and patterned onto a suitable substrate. Resonant structures, including multilayer arrangements, are also made with nanofabrication techniques. Compared to the operating wavelength, the overall size of the antenna structures themselves is subwavelength in dimension. It is useful to have about a factor of ten higher resolution available than the overall dimension of the structure, so that fine features and sharp corners can be implemented in the design, as seen in the example shown in Fig. 4.1.
Experimental research in device development often involves fabrication of one-of-a-kind devices, or at least small batches of devices. From a flexibility point of view, this indicates the convenience of electron-beam lithography so that evolving designs can be changed and adapted according to experimental results. This has the disadvantage of the relatively slow, serial nature of the electron-beam writing process. When device designs become more mature, mask-based optical lithography can be usefully employed to take advantage of the parallel nature of the process to increase the speed of fabrication and the device throughput. It is worth considering early on the choice of specific materials to be used in a device so that compatibility with standard foundry processes may be obtained if possible.
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