2015 XVIII AISEM Annual Conference 978-1-4799-8591-3/15/$31.00 ©2015 IEEE Micromachined Silicon Radiation Sensors – Part 1: Design And Experimental Characterization A. Bagolini, M. Boscardin, P. Conci, M. Crivellari, G. Giacomini, F. Mattedi, C. Piemonte, S. Ronchin, N. Zorzi Centro per i Materiali e i Microsistemi Fondazione Bruno Kessler Trento, Italy boscardi@fbk.eu M.A. Benkechkache, G.-F. Dalla Betta, R. Mendicino, L. Pancheri, M. Povoli, D.M.S. Sultan Dipartimento di Ingegneria Industriale Universita degli Studi di Trento Trento, Italy gianfranco.dallabetta@unitn.it Abstract—Silicon radiation sensors fabricated with micromachining technologies offer a number of advantages compared to their planar counterparts, making them appealing for an increasing number of applications. This paper provides an overview of the most interesting developments in this field by Fondazione Bruno Kessler in collaboration with the University of Trento. Keywords—silicon radiation sensor; 3D sensors; micromachining; TCAD simulations I. INTRODUCTION In the early 1980’s, the application of the planar process, derived from microelectronics, represented a key milestone in the history of silicon radiation sensors [1]. Thirty years later, another radiation sensor paradigm, based on bulk micromachining of silicon (e.g., by Deep Reactive Ion Etching – DRIE), is finally reaching its maturity, paving the way to several new interesting applications. These devices exploit the 3 rd dimension within the silicon substrate to offer several interesting features, either related to the very radiation sensing properties or to ancillary functions. The most famous example is that of 3D sensors, where the electrodes penetrate through the substrate, perpendicularly to the surface, rather than being confined to the wafer surfaces, like in planar sensors. This architecture enables the electrode distance to be decoupled from the sensor thickness, with significant advantages in terms of low operation voltage, high speed, and high radiation tolerance [2]. Derived as an extension of 3D sensor technology, active edges consist of deep trenches etched by DRIE around the sensor active area and doped to act as (normally ohmic) electrodes. By doing so, full signal sensitivity up to a few micrometers from the sensor physical edge can be obtained. This allows for large area seamlessly tiled detector matrices, i.e., omitting sensor overlap within the same layer, with major advantages in the detector assembly [3]. Very thin sensors, that are attractive in high-energy and nuclear physics e.g., for timing or particle identification, or to improve the momentum resolution by reducing multiple scattering, can be obtained by locally thinning the silicon substrate by DRIE or chemical etching by TMAH or KOH [4]. Microstructured silicon sensors with high aspect-ratio cavities filled by proper converting materials (e.g., 6 LiF, 10 B) are emerging as viable alternatives to gas based sensors for the detection of thermal neutrons with high efficiency and low cost, as requested by several applications like homeland security, forensics, material science, to cite a few [5]. Very small detection volumes can be accurately defined by a combination of DRIE and wet etching, as requested for microdosimetry in synchrotron and particle therapy and space radiation protection [6]. Other interesting options, not dealing to the very sensor but rather to related system issues, are micro-channels for cooling [7], and feed- through connections similar to TSVs but much deeper [8]. Micromachined sensors are nowadays a hot topic in radiation detection, but only a few laboratories worldwide have the capability to manage the related fabrication challenges. Among them the Center for Material and Microsystems of Fondazione Bruno Kessler (FBK-CMM), where R&D activities in this field have been carried out for more than ten years, mainly in collaboration with the University of Trento and INFN. Besides the technological challenges, that are covered in the “Part 2” paper, these devices also call for a thorough design and TCAD simulation approach, as well as an extensive experimental characterization, that are here addressed with some selected examples. II. SELECTED CASE STUDIES A. 3D silicon radiation sensors 3D silicon sensors have been developed since 2004 at FBK using a double-sided approach, that provides several advantages compared to the original technology pioneered at Stanford in terms of complexity and processing time. As a matter of fact this represented a key factor in allowing FBK to be involved, jointly with CNM (Barcelona, Spain), in the very first medium volume production of 3D sensors for the ATLAS Insertable B-Layer (IBL) [9-11]. The unique properties of 3D sensors in terms of high charge collection efficiency even after very large irradiation fluences are determined by the short distance in between the deeply penetrating electrodes, which can effectively attenuate the detrimental effect of charge trapping [12]. However, other properties of 3D sensors are affected by surface layout details to a non-negligible extent [13]: as an example, contrarily to This work has been partially funded by: (i) the Provincia Autonoma di Trento through the Project MEMS; (ii) the Italian National Institute for Nuclear Physics (INFN) through the Projects ATLAS, CMS, P-SUPERB (CSN1), TREDI, TRIDEAS, VIPIX, HYDE, and PIXFEL (CSN5).