Application of Silicon Micromachining Techniques for the Manufacturing of New Passive THz-Components Stephan Biber, Jan Sch¨ ur, Lorenz-Peter Schmidt University of Erlangen-Nuremberg, Institute for Microwave Technology, (LHFT) Cauerstr. 9, 91058 Erlangen, Germany, Tel.: (+49)/9131/85-27223, Fax.: (+49)/9131/85-27212 stephan@lhft.de Abstract— We present an overview on the application of silicon micromachining techniques to the fabrication of THz- components. Different machining techniques will be discussed with respect to their capability to generate complex 3-dimensional geometries and to meet the high mechanical tolerance require- ments for THz-components. In order to demonstrate the potential of the technology, results for the application of micromachining techniques to the design of new THz-components will be dis- cussed. Two different components such as a quasi-optical filter at 2.5 THz and a horn antenna at 600 GHz will be discussed exemplarily. We will emphasize the potential of silicon based micro-structures for the manufacturing of new devices. I. I NTRODUCTION The development of new components such as quasi-optical devices or waveguide structures for THz-frequencies is mainly limited by the lack of suitable manufacturing techniques [1]. Wavelengths between 1mm and 50m place extremely high requirements against the manufacturing tolerances and make it difficult to design sophisticated components for THz- frequencies. On one hand conventional machining techniques based on milling, cutting and drilling suffer from compar- atively poor tolerances and are limited by the minimum size of the machining tool. On the other hand the well developed structuring techniques used for micro-electronic and VLSI (very large scale integration) circuits, mainly based on photo-lithographical techniques, do not allow to generate 3D- structures with sizes up to several hundred microns as they are required in the THz-domain. The advent of silicon-based micromachining technologies driven by a strong economical demand for micro-electromechanical systems (MEMS) opens up new perspectives for the design of THz-circuits [2], [3]. The dimensions, shapes and aspect-ratios of the structures required for micromechanical sensors, microfluidic reactors and micro- optical systems are very similar to the geometries necessary to manufacture quasi-optical or waveguide components for frequencies between 0.3 and 5 THz. In section II of this paper a short introduction to the silicon micromachining technologies based on deep reactive ion etching (DRIE) and wet KOH- etching of silicon will be given. In section III we present two different exemplary components fabricated using these technologies in order to examine the new perspectives opened up for THz circuit technology. The two different examples presented here are a quasioptical bandpass filter based on a binary grating at 2.5 THz and an octagonal horn antenna for 600 GHz with waveguide interface. II. SILICON MICROMACHINING TECHNOLOGIES Silicon micromachining technologies have several advantages compared with conventional technologies. Firstly, the proceses are mask based processes which allow to manufacture many similar devices simultaneously. This is not possible using traditional tool based technologies such as milling, drilling or electric discharge machining (EDM). Secondly the structures are defined by a photolithographic process which provides high repeatability and allows to define structures with an accuracy of approximately 1 μm. Several of these micromachining processes have also become increasingly interesting in the THz-community because of their potential to manufacture new components. After photolithographically structuring a photoresist, the silicon areas which are not protected by the resist can be attacked using chemically dry or wet etching technologies. Anisotropic etching of silicon with KOH-solution generates complex geometrical structures due to the effect that the etching velocity stongly depends on the direction within the silicon crystal [4], [5]. KOH etches about 400 times faster along the 〈100〉-direction than along the 〈111〉-direction. Using silicon with different crystal orientation, this effect can be used to generate either oblique sidewalls with an angle of 54,7 ◦ for {100}-wafers or vertical sidewalls for {110} . This is illustrated in Fig. 1. The geometric flexibility for generating structures using KOH-etching is strongly limited by the principal planes of the silicon crystal. Although it is possible to etch trenches in {110} wafers using wet KOH- etching, it is not possible to generate intersecting trenches or trenches which are not parallel to each other. Therefore other processes, which are independent of the principal planes of the silicon crystal can be very useful. One of these processes is deep reactive ion etching (DRIE, ”Bosch-process”) of silicon [6]. Fig. 2 demonstrates how a DRIE-process can be used to