Micromachining for Terahertz Artificial Materials
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1016-CC05-07
Micromachining for Terahertz Artificial Materials Andrew J. Gallant1, G. Peter Swift2, De Chang Dai2, Mikhail Kaliteevski2, Dagou A Zeze1, David Wood1, Michael C Petty1, Stuart Brand2, Richard A. Abram2, and J. Martyn Chamberlain2 1 School of Engineering, Durham University, Science Laboratories, Durham University, South Road, Durham, DH1 3LE, United Kingdom 2 Physics Department, Durham University, Science Laboratories, Durham University, South Road, Durham, DH1 3LE, United Kingdom ABSTRACT In this paper we report on the development of micromachined filters for operation at terahertz frequencies. SU8, a negative photodefinable epoxy, is used to define arrays of high aspect ratio rods which are subsequently sputter coated in gold to form the filter. We fabricate and test a filter with a fixed period but variable diameter along the length of the array. By moving the array in the terahertz beam we demonstrate the ability to mechanically tune specific filter characteristics from a single device. INTRODUCTION In recent years, the terahertz region of the electromagnetic spectrum has received considerable interest in the literature. Traditionally this region has been largely ignored when compared to the microwave and infrared regions that bound it. However, various applications for terahertz technology are emerging. These include the detection of hidden explosives and materials through combined imaging and spectroscopy techniques [1]. Further applications have been found in biological sensing and manufacturing process control. Terahertz microscopes, which probe with a subwavelength resolution are under development with the ultimate aim of performing spectroscopy on single cells [2]. The development of new THz generation techniques and time domain spectroscopy has aided the progression of the technology [3]. However, many of the peripheral elements, which are used in other regions of the electromagnetic spectrum, such as lenses and filters are less commonplace at THz frequencies. Artificial materials can be engineered to provide properties such as filtering or focusing which may be unavailable or difficult to achieve reliably in nature. To date, these have been developed for operation from microwave to visible wavelengths. The feature sizes found in these materials are of the order of the incident radiation. Therefore, the millimeter scale fabrication techniques for microwave artificial materials are very different from the nanometre scale used for visible light. For terahertz operation the artificial materials need to have feature sizes measured in the micron range (where 1 THz = 300 µm). The fabrication of micron scale three dimensional surfaces can be achieved with micromachining techniques which are a variant of integrated circuit (IC) based processes. They share the IC benefits of batch processing and multilayer photolithography but also exploit the third dimension.
Here we use a negative photoresist (SU8) to form arrays of extremely high aspect ratio rods on a single substrate. The rods have diameters f
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