Investigation of a Membrane Supported D-Band Antenna with a 3D Printed Polyamide Lens Alina-Cristina Bunea 1,2 , Dan Neculoiu 1,2 , Andrei Avram 1 and Christian Rusch 3 1 National Institute of R&D in Microtechnologies (IMT), 077190 Bucharest, Romania; 2 Politehnica University of Bucharest, Bucharest, Romania; 3 Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany Abstract — This paper presents the results obtained for a D-Band double folded slot antenna (DFSA) supported by a thin dielectric membrane released by the deep reactive ion etching of low resistivity silicon (ρ = 10 Ωcm). The measurement results demonstrated a good matching (|S11| < – 10 dB) between 125 – 170 GHz, with a measured calibrated gain of 5 dBi at 140 GHz. It is demonstrated, by means of electromagnetic simulations, that the gain is increased by 15 dBi in the whole D-band by adding a 10 mm radius 3D printed polyamide lens in the near field of the DFSA chip placed over a metallized surface. The polyamide lens and the DFSA are integrated in a package with a total size of 20x20x20 mm 3 . This system demonstrates a simulated 3dB gain bandwidth between 124 – 162.5 GHz, with |S11| < – 9 dB between 128.5 – 170 GHz. Index Terms — 3D printing, folded slot antenna, millimeter wave (MMW), polyamide lens, silicon micromachining. I. INTRODUCTION The applications which are starting to take advantage of the D-band (110 – 170 GHz) include high resolution active/passive imaging, high-speed wireless communications, guided navigation and military applications [1]. In all these applications the on-chip antennas are an essential building block, but for standard BiCMOS processes, achieving high gain and efficiency is a challenge. The high permittivity and thick, low-resistivity silicon substrate leads to poor antenna performance [2]. The micromachined double folded slot antenna (DFSA) has proven suitable for millimeter wave applications up to 160 GHz frequency range, with a simulated directivity of about 6 dBi [3]. There are numerous works reporting on the benefits of adding dielectric lenses to antennas for gain increase from a few dB up to tens of dB [4]. The concept of substrate lens antennas is very popular and one commonly used shape is the extended hemispherical lens with the feeding antenna in close contact to the dielectric lens [5]. The dielectric lens fabrication methods fall into two main categories: mechanical machining and molding. In the last decade 3D fabrication processes have started to be used for the fabrication of truly 3D, all-dielectric structures [6] with high aspect ratio, arbitrary complex geometries, high accuracy at low cost. In this paper, we present the results of the investigation of the radiation performance improvement for an on-chip antenna fabricated using low-resistivity silicon micromachining. A DFSA with a central operating frequency of 140 GHz was designed to be used as a test vehicle. The fabricated structure was experimentally characterized in terms of reflection coefficient and transmission gain and the results are in good agreement with those obtained by full wave electromagnetic (EM) simulations. After the validation of the EM model, simulations show an increase of the gain by 2.2 dB at 140 GHz by placing the structure over a finite size metallized surface. Furthermore, it is shown that by placing a 10 mm radius 3D printed polyamide hyper-hemispherical lens over the antenna-on-metallized surface the total gain will increase up to 23 dBi at 140 GHz with good radiation properties and a gain greater than 20 dBi in the 125 –160 GHz frequency band. The lens is integrated into the package of the system that is designed to be fabricated by 3D printing of polyamide through laser sintering. II. DESIGN AND MEASUREMENTS OF THE DFSA The antenna was designed to be fabricated on a thin dielectric membrane consisting of a 1.5 µm SiO 2 layer grown through thermal oxidation and a 0.6 µm thick Si 3 N 4 layer, deposited through LPCVD on a 525 µm thick low resistivity (ρ = 10 Ωcm) silicon wafer. The membrane is released using the Bosch Deep Reactive Ion Etching (DRIE) process [7]. The metallization consists of a 1 µm thick Au layer. The 3D electromagnetic model developed in CST Microwave Studio (MWS) for the membrane supported antenna structure [3], surrounded by the low resistivity silicon bulk (conductivity of 10 S/m and relative dielectric permittivity of εr = 11.9) is presented in Fig.1a. A photo of the backside of the fabricated antenna with the gap-signal-gap dimensions is shown in Fig.1.b. The distance of 1200 µm between the DFSA and the surrounding silicon bulk ensures the minimum penetration of the EM field in the low resistivity silicon and prevents the degradation of the antenna performances. More information about the modeling and design of membrane supported DFSAs for frequencies beyond 110 GHz can be found in [3].